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1601. Metallicity of solar-type stars
ID:
ivo://CDS.VizieR/J/A+A/541/A40
Title:
Metallicity of solar-type stars
Short Name:
J/A+A/541/A40
Date:
21 Oct 2021
Publisher:
CDS
Description:
Around 16% of the solar-like stars in our neighbourhood show IR-excesses due to dusty debris discs and a fraction of them are known to host planets. Determining whether these stars follow any special trend in their properties is important to understand debris disc and planet formation. We aim to determine in a homogeneous way the metallicity of a sample of stars with known debris discs and planets. We attempt to identify trends related to debris discs and planets around solar-type stars Our analysis includes the calculation of the fundamental stellar parameters Teff, logg, microturbulent velocity, and metallicity by applying the iron ionisation equilibrium conditions to several isolated FeI and FeII lines. High-resolution echelle spectra (R~57000) from 2, 3m class telescopes are used. Our derived metallicities are compared with other results in the literature, which finally allows us to extend the stellar samples in a consistent way.
1602. Metallicity of the {gamma} Vel cluster
ID:
ivo://CDS.VizieR/J/A+A/567/A55
Title:
Metallicity of the {gamma} Vel cluster
Short Name:
J/A+A/567/A55
Date:
21 Oct 2021
Publisher:
CDS
Description:
Knowledge of the abundance distribution of star forming regions and young clusters is critical to investigate a variety of issues, from triggered star formation and chemical enrichment by nearby supernova explosions to the ability to form planetary systems. In spite of this, detailed abundance studies are currently available for relatively few regions. In this context, we present the analysis of the metallicity of the Gamma Velorum cluster, based on the products distributed in the first internal release of the Gaia-ESO Survey. The Gamma Velorum candidate members have been observed with FLAMES, using both UVES and Giraffe, depending on the target brightness and spectral type. In order to derive a solid metallicity determination for the cluster, membership of the observed stars must be first assessed. To this aim, we use several membership criteria including radial velocities, surface gravity estimates, and the detection of the photospheric lithium line. Out of the 80 targets observed with UVES, we identify 14 high-probability members. We find that the metallicity of the cluster is slightly sub-solar, with a mean [Fe/H]=-0.057+/-0.018dex. Although J08095427-4721419 is one of the high-probability members, its metallicity is significantly larger than the cluster average. We speculate about its origin as the result of recent accretion episodes of rocky bodies of about 60 Msun hydrogen-depleted material from the circumstellar disc.
1603. Metallicity profile of M31 HII regions and PNe
ID:
ivo://CDS.VizieR/J/ApJ/758/133
Title:
Metallicity profile of M31 HII regions and PNe
Short Name:
J/ApJ/758/133
Date:
21 Oct 2021
Publisher:
CDS
Description:
The oxygen abundance gradients among nebular emission line regions in spiral galaxies have been used as important constraints for models of chemical evolution. We present the largest-ever full-wavelength optical spectroscopic sample of emission line nebulae in a spiral galaxy (M31). We have collected spectra of 253 HII regions and 407 planetary nebulae (PNe) with the Hectospec multi-fiber spectrograph of the MMT. We measure the line-of-sight extinction for 199 HII regions and 333 PNe; we derive oxygen abundance directly, based on the electron temperature, for 51 PNe; and we use strong-line methods to estimate oxygen abundance for 192 HII regions and nitrogen abundance for 52 HII regions. The relatively shallow oxygen abundance gradient of the more extended HII regions in our sample is generally in agreement with the result of Zaritsky et al. (1994ApJ...420...87Z), based on only 19 M31 HII regions, but varies with the strong-line diagnostic employed. Our large sample size demonstrates that there is significant intrinsic scatter around this abundance gradient, as much as ~3 times the systematic uncertainty in the strong-line diagnostics. The intrinsic scatter is similar in the nitrogen abundances, although the gradient is significantly steeper. On small scales (deprojected distance <0.5kpc), HII regions exhibit local variations in oxygen abundance that are larger than 0.3dex in 33% of neighboring pairs. We do not identify a significant oxygen abundance gradient among PNe, but we do find a significant gradient in the [NII] ratio that varies systematically with surface brightness. Our results underscore the complex and inhomogeneous nature of the interstellar medium of M31, and our data set illustrates systematic effects relevant to future studies of the metallicity gradients in nearby spiral galaxies.
1604. Metallic line doubling phenomenon in RR Lyrae
ID:
ivo://CDS.VizieR/J/A+A/308/481
Title:
Metallic line doubling phenomenon in RR Lyrae
Short Name:
J/A+A/308/481
Date:
21 Oct 2021
Publisher:
CDS
Description:
For the first time, the observation of the line doubling phenomenon over two metallic absorption lines of a RR Lyrae star (RR Lyr) is reported. A resolving power of 42,000 and a time resolution close to 1% of the pulsating period were necessary. Although a smaller exposure time would be required to completely resolve this phenomenon over the whole spectrum, we interpret it as the consequence of a "two-step" Schwarzschild's mechanism. Thus a strong shock wave propagating throughout the photosphere around phase 0.93 would be at the origin of the observed line doubling. Because the shock undergoes a sudden acceleration phase, a "jump" appears in the line profile evolution. The shock is first receding and then almost stationary. Our qualitative interpretation needs a theoretical confirmation with the help of a nonlinear nonadiabatic pulsational model with an extended atmosphere taking into account the presence of shock waves. Nevertheless it appears from our observations that the dynamics of the atmosphere of RR Lyr is important just above the photosphere and that strong shock exists at this level because the doubling is already present in FeI lines.
1605. Metal-poor solar-type stars spectroscopy and masses
ID:
ivo://CDS.VizieR/J/A+A/526/A99
Title:
Metal-poor solar-type stars spectroscopy and masses
Short Name:
J/A+A/526/A99
Date:
21 Oct 2021
Publisher:
CDS
Description:
Stellar metallicity strongly correlates with the presence of planets and their properties. To check for new correlations between stars and the existence of an orbiting planet, we determine precise stellar parameters for a sample of metal-poor solar-type stars. This sample was observed with the HARPS spectrograph and is part of a program to search for new extrasolar planets.
1606. Metal-poor star RAVE J093730.5-062655 abundances
ID:
ivo://CDS.VizieR/J/ApJ/874/148
Title:
Metal-poor star RAVE J093730.5-062655 abundances
Short Name:
J/ApJ/874/148
Date:
21 Oct 2021
Publisher:
CDS
Description:
A new moderately r-process-enhanced metal-poor star, RAVEJ093730.5-062655, has been identified in the Milky Way halo as part of an ongoing survey by the R-Process Alliance. The temperature and surface gravity indicate that J0937-0626 is likely a horizontal branch star. At [Fe/H]=-1.86, J0937-0626 is found to have subsolar [X/Fe] ratios for nearly every light, {alpha}, and Fe-peak element. The low [{alpha}/Fe] ratios can be explained by an ~0.6dex excess of Fe; J0937-0626 is therefore similar to the subclass of "iron-enhanced" metal-poor stars. A comparison with Milky Way field stars at [Fe/H]=-2.5 suggests that J0937-0626 was enriched in material from an event, possibly a Type Ia supernova, that created a significant amount of Cr, Mn, Fe, and Ni and smaller amounts of Ca, Sc, Ti, and Zn. The r-process enhancement of J0937-0626 is likely due to a separate event, which suggests that its birth environment was highly enriched in r-process elements. The kinematics of J0937-0626, based on Gaia DR2 data, indicate a retrograde orbit in the Milky Way halo; J0937-0626 was therefore likely accreted from a dwarf galaxy that had significant r-process enrichment.
1607. Metal-poor stars in the thick disk of the Galaxy
ID:
ivo://CDS.VizieR/J/ApJ/794/58
Title:
Metal-poor stars in the thick disk of the Galaxy
Short Name:
J/ApJ/794/58
Date:
21 Oct 2021
Publisher:
CDS
Description:
A new set of very high signal-to-noise (S/N>100/1), medium-resolution (R~3000) optical spectra have been obtained for 302 of the candidate "weak-metal" stars selected by Bidelman & MacConnell (1973AJ.....78..687B, Cat. III/46). We use these data to calibrate the recently developed generalization of the Sloan Extension for Galactic Exploration and Understanding and Exploration (SEGUE) Stellar Parameter Pipeline, and obtain estimates of the atmospheric parameters (T_eff_, log g, and [Fe/H]) for these non-Sloan Digital Sky Survey/SEGUE data; we also obtain estimates of [C/Fe]. The new abundance measurements are shown to be consistent with available high-resolution spectroscopic determinations, and represent a substantial improvement over the accuracies obtained from the previous photometric estimates reported in Paper I of this series (Norris et al. 1985ApJS...58..463N). The apparent offset in the photometric abundances of the giants in this sample noted by several authors is confirmed by our new spectroscopy; no such effect is found for the dwarfs. The presence of a metal-weak thick-disk (MWTD) population is clearly supported by these new abundance data. Some 25% of the stars with metallicities -1.8<[Fe/H]<=-0.8 exhibit orbital eccentricities e<0.4, yet are clearly separated from members of the inner-halo population with similar metallicities by their location in a Lindblad energy versus angular momentum diagram. A comparison is made with recent results for a similar-size sample of Radial Velocity Experiment stars from Ruchti et al. (2010ApJ...721L..92R ; 2011ApJ...737....9R). We conclude, based on both of these samples, that the MWTD is real, and must be accounted for in discussions of the formation and evolution of the disk system of the Milky Way.
1608. Metal-poor stars with APF. I. LAMOST CEMP stars
ID:
ivo://CDS.VizieR/J/ApJ/875/89
Title:
Metal-poor stars with APF. I. LAMOST CEMP stars
Short Name:
J/ApJ/875/89
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report on the discovery of five carbon-enhanced metal-poor (CEMP) stars in the metallicity range of -3.3<[Fe/H]{<}-2.4. These stars were selected from the LAMOST DR3 low-resolution (R~2000) spectroscopic database as metal-poor candidates and followed up with high-resolution spectroscopy (R~110000) with the Lick/APF. Stellar parameters and individual abundances for 25 chemical elements (from Li to Eu) are presented for the first time. These stars exhibit chemical abundance patterns that are similar to those reported in other literature studies of very and extremely metal-poor stars. One of our targets, J2114-0616, shows high enhancement in carbon ([C/Fe]=1.37), nitrogen ([N/Fe]=1.88), barium ([Ba/Fe]=1.00), and europium ([Eu/Fe]=0.84). Such chemical abundance pattern suggests that J2114-0616 can be classified as CEMP-r/s star. In addition, the star J1054+0528 can be classified as a CEMP-rI star, with [Eu/Fe]=0.44 and [Ba/Fe]=-0.52. The other stars in our sample show no enhancements in neutron-capture elements and can be classified as CEMP-no stars. We also performed a kinematic and dynamical analysis of the sample stars based on Gaia DR2 data. The kinematic parameters, orbits, and binding energy of these stars show that J2114-0616 is member of the outer-halo population, while the remaining stars belong to the inner-halo population but with an accreted origin. Collectively, these results add important constraints on the origin and evolution of CEMP stars as well as on their possible formation scenarios.
1609. Metal-rich RRc stars in the Carnegie RR Lyrae Survey
ID:
ivo://CDS.VizieR/J/AJ/155/45
Title:
Metal-rich RRc stars in the Carnegie RR Lyrae Survey
Short Name:
J/AJ/155/45
Date:
21 Oct 2021
Publisher:
CDS
Description:
We describe and employ a stacking procedure to investigate abundances derived from the low signal-to-noise ratio spectra obtained in the Carnegie RR Lyrae Survey (CARRS). We find iron metallicities that extend from [Fe/H]~-2.5 to values at least as large as [Fe/H]~-0.5 in the 274-spectrum CARRS RRc data set. We consider RRc sample contamination by high amplitude solar metallicity {delta} Scuti stars (HADS) at periods less than 0.3 days, where photometric discrimination between RRc and {delta} Scuti stars has proven to be problematic. We offer a spectroscopic discriminant, the well-marked overabundance of heavy elements, principally [Ba/H], that is a common, if not universal, characteristic of HADS of all periods and axial rotations. No bona fide RRc stars known to us have verified heavy-element overabundances. Three out of 34 stars in our sample with [Fe/H]>-0.7 exhibit anomalously strong features of Sr, Y, Zr, Ba, and many rare earths. However, carbon is not enhanced in these three stars, and we conclude that their elevated n-capture abundances have not been generated in interior neutron-capture nucleosynthesis. Contamination by HADS appears to be unimportant, and metal-rich RRc stars occur in approximately the same proportion in the Galactic field as do metal-rich RRab stars. An apparent dearth of metal-rich RRc is probably a statistical fluke. Finally, we show that RRc stars have a similar inverse period-metallicity relationship as has been found for RRab stars.
1610. Metal-strong damped Ly{alpha} systems
ID:
ivo://CDS.VizieR/J/PASP/118/1077
Title:
Metal-strong damped Ly{alpha} systems
Short Name:
J/PASP/118/1077
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have identified a metal-strong [logN(Zn+)>=13.15 or logN(Si^+^)>=15.95] damped Ly{alpha} (MSDLA) population from an automated quasar (QSO) absorber search in the Sloan Digital Sky Survey (SDSS) Data Release 3 quasar sample and find that MSDLAs comprise >>5% of the entire DLA population with z_abs_>=2.2 found in QSO sight lines with r<19.5. We have also acquired 27 Keck ESI (Echellete Spectrograph and Imager) follow-up spectra of metal strong candidates in order to evaluate our automated technique and examine the MSDLA candidates at higher resolution.

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