- ID:
- ivo://CDS.VizieR/J/A+A/566/A118
- Title:
- A comprehensive view of Virgo stellar stream
- Short Name:
- J/A+A/566/A118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To explore the complex halo substructure that has been reported in the direction of the Virgo constellation, radial velocities and metallicities have been measured for 82 RR Lyrae stars (RRLS) that were identified by the QUEST survey. These stars are distributed over 90 sq. deg. of the sky, and lie from 4 to 23kpc from the Sun. Using an algorithm for finding groups in phase space and modeling the smooth halo component in the region, we identified the 5 most significant RRLS groups, some of which were previously known or suspected. We have examined the SEKBO and the Catalina catalog of RRLS (with available spectroscopic measurements), as well as the bright QUEST RRLS sample, the catalog of Red Giant stars from the Spaghetti survey, and three recent catalogs of blue horizontal branch (BHB) stars, for stars that may be related to the QUEST RRLS groups.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/157/234
- Title:
- ACRONYM. III. Candidate young low-mass stars
- Short Name:
- J/AJ/157/234
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Young, low-mass stars in the solar neighborhood are vital for completing the mass function for nearby, young coeval groups, establishing a more complete census for evolutionary studies, and providing targets for direct-imaging exoplanet and/or disk studies. We present properties derived from high-resolution optical spectra for 336 candidate young nearby, low-mass stars. These include measurements of radial velocities and age diagnostics such as H{alpha} and Li {lambda}6707 equivalent widths. Combining our radial velocities with astrometry from Gaia DR2 (Cat. I/345), we provide full 3D kinematics for the entire sample. We combine the measured spectroscopic youth information with additional age diagnostics (e.g., X-ray and UV fluxes, color-magnitude diagram positions) and kinematics to evaluate potential membership in nearby, young moving groups and associations. We identify 77 objects in our sample as bona fide members of 10 different moving groups, 14 of which are completely new members or have had their group membership reassigned. We also reject 44 previously proposed candidate moving group members. Furthermore, we have newly identified or confirmed the youth of numerous additional stars that do not belong to any currently known group and find 69 comoving systems using Gaia DR2 astrometry. We also find evidence that the Carina association is younger than previously thought, with an age similar to the {beta} Pictoris moving group (~22 Myr).
- ID:
- ivo://CDS.VizieR/J/AJ/154/69
- Title:
- ACRONYM II. The {beta} Pictoris Moving Group
- Short Name:
- J/AJ/154/69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We confirm 66 low-mass stellar and brown dwarf systems (K7-M9) plus 19 visual or spectroscopic companions of the {beta} Pictoris moving group (BPMG). Of these, 41 are new discoveries, increasing the known low-mass members by 45%. We also add four objects to the 14 known with masses predicted to be less than 0.07 M_{sun}_. Our efficient photometric + kinematic selection process identified 104 low-mass candidates, which we observed with ground-based spectroscopy. We collected infrared observations of the latest spectral types (>M5) to search for low-gravity objects. These and all <M5 candidates were observed with high-resolution optical spectrographs to measure the radial velocities and youth indicators, such as lithium absorption and H{alpha} emission, needed to confirm BPMG membership, achieving a 63% confirmation rate. We also compiled the most complete census of BPMG membership, with which we tested the efficiency and false-membership assignments using our selection and confirmation criteria. Using the new census, we assess a group age of 22+/-6 Myr, consistent with past estimates. With the now-densely sampled lithium depletion boundary, we resolve the broadening of the boundary by either an age spread or astrophysical influences on lithium-burning rates. We find that 69% of the now-known members with AFGKM primaries are M stars, nearing the expected value of 75%. However, the new initial mass function for the BPMG shows a deficit of 0.2-0.3 M_{sun}_ stars by a factor of ~2. We expect that the AFGK census of the BPMG is also incomplete, probably due to biases of searches toward the nearest stars.
- ID:
- ivo://CDS.VizieR/J/ApJS/153/223
- Title:
- ACS Virgo Cluster Survey. I.
- Short Name:
- J/ApJS/153/223
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Virgo Cluster is the dominant mass concentration in the Local Supercluster and the largest collection of elliptical and lenticular galaxies in the nearby universe. In this paper, we present an introduction to the ACS (Advanced Camera for Surveys) Virgo Cluster Survey: a program to image, in the F475W and F850LP bandpasses (~Sloan g and z), 100 early-type galaxies in the Virgo Cluster using the Advanced Camera for Surveys on the Hubble Space Telescope.
- ID:
- ivo://CDS.VizieR/J/ApJ/655/144
- Title:
- ACS Virgo Cluster Survey. XIII.
- Short Name:
- J/ApJ/655/144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The ACS Virgo Cluster Survey consists of HST-ACS Advance Camera for Surveys) imaging for 100 early-type galaxies in the Virgo Cluster, observed in the F475W (~SDSS g) and F850LP (~SDSS z) filters. We derive distances for 84 of these galaxies using the method of surface brightness fluctuations (SBFs), present the SBF distance catalog, and use this database to examine the three-dimensional distribution of early-type galaxies in the Virgo Cluster. The SBF distance moduli have a mean (random) measurement error of 0.07mag (0.5Mpc), or roughly 3 times better than previous SBF measurements for Virgo Cluster galaxies. Five galaxies lie at a distance of d~23Mpc and are members of the W' cloud. The remaining 79 galaxies have a narrow distribution around our adopted distance of <d>=16.5+/-0.1 (random mean error) +/-1.1Mpc (systematic). The rms distance scatter of this sample is {sigma}(d)=0.6+/-0.1Mpc, with little or no dependence on morphological type or luminosity class (i.e., 0.7+/-0.1 and 0.5+/-0.1Mpc for the giants and dwarfs, respectively). The back-to-front depth of the cluster measured from our sample of early-type galaxies is 2.4+/-0.4Mpc (i.e., +/-2{sigma} of the intrinsic distance distribution). The M87 (cluster A) and M49 (cluster B) subclusters are found to lie at distances of 16.7+/-0.2 and 16.4+/-0.2Mpc, respectively. There may be a third subcluster associated with M86. A weak correlation between velocity and line-of-sight distance may be a faint echo of the cluster velocity distribution not having yet completely virialized. In three dimensions, Virgo's early-type galaxies appear to define a slightly triaxial distribution, with axis ratios of (1:0.7:0.5). The principal axis of the best-fit ellipsoid is inclined ~20{deg}-40{deg} from the line of sight, while the galaxies belonging to the W' cloud lie on an axis inclined by ~10{deg}-15{deg}.
- ID:
- ivo://CDS.VizieR/J/ApJ/850/207
- Title:
- Action dynamics of the Local Supercluster
- Short Name:
- J/ApJ/850/207
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The fully nonlinear gravitationally induced trajectories of a nearly complete set of galaxies, groups, and clusters in the Local Supercluster are constructed in a numerical action method model constrained by data from the CosmicFlows survey and various distance indicators. We add the gravity field due to inhomogeneities external to the sample sphere by making use of larger-scale peculiar flow measurements. Assignments of total masses were made to find the best overall set of mutual attractions, as determined by a goodness criterion based on present-day radial velocities, individually for the Virgo Cluster, M31, and the Milky Way (MW), and via a mass-to-light ratio relationship for other masses. The low median chi-square found indicates that the model fits the present-day velocity flow well, but a slightly high mean chi-square may indicate that some masses underwent complex orbits. The best fit, when setting the value of H_0_ to the CosmicFlows value of 75km/s/Mpc and the WMAP value for {Omega}_m_=0.244 consistent with that H_0_, occurs with the following parameters: {Omega}_orphan_=0.077+/-0.016, M/L_K_=40+/-2L_10_^0.15^M_{sun}_/L_{sun}_ (L_10_ is the K-band luminosity in units of 10^10^L_{sun}_), a Virgo mass of 6.3+/-0.8x10^14^M_{sun}_ (M/L_K_=113+/-15M_{sun}_/L_{sun}_), and a mass for the MW plus M31 of 5.15+/-0.35x10^12^M_{sun}_. The best constant mass-to-light ratio is M/L_K_=58+/-3M_{sun}_/L_{sun}_. The Virgocentric turnaround radius is 7.3+/-0.3Mpc. We explain several interesting trends in peculiar motions for various regions now that we can construct the 3D orbital histories.
- ID:
- ivo://CDS.VizieR/J/A+A/575/A4
- Title:
- Activity and accretion in {gamma} Vel and Cha I
- Short Name:
- J/A+A/575/A4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the fundamental parameters (effective temperature, surface gravity, lithium abundance, and radial velocity) delivered by the GES consortium in the first internal data release to select the members of Gamma Vel and Cha I among the UVES and GIRAFFE spectroscopic observations. A total of 140 Gamma Vel members and 74 Cha I members were studied. The procedure adopted by the GES to derive stellar fundamental parameters provided also measures of the projected rotational velocity (vsini). We calculated stellar luminosities through spectral energy distributions, while stellar masses were derived by comparison with evolutionary tracks. The spectral subtraction of low-activity and slowly rotating templates, which are rotationally broadened to match the vsini of the targets, enabled us to measure the equivalent widths (EWs) and the fluxes in the H{alpha} and H{beta} lines. The H{alpha} line was also used for identifying accreting objects, on the basis of its equivalent width and the width at the 10% of the line peak (10%W), and for evaluating the mass accretion rate (M_acc_). The distribution of vsini for the members of Gamma Vel displays a peak at about 10km/s with a tail toward faster rotators. There is also some indication of a different vsini distribution for the members of its two kinematical populations. Most of these stars have H{alpha} fluxes corresponding to a saturated activity regime. We find a similar distribution, but with a narrower peak, for Cha I. Only a handful of stars in Gamma Vel display signatures of accretion, while many more accretors were detected in the younger Cha I, where the highest H{alpha} fluxes are mostly due to accretion, rather than to chromospheric activity. Accreting and active stars occupy two different regions in a T_eff-flux diagram and we propose a criterion for distinguishing them. We derive M_acc in the ranges 10^-11^-10^-9^M_{sun}_/yr and 10^-10^-10^-7^M_{sun}_/yr for Gamma Vel and Cha I accretors, respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/531/A8
- Title:
- Activity indices and velocities for 890 stars
- Short Name:
- J/A+A/531/A8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work we present chromospheric activity indices, kinematics, radial-velocities, and rotational velocities for more than 850 FGK-type dwarfs and subgiant stars in the southern hemisphere and test how best to calibrate and measure S -indices from echelle spectra. We measured our parameters using the high-resolution and high-S/N FEROS echelle spectra acquired for this purpose. Results. We confirm the bimodal distribution of chromospheric activities for such stars and highlight the role that the more active K-dwarfs play in biasing the number of active stars. We show that the age-activity relationship does appear to continue to ages older than the Sun if we simply compare main sequence stars and subgiant stars with an offset of around 2.5Gyr between the peaks of both distributions. Also we show evidence of an increased spin-down timescale for cool K dwarfs compared with earlier F and G type stars. We highlight that activities drawn from low-resolution spectra (R<2.500') significantly increase the rms scatter when calibrating onto common systems of measurements like the Mt. Wilson system. Also we show that older and widely used catalogues of activities in the south appear to be offset compared to more recent works at the ~0.1dex level in logR'HK through calibrator drift. In addition, we show how kinematics can be used to preselect inactive stars for future planet search projects. We see the well known trend between projected rotational velocity and activity, however we also find a correlation between kinematic space velocity and chromospheric activity. It appears that after the Vaughan-Preston gap there is a quick step function in the kinematic space motion towards a significantly broader spread in velocities. We speculate on reasons for this correlation and provide some model scenarios to describe the bimodal activity distribution through magnetic saturation, residual low level gas accretion, or accretion by the star of planets or planetesimals. Finally, we provide a new empirical measurement for the disk-heating law, using the latest age-activity relationships to reconstruct the age-velocity distribution for local disk stars. We find a value of 0.337+/-0.045 for the exponent of this power law, in excellent agreement with those found using isochrone fitting methods and with theoretical disk-heating models.
- ID:
- ivo://CDS.VizieR/J/other/Ap/62.147
- Title:
- Activity types of ROSAT/SDSS galaxies
- Short Name:
- J/other/Ap/62.14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this study we carry out detailed spectral classification of 173 AGN candidates from the Joint HRC/BHRC sample, which is a combination of HRC (Hamburg-ROSAT Catalogue) and BHRC (Byurakan-Hamburg-ROSAT Catalogue). These objects were revealed as optical counterparts for ROSAT X-ray sources, however spectra for 173 of them are given in SDSS without definite spectral classification. We studied these 173 objects using the SDSS spectra and revealed the detailed activity types for them. Three diagnostic diagrams and direct examination of the spectra were used to have more confident classification. We also made identification of these sources in other wavelength ranges and calculated some of their parameters.
- ID:
- ivo://CDS.VizieR/J/A+A/495/15
- Title:
- A959 galaxies r' magnitude and radial velocities
- Short Name:
- J/A+A/495/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The connection of cluster mergers with the presence of extended, diffuse radio sources in galaxy clusters is still being debated. We aim to obtain new insights into the internal dynamics of Abell 959, showing evidence of a diffuse radio source, analyzing velocities and positions of member galaxies. Our analysis is based on redshift data for 107 galaxies in the cluster field acquired at the Telescopio Nazionale Galileo. We also use photometric data from the Sloan Digital Sky Survey (Data Release 6). We combine galaxy velocities and positions to select 81 galaxies recognized as cluster members and determine global dynamical properties. We analyze the cluster searching for substructures by using the weighted gap analysis, the KMM method and the Dressler-Shectman statistics. We also study the 2D galaxy distribution in the field of the cluster. We compare our results with those from X-ray and gravitational lensing analyses.
