- ID:
- ivo://CDS.VizieR/J/ApJ/697/207
- Title:
- Cold stellar stream orbit fit
- Short Name:
- J/ApJ/697/207
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use velocity and metallicity information from Sloan Digital Sky Survey and Sloan Extension for Galactic Understanding and Exploration stellar spectroscopy to fit an orbit to the narrow 63{deg} stellar stream of Grillmair and Dionatos (GD; 2006ApJ...643L..17G). The stars in the stream have a retrograde orbit with eccentricity e=0.33 (perigalacticon of 14.4kpc and apogalacticon of 28.7kpc) and inclination approximately i~35{deg}. In the region of the orbit which is detected, it has a distance of about 7-11kpc from the Sun. Assuming a standard disk plus bulge and logarithmic halo potential for the Milky Way stars plus dark matter, the stream stars are moving with a large space velocity of approximately 276km/s at perigalacticon. Using this stream alone, we are unable to determine if the dark matter halo is oblate or prolate. The metallicity of the stream is [Fe/H]=-2.1+/-0.1. Observed proper motions for individual stream members above the main sequence turnoff are consistent with the derived orbit. None of the known globular clusters in the Milky Way have positions, radial velocities, and metallicities that are consistent with being the progenitor of the GD-1 stream.
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- ID:
- ivo://CDS.VizieR/J/A+A/562/A24
- Title:
- Cool carbon stars in the halo and Fornax dSph
- Short Name:
- J/A+A/562/A24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The population of cool carbon (C) stars located far from the galactic plane is probably made of debris of small galaxies such as the Sagittarius dwarf spheroidal galaxy (Sgr), which are disrupted by the gravitational field of the Galaxy. We aim to know this population better through spectroscopy, 2MASS photometric colours, and variability data. When possible, we compared the halo results to C star populations in the Fornax dwarf spheroidal galaxy, Sgr, and the solar neighbourhood. We first present a few new discoveries of C stars in the halo and in Fornax. The number of spectra of halo C stars is now 125. Forty percent show H{alpha} in emission. The narrow location in the JHK diagram of the halo C stars is found to differ from that of similar C stars in the above galaxies. The light curves of the Catalina and LINEAR variability databases were exploited to derive the pulsation periods of 66 halo C stars. A few supplementary periods were obtained with the TAROT telescopes. We confirm that the period distribution of the halo strongly resembles that of Fornax, and we found that it is very different from the C stars in the solar neighbourhood. There is a larger proportion of short-period Mira/SRa variables in the halo than in Sgr, but the survey for C stars in this dwarf galaxy is not complete, and the study of their variability needs to be continued to investigate the link between Sgr and the cool halo C stars.
- ID:
- ivo://CDS.VizieR/J/A+A/577/A81
- Title:
- Deep SDSS Optical Spectroscopy. II.
- Short Name:
- J/A+A/577/A81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze a sample of 3942 low-resolution (R~2000) optical spectra from the Sloan Digital Sky Survey (SDSS), focusing on stars with effective temperatures 5800<Teff<6300K, and distances from the Milky Way plane in excess of 5kpc, and determine their abundances of Fe, Ca, and Mg. This work follows the same methodology as in the previous paper in this series, deriving atmospheric parameters by chi^2^ minimization, but we now obtain the abundances of individual elements by fitting their associated spectral lines. Distances are calculated from absolute magnitudes obtained by a statistical comparison of our stellar parameters with stellar-evolution models. The observations reveal a decrease in the abundances of iron, calcium and magnesium at large distances from the Galactic center. The median abundances for the halo stars analyzed are fairly constant up to a Galactocentric distance r~20kpc, rapidly decrease between r~20 and r~40kpc, and flatten out to significantly lower values at larger distances, consistent with previous studies. In addition, we examine the Ca/Fe and Mg/Fe ratios as a function of Fe/H and Galactocentric distance. Our results show that the most distant parts of the halo show a steeper variation of the Ca/Fe and Mg/Fe with iron. We found that at the range -1.6<[Fe/H]<-0.4 the Ca/Fe ratio decreases with distance, in agreement with earlier results based on local stars. However, the opposite trend is apparent for Mg/Fe. Our conclusion that the outer regions of the halo are more metal-poor than the inner regions, based on in-situ observations of distant stars, is in concert with recent results based on inferences from the kinematics of more local stars, and with predictions of recent galaxy formation simulations for galaxies similar to the Milky Way.
- ID:
- ivo://CDS.VizieR/J/ApJ/753/64
- Title:
- Detailed abundances for 97 metal-poor stars
- Short Name:
- J/ApJ/753/64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- we present the abundance analysis of 97 nearby metal-poor (-3.3<[Fe/H]<-0.5) stars having kinematic characteristics of the Milky Way (MW) thick disk and inner and outer stellar halos. The high-resolution, high-signal-to-noise optical spectra for the sample stars have been obtained with the High Dispersion Spectrograph mounted on the Subaru Telescope. Abundances of Fe, Mg, Si, Ca, and Ti have been derived using a one-dimensional LTE abundance analysis code with Kurucz NEWODF model atmospheres. By assigning membership of the sample stars to the thick disk, inner halo, or outer halo components based on their orbital parameters, we examine abundance ratios as a function of [Fe/H] and kinematics for the three subsamples in wide metallicity and orbital parameter ranges. We show that, in the metallicity range of -1.5<[Fe/H]<=-0.5, the thick disk stars show constantly high mean [Mg/Fe] and [Si/Fe] ratios with small scatter. In contrast, the inner and the outer halo stars show lower mean values of these abundance ratios with larger scatter. The [Mg/Fe], [Si/Fe], and [Ca/Fe] for the inner and the outer halo stars also show weak decreasing trends with [Fe/H] in the range [Fe/H]>-2. These results favor the scenarios that the MW thick disk formed through rapid chemical enrichment primarily through Type II supernovae of massive stars, while the stellar halo has formed at least in part via accretion of progenitor stellar systems having been chemically enriched with different timescales.
- ID:
- ivo://CDS.VizieR/J/ApJ/771/67
- Title:
- Detailed abundances for 97 metal-poor stars. II.
- Short Name:
- J/ApJ/771/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present chemical abundance analyses of sodium, iron-peak, and neutron-capture elements for 97 kinematically selected thick disk, inner halo, and outer halo stars with metallicities -3.3<[Fe/H]<-0.5. The main aim of this study is to examine chemical similarities and differences among metal-poor stars belonging to these old Galactic components as a clue to determine their early chemodynamical evolution. In our previous paper, we obtained abundances of {alpha} elements by performing a one-dimensional LTE abundance analysis based on the high-resolution (R~50000) spectra obtained with the Subaru/HDS. In this paper, a similar analysis is performed to determine abundances of an additional 17 elements. We show that, in metallicities below [Fe/H]~-2, the abundance ratios of many elements in the thick disk, inner halo, and outer halo subsamples are largely similar. In contrast, in higher metallicities ([Fe/H]>~-1.5), differences in some of the abundance ratios among the three subsamples are identified. Specifically, the [Na/Fe], [Ni/Fe], [Cu/Fe], and [Zn/Fe] ratios in the inner and outer halo subsamples are found to be lower than those in the thick disk subsample.
- ID:
- ivo://CDS.VizieR/J/ApJ/711/573
- Title:
- Detailed abundances in a halo stellar stream
- Short Name:
- J/ApJ/711/573
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a detailed abundance analysis of one of the confirmed building blocks of the Milky Way stellar halo, a kinematically coherent metal-poor stellar stream. We have obtained high-resolution and high signal-to-noise spectra of 12 probable stream members using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan-Clay Telescope at Las Campanas Observatory and the 2dCoude spectrograph on the Smith Telescope at McDonald Observatory. We have derived abundances or upper limits for 51 species of 46 elements in each of these stars. The stream members show a range of metallicity (-3.4<[Fe/H]<-1.5) but are otherwise chemically homogeneous, with the same star-to-star dispersion in [X/Fe] as the rest of the halo. This implies that, in principle, a significant fraction of the Milky Way stellar halo could have formed from accreted systems like the stream. The stream stars show minimal evolution in the {alpha} or Fe-group elements over the range of metallicity. This stream is enriched with material produced by the main and weak components of the rapid neutron-capture process and shows no evidence for enrichment by the slow neutron-capture process.
- ID:
- ivo://CDS.VizieR/J/A+A/501/519
- Title:
- Extremely metal-poor turnoff stars abundances
- Short Name:
- J/A+A/501/519
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The detailed chemical abundances of extremely metal-poor (EMP) stars are key guides to understanding the early chemical evolution of the Galaxy. Most existing data, however, treat giant stars that may have experienced internal mixing later. We aim to compare the results for giants with new, accurate abundances for all observable elements in 18 EMP turnoff stars. VLT/UVES spectra at ~45000 and S/N ~130 per pixel (330-1000nm) are analysed with OSMARCS model atmospheres and the TURBOSPECTRUM code to derive abundances for C, Mg, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Zn, Sr, and Ba. For Ca, Ni, Sr, and Ba, we find excellent consistency with our earlier sample of EMP giants, at all metallicities. However, our abundances of C, Sc, Ti, Cr, Mn and Co are ~0.2dex larger than in giants of similar metallicity. Mg and Si abundances are ~0.2dex lower (the giant [Mg/Fe] values are slightly revised), while Zn is again ~0.4dex higher than in giants of similar [Fe/H] (6 stars only). For C, the dwarf/giant discrepancy could possibly have an astrophysical cause, but for the other elements it must arise from shortcomings in the analysis. Approximate computations of granulation (3D) effects yield smaller corrections for giants than for dwarfs, but suggest that this is an unlikely explanation, except perhaps for C, Cr, and Mn. NLTE computations for Na and Al provide consistent abundances between dwarfs and giants, unlike the LTE results, and would be highly desirable for the other discrepant elements as well. Meanwhile, we recommend using the giant abundances as reference data for Galactic chemical evolution models.
- ID:
- ivo://CDS.VizieR/J/A+A/415/993
- Title:
- FeII, ZNI and SI abundances on halo stars
- Short Name:
- J/A+A/415/993
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The table gives equivalent widths (in m{AA}) for 19 FeII lines, two ZnI lines, and four SI lines, as measured in high resolution VLT/UVES spectra of 34 metal-poor, main sequence and subgiant, halo stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/899/83
- Title:
- 723 Gaia DR2 White dwarfs cand. in Local Galactic Halo
- Short Name:
- J/ApJ/899/83
- Date:
- 14 Mar 2022 08:58:44
- Publisher:
- CDS
- Description:
- We present a catalog of 531 white dwarf candidates that have large apparent transverse motions relative to the Sun (v_T_>200km/s), thus making them likely members of the local Galactic halo population. The candidates were selected from the Gaia Data Release 2 and are located in a great circle with 20{deg} width running across both Galactic poles and the Galactic center and anticenter, a zone that spans 17.3% of the sky. The selection used a combination of kinematic and photometric properties, derived primarily from Gaia proper motions, G magnitudes, and G_BP_-G_RP_ color, and including parallax whenever available. Additional validation of the white dwarf candidates is made using PanSTARRS photometric (gri) data. Our final catalog includes not only stars having full kinematic and luminosity estimates from reliable Gaia parallax, but also stars with presently unreliable or no available Gaia parallax measurements. We argue that our method of selecting local halo objects with and without reliable parallax data leads us to round up all possible halo white dwarfs in the Gaia catalog (in that particular section of the sky) with recorded proper motions >40mas/yr and that pass our v_T_>200km/s threshold requirement. We expect this catalog will be useful for the study of the white dwarf population of the local Galactic halo.
- ID:
- ivo://CDS.VizieR/J/ApJ/852/50
- Title:
- Galactic halo with APOGEE. II. Abundances.
- Short Name:
- J/ApJ/852/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation processes that led to the current Galactic stellar halo are still under debate. Previous studies have provided evidence for different stellar populations in terms of elemental abundances and kinematics, pointing to different chemical and star formation histories (SFHs). In the present work, we explore, over a broader range in metallicity (-2.2<[Fe/H]<+0.5), the two stellar populations detected in the first paper of this series from metal-poor stars in DR13 of the Apache Point Observatory Galactic Evolution Experiment (APOGEE). We aim to infer signatures of the initial mass function (IMF) and the SFH from the two {alpha}-to-iron versus iron abundance chemical trends for the most APOGEE-reliable {alpha}-elements (O, Mg, Si, and Ca). Using simple chemical-evolution models, we infer the upper mass limit (Mup) for the IMF and the star formation rate, and its duration for each population. Compared with the low-{alpha} population, we obtain a more intense and longer-lived SFH, and a top-heavier IMF for the high-{alpha} population.
