Teses / dissertações sobre o tema "Double stars"

Orbits of spectroscopic binary systems have been studied for more than a century. Over three thousand orbits of spectroscopic binary systems have been derived. These orbits are based on the radial velocities measured from the spectra recorded by a photographic plate to a high precision spectrum observed from a modern spectrograph. In many cases, the shape of the orbit was assumed to be circular, of hence the eccentricity is zero. This assumption is based on the fact that a small eccentricity (e < 0.1) measured from the observed data might be a result from the error of observations or from the intrinsic variation of a spectroscopic binary system. Sixteen southern spectroscopic binary systems, including twelve single-lined binaries and four double-lined binaries, were selected to study in this research program. These systems were assumed to have circular orbits or have very nearly circular orbits (e < 0.1) from their previous published solutions. The HERCULES spectrograph was used in conjunction with the 1-m McLellan telescope at Mt John University Observatory to collect the spectra of these systems. The observations, taken from October 2004 to August 2007, comprised about 2000 high-resolution spectra of spectroscopic binary systems and standard radial-velocity stars. Radial velocities of spectroscopic binary systems were measured from these spectra and orbital solutions of the systems were derived from these radial velocities. It was found that from HERCULES data, we are able to achieve high-precision orbital solutions of all the systems studied. The best-fit solutions can be improved as much as 70 times from the literature’s orbital solutions. It has been found that the precision of a system depends on the rotational velocities of the components as well as the level of their chromospheric activity. We are able to confirm the eccentricity in the orbit of only one of the selected spectroscopic binary systems, HD194215. Its eccentricity is 0.123 29 ± 0.000 78. The small eccentricities of other systems are not confirmed. There are four systems; HD22905, HD38099, HD85622 and HD197649, that have circular orbital solutions from the large errors in their measured eccentricities. Two systems, HD77258 and HD124425, have too small eccentricities, e = 0.000 85±0.000 19 and 0.002 60 ± 0.000 99 to be acceptable. An intrinsic variation is a presumed cause of the spurious eccentricities derived from the data of the other eight systems. Photometric data from Mt John University Observatory service photometry program, as well as the photometric data from the Hipparcos satellite and information of these systems from the literature, using various methods and instruments, give a wider view on the systems’ behaviour. It is possible that the spurious eccentricities derived for these systems result from the eclipsing behaviour of a system (HD50337), or from the nature of the components, such as, the distortion of their shape (HD352 and HD136905), their chromospheric activity (HD9053, HD3405, HD77137, HD101379 and HD155555), or stellar pulsation (HD30021). Models of the active chromosphere system, HD101379, have been simulated. An analysis of synthetic radial velocity data shows that spots on the star’s photosphere can cause a spurious eccentricity. The values of the spurious eccentricity and the longitude of periastron are dependent on the spot size, the spot temperature, and the position of the spots.

Observations were made of 309 binary systems between RA 17h - 07h and Dec -70 degrees to -60 degrees. The images were calibrated against pairs measured for CCD astometry. Measurements were made of separations, position angles and differential magnitudes. Uncertainties in position angle and separation were 7.8o/p and 0.16 arcseconds respectively. The position angles, separations and differential V magnitudes were compared with WDS figures. It was determined that only 29% _+ 5% of the observed pairs had undergone significant movement since the last previous measurement, which agrees with the results of a survey of the WDS. A statistical study of 1q77 pairs found that the spread of calculated separations agreed with those found by other authors, while the distribution of periods, while falling within the range(s) calculated by other authors, were significantly longer. A short-arc fitting program was tested using data derived from the published orbit of Centauri before being applied to seven observed pairs. Orbits could be calculated for six of the seven pairs. For four of these pairs the observed movement may be due to proper motion rather than orbital motion
Master of Science (Hons)

Observations were made of 309 binary systems between RA 17h - 07h and Dec -70 degrees to -60 degrees. The images were calibrated against pairs measured for CCD astometry. Measurements were made of separations, position angles and differential magnitudes. Uncertainties in position angle and separation were 7.8o/p and 0.16 arcseconds respectively. The position angles, separations and differential V magnitudes were compared with WDS figures. It was determined that only 29% _+ 5% of the observed pairs had undergone significant movement since the last previous measurement, which agrees with the results of a survey of the WDS. A statistical study of 1q77 pairs found that the spread of calculated separations agreed with those found by other authors, while the distribution of periods, while falling within the range(s) calculated by other authors, were significantly longer. A short-arc fitting program was tested using data derived from the published orbit of Centauri before being applied to seven observed pairs. Orbits could be calculated for six of the seven pairs. For four of these pairs the observed movement may be due to proper motion rather than orbital motion

Paper discusses the expected uncertainty of orbital parameters of binary stars as measured by the space-based gravitational wave observatory LISA (Laser Interferometer Space Antenna) and how the inclusion of spin in the model of the binary stars affects the uncertainty. The uncertainties are found by calculating the received gravitational wave from a binary pair and then performing a linear least-squares parameter estimation. The case of a 1500 solar mass black hole that is 20 years from coalescing with a 1000 solar mass black hole--both of which are 50 x 10^6 light years away--is analyzed, and the results show that the inclusion of spin has a negligible effect upon the angular resolution of LISA but can increase the accuracy in mass and distance measurements by factors of 15 and 65, respectively.

Thesis (Ph. D.)--Ohio State University, 2005.
Title from first page of PDF file. Document formatted into pages; contains xv, 286 p.; also includes graphics (some col.). Includes bibliographical references (p. 275-286). Available online via OhioLINK's ETD Center

We present new 6 cm observations of the binary radio, X-ray and ɿ -ray star GT0236+610 (LSI+61°303) obtained in August 1984 and September 1986. Ve calculate an improved period for the source's periodic radio outbursts of 26.50 ± 0.03 days. No significant period derivative was found. Based on an analysis of 201 flux density measurements from 1977 August to 1986 September, we find evidence for a possible 4 year modulation of the amplitude of the 26.50 day periodic radio outbursts. A precessing jet model for this long period modulation is discussed.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

Spectroscopic and photometric observations of eight contact/near-contact binaries are presented and analysed. Spectroscopic observations were obtained at 4200 Å (radial velocity spectra) and 6563 Å (hydrogen-alpha line profiles). New photometric observations were obtained at visual and infrared wavelengths, and other previously published light curves are also re-analysed. Absolute dimensions have been obtained for five systems; TY Boo, VW Boo, BX And, SS Ari and AG Vir, and their evolutionary positions discussed. Four of the systems are found to be in marginal but poor thermal contact, exhibiting regions of apparent "excess luminosity" in their light curves. A qualitative analysis of these "hot spot" regions has been attempted for the first time using spot models now incorporated into a light curve synthesis programme. Substantial time for this project was awarded on telescopes funded by the United Kingdom Science and Engineering Research Council (SERC), comprising 14 nights at the Issac Newton Telescope (INT) on La Palma, and 4 nights at the United Kingdom Infrared Telescope (UKIRT) on Mauna Kea. Additional observations were made during an 8 night commissioning run on the Jacobus Kapteyn Telescope (JKT) on La Palma, and extensive observations were made with the Twin Photometric Telescope (TPT) at St Andrews University Observatory between 1985 and 1989. These resulted in over 100 spectra at 4200 Å and over 50 spectra at 6563 Å (INT and JKT observations), over 300 infrared photometric observations (UKIRT), and over 3500 visual photometric observations (TPT). Of the five systems analysed in detail in this work, TY Boo appears to be a normal shallow-contact W-type system. Both VW Boo and BX And exhibit regions of "excess luminosity" around the ingress and egress of secondary minimum which are well modelled by a warm spot on the cooler component sitting symmetrically around the neck joining the pair. Such a phenomenon may be expected to arise naturally in systems which have come into contact but are not yet/currently in thermal contact, exhibiting a temperature difference between the components. BXAnd like other B-type systems seems to be reaching this contact state for the first time, but the position of VW Boo is uncertain, and whilst evidence that it could be in the "broken contact" state predicted by the TRO Theory is far from conclusive, its lower orbital angular momentum clearly marks the system as worthy of further study. SS Ari and AG Vir exhibit light curves with unequal quadrature heights. Attempts to treat the higher quadrature as a region of "excess luminosity" due to an energy transfer "warm spot" does not however provide a good model of this phenomenon. Since invoking a dark starspot model also does not provide a good explanation for such systems, it may be that this form of light curve distortion is due to an entirely different form of distorting surface phenomenon. Like BX And, AG Vir appears to be just reaching contact for the first time, but like VW Boo, the slightly lower angular momentum of SS Ari warrants further study.

Si l'évolution des étoiles simples est relativement bien comprise, l'étude des étoiles binaires, qui représentent la majorité des étoiles, nécessite encore des progrès majeurs, particulièrement en ce qui concerne leurs différents modes d'interactions. Dans ces systèmes, la composition de surface d'une étoile peut être altérée non seulement par l'accrétion d'éléments synthétisés au sein de l'étoile compagnon, mais également par des processus de mélanges internes induits par les forces de marées et d'un transport du moment angulaire. Plusieurs classes d'étoiles post-transfert de masse (les étoiles à baryum, CH et S) possèdent effectivement des compositions de surface caractérisées par la présence d'éléments lourds, tel que le baryum. Ces systèmes sont présumés se former au sein de systèmes binaires incluant une étoile de la branche asymptotique des géantes (appelé étoile AGB). Ces dernières sont des étoiles remarquables qui représentent l'unique site d'une nucléosynthèse particulière. En effet, elles constituent les contributeurs essentiels de la production de fluor ou de baryum. Les étoiles AGB sont également caractérisées par une importante perte de masse par vent qui éjecte progressivement leur enveloppe enrichie en ces éléments. Au sein d'un système binaire, une partie de ce vent est accréditée par l'étoile compagnon et pollue ainsi sa surface, laissant une signature spectrale distincte qui subsistera longtemps après que l'étoile AGB ait disparu. Ce scénario est suggéré comme étant responsable de la formation d'une grande variété d'étoiles chimiquement particulières, tels que les étoiles à baryum.

Cependant, plusieurs propriétés clés de ces systèmes, en particulier leurs distributions de périodes orbitales et d'excentricités, demeurent inexpliquées depuis des décennies. L'incapacité de nos modèles à reproduire ces propriétés orbitales met en évidence notre compréhension limitée des mécanismes d'interaction qui gouvernent l'évolution des systèmes binaires. Plus particulièrement, des mécanismes qui génèrent des orbites excentriques au sein des étoiles à baryum et des systèmes analogues sont requis. Nous examinons ainsi la possibilité qu'à sa naissance l'étoile naine blanche subisse un kick ou que la présence d'un disque entourant le système binaire soit à l'origine des fortes excentricités observées chez les étoiles à baryum. Ces deux mécanismes permettent pour la première fois depuis l'étude de ces systèmes d'apporter une solution à ces problèmes. Il est montré comment comprendre les signatures induites par un compagnon étoile AGB et les corréler avec les propriétés orbitales du système binaire est essentiel pour tester et améliorer notre connaissance de l'évolution des étoiles binaires; l'objectif de ce travail.

Doctorat en Sciences
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Thesis (Ph.D) - Swinburne University of Technology, Faculty of Information & Communication Technologies, 2009.
A dissertation presented in fulfillment of the requirements for the degree of Doctor of Philosophy, [Faculty of Information and Communication Technologies], Swinburne University of Technology, 2009. Typescript. Bibliography: p. 207-223.

Observations of four massive x-ray binary stars are presented, based on data accumulated between February 1989 and August 1991. Using modern techniques of spectroscopic data analysis, velocity curves are derived for three of these systems. Two of these curves (SMC X-1, QV Nor) yield very precise mass estimates for the component stars, while the third (Cen X-3) offers a constraint on the possible masses. The fourth system (X Per) is not shown to exhibit periodic variations, despite an extensive study conducted over more than two years. For the two systems that yielded precise masses, the component neutron stars are shown to lie within the theoretical mass range based on theories of their formation via the supernova explosion of a helium star in a close binary system. This is a marked improvement on previous studies where both stars had estimated masses which lay well outside of the expected range. The derivation of these masses incorporates the use of non-Keplerian velocity corrections, arising from the non-spherical, asymmetrically illuminated primary stars. A study of the line profiles showed that the temperatures around both primary stars were consistent with the parameters in these calculations. For the third system, the inaccuracy of the published ephemeris resulted in a lack of observations at the times of maximum and minimum velocity. The semi-amplitude is thus not well constrained, but it is shown that the observations are consistent with the assumption of a normal mass neutron star secondary. The system is shown to have undergone a gradual decrease in its orbital period which follows a parabolic trend, suggesting substantial mass-transfer. For the fourth system, a periodicity analysis of 130 spectroscopic velocity measurements of a Be star, via Fouriergram and string-length techniques, failed to highlight any strong periodicity. The scatter in the data appears larger than would be expected for a non-variable B star. The absence of periodic velocity variations at the expected period is discussed in terms of the binarity (or otherwise) of the Be star. A transition from Be to shell-star or ordinary B star phase occurred during the study, which is not evident from the spectral variations observed in the blue.

The bright hydrogen-deficient binary Upsilon Sgr has been studied in detail in the areas of radial velocities, flux distribution, temperature, surface gravity, composition and mass loss using the analysis of spectroscopic data. From IUE high resolution spectra the primary radial velocity orbit has been confirmed (K1 = 47.3±0.8kms−1) and the secondary radial velocity curve determined for the first time (K2 = 29.7±1.7kms−1). The orbit has been constrained to an inclination of 65 - 78°. The masses of the primary and secondary are then 3.0 ± 0.3 and 4.8 ± 0.5M☉ respectively, with an orbital separation of 230±20R☉.The primary is expected to fill its Roche Lobe at a radius of ~60R☉.Using all the available photometry and line-blanketed hydrogen-deficient model atmospheres the primary effective temperature has been determined to be 11,800±500K. IUE spectra were used to determine an extinction of E[sub]B-v = 0.20±0.05 leading to a distance of ~1400pc and a luminosity of 61,000(+11,000)/(-5,000) L☉. The long standing problem of the flux distribution has been mostly solved and little of the UV flux shortward of 1400 Å comes from a hot bright secondary. The same model atmospheres and a high resolution CCD/echelle spectrum was used to confirm the temperature (Teff= 11,750±750K) and to obtain a surface gravity of log g = 1.5±0.5. υ Sgr is ~ 99.6% helium, 0.016% H with CNO abundances indicative of advanced evolution and high main sequence mass. From profile fitting of the UV resonance lines of C, N and Si the mass-loss rate from υ Sgr is at least 2.5 x10−1°M☉yr−1. The upper limit to the mass-loss rate is 1.0 x10 −5M☉yr−1 from the lack of observed changes in the orbital parameters. The mass of the primary component and the low likely mass-loss rate indicate that the primary component will not be able to shed enough material before core collapse, an event that will be classed as a type Ib supernova. This is the first solid evidence that hydrogen-deficient binaries are progenitors of these objects although other candidates are not ruled out. The other known hydrogen-deficient binaries (KS Per, LSS 1922 and LSS 4300) have had their temperatures (12,500±500K, 12,000±500K, 12,000±1,000K) and interstellar extinctions (0.55± 0.05, 0.80±0.05, 0.90±0.10) re-determined from a flux distribution analysis. Mass-loss rates from 6 O stars, 3 Extreme Helium stars and 2 sdO stars have also been determined. The O and EHe results broadly agree with the previous determinations. Results for the 2 sdO stars, BD H-37° 1977 and BD +37 ° 442, are presented from profile fitting for the first time and indicate a mass-loss rate slightly higher than for the EHe stars.

Building upon its success with the Hipparcos space astrometry mission launched in 1989, the European Space Agency has agreed to fund the construction of its successor, Gaia, and its launch in 2011. Despite the similarities between the two missions, Gaia will be orders of magnitude more powerful, more sensitive, but also more complex in terms of data processing. Growing from 120,000 stars with Hipparcos to about 120,000E4 stars with Gaia does not simply mean pushing the computing resources to their limits (1 second of processing per star yields 38 years for the whole Gaia-sky). It also means facing situations that did not occur with Hipparcos either by luck or because those cases were carefully removed from the Hipparcos Input Catalogue.

This manuscript illustrates how some chunks of the foreseen Gaia data reduction pipeline can be trained and assessed using the Hipparcos observations. This is especially true for unresolved binaries because they pop up so far down in the Gaia pipeline that, by the time they get there, there is essentially no difference between Hipparcos and Gaia data. Only the number of such binaries is different, going from two thousand to ten million.

Although the computing time clearly becomes an issue, one cannot sacrifice the robustness and correctness of the reduction pipeline for the sake of speed. However, owing to the requirement that everything must be Gaia-based (no help from ground-based results), the very robustness of the reduction has to be assessed as well. For instance, the underlying assumptions of some statistical tests used to assess the quality of the fits used in the Hipparcos pipeline might no longer hold with Gaia. That may not affect the fit itself but rather the quality indicators usually accompanying those fits. For the final catalogue to be a success, these issues must be addressed as soon as possible.

Agrégation de l'enseignement supérieur, Orientation sciences
info:eu-repo/semantics/nonPublished

Despite being observed since the XVIIIth century, Algol systems and related objects are

still rather poorly understood. We know that they are composed by a generally B-A main sequence

star and a lighter but more evolved companion star. This paradox is explained by the transfer of mass

between the two stars, but new problems arose. In particular, I studied the mass-transfer driven spin-

up of the accreting star that drives the star to critical rotation and the puzzling, indirectly observed, non-conservative evolution.
Doctorat en Sciences
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The application of the discrete Fourier transform to the determination of the frequency content of unevenly-sampled astronomical time series is discussed, and an interactive computer package which incorporates a variety of power-spectrum and time-domain techniques is described. A frequency analysis of the light curves of two hot, extreme helium stars, BD-9°4395 and HD160641, shows that their photometric variability is caused by non-radial pulsation. Spectroscopic evidence in support of non-uniform mass loss is presented for BD-9°4395. Spectroscopic and photometric observations of two early-type eclipsing binary systems, AL Sculptoris and DM Persei, have been analysed to yield their absolute dimensions. AL Scl is found to be a detached system in which both components rotate faster than synchronism. The origin of distortions in its light curve is unclear. DH Per is shown to be part of a triple system in which the third component is most probably a late-B star in a 98-day orbit with a semi-major axis of 0.9 A.U. The binary system is confirmed to be semi-detached and to have evolved through a phase of rapid mass transfer. DH Per joins a small group of massive, semi-detached systems whose characteristics differ significantly from the classical Algols, and which may result from case-A, mass-transfer processes. Spectroscopic and photometric observations of the F4V star HD123058 do not support the hypothesis that it is a binary system. Broad lines in its spectrum are attributed to a somewhat enhanced rotation rate, and the star is shown to be essentially unevolved. The derivation of the equation of condition in Sterne's rigorous method for the analysis of the spectroscopic elements of binary systems, and its modification for incorporating observed times of minimum light into the adjustment of the elements, are outlined. A computer code for the determination of orbital elements according to this scheme is described.

The results of a long term monitoring program on the massive X-ray binary Cygnus X-1, whose constituents are believed to consist of a normal 0 star primary and a black hole companion, are presented. Spectra of this system were collected between 1980 and 1984 using a Reticon detector. The resulting absorption line radial velocity (RV) curve is characteristic of a single line spectroscopic binary. These velocities were combined with those available in the literature to determine an orbital period of 5.59977 ± 0.00001 days. A P/P ≃ 10⁻⁵ day⁻¹ was found from analysis of all available velocity measures. This change in the period is larger than that expected as a result of mass loss from the primary or from- models of the system in which large mass transfer rates occur between the components. A fit of the orbital motion of the primary to the RV curve gives a K = 75.0 ± 1 km/s and no significant eccentricity. The vsini of the primary was found, using the fourier transform technique, to be 94.3 km/sec. This is substantially smaller than the literature value of vsini = 140 km/sec. The value of the K and vsini allow the ratio mp/mx to be determined as ≃ 2.0 . The equivalent width of Hƴ allows the absolute magnitude of the primary to be estimated at -6.5 ± 0.2 . A comparison of the spectrum of the primary to those of an array of standards allows the spectral type to be given as between 09.5 and 09.7 I . This spectral type is consistent that the primary is a normal star of mass ≃ 20 M⊙. The mass of the secondary is therefore 10 ± 3 Mʘ. Measurement of the interstellar lines to obtain an independent E(B-V) reveals that the interstellar line strength per unit E(B-V) is lower than in any other direction in the sky. Stars for which velocity-excitation slopes and mass loss estimates, from UV line profile modeling and/or radio free-free emission measures, are available in the literature were collated. An empirical fit to this material allowed the mass loss rate for HDE 226868 (the primary of Cygnus X-1) to be estimated at 5.7 ± 2 x 10⁻⁶ M/year. The He II λ4686 and Hɑ lines are found in emission. After removal of the contribution to the line profile from the primary the radial velocity curve of the residual He II λ4686 line is found to have small scatter from a smooth fit ( ± 10 km/sec ) with no significant eccentricity. No sizeable variation in the K amplitude at different epochs was found contrary to a previous investigation and the origin of the emission is thus apparently fixed and stable. A phase lag of 130° is measured between the absorption and emission velocity curves and thus the simple interpretation of the emmision originating near the secondary can not be correct. The He II emission equivalent width, corrected for the underlying primary absorption, shows strong modulation (30%) over the 5.6 day orbital period. This variation is probably the result of the profile of the primary varying with which face of the star is directed towards the observer. During two separate observing sessions in 1982 the He II equivalent widths were found to be 40% and 15% larger than the mean of all other observations while still showing the same variation with orbital phase. Such a change has been seen once before and may be associated with transitions to the X-ray high state. The Hƴ and Hβ lines show a 20% variation on the 294 day X-ray period in the sense of largest equvalent widths at X-ray minimum ( 0 phase ). The Balmer lines are a composite of an absorption component from the primary and a weak emission component. This is best explained by variations in the outflow from the star, which is the source of both the emission component and the X-ray flux via accretion. Such variations may be the result of pulsation of the primary. The Hɑ line profile has been decomposed into three components; the absorption component from the primary, emission from a shell with an inner radius 1.4 times that of the primary, arid a component with properties similar to the He II λ4686 line. The great width of the Hɑ line, previously explained as being the result of rotation of the disc, is instead shown to be the result of superposition of these components. The origin of the He II λ4686 emission is explained by assuming that a stellar wind enhanced in the direction of the secondary is completely ionized within a volume surrounding the secondary. The He II between the edge of this volume and the surface of the primary is enhanced as a result of X-ray heating and ionization. Model profiles appear in reasonable agreement with high dispersion spectra. The obvious explanation for the orbital variation in the He II line is that X-ray heating of the side of the primary facing the secondary produces a change in the effective temperature. Calculation of the size of this effect reveals that it is too small to explain the changes observed. X-ray observations made with EXOSAT with excellent time resolution allowed timing of the X-ray absorption features seen near orbital phase zero. Simultaneous X-ray spectra allowed an estimate of their column density as 2.0 x 1023 cm⁻². Two scale lengths of dips were found of 10⁸ and 10¹¹ cm. These values are in good agreement with theoretical predictions for the sizes of inhomogeneties in high mass loss stellar winds. The location of the material producing the absorption dips was calculated as being ≃ 4-8 R⊙ from the X-ray source.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

Photometric and spectroscopic analyses have shown that the Galactic bulge cluster Terzan 5 hosts several populations with different metallicities and ages that manifest as a double red horizontal branch (HB). A recent investigation of the massive bulge cluster NGC 6569 revealed a similar, though less extended, HB luminosity split, but little is known about the cluster's detailed chemical composition. Therefore, we have used high- resolution spectra from the Magellan-M2FS and VLT-FLAMES spectrographs to investigate the chemical compositions and radial velocity distributions of red giant branch and HB stars in NGC 6569. We found the cluster to have a mean heliocentric radial velocity of -48.8 km s(-1) (sigma = 5.3 km s(-1); 148 stars) and <[Fe/H]> = -0.87 dex (19 stars), but the cluster's 0.05 dex [Fe/H] dispersion precludes a significant metallicity spread. NGC 6569 exhibits light- and heavy-element distributions that are common among old bulge/inner Galaxy globular clusters, including clear (anti) correlations between [O/Fe], [Na/Fe], and [Al/Fe]. The light-element data suggest that NGC 6569 may be composed of at least two distinct populations, and the cluster's low <[La/Eu]> = -0.11 dex indicates significant pollution with r- process material. We confirm that both HBs contain cluster members, but metallicity and lightelement variations are largely ruled out as sources for the luminosity difference. However, He mass fraction differences as small as Delta Y similar to 0.02 cannot be ruled out and may be sufficient to reproduce the double HB.

This thesis examines an intermittent uncanniness that emerges in cultural responses to new image technologies, most recently in some impressions of the digital actor. The history of image technologies is punctuated by moments of fleeting strangeness: from Maxim Gorky's reading of the cinematographic image in terms of 'cursed grey shadows', to recent renderings of the computer-generated cast of Final Fantasy: The Spirits Within as silicon-skinned mannequins. It is not merely the image's unfamiliar and new aesthetics that render it uncanny. Rather, the image is received within a cultural framework where its perceived strangeness speaks allegorically of what it means to be human at that historical moment. In various ways Walter Benjamin, Anson Rabinbach and N. Katherine Hayles have claimed that the notion and the experience of 'being human' is continuously transformed through processes related to different stages of modernity including rational thought, industrialisation, urbanisation, media and technology. In elaborating this argument, each of the four chapters is organized around the elucidation of a particular motif: 'dummy', 'siren', 'doppelg??nger' and 'resurrection'. These motifs circulate through discourses on different categories of digital actor, from those conceived without physical referents to those that are created as digital likenesses of living or dead celebrities. These cultural responses suggest that even while writers on the digital actor are speculating about the future, they are engaging with ideas about life, death and identity that are very old and very ambivalent.

The goal of this study was to obtain photometry of three poorly studied close binary star systems. These observations were obtained at Lowell Observatory in Flagstaff, Arizona and the Ball State University Observatory. In both cases charged coupled device detectors were used. Light variations were detected in all three stars. For one of the binaries the temperatures of the component stars were found by fitting multi-color light curves with black body models. In addition, the temperature difference between the two hemispheres of the secondary star was found. This difference is believed to be the product of heating by the stellar companion.
Department of Physics and Astronomy

Thesis (Ph. D.)--Ohio State University, 2005.
Title from first page of PDF file. Document formatted into pages; contains xii, 190 p.; also includes graphics (some col.). Includes bibliographical references (p. 181-190). Available online via OhioLINK's ETD Center.

In this investigation of near-contact binary stars, the author fit a synthetic light, computer generated, curve model to observations by adjusting various parameters of two near-contact binary pairs, CN Andromeda and TZ Draconis. By fitting asymmetries in the light curves using spotting parameters, the spotting activity for both stars can be determined. From the spotting parameters it is possible to compare the spotting activity of these two near-contact binaries to the spotting activity of 47 contact binaries (Csizmadia et al., 2004). The author determined that, for both TZ Dra and CN And, spots are located at positions that were previously not seen in other observations of contact binaries (Hill, 2007).
Department of Physics and Astronomy

The work is situated in a literary and theoretical context by working with the concepts of authenticity and realism, and within that the story/world distinction. The literary context is examined in terms of realism, naturalism, and the novel of character or psychological novel. The associated research is then discussed. Finally, the novel’s societal context is analysed in terms of some prevailing philosophical views and the existing socio-political structure.

Gamma-ray binaries are systems that comprise a compact object orbiting a companion star and display the maximum of the non-thermal Spectral Energy Distribution (SED) in gamma rays. Currently we know five gamma-ray binaries. All of them host an early type star and a compact object of unknown nature, either a black hole or a neutron star, except for one of them where radio pulsations have been detected. The optical emission received from gamma-ray binaries is produced by the optical star and its environment. If the optical star is a Be star, then it presents a circumstellar decretion disk, being its size traced by the Equivalent Width of the Halpha line (EW). Numerical simulations of gamma-ray binaries hosting a Be star suggest that the circumstellar decretion disk is perturbed/disrupted during the periastron passage of the compact object by the tidal forces and/or the putative pulsar wind. The circumstellar disk contribution to the optical photometry is a significant fraction of the total optical emission. The observed optical photometric flux from it will be proportional to the projected area of the optically emitting disk. Therefore, any orbital variability in the optical light curves can be associated to changes in the circumstellar disk. We conducted long-term optical photometric and EW observations of the gamma-ray binary LS I +61 303, aimed to unveil the optical superorbital variability seen at other wavelengths. We obtained the following results from the observations: 1) The optical photometry and EW present a superorbital variability of the orbital phase of the maximum, as seen in radio and X-rays, providing an evidence of the coupling between the thermal and non-thermal emission processes in LS I +61 303. 2) The optical observations present a superorbital variability of the flux compatible with the 1667 d superorbital period. 3) This superorbital variability is attenuated or missing in some orbital phases. 4) Orbital variability in a multi-wavelength context presents lags that can be naturally interpreted considering different emitting regions. 5) The observations seem to be only compatible with an extended and (quasi)-coplanar circumstellar disk. 6) The observations are compatible with a density wave scenario, and with a very restrictive precessing-disk model. Gamma-ray binaries hosting a massive star and a young non-accreting pulsar present strong interaction between the relativistic pulsar wind, and the wind of the stellar companion, resulting in efficient particle acceleration and in the production of non-thermal radiation, from radio to gamma rays. The study of the dynamical interaction between the winds can be conducted through numerical simulations, allowing a qualitative analysis of the radiative output of the system. Furthermore, the two-wind interaction region might suffer the impact of an inhomogeneous stellar wind (hereafter clumps), making its dynamics and hence its radiative output more complex. We conducted RHD simulations of the interaction of relativistic winds from young pulsars with inhomogeneous stellar winds aimed to provide a plausible framework for the high-energy variability observed in gamma-ray binaries. We obtained the following results from the numerical simulations: 1) The two-wind interaction structure is very unstable and sensitive to the tiniest perturbations, which lead to quick Rayleigh-Taylor (RT) and in particular Kelvin-Helmholtz (KH) instability growth. 2) The arrival of clumps can have a very strong impact on the whole interaction structure, which is expected to strongly affect the non-thermal radiation as well. 3) The clumps trigger violent RT/KH instabilities leading to quick changes of the shocked pulsar-wind region. 4) Clumps generate quick and global variations in the shocked pulsar wind. This can lead to strong short time-scale flux variability in the non-thermal radiation of gamma-ray binaries.

The study of white dwarfs (WDs) provides insight into understanding WD formation rates, evolution, and space density. Individually, nearby WDs are excellent candidates for astrometric planetary searches because the astrometric signature is greater than for an identical, more distant WD system. As a population, a complete volume-limited sample is necessary to provide unbiased statistics; however, their intrinsic faintness has allowed some to escape detection. The aim of this dissertation is to identify nearby WDs, accurately characterize them, and target a subset of potentially interesting WDs for follow-up analyses. The most unambiguous method of identifying new WDs is by their proper motions. After evaluating all previous southern hemisphere proper motion catalogs and selecting viable candidates, we embarked on our own southern hemisphere proper motion survey, the SuperCOSMOS-RECONS (SCR) survey. A number of interesting objects were discovered during the survey, including the 24th nearest star system -- an M dwarf with a brown dwarf companion. After a series of spectroscopic observations, a total of 56 new WD systems was identified (18 from the SCR survey and 38 from other proper motion surveys). CCD photometry was obtained for most of the 56 new systems in an effort to model the physical parameters and obtain distance estimates via spectral energy distribution fitting. An independent distance estimate was also obtained by deriving a color-MV relation for several colors based on WDs with known distances. Any object whose distance estimate was within 25 pc was targeted for a trigonometric parallax via our parallax program, CTIOPI. Currently, there are 62 WD systems on CTIOPI. A subset of 53 systems has enough data for at least a preliminary parallax (24 are definitive). Of those 53 systems, nine are previously known WDs within 10 pc that we are monitoring for perturbations from unseen companions, and an additional 29 have distances within 25 pc. Previously, there were 109 known WDs with parallaxes placing them within 25 pc; therefore, our effort has already increased the nearby sample by 27%. In addition, at least two objects show hints of perturbations from unseen companions and need follow-up analyses.

In this thesis we have developed a tool for the computation of non-thermal emission in astrophysical sources. The code reads the hydrodynamic data coming from relativistic hydrodynamic simulations and compute the injection, evolution and radiation of non-thermal particles. The emission channels explored in the thesis are mainly Inverse Compton (IC) and synchrotron. Making use of this tools, we have studied the following sources: Star-jet interactions in agn Some galaxies with an Active Galactic Nucleus (AGN) present two jets of relativistic particles. The pressence of this jets is linked with the merge of galaxies, as well as the posibility of starbursts. Therefore, it is plausible that an important amount of stars could interact with the relativistic jets. We have expored that situation performing simulations of an encounter between the jet and an isolated star. The result or our simulations is a potentially observable gamma-ray emission related with this interactions. Pulsar wind interacting with a clumply stellar wind Gamma-ray binaries are two-body systems in which one of the objects is compact (either a neutron star or a black hole) and the other one is a star, with their spectral energy distribution (SED) peaking above 1 MeV (gamma rays). Here we focus on the cases in which the companion star is massive, presenting strongly inhomogeneous winds with clumps. The interaction of one of these clumps with a pulsar wind is simulated, and the results obtained showed that this type of inhomogeneities enhance the gamma radiation. An specific study of the source PSR B1259 − 63 was performed. Clumpy wind-jet interactions in hmmqs High-mass microquasars (HMMQs) are binaries compound by a high-mass star and a compact object accerting material. The compact object form two collimated jets and here we explore the possibility that the jet interacts with a stellar wind inhomogeneity, or clump. We found that for the clump with the studied characteristics, the inhomogeneity is able so survive enough time to emit gamma rays before disruption. Moreover, the luminosity levels found could be enough to explain the observations of Cyg X- 1 and Cyg X-3 adopting conservative parameters. A specific study for Cyg X-1 was carried out.
En estos más de tres años de investigación hemos trabajado en uno de los grandes problemas de la astrofísica de altas energías: cuál es el mecanismo de producción de radiación no térmica en fuentes relativistas. Nosotros hemos propuesto una serie de modelos centrándonos en la relación de outflows relativistas con su entorno, proponiendo que si éstos interaccionaban con ciertos obstáculos, formarían choques. En estos choques, aunque en el caso relativista aún no se tiene un conocimiento profundo de su funcionamiento, se sabe que se produce aceleración de partículas no térmicas, dando lugar también a emisión de altas energías. Distinguimos la emisión no térmica (responsable de los fenómenos que emiten rayos gamma, que son los que más nos interesan) de la térmica porque, a diferencia de ésta, no se produce por la agitación aleatoria de las partículas debido a su temperatura. La emisión no térmica involucra a menudo la interacción de las partículas con los campos electromagnéticos de sus alrededores. En nuestro caso, nos hemos centrado en la emisión IC (Inverse Compton, interacción partícula-fotón) y en la emisión sincrotrón (interacción partícula-campo magnético) porque eran las más relevantes en nuestros casos de interés. El método que hemos seguido para estudiar los distintos casos ha sido el siguiente: nuestros colaboradores hacían simulaciones hidrodinámicas (2D, relativistas, con simetría cilíndrica) de la fuente de interés, obteniendo una red de datos en dos dimensiones. Después reducían el problema a una serie de líneas de fluído , que contenían los datos hidrodinámicos que nos facilitaban a nosotros. Con estas líneas de fluido nosotros calculábamos la inyección de partículas no térmicas siguiendo una serie de prescripciones fenomenológicas sobre su distribución de energías, su evolución a lo largo de la línea de fluido y del tiempo, y por último su radiación no térmica (IC y sincrotrón). Con este método podíamos obtener las distribuciones espectrales de nuestras fuentes, así como mapas de emisión. Hemos empleado este método para estudiar tres tipos de fuentes: 1) Interacciones jet-estrella en AGNs Algunas galaxias que tienen un núcleo de galaxia activo (AGN, por sus siglas en inglés) presentan un par de chorros de partículas relativistas, muy colimados y opuestos, también conocidos como jets. La formación de estos jets está ligada a episodios de colisión de galaxias, un proceso llamado merging que también suele implicar que se dispare el ritmo de formación estelar. De esta forma, es esperable que el número de interacciones de estos jets con las poblaciones de estrellas circundantes sea alto. Nosotros nos centramos en una sola interacción, para la que simulamos un jet persistente interaccionando con una estrella individual. El resultado de estas simulaciones es que el área efectiva donde se produce la emisión no térmica es mucho mayor que el área asociada a la región donde el choque es más intenso, por lo que la cantidad de radiación que puede generar es mayor de la que se esperaba. En cuanto a los resultados radiativos, observamos que la orientación del jet con respecto al observador (situado en la Tierra) es de vital importancia, debido al efecto Doppler que sufre la radiación, al ser el jet relativista. También observamos que un campo magnético relativamente alto puede atenuar mucho la componente IC de la radiación y, por tanto, disminuir la emisión por encima del GeV. Los niveles energéticos que encontramos hacen pensar que una población de estrellas interactuando con el jet de un AGN podrían dar lugar a emisión gamma detectable desde la Tierra. 2) Púlsar interaccionando con un viento estelar inhomogéneo Las binarias de rayos gamma son sistemas de dos cuerpos en los que uno es un objeto compacto (básicamente, un agujero negro o una estrella de neutrones) y el otro es una estrella, con la peculiaridad de que su distrubución espectral de emisión (SED) tiene el máximo por encima de 1 MeV, es decir, están fuertemente dominados por procesos no térmicos. La emisión en rayos gamma de estas binarias ha sido estudiada con anterioridad, pero aquí nos centramos, de nuevo, en la interacción de un viento relativista (en este caso, proveniente del púlsar) con un obstáculo de gran inercia (en este caso, una inhomogeneidad del viento estelar). Estas inhomogeneidades, o grumos (clumps en inglés), pueden tener una densidad considerablemente mayor que el resto del viento estelar, y se espera que estén presentes en los vientos de las estrellas más masivas. La interacción del viento del púlsar con el grumo del viento estelar produce una región chocada alrededor de este último. En función del tamaño y la densidad del grumo, esta región chocada puede acercarse más al púlsar, siendo afectada así por un viento más potente, menos diluído, modificando los patrones de pérdidas de energía de las partículas. Con nuestros cálculos hemos podido comprobar cómo al introducir estas inhomogeneidades se consiguen efectivamente emisiones significativamente mayores en la mayoría de configuraciones. Este modelo se ha aplicado a una fuente concreta, la binaria PSR B1259-63, no siendo posible explicar los estallidos en la banda de los GeV observados por Fermi. Por otra parte, para esa misma fuente se encontró que si se modelaba el disco de decreción que se espera que tenga la estrella compañera como una inhomogeneidad grande interactuando con el viento del púlsar, la SED se acercaba más a las luminosidades en TeV observadas 20 días después del periastro, apuntando a una relación entre el objeto compacto y el disco de decreción como fuente de rayos gamma en el rango TeV. 3) Inhomogeneidades de un viento estelar en un jet de HMMQ Los microquásares de alta masa (HMMQ, por sus siglas en inglés) consisten en un objeto compacto orbitando alrededor de una estrella masiva. Parte del material de la estrella, que en este caso tiene vientos muy poderosos, es acretado por el objeto compacto formando una pareja de jets. En nuestro estudio, hemos intentado modelar la emisión gamma explorando el escenario en el que ciertas inhomogeneidades en el viento estelar (de nuevo, grumos) eran capaces de entrar en el jet, provocando un choque y, por lo tanto, acelerando partículas no térmicas. El estudio, en este caso, tuvo dos componentes importantes, el cálculo de las condiciones necesarias para que la interacción entre el grumo del viento estelar y el jet fuera posible y eficiente, y la simulación del proceso, llevadas a cabo por nuestros colaboradores; y el posterior cálculo de la radiación no térmica, llevada a cabo mediante el código desarrollado en esta tesis. La primera parte del estudio estimaba que básicamente deberíamos esperar que más o menos siempre hubiese una inhomogeneidad del tamaño y densidad estudiados interaccionando con el jet. Grumos más grandes serían menos probables y quizá demasiado masivos para el jet, disgregándolo en el proceso, mientras que grumos más pequeños, menos densos, o impactando en las zonas más cercanas a la base del jet, serían destruídos antes de poder penetrar. En este caso, aunque el trabajo se hizo de forma genérica para cualquier microquasar de alta masa, nos centramos en los dos HMMQs que emiten en rayos gamma que se conocen hasta la fecha, Cyg X-1 y Cyg X-3. El resultado de nuestro trabajo es que con los parámetros que nosotros manejamos pueden reproducirse las luminosidades de estas fuentes imponiendo eficiencias no térmicas conservadoras. Incluso comparamos las SED predichas con las observaciones Fermi de Cyg X-1, mostrando que son compatibles empleando valores razonables del campo magnético, ángulo de visión y eficiencia en la aceleración de partículas no térmicas.

Questa tesi di dottorato è focalizzata sulle controparti elettromagnetiche (EM) dei segnali di onde gravitazionali (GW) generati dai merger di sistemi di due stelle di neutroni (NSNS) e sistemi buco nero-stella di neutroni (BHNS). Ho sviluppato dei modelli semi-analitici per prevedere l’emissione a varie lunghezze d’onda dai merger di BHNS, includendo la kilonova, il suo radio remnant, la prompt emission del getto relativistico e il seguente gamma-ray burst (GRB) afterglow. Adottando delle formule di fit dalla letteratura, ho stabilito un legame tra i parametri della binaria e le proprietà delle controparti EM. Ho anticipato la varietà e l’alto grado di degenerazione delle controparti EM dai merger di BHNS. Ho mostrato come l’analisi congiunta GW+EM può ridurre questa degenerazione, eseguendo un esperimento concettuale di stima dei parametri multi-messaggera, considerando un merger BHNS con una kilonova associata. I miei risultati indicano che l’analisi congiunta può produrre migliore informazione sui parametri della binaria. Ciò porterebbe ad una maggiore comprensione della fisica fondamentale delle stelle di neutroni e dei buchi neri (ad esempio l’equazione di stato e la massa massima delle stelle di neutroni, la distribuzione di spin dei buchi neri) e darebbe informazioni sulla formazione ed evoluzione delle binarie di oggetti compatti. Ho analizzato i merger “ambigui” di binarie (ossia consistenti sia con NSNS che BHNS), la cui natura potrebbe non essere identificata attraverso il solo segnale gravitazionale. Nel caso BHNS, la binaria ospiterebbe un BH stellare “leggero”, la cui massa cadrebbe nella discontinuità tra le masse di stelle di neutroni e buchi neri (mass-gap) attesa teoricamente e ad oggi confermata osservativamente. Ho trovato che l’osservazione della kilonova associata potrebbe svelare la natura del sistema, poiché nel caso BHNS può essere molto più luminosa rispetto al caso NSNS. Applicando questa analisi all’evento GW190425, ho trovato che la kilonova sarebbe stata osservabile se la binaria avesse ospitato un buco nero (e se la sorgente fosse stata localizzata in cielo con precisione). Ciò avrebbe permesso potenzialmente di identificare la natura del sistema in coalescenza. L’osservazione di una kilonova da un evento “ambiguo” consistente con la natura BHNS sarebbe il primo indizio dell’esistenza di buchi neri stellari “leggeri”, confutando il mass-gap. Ciò fornirebbe nuove informazioni sulla massa massima delle stelle di neutroni e sulla loro equazione di stato, e avrebbe un forte impatto sui modelli di esplosione di supernova, favorendo quelli che producono uno spettro continuo per la massa dei relitti. Ho presentato un metodo per ottimizzare le campagne di follow-up EM, basato sulla conoscenza della massa di chirp del sistema. Con questa informazione, le configurazioni NSNS e BHNS compatibili possono essere ottenute ed il range atteso di curve di luce di kilonova in diverse bande può essere calcolato. La probabilità di osservare la controparte EM di un evento GW potrebbe essere aumentata se fosse data priorità al follow-up fotometrico e/o spettroscopico dei transienti che risultato consistenti alla loro prima osservazione con il range di kilonova atteso. Infine ho studiato le probabili distribuzioni delle proprietà EM dei merger NSNS e BHNS che saranno osservati in futuro con le onde gravitazionali. Ciò potrebbe rappresentare un ulteriore utile contributo per l’organizzazione della strategia di follow-up.
This PhD dissertation is focused on the electromagnetic (EM) counterparts of gravitational waves (GW) signals from double neutron star (NSNS) and black hole-neutron star (BHNS) mergers. I developed semi-analytical models to predict the multi-wavelength emission from BHNS mergers, including the kilonova, its radio remnant, the prompt emission from the relativistic jet and the related gamma-ray burst (GRB) afterglow. Adopting fitting formulae in the literature, I established a link between the binary parameters and the EM counterparts properties. I anticipated the variety and the high degree of degeneracy of EM counterparts from BHNS mergers. I showed how joint GW+EM analysis can reduce this degeneracy, performing a proof-of-concept multi-messenger parameter estimation, considering a BHNS merger with an associated kilonova. My results indicate that joint analysis can produce better constraints on the binary parameters. This would lead to a deeper understanding of the NS and BH fundamental physics (e.g. the NS equation of state and maximum mass, the BH spin distribution) and would give information on the formation and evolution of compact object binaries. I analyzed “ambiguous” coalescing binaries (consistent with both NSNS and BHNS), whose nature may not be identified through the GW signal alone. In the BHNS case, the binary would host a “light'' stellar BH, with the mass falling in the theoretically expected and to date observationally confirmed discontinuity between NS and BH mass distributions (mass-gap). I found that the observation of the associated kilonova could unveil the system’s nature, as in the BHNS case it can be far more luminous with respect to the NSNS case. Applying this analysis to the GW190425 event, I found that the kilonova would have been detectable if the binary had hosted a BH (if the source had been precisely localized), potentially disentangling the nature of the merging system. The observation of a kilonova from an “ambiguous'' event consistent with a BHNS nature would be the first hint of the existence of “light” stellar BHs, confuting the mass-gap. This would provide new constraints on the NS maximum mass and equation of state, and it would strongly impact the supernova explosion models, favoring those producing a continuum spectrum of remnant masses. I presented a method to optimize the EM follow-up campaigns, based on the knowledge of the system's chirp mass. With this information, the compatible NSNS and BHNS configurations can be obtained and the expected ranges of kilonova light curves in different bands can be computed. The probability of detecting the EM counterpart of a GW event could be enhanced if the observation of transients consistent at their first detection with the expected kilonova ranges was prioritized for photometric and/or spectroscopic follow-up. Finally I studied the EM counterparts properties distributions of future NSNS and BHNS mergers detected with gravitational waves. This could represent another useful contribution for EM follow-up strategy organization.

Gamma-ray binaries are extreme systems that produce non-thermal emission from radio to very-high-energy (above TeV) gamma rays, with the energy output in the spectral energy distribution (SED) dominated by the MeV–GeV photons. Their broadband emission is usually modulated by the orbital cycle of the system, which suggests that the physical conditions are also periodic and reproducible. The diversity of systems, together with the reproducibility of the conditions within each system, makes gamma-ray binaries excellent physical laboratories in which high energy particle acceleration, diffusion, absorption, and radiation mechanisms can be explored. Nevertheless, the number of known gamma-ray binaries is still very limited, and only a six binary systems have been classified as gamma-ray binaries. These systems produce outflows of relativistic particles emitting synchrotron radio emission that extend up to several astronomical units, which correspond to projected angular scales of a few milliarcseconds (mas) at typical distances of 2-3 kpc. Very Long Baseline Interferometry (VLBI) provide mas resolution and therefore can be used to directly see this radio outflow. In this thesis we present VLBI observations of five of the six gamma-ray binaries known. We have revealed for the first time the radio structure of two gamma-ray binaries, and found periodic changes in the structure of other two. Based on these results, we have established the basic properties and behaviour of the radio emission of gamma-ray binaries on AU scales, and we have contributed to find characteristics that are common to all of them.
En los últimos años se ha producido una mejora significativa de los instrumentos que permiten observar fenómenos astrofísicos en rayos gamma de alta y muy alta energía. Gracias a estos avances, se ha podido detectar emisión de rayos gamma en sistemas binarios. Tan sólo seis sistemas binarios han sido clasificados como estrellas binarias de rayos gamma (tres de ellos aún son candidatos). Estos sistemas producen chorros de material relativista que a su vez producen grandes cantidades de energía en todo el espectro electromagnético, desde ondas radio hasta emisión de rayos gamma hasta energías del teraelectronvolt (TeV). Estos chorros se desplazan a alta velocidad produciendo estructuras en escalas de varias unidades astronómicas (UA). Estas estructuras pueden ser observadas directamente mediante técnicas de interferometría radio de muy larga línea de base (VLBI). En esta tesis nos centramos en el estudio de las propiedades morfológicas y astrométricas de binarias de rayos gamma observadas mediante VLBI. De las seis binarias conocidas, se han observado cinco de ellas. Los resultados principales son los siguientes. Se ha detectado estructura extendida en escalas de 120 UA en el sistema binario PSR B1259-63. Esta ha sido la primera evidencia observacional de que púlsares jóvenes no acretantes interaccionando con estrellas jóvenes pueden producir emisión radio extendida. Se ha descubierto que la emisión del sistema LS 5039 muestra cambios periódicos en su morfología, que son estables en escalas de varios años. También se ha determinado el movimiento propio de este sistema y se ha obtenido su trayectoria galáctica en el pasado. Se ha confirmado que el sistema LS I +61 303 muestra variabilidad orbital periódica, aunque presenta cambios significativos en ciertas fases orbitales. Se ha encontrado un desplazamiento del pico de la emisión a varias frecuencias, así como un cambio en sus posiciones relativas. Se ha descubierto emisión extendida procedente de la fuente de rayos gamma HESS J0632+057, y se ha confirmado inequívocamente su asociación con el sistema binario MWC 148. Por último, no se ha encontrado contrapartida radio a la fuente de rayos gamma AGL 2241+4454, cuya contrapartida óptica ha sido propuesta en el sistema MWC 656. Estos resultados permiten sentar las bases de la estructura en escalas de varias UA de los sistemas binarios de rayos gamma, así como su comportamiento en función de la fase orbital. Las características comunes halladas en estos sistemas ha permitido encontrar enlaces observacionales entre estos sistemas, dando consistencia a este particular grupo de estrellas que presentan emisión en rayos gamma.

In the last decade, new kinds of European populist parties and movements characterized by a left wing, right wing or “eclectic” attitude have succeeded in entering in governments where they could exert a direct populist influence on their coalition partners or, conversely, become victims themselves of the influence of the institutional background. Such a scenario brought this research to formulate two questions: (i) “To what extent did populist parties succeed in influencing their government coalition partners, leading them to adopt populist rhetoric and change their policy positions?” and (ii) “Have populist parties been able to retain their populist “outside mainstream politics” identity, or have they been assimilated to mainstream parties?”. As a case study this project chose the Italian Five Star Movement. Since 2018 this eclectic populist actor has experienced three different governments first with the radical right wing populist League (2018-2019) and then with the mainstream center left Democratic Party (2019-2021). In addition to this, currently the Five Star Movement is a coalition partner of the ongoing Draghi’s government. Theoretically based on the ideological definition of populism (Mudde, 2004), on a new “revised” model of the inclusionary - exclusionary framework to classify populist parties and on a novel definition of “populist influence”,this research made use of both quantitative (bidimensional and text analysis) and qualitative methods (semi-structured interviews) and mainly focuses on the years 2017- 2020.The importance of this study is threefold. First it contributes to the study of populist influence in government in relation to the ideological attachment of the political actors involved. Second, it contributes to understand if populists in power necessarily need to tone down their anti-system character in order to survive. Third, this study introduces conceptual and methodological novelties within the study of populism and populist influence in government.

In this thesis, observations of the Earth's magnetotail from ESA's four Cluster and the two Sino-European Double Star spacecraft are presented. The observations are of intervals where data from the combination of Cluster and Double Star provide insights into the dynamics of the magnetotail that are not possible using data from one mission alone. In the first study, observations of three magnetic flux ropes are presented, two of which were detected near-simultaneously at Cluster and Double Star TC-1, while the third was detected by Cluster, along with a TCR a few minutes later. The observations represent the first observations of multiple flux ropes existing in the magnetotail simultaneously, providing evidence that flux rope orientation is influenced by neutral sheet tilt and provide further evidence that TCRs in the lobes are caused by the passage of flux ropes in the plasma sheet. In the second study, a detailed analysis of a plasma bubble is presented, including the first direct observations of the return flows around the flanks of the plasma bubble that are expected from theory and simulation. Furthermore a partially stagnant depleted wake behind the plasma bubble, not predicted by theory or simulation was discovered and the cross-tail extent of the bubble was measured to be 3RE. The first observations of near-Earth bubble features are also reported. Finally, in the third study, the substorm onset process itself is investigated using a wide array of space- and ground-based instrumentation. A pseudobreakup and later substorm onset are distinguished using both geomagnetic and auroral data and the establishment of the substorm current wedge is observed in-situ using the TC-2 and GOES12 spacecraft. A link between higher latitude geomagnetic activity and the fast flows and plasma sheet expansion related to the reconnection of lobe field lines is also posited.

The high energy astrophysics, specifically the gamma-ray astrophysics, studies the processes that cannot be caused by hot matter but by other mechanisms colled non thermaland processes, which involve matter with energies above ~ 1 MeV. There are currently a number of instruments able to detect this radiation, such as AGILE and Fermi satellites or Cherenkov telescopes like MAGIC at the Earth's surface. In this thesis we studied two main types of systems that, as it has been observed or theoretically predicted, can produce gamma radiation : young stellar objects and high-mass X-ray binaries. Young stellar objects are found in regions of star formation, which are the cradles where new stars are being formed. The star-forming regions are populated with protostars and young stars, among other objects. Protostars still accrete matter from the parent cloud through an accretion disk, while expelling material through a jet formed by magnetic interaction. In these jets the particles are ejected at high speeds out of the system and in some cases reach relativistic velocities, as evidenced by the detection of non-thermal radio emission in some of these objects. In this thesis we are interested to find more evidence of young stellar objects that present non-thermal emission, either in the range of X-rays or gamma rays. To find new candidates have used the first catalog of the Fermi satellite and the catalogs of young systems in our Galaxy. Besides the search through catalogs, we did a study using archival X-ray XMM-Newton data on the young stellar object IRAS 16547-4247, which is known to display non-thermal radio emission. This object is a protostar still accretes material through an accretion disk and also ejects jets of material through particle. We discovered its X-ray counterpart and studied the interaction of its jets through a theoretical model. Finally, we studied a region of star formation that has been found in spatial coincidence with a second Fermi source catalog, known as Monoceros R2 . We analyzed the Fermi data from this source and our results allow us to say that the detected gamma-ray emission is consistent with that expected by the collective effects of a population of protostars. Among the other large block of this thesis there are high-mass X-ray binares. The most relevant of which we have studied is MWC 656. This system consists of a Be star and a black hole, a combination that has never been detected before. We have observed this source with XMM-Newton in X-rays and with the MAGIC Telescopes in very high energy gamma rays. Our X-ray observation has led to the discovery of the X-ray counterpart of this binary system and has allowed us to classify it as a high-mass X-ray binary, the first composed of a Be star and a black hole. Other systems we studied with MAGIC are HESS J0632 +057 and SS 433. HESS J0632 +057 is a binary system consisting of a Be star and a compact object of unknown nature and was identified by us as a gamma-ray emitter. We have also observed SS 433, the first microquasar ever discovered. We observed this source during 2010 May and June, but it has not been detected. We have calculated upper limits to the emission of very high energy gamma-rays to put constraints on the physical parameters of the system.
L'astrofísica d'altes energies i en concret l'astrofísica de raigs gamma, estudia els processos d'emissió que no poden ser causats per matèria calenta, sinó per altres mecanismes que anomenem no tèrmics i que comporten que la matèria que emet aquesta radiació tingui energies per sobre d'1~MeV. Actualment disposem d'un bon nombre d'instruments capaços de detectar aquesta emissió, com ara els satèl•lits Fermi i AGILE o els telescopis Cherenkov com MAGIC, a la superfície terrestre. En aquesta tesi hem estudiat principalment dos tipus de sistemes que, tal com s'ha observat o predit teòricament, poden produir radiació gamma: els objectes estel•lars joves i els sistemes binaris de raigs X d’alta massa. Els objectes estel•lars joves els trobem a les regions de formació estel•lar, que són els bressols on noves estrelles s'estan formant. Els pobladors de les regions de formació estel•lar són les protoestrelles i les estrelles joves, entre altres objectes celests. Les protoestrelles encara acretem matèria del núvol progenitor a través d'un disc d'acreció, i al mateix temps expulsen material per mitjà d'uns dolls formats per interacció magnètica. En aquests dolls les partícules són expulsades a grans velocitats cap a fora del sistema i en alguns casos assoleixen velocitats relativistes tal com evidencia la detecció d'emissió ràdio no tèrmica en alguns d'aquests objectes. En aquesta tesi ens hem interessat per trobar evidència de més objectes estel•lars joves que presentin emissió no tèrmica, ja sigui en el rang dels raigs X o dels raigs gamma. Per a trobar nous candidats hem aprofitat el primer catàleg del satèl•lit Fermi i l'hem creuat amb catàlegs d'objectes joves de la Galàxia. A més a més de la cerca per mitjà de catàlegs, hem fet un estudi en raigs X a partir de dades d'arxiu disponibles sobre un objecte estel•lar jove del que ja es coneix emissió no tèrmica en ràdio: IRAS 16547-4247. Aquest objecte és una protoestrella que encara acreta material per mitjà d'un disc d'acreció i que alhora expulsa material a través de dolls de partícules. Hem descobert la contrapartida en raigs X d'aquest sistema i l'hem estudiat per mitjà d'un model teòric. Finalment, hem estudiat una regió de formació estel•lar que s'ha trobat en coincidència espacial amb una font del segon catàleg de Fermi, coneguda com Monoceros R2. Hem analitzat les dades de Fermi d'aquesta font i els nostres resultats ens permeten dir que l'emissió gamma detectada és compatible amb el que s'esperaria que produissin un conjunt de protoestrelles. Dins de l'altre gran bloc d'aquesta tesi trobem les estrelles binàries de raigs X d'alta massa. El cas més rellevant dels que hem estudiat és el de MWC 656. Aquest sistema està format per una estrella Be i un forat negre, una combinació que mai s'havia detectat. Nosaltres hem observat aquesta font amb el telescopi de raigs X XMM-Newton i amb els Telescopis MAGIC, en raigs gamma de molt alta energia. La nostra observació de raigs X ha suposat la descoberta de la contrapartida de raigs X d'aquest sistema binari i ens ha permès classificar-la com a binària de raigs X d'alta massa, la primera composada per una estrella Be i un forat negre. Altres sistemes que hem estudiat amb MAGIC són HESS J0632+057 i SS 433. HESS J0632+057 és un sistema binari format per una estrella Be i un objecte compacte de natura desconeguda i va ser detectat per nosaltres com a emissor de raigs gamma. També hem observat SS 433, el primer microquàsar que es va descobrir. Hem observat aquesta font durant els mesos de maig i juny de 2010 però no s'ha detectat. Així, hem calculat límits superiors a l'emissió gamma de molt alta energia que serveixen per a posar restriccions en paràmetres físics.

Neste trabalho determinamos a estrutura dos níveis dos estados quase-ligados e virtuais em sistemas de poços quânticos acoplados de AlGaAs-GaAs na presença de um campo elétrico externo (Voltagem) perpendicular às camadas semicondutoras. As heteroestruturas de AlGaAs-GaAs são modeladas por um conjunto de poços quânticos de potencial unidimensionais. Utilizamos a aproximação de função envelope que reduz o problema à solução usual da Equação de Schroedinger de massa efetiva. Os níveis eletrônicos são então determinados utilizando a solução exata da Eq. de Schroedinger em termos das funções de Airy nos poços e barreiras e um formalismo de Matriz de Iteração com Análise de \"Phase-shift\". Nossos resultados estão em boa concordância com resultados experimentais de transições ópticas. Motivados pelas propriedades singulares dos sistemas de dupla barreira, investigamos o tunelamento ressonante de elétrons através de multi-barreiras e a formação de regiões de resistência negativa na curva característica de corrente X voltagem. Para os processos de tunelamento em multi-barreiras determinamos o Coeficiente de Transmissão, como função da energia do elétron incidente, usando o formalismo de Matriz de Iteração. Este método pode ser bastante útil na interpretação de resultados experimentais nestes dispositivos. Calculamos também a densidade de corrente de tunelamento versus a voltagem aplicada no caso de dupla barreira de modo a interpretar recentes resultados experimentais.
In this work the quasi-bound and virtual levels of both electrons and holes are determined in the case of coupled AlxGa1-xAs-GaAs quantum wells in the presence of an external electric (Voltage) perpendicular to the layers. The heterostructures field of AlxGa1-xAs-GaAs are mimicked by a set of unidimensional quantum well potentials. We employ the envelope function approximation and solve the usual effective mass Schrödinger Equation. The electronic levels are then determined by using the exact solution of Schrödinger Eq. in terms of Airy functions into the wells and barriers and an Iteraction Matrix formalism with the Phase-shift method. Our results are in a good agreement with the experimental results of optical measurements. Motivated by the unusual properties of double-barriers devices we investigated the resonant tunneling of electrons through multi-barriers. The transmission Coefficient as a function of energy of the incident electron is determined by using an Interaction Matrix formalism. This method can be very useful in the interpretation of experimental results in semiconductor devices. We also calculate the tunneling current density as a function of applied voltage in the case of a double-barrier in order to interpret recent experimental results.

The multiple star system omicron Andromedae has been studied using high signal-to-noise ratio Reticon spectra. The narrow absorption features superimposed on the rotationally broadened Mg II ⋋ 4481 line of o And A are almost certainly from the spectrum of o And B which is shown to be a double-lined spectroscopic binary with a period of 33 days. The speckle interferometrically measured separations of A-a and A-B indicate that the system contains at least two binaries separated by some 25 AU, based on a parallax of 0.015 ± 0.008 arcseconds. Based on this parallax the A-a separation of is about 4 AU. The two stars which make up the unresolved spectroscopic binary o And B are separated by about 0.4 AU based on an orbital solution. The periods, based on the parallax and reasonable mass estimates, for A-a and Aa-B, are on the order of four and thirty years respectively. The two stars which constitute o And B are shown to most likely be late B stars of luminosity class V-IV. After compensating for the presence in the spectrum of a contribution from component B, o And A is reclassified as B5lIIe. The spectral type of o And a is not known and no contribution to the spectrum from it is observed. High signal-to-noise time series of spectra have revealed the presence of nonradial pulsations. An intermediate order, Ɩ = 6 mode, reveals itself through moving subfea-tures in the line profiles. Line width variations are detected which probably arise from an Ɩ = 2 low order mode. The co-existence of these two modes is capable of explaining the 1.57 day photometric variations. This period is twice that of the line width variations. Rapid radial velocity variations measured from the line wings were found but the line profile variations and the nature of the light curve do not support the existence of a fifth star. The measured radial velocity variations could be a result of the underlying profile variations as opposed to motion of o And A.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

Les nébuleuses planétaires (NP) sont le produit de l'évolution d'étoiles de masses intermédiaires après leur expansion sphérique à la fin de leurs vies. Il a été estimé observationnellement que 80 % des NP ont des formes non-sphériques. Une fraction si élevée est déroutante et a mobilisé la communauté de recherche sur les NP pendant plus de trente ans. Un scénario qui permettrait de justifier les formes observées serait que les étoiles progénitrices de noyaux de NP (NNP) ne sont pas simples, mais possèdent un compagnon. Les formes des nébuleuses seraient ainsi le résultat de l'interaction avec le compagnon. La fraction si élevée de NP non-sphériques impliquerait donc une fraction élevée de NNP binaires, faisant de la parité stellaire un canal de formation privilégié pour les NP. Après avoir présenté l'état de connaissance actuelle concernant la formation et la mise en forme des NP, je présente mes travaux visant à détecter un excès infrarouge qui serait la signature de la présence d'un compagnon orbitant le NNP. La première partie de ce projet consiste en l'analyse de données et photométrie acquises par moi-même. Dans la deuxième partie je présente une tentative d'utilisation de jeux de données d'archives : la campagne optique Sloan Digital Sky Survey Data Release 7 et la version étendue de la base de données assemblée par Frew (2008). Je présente aussi les résultats d'une analyse de vitesses radiales de spectres VLT/UVES pour 14 NNP dans le but de détecter des compagnons spectroscopiques. Finalement j'expose les détails d'une analyse de photométrie de données optiques dans le but de détecter des compagnons orbitant autour de NNP en utilisant la technique de variabilité photométrique. Le résultat principal de cette thèse réside dans les analyses d'excès infrarouge proche que je combine avec des données publiées précédemment. Je conclus que si la fraction détectée d'excès infrarouge proche est attribuée à la présence de compagnons stellaires, alors la fraction binaire de NNP est plus grande que celle attendue en se basant sur la population binaire de progéniteurs de la séquence principale et ainsi conclus que la multiplicité stellaire est un canal de formation privilégié pour la formation des NP. Je clos en soulignant la nécessité d'un échantillon d'étude d'environ 150 objets pour réduire l'incertitude sur la fraction binaire et appuyer les conclusions statistiques de ce résultat
Planetary nebulae (PNe) are the products of the evolution of intermediate mass stars that have expanded spherically at the end of their lives. Observationally, it has been estimated that 80% of them have non-spherical shapes. Such a high fraction is puzzling and has occupied the PN community for more than 30 years. One scenario that would allow to justify the observed shapes is that a comparable fraction of the progenitors of central stars of PN (CSPN) are not single, but possess a companion. The shape of the nebulae would then be the result of an interaction with this companion. The high fraction of non-spherical PNe would thus imply a high fraction of binary CSPN, making binarity a preferred channel for PN formation. After presenting the current state of knowledge regarding PN formation and shaping and reviewing the diverse efforts to find binaries in PNe, I present my work to detect a near-infrared excess that would be the signature of the presence of cool companions. The first part of the project consists in the analysis of data and photometry acquired and conducted by myself. The second part details an attempt to make use of archived datasets: the Sloan Digital Sky Survey Data Release 7 optical survey and the extended database assembled by Frew (2008). I also present results from a radial velocity analysis of VLT/UVES spectra for 14 objects aiming to the detection of spectroscopic companions. Finally I give details of the analysis of optical photometry data from our observations associated to the detection of companions around CSPN using the photometric variability technique. The main result of this thesis is from the near-infrared excess studies which I combine with previously-published data. I conclude that the if the detected red and NIR flux excess is indicative of a stellar companion then the binary fraction is larger than what we may expect based on the main-sequence progenitor population binary fraction and therefore conclude that binarity is a preferential channel for the formation of PN. I finish by underlining the need for a sample size of ∼ 150 objects to decrease the uncertainty on the PN population binary fraction and increase the statistical significance of this result

Cette thèse est consacrée à l'étude des étoiles de faible masse ayant dans leur environnement proche d'autres étoiles ou des planètes. Nous nous sommes concentrés sur l'influence des interactions avec ces compagnons sur l'évolution stellaire ainsi que leurs conséquences observables.Dans la première partie, nous présentons le modèle d'évolution des systèmes étoile–planète que nous avons développé au cours de cette thèse, nommé ESPEM (Évolution des Systèmes Planétaires Et Magnétisme). Ce modèle prend en compte de façon ab-initio des effets du vent stellaire magnétisé et de la dissipation de marée sur la rotation stellaire et l'orbite planétaire, simultanément avec l'évolution structurelle de l'étoile. Premièrement, nous l'utilisons pour étudier l'évolution séculaire de la rotation des étoiles hôtes de systèmes planétaires et montrons notamment que cette évolution peut être significativement différente de celle des étoiles isolées. Ensuite, nous examinons les prédictions de ce modèle concernant l'architecture orbitale des systèmes étoile–planète. Nos résultats suggèrent une interprétation aux distributions de périodes orbitales et de de rotation stellaire observées.Dans la deuxième partie, nous montrons en quoi l'observation d'étoiles binaires évoluées permet de tester les théories astrophysiques, notamment l'astérosismologie et l'interaction de marée. Dans un premier temps, nous présentons les résultats d'un programme d'observations que nous avons mené pendant plus de deux ans et qui nous a permis de caractériser 16 systèmes binaires à éclipses. Ensuite, nous comparons ces résultats avec ceux que nous avons obtenus en analysant cet échantillon à l'aide d'outils astérosismiques dans le but de vérifier l'exactitude de ces derniers. Enfin, en élargissant l'échantillon étudié à 30 autres étoiles binaires évoluées, nous testons la théorie de l'évolution de marée. Ceci nous permet à la fois de valider la théorie et de comprendre l'évolution des systèmes observés dans ce travail.Ce travail met en avant deux aspects de la spécificité des systèmes multiples. Premièrement, il montre en quoi l'évolution des étoiles est impactée par la présence d'un compagnon stellaire ou planétaire. Deuxièmement, il met en avant l'intérêt des étoiles binaires pour tester les théories astrophysiques et renforce la compréhension actuelle de l'évolution stellaire
This thesis is devoted to the study of low-mass stars having other stars or planets in their immediate environment. We focused on the influence of interactions with these companions on stellar evolution and their observable consequences.In the first part, we present the model of evolution of star–planet systems that we developed during this thesis, called ESPEM (French acronym for Evolution of Planetary Systems and Magnetism). This model incorporates ab-initio prescriptions to quantify the effects of magnetized stellar wind and tidal dissipation on stellar rotation and planetary orbit, simultaneously with the star's structural evolution. First, we use it to study the secular evolution of the rotation of planet-host stars and show that this evolution can be significantly different from that of isolated stars. Next, we examine the predictions of this model regarding the orbital architecture of star–planet systems. Our results suggest an interpretation to the observed distributions of orbital and stellar rotation periods.In the second part of the manuscript, we show how the observation of advanced binary stars allows us to test astrophysical theories, in particular asteroseismology and tidal interaction. First, we present the results of an observation program that we conducted for more than two years and that allowed us to characterize 16 eclipsing binary systems. Then, we compare these results with those obtained by analyzing this sample using asteroseismic tools to verify the accuracy of the latter. Finally, by extending the studied sample to 30 other advanced binary stars including an evolved primary, we test the theory of tidal evolution. This allows us both to validate the theory and to understand the evolution of the systems observed in this work.This work highlights two aspects of the specificity of multiple systems. First, it shows how the evolution of stars is affected by the presence of a stellar or planetary companion. Second, it emphasizes the interest of binary stars in testing astrophysical theories and reinforces the current understanding of stellar evolution

Cette étude s'inscrit dans le cadre de la recherche de la formation d'un plasma de quarks et de gluons dans l'expérience STAR au RHIC. Elle concerne l'ajout d'un ensemble cylindrique de détecteurs en silicium, à micropistes, double face (SSD) au trajectographe interne du détecteur STAR. Cet ajout permet une amélioration globale de la trajectographie du détecteur STAR. Le SSD forme un cylindre de 1 m de long pour 23 cm de rayon et est composé de 320 modules compacts identiques. Les modules sont formés d'un détecteur, de 12 circuits de lecture ALICE 128C, de 12 rubans TAB, d'un circuit de contrôle COSTAR et de 2 circuits hybrides qui supportent l'ensemble des composants. La thèse montre le gain en performances physiques apportées par le SSD, ainsi que les différents choix technologiques, en particulier celui des détecteurs en silicium à micropistes, ainsi qu'une caractérisation des performances sous faisceau. Tous les composants sont décrits ainsi que leurs caractéristiques et l'ensemble des procédures de test qui ont été définie pour chacun des composants afin d'en établir la fonctionnalité et les propriétés. L'ensemble des données des composants et des tests est stocké dans une base de données. Les résultats obtenus pour la production des modules et de leurs composants sont présentés. Deux études parallèles ont été menées : l'une sur l'influence de la température environnementale, l'autre sur le réglage optimal des blocs analogiques du circuit ALICE 128C. L'installation du SSD sur le site de RHIC, sa mise en opération et les premières prises de données physiques sont présentées
This study has been performed in the frame of quark gluon plasma physics research in the STAR experiment at RHIC. It deals with the design, the construction and the commissioning of a barrel of silicon-strip detectors (SSD). Added to the Silicon Vertex Tracker (SVT) of the STAR detector, it extends the capabilities of track reconstruction for charged particles emitted in ultra-relativistic heavy-ion collisions. It also contributes to the general study of the quark-gluon plasma production undertaken at STAR. The SSD is a cylinder of 1 m long and of 23 cm radius, and it is composed of 320 compact identical modules. Each module includes one double-sided silicon micro-strip detector, 12 readout chips ALICE 128C, 12 TAB ribbons, 2 COSTAR control chips and 2 hybrids supporting all the components. The document explains why the SSD is an important and relevant element, and justifies the technologic choices as well as their validation by in-beam characterization. All component functionalities, characteristics and test procedures are presented. The data and test results are stored in a database for tracing purpose. Component and module production is described. Two parallel studies have been performed, analysed and described. One on the temperature dependence of the module performances and the other one on the optimal adjustments of the analogue blocks inside the ALICE 128C chip. The SSD installation on the RHIC site as well as the commissioning are presented together with the first data takings

Gamma-ray binaries are systems that comprise a young, massive star and a compact object that can be either a young pulsar or a black hole. They emit radiation from radio up to tens of TeV and show flux variability along the whole electromagnetic spectrum. For three of the four detected gamma-ray binaries, the nature of the compact object is unknown. In this thesis we present a study of gamma-ray binaries through three approaches that involve the simultaneous study of these sources in X-rays and very high energy (VHE) gamma-rays. We present the discovery of correlated X-ray and VHE gamma-ray emission from LS I +61 303. The correlations indicates that the emission from these two bands could be originated in the same parent particle population, and we explore this idea through the calculation of a radiative model. This model allows us to significantly constrain the physical properties of the non-thermal emitter in LS I +61 303. For those systems where the compact object is a young pulsar, the interaction between the stellar and pulsar winds will give rise to strong shocks. The shocked pulsar wind is the candidate location for non-thermal emission from these systems. The shocked stellar wind should give rise to a thermal X-ray spectrum, but no such features have been detected in the X-ray spectrum of gamma-ray binaries. We present a model of the thermal emission of the shocked stellar wind and use it to constrain the pulsar properties. We have applied this method to two X-ray observations of LS 5039 and have successfully constrained the pulsar spin-down luminosity. Finally, we present a search for VHE emission from Scorpius X-1 through a simultaneous X-ray and VHE gamma-ray campaign. The X-ray observations allowed us to select black-hole states where non-thermal X-ray emission has been detected. We did not find significant VHE emission in any of the black hole states, but the upper limits derived will prove useful in future modelling of the non-thermal emitter in the source.
Les binàries de raigs gamma són sistemes binaries formats per una estrella jove i massiva i un objecte compacte, que pot ser un púlsar jove o un forat negre, que emeten radiació fins a desenes de TeV i mostren variabilitat orbital en totes les bandes d'emissió, des de radio fins a raigs gamma. En el cas de tres de les quatre binàries de raigs gamma detectades avui dia, se'n desconeix la natura de l'objecte compacte. En aquesta tesi presentem un estudi de les binàries de raigs gamma mitjançant tres treballs complementaris que involucren l'estudi simultani d'aquestes fonts en raigs X i raigs gamma de molt alta energia. En primer lloc presentem el descobriment d'emissió en raigs X i raigs gamma de molt alta energia correlades en el temps al sistema LS I +61 303. Aquesta correlació ens indica que l'emissió en les dues bandes pot provenir d'una única població d'electrons, i ho confirmem mitjançant la realització d'un model teòric de radiació que ens permet restringir significativament les propietats físiques de l'emissor no tèrmic de la font. En cas que la font energètica dels sistemes sigui un púlsar, la interacció entre els vents de l'estrella i el púlsar dona lloc a una regió d'interacció on el vent xocat del púlsar accelera partícules i emet des de radio fins a raigs gamma. A l'espectre de raigs X, però, no es detecta l'emissió tèrmica del vent xocat de l'estrella, que s'escalfa fins a desenes de milers de graus. Això ens ha permès estudiar la forma de la regió d'interacció, determinada principalment per la potència del púlsar, i fer un càlcul teòric de l'emissió en raigs X tèrmics. Hem aplicat aquest model al sistema LS 5039 i hem pogut determinar la potència del púlsar, fet important per a la modelització de l'emissió no tèrmica de la font. Finalment, presentem la cerca d'emissió de raigs gamma provinent de sistemes binaris fins ara no detectats. Una campanya simultània en raigs X i raigs gamma ens va permetre seleccionar les dades de molt alta energia del microquàsar Sco X-1 en funció de l'estat d'acreció sobre l'objecte compacte. Tot i no detectar la font en raigs gamma, els límits superiors obtinguts permeten restringir les propietats físiques de Sco X-1 rellevants per a l'emissió en molt alta energia.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.
Cataloged from PDF version of thesis. In title on title page, "the square root of sigma" appears as the mathematical symbol.
Includes bibliographical references (p. 109-112).
One of the primary goals of the spin physics program at the STAR experiment is to constrain the polarized gluon distribution function, [delta]g(X,Q²), by measuring the double longitudinal spin asymmetry, ALL, of various final-state channels. Neutral pions provide a potentially powerful final state because they are copiously produced in p+p collisions and have few backgrounds. In 2009, STAR took 14 pb-¹ of integrated luminosity of 200 GeV p+p collisions, with average beam longitudinal polarization of 59%. Neutral pions produced in these collisions can be identified using STAR's large-acceptance electromagnetic calorimeter, with help from tracking from the STAR Time Projection Chamber. This work presents a measurement of the inclusive neutral pion ALL from this data, based on a new [pi]⁰ reconstruction algorithm. A comparison to theoretical predictions and other experimental results suggests that the current best-fit value of AG, the gluon contribution to the proton spin, is too small and that [delta]G is actually comparable in magnitude to the quark contribution to the proton spin [delta][sigma].
by William Leight.
Ph.D.

Physics
Ph.D.
Understanding what contributes to the intrinsic angular momentum (spin) of the proton has been a major goal of the nuclear physics community. In the 1980s, it was discovered that quarks contribute 30% to the spin of the proton. This information led to a search to find other contributions to the spin of the proton. At STAR, the double spin asymmetry (ALL) is measured as it is sensitive to the polarized gluon distribution (Dg(x)). The STAR 2009 inclusive jet ALL at sqrt(s) = 200 GeV has been incorporated into two independent global fits. These fits show for the first time a statistically significant non-zero gluon contribution to the spin of the proton in the parton momentum fraction range x > 0.05. Dijet ALL is also measured at STAR. Dijets are advantageous since the parton momentum fraction (x) of the initial partons may be reconstructed to first order from final state measurements. In 2013 STAR collected an estimated 250 pb-1 of data at sqrt(s) = 510 GeV. The higher center of mass energy will allow STAR to probe Dg(x) at x values as low as 0.02. The large statistics will allow a reduction in the uncertainties. Once the data is incorporated into future global fits, it will allow for a more precise determination of Dg(x). The 2013 dijet ALL results will be presented. The results show good agreement with both global fits and previous STAR results dijet measurements.
Temple University--Theses

This thesis is an archive-based research on the UN’s initial efforts at global tax coordination under its Fiscal Commission in succeeding the mantle of the Fiscal Committee of the League of Nations. It focuses on explaining, within the context of international relations and global political economy, the progress, or lack thereof, of double taxation matters by the UN during the first decade of the American-led post-WWII world order. The narrative reveals, firstly, developing countries’ fierce contention in guarding and asserting source taxation rights to advance their economic development, and secondly, the UN Secretariat’s attempts to broker new equitable tax rules for relations between developed and developing countries, and to secure its position as the overarching international organisation for fiscal matters. This activism was heavily resisted by developed countries, particularly the United States and United Kingdom, leading them to divest the UN of its originally broad fiscal competence and to dissolve the Commission to forestall the development of policies and principles unfavourable to their interests. The narrative also addresses a prehistory in the wartime work of the League’s Princeton Mission that facilitated the premature and questionable induction of Latin America into double taxation questions as well as the creation of the Fiscal Commission despite underwhelming international support. This thesis revises prevalent understandings in the literature on international tax history and demonstrates that international tax coordination between developed and developing countries is more nuanced than a straightforward negotiation of technical rules, involving an interplay of hegemonic influences, power imbalances, global governance and private business pressures.