- ID:
- ivo://CDS.VizieR/J/ApJ/889/99
- Title:
- Gaia DR2 Blanco 1 member candidates
- Short Name:
- J/ApJ/889/99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the stellar population, using Gaia DR2 parallax, kinematics, and photometry, of the young (~100Myr), nearby (~230pc) open cluster, Blanco 1. A total of 644 member candidates are identified via the unsupervised machine learning method StarGO to find the clustering in the 5-dimensional position and proper motion parameter (X, Y, Z, {mu}{alpha}*cos{delta}, {mu}{delta}) space. Within the tidal radius of 10.0+/-0.3pc, there are 488 member candidates, 3 times more than those outside. A leading tail and a trailing tail, each of 50-60pc in the Galactic plane, are found for the first time for this cluster, with stars further from the cluster center streaming away faster, manifest stellar stripping. Blanco 1 has a total detected mass of 285+/-32M_{sun}_ with a mass function consistent with a slope of alpha=1.35+/-0.2 in the sense of dN/dm{prop.to}m^-alpha^, in the mass range of 0.25-2.51M_{sun}_, where N is the number of members and $m$ is stellar mass. A Minimum Spanning Tree ({LAMBDA}_MSR_) analysis shows the cluster to be moderately mass segregated among the most massive members (>~1.4M_{sun}_), suggesting an early stage of dynamical disintegration.
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- ID:
- ivo://CDS.VizieR/J/A+A/627/A34
- Title:
- GC hot UV-bright stars model spectra
- Short Name:
- J/A+A/627/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed a census of the UV-bright population in 78 globular clusters using wide-field UV telescopes. This population includes a variety of phases of post-horizontal branch (HB) evolution, including hot post-asymptotic giant branch (AGB) stars, and post-early AGB stars. There are indications that old stellar systems like globular clusters produce fewer post-(early) AGB stars than currently predicted by evolutionary models, but observations are still scarce. We wish to derive effective temperatures, surface gravities, and helium abundances of the luminous hot UV-bright stars in these clusters to determine their evolutionary status and compare the observed numbers to predictions from evolutionary theory. We obtained FORS2 spectroscopy of 11 of these UV-selected objects (covering a range of -2.3<[Fe/H]<-1.0), which we (re-)analysed together with previously observed data. We used model atmospheres of different metallicities, including super-solar ones. Where possible, we verified our atmospheric parameters using UV spectrophotometry and searched for metal lines in the optical spectra. We calculated evolutionary sequences for four metallicity regimes and used them together with information about the HB morphology of the globular clusters to estimate the expected numbers of post-AGB stars. We find that metal-rich model spectra are required to analyse stars hotter than 40000 K. Seven of the eleven new luminous UV-bright stars are post-AGB or post-early AGB stars, two are evolving away from the HB, one is a foreground white dwarf, and another is a white dwarf merger. Taking into account published information on other hot UV-bright stars in globular clusters, we find that the number of observed hot post-AGB stars generally agrees with the predicted values, although the numbers are still low. Spectroscopy is clearly required to identify the evolutionary status of hot UV-bright stars. For hotter stars, metal-rich model spectra are required to reproduce their optical and UV spectra, which may affect the flux contribution of hot post-AGB stars to the UV spectra of evolved populations. Adding published information on other hot UV-bright stars in globular clusters, we find that the number of observed hot post-AGB stars generally agrees with the predicted values, although the numbers are still low.
- ID:
- ivo://CDS.VizieR/J/MNRAS/488/3024
- Title:
- Globular clusters members with Gaia DR2
- Short Name:
- J/MNRAS/488/3024
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we present a method to identify possible members of globular clusters using data from Gaia DR2. The method consists of two stages: the first one based on a clustering algorithm, and the second one based on the analysis of the projected spatial distribution of stars with different proper motions. In order to confirm that the clusters members extracted by the method correspond to actual globular clusters, the spatial distribution, the vector point diagram of the proper motions, and the colour-magnitude diagrams are analysed. We apply the developed method to eight clusters: NGC 1261, NGC 3201, NGC 6139, NGC 6205, NGC 6362, NGC 6397, NGC 6712, and Palomar 13; we show the number of members extracted, the mean proper motions derived from them and finally we compare our results with other authors. In order to analyse the efficiency of the extraction method, we perform an estimation of the completeness and the degree of contamination of the extracted members.
- ID:
- ivo://CDS.VizieR/J/A+A/611/A38
- Title:
- Hints for a bar in M31 kinematics and morphology
- Short Name:
- J/A+A/611/A38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As the nearest large spiral galaxy, M 31 provides a unique opportunity to study the structure and evolutionary history of this galaxy type in great detail. Among the many observing programs aimed at M 31 are microlensing studies, which require good three-dimensional models of the stellar mass distribution. Possible non-axisymmetric structures like a bar need to be taken into account. Due to M 31's high inclination, the bar is difficult to detect in photometry alone. Therefore, detailed kinematic measurements are needed to constrain the possible existence and position of a bar in M 31. We obtained ~=220 separate fields with the optical integral-field unit spectrograph VIRUS-W, covering the whole bulge region of M 31 and parts of the disk. We derived stellar line-of-sight velocity distributions from the stellar absorption lines, as well as velocity distributions and line fluxes of the emission lines H{beta}, [OIII] and [NI]. Our data supersede any previous study in terms of spatial coverage and spectral resolution. We find several features that are indicative of a bar in the kinematics of the stars, we see intermediate plateaus in the velocity and the velocity dispersion, and correlation between the higher moment h3 and the velocity. The gas kinematics is highly irregular, but is consistent with non-triaxial streaming motions caused by a bar. The morphology of the gas shows a spiral pattern, with seemingly lower inclination than the stellar disk. We also look at the ionization mechanisms of the gas, which happens mostly through shocks and not through starbursts.
- ID:
- ivo://CDS.VizieR/J/AJ/136/2259
- Title:
- HST photometry of stars in NGC 2419
- Short Name:
- J/AJ/136/2259
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of optical and ultraviolet Hubble Space Telescope photometry for evolved stars in the core of the distant massive globular cluster NGC 2419. We characterize the horizontal branch (HB) population in detail including corrections for incompleteness on the long blue tail. The majority of the HB stars can be identified with two main groups (one slightly bluer than the instability strip, and the other at the extreme end of the HB). We present a method for removing (to first-order) lifetime effects from the distribution of HB stars to facilitate more accurate measurements of helium abundance for clusters with blue HBs and to clarify the distribution of stars reaching the zero-age HB.
- ID:
- ivo://CDS.VizieR/J/A+A/621/L2
- Title:
- Hyades tidal tails revealed by Gaia DR2
- Short Name:
- J/A+A/621/L2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Within a 200pc sphere around the Sun, we search for the Hyades tidal tails in the Gaia DR2 dataset. We used a modified convergent-point method to search for stars with space velocities close to the space velocity of the Hyades cluster. We find a clear indication for the existence of the Hyades tidal tails, a leading tail extending up to 170pc from the centre of the Hyades with 292 stars (36 contaminants), and a trailing tail up to 70pc with 237 stars (32 contaminants). A comparison with an N-body model of the cluster and its tails shows remarkably good coincidence. Five white dwarfs are found in the tails.
- ID:
- ivo://CDS.VizieR/J/A+AS/97/587
- Title:
- JHK photometry of Galactic center stars
- Short Name:
- J/A+AS/97/587
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present K-counts and JHK detailed photometry for a number of stars with K<=+9.0 in three clear regions near the galactic centre. These regions are all located approximately at l~0.0 and at latitudes b~-3.5,-4.0 and 4.5 respectively. Their Cumulative Counts Functions (CCF's) are formed, and with the aid of an exponential disk model for the Galaxy they are separated into disk and bulge CCF. As for the case in Baade's Window (BW) (Ruelas-Mayorga & Teague, 1992A&AS...95..379R) the disk is dominant at bright magnitudes whereas the bulge dominates at the faint end of the CCF. The slope of the bulge CCF is steeper than that for the disk in all three cases corroborating the result obtained for BW. The two colour JHK diagram and the K vs J-K diagram for the three regions show that the stellar population in these areas is similar to that studied in BW by us and by Frogel & Whitford (1987ApJ...320..199F). An average value of E(J-K)~0.42mag for the reddening is obtained, which is somewhat larger than that found for BW (0.27). Finally it is shown that at K<=+9.0, the disk population may be accounted for by those sources with J-K<=+1.6 whereas the bulge population presents values for J-K in excess of +1.6.
- ID:
- ivo://CDS.VizieR/J/PASP/131/D4101
- Title:
- Likely Pleiades members with Gaia DR2
- Short Name:
- J/PASP/131/D4101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents an investigation on fundamental astrophysical properties of the Pleiades cluster (M 45) using high-precision astrometric and photometric data from the Gaia Data Release 2 (Gaia-DR2). To obtain reliable cluster members, a machine-learning (ML) method is used to compute membership probabilities for 31462 sample stars within a radius of 6.5{deg} from the cluster center, both the astrometric and photometric data are taken into account. We obtain a total number of 1454 likely cluster members with membership probabilities larger than 0.6, including a well-known white dwarf (LB 1497) with a high membership probability of ~0.96. We find a well-defined relationship between the parallaxes and proper motions of the cluster members, the most likely explanation for the relationship is that the depth effect of the cluster along the line of sight must be taken into consideration. Using Monte Carlo simulations, the most likely distance, proper motion, and radial velocity of the cluster are determined to be D=136.0+/-0.1pc, (<{mu}_{alpha}_cos{delta}>, <{mu}_{delta}_>)=(+20.141+/-0.093, -45.536+/ -0.081)mas/yr, and <V_r_>=+5.8+/-0.1km/s, respectively. It is found that the likely cluster members extend outward to a limiting radius of R_lim_=310'+/-12' (12.3+/-0.5pc) from the cluster center, and the total mass of the cluster within this radius is M_tot_=721+/-93M_{sun}_. We find clear evidence for the presence of spatial mass segregation in this young cluster by analyzing the photometry and spatial positions of the likely cluster members. Interestingly, we also find that four high-mass cluster members with high membership probabilities (>0.99) are being ejected from the inner region of the cluster, they may have formed via close encounters between single and binary stars.
- ID:
- ivo://CDS.VizieR/J/AJ/137/4377
- Title:
- List of SEGUE plate pairs
- Short Name:
- J/AJ/137/4377
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Sloan Extension for Galactic Understanding and Exploration (SEGUE) Survey obtained ~240000 moderate-resolution (R~1800) spectra from 3900{AA} to 9000{AA} of fainter Milky Way stars (14.0<g<20.3) of a wide variety of spectral types, both main-sequence and evolved objects, with the goal of studying the kinematics and populations of our Galaxy and its halo. The spectra are clustered in 212 regions spaced over three quarters of the sky. Radial velocity accuracies for stars are {sigma}(RV)~4km/s at g<18, degrading to {sigma}(RV)~15km/s at g~20. For stars with signal-to-noise ratio >10 per resolution element, stellar atmospheric parameters are estimated, including metallicity, surface gravity, and effective temperature. SEGUE obtained 3500deg^2^ of additional ugriz imaging (primarily at low Galactic latitudes) providing precise multicolor photometry ({sigma}(g,r,i) ~2%), ({sigma}(u,z)~3%) and astrometry (~0.1") for spectroscopic target selection. The stellar spectra, imaging data, and derived parameter catalogs for this survey are publicly available as part of Sloan Digital Sky Survey Data Release 7. Individual images of spectra in this data set may be examined by fetching from the DAS, with a link like wget http://das.sdss.org/spectro/1d_26/1880/gif/spPlot-53262-1880-014.gif A FITS data file of the calibrated 1D spectrum is available from wget http://das.sdss.org/spectro/1d_26/1880/1d/spSpec-53262-1880-014.fit
- ID:
- ivo://CDS.VizieR/J/MNRAS/342/1241
- Title:
- Low-mass stars in M45 and M44
- Short Name:
- J/MNRAS/342/1241
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present near-infrared J-, H- and K-band photometry and optical spectroscopy of low-mass star and brown dwarf (BD) candidates in the Pleiades and Praesepe open clusters. We flag non-members from their position in K, I-K and J, J-K colour-magnitude diagrams (CMDs), and J-H, H-K two-colour diagrams.
