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1
Mindham, R. H. S., and A. C. P. Sims. "Brian Lake: Formerly Consultant Psychotherapist, Leeds." Psychiatric Bulletin 32, no. 8 (August 2008): 319. http://dx.doi.org/10.1192/pb.bp.108.021618.
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Brian was born in 1922 into a religious family who lived near Liverpool where his father was a jobber at the Liverpool Stock Exchange. He was the youngest of three brothers of whom the eldest, Frank, like Brian, studied medicine with a view to becoming a missionary in India. Brian began his studies in Edinburgh in 1940 and qualified with the ‘Scottish Triple’ in 1945. After house jobs at the Edinburgh Royal Infirmary and a period as Senior R.M.O. at the Royal Liverpool Children's Hospital. He was rejected for military service on medical grounds, so he decided to go to sea; he served with the Cunard White Star Line for the greater part of the 1950s. However, it was his contact with the crew and his involvement in negotiations to settle conflicts between them which most interested him and led to him to develop an interest in psychiatry. In the late 1950s he joined the junior staff at Warlingham Park Hospital in Surrey where he found himself among a stimulating group of trainees, many of whom later became distinguished in the psychiatric world. He obtained the DPM in 1961.
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Reindl, N., V. Schaffenroth, M. M. Miller Bertolami, S. Geier, N. L. Finch, M. A. Barstow, S. L. Casewell, and S. Taubenberger. "An in-depth reanalysis of the alleged type Ia supernova progenitor Henize 2−428." Astronomy & Astrophysics 638 (June 2020): A93. http://dx.doi.org/10.1051/0004-6361/202038117.
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Context. The nucleus of the planetary nebula Hen 2-428 is a short orbital-period (4.2 h), double-lined spectroscopic binary, whose status as a potential supernova type Ia progenitor has raised some controversy in the literature. Aims. With the aim of resolving this debate, we carried out an in-depth reanalysis of the system. Methods. Our approach combines a refined wavelength calibration, thorough line-identifications, improved radial-velocity measurements, non-LTE spectral modeling, as well as multi-band light-curve fitting. Our results are then discussed in view of state-of-the-art stellar evolutionary models. Results. Besides systematic zero-point shifts in the wavelength calibration of the OSIRIS spectra which were also used in the previous analysis of the system, we found that the spectra are contaminated with diffuse interstellar bands. Our Voigt-profile radial velocity fitting method, which considers the additional absorption of these diffuse interstellar bands, reveals significantly lower masses (M1 = 0.66 ± 0.11 M⊙ and M2 = 0.42 ± 0.07 M⊙) than previously reported and a mass ratio that is clearly below unity. Our spectral and light curve analyses lead to consistent results, however, we find higher effective temperatures and smaller radii than previously reported. Moreover, we find that the red-excess that was reported before to prove to be a mere artifact of an outdated reddening law that was applied. Conclusions. Our work shows that blends of He II λ 5412 Å with diffuse interstellar bands have led to an overestimation of the previously reported dynamical masses of Hen 2−428. The merging event of Hen 2−428 will not be recognised as a supernova type Ia, but most likely leads to the formation of a H-deficient star. We suggest that the system was formed via a first stable mass transfer episode, followed by common envelope evolution, and it is now composed of a post-early asymptotic giant branch star and a reheated He-core white dwarf.
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Kuuttila, J., and M. Gilfanov. "Optical emission-line spectra of symbiotic binaries." Monthly Notices of the Royal Astronomical Society 507, no. 1 (August 18, 2021): 594–607. http://dx.doi.org/10.1093/mnras/stab2025.
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ABSTRACT Symbiotic stars are long-period interacting binaries where the compact object, most commonly a white dwarf, is embedded in the dense stellar wind of an evolved companion star. Ultraviolet and soft X-ray emission of the accretion disc and the nuclear-burning white dwarf plays a major role in shaping the ionization balance of the surrounding wind material, giving rise to the rich line emission. In this paper, we employ two-dimensional photoionization calculations based on the cloudy code to study the ionization state of the circumbinary material in symbiotic systems and to predict their emission-line spectra. Our simulations are parametrized via the orbital parameters of the binary and the wind mass-loss rate of the donor star, while the mass accretion rate, temperature and luminosity of the white dwarf are computed self-consistently. We explore the parameter space of symbiotic binaries and compute luminosities of various astrophysically important emission lines. The line ratios are compared with traditional diagnostic diagrams used to distinguish symbiotic binaries from other types of sources, and it is shown how the binary system parameters shape these diagrams. In the significant part of the parameter space, the wind material is nearly fully ionized, except for the ‘shadow’ behind the donor star, so the white dwarf emission is typically freely escaping the system.
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Gladden, Graham P. "Marketing Ocean Travel: Cunard and the White Star Line, 1910–1940." Journal of Transport History 35, no. 1 (June 2014): 57–77. http://dx.doi.org/10.7227/tjth.35.1.5.
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The Cunard shipping line regarded itself as the premier provider of transatlantic passenger transport. As the structure of society on both sides of the Atlantic changed between 1910 and 1940 the company sought to maintain its market amongst the richest of society whilst attracting new passengers from the emerging middle class. Accordingly, Cunard adjusted its marketing in advertisements, brochures, promotional films and ship designs. Two passenger classes, the well-established First Class and the new Tourist Third Class are used to show how the company used all these media to both influence potential passengers' travel decisions and to reassure them of a safe, comfortable voyage in surroundings appropriate to their status, tastes and expectations.
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Gies, Douglas R., Luqian Wang, and Robert Klement. "Gamma Cas Stars as Be+White Dwarf Binary Systems." Astrophysical Journal Letters 942, no. 1 (December 28, 2022): L6. http://dx.doi.org/10.3847/2041-8213/acaaa1.
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Abstract The origin of the bright and hard X-ray emission flux among the γ Cas subgroup of B-emission line (Be) stars may be caused by gas accretion onto an orbiting white dwarf (WD) companion. Such Be+WD binaries are the predicted outcome of a second stage of mass transfer from a helium star mass donor to a rapidly rotating mass gainer star. The stripped donor stars become small and hot white dwarfs that are extremely faint compared to their Be star companions. Here we discuss model predictions about the physical and orbital properties of Be+WD binaries, and we show that current observational results on γ Cas systems are consistent with the expected large binary frequency, companion faintness and small mass, and relatively high mass range of the Be star hosts. We determine that the companions are probably not stripped helium stars (hot subdwarf sdO stars), because these are bright enough to detect in ultraviolet spectroscopy, yet their spectroscopic signatures are not observed in studies of γ Cas binaries. Interferometry of relatively nearby systems provides the means to detect very faint companions including hot subdwarf and cooler main-sequence stars. Preliminary observations of five γ Cas binaries with the CHARA Array interferometer show no evidence of the companion flux, leaving white dwarfs as the only viable candidates for the companions.
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Rauch, Thomas, Sebastian Köper, Stefan Dreizler, Klaus Werner, Ulrich Heber, and I. Neill Reid. "The Rotational Velocity of Helium-rich Pre-White Dwarfs." Symposium - International Astronomical Union 215 (2004): 573–74. http://dx.doi.org/10.1017/s0074180900196214.
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Previous investigations on hydrogen-rich white dwarfs generally yield only very small rotational velocities (v sin i). We have analyzed line profiles in high-resolution optical spectra of eight hydrogen-deficient (pre-) white dwarfs and find deviations from the dominant Stark line broadening in five cases which, interpreted as an effect of stellar rotation, indicate projected rotational velocities of 40 – 70 km s–1. For the three least luminous stars upper limits of v sin i = 15 – 25 km s–1 could be derived only. The resulting velocities correlate with luminosity and mass. However, since the mass-loss rate is correlated to the luminosity of a star, the observed line profiles may be affected by a stellar wind as well. In the case of RX J2117.1+3412, this would solve discrepancies to results of pulsational modeling (v sin i ≈ 0).
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Manser, Christopher J., Boris T. Gänsicke, Siegfried Eggl, Mark Hollands, Paula Izquierdo, Detlev Koester, John D. Landstreet, et al. "A planetesimal orbiting within the debris disc around a white dwarf star." Science 364, no. 6435 (April 4, 2019): 66–69. http://dx.doi.org/10.1126/science.aat5330.
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Many white dwarf stars show signs of having accreted smaller bodies, implying that they may host planetary systems. A small number of these systems contain gaseous debris discs, visible through emission lines. We report a stable 123.4-minute periodic variation in the strength and shape of the Ca ii emission line profiles originating from the debris disc around the white dwarf SDSS J122859.93+104032.9. We interpret this short-period signal as the signature of a solid-body planetesimal held together by its internal strength.
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Hubeny, Ivan, and Thierry Lanz. "EUV Radiation from Hot Star Photospheres: Theory Versus Observations." International Astronomical Union Colloquium 152 (1996): 381–88. http://dx.doi.org/10.1017/s0252921100036265.
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The only stars other than white dwarfs whose photospheric extreme ultraviolet radiation has been detected are ϵ and β CMa. It is therefore of considerable theoretical interest to compare the EUVE observations of these two giant B stars to predicted spectra. However, both LTE and non-LTE very sophisticated line blanketed model atmospheres fail to match the observed flux. This failure leaves the stellar photosphere theory, even for seemingly “simple” objects as normal B giants were believed to be, in a rather dubious position. This paper briefly summarizes possible reasons for the failure of existing models to describe the EUVE observations of hot stars. In particular, we discuss the effects of uncertainties in the line blanketing, and the effects of the photosphere-wind interaction.
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Iłkiewicz, Krystian, Joanna Mikołajewska, Simone Scaringi, François Teyssier, Kiril A. Stoyanov, and Matteo Fratta. "SU Lyn - a transient symbiotic star." Monthly Notices of the Royal Astronomical Society 510, no. 2 (December 28, 2021): 2707–17. http://dx.doi.org/10.1093/mnras/stab3637.
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ABSTRACT SU Lyn is a binary system composed of a white dwarf and a red giant star. Although it is known to be bright and variable at X-ray wavelengths, the optical counterpart of the source appeared as a single red giant without prominent emission lines. Because of the lack of optical features typical for interacting systems, the system was classified as a hidden symbiotic star. We present the results of optical monitoring of the system. While SU Lyn did not show substantial photometric variability, the spectroscopic observations revealed a complex behaviour. The system showed strong emission line variability, including P Cygni profiles, changing line emission environments, and variable reddening. Both X-ray and optical observations indicate that the components of SU Lyn were interacting only for a short time during the last twelve years of monitoring. For the first time, we showed that SU Lyn resembled a classical symbiotic star when it was X-ray bright, and remained hidden afterwards. We also discuss the current evolutionary status of the red giant, as well as possible future evolution of the system. We suggest that SU Lyn could be a progenitor of a classical, persistent symbiotic system.
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Walters, N., J. Farihi, T. R. Marsh, S. Bagnulo, J. D. Landstreet, J. J. Hermes, N. Achilleos, A. Wallach, M. Hart, and C. J. Manser. "A test of the planet–star unipolar inductor for magnetic white dwarfs." Monthly Notices of the Royal Astronomical Society 503, no. 3 (March 5, 2021): 3743–58. http://dx.doi.org/10.1093/mnras/stab617.
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ABSTRACT Despite thousands of spectroscopic detections, only four isolated white dwarfs exhibit Balmer emission lines. The temperature inversion mechanism is a puzzle over 30 years old that has defied conventional explanations. One hypothesis is a unipolar inductor that achieves surface heating via ohmic dissipation of a current loop between a conducting planet and a magnetic white dwarf. To investigate this model, new time-resolved spectroscopy, spectropolarimetry, and photometry of the prototype GD 356 are studied. The emission features vary in strength on the rotational period, but in antiphase with the light curve, consistent with a cool surface spot beneath an optically thin chromosphere. Possible changes in the line profiles are observed at the same photometric phase, potentially suggesting modest evolution of the emission region, while the magnetic field varies by 10 per cent over a full rotation. These comprehensive data reveal neither changes to the photometric period, nor additional signals such as might be expected from an orbiting body. A closer examination of the unipolar inductor model finds points of potential failure: the observed rapid stellar rotation will inhibit current carriers due to the centrifugal force, there may be no supply of magnetospheric ions, and no antiphase flux changes are expected from ohmic surface heating. Together with the highly similar properties of the four cool, emission-line white dwarfs, these facts indicate that the chromospheric emission is intrinsic. A tantalizing possibility is that intrinsic chromospheres may manifest in (magnetic) white dwarfs, and in distinct parts of the Hertzsprung–Russell diagram based on structure and composition.
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Swan, Andrew, Jay Farihi, Detlev Koester, Mark Hollands, Steven Parsons, P. Wilson Cauley, Seth Redfield, and Boris T. Gänsicke. "Interpretation and diversity of exoplanetary material orbiting white dwarfs." Monthly Notices of the Royal Astronomical Society 490, no. 1 (October 4, 2019): 202–18. http://dx.doi.org/10.1093/mnras/stz2337.
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ABSTRACT Nine metal-polluted white dwarfs are observed with medium-resolution optical spectroscopy, where photospheric abundances are determined and interpreted by comparison with Solar system objects. An improved method for making such comparisons is presented, which overcomes potential weaknesses of prior analyses, with numerous sources of error considered to highlight the limitations on interpretation. The stars are inferred to be accreting rocky, volatile-poor asteroidal materials with origins in differentiated bodies, in line with the consensus model. The most heavily polluted star in the sample has 14 metals detected, and appears to be accreting material from a rocky planetesimal, whose composition is mantle-like with a small Fe–Ni core component. Some unusual abundances are present. One star is strongly depleted in Ca, while two others show Na abundances elevated above bulk-Earth abundances; it is speculated that either the latter reflect diversity in the formation conditions of the source material, or they are traces of past accretion events. Another star shows clear signs that accretion ceased around 5 Myr ago, causing Mg to dominate the photospheric abundances, as it has the longest diffusion time of the observed elements. Observing such post-accretion systems allows constraints to be placed on models of the accretion process.
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Kovacs, G. "Is Delta Scuti Star Seismology Possible?" International Astronomical Union Colloquium 111 (1989): 271. http://dx.doi.org/10.1017/s0252921100011799.
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AbstractThe direct fit of theoretical pulsation frequencies to the observations (i.e. stellar seismology) proved to be a very efficient tool in the study of solar oscillations. In the case of other multiperiodic variables, like δ Scuti stars, Ap stars and white dwarfs the method suffers from the disturbing abundance of possible nonradial modes. Colour and/or radial velocity (or line profile) measurements can narrow down the number of possibilities, but these kinds of data are not often available with the desired accuracy and sampling rate. Since pulsational frequencies are the most readily and accurately computed and measured quantities of pulsation, we address the question of the accurate fit of the nonradial pulsation frequencies to the observations in the case of δ Scuti stars.
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M. Walter, Frederick. "Resolving Atmospheric Structure in V471 Tauri." Symposium - International Astronomical Union 219 (2004): 233–37. http://dx.doi.org/10.1017/s0074180900182166.
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The K2V-DA binary V471 Tau has an extended atmosphere. By using the DA white dwarf as a probe, we can probe the atmosphere along the line of sight to the white dwarf with a spatial resolution of order 10,000 km. We observe absorption lines from C II through N V in absorption against the DA photospheric continuum. The velocities are those of gas in co-rotation with the K star.
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Cully, S. L., J. Dupuis, T. Rodriguez-Bell, G. Basri, O. H. W. Siegmund, J. Lim, and S. M. White. "EUVE and VLA Observations of the Eclipsing Pre-Cataclysmic Variable V471 Tauri." International Astronomical Union Colloquium 152 (1996): 349–54. http://dx.doi.org/10.1017/s0252921100036216.
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We present observations of the eclipsing binary V471 Tauri by the Extreme Ultraviolet Explorer (EUVE) and the Very Large Array (VLA). The EUV spectrum is dominated by the continuum of the hot white dwarf and the time-averaged spectrum is fitted by a 33.1 ± 0.5 × 103 K pure hydrogen white dwarf atmosphere assuming log g = 8.5. An ISM hydrogen column density of 1.5 ± 0.4 × 1018 cm−2 is required to explain the attenuation of the white dwarf spectrum thus setting the HI column in the line of sight of the Hyades cluster. The He II λ304 Å line is in emission and varies over the orbital period of V471 Tauri following a sinusoidal modulation with the maximum reached when the K star is at inferior conjunction. Transient dips are detected at orbital phase −0.12 in the SW and MW spectrometers integrated lightcurves but are notably absent in the LW lightcurve indicating the occulting material is ionized. The VLA observation suggest the presence of a K star coronal magnetic loop between the two stars reconnecting with the white dwarf magnetic field. Such a structure could be the occulting source needed to explain the dips seen in the lightcurves of V471 Tauri in the EUV.
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Bues, I. "Line Band Profiles in the Spectra of Cool Magnetic Helium-Rich White Dwarfs." International Astronomical Union Colloquium 87 (1985): 391–95. http://dx.doi.org/10.1017/s0252921100090989.
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For white dwarfs with effective temperatures smaller than 12000 K, the percentage of objects with a helium-rich atmosphere increases compared to the hydrogen-rich sequence. The carbon abundance, which can be determined from line and band strengths (Bues, 1973; Koester et al., 1982), varies by more than a factor of 1000 within this class. Moreover, for the subclass of white dwarfs with strong magnetic fields, the abundance ratio of H/He differs from that of the DB and DA sequences. The hot star Feige 7, analyzed by Liebert et al. (1977), shows lines of hydrogen and helium at a comparable strength for a moderately strong field of 103 Tesla. If there is any chance of finding white dwarfs which are descendants of hot, non-degenerate helium stars with rotation and magnetic fields, then it should be within these objects of mixed composition.
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Ferrario, Lilia, D. T. Wickramasinghe, and I. R. Tuohy. "An Emission Line Model for AM Herculis Systems: Application to E1405-451." Publications of the Astronomical Society of Australia 7, no. 2 (1987): 119–22. http://dx.doi.org/10.1017/s1323358000022049.
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AbstractThe optical spectra of the AM Herculis binaries are characterized by extremely complex emission lines whose profiles can be resolved into at least three components which are formed in different regions of the accretion stream leading from the companion star towards the magnetic white dwarf. We present a theoretical model which localizes the formation region of the broad emission line component and provides information regarding the structure of this emitting region. In our model the particle trajectories are integrated in a Roche potential and the volume between the white dwarf and the companion has been divided into two different regimes of motion. In one region the gas escapes from the secondary near the inner Lagrange point and is accelerated along a straight line towards the white dwarf. In the other region the magnetic field is strong enought to divert the gas out of the orbital plane and to channel it towards the white dwarfs surface. The model has been used to interpret radial velocity and velocity dispersion data from the AM Herculis system E1405-451.
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Namekata, Kosuke, Hiroyuki Maehara, Satoshi Honda, Yuta Notsu, Soshi Okamoto, Jun Takahashi, Masaki Takayama, et al. "Discovery of a Long-duration Superflare on a Young Solar-type Star EK Draconis with Nearly Similar Time Evolution for Hα and White-light Emissions." Astrophysical Journal Letters 926, no. 1 (February 1, 2022): L5. http://dx.doi.org/10.3847/2041-8213/ac4df0.
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Abstract Young solar-type stars are known to show frequent “superflares,” which may severely influence the habitable worlds on young planets via intense radiation and coronal mass ejections. Here we report an optical spectroscopic and photometric observation of a long-duration superflare on the young solar-type star EK Draconis (50–120 Myr age) with the Seimei telescope and Transiting Exoplanet Survey Satellite. The flare energy 2.6 × 1034 erg and white-light flare duration 2.2 hr are much larger than those of the largest solar flares, and this is the largest superflare on a solar-type star ever detected by optical spectroscopy. The Hα emission profile shows no significant line asymmetry, meaning no signature of a filament eruption, unlike the only previous detection of a superflare on this star. Also, it did not show significant line broadening, indicating that the nonthermal heating at the flare footpoints is not essential or that the footpoints are behind the limb. The time evolution and duration of the Hα flare are surprisingly almost the same as those of the white-light flare, which is different from general M-dwarf (super-)flares and solar flares. This unexpected time evolution may suggest that different radiation mechanisms than general solar flares are predominant, such as: (1) radiation from (off-limb) flare loops and (2) re-radiation via radiative back-warming, in both of which the cooling timescales of flare loops could determine the timescales of Hα and white light.
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Skinner, Raymond J. "ROBERT KEMBALL (1823–87), MASTER OF THE CLIPPERTHERMOPYLAEAND COMMODORE OF THE ABERDEEN WHITE STAR LINE." Mariner's Mirror 89, no. 1 (January 2003): 59–70. http://dx.doi.org/10.1080/00253359.2003.10659274.
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Sternberg, Assaf. "Evidence for Circumstellar Material in Type Ia Supernovae via Sodium Absorption Features." Proceedings of the International Astronomical Union 7, S281 (July 2011): 299–302. http://dx.doi.org/10.1017/s1743921312015232.
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AbstractType Ia supernovae are very good tools for measuring distances on a cosmic scale. The consensus view is that mass transfer onto a white dwarf in a close binary system leads to a thermonuclear explosion, though the nature of the mass donor is still uncertain. In the single-degenerate model it is a main-sequence star or an evolved star. In the double-degenerate model it is another white dwarf. We study the velocity structure of absorbing material along the line of sight to 35 Type Ia supernovae and find a statistical preference for blueshifted structures, likely arising in gas outflows from the supernova progenitor systems, consistent with a single-degenerate progenitor for a substantial fraction of Type Ia supernovae in nearby spiral galaxies.
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Córsico, A. H., M. Uzundag, S. O. Kepler, R. Silvotti, L. G. Althaus, D. Koester, A. S. Baran, et al. "Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS." Astronomy & Astrophysics 659 (March 2022): A30. http://dx.doi.org/10.1051/0004-6361/202142153.
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Context. The collection of high-quality photometric data by space telescopes, such as the completed Kepler mission and the ongoing TESS program, is revolutionizing the area of white-dwarf asteroseismology. Among the different kinds of pulsating white dwarfs, there are those that have He-rich atmospheres, and they are called DBVs or V777 Her variable stars. The archetype of these pulsating white dwarfs, GD 358, is the focus of the present paper. Aims. We report a thorough asteroseismological analysis of the DBV star GD 358 (TIC 219074038) based on new high-precision photometric data gathered by the TESS space mission combined with data taken from the Earth. Methods. We reduced TESS observations of the DBV star GD 358 and performed a detailed asteroseismological analysis using fully evolutionary DB white-dwarf models computed accounting for the complete prior evolution of their progenitors. We assessed the mass of this star by comparing the measured mean period separation with the theoretical averaged period spacings of the models, and we used the observed individual periods to look for a seismological stellar model. We detected potential frequency multiplets for GD 358, which we used to identify the harmonic degree (ℓ) of the pulsation modes and rotation period. Results. In total, we detected 26 periodicities from the TESS light curve of this DBV star using standard pre-whitening. The oscillation frequencies are associated with nonradial g(gravity)-mode pulsations with periods from ∼422 s to ∼1087 s. Moreover, we detected eight combination frequencies between ∼543 s and ∼295 s. We combined these data with a huge amount of observations from the ground. We found a constant period spacing of 39.25 ± 0.17 s, which helped us to infer its mass (M⋆ = 0.588 ± 0.024 M⊙) and constrain the harmonic degree ℓ of the modes. We carried out a period-fit analysis on GD 358, and we were successful in finding an asteroseismological model with a stellar mass (M⋆ = 0.584−0.019+0.025 M⊙), compatible with the stellar mass derived from the period spacing, and in line with the spectroscopic mass (M⋆ = 0.560 ± 0.028 M⊙). In agreement with previous works, we found that the frequency splittings vary according to the radial order of the modes, suggesting differential rotation. Obtaining a seismological model made it possible to estimate the seismological distance (dseis = 42.85 ± 0.73 pc) of GD 358, which is in very good accordance with the precise astrometric distance measured by Gaia EDR3 (π = 23.244 ± 0.024, dGaia = 43.02 ± 0.04 pc). Conclusions. The high-quality data measured with the TESS space telescope, used in combination with data taken from ground-based observatories, provides invaluable information for conducting asteroseismological studies of DBV stars, analogously to what happens with other types of pulsating white-dwarf stars. The currently operating TESS mission, together with the advent of other similar space missions and new stellar surveys, will give an unprecedented boost to white dwarf asteroseismology.
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Chen, Hai-Liang, Tyrone E. Woods, Lev Yungelson, Marat Gilfanov, and Zhanwen Han. "Populations of accreting white dwarfs." Proceedings of the International Astronomical Union 14, S343 (August 2018): 371–72. http://dx.doi.org/10.1017/s1743921318005070.
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AbstractUsing a hybrid binary population synthesis approach, we modelled the formation and evolution of populations of accreting white dwarfs (WDs) for differing star formation histories. We found that the delay time distribution of SNe Ia in the single degenerate scenario is inconsistent with observations. Additionally, we found that our predicted X-ray and UV emission of populations of accreting WDs are consistent with the X-ray luminosities of early-type galaxies observed by Chandra and the HeII 4686 Å/Hβ line ratio measured in stacked SDSS spectra of passively evolving galaxies. Moreover, we found that the majority of current novae in elliptical-like galaxies have low-mass WDs, long decay times, long recurrence periods and are relatively faint. In contrast, the majority of current novae in spiral-like galaxies have massive WDs, short decay times, short recurrence periods and are relatively bright. Our predicted distribution of mass-loss timescales in an M31-like galaxy is consistent with observations for Andromeda.
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Ahumada, Andrea V., Juan J. Clariá, Eduardo Bica, Andrés E. Piatti, João F. C. Santos, M. Lorena Talavera, Tali Palma, et al. "Further developments in star cluster spectral libraries." Proceedings of the International Astronomical Union 5, S266 (August 2009): 347–50. http://dx.doi.org/10.1017/s1743921309991244.
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AbstractWe present flux-calibrated integrated spectra in the optical spectral range of Galactic open clusters (GOCs) and Magellanic Cloud (MC) stellar clusters (SCs) obtained at CASLEO (Argentina). The SC parameters were derived using the equivalent-width (EW) method and the template-matching procedure by comparing the line strengths and continuum distribution of the cluster spectra with those of template spectra with known parameters. MC cluster reddening values were also estimated by interpolation between the available extinction maps. The derived ages for the GOCs range from 3 Myr to 4 Gyr, while those of the MC SCs vary from 3 Myr to 7 Gyr. E(B−V) colour-excess values in the MCs appear to be all lower than 0.17 mag, while those of the GOCs range from 0.00 to 2.40 mag. The present data led us to upgrade the spectral libraries of reference spectra or templates of solar and MC metallicities.
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Namekata, Kosuke, Kiyoshi Ichimoto, Takako T. Ishii, and Kazunari Shibata. "Sun-as-a-star Analysis of Hα Spectra of a Solar Flare Observed by SMART/SDDI: Time Evolution of Red Asymmetry and Line Broadening." Astrophysical Journal 933, no. 2 (July 1, 2022): 209. http://dx.doi.org/10.3847/1538-4357/ac75cd.
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Abstract Stellar flares sometimes show red/blue asymmetries of the Hα line, which can indicate chromospheric dynamics and prominence activations. However, the origin of asymmetries is not completely understood. For a deeper understanding of stellar data, we performed a Sun-as-a-star analysis of Hα line profiles of an M4.2-class solar flare showing dominant emissions from flare ribbons by using the data of the Solar Dynamics Doppler Imager on board the Solar Magnetic Activity Research Telescope at the Hida Observatory. Sun-as-a-star Hα spectra of the flare show red asymmetry of up to ∼95 km s−1 and line broadening of up to ∼7.5 Å. The Sun-as-a-star Hα profiles are consistent with spectra from flare regions with weak intensity, but they take smaller redshift velocities and line widths by a factor of ∼2 than those with strong intensity. The redshift velocities, as well as line widths, peak out and decay more rapidly than the Hα equivalent widths, which is consistent with the chromospheric condensation model and spatially resolved flare spectra. This suggests that as a result of superposition, the nature of chromospheric condensation is observable even from stellar flare spectra. The time evolution of redshift velocities is found to be similar to that of luminosities of near-ultraviolet rays (1600 Å), while the time evolution of line broadening is similar to that of optical white lights. These Hα spectral behaviors in Sun-as-a-star view could be helpful to distinguish whether the origin of Hα red asymmetry of stellar flares is a flare ribbon or other phenomena.
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Sekeráš, M., and A. Skopal. "Diagnostic of the Symbiotic Stars Environment by Thomson, Raman and Rayleigh Scattering Processes." Acta Polytechnica CTU Proceedings 2, no. 1 (February 23, 2015): 282–85. http://dx.doi.org/10.14311/app.2015.02.0282.
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Symbiotic stars are long-period interacting binaries consisting of a cool giant as the donor star and a white dwarf as the acretor. Due to acretion of the material from the giant’s stellar wind, the white dwarf becomes very hot and luminous. The circumstellar material partially ionized by the hot star, represents an ideal medium for processes of scattering. To investigate the symbiotic nebula we modeled the wide wings of the resonance lines OVI λ1032 Å, λ1038 Å and HeII λ1640 Å emission line in the spectrum of AG Dra, broadened by Thomson scattering. On the other hand, Raman and Rayleigh scattering arise in the neutral part of the circumstellar matter around the giant and provide a powerful tool to probe e.g. the ionization structure of the symbiotic systems and distribution of the neutral hydrogen atoms in the giant’s wind.
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Buitrago, Diego González, Gagik Tovmassian, Juan Echevarría, Sergey Zharikov, Takamitsu Miyaji, Andres Avilés, and Gennady Valyavin. "V479 And: CV, LMXB, or Symbiotic?" Proceedings of the International Astronomical Union 7, S281 (July 2011): 113–16. http://dx.doi.org/10.1017/s1743921312014780.
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AbstractV479 And is a 14.26 hour, close binary system, comprised of a G8-K0 star departing from the main sequence and a compact primary star accreting matter from the donor. The object is an X-ray source, modulated with the orbital period. This, and the presence of an intense He II line, leads us to speculate that the compact object is a magnetic white dwarf. However, we do not find strong constraints on the upper mass limit of the compact object, and we may have a neutron star in a low mass X-ray binary instead of a cataclysmic variable. The orbital period is certainly too short for the donor star to be an evolved giant star, so classifying this object as a symbiotic binary may be a big stretch; however there is an evidence that the mass transfer occurs via stellar winds, rather than through the L1 point of Roche filling secondary, a phenomenon more common for symbiotic stars.
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Sahal-Bréchot, S., and H. Elabidi. "Stark broadening for Br VI and Kr V-VII lines in hot star atmospheres." Astronomy & Astrophysics 652 (August 2021): A47. http://dx.doi.org/10.1051/0004-6361/202140729.
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Context. This paper provides missing Stark broadening of the Br VI and Kr V-VII lines recently discovered in the ultraviolet spectrum of the hot white dwarf RE 0503–289 and investigates the importance of the Stark broadening mechanism versus the Doppler mechanism in that star. As far as we know, this is the first time that Stark widths of Br VI and Kr V-VII lines have been calculated. Aims. The recent discovery of new lines of Br VI and Kr V-VII encourages us to provide their Stark broadening to enrich the STARK-B database and for use in interpretations of the observed spectra. Methods. We used our quantum mechanical method for calculating electron impact broadening to provide Stark widths. The method starts with an evaluation of the structure and collision parameters using the University College London codes SUPERSTRUCTURE/DISTORTED WAVE/JAJOM, which are adapted to the line broadening calculations. We then used the collision parameters to calculate the line widths using our programs. Results. We provide the missing widths of 35 lines of Br VI and Kr V-VII at different electron temperatures and at density Ne = 1017 cm−3. We find that the Stark broadening mechanism is preponderant compared to the Doppler one for almost all the plasma conditions of the considered DO white dwarf atmospheres.
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Sekeráš, Matej, and Augustin Skopal. "On the accretion onto the white dwarfs in symbiotic binaries: A test with the Thomson scattering process." Proceedings of the International Astronomical Union 8, S290 (August 2012): 305–6. http://dx.doi.org/10.1017/s1743921312020133.
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AbstractWe tested the origin of the nebular radiation in the symbiotic star AG Dra, during different levels of its activity. We modeled the broad wings of the OVI 1032, 1038 Å resonance lines and HeII 1640 Å line by the Thomson scattering process, and determined the electron-scattering optical depth, τe, of the symbiotic nebula. The increase of τe during active phases results from an increase in the accretion rate onto the white dwarf.
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Avior, Y., S. Ron, D. Kroitorou, E. Nitzan, B. Corneo, D. Laifenfeld, and T. Cohen Solal. "Depression patient-derived cortical neurons reveal potential biomarkers for antidepressant response." European Psychiatry 64, S1 (April 2021): S143. http://dx.doi.org/10.1192/j.eurpsy.2021.392.
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IntroductionMajor depressive disorder is highly prevalent worldwide and has been affecting an increasing number of people each year. Current first line antidepressants show merely 37% remission, and physicians are forced to use a trial-and-error approach when choosing a single antidepressant out of dozens of available medications.ObjectivesWe sought to identify a method of testing that would provide patient-specific information on whether a patient will respond to a medication using in vitro modeling.MethodsPatient-derived lymphoblastoid cell lines from the STAR*D study were used to rapidly generate cortical neurons and screen them for bupropion effects, for which the donor patients showed remission or non-remission.ResultsWe provide evidence for biomarkers specific for bupropion response, including synaptic connectivity and morphology changes as well as specific gene expression alterations.ConclusionsThese biomarkers support the concept of personalized antidepressant treatment based on in vitro platforms and could be utilized as predictors to patient response in the clinic.DisclosureThis work was funded by Genetika+ Ltd, Jerusalem, Israel. YA, DK, EN, DL and TCS are employees of Genetika+ Ltd and received salary and/or stock options for the submitted work.
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Wang, Y., R. B. Dong, D. N. C. Lin, and X. W. Liu. "Origin of debris disks and the supply of metals in DZ white dwarfs." Proceedings of the International Astronomical Union 3, S249 (October 2007): 389–92. http://dx.doi.org/10.1017/s1743921308016876.
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AbstractWe discuss the dynamical evolution of minor planetary bodies in the outer regions of planetary systems around the progenitors of DZ white dwarfs. We show that during the planetary-nebula phase of these stars, mass loss can lead to the expansion of all planetary bodies. The orbital eccentricity of the minor bodies, as relics of planetesimals, may be largely excited by the perturbation due to both gas drag effects and nearby gas giant planets. Some of these bodies migrate toward the host star, while others are scattered out of the planetary system. The former have modest probability of being captured by the sweeping secular resonances of giant planets, and induced to migrate toward the host star. When they venture close to their host stars, their orbits are tidally circularized so that they form compact disks where they may undergo further collisionally driven evolution. During the subsequent post main sequence evolution of their host stars, this process may provide an avenue which continually channels heavy elements onto the surface of the white dwarfs. We suggest that this scenario provides an explanation for the recently discovered Calcium line variation in G29-38.
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Phan, Thanh Thao, Thi Thu Uyen Nguy, and Duy-Nam Phan. "Building Rules of Some Influential Technological Factors on Sewing Time for Products from Knitted Fabrics." ECS Transactions 107, no. 1 (April 24, 2022): 7649–59. http://dx.doi.org/10.1149/10701.7649ecst.
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This paper presents the results of research on building empirical regression equations showing the law of simultaneous influence of the group of technology factors on the upper sewing time when sewing polo shirt and t-shirt products from single jersey at Star Hanoi Fashion Co., Ltd. The studies on the factors affecting time on the sewing machine include the length line (cm) and the stitch density (stitch/cm), the experiment on 04 devices, and 03 patterns of knitted fabric different thickness single woven tops. Thereby showing the difference in sewing time value on 04 sewings, corresponding to specific values of 2 research variables, which are stitch density and seam length when sewing on single fabric with 03 different thicknesses for polo shirt and t-shirt.
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Preval, Simon P., Martin A. Barstow, Matthew Bainbridge, Nicole Reindl, Thomas Ayres, Jay B. Holberg, John D. Barrow, Chung-Chi Lee, John K. Webb, and Jiting Hu. "A far-UV survey of three hot, metal-polluted white dwarf stars: WD0455−282, WD0621−376, and WD2211−495." Monthly Notices of the Royal Astronomical Society 487, no. 3 (June 4, 2019): 3470–87. http://dx.doi.org/10.1093/mnras/stz1506.
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ABSTRACT Using newly obtained high-resolution data (R ∼ 1 × 105) from the Hubble Space Telescope, and archival UV data from the Far Ultraviolet Spectroscopic Explorer, we have conducted a detailed UV survey of the three hot, metal-polluted white dwarfs WD0455−282, WD0621−376, and WD2211−495. Using bespoke model atmospheres, we measured Teff, log g, and photospheric abundances for these stars. In conjunction with data from Gaia, we measured masses, radii, and gravitational redshift velocities for our sample of objects. We compared the measured photospheric abundances with those predicted by radiative levitation theory, and found that the observed Si abundances in all three white dwarfs, and the observed Fe abundances in WD0621−376 and WD2211−495, were larger than those predicted by an order of magnitude. These findings imply not only an external origin for the metals, but also ongoing accretion, as the metals not supported by radiative levitation would sink on extremely short time-scales. We measured the radial velocities of several absorption features along the line of sight to the three objects in our sample, allowing us to determine the velocities of the photospheric and interstellar components along the line of sight for each star. Interestingly, we made detections of circumstellar absorption along the line of sight to WD0455−282 with three velocity components. To our knowledge, this is the first such detection of multicomponent circumstellar absorption along the line of sight to a white dwarf.
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Ramstedt, S., S. Mohamed, T. Olander, W. H. T. Vlemmings, T. Khouri, and S. Liljegren. "CO envelope of the symbiotic star R Aquarii seen by ALMA." Astronomy & Astrophysics 616 (August 2018): A61. http://dx.doi.org/10.1051/0004-6361/201833394.
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The symbiotic star R Aqr is part of a small sample of binary AGB stars observed with the Atacama Large Millimeter/submillimeter Array (ALMA). The sample stars are: R Aqr, Mira, W Aql, and π1 Gru. The sample covers a range in binary separation and wind properties, where R Aqr is the source with the smallest separation. The R Aqr binary pair consists of an M-type AGB star and a white dwarf at a separation of 45 mas, equivalent to about 10 AU at 218 pc. The aim of the ALMA study is to investigate the dependence of the wind shaping on the binary separation and to provide constraints for hydrodynamical binary interaction models. R Aqr is particularly interesting as the source with the smallest separation and a complex circumstellar environment that is strongly affected by the interaction between the two stars and by the high-energy radiation resulting from this interaction and from the hot white dwarf companion. The CO(J = 3 →2) line emission has been observed with ALMA at ~0.5′′ spatial resolution. The CO envelope around the binary pair is marginally resolved, showing what appears to be a rather complex distribution. The outer radius of the CO emitting region is estimated from the data and found to be about a factor of 10 larger than previously thought. This implies an average mass-loss rate during the past ~100 yr of Ṁ ≈ 2×10−7 M⊙ yr−1, a factor of 45 less than previous estimates. The channel maps are presented and the molecular gas distribution is discussed and set into the context of what was previously known about the system from multiwavelength observations. Additional molecular line emission detected within the bandwidth covered by the ALMA observations is also presented. Because of the limited extent of the emission, firm conclusions about the dynamical evolution of the system will have to wait for higher spatial resolution observations. However, the data presented here support the assumption that the mass-loss rate from the Mira star strongly varies and is focused on the orbital plane.
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Kocevski, D., N. Nikolova, and A. Kuzelov. "The influence of strain and age on some egg quality parameters of commercial laying hens." Biotehnologija u stocarstvu 27, no. 4 (2011): 1649–58. http://dx.doi.org/10.2298/bah1104649k.
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The experiment was conducted to evaluate the influence of strain and age on some egg quality parameters (egg weight and egg shell strength) of commercial laying hens. Layers of lines ISA Brown and DeKalb White were examined in period of nine months. Both lines were at same age (28 weeks) and were confined in common facility in battery cages. Laying hens were reared and fed according to standard breeding technology. Once a month 25 eggs of each line were taken to be examined for eggshell strength and egg weight, or in other words, total 450 table eggs were tested. Analises were done in Laboratory for testing egg quality by gaudges Egg Multi Tester EMT 5200 and Egg shell Gauge (Robotmation Co. Ltd., Tokyo, Japan) which have computerised equipment to examine quality and physical characteristics of eggs. Statistic analyses on results were done by computer sub-programme ANOVA and Fisher's LSD test to determine the level of statistical significant difference between examined factors. Egg weight was under significant impact of age (P ? 0,05), but not under the influence of strain, although eggs of ISA Brown line were insignificantly heavier than eggs of DeKalb White line. Eggs were heaviest at layers with older age, while they were lightest at younger birds. The results have shown significant differences (P ? 0,05) in eggshell strength compared to line influence (genotype) and months of age. Eggs from ISA Brown laying hens had much better and eggshell strength than those eggs from DeKalb White. Correlations between eggshell strength and egg weight were with significant (R < 0,05) negative value, which indicating that with increasing egg weight decreases of eggshell strength.
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Oskinova, Lidia M., Vasilii V. Gvaramadze, Götz Gräfener, Norbert Langer, and Helge Todt. "X-rays observations of a super-Chandrasekhar object reveal an ONe and a CO white dwarf merger product embedded in a putative SN Iax remnant." Astronomy & Astrophysics 644 (December 2020): L8. http://dx.doi.org/10.1051/0004-6361/202039232.
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The merger of two white dwarfs (WDs) is a natural outcome of the evolution of many binary stars. Recently, a WD merger product, IRAS 00500+6713, was identified. IRAS 00500+6713 consists of a central star embedded in a circular nebula. The analysis of the optical spectrum of the central star revealed that it is hot, hydrogen, and helium free, and it drives an extremely fast wind with a record breaking speed. The nebula is visible in infrared and in the [O III] λ5007 Å line images. No nebula spectroscopy was obtained prior to our observations. Here we report the first deep X-ray imaging spectroscopic observations of IRAS 00500+6713. Both the central star and the nebula are detected in X-rays, heralding the WD merger products as a new distinct type of strong X-ray sources. Low-resolution X-ray spectra reveal large neon, magnesium, silicon, and sulfur enrichment of the central star and the nebula. We conclude that IRAS 00500+6713 resulted from a merger of an ONe and a CO WD, which supports earlier suggestion for a super-Chandrasekhar mass of this object. X-ray analysis indicates that the merger was associated with an episode of carbon burning and possibly accompanied by an SN Iax. In X-rays, we observe the point source associated with the merger product while the surrounding diffuse nebula is a supernova remnant. IRAS 00500+6713 will likely terminate its evolution with another peculiar Type I supernova, where the final core collapse to a neutron star might be induced by electron captures.
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Werner, Klaus, Nicole Reindl, Lisa Löbling, Ingrid Pelisoli, Veronika Schaffenroth, Alberto Rebassa-Mansergas, Puji Irawati, and Juanjuan Ren. "An extremely hot white dwarf with a rapidly rotating K-type subgiant companion: UCAC2 46706450." Astronomy & Astrophysics 642 (October 2020): A228. http://dx.doi.org/10.1051/0004-6361/202038574.
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The subgiant UCAC2 46706450 is a late-type star with an ultraviolet (UV) excess. It was considered as a candidate to establish a sample of stars of spectral type F, G, and K with white dwarf (WD) companions that could be used to test binary evolution models. To verify the WD nature of the companion, UV spectroscopy has previously been performed by other authors. Via a detailed model-atmosphere analysis, we show that the UV source is an extremely hot WD with an effective temperature of Teff = 105 000 ± 5000 K, mass of M∕M⊙ = 0.54 ± 0.02, radius of R/R⊙ = 0.040−0.004+0.005, and luminosity of L/L⊙ = 176−49+55, meaning that the compact object is just about to enter the WD cooling sequence. Investigating spectra of the cool star (Teff = 4945 ± 250 K), we found that it is a K-type subgiant with M∕M⊙ = 0.8−2.4, R/R⊙ = 5.9−0.5+0.7, and L/L⊙ = 19−5+5 that is rapidly rotating with vsin(i) = 81 km s−1. Optical light curves reveal a period of two days and an o-band peak-to-peak amplitude of 0.06 mag. We suggest that it is caused by stellar rotation in connection with star spots. With the radius, we infer an extremely high rotational velocity of vrot = 151−13+18 km s−1, thus marking the star as one of the most rapidly rotating subgiants known. This explains chromospheric activity observed by H α emission and emission-line cores in Ca II H and K as well as NUV flux excess. From equal and constant radial velocities of the WD and the K subgiant as well as from a fit to the spectral energy distribution, we infer that they form a physical, wide (though unresolved) binary system. Both components exhibit similar metal abundances and show iron-group elements with slightly oversolar (up to 0.6 dex) abundance, meaning that atomic diffusion in the WD atmosphere is not yet active due to a residual, weak radiation-driven wind. Kinematically and from its height above the Galactic plane, the system belongs to the Galactic thick disk, indicating that it is an old system and that the initial masses of both stars were close to 1 M⊙.
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Cox, Arthur N. "White Dwarf and Pre-White Dwarf Oscillations." International Astronomical Union Colloquium 139 (1993): 107–15. http://dx.doi.org/10.1017/s0252921100117038.
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AbstractCompact stars that result from extreme mass loss on the asymptotic giant branch and planetary nebula formation are observed to pulsate in a very large surface effective temperature range as they cool to become the classical white dwarfs. The hottest and most luminous of these display periods in excess of 1000 seconds because they are large, but when the stars arrive on the cooling line on the Hertzsprung-Russell diagram, their periods become generally less than 1000 seconds. Then the stars have masses near 0.6 M⊙ and radii near 109 cm. Their luminosity depends then almost entirely on the surface effective temperature as the entire star with its legacy of complicated internal luminosity peaks cools to the classical simple electron degenerate structure. Very thin surface layers of hydrogen and helium cover the bulk of the carbon- and oxygen-rich mass that results from hydrogen and helium burning in earlier intermediate mass stellar evolution. The cause of the nonradial pulsations of low angular degree, but rather high radial order, for the most luminous of these stars is the cyclical ionization of carbon and oxygen in layers not too deep that their effectiveness is limited by a long luminosity time scale. Thus the surface hydrogen and helium must be thin, probably thinner than the current period spacings interpretation for PG 1159-035 suggests. For the classical DBV and DAV pulsators, it appears that neither the hydrogen ionization K and γ effects or convection blocking at the bottom of a hydrogen convection zone can destabilize the observed pulsations when the overriding short time scale effects of time-dependent convection are included. It appears, however, that a thin CO convection shell can produce pulsations by its time-dependent effects, but again only very thin H and He surface layers are allowed. This new pulsation mechanism can alleviate the serious problem that DAV variables are observed hotter than the hydrogen K and γ effects and convection blocking can predict. The appearance of non-pulsators in the DAV and DBV instability strips can be explained by a too-thick hydrogen and helium surface layer that interferes with (poisons) the CO ionization convection zone. Finally time-dependent convection predicts that only a few of the many possible modes exist due to their internal amplitude structure that can result in both strong driving and strong damping. Thus actually observed pulsating modes can assist in mapping individual internal white dwarf composition structures, not only by their periods but also the fact that they pulsate.
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Gillon, Michaël, Artem Burdanov, and Jason T. Wright. "Search for an Alien Message to a Nearby Star." Astronomical Journal 164, no. 5 (October 27, 2022): 221. http://dx.doi.org/10.3847/1538-3881/ac9610.
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Abstract If alien probes have colonized the whole galaxy, they could have formed an efficient galactic-scale communication network by establishing direct gravitationally lensed links between neighboring systems. Under this scenario, observing the positions opposite the nearest ecliptic stars represents a promising artifact SETI strategy that could make it possible to “eavesdrop” on the emission of local probes to one of these stars. In this context, we present here a first attempt to detect optical messages emitted from the solar system to the ecliptic star Wolf 359, the third-nearest stellar system, based on observations gathered by the TRAPPIST-South and SPECULOOS-South robotic telescopes. While sensitive enough to detect constant emission with emitting power as small as a few watts, this search led to a null result. We note that the putative alien probes could be emitting “off-axis” and be located much closer to the Sun than the start of the “solar gravitational line” at 550 au. We performed a search for such an off-axis emitter in our data, whose result turned out negative too.
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Isern, J., and R. Canal. "Gravitational Collapse versus Thermonuclear Explosion of Degenerate Stellar Cores." International Astronomical Union Colloquium 147 (1994): 186–213. http://dx.doi.org/10.1017/s0252921100026373.
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AbstractIn this paper we review the behavior of growing stellar degenerate cores. It is shown that ONeMg white dwarfs and cold CO white dwarfs can collapse to form a neutron star. This collapse is completely silent since the total amount of radioactive elements that are expelled is very small and a burst of γ-rays is never produced. In the case of an explosion (always carbonoxygen cores), the outcome fits quite well the observed properties of Type Ia supernovae. Nevertheless, the light curves and the velocities measured at maximum are very homogeneous and the diversity introduced by igniting at different densities is not enough to account for the most extreme cases observed. It is also shown that a promising way out of this problem could be the He-induced detonation of white dwarfs with different masses. Finally, we outline that the location of the border line which separetes explosion from collapse strongly depends on the input physics adopted.
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Dupuis, Jean, and Stéphane Vennes. "A Spectroscopic Survey in the EUV of the “Coolest” Hot DA Stars." International Astronomical Union Colloquium 152 (1996): 217–22. http://dx.doi.org/10.1017/s0252921100036009.
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We present an analysis of the extreme ultraviolet (EUV) spectroscopy of a sample of 10 DA white dwarfs observed by the Extreme Ultraviolet Explorer (EUVE). We have selected white dwarfs cooler than about 50,000 K and with presumably low heavy element abundances. The goal of this study is to determine the fundamental atmospheric parameters, namely the effective temperature and chemical composition, of these stars by fitting their continua with synthetic spectra computed from pure hydrogen LTE/line-blanketed model atmospheres. The question of the presence (or absence) of trace elements is explored by comparing EUV-determined effective temperatures to the one obtained from a fit of hydrogen balmer lines. It is found that the majority of the DA in the sample are consistent with having a pure hydrogen atmosphere. One of the star, MCT0027-634, is another possible example of a HZ 43-type white dwarf, having an effective temperature above 50000 K and a low heavy element abundance, i.e., much lower than predicted by diffusion theory.
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Patrick, Stephanie. "Life Is But a Story: Female pleasure and agency in Beyoncé’s autobiographical film." Journal of Fandom Studies 8, no. 3 (September 1, 2020): 251–63. http://dx.doi.org/10.1386/jfs_00022_1.
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While the rise of new media has led to a blurring of stars’ public personae and private, intimate lives, the musician, in particular, has long been expected to share their private, authentic self through their music. This is certainly the case with superstar Beyoncé, whose 2016 solo album Lemonade was widely received as a revealing portrait of her marriage to hip hop mogul Jay-Z. Yet Beyoncé has long been playing with the public‐private divide as a key part of her star persona. Her decision to limit media interviews has allowed her to maintain unprecedented control of her star image; an image that is now corralled through the texts that she herself circulates via her music, videos and other media. One such notable, yet under-examined text is her 2013 autobiographical film Life Is But a Dream. Both the narrative and the production of the film serve to teach audiences how to read the rest of Beyoncé’s cultural work; as work that is fully controlled by her and intended for women. This pedagogical film disrupts common readings of her image and performances as being in the service of a male gaze, thus opening up new pleasures and potentials for female fans more broadly and Black female fans more specifically. Life Is But a Dream is thus a central, rather than a periphery text in Beyoncé’s star image, complementing and complicating the work she produces across other media formats.
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Whitney, Barbara. "Thomson Scattering in Magnetic Fields." International Astronomical Union Colloquium 114 (1989): 392–95. http://dx.doi.org/10.1017/s0252921100099942.
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AbstractThe equation of transfer in Thomson scattering atmospheres with magnetic fields is solved using Monte Carlo methods. Two cases, a plane parallel atmosphere with a magnetic field perpendicular to the atmosphere, and a dipole star, are investigated. The wavelength dependence of polarization from a plane-parallel atmosphere is qualitatively similar to that observed in the magnetic white dwarf Grw+70°8247, and the field strength determined by the calculation, 3.2×l08 G, is quantitatively similar to that determined from the line spectrum. The dipole model does not resemble the data as well as the single plane-parallel atmosphere.
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Shields, Joshua V., Wolfgang Kerzendorf, Matthew W. Hosek, Ken J. Shen, Armin Rest, Tuan Do, Jessica R. Lu, Andrew G. Fullard, Giovanni Strampelli, and Alfredo Zenteno. "Searching for a Hypervelocity White Dwarf SN Ia Companion: A Proper-motion Survey of SN 1006." Astrophysical Journal Letters 933, no. 2 (July 1, 2022): L31. http://dx.doi.org/10.3847/2041-8213/ac7950.
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Abstract Type Ia supernovae (SNe Ia) are securely understood to come from the thermonuclear explosion of a white dwarf as a result of binary interaction, but the nature of that binary interaction and the secondary object is uncertain. Recently, a double white dwarf model known as the dynamically driven double-degenerate double-detonation (D6) model has become a promising explanation for these events. One realization of this scenario predicts that the companion may survive the explosion and reside within the remnant as a fast moving (V peculiar > 1000 km s−1), overluminous (L > 0.1 L ⊙) white dwarf. Recently, three objects that appear to have these unusual properties have been discovered in the Gaia survey. We obtained photometric observations of the SN Ia remnant SN 1006 with the Dark Energy Camera over four years to attempt to discover a similar star. We present a deep, high-precision astrometric proper-motion survey of the interior stellar population of the remnant. We rule out the existence of a high-proper-motion object consistent with our tested realization of the D6 scenario (V transverse > 600 km s−1 with m r < 21 corresponding to an intrinsic luminosity of L > 0.0176 L ⊙). We conclude that such a star does not exist within the remnant or is hidden from detection by either strong localized dust or the unlikely possibility of ejection from the binary system almost parallel to the line of sight.
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Krtička, J., J. Kubát, and I. Krtičková. "Stellar wind models of central stars of planetary nebulae." Astronomy & Astrophysics 635 (March 2020): A173. http://dx.doi.org/10.1051/0004-6361/201937150.
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Context. Fast line-driven stellar winds play an important role in the evolution of planetary nebulae, even though they are relatively weak. Aims. We provide global (unified) hot star wind models of central stars of planetary nebulae. The models predict wind structure including the mass-loss rates, terminal velocities, and emergent fluxes from basic stellar parameters. Methods. We applied our wind code for parameters corresponding to evolutionary stages between the asymptotic giant branch and white dwarf phases for a star with a final mass of 0.569 M⊙. We study the influence of metallicity and wind inhomogeneities (clumping) on the wind properties. Results. Line-driven winds appear very early after the star leaves the asymptotic giant branch (at the latest for Teff ≈ 10 kK) and fade away at the white dwarf cooling track (below Teff = 105 kK). Their mass-loss rate mostly scales with the stellar luminosity and, consequently, the mass-loss rate only varies slightly during the transition from the red to the blue part of the Hertzsprung–Russell diagram. There are the following two exceptions to the monotonic behavior: a bistability jump at around 20 kK, where the mass-loss rate decreases by a factor of a few (during evolution) due to a change in iron ionization, and an additional maximum at about Teff = 40−50 kK. On the other hand, the terminal velocity increases from about a few hundreds of km s−1 to a few thousands of km s−1 during the transition as a result of stellar radius decrease. The wind terminal velocity also significantly increases at the bistability jump. Derived wind parameters reasonably agree with observations. The effect of clumping is stronger at the hot side of the bistability jump than at the cool side. Conclusions. Derived fits to wind parameters can be used in evolutionary models and in studies of planetary nebula formation. A predicted bistability jump in mass-loss rates can cause the appearance of an additional shell of planetary nebula.
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Bellotti, S., P. Petit, J. Morin, G. A. J. Hussain, C. P. Folsom, A. Carmona, X. Delfosse, and C. Moutou. "Mitigating stellar activity jitter with different line lists for least-squares deconvolution." Astronomy & Astrophysics 657 (January 2022): A107. http://dx.doi.org/10.1051/0004-6361/202141812.
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Context. Stellar activity limits the radial velocity (RV) search and characterisation of exoplanets, as it introduces spurious noise (called jitter) in the data sets and prevents the correct retrieval of a planetary signal. This is key for M dwarfs, considering that they manifest high activity levels and are primary targets for present and future searches of habitable Earth-like planets. To perform precise RV measurements, multi-line numerical techniques like cross-correlation and least-squares deconvolution (LSD) are typically employed. Aims. Effective filtering of activity is crucial to achieving the sensitivity required for small planet detections. Here we analyse the impact of selecting different line lists for LSD on the dispersion in our RV data sets, to identify the line list that most effectively reduces the jitter. Methods. We employ optical spectropolarimetric observations of the active M dwarf EV Lac collected with ESPaDOnS and NARVAL, and study two line down-selection approaches: a parametric method based on line properties (depth, wavelength, magnetic sensitivity) and a randomised algorithm that samples the line combination space. We test the latter further to find the line list that singles out the activity signal from other sources of noise, and on AD Leo and DS Leo to examine its consistency at mitigating jitter for different activity levels. The analysis is complemented with planetary injection tests. Results. The parametric selection yields a RV RMS reduction of less than 10%, while the randomised selection yields a systematic improvement (>50%) regardless of the activity level of the star examined. Furthermore, if activity is the dominant source of noise, this approach allows the construction of lists containing mainly activity-sensitive lines, which could be used to enhance the rotational modulation of the resulting data sets and determine the stellar rotation period more robustly. Finally, the output line lists allow the recovery of a synthetic planet (0.3–0.6 MJup on a 10 d orbit) in the presence of both moderate (20 m s−1 semi-amplitude) and high (200 m s−1) activity levels, without substantially affecting the planet signal (between 60 and 120 m s−1).
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Jayaraman, Rahul, Gerald Handler, Saul A. Rappaport, Jim Fuller, Donald W. Kurtz, Stéphane Charpinet, and George R. Ricker. "Tidally Tilted Pulsations in HD 265435, a Subdwarf B Star with a Close White Dwarf Companion." Astrophysical Journal Letters 928, no. 2 (March 30, 2022): L14. http://dx.doi.org/10.3847/2041-8213/ac5c59.
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Abstract Tidally tilted pulsators (TTPs) are an intriguing new class of oscillating stars in binary systems; in such stars, the pulsation axis coincides with the line of apsides, or tidal axis, of the binary. All three TTPs discovered so far have been δ Scuti stars. In this Letter, we report the first conclusive discovery of tidally tilted pulsations in a subdwarf B (sdB) star. HD 265435 is an sdB–white dwarf binary with a 1.65 hr period that has been identified and characterized as the nearest potential Type Ia supernova progenitor. Using TESS 20 s cadence data from Sectors 44 and 45, we show that the pulsation axis of the sdB star has been tidally tilted into the orbital plane and aligned with the tidal axis of the binary. We identify 31 independent pulsation frequencies, 27 of which have between 1 and 7 sidebands separated by the orbital frequency (ν orb) or multiples thereof. Using the observed amplitude and phase variability due to tidal tilting, we assign ℓ and m values to most of the observed oscillation modes and use these mode identifications to generate preliminary asteroseismic constraints. Our work significantly expands our understanding of TTPs, as we now know that (i) they can be found in stars other than δ Scuti pulsators, especially highly evolved stars that have lost their H-rich envelopes, and (ii) tidally tilted pulsations can be used to probe the interiors of stars in very tight binaries.
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Göttgens, Fabian, Peter M. Weilbacher, Martin M. Roth, Stefan Dreizler, Benjamin Giesers, Tim-Oliver Husser, Sebastian Kamann, et al. "Discovery of an old nova remnant in the Galactic globular cluster M 22." Astronomy & Astrophysics 626 (June 2019): A69. http://dx.doi.org/10.1051/0004-6361/201935221.
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A nova is a cataclysmic event on the surface of a white dwarf in a binary system that increases the overall brightness by several orders of magnitude. Although binary systems with a white dwarf are expected to be overabundant in globular clusters compared with in the Galaxy, only two novae from Galactic globular clusters have been observed. We present the discovery of an emission nebula in the Galactic globular cluster M 22 (NGC 6656) in observations made with the integral-field spectrograph MUSE. We extracted the spectrum of the nebula and used the radial velocity determined from the emission lines to confirm that the nebula is part of NGC 6656. Emission-line ratios were used to determine the electron temperature and density. It is estimated to have a mass of 1–17 × 10−5M⊙. This mass and the emission-line ratios indicate that the nebula is a nova remnant. Its position coincides with the reported location of a “guest star”, an ancient Chinese term for transients, observed in May 48 BCE. With this discovery, this nova may be one of the oldest confirmed extra-solar events recorded in human history.
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Landstreet, J. D., and S. Bagnulo. "A new weak-field magnetic DA white dwarf in the local 20 pc volume." Astronomy & Astrophysics 628 (July 26, 2019): A1. http://dx.doi.org/10.1051/0004-6361/201936009.
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We report the discovery of a new magnetic DA white dwarf (WD), WD 0011 − 721, which is located within the very important 20 pc volume-limited sample of the closest WDs to the Sun. This star has a mean field modulus ⟨|B|⟩ of 343 kG, and from the polarisation signal we deduce a line-of-sight field component of 75 kG. The magnetic field is sufficiently weak to have escaped detection in classification spectra. We then present a preliminary exploration of the data concerning the frequency of such fields among WDs with hydrogen-rich atmospheres (DA stars). We find that 20 ± 5% of the DA WDs in this volume have magnetic fields, mostly weaker than 1 MG. Unlike the slow field decay found among the magnetic Bp stars of the upper main sequence, the WDs in this sample show no evidence of magnetic field or flux changes over several Gyr.
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Gänsicke, Boris T., Pablo Rodríguez-Gil, Nicola P. Gentile Fusillo, Keith Inight, Matthias R. Schreiber, Anna F. Pala, and Pier-Emmanuel Tremblay. "Single magnetic white dwarfs with Balmer emission lines: a small class with consistent physical characteristics as possible signposts for close-in planetary companions." Monthly Notices of the Royal Astronomical Society 499, no. 2 (September 29, 2020): 2564–74. http://dx.doi.org/10.1093/mnras/staa2969.
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ABSTRACT We report the identification of SDSS J121929.45+471522.8 as the third apparently isolated magnetic (B ≃ 18.5 ± 1.0 MG) white dwarf exhibiting Zeeman-split Balmer emission lines. The star shows coherent variability at optical wavelengths with an amplitude of ≃0.03 mag and a period of 15.26 h, which we interpret as the spin period of the white dwarf. Modelling the spectral energy distribution and Gaia parallax, we derive a white dwarf temperature of 7500 ± 148 K, a mass of 0.649 ± 0.022 M⊙, and a cooling age of 1.5 ± 0.1 Gyr, as well as an upper limit on the temperature of a sub-stellar or giant planet companion of ≃250 K. The physical properties of this white dwarf match very closely those of the other two magnetic white dwarfs showing Balmer emission lines: GD356 and SDSS J125230.93−023417.7. We argue that, considering the growing evidence for planets and planetesimals on close orbits around white dwarfs, the unipolar inductor model provides a plausible scenario to explain the characteristics of this small class of stars. The tight clustering of the three stars in cooling age suggests a common mechanism switching the unipolar inductor on and off. Whereas Lorentz drift naturally limits the lifetime of the inductor phase, the relatively late onset of the line emission along the white dwarf cooling sequence remains unexplained.
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van Sluijs, Lennart, Ernst de Mooij, Matthew Kenworthy, Maggie Celeste, Matthew J. Hooton, Eric E. Mamajek, Brigitta Sipőcz, Ignas A. G. Snellen, Andrew R. Ridden-Harper, and Paul A. Wilson. "Spectroscopic transit search: a self-calibrating method for detecting planets around bright stars." Astronomy & Astrophysics 626 (June 2019): A97. http://dx.doi.org/10.1051/0004-6361/201935066.
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Aims. We aim to search for transiting exoplanets around the star β Pictoris using high-resolution spectroscopy and Doppler imaging that removes the need for standard star observations. These data were obtained on the VLT with UVES during the course of an observing campaign throughout 2017 that monitored the Hill sphere transit of the exoplanet β Pictoris b. Methods. We utilized line profile tomography as a method for the discovery of transiting exoplanets. By measuring the exoplanet distortion of the stellar line profile, we removed the need for reference star measurements. We demonstrated the method with white noise simulations, and then looked at the case of β Pictoris, which is a δ Scuti pulsator. We describe a method to remove the stellar pulsations and perform a search for any transiting exoplanets in the resultant data set. We injected fake planet transits with varying orbital periods and planet radii into the spectra and determined the recovery fraction. Results. In the photon noise limited case we can recover planets down to a Neptune radius with an ~80% success rate, using an 8 m telescope with a R ~ 100 000 spectrograph and 20 min of observations per night. The pulsations of β Pictoris limit our sensitivity to Jupiter-sized planets, but a pulsation removal algorithm improves this limit to Saturn-sized planets. We present two planet candidates, but argue that their signals are most likely caused by other phenomena. Conclusions. We have demonstrated a method for searching for transiting exoplanets that (i) does not require ancillary calibration observations, (ii) can work on any star whose rotational broadening can be resolved with a high spectral dispersion spectrograph, and (iii) provides the lowest limits so far on the radii of transiting Jupiter-sized exoplanets around β Pictoris with orbital periods from 15 days to 200 days with >50% coverage.
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Merc, J., J. Mikołajewska, M. Gromadzki, C. Gałan, K. Iłkiewicz, J. Skowron, Ł. Wyrzykowski, et al. "Gaia18aen: First symbiotic star discovered by Gaia." Astronomy & Astrophysics 644 (November 30, 2020): A49. http://dx.doi.org/10.1051/0004-6361/202039132.
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Context. Besides the astrometric mission of the Gaia satellite, its repeated and high-precision measurements also serve as an all-sky photometric transient survey. The sudden brightenings of the sources are published as Gaia Photometric Science Alerts and are made publicly available, allowing the community to photometrically and spectroscopically follow up on the object. Aims. The goal of this paper is to analyze the nature and derive the basic parameters of Gaia18aen, a transient detected at the beginning of 2018. This object coincides with the position of the emission-line star WRAY 15-136. The brightening was classified as a “nova?” on the basis of a subsequent spectroscopic observation. Methods. We analyzed two spectra of Gaia18aen and collected the available photometry of the object covering the brightenings in 2018 and also the preceding and following periods of quiescence. Based on this observational data, we derived the parameters of Gaia18aen and discussed the nature of the object. Results. Gaia18aen is the first symbiotic star discovered by Gaia satellite. The system is an S-type symbiotic star and consists of an M giant of a slightly super-solar metallicity, where Teff ∼ 3500 K, a radius of ∼230 R⊙, and a high luminosity L ∼ 7400 L⊙. The hot component is a hot white dwarf. We tentatively determined the orbital period of the system ∼487 d. The main outburst of Gaia18aen in 2018 was accompanied by a decrease in the temperature of the hot component. The first phase of the outburst was characterized by the high luminosity L ∼ 27 000 L⊙, which remained constant for about three weeks after the optical maximum, later followed by the gradual decline of luminosity and increase of temperature. Several re-brightenings have been detected on the timescales of hundreds of days.