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- 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.
- 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.
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/808/108
- Title:
- M2FS stellar spectroscopy of Reticulum 2
- Short Name:
- J/ApJ/808/108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from spectroscopic observations with the Michigan/Magellan Fiber System (M2FS) of 182 stellar targets along the line of sight (LOS) to the newly discovered "ultrafaint" object Reticulum 2 (Ret 2). For 37 of these targets, the spectra are sufficient to provide simultaneous estimates of LOS velocity ({nu}i_los_, median random error {delta}_{nu}los_=1.4km/s), effective temperature (T_eff_, {delta}_Tef_=478K), surface gravity (logg, {delta}_logg_=0.63dex), and iron abundance ([Fe/H], {delta}_[Fe/H]_=0.47dex). We use these results to confirm 17 stars as members of Ret 2. From the member sample we estimate a velocity dispersion of {sigma}_{nu}los_=3.6_-0.7_^+1.0^km/s about a mean of <{nu}_los_>=64.3_1.2_^+1.2^km/s in the solar rest frame (~-90.9km/s in the Galactic rest frame), and a metallicity dispersion of {sigma}_[Fe/H]_=0.49_-0.14_^+0.19^dex about a mean of <[Fe/H]_>=-2.58_-0.33_^+0.34^. These estimates marginalize over possible velocity and metallicity gradients, which are consistent with zero. Our results place Ret 2 on chemodynamical scaling relations followed by the Milky Way's dwarf-galactic satellites. Under assumptions of dynamic equilibrium and negligible contamination from binary stars --both of which must be checked with deeper imaging and repeat spectroscopic observations-- the estimated velocity dispersion suggests a dynamical mass of M(R_h_)~5R_h_{sigma}_{nu}los_^2^/(2G)=2.4_-0.8_^+1.4^x10^5^M_{sun}_ enclosed within projected halflight radius R_h_~32pc, with mass-to-light ratio ~2M(R_h_)/L_V_=467_-168_^+286^ in solar units.
- ID:
- ivo://CDS.VizieR/J/ApJ/890/132
- Title:
- MgII abs. toward SDSS QSOs with rotation measures
- Short Name:
- J/ApJ/890/132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We probed the magnetic fields in high-redshift galaxies using excess extragalactic contribution to residual rotation measure (RRM) for quasar sightlines with intervening MgII absorbers. Based on a large sample of 1132 quasars, we have computed RRM distributions broadening using median absolute deviation from the mean ({sigma}_rrm_^md^), and found it to be 17.1+/-0.7rad/m^2^ for 352 sightlines having MgII intervening absorbers in comparison to its value of 15.1+/-0.6rad/m^2^ for 780 sightlines without such absorbers, resulting in an excess broadening ({sigma}_rrm_^ex^) of 8.0+/-1.9rad:m^2^ among these two subsamples. This value of {sigma}_rrm_^ex^, has allowed us to constrain the average strength of magnetic field (rest frame) in high-redshift galaxies responsible for these Mg II absorbers, to be ~1.3+/-0.3{mu}G at a median redshift of 0.92. This estimate of magnetic field is consistent with the reported estimate in earlier studies based on radio-infrared correlation and energy equipartition for galaxies in the local universe. A similar analysis on subsample split based on the radio spectral index, {alpha} (with F_{nu}_{propto}{nu}^{alpha}^), for flat ({alpha}>=-0.3; 315 sources) and steep ({alpha}<=-0.7; 476 sources) spectrum sources shows a significant {sigma}_rrm_^ex^ (at 3.5{sigma} level) for the former and absent in the latter. An anticorrelation found between the {sigma}_rrm_^md^ and percentage polarization (p) with a similar Pearson correlation of -0.62 and -0.87 for subsamples with and without MgII, respectively, suggests the main contribution for decrements in the p value to be intrinsic to the local environment of quasars.
- ID:
- ivo://CDS.VizieR/J/ApJS/242/28
- Title:
- MgII-BAL quasar variability in SDSS spectra
- Short Name:
- J/ApJS/242/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present absorption variability results for 134 bona fide MgII broad absorption-line (BAL) quasars at 0.46<=z<=2.3 covering days to ~10yr in the rest frame. We use multiple-epoch spectra from the Sloan Digital Sky Survey, which has delivered the largest such BAL variability sample ever studied. MgII-BAL identifications and related measurements are compiled and presented in a catalog. We find a remarkable time-dependent asymmetry in the equivalent width (EW) variation from the sample, such that weakening troughs outnumber strengthening troughs, the first report of such a phenomenon in BAL variability. Our investigations of the sample further reveal that (i) the frequency of BAL variability is significantly lower (typically by a factor of 2) than that in high-ionization BALQSO samples, (ii) MgII-BAL absorbers tend to have relatively high optical depths and small covering factors along our line of sight, (iii) there is no significant EW-variability correlation between MgII troughs at different velocities in the same quasar, and (iv) the EW-variability correlation between MgII and AlIII BALs is significantly stronger than that between MgII and CIV BALs at the same velocities. These observational results can be explained by a combined transverse-motion/ionization-change scenario, where transverse motions likely dominate the strengthening BALs while ionization changes and/or other mechanisms dominate the weakening BALs.
- ID:
- ivo://CDS.VizieR/J/ApJ/843/30
- Title:
- MgII line vs 3000{AA} continuum analysis in 68 QSOs
- Short Name:
- J/ApJ/843/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the relationship between the MgII{lambda}2798 emission line and the 3000{AA} continuum variations using a sample of 68 intermediate-redshift (z~0.65-1.50) broad-line quasars spanning a bolometric luminosity range of 44.49erg/s<=logL_bol_<=46.31erg/s (Eddington ratio from ~0.026 to 0.862). This sample is constructed from SDSS-DR7Q and BOSS-DR12Q, each with at least two spectroscopic epochs in SDSS-I/II/III surveys. In addition, we adopt the following signal-to-noise ratio (S/N) selection criteria: (a) for MgII and the 3000{AA} continuum, S/N>=10; and (b) for narrow lines, S/N>=5. All our quasar spectra are recalibrated based on the assumption of constant narrow emission- line fluxes. In an analysis of spectrum-to-spectrum variations, we find a fairly close correlation (Spearman {rho}=0.593) between the variations in broad MgII and in the continuum. This is consistent with the idea that MgII is varying in response to the continuum emission variations. Adopting the modified weighted least squares regression method, we statistically constrain the slopes (i.e., the responsivity {alpha} of the broad MgII) between the variations in both components for the sources in different luminosity bins after eliminating intrinsic biases introduced by the rescaling process itself. It is shown that the responsivity is quite small (average {bar}{alpha}~0.464) and anti- correlates with the quasar luminosity. Our results indicate that high signal- to-noise flux measurements are required to robustly detect the intrinsic variability and the time lag of the MgII line.
- ID:
- ivo://CDS.VizieR/J/ApJS/255/28
- Title:
- ~420MHz uGMRT obs. of MIR selected radio-loud AGN
- Short Name:
- J/ApJS/255/28
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- We present results from a spectroscopically blind search for associated and intervening HI 21cm and OH 18cm absorption lines toward 88 active galactic nuclei (AGN) at 2<z<5 using the uGMRT. The sample of AGN with 1.4GHz spectral luminosity in the range 10^27-29.3^W/Hz is selected using mid-infrared colors and closely resembles the distribution of the underlying quasar population. The search for associated or proximate absorption, defined to be within 3000km/s of the AGN redshift, led to one HI 21cm absorption detection (M1540-1453; z_abs_=2.1139). This is only the fourth known absorption at z>2. The detection rate (1.6_-1.4_^+3.8^%) suggests a low covering factor of the cold neutral medium (CNM; T~100K) associated with these powerful AGN. The intervening absorption line search, with a sensitivity to detect the CNM in damped Ly{alpha} systems (DLAs), has comoving absorption path lengths of {Delta}X=130.1 and 167.7 for HI and OH, respectively. The corresponding number of absorbers per unit comoving path length are <=0.014 and <=0.011, respectively. The former is at least 4.5 times lower than that of DLAs and consistent with the CNM cross section estimated using H_2_ and CI absorbers at z>2. Our AGN sample is optically fainter compared to the quasars used to search for DLAs in the past. In our optical spectra obtained using SALT and NOT, we detect five intervening (redshift path ~9.3) and two proximate DLAs. This is slightly excessive compared to the statistics based on optically selected quasars. The nondetection of HI 21cm absorption from these DLAs suggests a small CNM covering fraction around galaxies at z>2.