- ID:
- ivo://CDS.VizieR/J/ApJ/636/821
- Title:
- Abundances of Baade's Window K giants
- Short Name:
- J/ApJ/636/821
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results of a new abundance survey of the Milky Way bulge based on Keck HIRES spectra of 27 K giants in the Baade's Window (l=1{deg},b=-4{deg}) field. The spectral data used in this study are of much higher resolution and signal-to-noise ratio than previous optical studies of Galactic bulge stars. The [Fe/H] values of our stars, which range between 1.29 and +0.51, were used to recalibrate large low-resolution surveys of bulge stars. Our best value for the mean [Fe/H] of the bulge is -0.10+/-0.04. This mean value is similar to the mean metallicity of the local disk and indicates that there cannot be a strong metallicity gradient inside the solar circle. The metallicity distribution of stars confirms that the bulge does not suffer from the so-called G dwarf problem. This paper also details the new abundance techniques necessary to analyze very metal-rich K giants, including a new Fe line list and regions of low blanketing for continuum identification.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/454/895
- Title:
- Abundances of 26 barium stars. I.
- Short Name:
- J/A+A/454/895
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The abundances for Na, Al, alpha-, iron-peak, s-, and r-elements have been derived by using spectrum synthesis for a sample of 26 barium stars, including dwarf barium stars. High-resolution spectra were obtained with the FEROS spectrograph at the ESO-1.52m Telescope, along with photometric data with Fotrap at the Zeiss telescope at the LNA.
- ID:
- ivo://CDS.VizieR/J/A+A/454/917
- Title:
- Abundances of 26 barium stars. II.
- Short Name:
- J/A+A/454/917
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this work is to quantify the contributions of the s-, r-, and p-processes for the total abundance of heavy elements from abundances derived for a sample of 26 barium stars. The abundances of the sample stars were compared to those of normal stars, thus identifying the fraction relative to the main component of the s-process s. The fittings of the sigmaN curves (neutron-capture cross-section times abundance, plotted against atomic mass number) for the sample stars suggest that the material from the companion asymptotic giant branch star had approximately the solar isotopic composition as concerns fractions of abundances relative to the s-process main component.
- ID:
- ivo://CDS.VizieR/J/A+A/434/235
- Title:
- Abundances of BHB stars in NGC 1904
- Short Name:
- J/A+A/434/235
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The abundance measurements are based on high-resolution optical spectroscopical data, obtained during 2 observing runs with the Ultraviolet and Visual Echelle Spectrograph mounted on Kueyen (Very Large Telescope UT2). Ten target stars in the extended blue horizontal branch of the Galactic globular cluster NGC 1904 (M79) have been analysed.
- ID:
- ivo://CDS.VizieR/J/ApJ/864/43
- Title:
- Abundances of 3 bright extremely metal-poor giants
- Short Name:
- J/ApJ/864/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present detailed chemical abundances of three new bright (V~11), extremely metal-poor ([Fe/H]~-3.0), r-process-enhanced halo red giants based on high-resolution, high-S/N Magellan/MIKE spectra. We measured abundances for 20-25 neutron-capture elements in each of our stars. J1432-4125 is among the most r-process-rich r-II stars, with [Eu/Fe]=+1.44+/-0.11. J2005-3057 is an r-I star with [Eu/Fe]=+0.94+/-0.07. J0858-0809 has [Eu/Fe]=+0.23+/-0.05 and exhibits a carbon abundance corrected for an evolutionary status of [C/Fe]_corr_=+0.76, thus adding to the small number of known carbon-enhanced r-process stars. All three stars show remarkable agreement with the scaled solar r-process pattern for elements above Ba, consistent with enrichment of the birth gas cloud by a neutron star merger. The abundances for Sr, Y, and Zr, however, deviate from the scaled solar pattern. This indicates that more than one distinct r-process site might be responsible for the observed neutron-capture element abundance pattern. Thorium was detected in J1432-4125 and J2005-3057. Age estimates for J1432-4125 and J2005-3057 were adopted from one of two sets of initial production ratios each by assuming the stars are old. This yielded individual ages of 12+/-6Gyr and 10+/-6Gyr, respectively.
- ID:
- ivo://CDS.VizieR/J/ApJ/797/13
- Title:
- Abundances of bright metal-poor stars
- Short Name:
- J/ApJ/797/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chemical abundances of large samples of extremely metal-poor (EMP) stars can be used to investigate metal-free stellar populations, supernovae, and nucleosynthesis as well as the formation and galactic chemical evolution of the Milky Way and its progenitor halos. However, current progress on the study of EMP stars is being limited by their faint apparent magnitudes. The acquisition of high signal-to-noise spectra for faint EMP stars requires a major telescope time commitment, making the construction of large samples of EMP star abundances prohibitively expensive. We have developed a new, efficient selection that uses only public, all-sky APASS optical, 2MASS near-infrared, and WISE mid-infrared photometry to identify bright metal-poor star candidates through their lack of molecular absorption near 4.6 microns.
- ID:
- ivo://CDS.VizieR/J/AJ/148/67
- Title:
- Abundances of 156 bulge red giants
- Short Name:
- J/AJ/148/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radial velocities and chemical abundances of O, Na, Mg, Al, Si, Ca, Cr, Fe, Co, Ni, and Cu for a sample of 156 red giant branch stars in two Galactic bulge fields centered near (l,b)=(+5.25,-3.02) and (0,-12). The (+5.25,-3.02) field also includes observations of the bulge globular cluster NGC 6553. The results are based on high-resolution (R~20000), high signal-to-noise ration (S/N>~70) FLAMES-GIRAFFE spectra obtained through the European Southern Observatory archive. However, we only selected a subset of the original observations that included spectra with both high S/N and that did not show strong TiO absorption bands. This work extends previous analyses of this data set beyond Fe and the {alpha}-elements Mg, Si, Ca, and Ti. While we find reasonable agreement with past work, the data presented here indicate that the bulge may exhibit a different chemical composition than the local thick disk, especially at [Fe/H]>~-0.5. In particular, the bulge [{alpha}/Fe] ratios may remain enhanced to a slightly higher [Fe/H] than the thick disk, and the Fe-peak elements Co, Ni, and Cu appear enhanced compared to the disk. There is also some evidence that the [Na/Fe] (but not [Al/Fe]) trends between the bulge and local disk may be different at low and high metallicity. We also find that the velocity dispersion decreases as a function of increasing [Fe/H] for both fields, and do not detect any significant cold, high-velocity populations. A comparison with chemical enrichment models indicates that a significant fraction of hypernovae may be required to explain the bulge abundance trends, and that initial mass functions that are steep, top-heavy (and do not include strong outflow), or truncated to avoid including contributions from stars >40M_{sun}_ are ruled out, in particular because of disagreement with the Fe-peak abundance data. For most elements, the NGC 6553 stars exhibit abundance trends nearly identical to comparable metallicity bulge field stars. However, the star-to-star scatter and mean [Na/Fe] ratios appear higher in the cluster, perhaps indicating additional self-enrichment.
- ID:
- ivo://CDS.VizieR/J/A+A/530/A54
- Title:
- Abundances of 650 bulge red giants
- Short Name:
- J/A+A/530/A54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the analysis of the [alpha/Fe] abundance ratios for a large number of stars at several locations in the Milky Way bulge with the aim of constraining its formation scenario. We obtained FLAMES-GIRAFFE spectra (R=22500) at the ESO Very Large Telescope for 650 bulge red giant branch (RGB) stars and performed spectral synthesis to measure Mg, Ca, Ti, and Si abundances. This sample is composed of 474 giant stars observed in 3 fields along the minor axis of the Galactic bulge and at latitudes b=-4{deg}, b=-6{deg}, b=-12{deg}. Another 176 stars belong to a field containing the globular cluster NGC 6553, located at b=-3{deg} and 5{deg} away from the other three fields along the major axis.
- ID:
- ivo://CDS.VizieR/J/A+A/548/A34
- Title:
- Abundances of carbon-enhanced metal-poor stars
- Short Name:
- J/A+A/548/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed study of Carbon-Enhanced Metal-Poor (CEMP) stars, based on high-resolution spectroscopic observations of a sample of 18 stars. The stellar spectra for this sample were obtained at the 4.2m William Herschel Telescope (WHT) in 2001 and 2002, using the Utrecht Echelle Spectrograph (UES), at a resolving power R~52000 and S/N~40, covering the wavelength range {lambda}-{lambda}3700-5700{AA}. The atmospheric parameters determined for this sample indicate temperatures ranging from 4750K to 7100K, log g from 1.5 to 4.3, and metallicities -3.0<=[Fe/H]<=-1.7. Elemental abundances for C, Na, Mg, Sc, Ti, Cr, Cu, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, Eu, Gd, Dy are determined. Abundances for an additional 109 stars were taken from the literature and combined with the data of our sample. The literature sample reveals a lack of reliable abundance estimates for species that might be associated with the r-process elements for about 67% of CEMP stars, preventing a complete understanding of this class of stars, since [Ba/Eu] ratios are used to classify them. Although eight stars in our observed sample are also found in the literature sample, Eu abundances or limits are determined for four of these stars for the first time. From the observed correlations between C, Ba, and Eu, we argue that the CEMP-r/s class has the same astronomical origin as CEMP-s stars, highlighting the need for a more complete understanding of Eu production.
- ID:
- ivo://CDS.VizieR/J/ApJ/658/367
- Title:
- Abundances of carbon stars in Galactic halo
- Short Name:
- J/ApJ/658/367
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is known that the carbon-enhanced, extremely metal-poor (CEMP) stars constitute a substantial proportion of the extremely metal-poor (EMP) stars of the Galactic halo, and a by far larger proportion than CH stars among Population II stars. We investigate their origin by taking into account an additional evolutionary path to the surface carbon enrichment, triggered by hydrogen engulfment by the helium flash convection, in EMP stars with [Fe/H]<~-2.5. This process is distinct from the third dredge-up operating in more metal-rich stars and in EMP stars. In binary systems of EMP stars, the secondary stars become CEMP stars through mass transfer from the low- and intermediate- mass primary stars that have developed the surface carbon enhancement. Our binary scenario can predict the variations in the abundances not only for carbon but also for nitrogen and s-process elements and can reasonably explain the observed properties such as the stellar distributions of the carbon abundances, the binary periods, and the evolutionary stages.
