- ID:
- ivo://CDS.VizieR/J/A+A/466/L1
- Title:
- VLTI observations of RY Sgr
- Short Name:
- J/A+A/466/L1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high spatial resolution observations in the mid-infrared of the R CrB star RY Sgr obtained with the Very Large Telescope Interferometer (VLTI) of ESO's Paranal Observatory and MIDI, the MID-infrared Interferometric recombiner. MIDI combines the light of two telescopes and provides spectrally resolved visibilities in the N band atmospheric window. The observations of RY Sgr were conducted with the VLT Unit Telescopes (UTs) UT1, UT3 and UT4, providing projected baselines in the range of 57-129 meters oriented from PA=34{deg} to 135{deg}. The UTs observations were made during the nights of May 25-26th 2005, June 24-25th 2005, June 25-26th 2005 and June 27-28th 2005. All the observations were made under rather good atmospheric conditions. The files include all visibility data recorded from these observations as well as all the characteristics concerning the observations. The log of the observations is shown in Table 1 of the paper (table1.dat).
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- ID:
- ivo://CDS.VizieR/J/A+A/493/L17
- Title:
- VLTI observations of V4334 Sgr
- Short Name:
- J/A+A/493/L17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high spatial resolution observations in the mid-infrared of the Sakurai's object (V4334 Sgr) obtained with the Very Large Telescope Interferometer (VLTI) of ESO's Paranal Observatory and MIDI, the MID-infrared Interferometric recombiner. MIDI combines the light of two telescopes and provides spectrally resolved visibilities in the N band atmospheric window. The optical interferometry data are used in the paper from Chesneau et al. entitled "A dense disk of dust around the born-again Sakurai's object" and are available in OI-FITS format. The data were recorded in June 2007 under rather good atmospheric conditions and were reduced with the EWS package. The data set contains 6 spectrally dispersed calibrated visibilities and 6 differential phases. The files include all visibility data recorded from these observations as well as all the characteristics concerning the observations in the form of two OI-FITS files, for each night of observation. The log of the observations is shown in Table 1. The data products are stored in the FITS-based, optical interferometry data exchange format (OI-FITS), described in Pauls et al. (2005PASP..117.1255P). The OI Exchange Format is a standard for exchanging calibrated data from optical (visible/infrared) stellar interferometers. The standard is based on the Flexible Image Transport System (FITS), and supports storage of the optical interferometric observations including visibilities and differential phases. Several routines to read and write this format in various languages can be found in: Webpage http://www.mrao.cam.ac.uk/~jsy1001/exchange .
- ID:
- ivo://CDS.VizieR/J/A+A/636/A116
- Title:
- VLTI/PIONIER images of 15 Herbig Ae/Be stars
- Short Name:
- J/A+A/636/A116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The innermost astronomical unit (au) in protoplanetary disks is a key region for stellar and planet formation, as exoplanet searches have shown a large occurrence of close-in planets, located within the first au around their host star. We aim to reveal the morphology of the disk inner rim using near-infrared interferometric observations with milli-arcsecond resolution provided by near-infrared multi-telescope interferometry. Methods: We provide model-independent reconstructed images of 15 objects selected from the Herbig AeBe survey carried out with VLTI/PIONIER, using the semi-parametric approach for image reconstruction of chromatic objects (SPARCO). We propose a set of methods to reconstruct and analyze the images in a consistent way. 40% of the systems (6/15) are found to be centro-symmetric at the angular resolution of the observations. For the rest of the objects, we find evidence for asymmetric emission due to moderate-to-strong inclination of a disk-like structure for ~30% of the objects (5/15), and non-centro-symmetric morphology due to an non-axisymmetric and possible variable environment (4/15, ~27%). Among the systems with disk-like structure, 20% (3/15) show a resolved dust-free cavity. Finally, we do not detect extended emission beyond the inner rim. The image reconstruction process is a powerful tool to reveal complex disk inner rim morphologies which is complementary to the fit of geometrical models. At the angular resolution reached by near-infrared interferometric observations most of the images are compatible with a centrally peaked emission (no cavity). For the most resolved targets, image reconstruction reveals morphologies that cannot be reproduced by generic parametric models (e.g., perturbed inner rims, complex brightness distributions). Moreover, the non-axisymmetric disks show that the spatial resolution probed by optical interferometers makes the observations of the near-infrared emission (inside a few au) sensitive to temporal evolution with a time-scale down to few weeks. The evidence of non-axisymmetric emission that cannot be explained by simple inclination and radiative transfer effects requires for alternative explanations such as a warping of the inner disks. Interferometric observations can therefore be used to follow the evolution of the asymmetry of those disks at an au or sub-au scale.
- ID:
- ivo://CDS.VizieR/J/A+A/614/A12
- Title:
- VLTI/PIONIER observations of CE Tauri
- Short Name:
- J/A+A/614/A12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Red supergiant stars represent one of the latest stages of the evolution of massive stars. Their photospheric convection may play an important role in the launching mechanism of their mass loss. Yet, its characteristics and dynamics are poorly constrained. By observing red supergiant stars with near infrared interferometry at different epochs, we expect to unveil the evolution of bright convective features on their stellar surface. We observed the M2Iab-Ib red supergiant star CE Tau with the VLTI/PIONIER instrument in the H band at two different epochs separated by one month. We derive the angular diameter of the star, basic stellar parameters and reconstruct two reliable images of its H band photosphere. The contrast of the convective pattern of the reconstructed images is 5+/-1% and 6+/-1 % for our two epochs of observation. The stellar photosphere shows few changes between the two epochs. The contrast of the convective pattern is below the average contrast variations obtained on 30 randomly chosen snapshots of the best matching 3D radiative hydrodynamics simulation: 23+/-1% for the original simulation images, and 16+/-1% for the maps degraded to the reconstruction resolution. We offer two hypotheses to explain this observation: CE Tau may be experiencing a quiet convective activity episode or it could be a consequence of its warmer effective temperature (hence its smaller radius) compared to the simulation.
- ID:
- ivo://CDS.VizieR/J/PASJ/52/997
- Title:
- VSOP 5 GHz AGN Survey
- Short Name:
- J/PASJ/52/997
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The VSOP mission is a Japanese-led project to image radio sources with sub-milliarcsec resolution by correlating the signal from the orbiting 8-m telescope, HALCA, with a global array of telescopes. Twenty- five percent of the scientific time of this mission is devoted to a survey of 402 bright, small-diameter extra-galactic radio sources at 5-GHz. The major goals of the VSOP Survey are statistical in nature: to determine the brightness temperature and approximate structure; to provide a source list for use with future space VLBI missions; and to compare radio properties with other data throughout the EM spectrum. This paper describes: the compilation of a complete list of radio sources associated with active galactic nuclei (AGN); the selection of the subsample of sources to be observed with VSOP; the extensive ground resources used for the Survey; the status of the observations as of 2000 July; the data-analysis methods; and several examples of results from the VSOP Survey. More detailed results from the full sample will be given in future papers.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A76
- Title:
- VY CMa ALMA NaCl images
- Short Name:
- J/A+A/592/A76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- At the end of their lives, most stars lose a significant amount of mass through a stellar wind. The specific physical and chemical circumstances that lead to the onset of the stellar wind for cool luminous stars are not yet understood. Complex geometrical morphologies in the circumstellar envelopes prove that various dynamical and chemical processes are interlocked and that their relative contributions are not easy to disentangle. We aim to study the inner-wind structure (R<250R*) of the well-known red supergiant VY CMa, the archetype for the class of luminous red supergiant stars experiencing high mass loss. Specifically, the objective is to unravel the density structure in the inner envelope and to examine the chemical interaction between gas and dust species. We analyse high spatial resolution (~0.24"x0.13") ALMA Science Verification (SV) data in band 7, in which four thermal emission lines of gaseous sodium chloride (NaCl) are present at high signal-to-noise ratio.
- ID:
- ivo://CDS.VizieR/J/MNRAS/473/1685
- Title:
- Weak Galactic radio sources spectral indices
- Short Name:
- J/MNRAS/473/1685
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the next few years the classification of radio sources observed by the large surveys will be a challenging problem and spectral index is a powerful tool for addressing it. Here we present an algorithm to estimate the spectral index of sources from multiwavelength radio images. We have applied our algorithm to SCORPIO, a Galactic plane survey centred around 2.1GHz carried out with Australian Telescope Compact Array and found we can measure reliable spectral indices only for sources stronger than 40 times the rms noise. Above a threshold of 1mJy, the source density in SCORPIO is 20 per cent greater than in a typical extragalactic field, like Australia Telescope Large Area Survey because of the presence of Galactic sources. Among this excess population, 16 sources per square degree have a spectral index of about zero suggesting optically thin thermal emission such as HII regions and planetary nebulae, while 12 per square degree present a rising spectrum, suggesting optically thick thermal emission such as stars and UCHII regions.
- ID:
- ivo://CDS.VizieR/J/ApJ/820/90
- Title:
- 4yr 1.3mm VLBI observations of SgrA* with EHT
- Short Name:
- J/ApJ/820/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Galactic Center black hole Sagittarius A* (Sgr A*) is a prime observing target for the Event Horizon Telescope (EHT), which can resolve the 1.3mm emission from this source on angular scales comparable to that of the general relativistic shadow. Previous EHT observations have used visibility amplitudes to infer the morphology of the millimeter-wavelength emission. Potentially much richer source information is contained in the phases. We report on 1.3mm phase information on Sgr A* obtained with the EHT on a total of 13 observing nights over four years. Closure phases, which are the sum of visibility phases along a closed triangle of interferometer baselines, are used because they are robust against phase corruptions introduced by instrumentation and the rapidly variable atmosphere. The median closure phase on a triangle including telescopes in California, Hawaii, and Arizona is nonzero. This result conclusively demonstrates that the millimeter emission is asymmetric on scales of a few Schwarzschild radii and can be used to break 180{deg} rotational ambiguities inherent from amplitude data alone. The stability of the sign of the closure phase over most observing nights indicates persistent asymmetry in the image of Sgr A* that is not obscured by refraction due to interstellar electrons along the line of sight.
- ID:
- ivo://CDS.VizieR/J/ApJS/242/5
- Title:
- 40yr of geodetic/astrometric VLBI obs. of ICRF sources
- Short Name:
- J/ApJS/242/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Geodetic/astrometric very long baseline interferometry (VLBI) has been routinely observing using various global networks for 40yr, and it has produced more than 10 million baseline group delay, phase, and amplitude observables. These group delay observables are analyzed worldwide for geodetic and astrometric applications, for instance, to create the International Celestial Reference Frame (ICRF). The phase and amplitude observables are used in this paper, by means of closure analysis, to study intrinsic source structures and their evolution over time. The closure amplitude rms, CARMS, indicating how far away a source is from being compact in terms of morphology, is calculated for each individual source. The overall structure-effect magnitudes for 3417 ICRF radio sources are quantified. CARMS values larger than 0.3 suggest significant source structures and those larger than 0.4 indicate very extended source structures. The 30 most frequently observed sources, which constitute 40% of current geodetic VLBI observables, are studied in detail. The quality of ICRF sources for astrometry is evaluated by examining the CARMS values. It is confirmed that sources with CARMS values larger than 0.30 can contribute residual errors of about 15ps to geodetic VLBI data analysis and those with the CARMS values larger than 0.4 generally can contribute more than 20ps. We recommend CARMS values as an indicator of the astrometric quality for the ICRF sources and the continuous monitoring of the ICRF sources to update CARMS values with new VLBI observations as they become available.
- ID:
- ivo://CDS.VizieR/J/ApJS/194/43
- Title:
- YSOs candidates and knots in CrA cloud
- Short Name:
- J/ApJS/194/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Spitzer Space Telescope IRAC and MIPS observations of a 0.85deg^2^ field including the Corona Australis (CrA) star-forming region. At a distance of 130pc, CrA is one of the closest regions known to be actively forming stars, particularly within its embedded association, the Coronet. Using the Spitzer data, we identify 51 young stellar objects (YSOs) in CrA which include sources in the well-studied Coronet cluster as well as sources distributed throughout the molecular cloud. Twelve of the YSOs discussed are new candidates, one of which is located in the Coronet. Known YSOs retrieved from the literature are also added to the list, and a total of 116 candidate YSOs in CrA are compiled. A clustering analysis was also performed, finding that the main cluster core, consisting of 68 members, is elongated (having an aspect ratio of 2.36), with a circular radius of 0.59pc and mean surface density of 150pc^-2^. In addition, we analyze outflows and jets in CrA by means of new CO and H2 data. We present 1.3mm interferometric continuum observations made with the Submillimeter Array (SMA) covering R CrA, IRS 5, IRS 7, and IRAS 18595-3712 (IRAS 32).
