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Start Over Subject astrometry Publisher CDS
241. HK survey emission-line candidates
ID:
ivo://CDS.VizieR/J/AJ/112/1188
Title:
HK survey emission-line candidates
Short Name:
J/AJ/112/1188
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a list of 218 additional candidate emission-line objects discovered with the northern and southern HK interference-filter/ objective-prism survey of Beers and collaborators. The objects have apparent magnitudes in the range 10<=B<=16, several magnitudes fainter than obtained with previous prism surveys of similar resolution. Of the new candidates, 73 have been previously identified. The total list of HK-survey emission-line candidates now numbers 376 objects, 104 of which were noted by previous surveys.
242. Hot Stuff for One Year (HSOY)
ID:
ivo://CDS.VizieR/I/339
Title:
Hot Stuff for One Year (HSOY)
Short Name:
I/339
Date:
21 Oct 2021
Publisher:
CDS
Description:
Recently, the first installment of data from ESA's Gaia astrometric satellite mission (Gaia DR1) was released, containing positions of more than 1 billion stars with unprecedented precision, as well as proper motions and parallaxes, however only for a subset of 2 million objects. The second release will include those quantities for most objects. In order to provide a dataset that bridges the time gap between the Gaia DR1 and Gaia DR2 releases and partly remedies the lack of proper motions in the former, HSOY ("Hot Stuff for One Year") was created as a hybrid catalog between Gaia and ground-based astrometry, featuring proper motions (but no parallaxes) for a large fraction of the DR1 objects. While not attempting to compete with future Gaia releases in terms of data quality or number of objects, the aim of HSOY is to provide improved proper motions partly based on Gaia data, allowing studies to be carried out just now or as pilot studies for later projects requiring higher-precision data. The HSOY catalog was compiled using the positions taken from Gaia DR1 combined with the input data from the PPMXL catalog, employing the same weighted least-squares technique that was used to assemble the PPMXL catalog itself. This effect resulted in a four-parameter astrometric catalog containing 583 million stars, with Gaia DR1 quality positions and proper motions with precisions from far less than 1 mas/yr to 5 mas/yr, depending on object brightness and location on the sky.
243. HST astrometry of TNOs
ID:
ivo://CDS.VizieR/J/ApJS/189/336
Title:
HST astrometry of TNOs
Short Name:
J/ApJS/189/336
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present 1428 individual astrometric measurements of 256 trans-Neptunian objects made with Hubble Space Telescope (HST). The observations were collected over three years with two instruments, the Wide Field Planetary Camera 2 and the Advanced Camera for Surveys High Resolution Camera, as part of four HST programs. We briefly describe the data and our analysis procedures. The submission of these measurements to the Minor Planet Center increased the individual arc length of objects by 1.83 days to 8.11 years. Of the 256 total objects, 62 (24.2%) had arc length increases of >=3 years. The arc length for 60 objects (23.4%) was increased by a factor of 2 or greater.
244. HST FGS-1r parallaxes for 8 metal-poor stars
ID:
ivo://CDS.VizieR/J/ApJ/835/152
Title:
HST FGS-1r parallaxes for 8 metal-poor stars
Short Name:
J/ApJ/835/152
Date:
21 Oct 2021
Publisher:
CDS
Description:
Hubble Space Telescope (HST) fine guidance sensor observations were used to obtain parallaxes of eight metal-poor ([Fe/H]< -1.4) stars. The parallaxes of these stars determined by the new Hipparcos reduction average 17% accuracy, in contrast to our new HST parallaxes, which average 1% accuracy and have errors on the individual parallaxes ranging from 85 to 144{mu}as. These parallax data were combined with HST Advanced Camera for Surveys photometry in the F606W and F814W filters to obtain the absolute magnitudes of the stars with an accuracy of 0.02-0.03 mag. Six of these stars are on the main sequence (MS) (with -2.7<[Fe/H]< -1.8) and are suitable for testing metal-poor stellar evolution models and determining the distances to metal-poor globular clusters (GCs). Using the abundances obtained by O'Malley+ (2017ApJ...838...90O), we find that standard stellar models using the VandenBerg & Clem (2003AJ....126..778V) color transformation do a reasonable job of matching five of the MS stars, with HD 54639 ([Fe/H]=-2.5) being anomalous in its location in the color-magnitude diagram. Stellar models and isochrones were generated using a Monte Carlo analysis to take into account uncertainties in the models. Isochrones that fit the parallax stars were used to determine the distances and ages of nine GCs (with -2.4{<=}[Fe/H]{<=}-1.9). Averaging together the age of all nine clusters led to an absolute age of the oldest, most metal-poor GCs of 12.7+/-1.0Gyr, where the quoted uncertainty takes into account the known uncertainties in the stellar models and isochrones, along with the uncertainty in the distance and reddening of the clusters.
245. HST Observations of core of 47 Tuc
ID:
ivo://CDS.VizieR/J/ApJS/85/293
Title:
HST Observations of core of 47 Tuc
Short Name:
J/ApJS/85/293
Date:
21 Oct 2021
Publisher:
CDS
Description:
(no description available)
246. Hyades tidal tails with Gaia DR2
ID:
ivo://CDS.VizieR/J/A+A/621/L3
Title:
Hyades tidal tails with Gaia DR2
Short Name:
J/A+A/621/L3
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the discovery of two well-defined tidal tails emerging from the Hyades star cluster. The tails were detected in Gaia DR2 data by selecting cluster members in the 3D galactocentric cylindrical velocity space. The robustness of our member selection is reinforced by the fact that the sources depict an almost noiseless, coeval stellar main sequence in the observational Hertzsprung-Russel diagram. The spatial arrangement of the selected members represents a highly flattened shape with respect to the direction of movement along the clusters' orbit in the Galaxy. The size of the entire structure, within the limits of the observations, measures about 200pc in its largest extent, while being only about 25pc thick. This translates into an on-sky extent of well beyond 100deg. Intriguingly, a top-down view on the spatial distribution reveals a distinct S-shape, reminiscent of tidal tails that have been observed for globular clusters and also of tails that were modeled for star clusters bound to the Galactic disk. Even more remarkable, the spatial arrangement as well as the velocity dispersion of our source selection is in excellent agreement with previously published theoretical predictions for the tidal tails of the Hyades. An investigation into observed signatures of equipartition of kinetic energy, that is, mass segregation, remains unsuccessful, most likely because of the sensitivity limit for radial velocity measurements with Gaia.
247. IC 4665
ID:
ivo://CDS.VizieR/J/AJ/105/1441
Title:
IC 4665
Short Name:
J/AJ/105/1441
Date:
21 Oct 2021
Publisher:
CDS
Description:
The results of a combined astrometric, photometric, and spectroscopic program to identify members of the open cluster IC 4665 are presented. Numerous new proper motion/photometric candidate members and at least 23 M dwarfs with H-alpha emission have been identified. A reanalysis of IC 4665's age using different methods yields conflicting results ranging from approx. 3x10^7^ yr to the age of the Pleiades. This study provides a list of candidate cluster members in the intermediate and low-mass regime of this cluster. Future spectroscopic observations of these candidates should eventually identify true cluster members. The results of new echelle observations of some candidates and the photometric monitoring of one apparent cluster member are given in an appendix.
248. ICRF3 radio-loud quasars with Gaia DR2 data
ID:
ivo://CDS.VizieR/J/ApJ/873/132
Title:
ICRF3 radio-loud quasars with Gaia DR2 data
Short Name:
J/ApJ/873/132
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate a sample of 3413 International Celestial Reference Frame (ICRF3) extragalactic radio-loud sources with accurate positions determined by very long baseline interferometry in the S/X band, mostly active galactic nuclei and quasars, which are cross-matched with optical sources in the second Gaia data release (Gaia DR2). The main goal of this study is to determine a core sample of astrometric objects that define the mutual orientation of the two fundamental reference frames, the Gaia (optical) and the ICRF3 (radio) frames. The distribution of normalized offsets between the VLBI sources and their optical counterparts is non-Rayleigh, with a deficit around the modal value and a tail extending beyond the 3{sigma} confidence level. A few filters are applied to the sample in order to discard double cross-matches, confusion sources, and Gaia astrometric solutions of doubtful quality. Panoramic Survey Telescope and Rapid Response System and Dark Energy Survey stacked multicolor images are used to further deselect objects that are less suitable for precision astrometry, such as extended galaxies, double and multiple sources, and obvious misidentifications. After this cleaning, 2643 quasars remain, of which 20% still have normalized offset magnitudes exceeding 3, or a 99% confidence level. We publish a list of 2119 radio-loud quasars of prime astrometric quality. The observed dependence of binned median offset on redshift shows the expected decline at small redshifts, but also an unexpected rise at z~1.6, which may be attributed to the emergence of the CIV emission line in the Gaia's G band. The Gaia DR2 parallax zero-point is found to be color-dependent, suggesting an uncorrected instrumental calibration effect.
249. ICRF2 sources of the Rio survey
ID:
ivo://CDS.VizieR/J/MNRAS/430/2797
Title:
ICRF2 sources of the Rio survey
Short Name:
J/MNRAS/430/2797
Date:
21 Oct 2021
Publisher:
CDS
Description:
We obtained improved optical positions for 300 ICRF2 sources - the Rio survey. We compared the Rio survey with 10 other selected optical astrometric surveys and studied the link between the Hipparcos Catalogue Reference Frame (HCRF) and the International Celestial Reference Frame, Second Realization (ICRF2). We investigated the possible causes for the observed non-coincidence between the optical and ICRF2 positions. The Rio survey positions were referred to the second version of the United States Naval Observatory CCD Astrograph Catalog (UCAC2), currently the best tested HCRF densification. The sources are between -90{deg}<{delta}<+30{deg}. We used two telescopes with suitable diameters and focal lengths to properly link the observed ICRF2 sources with the UCAC2, using intermediate brightness stars. We certified the astrometry done with many statistical tests. The average 'optical minus ICRF2' offsets and respective standard deviations in ({alpha}, {delta}) were -3mas (41mas) and +4 (45mas). The Rio survey represents well the zero-point offset of the other surveys. The standard error of 3.5mas found for the HCRF/ICRF2 link indicates an error excess that can be originated by a non-coincidence between the observed optical/VLBI positions. We thus discussed the influence of the errors from the UCAC2. Then, we searched for correlations with the source morphology, represented by structure indices defined in the radio and in the optical domain. Finally, we studied how the position offsets could originate from the perturbation of the optical point spread function (PSF) of the source's core, by a second source of flux. We found an analytical relation that describes the resulting centroid shift, as a function of the atmospheric seeing, the brightness ratio and the relative distance between the two contributing flux sources. Two scenarios, modelled by this relation, are discussed: an extinction window in the dust torus nearby the core, and a Galactic star near the line of sight.
250. ICRF stars near extragalactic radio sources
ID:
ivo://CDS.VizieR/J/other/KFNT/27.299
Title:
ICRF stars near extragalactic radio sources
Short Name:
J/other/KFNT/27.
Date:
21 Oct 2021
Publisher:
CDS
Description:
The compiled catalogue of 231044 stars was created from photographic and CCD observations of position catalogues observed by ground based telescopes. The catalogue destine for optical observations VLBI-ICRS astrometrical extragalactic radiosources (ERS) with telescopes equiped with CCD-cameras. The main purpose of this catalogue is to ensure the reference stars in optics for reducing positions of faint astrometrical ERS 17-22mag relative to more bright reference stars 14-17mag. The catalogue contains 231044 star positions in fields 40'x40' near 240 ERS. More than nine catalogues of stars coordinates were used for compiling the Pul-ERS catalogue. For 69% of stars the proper motions were taken from UCAC3 catalogue to convert the position stars to the common epoch. The number of position measurements for each star varies from one to more than ten records. The inner precision of positions of stars in Pul-ERS is from 4 to 150mas. 159331 stars of the compiled catalogue were identified with stars of the UCAC3. The average internal accuracy of positions on both coordinates is not worse 0.11".

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