- ID:
- ivo://CDS.VizieR/J/ApJS/230/28
- Title:
- The populations of Carina. II. Abundances
- Short Name:
- J/ApJS/230/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chemical abundances are presented for 19 elements in a sample of 63 red giants in the Carina dwarf spheroidal galaxy (dSph), based on homogeneous 1D/LTE model atmosphere analyses of our own observations (32 stars) and data available in the literature (a further 31 independent stars). The (Fe) metallicity and [{alpha}/Fe] distribution functions have mean values and dispersions of -1.59 and 0.33dex ([Fe/H] range: -2.68 to -0.64) and 0.07 and 0.13dex ([{alpha}/Fe] range: -0.27 to 0.25), respectively. We confirm the finding of Venn+ (2012, J/ApJ/751/102) that a small percentage (some 10% in the present investigation) of the sample shows clear evidence for significant enrichment by Type Ia supernova (SN Ia) ejecta. Calcium, with the most accurately determined abundance of the {alpha}-elements, shows an asymmetric distribution toward smaller values of [Ca/Fe] at all [Fe/H], most significantly over -2.0<[Fe/H]<-1.0, suggestive of incomplete mixing of the ejecta of SNe Ia with the ambient medium of each of Carina's generations. Approximate color-magnitude diagram age estimates are presented for the sample, and together with our chemical abundances, compared with the results of our previous synthetic color-magnitude diagram analysis, which reported the details of Carina's four well-defined populations. We searched for the Na-O anticorrelation universally reported in the Galaxy's globular clusters and confirm that this phenomenon does not exist in Carina. We also found that one of the 32 stars in our sample has an extremely enhanced lithium abundance-A(Li)_NLTE_=+3.36, consistent with membership of the ~1% group of Li-rich stars in dSph described by Kirby+ (2012ApJ...752L..16K).
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Search Results
1712. The R CrB stars
- ID:
- ivo://CDS.VizieR/J/A+A/353/287
- Title:
- The R CrB stars
- Short Name:
- J/A+A/353/287
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Adopted line data, measured equivalent widths and derived elemental abundances for the individual lines observed in R Coronae Borealis and Extreme Helium stars.
- ID:
- ivo://CDS.VizieR/J/A+A/339/165
- Title:
- The red spectrum of HD 101065
- Short Name:
- J/A+A/339/165
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Wavelength list for Przybylski's star (a rapidly rotation Ap star) including a measurement of the line depths.
- ID:
- ivo://CDS.VizieR/J/A+A/624/A94
- Title:
- The role of the host star's metallicity
- Short Name:
- J/A+A/624/A94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Most of our current understanding of the planet formation mechanism is based on the planet metallicity correlation derived mostly from solar-type stars harbouring gas-giant planets. To achieve a more extensive grasp on the substellar formation process, we aim to analyse in terms of their metallicity a diverse sample of stars (in terms of mass and spectral type) covering the whole range of possible outcomes of the planet formation process (from planetesimals to brown dwarfs and low-mass binaries). Our methodology is based on the use of high-precision stellar parameters derived by our own group in previous works from high-resolution spectra by using the iron ionisation and equilibrium conditions. All values were derived in an homogeneous way, except for the M dwarfs where a methodology based on the use of pseudo equivalent widths of spectral features was used. Our results show that as the mass of the substellar companion increases the metallicity of the host star tends to lower values. The same trend is maintained when analysing stars with low-mass stellar companions and a tendency towards a wide range of host star's metallicity is found for systems with low-mass planets. We also confirm that more massive planets tend to orbit around more massive stars. The core-accretion formation mechanism for planet formation achieves its maximum efficiency for planets with masses in the range 0.2 and 2M_{Jup}_. Substellar objects with higher masses have higher probabilities of being formed as stars. Low-mass planets and planetesimals might be formed by core-accretion even around low-metallicity stars.
- ID:
- ivo://CDS.VizieR/J/AJ/155/38
- Title:
- The rotation of M dwarfs observed by APOGEE
- Short Name:
- J/AJ/155/38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a spectroscopic analysis of rotational velocities in 714 M-dwarf stars observed by the SDSS-III Apache Point Galactic Evolution Experiment (APOGEE) survey. We use a template-fitting technique to estimate v sin i while simultaneously estimating log g, [M/H], and T_eff_. We conservatively estimate that our detection limit is 8 km/s. We compare our results to M-dwarf rotation studies in the literature based on both spectroscopic and photometric measurements. Like other authors, we find an increase in the fraction of rapid rotators with decreasing stellar temperature, exemplified by a sharp increase in rotation near the M4 transition to fully convective stellar interiors, which is consistent with the hypothesis that fully convective stars are unable to shed angular momentum as efficiently as those with radiative cores. We compare a sample of targets observed both by APOGEE and the MEarth transiting planet survey and find no cases where the measured v sin i and rotation period are physically inconsistent, requiring sin i>1. We compare our spectroscopic results to the fraction of rotators inferred from photometric surveys and find that while the results are broadly consistent, the photometric surveys exhibit a smaller fraction of rotators beyond the M4 transition by a factor of ~2. We discuss possible reasons for this discrepancy. Given our detection limit, our results are consistent with a bimodal distribution in rotation that is seen in photometric surveys.
- ID:
- ivo://CDS.VizieR/J/ApJ/784/170
- Title:
- The SEGUE K giant survey. II. Distances of 6036 stars
- Short Name:
- J/ApJ/784/170
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an online catalog of distance determinations for 6036 K giants, most of which are members of the Milky Way's stellar halo. Their medium-resolution spectra from the Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding and Exploration are used to derive metallicities and rough gravity estimates, along with radial velocities. Distance moduli are derived from a comparison of each star's apparent magnitude with the absolute magnitude of empirically calibrated color-luminosity fiducials, at the observed (g-r)_0_ color and spectroscopic [Fe/H]. We employ a probabilistic approach that makes it straightforward to properly propagate the errors in metallicities, magnitudes, and colors into distance uncertainties. We also fold in prior information about the giant-branch luminosity function and the different metallicity distributions of the SEGUE K-giant targeting sub-categories. We show that the metallicity prior plays a small role in the distance estimates, but that neglecting the luminosity prior could lead to a systematic distance modulus bias of up to 0.25mag, compared to the case of using the luminosity prior. We find a median distance precision of 16%, with distance estimates most precise for the least metal-poor stars near the tip of the red giant branch. The precision and accuracy of our distance estimates are validated with observations of globular and open clusters. The stars in our catalog are up to 125kpc from the Galactic center, with 283 stars beyond 50kpc, forming the largest available spectroscopic sample of distant tracers in the Galactic halo.
- ID:
- ivo://CDS.VizieR/J/ApJ/816/80
- Title:
- The SEGUE K giant survey. III. Galactic halo
- Short Name:
- J/ApJ/816/80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We statistically quantify the amount of substructure in the Milky Way stellar halo using a sample of 4568 halo K giant stars at Galactocentric distances ranging over 5-125kpc. These stars have been selected photometrically and confirmed spectroscopically as K giants from the Sloan Digital Sky Survey's Sloan Extension for Galactic Understanding and Exploration (SEGUE) project. Using a position-velocity clustering estimator (the 4distance) and a model of a smooth stellar halo, we quantify the amount of substructure in the halo, divided by distance and metallicity. Overall, we find that the halo as a whole is highly structured. We also confirm earlier work using blue horizontal branch (BHB) stars which showed that there is an increasing amount of substructure with increasing Galactocentric radius, and additionally find that the amount of substructure in the halo increases with increasing metallicity. Comparing to resampled BHB stars, we find that K giants and BHBs have similar amounts of substructure over equivalent ranges of Galactocentric radius. Using a friends-of-friends algorithm to identify members of individual groups, we find that a large fraction (~33%) of grouped stars are associated with Sgr, and identify stars belonging to other halo star streams: the Orphan Stream, the Cetus Polar Stream, and others, including previously unknown substructures. A large fraction of sample K giants (more than 50%) are not grouped into any substructure. We find also that the Sgr stream strongly dominates groups in the outer halo for all except the most metal-poor stars, and suggest that this is the source of the increase of substructure with Galactocentric radius and metallicity.
- ID:
- ivo://CDS.VizieR/J/A+A/596/A113
- Title:
- The Seven Sisters DANCe. II. Pleiades
- Short Name:
- J/A+A/596/A113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stellar clusters are open windows to understand stellar evolution. Specifically, the change with time and the dependence on mass of different stellar properties. As such, they are our laboratories where different theories can be tested. We try to understand the origin of the connection between lithium depletion in F, G and K stars, rotation and activity, in particular in the Pleiades open cluster. We have collected all the relevant data in the literature, including information regarding rotation period, binarity and activity, and cross-matched with proper motions, multi-wavelength photometry and membership probability from the DANCe database. In order to avoid biases, only Pleiades single members with probabilities larger than 75% have been included in the discussion. Results. The analysis confirms that there is a strong link between activity, rotation and the lithium equivalent width excess, specially for the range Lum(bol)=0.5-0.2L_{sun}_ (about K2-K7 spectral types or 0.75-0.95M_{sun}_). It is not possible to disentangle these effects but we cannot exclude that the observed lithium overabundance is partially an observational effect due to enhanced activity, due to a large coverage by stellar spots induced by high rotation rates. Since a bona fide lithium enhancement is present in young, fast rotators, both activity and rotation should play a role in the lithium problem.
1719. The solar CNO abundances
- ID:
- ivo://CDS.VizieR/J/A+A/656/A113
- Title:
- The solar CNO abundances
- Short Name:
- J/A+A/656/A113
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Carbon, nitrogen, and oxygen are the fourth, sixth, and third most abundant elements in the Sun. Their abundances remain hotly debated due to the so-called solar modelling problem that has persisted for almost 20 years. We revisit this issue by presenting a homogeneous analysis of 408 molecular lines across 12 diagnostic groups, observed in the solar intensity spectrum. Using a realistic 3D radiative-hydrodynamic model solar photosphere and local thermodynamic equilibrium (LTE) line formation, we find log{epsilon}C=8.47+/-0.02, log{epsilon}N=7.89+/-0.04, and log{epsilon}O=8.70+/-0.04. The stipulated uncertainties mainly reflect the sensitivity of the results to the model atmosphere; this sensitivity is correlated between the different diagnostic groups, which all agree with the mean result to within 0.03dex. For carbon and oxygen, the molecular results are in excellent agreement with our 3D non-LTE analyses of atomic lines. For nitrogen, however, the molecular indicators give a 0.12dex larger abundance than the atomic indicators, and our best estimate of the solar nitrogen abundance is given by the mean: 7.83dex. The solar oxygen abundance advocated here is close to our earlier determination of 8.69dex, and so the present results do not significantly alleviate the solar modelling problem.
- ID:
- ivo://CDS.VizieR/J/A+A/276/389
- Title:
- The spectrum of FG Sge in 1992
- Short Name:
- J/A+A/276/389
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Wavelength measurements and line identifications from the 0.14A/pixel echelle spectra of FG Sge secured two weeks before the drastic dimming of the star in 1992 are presented. The abundances of 18 elements are derived. These abundances have not changed from 1986. The main features of the chemical composition of FG Sge atmosphere are the depletion of iron-group elements and the marked overabundances (up to 3 dex) of s-process elements. First time in the observational history of FG Sge C_2_ Swan bands are identified in its spectrum.
