- ID:
- ivo://CDS.VizieR/J/MNRAS/466/3344
- Title:
- Red-giant stars classification
- Short Name:
- J/MNRAS/466/3344
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Determining the ages of red-giant stars is a key problem in stellar astrophysics. One of the difficulties in this determination is to know the evolutionary state of the individual stars - i.e. have they started to burn Helium in their cores? That is the topic of this paper. Asteroseismic data provide a route to achieving this information. What we present here is a highly autonomous way of determining the evolutionary state from an analysis of the power spectrum of the light curve. The method is fast and efficient and can provide results for a large number of stars. It uses the structure of the dipole-mode oscillations, which have a mixed character in red-giant stars, to determine some measures that are used in the categorization. It does not require that all the individual components of any given mode be separately characterized. Some 6604 red-giant stars have been classified. Of these, 3566 are determined to be on the red-giant branch, 2077 are red-clump and 439 are secondary-clump stars. We do not specifically identify the low-metallicity, horizontal-branch stars. The difference between red-clump and secondary-clump stars is dependent on the manner in which Helium burning is first initiated. We discuss that the way the boundary between these classifications is set may lead to mis-categorization in a small number of stars. The remaining 522 stars were not classified either because they lacked sufficient power in the dipole modes (so-called depressed dipole modes) or because of conflicting values in the parameters.
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- ID:
- ivo://CDS.VizieR/J/AJ/137/4282
- Title:
- Red giant stars in clusters. II. M13 and M92
- Short Name:
- J/AJ/137/4282
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-resolution spectra of 123 red giant stars in the globular cluster M13 and 64 red giant stars in M92 were obtained with Hectochelle at the MMT telescope. Emission and line asymmetries in H{alpha} and CaIIK are identified, characterizing motions in the extended atmospheres and seeking differences attributable to metallicity in these clusters and M15. On the red giant branch, emission in H{alpha} generally appears in stars with T_eff_<~4500K and logL/L_{sun}_>~2.75. Fainter stars showing emission are asymptotic giant branch (AGB) stars or perhaps binary stars. The line-bisector for H{alpha} reveals the onset of chromospheric expansion in stars more luminous than log(L/L_{sun}_)~2.5 in all clusters, and this outflow velocity increases with stellar luminosity. However, the coolest giants in the metal-rich M13 show greatly reduced outflow in H{alpha} most probably due to decreased T_eff_ and changing atmospheric structure. The CaIIK_3_ outflow velocities are larger than shown by H{alpha} at the same luminosity and signal accelerating outflows in the chromospheres. Stars clearly on the AGB show faster chromospheric outflows in H{alpha} than RGB objects. While the H{alpha} velocities on the RGB are similar for all metallicities, the AGB stars in the metal-poor M15 and M92 have higher outflow velocities than in the metal-rich M13. Comparison of these chromospheric line profiles in the paired metal-poor clusters, M15 and M92, shows remarkable similarities in the presence of emission and dynamical signatures, and does not reveal a source of the "second-parameter" effect.
- ID:
- ivo://CDS.VizieR/J/AJ/153/261
- Title:
- Red giant stellar parameters in the LMC bar
- Short Name:
- J/AJ/153/261
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report new spectroscopic observations obtained with the Michigan/Magellan Fiber System of 308 red giants (RGs) located in two fields near the photometric center of the bar of the Large Magellanic Cloud. This sample consists of 131 stars observed in previous studies (in one field) and 177 newly observed stars (in the second field) selected specifically to more reliably establish the metallicity and age distributions of the bar. For each star, we measure its heliocentric line-of-sight velocity, surface gravity, and metallicity from its high-resolution spectrum (effective temperatures come from photometric colors). The spectroscopic Hertzsprung-Russell diagrams- modulo small offsets in surface gravities-reveal good agreement with model isochrones. The mean metallicity of the 177-RG sample is [Fe/H]=-0.76+/-0.02 with a metallicity dispersion {sigma}=0.28+/-0.03. The corresponding metallicity distribution-corrected for selection effects-is well fitted by two Gaussian components: one metal-rich with a mean -0.66+/-0.02 and a standard deviation 0.17+/-0.01, and the other metal-poor with -1.20+/-0.24 and 0.41+/-0.06. The metal-rich and metal-poor populations contain approximately 85% and 15% of stars, respectively. We also confirm that the velocity dispersion in the bar center decreases significantly from 31.2+/-4.3 to 18.7+/-1.9km/s with increasing metallicity over the range -2.09 to -0.38. Individual stellar masses are estimated using the spectroscopic surface gravities and the known luminosities. We find that lower mass, hence older, RGs have larger metallicity dispersion and lower mean metallicity than the higher-mass, younger RGs. The estimated masses, however, extend to implausibly low values (~0.1M_{sun}_), making it impossible to obtain an absolute age-metallicity or age distribution of the bar.
- ID:
- ivo://CDS.VizieR/J/ApJ/617/L41
- Title:
- Red giant variable candidates in UMi dSph
- Short Name:
- J/ApJ/617/L41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed two epochs of Hubble Space Telescope Wide Field Planetary Camera 2 observations of the Ursa Minor dwarf spheroidal galaxy using the HSTphot photometric reduction package. We report the detection of nine faint (M_V_>~0.0mag) red giant variable stars that exhibit low-amplitude brightness fluctuations on 10 minute timescales with amplitudes ranging from 36 to 130mmag.
- ID:
- ivo://CDS.VizieR/J/A+A/547/A15
- Title:
- Red supergiants around Stephenson 2
- Short Name:
- J/A+A/547/A15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Several clusters of red supergiants have been discovered in a small region of the Milky Way close to the base of the Scutum-Crux Arm and the tip of the Long Bar. Population synthesis models indicate that they must be very massive to harbour so many supergiants. Amongst these clusters, Stephenson 2, with a core grouping of 26 red supergiants, is a strong candidate to be the most massive young cluster in the Galaxy. Stephenson 2 is located close to a region where a strong over-density of red supergiants had been found. We explore the actual cluster size and its possible connection to this over-density. Taking advantage of Virtual Observatory tools, we have performed a cross-match between the DENIS, USNO-B1 and 2MASS catalogues to identify candidate obscured luminous red stars around Stephenson 2, and in a control nearby region. More than 600 infrared bright stars fulfill our colour criteria, with the vast majority having a counterpart in the I band and >400 being sufficiently bright in I to allow observation with a 4-m class telescope. We observed a subsample of ~250 stars, using the multi-object, wide-field, fibre spectrograph AF2 on the WHT telescope in La Palma, obtaining intermediate-resolution spectroscopy in the 7500-9000{AA} range. We derived spectral types and luminosity classes for all these objects and measured their radial velocities.
- ID:
- ivo://CDS.VizieR/J/AJ/128/2965
- Title:
- Red variables in the NSVS
- Short Name:
- J/AJ/128/2965
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 8678 slowly varying stars with near-infrared colors corresponding to the evolved asymptotic giant branch population. Objects were selected from the Northern Sky Variability Survey (NSVS, Wozniak et al., 2004AJ....127.2436W) covering the entire sky above declination {delta}=-38{deg} in a single unfiltered photometric band corresponding to a V-band magnitude range of ~8-15.5mag.
- ID:
- ivo://CDS.VizieR/J/other/JAVSO/37.169
- Title:
- Red variable stars in NSVS
- Short Name:
- J/other/JAVSO/37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Candidate variable stars in the publicly available data of the Northern Sky Variability Survey (NSVS) were identified by data mining the 2MASS survey for entries that matched the following criteria: DE>20.000,(J-K)>1.2, and Jmag<7.000. A total of 1233 such stars were identified: 1 type M, 64 type M:, 26 type SR:, and 1142 type L:, with amplitudes between 0.3 magnitude and 3.4 magnitudes. Only stars not listed in the International Variable Star Index (VSX) at the time of submission or not identified as variable in Simbad have been included.
- ID:
- ivo://CDS.VizieR/J/ApJS/211/2
- Title:
- Revised stellar properties of Q1-16 Kepler targets
- Short Name:
- J/ApJS/211/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present revised properties for 196468 stars observed by the NASA Kepler mission and used in the analysis of Quarter 1-16 (Q1-16; May 2009 to Dec 2012) data to detect and characterize transiting planets. The catalog is based on a compilation of literature values for atmospheric properties (temperature, surface gravity, and metallicity) derived from different observational techniques (photometry, spectroscopy, asteroseismology, and exoplanet transits), which were then homogeneously fitted to a grid of Dartmouth stellar isochrones. We use broadband photometry and asteroseismology to characterize 11532 Kepler targets which were previously unclassified in the Kepler Input Catalog (KIC). We report the detection of oscillations in 2762 of these targets, classifying them as giant stars and increasing the number of known oscillating giant stars observed by Kepler by ~20% to a total of ~15500 stars. Typical uncertainties in derived radii and masses are ~40% and ~20%, respectively, for stars with photometric constraints only, and 5%-15% and ~10% for stars based on spectroscopy and/or asteroseismology, although these uncertainties vary strongly with spectral type and luminosity class. A comparison with the Q1-Q12 catalog shows a systematic decrease in radii of M dwarfs, while radii for K dwarfs decrease or increase depending on the Q1-Q12 provenance (KIC or Yonsei-Yale isochrones). Radii of F-G dwarfs are on average unchanged, with the exception of newly identified giants. The Q1-Q16 star properties catalog is a first step toward an improved characterization of all Kepler targets to support planet-occurrence studies.
- ID:
- ivo://CDS.VizieR/J/ApJ/889/177
- Title:
- RGB abundances in the disk, stream & halo of M31
- Short Name:
- J/ApJ/889/177
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We measured [Fe/H] and [{alpha}/Fe] using spectral synthesis of low-resolution stellar spectroscopy for 70 individual red-giant-branch stars across four fields spanning the outer disk, Giant Stellar Stream (GSS), and inner halo of M31. Fields at M31-centric projected distances of 23kpc in the halo, 12kpc in the halo, 22kpc in the GSS, and 26kpc in the outer disk are {alpha}-enhanced, with <[{alpha}/Fe]>=0.43, 0.50, 0.41, and 0.58, respectively. The 23 and 12kpc halo fields are relatively metal-poor, with <[Fe/H]>=-1.54 and -1.30, whereas the 22kpc GSS and 26kpc outer disk fields are relatively metal-rich with <[Fe/H]>=-0.84 and -0.92, respectively. For fields with substructure, we separated the stellar populations into kinematically hot stellar halo components and kinematically cold components. We did not find any evidence of a radial [{alpha}/Fe] gradient along the high surface brightness core of the GSS between ~17 and 22kpc. However, we found tentative suggestions of a negative radial [{alpha}/Fe] gradient in the stellar halo, which may indicate that different progenitor(s) or formation mechanisms contributed to the build up of the inner versus outer halo. Additionally, the [{alpha}/Fe] distribution of the metal-rich ([Fe/H]>-1.5), smooth inner stellar halo (r_proj_<~26kpc) is inconsistent with having formed from the disruption of a progenitor(s) similar to present-day M31 satellite galaxies. The 26kpc outer disk is most likely associated with the extended disk of M31, where its high {alpha}-enhancement provides support for an episode of rapid star formation in M31's disk possibly induced by a major merger.
- ID:
- ivo://CDS.VizieR/J/AJ/155/71
- Title:
- RGB & HB members of the bulge cluster NGC 6569
- Short Name:
- J/AJ/155/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photometric and spectroscopic analyses have shown that the Galactic bulge cluster Terzan 5 hosts several populations with different metallicities and ages that manifest as a double red horizontal branch (HB). A recent investigation of the massive bulge cluster NGC 6569 revealed a similar, though less extended, HB luminosity split, but little is known about the cluster's detailed chemical composition. Therefore, we have used high-resolution spectra from the Magellan-M2FS and VLT-FLAMES spectrographs to investigate the chemical compositions and radial velocity distributions of red giant branch and HB stars in NGC 6569. We found the cluster to have a mean heliocentric radial velocity of -48.8 km/s ({sigma}=5.3 km/s; 148 stars) and <[Fe/H]>=-0.87 dex (19 stars), but the cluster's 0.05 dex [Fe/H] dispersion precludes a significant metallicity spread. NGC 6569 exhibits light- and heavy-element distributions that are common among old bulge/inner Galaxy globular clusters, including clear (anti)correlations between [O/Fe], [Na/Fe], and [Al/Fe]. The light-element data suggest that NGC 6569 may be composed of at least two distinct populations, and the cluster's low <[La/Eu]>=-0.11 dex indicates significant pollution with r-process material. We confirm that both HBs contain cluster members, but metallicity and light-element variations are largely ruled out as sources for the luminosity difference. However, He mass fraction differences as small as {Delta}Y~0.02 cannot be ruled out and may be sufficient to reproduce the double HB.
