- ID:
- ivo://CDS.VizieR/J/ApJ/479/427
- Title:
- Abundance Analyses of RV Tauri Variables
- Short Name:
- J/ApJ/479/427
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Analyses of the photospheric compositions of the four field RV Tauri stars, EP Lyr, DY Ori, AR Pup, and R Sge, indicate that to varying degrees they have experienced fractionation processes that have preferentially depleted their atmospheres of elements with high condensation temperatures. The depletion, as indicated by, for instance, [S/Fe], is greatest for DY Ori, [S/Fe]=2.5, and least for R Sge, [S/Fe]=0.9. The initial composition, presumably indicated by the sulfur abundance, was nearly solar for AR Pup, R Sge, and DY Ori, while it was about 0.6--- less than solar for EP Lyr. This implies that the RV Tauri stars as a group may not be as metal-poor as previously thought---they are instead ``metal-depleted''. The field RV Tauri's are not halo stars, but probably belong to the thick disk. This brings to seven the number of type II Cepheids that show such a trend; the other three are IW Car and V1 in omega Cen, RV Tauri stars, and ST Pup, a W Virginis star. The 12C/13C ratios for EP Lyr and DY Ori are 9+/-1 and 6+/-3, respectively, indicating that CN-cycled material has been mixed with their surface layers. This is consistent with the general consensus that RV Tau stars are in a post-AGB evolutionary stage. There is also evidence that EP Lyr has a stellar mass companion, but additional observations are required to calculate an orbit; hence, EP Lyr could be a link to the group of metal-depleted, high-latitude A-F supergiants, all of which are binaries.
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- ID:
- ivo://CDS.VizieR/J/ApJ/865/129
- Title:
- Abundance analysis of HD 222925
- Short Name:
- J/ApJ/865/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed abundance analysis of the bright (V=9.02), metal-poor ([Fe/H]=-1.47+/-0.08) field red horizontal-branch star HD222925, which was observed as part of an ongoing survey by the R-Process Alliance. We calculate stellar parameters and derive abundances for 46 elements based on 901 lines examined in a high-resolution optical spectrum obtained using the Magellan Inamori Kyocera Echelle spectrograph. We detect 28 elements with 38<=Z<=90; their abundance pattern is a close match to the solar r-process component. The distinguishing characteristic of HD222925 is an extreme enhancement of r-process elements ([Eu/Fe]=+1.33+/-0.08, [Ba/Eu]=-0.78+/-0.10) in a moderately metal-poor star, so the abundance of r-process elements is the highest ([Eu/H]=-0.14+/-0.09) in any known r-process-enhanced star. The abundance ratios among lighter (Z<=30) elements are typical for metal-poor stars, indicating that production of these elements was dominated by normal Type II supernovae, with no discernible contributions from Type Ia supernovae or asymptotic giant branch stars. The chemical and kinematic properties of HD 222925 suggest it formed in a low-mass dwarf galaxy, which was enriched by a high-yield r-process event before being disrupted by interaction with the Milky Way.
- ID:
- ivo://CDS.VizieR/J/AJ/110/2319
- Title:
- Abundances in RR Lyr variables
- Short Name:
- J/AJ/110/2319
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used moderately high-resolution, high S/N spectra to study the chemical composition of ten field ab-type RR Lyrae stars. Variables having accurate photometric and radial-velocity data were selected, in order to derive a precise estimate of the atmospheric parameters independently of excitation and ionization equilibria. A new temperature scale was determined from literature "Infrared Flux Method" measures of subdwarfs and the Kurucz (1992) (priv. com.) model atmospheres, and used to calibrate colors for both dwarfs and RR Lyraes. Photometric reddening estimates for the program stars were carefully examined, and compared with other determinations. The applicability of Kurucz (1992) (priv. com.) model atmospheres in the analysis of RR Lyraes at minimum light was analyzed: we found that they are able to reproduce colors, excitation, and ionization equilibria as well as the wings of Halpha. The comparison solar abundances were carefully determined. From a new analysis of weak Fe I lines with accurate gfs [Bard & Kock, A&A, 282, 1014 (1994)] we derived log epsilon(Fe)_Sun=7.52, in agreement with the Fe abundances determined from meteorites and Fe II lines. We derived abundances for 21 species. Main results are: The metal abundances of the program stars span the range -2.50<[Fe/H]<+0.17. Lines of most elements are found to form in LTE conditions. Fe lines satisfy very well the excitation and ionization equilibria. A comparison with statistical equilibrium computations shows that rather large collisional cross sections are required to reproduce observations. If these cross sections are then used in the analysis of the formation of Fe lines in subdwarfs and RGB stars, no significant departures from LTE are found for these stars, thus validating the very numerous LTE analyses. RR Lyraes share the typical abundance pattern of other stars of similar [Fe/H]: alpha-elements are overabundant by ~0.4dex and Mn is underabundant by ~0.6dex in stars with [Fe/H]<-1. Solar scaled abundances are found for most of the other species, except for the low Ba abundance in the extremely metal-poor star X Ari ([Fe/H]~-2.5). Significant departures from LTE are found for a few species: Nd II, Ce II, Y II, and Sc II are severely underabundant (~0.5dex) in metal-rich variables; Ti I and Cr I are slightly (~0.1-0.2dex) underabundant in metal-poor stars. These effects are attributed to overionization. We suggest that the photoionization of the alkaline earth-like ions is due to Lyman lines emission produced by the shock waves that propagate in the atmosphere of these variables [Fokin (1992MNRAS.256...26F)]. Departures from LTE were considered in detail in the derivation of abundances for the light elements (O and Na). Significant corrections were required for the O I IR triplet and the Na D lines. The resulting pattern reproduces that observed in less evolved field stars. We did not find any evidence for an O-Na anticorrelation among these field HB stars, suggesting that the environment is likely to be responsible for the anticorrelation found in metal-poor globular cluster stars [Sneden et al. =1992AJ....104.2121S]. We used our new [Fe/H] abundances, as well as values from Butler and co-workers (corrected to our system), and from high- resolution spectroscopy of globular clusters giants, to obtain a revised calibration of the low-resolution metallicity index Delta(S) [Preston =1959ApJ...130..507P]: [Fe/H]=-0.194(+/-0.011)Delta(S)-0.08(+/-0.18). Our new metallicity scale is stretched on both low and high metallicity ends with respect to Butler's [1975ApJ...200...68B]. The error in [Fe/H] by Delta(S) observations is 0.16dex, well of the same order of high-resolution metallicity determinations. The slope of the calibration obtained considering only stars with 4<Delta(S)<10 is slightly smaller than that obtained using all stars. While this difference is only barely significant, it might point out the presence of a nonlinearity of the Delta(S) vs [Fe/H] relation, as suggested by Manduca [ApJ, 245, 258 (1981)]. The new [Fe/H] values were used to update the metallicity calibration of the Ca II K line index [Clementini et al. =1991AJ....101.2168C]. Using the present new metallicities, and W'(K) values and relative errors from Clementini et al. (1991), a least-squares fit weighted both in W'(K) and [Fe/H] gives [Fe/H]=0.65(+/-0.17)W'(K)-3.49(+/-0.39). Finally, our new metallicity scale was used to revise the metallicity dependence of the absolute magnitude of RR Lyrae stars, M_V. Using M_V values from Fernley [1994A&A...284L..16F] for the field stars, and estimates from Liu & Janes [1990ApJ...360..561L] and Storm et al. [1994A&A...290..443S] for the cluster variables, we found M_V=0.20(+/-0.03) [Fe/H]+1.06(+/-0.04) and M_V=0.19(+/-0.03)[Fe/H]+0.96(+/-0.04), the last being obtained by using M_V estimates derived for a value of the conversion factor between observed and true pulsation velocity p=1.38 (Fernley 1994). The adoption of the new metallicity scale does not yield significant changes in the slope or zero point of the M_V vs [Fe/H] relation. Observations do not rule out the possibility that the slope of the M_V vs [Fe/H] relation might be different for metal-poor and metal-rich variables. However, a larger sample of Baade-Wesselink M_V determinations is required to definitely settle this question.
- ID:
- ivo://CDS.VizieR/J/ApJ/865/44
- Title:
- Abundances of evolved stars from IGRINS. I.
- Short Name:
- J/ApJ/865/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have derived elemental abundances of three field red horizontal branch stars using high-resolution (R~45000), high signal-to-noise ratio (S/N>~200) H- and K-band spectra obtained with the Immersion Grating Infrared Spectrograph (IGRINS). We have determined the abundances of 21 elements, including {alpha} (Mg, Si, Ca, S), odd-Z (Na, Al, P, K), Fe-group (Sc, Ti, Cr, Co, Ni), neutron-capture (Ce, Nd, Yb), CNO-group elements. S, P, and K are determined for the first time in these stars. H- and K-band spectra provide a substantial number of S I lines, which potentially can lead to a more robust exploration of the role of sulfur in the cosmochemical evolution of the Galaxy. We have also derived ^12^C/^13^C ratios from synthetic spectra of the first-overtone ^12^CO (2-0) and (3-1) and ^13^CO (2-0) lines near 23440{AA} and ^13^CO (3-1) lines at about 23730{AA}. Comparison of our results with the ones obtained from the optical region suggests that the IGRINS high-resolution H- and K-band spectra offer more internally self-consistent line abundances of the same species for several elements, especially the {alpha}-elements. This in turn provides more reliable abundances for the elements with analytical difficulties in the optical spectral range.
- ID:
- ivo://CDS.VizieR/J/A+A/493/913
- Title:
- Abundances of 9 HB stars in NGC 6352
- Short Name:
- J/A+A/493/913
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Metal-rich globular clusters provide important tracers of the formation of our Galaxy. Moreover, and not less important, they are very important calibrators for the derivation of properties of extra-galactic metal-rich stellar populations. Nonetheless, only a few of the metal-rich globular clusters in the Milky Way have been studied using high-resolution stellar spectra to derive elemental abundances. Additionally, Rosenberg et al. identified a small group of metal-rich globular clusters that appeared to be about 2 billion years younger than the bulk of the Milky Way globular clusters. However, it is unclear if like is compared with like in this dataset as we do not know the enhancement of alpha-elements in the clusters and the amount of alpha-elements is well known to influence the derivation of ages for globular clusters. We present a study of elemental abundances for alpha and iron-peak elements for nine HB stars in the metal-rich globular cluster NGC 6352. The elemental abundances are based on high-resolution, high signal-to-noise spectra obtained with the UVES spectrograph on VLT. The elemental abundances have been derived using standard LTE calculations and stellar parameters have been derived from the spectra themselves by requiring ionizational as well as excitational equilibrium. We find that NGC 6352 has [Fe/H]=-0.55, is enhanced in the alpha-elements to about +0.2dex for Ca, Si, and Ti relative to Fe. For the iron-peak elements we find solar values. Based on the spectroscopically derived stellar parameters we find that an E(B-V)=0.24 and (m-M).
- ID:
- ivo://CDS.VizieR/J/A+A/431/933
- Title:
- Abundances of NGC 7789 evolved stars
- Short Name:
- J/A+A/431/933
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-resolution spectra of six giants and three core-helium-burning "clump" stars in the open cluster NGC 7789 have been obtained with the SOFIN spectrograph on the Nordic Optical Telescope to investigate abundances of up to 20 chemical elements. Abundances of carbon were studied using the C_2_ Swan (0, 1) band head at 5635.5{AA}. The wavelength interval 7980-8130{AA} with strong CN features was analysed in order to determine nitrogen abundances and ^12^C/^13^C isotope ratios. The oxygen abundances were determined from the [O I] line at 6300{AA}.
- ID:
- ivo://CDS.VizieR/J/AJ/140/1694
- Title:
- Abundances of non-variable red and blue HB stars
- Short Name:
- J/AJ/140/1694
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new detailed abundance study of field red horizontal branch (RHB) and blue horizontal branch (BHB) non-variable stars. High resolution and high signal-to-noise ratio echelle spectra of 11 RHB and 12 BHB were obtained with the McDonald 2.7m telescope, and the RHB sample was augmented by reanalysis of spectra of 25 stars from a recent survey. We derived stellar atmospheric parameters based on spectroscopic constraints and computed relative abundance ratios for 24 species of 19 elements.
- ID:
- ivo://CDS.VizieR/J/MNRAS/416/L6
- Title:
- AGB and RGB stars in {omega} Cen
- Short Name:
- J/MNRAS/416/L6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We herein determine the average integrated mass-loss from stars belonging to the dominant metal-poor population ([Fe/H]~-1.7) of the Galactic globular cluster {omega} Centauri (NGC 5139) during their red giant and horizontal branch (HB) evolution.
- ID:
- ivo://CDS.VizieR/J/AJ/155/240
- Title:
- A spectroscopic survey of field RHB stars
- Short Name:
- J/AJ/155/240
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A metallicity, chemical composition, and kinematic survey has been conducted for a sample of 340 candidate field red horizontal-branch (RHB) stars. Spectra with high resolution and high signal-to-noise ratio were gathered with the McDonald Observatory 2.7 m Tull and the Hobby-Eberly Telescope echelle spectrographs, and were used to determine effective temperatures, surface gravities, microturbulent velocities, [Fe/H] metallicities, and abundance ratios [X/Fe] for seven {alpha} and Fe-group species. The derived temperatures and gravities confirm that at least half of the candidates are true RHB stars, with (average) parameters T_eff_~5000 K and log g~2.5. From the {alpha} abundances alone, the thin and thick Galactic populations are apparent in our sample. Space motions for 90% of the program stars were computed from Hipparcos and Gaia parallaxes and proper motions. Correlations between chemical compositions and Galactic kinematics clearly indicate the existence of both thin-disk and thick-disk RHB stars.
- ID:
- ivo://CDS.VizieR/J/AJ/157/153
- Title:
- Atomic lines in spectra of RR Lyrae & RHB stars
- Short Name:
- J/AJ/157/153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have derived relations between FWHMs and equivalent widths of metallic absorption lines in the spectra of RR Lyrae stars to estimate new upper limits on the axial equatorial rotational velocities of RR Lyrae and metal-poor red horizontal branch (RHB) stars. We have also derived the variations of RR Lyrae macroturbulent velocities during the pulsation cycles. In RRab cycles, the line widths are dominated by phase-dependent convolutions of axial rotation and macroturbulence, which we designate as V_macrot_. The behavior of V_macrot_ is remarkably uniform among the RRab stars, but the behavior of V_macrot_ among RRc stars varies strongly from star to star. The RRab stars exhibit an upper limit on V_macrot_ of 5+/-1 km/s with weak evidence of an anticorrelation with T_eff_. The RRc minima range from 2 to 12 km/s. The abrupt decline in large rotations with decreasing T_eff_ at the blue boundary of the instability strip and the apparently smooth continuous variation among the RRab and RHB stars suggests that HB stars gain/lose surface angular momentum on timescales that are short compared to HB lifetimes. The V_macrot_ values for our metal-poor RHB stars agree well with those derived by Fourier analysis of an independent but less metal-poor sample of Carney et al. (2008AJ....135..892C); they conform qualitatively to the expectations of Tanner et al. (2013ApJ...778..117T). A general conclusion of our investigation is that surface angular momentum as measured by V_rot_sin(i) is not a reliable indicator of total stellar angular momentum anywhere along the HB.
