- ID:
- ivo://CDS.VizieR/J/A+A/554/A84
- Title:
- Abundances of evolved stars
- Short Name:
- J/A+A/554/A84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Currently, the core accretion model has its strongest observational evidence on the chemical signature of mostly main sequence stars with planets. We aim to test whether the well-established correlation between the metallicity of the star and the presence of giant planets found for main sequence stars still holds for the evolved and generally more massive giant and subgiant stars. Although several attempts have been made so far, the results are not conclusive since they are based on small or inhomogeneous samples. We determine in a homogeneous way the metallicity and individual abundances of a large sample of evolved stars, with and without known planetary companions, and discuss their metallicity distribution and trends. Our methodology is based on the analysis of high-resolution echelle spectra (R~67000) from 2-3 meter class telescopes. It includes the calculation of the fundamental stellar parameters (effective temperature, surface gravity, microturbulent velocity, and metallicity) by applying iron ionisation and excitation equilibrium conditions to several isolated FeI and FeII lines, as well as, calculating individual abundances of different elements such as Na, Mg, Si, Ca, Ti, Cr, Co, or Ni.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/797/69
- Title:
- Abundances of late-type stars
- Short Name:
- J/ApJ/797/69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the detection of several absorption lines of neutral phosphorus (P, Z=15) in archival near-ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. We derive phosphorus abundances or interesting upper limits in 14 late-type stars with metallicities spanning -3.8<[Fe/H]<-0.1. Previously, phosphorus had only been studied in Galactic stars with -1.0<[Fe/H]<+0.3. Iron lines reveal abundance offsets between the optical and ultraviolet regions, and we discuss and apply a correction factor to account for this offset. In stars with [Fe/H]>-1.0, the [P/Fe] ratio decreases toward the solar value with increasing metallicity, in agreement with previous observational studies. In stars with [Fe/H]<-1.0, $<[P/Fe]$>=+0.04+/-0.10, which overlaps with the [P/Fe] ratios found in several high-redshift damped Lyman-{alpha} systems. This behavior hints at a primary origin in massive stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/882/177
- Title:
- Abundances of 4 member stars of Tucana III
- Short Name:
- J/ApJ/882/177
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a chemical abundance analysis of four additional confirmed member stars of Tucana III, a Milky Way satellite galaxy candidate in the process of being tidally disrupted as it is accreted by the Galaxy. Two of these stars are centrally located in the core of the galaxy while the other two stars are located in the eastern and western tidal tails. The four stars have chemical abundance patterns consistent with the one previously studied star in Tucana III: they are moderately enhanced in r-process elements, i.e., they have <[Eu/Fe]>~+0.4dex. The non-neutron-capture elements generally follow trends seen in other dwarf galaxies, including a metallicity range of 0.44 dex and the expected trend in {alpha}-elements, i.e., the lower metallicity stars have higher Ca and Ti abundances. Overall, the chemical abundance patterns of these stars suggest that Tucana III was an ultra-faint dwarf galaxy, and not a globular cluster, before being tidally disturbed. As is the case for the one other galaxy dominated by r-process enhanced stars, Reticulum II, Tucana III's stellar chemical abundances are consistent with pollution from ejecta produced by a binary neutron star merger, although a different r-process element or dilution gas mass is required to explain the abundances in these two galaxies if a neutron star merger is the sole source of r-process enhancement.
- ID:
- ivo://CDS.VizieR/J/A+A/520/A95
- Title:
- Abundances of red giants in M54 and Sgr dSph
- Short Name:
- J/A+A/520/A95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Homogeneous abundances of light elements, alpha-elements, and Fe-group elements from high-resolution FLAMES spectra are presented for 76 red giant stars in NGC 6715 (M 54), a massive globular cluster (GC) lying in the nucleus of the Sagittarius dwarf galaxy. We also derived detailed abundances for 27 red giants belonging to the Sgr nucleus. Our abundances assess the intrinsic metallicity dispersion (~0.19dex, rms scatter) of M 54, with the bulk of stars peaking at [Fe/H]~-1.6 and a long tail extending to higher metallicities, similar to {omega} Cen. The spread in these probable nuclear star clusters exceeds those of most GCs: these massive clusters are located in a region intermediate between normal GCs and dwarf galaxies. M 54 shows the Na-O anticorrelation, typical signature of GCs, which is instead absent in the Sgr nucleus. The light elements (Mg, Al, Si) participating to the high temperature Mg-Al cycle show that the entire pattern of (anti)correlations produced by proton-capture reactions in H-burning is clearly different between the most metal-rich and most metal-poor components in the two most massive GCs in the Galaxy, confirming early result based on the Na-O anticorrelation. As in {omega} Cen, stars affected by most extreme processing, i.e. showing the signature of more massive polluters, are those of the metal-rich component. These observations can be understood if the burst of star formation giving birth to the metal-rich component was delayed by as much as 10-30Myr with respect to the metal-poor one. The evolution of these massive GCs can be easily reconciled in the general scenario for the formation of GCs recently sketched in Carretta et al.(2010a) taking into account that {omega} Cen could have already incorporated the surrounding nucleus of its progenitor and lost the rest of the hosting galaxy while the two are still observable as distinct components in M 54 and the surrounding field.
- ID:
- ivo://CDS.VizieR/J/ApJ/681/1505
- Title:
- Abundances of red giants in {omega} Cen
- Short Name:
- J/ApJ/681/1505
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radial velocities and Fe and Al abundances for 180 red giant branch (RGB) stars in the Galactic globular cluster Omega Centauri ({omega} Cen). The majority of our data lie in the range 11.0<V<13.5, which covers the RGB from about 1mag above the horizontal branch to the RGB tip. The selection procedures are biased toward preferentially observing the more metal-poor and luminous stars of {omega} Cen. Abundances were determined using equivalent width measurements and spectrum synthesis analyses of moderate resolution spectra (R~13000) obtained with the Blanco 4m telescope and Hydra multifiber spectrograph. Our results are in agreement with previous studies as we find at least four different metallicity populations with [Fe/H]=-1.75, -1.45, -1.05, and -0.75, with a full range of -2.20<~[Fe/H]<~-0.70. Results seem to fit in the adopted scheme that star formation occurred in {omega} Cen over >1Gyr.
- ID:
- ivo://CDS.VizieR/J/ApJ/698/2048
- Title:
- Abundances of red giants in {omega} Cen
- Short Name:
- J/ApJ/698/2048
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present abundances of several light, {alpha}, Fe-peak, and neutron-capture elements for 66 red giant branch (RGB) stars in the Galactic globular cluster Omega Centauri ({omega} Cen). Our observations lie in the range 12.0<V<13.5 and focus on the intermediate and metal-rich RGBs. Abundances were determined using equivalent width measurements and spectrum synthesis analyses of moderate resolution (R~18000) spectra obtained with the Blanco 4m telescope and Hydra multifiber spectrograph. Combining these data with previous work, we find that there are at least four peaks in the metallicity distribution function at [Fe/H]=-1.75, -1.45, -1.05, and -0.75, which correspond to about 55%, 30%, 10%, and 5% of our sample, respectively. We conclude that the metal-rich population must be at least 1-2Gyr younger than the metal-poor stars, owing to the long timescales needed for strong s-process enrichment and the development of a large contingent of mass transfer binaries.
- ID:
- ivo://CDS.VizieR/J/A+A/465/815
- Title:
- Abundances of Sgr dSph stars
- Short Name:
- J/A+A/465/815
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Sagittarius dwarf spheroidal galaxy is the nearest neighbor of the Milky Way. Moving along a short period quasi-polar orbit within the Halo, it is being destroyed by the tidal interaction with our Galaxy, losing its stellar content along a huge stellar stream. We study the detailed chemical composition of 12 giant stars in the Sagittarius dwarf Spheroidal main body, together with 5 more in the associated globular cluster Terzan 7, by means of high resolution VLT-UVES spectra. Abundances are derived for up to 21 elements from O to Nd, by fitting lines EW or line profiles against ATLAS 9 model atmospheres and SYNTHE spectral syntheses calculated ad-hoc. Temperatures are derived from (V-I)_0_ or (B-V)_0_ colors and gravities from FeI-FeII ionization equilibrium. The metallicity of the observed stars is between [Fe/H]=-0.9 and 0. We detected a highly peculiar "chemical signature", with undersolar alpha elements, Na, Al , Sc, V, Co, Ni, Cu, and Zn, among others, and overabundant La, Ce, and Nd. Many of these abundance ratios (in particular light-odd elements and iron peak ones) are strongly at odds with what is observed within the Milky Way, so they may be a very useful tool for recognizing populations originating within the Sagittarius dwarf. This can be clearly seen in the case of the globular Palomar 12, which is believed to have been stripped from Sagittarius: the cluster shows precisely the same chemical "oddities", thus finally confirming its extragalactic origin.
- ID:
- ivo://CDS.VizieR/J/ApJ/839/94
- Title:
- Abundances of solar twins from Keck/HIRES
- Short Name:
- J/ApJ/839/94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The six planets of the Kepler-11 system are the archetypal example of a population of surprisingly low-density transiting planets revealed by the Kepler mission. We have determined the fundamental parameters and chemical composition of the Kepler-11 host star to unprecedented precision using an extremely high-quality spectrum from Keck-HIRES (R~67000, S/N per pixel ~260 at 600nm). Contrary to previously published results, our spectroscopic constraints indicate that Kepler-11 is a young main-sequence solar twin. The revised stellar parameters and new analysis raise the densities of the Kepler-11 planets by between 20% and 95% per planet, making them more typical of the emerging class of "puffy" close-in exoplanets. We obtain photospheric abundances of 22 elements and find that Kepler-11 has an abundance pattern similar to that of the Sun with a slightly higher overall metallicity. We additionally analyze the Kepler light curves using a photodynamical model and discuss the tension between spectroscopic and transit/TTV-based estimates of stellar density.
- ID:
- ivo://CDS.VizieR/J/ApJ/871/193
- Title:
- A combined Chandra & LAMOST study of stellar activity
- Short Name:
- J/ApJ/871/193
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We probed stellar X-ray activity over a wide range of stellar parameters, using Chandra and Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) data. We measured the X-ray-to-bolometric luminosity ratio (R_X_=L_X_/L_bol_) for 484 main-sequence stars and found a bimodal distribution for G and K types. We interpret this bimodality as evidence of two subpopulations with different coronal temperatures, which are caused by different coronal heating rates. Using the metallicity and velocity information, we find that both of the subpopulations are mostly located in the thin disk. We find no trend of R_X_ with stellar age for stars older than ~4Gyr; there is a trough in the R_X_ versus age distribution, with the lowest range of R_X_ appearing at ages around 2Gyr. We then examined the correlation between R_X_ and R_H{alpha}_ (proxy of chromospheric activity): we find that the two quantities are well correlated, as found in many earlier studies. Finally, we selected a sample of 12 stars with X-ray flares and studied the light-curve morphology of the flares. The variety of flare profiles and timescales observed in our sample suggests the contribution of different processes of energy release.
- ID:
- ivo://CDS.VizieR/J/A+A/566/A118
- Title:
- A comprehensive view of Virgo stellar stream
- Short Name:
- J/A+A/566/A118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To explore the complex halo substructure that has been reported in the direction of the Virgo constellation, radial velocities and metallicities have been measured for 82 RR Lyrae stars (RRLS) that were identified by the QUEST survey. These stars are distributed over 90 sq. deg. of the sky, and lie from 4 to 23kpc from the Sun. Using an algorithm for finding groups in phase space and modeling the smooth halo component in the region, we identified the 5 most significant RRLS groups, some of which were previously known or suspected. We have examined the SEKBO and the Catalina catalog of RRLS (with available spectroscopic measurements), as well as the bright QUEST RRLS sample, the catalog of Red Giant stars from the Spaghetti survey, and three recent catalogs of blue horizontal branch (BHB) stars, for stars that may be related to the QUEST RRLS groups.
