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271. 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)
272. 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.
273. 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.
274. 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.
275. 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.
276. 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".
277. Identification and coordinates in M4
ID:
ivo://CDS.VizieR/J/PAZh/22/847
Title:
Identification and coordinates in M4
Short Name:
J/PAZh/22/847
Date:
21 Oct 2021
Publisher:
CDS
Description:
Accurate equatorial coordinates have been determined for 54 variable stars in the globular cluster M 4=NGC 6121.
278. Identification and coordinates in M5
ID:
ivo://CDS.VizieR/J/PAZh/21/509
Title:
Identification and coordinates in M5
Short Name:
J/PAZh/21/509
Date:
21 Oct 2021
Publisher:
CDS
Description:
Accurate equatorial coordinates have been determined for 143 variable and suspected variable stars in the globular cluster M5=NGC 5904. For 28 stars, identifications with Kustner (1933VeUSB..26....1K) catalogue were found for the first time.
279. Identification and coordinates in M 53
ID:
ivo://CDS.VizieR/J/PAZh/23/454
Title:
Identification and coordinates in M 53
Short Name:
J/PAZh/23/454
Date:
21 Oct 2021
Publisher:
CDS
Description:
Equatorial coordinates have been determined for 61 variables in the northern globular cluster M 53 and for 12 variables in the southern globular cluster NGC 2808 with accuracy sufficient for reliable identifications. A number of errors have been revealed in publications on variable starts in M 53.
280. Identification and coordinates in NGC 5272
ID:
ivo://CDS.VizieR/J/PAZh/20/693
Title:
Identification and coordinates in NGC 5272
Short Name:
J/PAZh/20/693
Date:
21 Oct 2021
Publisher:
CDS
Description:
Equatorial coordinates of variable stars in the globular cluster M3 (NGC 5272) and its nearest surroundings, mainly measured on a plate taken with The Zeiss-1000 telescope, are presented. Positions in a homogeneous system are presented for the first time for objects from the Catalogue of variable stars in globular clusters as well as for GCVS and NSV catalogue stars.

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