- ID:
- ivo://CDS.VizieR/J/A+A/435/1087
- Title:
- Nebular abundances of southern symbiotic stars
- Short Name:
- J/A+A/435/1087
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have calculated relative element abundances for a sample of 43 symbiotic stars. Helium abundances and the relative elemental abundances N/O, Ne/O, Ar/O were derived from new spectra collected in the optical range through low dispersion spectroscopy. The He ionic abundances were derived taking into account self-absorption effects in Balmer lines. We found that the symbiotic stars in the galactic bulge have heavy element abundances showing the same wide distribution as other bulge objects. In the galactic disk, the symbiotic stars follow the abundance gradient as derived from different kinds of objects.
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- ID:
- ivo://CDS.VizieR/J/PASP/124/164
- Title:
- New lithium measurements in metal-poor stars
- Short Name:
- J/PASP/124/164
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We provide {lambda}6708 LiI measurements in 37 metal-poor stars, most of which are poorly studied or have no previous measurements, from high-resolution and high-S/N spectroscopy obtained with the McDonald Observatory 2.1m and 2.7m telescopes.
- ID:
- ivo://CDS.VizieR/J/ApJ/847/16
- Title:
- NLTE spectroscopy. II. Galactic metal-poor stars
- Short Name:
- J/ApJ/847/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From exploratory studies and theoretical expectations it is known that simplifying approximations in spectroscopic analysis (local thermodynamic equilibrium (LTE), 1D) lead to systematic biases of stellar parameters and abundances. These biases depend strongly on surface gravity, temperature and, in particular, for LTE versus non-LTE (NLTE), on metallicity of the stars. Here we analyze the [Mg/Fe] and [Fe/H] plane of a sample of 326 stars, comparing LTE and NLTE results obtained using 1D hydrostatic models and averaged <3D> models. We show that compared to the <3D> NLTE benchmark, the other three methods display increasing biases toward lower metallicities, resulting in false trends of [Mg/Fe] against [Fe/H], which have profound implications for interpretations by chemical evolution models. In our best <3D> NLTE model, the halo and disk stars show a clearer behavior in the [Mg/Fe]-[Fe/H] plane, from the knee in abundance space down to the lowest metallicities. Our sample has a large fraction of thick disk stars and this population extends down to at least [Fe/H]~-1.6dex, further than previously proven. The thick disk stars display a constant [Mg/Fe]~0.3dex, with a small intrinsic dispersion in [Mg/Fe] that suggests that a fast SN Ia channel is not relevant for the disk formation. The halo stars reach higher [Mg/Fe] ratios and display a net trend of [Mg/Fe] at low metallicities, paired with a large dispersion in [Mg/Fe]. These indicate the diverse origin of halo stars from accreted low-mass systems to stochastic/inhomogeneous chemical evolution in the Galactic halo.
- ID:
- ivo://CDS.VizieR/J/ApJ/891/28
- Title:
- N-rich field stars from LAMOST and APOGEE data
- Short Name:
- J/ApJ/891/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Interesting chemically peculiar field stars may reflect their stellar evolution history and their possible origin in a different environment from where they are found now; this is one of the most important research fields in Galactic archeology. To explore this further, we have used the CN-CH bands around 4000{AA} to identify N-rich metal-poor field stars in LAMOST DR3. Here we expand our N-rich, metal-poor field star sample to ~100 stars in LAMOST DR5, where 53 of them are newly found in this work. We investigate light elements of common stars between our sample and APOGEE DR14. While Mg, Al, and Si abundances generally agree with the hypothesis that N-rich metal-poor field stars come from enriched populations in globular clusters, it is still inconclusive for C, N, and O. After integrating the orbits of our N-rich field stars and a control sample of normal metal-poor field stars, we find that N-rich field stars have different orbital parameter distributions compared to the control sample-specifically, apocentric distances, maximum vertical amplitude (Zmax), orbital energy, and z-direction angular momentum (Lz). The orbital parameters of N-rich field stars indicate that most of them are inner-halo stars. The kinematics of N-rich field stars support their possible GC origin. The spatial and velocity distributions of our bona fide N-rich field star sample are important observational evidence to constrain simulations of the origin of these interesting objects.
- ID:
- ivo://CDS.VizieR/J/ApJ/595/1154
- Title:
- Oxygen abundances in metal-poor stars
- Short Name:
- J/ApJ/595/1154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present oxygen abundances derived from both the permitted and forbidden oxygen lines for 54 subgiants and giants with [Fe/H] values between -2.7 and solar with the goal of understanding the discrepancy in the derived abundances. A first attempt, using Teff values from photometric calibrations and surface gravities from luminosities obtained agreement between the indicators for turn-off stars, but the disagreement was large for evolved stars. We find that the difference in the oxygen abundances derived from the permitted and forbidden lines is most strongly affected by Teff, and we derive a new Teff scale based on forcing the two sets of lines to give the same oxygen abundances. These new parameters, however, do not agree with other observables, such as theoretical isochrones or Balmer-line profile based Teff determinations. Our analysis finds that one-dimensional, LTE analyses (with published non-LTE corrections for the permitted lines) cannot fully resolve the disagreement in the two indicators without adopting a temperature scale that is incompatible with other temperature indicators. We also find no evidence of circumstellar emission in the forbidden lines, removing such emission as a possible cause for the discrepancy.
- ID:
- ivo://CDS.VizieR/J/AJ/159/254
- Title:
- Parameters for 453 metal-poor stars in NGC5139
- Short Name:
- J/AJ/159/254
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The most massive and complex globular clusters in the Galaxy are thought to have originated as the nuclear cores of now tidally disrupted dwarf galaxies, but the connection between globular clusters and dwarf galaxies is tenuous with the M54/Sagittarius system representing the only unambiguous link. The globular cluster Omega Centauri ({omega}Cen) is more massive and chemically diverse than M54, and is thought to have been the nuclear star cluster of either the Sequoia or Gaia-Enceladus galaxy. Local Group dwarf galaxies with masses equivalent to these systems often host significant populations of very metal-poor stars ([Fe/H]<-2.5), and one might expect to find such objects in {omega}Cen. Using high-resolution spectra from Magellan-M2FS, we detected 11 stars in a targeted sample of 395 that have [Fe/H] ranging from -2.30 to -2.52. These are the most metal-poor stars discovered in the cluster, and are five times more metal-poor than {omega}Cen's dominant population. However, these stars are not so metal-poor as to be unambiguously linked to a dwarf galaxy origin. The cluster's metal-poor tail appears to contain two populations near [Fe/H]~-2.1 and -2.4, which are very centrally concentrated but do not exhibit any peculiar kinematic signatures. Several possible origins for these stars are discussed.
- ID:
- ivo://CDS.VizieR/J/PASP/103/973
- Title:
- Photoelectric UBV from HK survey. II.
- Short Name:
- J/PASP/103/973
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photoelectric UBV photometry is presented for a sample of 165 stars drawn from the extension of the HK objective-prism/interference-filter survey of Beers, Preston and Shectman (1985AJ.....90.2089B) to the northern galactic hemisphere. These results are part of continuing follow-up observations of candidate metal-deficient and horizontal-branch field stars and other interesting stars identified in the survey. A complete set of photometric observations is now available for three of the 25-square-degree survey fields. We estimate that the complete photometric sample of 299 northern HK candidates obtained to date contains on order 90 main-sequences turnoff, subgiant, and giant stars with [Fe/H]<=-1.0, 50 field blue horizontal-branch stars, and 30 stars with the photometric properties of field blue stragglers.
- ID:
- ivo://CDS.VizieR/J/A+A/651/A102
- Title:
- Photometry of M31 globular cluster EXT8
- Short Name:
- J/A+A/651/A102
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We recently found the globular cluster (GC) EXT8 in M31 to have an extremely low metallicity of [Fe/H]=-2.91+/-0.04 using high-resolution spectroscopy. Here we present a colour-magnitude diagram (CMD) for EXT8, obtained with the Wide Field Camera 3 on board the Hubble Space Telescope. Compared with the CMDs of metal-poor Galactic GCs, we find that the upper red giant branch (RGB) of EXT8 is about 0.03mag bluer in F606W-F814W and slightly steeper, as expected from the low spectroscopic metallicity. The observed colour spread on the upper RGB is consistent with being caused entirely by the measurement uncertainties, and we place an upper limit of sigma(F606W-F814W)=0.015mag on any intrinsic colour spread. The corresponding metallicity spread can be up to sigma([Fe/H])=0.2dex or >0.7dex, depending on the isochrone library adopted. The horizontal branch (HB) is located mostly on the blue side of the instability strip and has a tail extending to at least M(F606W)=+3, as in the Galactic GC M15. We identify two candidate RR Lyrae variables and several UV-luminous post-HB/post-AGB star candidates, including one very bright (M(F300X)=-3.2) source near the centre of EXT8. The surface brightness of EXT8 out to a radius of 25 arcsec is well fitted by a Wilson-type profile with an ellipticity of epsilon=0.20, a semi-major axis core radius of 0.25", and a central surface brightness of 15.2mag per square arcsec in the F606W band, with no evidence of extra-tidal structure. Overall, EXT8 has properties consistent with it being a "normal", but very metal-poor GC, and its combination of relatively high mass and very low metallicity thus remains challenging to explain in the context of GC formation theories operating within the hierarchical galaxy assembly paradigm.
- ID:
- ivo://CDS.VizieR/J/ApJ/697/544
- Title:
- Planets orbiting metal-poor dwarfs. II.
- Short Name:
- J/ApJ/697/544
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of three years of precision radial velocity (RV) measurements of 160 metal-poor stars observed with HIRES on the Keck 1 telescope. We report on variability and long-term velocity trends for each star in our sample. We identify several long-term, low-amplitude RV variables worthy of followup with direct imaging techniques. We place lower limits on the detectable companion mass as a function of orbital period. Our survey would have detected, with a 99.5% confidence level, over 95% of all companions on low-eccentricity orbits with velocity semiamplitude K>~100m/s, or M_p_sini>~3.0M_J_(P/yr)^(1/3)^, for orbital periods P<~3yr. None of the stars in our sample exhibits RV variations compatible with the presence of Jovian planets with periods shorter than the survey duration.
- ID:
- ivo://CDS.VizieR/J/AN/338/686
- Title:
- Pristine survey II. Bright stars abundances
- Short Name:
- J/AN/338/686
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Extremely metal-poor (EMP) stars are old objects formed in the first Gyr of the Universe. They are rare and, to select them the most successful strategy has been to build on large and low-resolution spectroscopic surveys. The combination of narrow- and broad-band photometry provides a powerful and cheaper alternative to select metal-poor stars. The ongoing Pristine Survey is adopting this strategy, conducting photometry with the Canada France Hawaii Telescope MegaCam wide-field imager and a narrow-band filter centered at 395.2nm on the Ca II-H and -K lines. In this paper, we present the results of the spectroscopic follow-up conducted on a sample of 26 stars at the bright end of the magnitude range of the Survey (g<=15), using FEROS at the MPG/ESO 2.2-m telescope (manufactured by Zeiss, Oberkochen, Germany). From our chemical investigation on the sample, we conclude that this magnitude range is too bright to use the Sloan Digital Sky Survey (SDSS) gri bands, which are typically saturated. Instead, the Pristine photometry can be usefully combined with the AAVSO Photometric All Sky Survey (APASS) gri photometry to provide reliable metallicity estimates. Data from FEROS.
