- ID:
- ivo://CDS.VizieR/J/A+A/618/A134
- Title:
- Omega Cen lower red giant stars abundances
- Short Name:
- J/A+A/618/A134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Li, Na, Al and Fe abundances of 199 lower red giant branch stars members of the stellar system Omega Centauri, using high-resolution spectra acquired with FLAMES at the Very Large Telescope. The A(Li) distribution is peaked at A(Li)~1dex with a prominent tail toward lower values. The peak of the distribution well agrees with the lithium abundances measured in lower red giant branch stars in globular clusters and Galactic field stars. Stars with A(Li)~1dex are found at metallicities lower than [Fe/H]~-1.3dex but they disappear at higher metallicities. On the other hand, Li-poor stars are found at all the metallicities. The most metal-poor stars exhibit a clear Li-Na anticorrelation, with about 30% of the sample with A(Li) lower than ~0.8dex, while in normal globular clusters these stars represent a small fraction. Most of the stars with [Fe/H]>-1.6dex are Li-poor and Na-rich. The Li depletion measured in these stars is not observed in globular clusters with similar metallicities and we demonstrate that it is not caused by the proposed helium enhancements and/or young ages. Hence, these stars formed from a gas already depleted in lithium. Finally, we note that Omega Centauri includes all the populations (Li-normal/Na-normal, Li-normal/Na-rich and Li-poor/Na-rich stars) observed, to a lesser extent, in mono-metallic GCs.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/602/L117
- Title:
- Oxygen in Pleiades and M34 dwarfs
- Short Name:
- J/ApJ/602/L117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the high-excitation O I {lambda}7774 triplet in high-resolution, moderate signal-to-noise ratio spectra of 15 Pleiades and eight M34 open cluster dwarfs over the effective temperature range of 5048-6172K. Relative O abundances have been derived using model atmospheres interpolated from four different sets of ATLAS9 grids. In contrast to existing non-LTE (NLTE) predictions, a dramatic increase in the O I triplet abundance with decreasing temperature is seen for both clusters, regardless of the atmospheric model. S I abundances of three Pleiades stars derived from the high-excitation {lambda}6053 feature mimic the O I abundance behavior. O abundances have also been derived from the [O I] {lambda}6300 feature in three Pleiades stars; the abundances exhibit a much lower mean value than do the cool dwarf triplet results. Inasmuch as the [O I] abundances are presumed to be free from NLTE effects, their mean values ([O/H]_6300_=+0.14) provide the current best estimate of the Pleiades O abundance. Spreads in [O/H]_Trip_ at a given temperature are also seen in both clusters; no correlation is found between the spreads and the chromospheric emission measures.
- ID:
- ivo://CDS.VizieR/J/A+A/600/A104
- Title:
- Potassium abundance in 3 globular clusters
- Short Name:
- J/A+A/600/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derived Potassium abundances in red giant branch stars in the Galactic globular clusters NGC 104 (144 stars), NGC 6752 (134 stars) and NGC 6809 (151 stars) using high-resolution spectra collected with FLAMES at the ESO - Very Large Telescope. In the considered samples we do not find significant intrinsic spreads in [K/Fe] (confirming the previous findings by Carretta et al.), at variance with the cases of the massive clusters NGC 2419 and NGC 2808. Additionally, marginally significant [K/Fe]-[O/Fe] anti-correlations are found in NGC 104 and NGC 6809, and [K/Fe]-[Na/Fe] correlations are found in NGC 104 and NGC 6752. No evidence of [K/Fe]-[Mg/Fe] anti-correlation are found. The results of our analysis are consistent with a scenario in which the process leading to the multi-populations in globular clusters implies also enrichment in the K abundance, the amplitude of the associated [K/Fe] enhancement becoming measurable only in stars showing the most extreme effects of O and Mg depletion. Stars enhanced in [K/Fe] have been found so far only in clusters harbouring some Mg-poor stars, while the other globulars, without a Mg-poor sub-population, show small or null [K/Fe] spreads.
- ID:
- ivo://CDS.VizieR/J/ApJ/852/49
- Title:
- Properties of metal-poor stars in APOGEE DR13
- Short Name:
- J/ApJ/852/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We find two chemically distinct populations separated relatively cleanly in the [Fe/H]-[Mg/Fe] plane, but also distinguished in other chemical planes, among metal-poor stars (primarily with metallicities [Fe/H]<-0.9) observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and analyzed for Data Release 13 (DR13) of the Sloan Digital Sky Survey. These two stellar populations show the most significant differences in their [X/Fe] ratios for the {alpha}-elements, C+N, Al, and Ni. In addition to these populations having differing chemistry, the low metallicity high-Mg population (which we denote "the HMg population") exhibits a significant net Galactic rotation, whereas the low-Mg population (or "the LMg population") has halo-like kinematics with little to no net rotation. Based on its properties, the origin of the LMg population is likely an accreted population of stars. The HMg population shows chemistry (and to an extent kinematics) similar to the thick disk, and is likely associated with in situ formation. The distinction between the LMg and HMg populations mimics the differences between the populations of low- and high-{alpha} halo stars found in previous studies, suggesting that these are samples of the same two populations.
- ID:
- ivo://CDS.VizieR/J/ApJ/889/63
- Title:
- Properties of Sgr Stars
- Short Name:
- J/ApJ/889/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using 3D positions and kinematics of stars relative to the Sagittarius (Sgr) orbital plane and angular momentum, we identify 166 Sgr stream members observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) that also have Gaia DR2 astrometry. This sample of 63/103 stars in the Sgr trailing/leading arm is combined with an APOGEE sample of 710 members of the Sgr dwarf spheroidal core (385 of them newly presented here) to establish differences of 0.6dex in median metallicity and 0.1dex in [{alpha}/Fe] between our Sgr core and dynamically older stream samples. Mild chemical gradients are found internally along each arm, but these steepen when anchored by core stars. With a model of Sgr tidal disruption providing estimated dynamical ages (i.e., stripping times) for each stream star, we find a mean metallicity gradient of 0.12+/-0.03dex/Gyr for stars stripped from Sgr over time. For the first time, an [{alpha}/Fe] gradient is also measured within the stream, at 0.02_/-0.01dex/Gyr using magnesium abundances and at 0.04+/-0.01dex/Gyr^ using silicon, which imply that the Sgr progenitor had significant radial abundance gradients. We discuss the magnitude of those inferred gradients and their implication for the nature of the Sgr progenitor within the context of the current family of Milky Way satellite galaxies, and we suggest that more sophisticated Sgr models are needed to properly interpret the growing chemodynamical detail we have on the Sgr system.
- ID:
- ivo://CDS.VizieR/J/A+A/575/A26
- Title:
- Properties of the Population II star HD 140283
- Short Name:
- J/A+A/575/A26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Metal-poor halo stars are important astrophysical laboratories that allow us to unravel details about many aspects of astrophysics, including the chemical conditions at the formation of our Galaxy, understanding the processes of diffusion in stellar interiors, and determining precise effective temperatures and calibration of colour-effective temperature relations. To address any of these issues the fundamental properties of the stars must first be determined. HD 140283 is the closest and brightest metal-poor Population II halo star (distance = 58pc and V=7.21), an ideal target that allows us to approach these questions, and one of a list of 34 benchmark stars defined for Gaia astrophysical parameter calibration. In the framework of characterizing these benchmark stars, we determined the fundamental properties of HD 140283 (radius, mass, age, and effective temperature) by obtaining new interferometric and spectroscopic measurements and combining them with photometry from the literature. The interferometric measurements were obtained using the visible interferometer VEGA on the CHARA array and we determined a 1D limb-darkened angular diameter of {theta}_1D_=0.353+/-0.013-milliarcsec.
- ID:
- ivo://CDS.VizieR/J/ApJ/859/L8
- Title:
- Properties of TriAnd stars
- Short Name:
- J/ApJ/859/L8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nature of the Triangulum-Andromeda (TriAnd) system has been debated since the discovery of this distant, low-latitude Milky Way (MW) overdensity more than a decade ago. Explanations for its origin are either as a halo substructure from the disruption of a dwarf galaxy, or a distant extension of the Galactic disk. We test these hypotheses using the chemical abundances of a dozen TriAnd members from the Sloan Digital Sky Survey-IV's (SDSS-IV's) 14th Data Release (DR14) of Apache Point Observatory Galactic Evolution Experiment (APOGEE) data to compare to APOGEE abundances of stars with similar metallicity from both the Sagittarius (Sgr) dSph and the outer MW disk. We find that TriAnd stars are chemically distinct from Sgr across a variety of elements, (C+N), Mg, K, Ca, Mn, and Ni, with a separation in [X/Fe] of about 0.1 to 0.4dex depending on the element. Instead, the TriAnd stars, with a median metallicity of about -0.8, exhibit chemical abundance ratios similar to those of the lowest metallicity ([Fe/H]~-0.7) stars in the outer Galactic disk, and are consistent with expectations of extrapolated chemical gradients in the outer disk of the MW. These results suggest that TriAnd is associated with the MW disk, and, therefore, that the disk extends to this overdensity-i.e., past a Galactocentric radius of 24kpc-albeit vertically perturbed about 7kpc below the nominal disk midplane in this region of the Galaxy.
- ID:
- ivo://CDS.VizieR/III/134
- Title:
- Radial Velocities of Bright Population II F Stars
- Short Name:
- III/134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalog presents new radial velocity determinations, based on 2nm/mm Coude plates, for 146 southern stars brighter than m(v)=8.3. Drawn from the catalog of uvby-{beta} photometry of southern A5-G0 stars by Olsen (1983, Cat. II/90), the program stars are certain or suspected Population II stars. One triple-lined and 10 double-lined binaries have been detected, including HD 210737, for which a preliminary orbit has been derived. Notes on spectral peculiarities are given. The catalog is in two files. The first file lists HD number, heliocentric Julian date of observation, radial velocity with error and number of lines observed for both the primary and secondary stars, rotation class, and remarks for each observation. The second file contains additional remarks to the data of the first file, sorted by HD number.
- ID:
- ivo://CDS.VizieR/J/BaltA/8/325
- Title:
- Radial velocities of Pop. II stars
- Short Name:
- J/BaltA/8/325
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Population II radial velocity measurement programme was carried out in 1988-1993. Metal-deficient stars, components of Population II visual binaries or common proper motion stars, suspected radial velocity variables, Hipparcos programme stars are included into the observation programme. The measurements were made with the CORAVEL-type photoelectric radial velocity speedometer attached to the 1m reflector at the Mount Maidanak observatory (h=2560m, Uzbekistan). The average error of a single measurement is about 0.6km/s, but for the stars as faint as 13mag, or for extreme metal-deficient stars it drop down to 2.5km/s. 621 measurements for 164 stars are presented.
- ID:
- ivo://CDS.VizieR/J/MNRAS/396/2183
- Title:
- Radial velocities of red giants in {omega} Cen
- Short Name:
- J/MNRAS/396/2183
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a survey of radial velocities over a wide region extending from r~=10 out to 80' (~1.5 tidal radii) within the massive star cluster omega Centauri (omega Cen). The survey was performed with FLAMES@VLT, to study the velocity dispersion profile in the outer regions of this stellar system. We derived accurate radial velocities for a sample of 2557 newly observed stars, identifying 318 bona fide cluster red giants. Merging our data with those provided by our previous survey, we assembled a final homogeneous sample of 946 cluster members that allowed us to trace the velocity dispersion profile from the centre out to r~32'.
