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1
Pan, Xiaopei, Shri Kulkarni, Michael Shao e M. Mark Colavita. "Narrow-Angle and Wide-Angle Astrometry via Long Baseline Optical/Infrared Interferometers". Symposium - International Astronomical Union 166 (1995): 13–18. http://dx.doi.org/10.1017/s0074180900227769.
Testo completoAbstract (sommario):
Long baseline optical/infrared interferometers, such as the Mark III Stellar Interferometer1 on Mt. Wilson and the ASEPS-0 Testbed Interferometer2 on Palomar Mountain, California, have good capabilities for narrow-angle and wide-angle astrometry with very high precision. Using the Mark III Interferometer many spectroscopic binaries became “visual” for the first time. The measurement accuracy of angular separation is 0.2 mas, the smallest separation measured between two components is 2 mas, the maximum magnitude difference is 4 mag, and the smallest semimajor axis is 4 mas. Such high angular resolution and dynamic range have been used to determine stellar masses with precision of 2% and differential stellar luminosities to better than 0.05 mag for separations of less than 0.″2. For some binary stars, not only have the systems been resolved, but also the diameter of the primary component has been determined, yielding direct measurements of stellar effective temperature with high accuracy. For parallax determination, the precision is 1 mas or better and is unaffected by interstellar extinction. For wide-angle astrometry with the Mark III interferometer, the observation results yielded average formal 1σ errors for FK5 stars of about 10 mas. Presently a new infrared interferometer, the ASEPS-0 Testbed Interferometer on Palomar Mountain is under construction, and is being optimized to perform high accuracy narrow-angle astrometry using long baseline observations at 2.2 μm, with phase referencing for increased sensitivity. The goal is to demonstrate differential astrometric accuracies of 0.06–0.1 mas3 in order to allow for detection of extra-solar planets in the near future.
2
Jankov, S. "Astronomical optical interferometry, II: Astrophysical results". Serbian Astronomical Journal, n. 183 (2011): 1–35. http://dx.doi.org/10.2298/saj1183001j.
Testo completoAbstract (sommario):
Optical interferometry is entering a new age with several ground- based long-baseline observatories now making observations of unprecedented spatial resolution. Based on a great leap forward in the quality and quantity of interferometric data, the astrophysical applications are not limited anymore to classical subjects, such as determination of fundamental properties of stars; namely, their effective temperatures, radii, luminosities and masses, but the present rapid development in this field allowed to move to a situation where optical interferometry is a general tool in studies of many astrophysical phenomena. Particularly, the advent of long-baseline interferometers making use of very large pupils has opened the way to faint objects science and first results on extragalactic objects have made it a reality. The first decade of XXI century is also remarkable for aperture synthesis in the visual and near-infrared wavelength regimes, which provided image reconstructions from stellar surfaces to Active Galactic Nuclei. Here I review the numerous astrophysical results obtained up to date, except for binary and multiple stars milliarcsecond astrometry, which should be a subject of an independent detailed review, taking into account its importance and expected results at microarcsecond precision level. To the results obtained with currently available interferometers, I associate the adopted instrumental settings in order to provide a guide for potential users concerning the appropriate instruments which can be used to obtain the desired astrophysical information.
3
Wittkowski, Markus. "Round Table Summary: Stellar Interferometry as a Tool to Investigate Atmospheres and to Compare Observations with Models". Symposium - International Astronomical Union 210 (2003): 313–21. http://dx.doi.org/10.1017/s0074180900133455.
Testo completoAbstract (sommario):
Long-baseline interferometry at optical and near-infrared wavelengths is an emerging technology which is quickly becoming a useful tool to investigate stellar atmospheres and to compare observations with models. Stellar atmosphere models have so far mainly been constrained by comparisons with stellar spectra which are integrated over the stellar disks. Interferometric observations provide spatially and spectrally resolved information and can thus provide important complementary observational information which can be compared to model predictions. Here, I summarize the different aspects on this topic which were discussed at a round table on Thursday, June 20, 2002, during IAU Symposium 210. This summary gives an overview on discussed interferometric facilities and techniques, concepts to study atmospheres by optical interferometry, and particular classes of objects. We conclude that more frequent interactions between the efforts of atmosphere modelling and interferometric observations promise to lead to increased confidence in stellar model atmospheres and to further advancement of the field in the next years.
4
Kraus, S., Th Preibisch e K. Ohnaka. "The inner gaseous accretion disk around a Herbig Be star revealed by near- and mid-infrared spectro-interferometry". Proceedings of the International Astronomical Union 3, S243 (maggio 2007): 337–44. http://dx.doi.org/10.1017/s1743921307009696.
Testo completoAbstract (sommario):
AbstractHerbig Ae/Be stars are pre-main-sequence stars of intermediate mass, which are still accreting material from their environment, probably via a disk composed of gas and dust. Here we present a recent study of the geometry of the inner (AU-scale) circumstellar region around the Herbig Be star MWC 147 using long-baseline interferometry. By combining for the first time near- and mid-infrared spectro-interferometry on a Herbig star, our VLTI/AMBER and VLTI/MIDI data constrain not only the geometry of the brightness distribution, but also the radial temperature distribution in the disk. The emission from MWC 147 is clearly resolved and has a characteristic physical size of ∼1.3 AU and ∼9 AU at 2.2 μm and 11 μm respectively. This increase in apparent size towards longer wavelengths is much steeper than predicted by analytic disk models assuming power-law radial temperature distributions. For a detailed modeling of the interferometric data and the spectral energy distribution of MWC 147, we employ 2-D frequency-dependent radiation transfer simulations. This analysis shows that passive irradiated Keplerian dust disks can easily fit the SED, but predict much lower visibilities than observed, so these models can clearly be ruled out. Models of a Keplerian disk with emission from an optically thick inner gaseous accretion disk (inside the dust sublimation zone), however, yield a good fit of the SED and simultaneously reproduce the observed near- and mid-infrared visibilities. We conclude that the near-infrared continuum emission from MWC 147 is dominated by accretion luminosity emerging from an optically thick inner gaseous disk, while the mid-infrared emission also contains strong contributions from the passive irradiated dust disk.
5
Dexter, J. "Event horizon scale emission models for Sagittarius A*". Proceedings of the International Astronomical Union 9, S303 (ottobre 2013): 298–302. http://dx.doi.org/10.1017/s1743921314000775.
Testo completoAbstract (sommario):
AbstractVery long baseline interferometry observations at millimeter wavelengths have detected source structure in Sgr A* on event horizon scales. Near-infrared interferometry will achieve similar resolution in the next few years. These experiments provide an unprecedented opportunity to explore strong gravity around black holes, but interpreting the data requires physical modeling. I discuss the calculation of images, spectra, and light curves from relativistic MHD simulations of black hole accretion. The models provide an excellent description of current observations, and predict that we may be on the verge of detecting a black hole shadow, which would constitute the first direct evidence for the existence of black holes.
6
Cruzalèbes, P., R. G. Petrov, S. Robbe-Dubois, J. Varga, L. Burtscher, F. Allouche, P. Berio et al. "A catalogue of stellar diameters and fluxes for mid-infrared interferometry★". Monthly Notices of the Royal Astronomical Society 490, n. 3 (7 ottobre 2019): 3158–76. http://dx.doi.org/10.1093/mnras/stz2803.
Testo completoAbstract (sommario):
Abstract We present the Mid-infrared stellar Diameters and Fluxes compilation Catalogue (MDFC) dedicated to long-baseline interferometry at mid-infrared wavelengths (3–13 $\mu$m). It gathers data for half a million stars, i.e. nearly all the stars of the Hipparcos-Tycho catalogue whose spectral type is reported in the SIMBAD data base. We cross-match 26 data bases to provide basic information, binarity elements, angular diameter, magnitude and flux in the near and mid-infrared, as well as flags that allow us to identify the potential calibrators. The catalogue covers the entire sky with 465 857 stars, mainly dwarfs and giants from B to M spectral types closer than 18 kpc. The smallest reported values reach 0.16 $\mu$Jy in L and 0.1 $\mu$Jy in N for the flux, and 2 microarcsec for the angular diameter. We build four lists of calibrator candidates for the L and Nbands suitable with the Very Large Telescope Interferometer (VLTI) sub- and main arrays using the MATISSE instrument. We identify 1621 candidates for L and 44 candidates for N with the Auxiliary Telescopes (ATs), 375 candidates for both bands with the ATs, and 259 candidates for both bands with the Unit Telescopes (UTs). Predominantly cool giants, these sources are small and bright enough to belong to the primary lists of calibrator candidates. In the near future, we plan to measure their angular diameter with 1 per cent accuracy.
7
Petersen, Eric, e Charles Gammie. "Non-thermal models for infrared flares from Sgr A*". Monthly Notices of the Royal Astronomical Society 494, n. 4 (1 maggio 2020): 5923–35. http://dx.doi.org/10.1093/mnras/staa826.
Testo completoAbstract (sommario):
ABSTRACT Recent observations with mm very long baseline interferometry (mm-VLBI) and near-infrared (NIR) interferometry provide mm images and NIR centroid proper motion for Sgr A*. Of particular interest are the NIR flares that have more than an order of magnitude higher flux density than the quiescent state. Here, we model the flares using time-dependent, axisymmetric, general relativistic magnetohydrodynamic (GRMHD) simulations with an electron distribution function that includes a small, variable, non-thermal component motivated by magnetic reconnection models. The models simultaneously match the observed mm mean flux density, mm image size, NIR quiescent flux density, NIR flare flux density, and NIR spectral slope. They also provide a better fit to the observed NIR flux density probability density function than previously reported models by reproducing the power-law tail at high flux density, though with some discrepancy at low flux density. Further, our modelled NIR image centroid shows very little movement: centroid excursions of more than 10 μas (the resolution of GRAVITY) are rare and uncorrelated with flux.
8
Wittkowski, Markus, David A. Boboltz, Malcolm D. Gray, Elizabeth M. L. Humphreys, Iva Karovicova e Michael Scholz. "Radio and IR interferometry of SiO maser stars". Proceedings of the International Astronomical Union 8, S287 (gennaio 2012): 209–16. http://dx.doi.org/10.1017/s1743921312006989.
Testo completoAbstract (sommario):
AbstractRadio and infrared interferometry of SiO maser stars provide complementary information on the atmosphere and circumstellar environment at comparable spatial resolution. Here, we present the latest results on the atmospheric structure and the dust condensation region of AGB stars based on our recent infrared spectro-interferometric observations, which represent the environment of SiO masers. We discuss, as an example, new results from simultaneous VLTI and VLBA observations of the Mira variable AGB star R Cnc, including VLTI near- and mid-infrared interferometry, as well as VLBA observations of the SiO maser emission toward this source. We present preliminary results from a monitoring campaign of high-frequency SiO maser emission toward evolved stars obtained with the APEX telescope, which also serves as a precursor of ALMA images of the SiO emitting region. We speculate that large-scale long-period chaotic motion in the extended molecular atmosphere may be the physical reason for observed deviations from point symmetry of atmospheric molecular layers, and for the observed erratic variability of high-frequency SiO maser emission.
9
Christou, J. C. "Speckle Interferometry". Highlights of Astronomy 8 (1989): 561–62. http://dx.doi.org/10.1017/s1539299600008340.
Testo completoAbstract (sommario):
Speckle interferometry is a technique which utilizes the full diffraction-limited imaging potential of ground-based telescopes. Short exposure images, or specklegrams, with an exposure time less than that of the atmospheric correlation time (~5- 50 ms) preserve the high-spatial frequency information lost in long exposure imaging. In 1970, Labeyrie computed the power spectrum of a set of specklegrams and showed that they contained diffraction-limited information. Since then the field has grown with improvements in both instrumentation and the phase recovery algorithms necessary for imaging. It has been applied at both visible and near-infrared wavelengths although, until recently, the latter has used slit-scanning techniques with single pixel detectors because of the lack of array detectors. The current state of speckle interferometry has been well covered in the proceedings of two recent joint National Optical Astronomy Observatories – European Southern Observatory workshops on Interferometric Imaging in Astronomy (Oracle, 1987 & Garching, 1988).
10
Choquet, É., J. Menu, G. Perrin, F. Cassaing, S. Lacour e F. Eisenhauer. "Comparison of fringe-tracking algorithms for single-mode near-infrared long-baseline interferometers". Astronomy & Astrophysics 569 (settembre 2014): A2. http://dx.doi.org/10.1051/0004-6361/201220223.
Testo completo
11
Townes, C. H., M. Bester, W. C. Danchi, C. G. Degiacomi e L. J. Greenhill. "Heterodyne Interferometry in the Infrared". Symposium - International Astronomical Union 158 (1994): 19–25. http://dx.doi.org/10.1017/s0074180900107284.
Testo completoAbstract (sommario):
The University of California Infrared Spatial Interferometer (ISI) for the 10 μm wavelength region is briefly described along with results obtained on prominent stars and on atmospheric phenomena. The system has two movable telescopes of 1.65 m aperture. It operates in principle like a modern radio interferometer, using heterodyne detection, CO2 laser local oscillators, RF delay lines, and lobe rotation to maintain a fixed-frequency fringe rate.Rather extensive measurements have been made on atmospheric pathlength or phase fluctuation characteristics which show substantial deviations from the Kolmogorov-Taylor model, fortunately in a direction favoring adaptive optics, long baselines, and the use of infrared wavelengths. Outer scales as small as about 10 meters occur under good seeing conditions. Visibility results on 13 stars show that 6 of them have dust shells rather far from the star and give evidence for episodic emission of gas. Others of the 13 stars also vary with time, but are characterized by more continuous emission and dust formation near the stars at temperatures as high as 1300 K.
12
Abuter, R., M. Accardo, A. Amorim, N. Anugu, G. Ávila, N. Azouaoui, M. Benisty et al. "First light for GRAVITY: Phase referencing optical interferometry for the Very Large Telescope Interferometer". Astronomy & Astrophysics 602 (giugno 2017): A94. http://dx.doi.org/10.1051/0004-6361/201730838.
Testo completoAbstract (sommario):
GRAVITY is a new instrument to coherently combine the light of the European Southern Observatory Very Large Telescope Interferometer to form a telescope with an equivalent 130 m diameter angular resolution and a collecting area of 200 m2. The instrument comprises fiber fed integrated optics beam combination, high resolution spectroscopy, built-in beam analysis and control, near-infrared wavefront sensing, phase-tracking, dual-beam operation, and laser metrology. GRAVITY opens up to optical/infrared interferometry the techniques of phase referenced imaging and narrow angle astrometry, in many aspects following the concepts of radio interferometry. This article gives an overview of GRAVITY and reports on the performance and the first astronomical observations during commissioning in 2015/16. We demonstrate phase-tracking on stars as faint as mK ≈ 10 mag, phase-referenced interferometry of objects fainter than mK ≈ 15 mag with a limiting magnitude of mK ≈ 17 mag, minute long coherent integrations, a visibility accuracy of better than 0.25%, and spectro-differential phase and closure phase accuracy better than 0.5°, corresponding to a differential astrometric precision of better than ten microarcseconds (μas). The dual-beam astrometry, measuring the phase difference of two objects with laser metrology, is still under commissioning. First observations show residuals as low as 50 μas when following objects over several months. We illustrate the instrument performance with the observations of archetypical objects for the different instrument modes. Examples include the Galactic center supermassive black hole and its fast orbiting star S2 for phase referenced dual-beam observations and infrared wavefront sensing, the high mass X-ray binary BP Cru and the active galactic nucleus of PDS 456 for a few μas spectro-differential astrometry, the T Tauri star S CrA for a spectro-differential visibility analysis, ξ Tel and 24 Cap for high accuracy visibility observations, and η Car for interferometric imaging with GRAVITY.
13
Mérand, A., P. Bordé e V. Coudé du Foresto. "A catalog of bright calibrator stars for 200-m baseline near-infrared stellar interferometry". Astronomy & Astrophysics 433, n. 3 (29 marzo 2005): 1155–62. http://dx.doi.org/10.1051/0004-6361:20041323.
Testo completo
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Mérand, A., P. Bordé e V. Coudé du Foresto. "A catalog of bright calibrator stars for 200-m baseline near-infrared stellar interferometry". Astronomy & Astrophysics 447, n. 2 (febbraio 2006): 783. http://dx.doi.org/10.1051/0004-6361:20041323e.
Testo completo
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Gies, Douglas R., Yamina N. Touhami e Gail H. Schaefer. "Infrared continuum sizes of Be star disks". Proceedings of the International Astronomical Union 6, S272 (luglio 2010): 390–91. http://dx.doi.org/10.1017/s1743921311010866.
Testo completoAbstract (sommario):
AbstractLong baseline interferometry now offers us the opportunity to measure the dimensions of Be star circumstellar disks across the spectrum. This includes the near-infrared continuum where the emission is dominated by bound-free and free-free emission from the ionized disk gas. Here we present the results of calculations of the disk sizes and continuum flux excesses for a simple version of the viscous decretion model of the disk. We compare these results to recent 18 μm flux measurements from the AKARI infrared satellite all-sky survey.
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Kervella, Pierre, Alexandre Gallenne e Antoine Mérand. "Circumstellar envelopes of Cepheids: a possible bias affecting the distance scale?" Proceedings of the International Astronomical Union 8, S289 (agosto 2012): 157–60. http://dx.doi.org/10.1017/s1743921312021291.
Testo completoAbstract (sommario):
AbstractCircumstellar envelopes (CSEs) have been detected around many Cepheids, first based on long-baseline interferometry, and now also using other observing techniques. These envelopes are particularly interesting for two reasons: their presence could impact the Cepheid distance scale, and they may be valuable tracers of stellar mass loss. Here we focus on their potential impact on the calibration of the Cepheid distance scale. We consider the photometric contribution of the envelopes in the visible, near-, and thermal-infrared domains. We conclude that the impact of CSEs on the apparent luminosities of Cepheids is negligible at visible wavelengths and generally weak (<5%) in the near-infrared (λ ≈ 2 μm). In the thermal-infrared domain (λ ≈ 8 μm), the flux contribution of the CSEs differs depending on the pulsation period: it is relatively weak (<15%) for stars with periods shorter than P ≈ 10 days, but can reach ≈ 30% for long-period Cepheids. We specifically discuss the long-period Galactic Cepheid RS Puppis, which exhibits a very large circumstellar, dusty envelope, and we conclude that this is not a representative case. Overall, the contribution of CSEs to the usual period–luminosity relations (from the visible to the K band) is mostly negligible. They could affect calibrations at longer wavelengths, although the presence of envelopes may have been partially taken into account in the existing empirical calibrations.
17
Groh, Jose H. "Effects of fast rotation on the wind of Luminous Blue Variables". Proceedings of the International Astronomical Union 6, S272 (luglio 2010): 56–61. http://dx.doi.org/10.1017/s1743921311009975.
Testo completoAbstract (sommario):
AbstractWhile theoretical studies have long suggested a fast-rotating nature of Luminous Blue Variables (LBVs), observational confirmation of fast rotation was not detected until recently. Here I discuss the diagnostics that have allowed us to constrain the rotational velocity of LBVs: broadening of spectral lines and latitude-dependent variations of the wind density structure. While rotational broadening can be directly detected using high-resolution spectroscopy, long-baseline near-infrared interferometry is needed to directly measure the shape of the latitude-dependent photosphere that forms in a fast-rotating star. In addition, complex 2-D radiative transfer models need to be employed if one's goal is to constrain rotational velocities of LBVs. Here I illustrate how the above methods were able to constrain the rotational velocities of the LBVs AG Carinae, HR Carinae, and Eta Carinae.
18
Millan‐Gabet, R. "Investigation of Herbig Ae/Be Stars in the Near‐Infrared with a Long‐Baseline Interferometer". Publications of the Astronomical Society of the Pacific 112, n. 771 (maggio 2000): 742–43. http://dx.doi.org/10.1086/316572.
Testo completo
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Koresko, C. D., G. T. van Belle, A. F. Boden, M. M. Colavita, M. J. Creech-Eakman, P. J. Dumont, J. Gubler et al. "The Visual Orbit of the 0[farcs]002 RS CV[CLC]n[/CLC] Binary Star TZ Triangulifrom Near-Infrared Long-Baseline Interferometry". Astrophysical Journal 509, n. 1 (10 dicembre 1998): L45—L48. http://dx.doi.org/10.1086/311759.
Testo completo
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Kammerer, Jens, Rachel A. Cooper, Thomas Vandal, Deepashri Thatte, Frantz Martinache, Anand Sivaramakrishnan, Alexander Chaushev et al. "The Near Infrared Imager and Slitless Spectrograph for JWST. V. Kernel Phase Imaging and Data Analysis". Publications of the Astronomical Society of the Pacific 135, n. 1043 (1 gennaio 2023): 014502. http://dx.doi.org/10.1088/1538-3873/ac9a74.
Testo completoAbstract (sommario):
Abstract Kernel phase imaging (KPI) enables the direct detection of substellar companions and circumstellar dust close to and below the classical (Rayleigh) diffraction limit. The high-Strehl full pupil images provided by the James Webb Space Telescope (JWST) are ideal for application of the KPI technique. We present a kernel phase analysis of JWST NIRISS full pupil images taken during the instrument commissioning and compare the performance to closely related NIRISS aperture masking interferometry (AMI) observations. For this purpose, we develop and make publicly available the custom Kpi3Pipeline data reduction pipeline enabling the extraction of kernel phase observables from JWST images. The extracted observables are saved into a new and versatile kernel phase FITS file data exchange format. Furthermore, we present our new and publicly available fouriever toolkit which can be used to search for companions and derive detection limits from KPI, AMI, and long-baseline interferometry observations while accounting for correlated uncertainties in the model fitting process. Among the four KPI targets that were observed during NIRISS instrument commissioning, we discover a low-contrast (∼1:5) close-in (∼1 λ/D) companion candidate around CPD-66 562 and a new high-contrast (∼1:170) detection separated by ∼1.5 λ/D from 2MASS J062802.01-663738.0. The 5σ companion detection limits around the other two targets reach ∼6.5 mag at ∼200 mas and ∼7 mag at ∼400 mas. Comparing these limits to those obtained from the NIRISS AMI commissioning observations, we find that KPI and AMI perform similar in the same amount of observing time. Due to its 5.6 times higher throughput if compared to AMI, KPI is beneficial for observing faint targets and superior to AMI at separations ≳325 mas. At very small separations (≲100 mas) and between ∼250 and 325 mas, AMI slightly outperforms KPI which suffers from increased photon noise from the core and the first Airy ring of the point-spread function.
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Serabyn, E., B. Mennesson, S. Martin, K. Liewer e J. Kühn. "Nulling at short wavelengths: theoretical performance constraints and a demonstration of faint companion detection inside the diffraction limit with a rotating-baseline interferometer". Monthly Notices of the Royal Astronomical Society 489, n. 1 (12 agosto 2019): 1291–303. http://dx.doi.org/10.1093/mnras/stz2163.
Testo completoAbstract (sommario):
ABSTRACT The Palomar Fiber Nuller (PFN) is a rotating-baseline nulling interferometer that enables high-accuracy near-infrared (NIR) nulling observations with full azimuth coverage. To achieve NIR null-depth accuracies of several x 10−4, the PFN uses a common-mode optical system to provide a high degree of symmetry, single-mode-fibre beam combination to reduce sensitivity to pointing and wavefront errors, extreme adaptive optics to stabilize the fibre coupling and the cross-aperture fringe phase, rapid signal calibration and camera readout to minimize temporal effects, and a statistical null-depth fluctuation analysis to relax the phase stabilization requirement. Here, we describe the PFN’s final design and performance and provide a demonstration of faint-companion detection by means of nulling-baseline rotation, as originally envisioned for space-based nulling interferometry. Specifically, the Ks-band null-depth rotation curve measured on the spectroscopic binary η Peg reflects both a secondary star 1.08 ± 0.06 × 10−2 as bright as the primary, and a null-depth contribution of 4.8 ± 1.6 × 10−4 due to the size of the primary star. With a 30 mas separation at the time, η Peg B was well inside both the telescope’s diffraction-limited beam diameter (88 mas) and typical coronagraphic inner working angles. Finally, we discuss potential improvements that can enable a number of small-angle nulling observations on larger telescopes.
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Dexter, J., A. Jiménez-Rosales, S. M. Ressler, A. Tchekhovskoy, M. Bauböck, P. T. de Zeeuw, F. Eisenhauer et al. "A parameter survey of Sgr A* radiative models from GRMHD simulations with self-consistent electron heating". Monthly Notices of the Royal Astronomical Society 494, n. 3 (7 aprile 2020): 4168–86. http://dx.doi.org/10.1093/mnras/staa922.
Testo completoAbstract (sommario):
ABSTRACT The Galactic centre black hole candidate Sgr A* is the best target for studies of low-luminosity accretion physics, including with near-infrared (NIR) and submillimetre wavelength long baseline interferometry experiments. Here, we compare images and spectra generated from a parameter survey of general relativistic MHD simulations to a set of radio to NIR observations of Sgr A*. Our models span the limits of weak and strong magnetization and use a range of sub-grid prescriptions for electron heating. We find two classes of scenarios can explain the broad shape of the submillimetre spectral peak and the highly variable NIR flaring emission. Weakly magnetized ‘disc-jet’ models where most of the emission is produced near the jet wall, consistent with past work, as well as strongly magnetized (magnetically arrested disc) models where hot electrons are present everywhere. Disc-jet models are strongly depolarized at submillimetre wavelengths as a result of strong Faraday rotation, inconsistent with observations of Sgr A*. We instead favour the strongly magnetized models, which provide a good description of the median and highly variable linear polarization signal. The same models can also explain the observed mean Faraday rotation measure and potentially the polarization signals seen recently in Sgr A* NIR flares.
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Kool, E. C., T. M. Reynolds, S. Mattila, E. Kankare, M. A. Pérez-Torres, A. Efstathiou, S. Ryder et al. "AT 2017gbl: a dust obscured TDE candidate in a luminous infrared galaxy". Monthly Notices of the Royal Astronomical Society 498, n. 2 (19 agosto 2020): 2167–95. http://dx.doi.org/10.1093/mnras/staa2351.
Testo completoAbstract (sommario):
ABSTRACT We present the discovery with Keck of the extremely infrared (IR) luminous transient AT 2017gbl, coincident with the Northern nucleus of the luminous infrared galaxy (LIRG) IRAS 23436+5257. Our extensive multiwavelength follow-up spans ∼900 d, including photometry and spectroscopy in the optical and IR, and (very long baseline interferometry) radio and X-ray observations. Radiative transfer modelling of the host galaxy spectral energy distribution and long-term pre-outburst variability in the mid-IR indicate the presence of a hitherto undetected dust obscured active galactic nucleus (AGN). The optical and near-IR spectra show broad ∼2000 km s−1 hydrogen, He i, and O i emission features that decrease in flux over time. Radio imaging shows a fast evolving compact source of synchrotron emission spatially coincident with AT 2017gbl. We infer a lower limit for the radiated energy of 7.3 × 1050 erg from the IR photometry. An extremely energetic supernova would satisfy this budget, but is ruled out by the radio counterpart evolution. Instead, we propose AT 2017gbl is related to an accretion event by the central supermassive black hole, where the spectral signatures originate in the AGN broad line region and the IR photometry is consistent with re-radiation by polar dust. Given the fast evolution of AT 2017gbl, we deem a tidal disruption event (TDE) of a star a more plausible scenario than a dramatic change in the AGN accretion rate. This makes AT 2017gbl the third TDE candidate to be hosted by a LIRG, in contrast to the so far considered TDE population discovered at optical wavelengths and hosted preferably by post-starburst galaxies.
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Sezestre, É., J. C. Augereau e P. Thébault. "Hot exozodiacal dust: an exocometary origin?" Astronomy & Astrophysics 626 (30 maggio 2019): A2. http://dx.doi.org/10.1051/0004-6361/201935250.
Testo completoAbstract (sommario):
Context. Near- and mid-infrared interferometric observations have revealed populations of hot and warm dust grains populating the inner regions of extrasolar planetary systems. These are known as exozodiacal dust clouds, or exozodis, reflecting the similarity with the solar system’s zodiacal cloud. Radiative transfer models have constrained the dust to be dominated by tiny submicron-sized, carbon-rich grains that are accumulated very close to the sublimation radius. The origin of this dust is an unsolved issue. Aims. We explore two exozodiacal dust production mechanisms, first re-investigating the Poynting-Robertson drag pile-up scenario, and then elaborating on the less explored but promising exocometary dust delivery scenario. Methods. We developed a new, versatile numerical model that calculates the dust dynamics, with non-orbit-averaged equations for the grains close to the star. The model includes dust sublimation and incorporates a radiative transfer code for direct comparison to the observations. We consider in this study four stellar types, three dust compositions, and we assume a parent belt at 50 au. Results. In the case of the Poynting-Robertson drag pile-up scenario, we find that it is impossible to produce long-lived submicron-sized grains close to the star. The inward drifting grains fill in the region between the parent belt and the sublimation distance, producing an unrealistically strong mid-infrared excess compared to the near-infrared excess. The dust pile-up at the sublimation radius is by far insufficient to boost the near-IR flux of the exozodi to the point where it dominates over the mid-infrared excess. In the case of the exocometary dust delivery scenario, we find that a narrow ring can form close to the sublimation zone, populated with large grains from several tens to several hundreds of micrometers in radius. Although not perfect, this scenario provides a better match to the observations, especially if the grains are carbon-rich. We also find that the number of active exocomets required to sustain the observed dust level is reasonable. Conclusions. We conclude that the hot exozodiacal dust detected by near-infrared interferometry is unlikely to result from inward grain migration by Poynting-Robertson drag from a distant parent belt, but could instead have an exocometary origin.
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Sanchez-Bermudez, J., A. Alberdi, R. Schödel, W. Brandner, R. Galván-Madrid, J. C. Guirado, R. Herrero-Illana, C. A. Hummel, J. M. Marcaide e M. A. Pérez-Torres. "A VLBI study of the wind-wind collision region in the massive multiple HD 167971". Astronomy & Astrophysics 624 (aprile 2019): A55. http://dx.doi.org/10.1051/0004-6361/201834659.
Testo completoAbstract (sommario):
Context. Colliding winds in massive binaries are able to accelerate particles up to relativistic speeds as the result of the interaction between the winds of the different stellar components. HD 167971 exhibits this phenomenon which makes it a strong radio source. Aims. We aim at characterizing the morphology of the radio emission and its dependence on the orbital motion, traced independently by near-infrared (NIR) interferometry of both the spectroscopic binary and the tertiary component comprising HD 167971. Methods. We analyze 2006 and 2016 very long baseline interferometric data at C and X bands. We complement our analysis with a geometrical model of the wind-wind collision region and an astrometric description of the system. Results. We confirm that the detected nonthermal radio emission is associated with the wind-wind collision region of the spectroscopic binary and the tertiary component in HD 167971. The wind-wind collision region changes orientation in agreement with the orbital motion of the tertiary around the spectroscopic binary. The total intensity also changes between the two observing epochs in a way that is inversely proportional to the separation between the two components, with a negative-steep spectral index typical of an optically thin synchrotron emission possibly steepened by an inverse Compton cooling effect. The wind-wind collision bow-shock shape and its position with respect to the stars indicates that the wind momentum from the spectroscopic binary is stronger than that of the tertiary. Finally, the astrometric solution derived for the stellar system and the wind-wind collision region is consistent with independent Gaia data.
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Bhattacharya, Rajorshi, Brandon M. Medina, Ylva M. Pihlström, Loránt O. Sjouwerman, Megan O. Lewis, Raghvendra Sahai, Michael C. Stroh et al. "Distance Estimate Method for Asymptotic Giant Branch Stars Using Infrared Spectral Energy Distributions". Astrophysical Journal 969, n. 2 (1 luglio 2024): 109. http://dx.doi.org/10.3847/1538-4357/ad463e.
Testo completoAbstract (sommario):
Abstract We present a method to estimate distances to asymptotic giant branch (AGB) stars in the Galaxy, using spectral energy distributions (SEDs) in the near- and mid-infrared. By assuming that a given set of source properties (initial mass, stellar temperature, composition, and evolutionary stage) will provide a typical SED shape and brightness, sources are color matched to a distance-calibrated template and thereafter scaled to extract the distance. The method is tested by comparing the distances obtained to those estimated from very long baseline interferometry or Gaia parallax measurements, yielding a strong correlation in both cases. Additional templates are formed by constructing a source sample likely to be close to the Galactic center, and thus with a common, typical distance for calibration of the templates. These first results provide statistical distance estimates to a set of almost 15,000 Milky Way AGB stars belonging to the Bulge Asymmetries and Dynamical Evolution (BAaDE) survey, with typical distance errors of ±35%. With these statistical distances, a map of the intermediate-age population of stars traced by AGBs is formed, and a clear bar structure can be discerned, consistent with the previously reported inclination angle of 30° to the GC–Sun direction vector. These results motivate deeper studies of the AGB population to tease out the intermediate-age stellar distribution throughout the Galaxy, as well as determining statistical properties of the AGB population luminosity and mass-loss-rate distributions.
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Hone, Edward, Stefan Kraus, Claire L. Davies, Alexander Kreplin, John D. Monnier, Fabien Baron, Rafael Millan-Gabet et al. "Compact gaseous accretion disk in Keplerian rotation around MWC 147". Astronomy & Astrophysics 623 (28 febbraio 2019): A38. http://dx.doi.org/10.1051/0004-6361/201834626.
Testo completoAbstract (sommario):
Context. The disks around some Herbig Be stars have been observed to be more compact than the expected dust sublimation radius for such objects. Highly refractory dust grains and optically thick gas emission have been proposed as possible explanations for this phenomenon. Aims. Previously, the “undersized” Herbig Be star MWC 147 was observed with interferometry, and the results indicated a presence of a compact gaseous disk based on the measured wavelength-dependence of near-infrared or mid-infrared visibilities. Our aim is to search for direct evidence for the presence of hot gas inside of the expected dust sublimation radius of MWC 147. Methods. By combining VLTI/AMBER spectro-interferometry (R = 12 000) with CRIRES spectroscopy (R = 100 000) we can both spectrally and spatially resolve the Brγ line-emitting gas around MWC 147. Additionally, using CHARA/CLIMB enables us to achieve baseline lengths up to 330 m, offering ~2 times higher angular resolution (and a better position angle coverage) than has previously been achieved with interferometry for MWC 147. To model the continuum we fit our AMBER and CLIMB measurements with a geometric model of an inclined Gaussian distribution as well as a ring model. We fit our high-resolution spectra and spectro-interferometric data with a kinematic model of a disk in Keplerian rotation. Results. Our interferometric visibility modelling of MWC 147 indicates the presence of a compact continuum disk with a close to face-on orientation. We model the continuum with an inclined Gaussian and a ring with a radius of 0.60 mas (0.39 au), which is well within the expected dust sublimation radius of 1.52 au. We detect no significant change in the measured visibilities across the Brγ line, indicating that the line-emitting gas is located in the same region as the continuum-emitting disk. Using our differential phase data we construct photocentre displacement vectors across the Brγ line, revealing a velocity profile consistent with a rotating disk. We fit our AMBER spectro-interferometry data with a kinematic model of a disk in Keplerian rotation, where both the line-emitting and continuum-emitting components of the disk originate from the same compact region close to the central star. The presence of line-emitting gas in the same region as the K-band continuum supports the interpretation that the K-band continuum traces an optically thick gas disk. Conclusions. Our spatially and spectrally resolved observations of MWC 147 reveal that the K-band continuum and Brγ emission both originate from a similar region which is 3.9 times more compact than the expected dust sublimation radius for the star; Brγ is emitted from the accretion disk or disk wind region and exhibits a rotational velocity profile. We conclude that we detect the presence of a compact, gaseous accretion disk in Keplerian rotation around MWC 147.
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Chrenko, Ondřej, Mario Flock, Takahiro Ueda, Antoine Mérand, Myriam Benisty e Raúl O. Chametla. "The Inner Disk Rim of HD 163296: Linking Radiative Hydrostatic Models with Infrared Interferometry". Astronomical Journal 167, n. 3 (22 febbraio 2024): 124. http://dx.doi.org/10.3847/1538-3881/ad234d.
Testo completoAbstract (sommario):
Abstract Previous studies of the protoplanetary disk HD 163296 revealed that the morphology of its sub-au infrared emission encompasses the terminal sublimation front of dust grains, referred to as the inner rim, but also extends into the (supposedly) dust-free region within it. Here, we present a set of radiative hydrostatic simulations of the inner rim in order to assess how much the rim alone can contribute to the observed interferometric visibilities V, half-light radii R hl, and fractional disk fluxes F in the wavelength range 1.5–13 μm. In our set of models, we regulate the cooling efficiency of the disk via the boundary condition for radiation diffusion and we also modify the shape of the sublimation front. We find that when the cooling efficiency is reduced, the infrared photosphere at the rim becomes hotter, leading to an increase in R hl sufficient to match the observations. However, the near-infrared disk flux is typically too low ( F ≃ 0.25 at 1.5 μm), resulting in H-band visibility curves located above the observed data. We show that the match to the H-band observations up to moderate baselines can be improved when a wall-shaped rather than curved sublimation front is considered. Nevertheless, our model visibilities always exhibit a bounce at long baselines, which is not observed, confirming the need for additional emission interior to the rim. In summary, our study illustrates how the temperature structure and geometry of the inner rim need to change in order to boost the rim’s infrared emission.
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Hofmann, K. H., T. Blöcker, G. Weigelt e Y. Balega. "A Multi-Wavelength Study of the Oxygen-Rich AGB Star CIT 3: Bispectrum speckle interferometry and dust-shell modelling". Symposium - International Astronomical Union 209 (2003): 121. http://dx.doi.org/10.1017/s0074180900208267.
Testo completoAbstract (sommario):
CIT 3 is an oxygen-rich long-period variable evolving along the Asymptotic Giant Branch and is one of the most extreme infrared AGB objects. Due to substantial mass loss it is surrounded by an optically thick dust shell which absorbs almost all visible light radiated by the star and finally re-emits it in the infrared regime. We present the first near infrared bispectrum speckle-interferometry observations of CIT 3 in the J-, H-, and K′-band (resolution: 48 mas, 56 mas, and 73 mas). The interferograms were obtained with the Russian SAO 6 m telescope. While CIT 3 appears almost spherically symmetric in the H- and K′-band it is clearly elongated in the J-band along a symmetry axis of position angle −28°. Two structures can be identified: a compact elliptical core (eccentricity ~0.8) and a fainter north-western fan-like structure (full opening angle ~ 40°). The development of such asphericities close to the central star suggests that CIT 3 is in the very end of its AGB evolution or even in transition to the proto-planetary nebula phase where most objects are observed in axisymmetric geometry.
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Margutti, Raffaella, e Ryan Chornock. "First Multimessenger Observations of a Neutron Star Merger". Annual Review of Astronomy and Astrophysics 59, n. 1 (8 settembre 2021): 155–202. http://dx.doi.org/10.1146/annurev-astro-112420-030742.
Testo completoAbstract (sommario):
We describe the first observations of the same celestial object with gravitational waves and light. ▪ GW170817 was the first detection of a neutron star merger with gravitational waves. ▪ The detection of a spatially coincident weak burst of gamma-rays (GRB 170817A) 1.7 s after the merger constituted the first electromagnetic detection of a gravitational wave source and established a connection between at least some cosmic short gamma-ray bursts (SGRBs) and binary neutron star mergers. ▪ A fast-evolving optical and near-infrared transient (AT 2017gfo) associated with the event can be interpreted as resulting from the ejection of ∼0.05 M⊙ of material enriched in r-process elements, finally establishing binary neutron star mergers as at least one source of r-process nucleosynthesis. ▪ Radio and X-ray observations revealed a long-rising source that peaked ∼160,d after the merger. Combined with the apparent superluminal motion of the associated very long baseline interferometry source, these observations show that the merger produced a relativistic structured jet whose core was oriented ≈20 deg from the line of sight and with properties similar to SGRBs. The jet structure likely results from interaction between the jet and the merger ejecta. ▪ The electromagnetic and gravitational wave information can be combined to produce constraints on the expansion rate of the Universe and the equation of state of dense nuclear matter. These multimessenger endeavors will be a major emphasis of future work.
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MichałowskI, Michał J., Dong Xu, Jamie Stevens, Andrew Levan, Jun Yang, Zsolt Paragi, Atish Kamble et al. "The second-closest gamma-ray burst: sub-luminous GRB 111005A with no supernova in a super-solar metallicity environment". Astronomy & Astrophysics 616 (agosto 2018): A169. http://dx.doi.org/10.1051/0004-6361/201629942.
Testo completoAbstract (sommario):
We report the detection of the radio afterglow of a long gamma-ray burst (GRB) 111005A at 5-345 GHz, including very long baseline interferometry observations with a positional error of 0.2 mas. The afterglow position is coincident with the disc of a galaxy ESO 58049 at z = 0.01326 (∼1″ from its centre), which makes GRB 111005A the second-closest GRB known to date, after GRB 980425. The radio afterglow of GRB 111005A was an order of magnitude less luminous than those of local low-luminosity GRBs, and obviously less luminous than those of cosmological GRBs. The radio flux was approximately constant and then experienced an unusually rapid decay a month after the GRB explosion. Similarly to only two other GRBs, we did not find the associated supernovae (SNe), despite deep near- and mid-infrared observations 1-9 days after the GRB explosion, reaching ∼20 times fainter than other SNe associated with GRBs. Moreover, we measured a twice-solar metallicity for the GRB location. The low y-ray and radio luminosities, rapid decay, lack of a SN, and super-solar metallicity suggest that GRB 111005A represents a rare class of GRB that is different from typical core-collapse events. We modelled the spectral energy distribution of the GRB 111005A host finding that it is a moderately star-forming dwarf galaxy, similar to the host of GRB 980425. The existence of two local GRBs in such galaxies is still consistent with the hypothesis that the GRB rate is proportional to the cosmic star formation rate (SFR) density, but suggests that the GRB rate is biased towards low SFRs. Using the far-infrared detection of ESO 580-49, we conclude that the hosts of both GRBs 111005A and 980425 exhibit lower dust content than what would be expected from their stellar masses and optical colors.
32
Sfarra, Stefano, Clemente Ibarra-Castanedo, Carlo Santulli, Domenica Paoletti e Xavier Maldague. "Monitoring of jute/hemp fiber hybrid laminates by nondestructive testing techniques". Science and Engineering of Composite Materials 23, n. 3 (1 maggio 2016): 283–300. http://dx.doi.org/10.1515/secm-2013-0138.
Testo completoAbstract (sommario):
AbstractDamage following static indentation of jute/hemp (50 wt.% total fiber content) hybrid laminates was detected by a number of nondestructive testing (NDT) techniques, in particular, near (NIR) and short-wave (SWIR) infrared reflectography and transmittography, infrared thermography (IRT), digital speckle photography (DSP), and holographic interferometry (HI), to discover and evaluate real defects in a laminate with a complex structure. A comparative study between thermographic data acquired in the mid- (MWIR) and long-wave infrared (LWIR) spectrum bands, by pulsed (PT) and square pulse (SPT) thermography, is reported and analyzed. A thermal simulation by COMSOL® Multiphysics (COMSOL Inc., Burlington, MA, USA) to validate the heating provided is also added. The robust SOBI (SOBI-RO) algorithm, available into the ICALAB Toolbox (BSI RIKEN ABSP Lab, Hirosawa, Japan) and operating in the MATLAB® (The MathWorks, Inc., Natick, MA, USA) environment, was applied on SPT data with results comparable to the ones acquired by several thermographic techniques. Finally, segmentation operators were applied both to the NIR/SWIR transmittography images and to a characteristic principal component thermography (PCT) image (EOFs) to visualize damage in the area surrounding indentation.
33
Koutoulaki, M., R. Garcia Lopez, A. Natta, A. Caratti o Garatti, D. Coffey, J. Sanchez-Bermudez e T. P. Ray. "The circumstellar environment of HD 50138 revealed by VLTI/AMBER at high angular resolution". Astronomy & Astrophysics 614 (giugno 2018): A90. http://dx.doi.org/10.1051/0004-6361/201832814.
Testo completoAbstract (sommario):
Context. HD 50138 is a Herbig B[e] star with a circumstellar disc detected at infrared and millimeter wavelength. Its brightness makes it a good candidate for near-infrared interferometry observations. Aims. We aim to resolve, spatially and spectrally, the continuum and hydrogen emission lines in the 2.12–2.47 micron region, to shed light on the immediate circumstellar environment of the star. Methods. VLTI/AMBER K-band observations provide spectra, visibilities, differential phases, and closure phases along three long baselines for the continuum, and H I emission in Brγ and five high-n Pfund lines. By computing the pure line visibilities, we derive the angular size of the different line-emitting regions. A simple local thermodynamic equilibrium (LTE) model was created to constrain the physical conditions of H I emitting region. Results. The continuum region cannot be reproduced by a geometrical two-dimensional (2D) elongated Gaussian fitting model. We estimate the size of the region to be 1 au. We find the detected hydrogen lines (Brγ and Pfund lines) come from a more compact region of size 0.4 au. The Brγ line exhibits an S-shaped differential phase, indicative of rotation. The continuum and Brγ line closure phases show offsets of ~ −25 ± 5° and 20 ± 10° respectively. This is evidence of an asymmetry in their origin, but with opposing directions. We find that we cannot converge on constraints for the HI physical parameters without a more detailed model. Conclusions. Our analysis reveals that HD 50138 hosts a complex circumstellar environment. Its continuum emission cannot be reproduced by a simple disc brightness distribution. Similarly, several components must be evoked to reproduce the interferometric observables within the Brγ line. Combining the spectroscopic and interferometric data of the Brγ and Pfund lines favours an origin in a wind region with a large opening angle. Finally, although we cannot exclude the possibility that HD 50138 is a young star our results point to an evolved source.
34
Eupen, F., L. Labadie, R. Grellmann, K. Perraut, W. Brandner, G. Duchêne, R. Köhler et al. "The GRAVITY young stellar object survey". Astronomy & Astrophysics 648 (aprile 2021): A37. http://dx.doi.org/10.1051/0004-6361/202039599.
Testo completoAbstract (sommario):
Context. Close young binary stars are unique laboratories for the direct measurement of pre-main-sequence (PMS) stellar masses and their comparison to evolutionary theoretical models. At the same time, a precise knowledge of their orbital parameters when still in the PMS phase offers an excellent opportunity for understanding the influence of dynamical effects on the morphology and lifetime of the circumstellar as well as circumbinary material. Aims. The young T Tauri star WW Cha was recently proposed to be a close binary object with strong infrared and submillimeter excess associated with circum-system emission, which makes it dynamically a very interesting source in the above context. The goal of this work is to determine the astrometric orbit and the stellar properties of WW Cha using multi-epoch interferometric observations. Methods. We derive the relative astrometric positions and flux ratios of the stellar companion in WW Cha from the interferometric model fitting of observations made with the VLTI instruments AMBER, PIONIER, and GRAVITY in the near-infrared from 2011 to 2020. For two epochs, the resulting uv-coverage in spatial frequencies permits us to perform the first image reconstruction of the system in the K band. The positions of nine epochs are used to determine the orbital elements and the total mass of the system. Combining the orbital solution with distance measurements from Gaia DR2 and the analysis of evolutionary tracks, we constrain the mass ratio. Results. We find the secondary star orbiting the primary with a period of T = 206.55 days, a semimajor axis of a = 1.01 au, and a relatively high eccentricity of e = 0.45. The dynamical mass of Mtot = 3.20 M⊙ can be explained by a mass ratio between ∼0.5 and 1, indicating an intermediate-mass T Tauri classification for both components. The orbital angular momentum vector is in close alignment with the angular momentum vector of the outer disk as measured by ALMA and SPHERE, resulting in a small mutual disk inclination. The analysis of the relative photometry suggests the presence of infrared excess surviving in the system and likely originating from truncated circumstellar disks. The flux ratio between the two components appears variable, in particular in the K band, and may hint at periods of triggered higher and lower accretion or changes in the disks’ structures. Conclusions. The knowledge of the orbital parameters, combined with a relatively short period, makes WW Cha an ideal target for studying the interaction of a close young T Tauri binary with its surrounding material, such as time-dependent accretion phenomena. Finding WW Cha to be composed of two (probably similar) stars led us to reevaluate the mass of WW Cha, which had been previously derived under the assumption of a single star. This work illustrates the potential of long baseline interferometry to precisely characterize close young binary stars separated by a few astronomical units. Finally, when combined with radial velocity measurements, individual stellar masses can be derived and used to calibrate theoretical PMS models.
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Goddi, C., H. Falcke, M. Kramer, L. Rezzolla, C. Brinkerink, T. Bronzwaer, J. R. J. Davelaar et al. "BlackHoleCam: Fundamental physics of the galactic center". International Journal of Modern Physics D 26, n. 02 (febbraio 2017): 1730001. http://dx.doi.org/10.1142/s0218271817300014.
Testo completoAbstract (sommario):
Einstein’s General theory of relativity (GR) successfully describes gravity. Although GR has been accurately tested in weak gravitational fields, it remains largely untested in the general strong field cases. One of the most fundamental predictions of GR is the existence of black holes (BHs). After the recent direct detection of gravitational waves by LIGO, there is now near conclusive evidence for the existence of stellar-mass BHs. In spite of this exciting discovery, there is not yet direct evidence of the existence of BHs using astronomical observations in the electromagnetic spectrum. Are BHs observable astrophysical objects? Does GR hold in its most extreme limit or are alternatives needed? The prime target to address these fundamental questions is in the center of our own Milky Way, which hosts the closest and best-constrained supermassive BH candidate in the universe, Sagittarius A* (Sgr A*). Three different types of experiments hold the promise to test GR in a strong-field regime using observations of Sgr A* with new-generation instruments. The first experiment consists of making a standard astronomical image of the synchrotron emission from the relativistic plasma accreting onto Sgr A*. This emission forms a “shadow” around the event horizon cast against the background, whose predicted size ([Formula: see text]as) can now be resolved by upcoming very long baseline radio interferometry experiments at mm-waves such as the event horizon telescope (EHT). The second experiment aims to monitor stars orbiting Sgr A* with the next-generation near-infrared (NIR) interferometer GRAVITY at the very large telescope (VLT). The third experiment aims to detect and study a radio pulsar in tight orbit about Sgr A* using radio telescopes (including the Atacama large millimeter array or ALMA). The BlackHoleCam project exploits the synergy between these three different techniques and contributes directly to them at different levels. These efforts will eventually enable us to measure fundamental BH parameters (mass, spin, and quadrupole moment) with sufficiently high precision to provide fundamental tests of GR (e.g. testing the no-hair theorem) and probe the spacetime around a BH in any metric theory of gravity. Here, we review our current knowledge of the physical properties of Sgr A* as well as the current status of such experimental efforts towards imaging the event horizon, measuring stellar orbits, and timing pulsars around Sgr A*. We conclude that the Galactic center provides a unique fundamental-physics laboratory for experimental tests of BH accretion and theories of gravity in their most extreme limits.
36
Danchi, W. C., M. Bester, P. R. McCullough e C. H. Townes. "Infrared Long Baseline Interferometry". Highlights of Astronomy 8 (1989): 563–64. http://dx.doi.org/10.1017/s1539299600008352.
Testo completoAbstract (sommario):
During the last few years, two new instruments using long baseline interferometry have been constructed for high angular resolution astronomy in the mid-infrared spectral region (8-12 μxm). One called SOIRDETE-Synthese d’Overture en InfraRouge a DEux TElescopes-was built by J. Gay and his collaborators at CERGA. SOIRDETE has a fixed E-W 15 m baseline and two 1 m diameter telescopes of conventional design. This instrument obtains interference fringes by adjusting an optical-precision delay line in discrete steps to compensate for the geometrical delay of the projected baseline. The interference fringe from the source is detected using HgCdTe photodiodes. Because the instrumental delay has discrete steps a time-domain interferogram is created. This interferogram, upon Fourier transformation to the frequency domain, yields information about the spectral characteristics of the source. First fringes have recently been obtained with this instrument (Gay, 1988).
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Dharmawardena, T. E., C. A. L. Bailer-Jones, M. Fouesneau e D. Foreman-Mackey. "Three-dimensional dust density structure of the Orion, Cygnus X, Taurus, and Perseus star-forming regions". Astronomy & Astrophysics 658 (febbraio 2022): A166. http://dx.doi.org/10.1051/0004-6361/202141298.
Testo completoAbstract (sommario):
Interstellar dust affects many astronomical observations through absorption and reddening, yet this extinction is also a powerful tool for studying interstellar matter in galaxies. Three-dimensional (3D) reconstructions of dust extinction and density in the Milky Way have suffered from artefacts such as the fingers-of-god effect and negative densities, and have been limited by large computational costs. Here, we aim to overcome these issues with a novel algorithm that derives the 3D extinction density of dust in the Milky Way using a latent variable Gaussian process in combination with variational inference. Our model maintains non-negative density and hence monotonically non-decreasing extinction along all lines-of-sight, while performing the inference within a reasonable computational time. Using extinctions for hundreds of thousands of stars computed from optical and near-infrared photometry, together with distances based on Gaia parallaxes, we employ our algorithm to infer the structure of the Orion, Taurus, Perseus, and Cygnus X star-forming regions. A number of features that are superimposed in 2D extinction maps are clearly deblended in 3D dust extinction density maps. For example, we find a large filament on the edge of Orion that may host a number of star clusters. We also identify a coherent structure that may link the Taurus and Perseus regions, and we show that Cygnus X is located at 1300–1500 pc, in line with very-long-baseline interferometry measurements. We compute dust masses of the regions and find these to be slightly higher than previous estimates, likely a consequence of our input data recovering the highest column densities more effectively. By comparing our predicted extinctions to Planck data, we find that known relationships between density and dust processing, where high-extinction lines-of-sight have the most processed grains, hold up in resolved observations when density is included, and that they exist at smaller scales than previously suggested. This can be used to study the changes in size or composition of dust as they are processed in molecular clouds.
38
Ridgway, S. T. "Long Baseline Optical Interferometry". Highlights of Astronomy 8 (1989): 559–60. http://dx.doi.org/10.1017/s1539299600008339.
Testo completoAbstract (sommario):
During the last three years significant results have been obtained from several operational, long baseline optical interferometers. Precision stellar angular diameters (accuracy of order 2% and better) have been reported in the infrared (DiBenedetto and Rabbia, 1987) and in the visible (Davis and Tango, 1986). Astrometric precision of order 20 milliarcsec has been demonstrated over large angles (Shao et al, in press). Spectro-spatial resolution of the disk of a Be star in the hydrogen emission line (Thom et al., 1986) suggests spectacular imaging science to come with many-telescope coherent and phased optical arrays.
39
Kervella, P., D. Bersier, D. Mourard, N. Nardetto e V. Coudé du Foresto. "Cepheid distances from infrared long-baseline interferometry". Astronomy & Astrophysics 423, n. 1 (29 luglio 2004): 327–33. http://dx.doi.org/10.1051/0004-6361:20035596.
Testo completo
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Kervella, P., D. Bersier, D. Mourard, N. Nardetto, P. Fouqué e V. Coudé du Foresto. "Cepheid distances from infrared long-baseline interferometry". Astronomy & Astrophysics 428, n. 2 (26 novembre 2004): 587–93. http://dx.doi.org/10.1051/0004-6361:20041416.
Testo completo
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Shao, M., e M. M. Colavita. "Long-Baseline Optical and Infrared Stellar Interferometry". Annual Review of Astronomy and Astrophysics 30, n. 1 (settembre 1992): 457–98. http://dx.doi.org/10.1146/annurev.aa.30.090192.002325.
Testo completo
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Kervella, P., N. Nardetto, D. Bersier, D. Mourard e V. Coudé du Foresto. "Cepheid distances from infrared long-baseline interferometry". Astronomy & Astrophysics 416, n. 3 (marzo 2004): 941–53. http://dx.doi.org/10.1051/0004-6361:20031743.
Testo completo
43
Labdon, Aaron, Stefan Kraus, Claire L. Davies, Alexander Kreplin, Jacques Kluska, Tim J. Harries, John D. Monnier et al. "Dusty disk winds at the sublimation rim of the highly inclined, low mass young stellar object SU Aurigae". Astronomy & Astrophysics 627 (27 giugno 2019): A36. http://dx.doi.org/10.1051/0004-6361/201935331.
Testo completoAbstract (sommario):
Context. T Tauri stars are low-mass young stars whose disks provide the setting for planet formation. Despite this, their structure is poorly understood. We present new infrared interferometric observations of the SU Aurigae circumstellar environment that offer resolution that is three times higher and a better baseline position angle coverage than previous observations. Aims. We aim to investigate the characteristics of the circumstellar material around SU Aur, constrain the disk geometry, composition and inner dust rim structure. Methods. The CHARA array offers unique opportunities for long baseline observations, with baselines up to 331 m. Using the CLIMB three-telescope combiner in the K-band allows us to measure visibilities as well as closure phase. We undertook image reconstruction for model-independent analysis, and fitted geometric models such as Gaussian and ring distributions. Additionally, the fitting of radiative transfer models constrain the physical parameters of the disk. For the first time, a dusty disk wind is introduced to the radiative transfer code TORUS to model protoplanetary disks. Our implementation is motivated by theoretical models of dusty disk winds, where magnetic field lines drive dust above the disk plane close to the sublimation zone. Results. Image reconstruction reveals an inclined disk with slight asymmetry along its minor-axis, likely due to inclination effects obscuring the inner disk rim through absorption of incident star light on the near-side and thermal re-emission and scattering of the far-side. Geometric modelling of a skewed ring finds the inner rim at 0.17 ± 0.02 au with an inclination of 50.9 ± 1.0° and minor axis position angle 60.8 ± 1.2°. Radiative transfer modelling shows a flared disk with an inner radius at 0.18 au which implies a grain size of 0.4 μm assuming astronomical silicates and a scale height of 15.0 at 100 au. Among the tested radiative transfer models, only the dusty disk wind successfully accounts for the K-band excess by introducing dust above the mid-plane.
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Davelaar, Jordy, Hector Olivares, Oliver Porth, Thomas Bronzwaer, Michael Janssen, Freek Roelofs, Yosuke Mizuno, Christian M. Fromm, Heino Falcke e Luciano Rezzolla. "Modeling non-thermal emission from the jet-launching region of M 87 with adaptive mesh refinement". Astronomy & Astrophysics 632 (21 novembre 2019): A2. http://dx.doi.org/10.1051/0004-6361/201936150.
Testo completoAbstract (sommario):
Context. The galaxy M 87 harbors a kiloparsec-scale relativistic jet, whose origin coincides with a compact source thought to be a supermassive black hole. Observational millimeter very long baseline interferometry campaigns are capable of resolving the jet-launching region at the scale of the event horizon. In order to provide a context for interpreting these observations, realistic general-relativistic magnetohydrodynamical (GRMHD) models of the accretion flow are constructed. Aims. Electrons in the jet are responsible for the observed synchrotron radiation, which is emitted in frequencies ranging from radio to near-infrared (NIR) and optical. The characteristics of the emitted radiation depend on the shape of the electrons’ energy-distribution function (eDF). The dependency on the eDF is omitted in the modeling of the first Event Horizon Telescope results. In this work, we aim to model the M 87 spectral-energy distribution from radio up to optical frequencies using a thermal-relativistic Maxwell–Jüttner distribution, as well as a relativistic κ-distribution function. The power-law index of the eDF is modeled based on sub-grid, particle-in-cell parametrizations for sub-relativistic reconnection. Methods. A GRMHD simulation in Cartesian–Kerr–Schild coordinates, using eight levels of adaptive mesh refinement (AMR), forms the basis of our model. To obtain spectra and images, the GRMHD data was post-processed with the ray-tracing code RAPTOR, which is capable of ray tracing through GRMHD simulation data that is stored in multi-level AMR grids. The resulting spectra and images maps are compared with observations. Results. We obtain radio spectra in both the thermal-jet and κ-jet models consistent with radio observations. Additionally, the κ-jet models also recover the NIR and optical emission. The images show a more extended structure at 43 GHz and 86 GHz and more compact emission at 228 GHz. The models recover the observed source sizes and core shifts and obtain a jet power of ≈1043 ergs s−1. In the κ-jet models, both the accretion rates and jet powers are approximately two times lower than the thermal-jet model. The frequency cut-off observed at ν ≈ 1015 Hz is recovered when the accelerator size is 106 − 108 cm, this could potentially point to an upper limit for plasmoid sizes in the jet of M 87.
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Pfuhl, O., R. Davies, J. Dexter, H. Netzer, S. Hönig, D. Lutz, M. Schartmann et al. "An image of the dust sublimation region in the nucleus of NGC 1068". Astronomy & Astrophysics 634 (28 gennaio 2020): A1. http://dx.doi.org/10.1051/0004-6361/201936255.
Testo completoAbstract (sommario):
We present near-infrared interferometric data on the Seyfert 2 galaxy NGC 1068, obtained with the GRAVITY instrument on the European Southern Observatory Very Large Telescope Interferometer. The extensive baseline coverage from 5 to 60 Mλ allowed us to reconstruct a continuum image of the nucleus with an unrivaled 0.2 pc resolution in the K-band. We find a thin ring-like structure of emission with a radius r = 0.24 ± 0.03 pc, inclination i = 70 ± 5°, position angle PA = −50 ± 4°, and h/r < 0.14, which we associate with the dust sublimation region. The observed morphology is inconsistent with the expected signatures of a geometrically and optically thick torus. Instead, the infrared emission shows a striking resemblance to the 22 GHz maser disc, which suggests they share a common region of origin. The near-infrared spectral energy distribution indicates a bolometric luminosity of (0.4–4.7) × 1045 erg s−1, behind a large AK ≈ 5.5 (AV ≈ 90) screen of extinction that also appears to contribute significantly to obscuring the broad line region.
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Grimani, Catia. "Clues from 4U 0142+61 on supernova fallback disc formation and precession". Monthly Notices of the Royal Astronomical Society 507, n. 1 (21 luglio 2021): 261–66. http://dx.doi.org/10.1093/mnras/stab2078.
Testo completoAbstract (sommario):
ABSTRACT The Nuclear Spectroscopic Telescope Array (NuSTAR) experiment detected a hard X-ray emission (10–70 keV) with a period of 8.68917 s and a pulse-phase modulation at 55 ks, or half this value, from the anomalous X-ray pulsar (AXP) 4U 0142+61. It is shown here that this evidence is naturally explained by the precession of a Keplerian supernova fallback disc surrounding this AXP. It is also found that the precession of discs formed around young neutron stars at distances larger than those considered in the past, may constitute almost neglected sources of gravitational waves with frequencies belonging to the sensitivity bands of the future space interferometers: Laser Interferometer Space Antenna (LISA), Advanced Laser Interferometer Antenna (ALIA), DECi-hertz Interferometer Gravitational wave Observatory (DECIGO), and Big Bang Observer (BBO). In this work, the gravitational wave emission from precessing fallback discs possibly formed around young pulsars such as Crab in a region extending beyond 8 × 107 m from the pulsar surface is estimated. It is also evaluated the role that infrared radiation emission from circumpulsar discs may play in contributing to inverse Compton scattering of TeV energy positrons and electrons. Extensive observational campaigns of disc formation around young and middle-aged pulsars may also contribute to solve the long-standing problem of a pulsar origin for the excess of positrons in cosmic rays observed near the Earth above 7 GeV. In the near future the James Webb Space Telescope, with unprecedented near- and mid-infrared observation capabilities, may provide direct evidence of a large sample of supernova fallback discs.
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Millour, Florentin, Thomas Driebe, Jose H. Groh, Olivier Chesneau, Gerd Weigelt, Adriane Liermann e Anthony Meilland. "Imaging “Pinwheel” nebulae with optical long-baseline interferometry". Proceedings of the International Astronomical Union 6, S272 (luglio 2010): 408–9. http://dx.doi.org/10.1017/s1743921311010957.
Testo completoAbstract (sommario):
AbstractDusty Wolf-Rayet stars are few but remarkable in terms of dust production rates (up to Ṁ = 10−6 M⊙/yr). Infrared excesses associated to mass-loss are found in the sub-types WC8 and WC9. Few WC9d stars are hosting a “pinwheel” nebula, indirect evidence of a companion star around the primary. While few other WC9d stars have a dust shell which has been barely resolved so far, the available angular resolution offered by single telescopes is insufficient to confirm if they also host “pinwheel” nebulae or not. In this article, we present the possible detection of such nebula around the star WR 118. We discuss about the potential of interferometry to image more “pinwheel” nebulae around other WC9d stars.
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Davis, John. "Stellar angular diameter measurements by interferometry". Symposium - International Astronomical Union 189 (1997): 31–38. http://dx.doi.org/10.1017/s0074180900116468.
Testo completoAbstract (sommario):
Stellar angular diameter measurements have been made with a range of interferometric techniques including speckle, aperture masking and long baseline optical/infrared interferometry. The current status of these measurements are summarised in terms of the range of spectral types and luminosity classes measured, the accuracies achieved, the wavelengths used for observations, and the reliability of the results. A number of major long-baseline interferometers are coming on-line, or are under development, and their potential is assessed in terms of wavelength cover, accuracy, angular resolution, and the range of spectral type and luminosity class cover.
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Norris, Ray P., Steven Tingay, Chris Phillips, Enno Middelberg, Adam Deller e Philip N. Appleton. "Very long baseline interferometry detection of an Infrared-Faint Radio Source". Monthly Notices of the Royal Astronomical Society 378, n. 4 (16 giugno 2007): 1434–38. http://dx.doi.org/10.1111/j.1365-2966.2007.11883.x.
Testo completo
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Quirrenbach, Andreas. "Optical and Infrared Long–Baseline Interferometry: Application to Binary Star Science". Symposium - International Astronomical Union 200 (2001): 539–46. http://dx.doi.org/10.1017/s0074180900225655.
Testo completoAbstract (sommario):
Interferometric observations of binary stars have a profound impact on many areas of stellar astrophysics. This article gives a brief review of interferometric techniques applied to binaries, and of orbit determination and binary surveys with optical and infrared interferometers.