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1591. 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.
1592. 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.
1593. 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.
1594. 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.
1595. 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.
1596. 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.
1597. 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.
1598. 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.
1599. Methane partition function
ID:
ivo://CDS.VizieR/J/ApJ/789/2
Title:
Methane partition function
Short Name:
J/ApJ/789/2
Date:
21 Oct 2021
Publisher:
CDS
Description:
The paper describes the construction of complete sets of hot methane lines based on accurate ab initio potential and dipole moment surfaces and extensive first-principle calculations. Four line lists spanning the [0-5000]/cm infrared region were built at T = 500, 1000, 1500, and 2000 K. For each of these four temperatures, we have constructed two versions of line lists: a version for high-resolution applications containing strong and medium lines and a full version appropriate for low-resolution opacity calculations. A comparison with available empirical databases is discussed in detail for both cold and hot bands giving a very good agreement for line positions, typically <0.1-0.5/cm and ~5% for intensities of strong lines. Together with numerical tests using various basis sets, this confirms the computational convergence of our results for the most important lines, which is the major issue for theoretical spectra predictions. We showed that transitions with lower state energies up to 14,000/cm could give significant contributions to the methane opacity and have to be systematically taken into account. Our list at 2000 K calculated up to J = 50 contains 11.5 billion transitions for I > 10^-29^ cm/mol. These new lists are expected to be quantitatively accurate with respect to the precision of available and currently planned observations of astrophysical objects with improved spectral resolution.
1600. Methyl isocyanate in Orion
ID:
ivo://CDS.VizieR/J/A+A/587/L4
Title:
Methyl isocyanate in Orion
Short Name:
J/A+A/587/L4
Date:
21 Oct 2021
Publisher:
CDS
Description:
The recent analysis of the composition of the frozen surface of comet 67P/Churyumov-Gerasimenko has revealed a significant number of complex organic molecules. Methyl isocyanate (CH_3_NCO) is one of the more abundant species detected on the comet surface. In this work we report extensive characterization of its rotational spectrum resulting in a list of 1269 confidently assigned laboratory lines and its detection in space towards the Orion clouds where 399 lines of the molecule have been unambiguously identified. We find that the limited mm-wave laboratory data reported prior to our work require some revision. The abundance of CH_3_NCO in Orion is only a factor of ten below those of HNCO and CH_3_CN. Unlike the molecular abundances in the coma of comets, which correlate with those of warm molecular clouds, molecular abundances in the gas phase in Orion are only weakly correlated with those measured on the comet surface. We also compare our abundances wit those derived recently for this molecule towards Sgr B2 (Halfen et al., 2015ApJ...812L...5H). A more accurate abundance of CH_3_NCO is provided for this cloud based on our extensive laboratory work.

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