- ID:
- ivo://CDS.VizieR/J/A+A/622/A191
- Title:
- 885 globular cluster giants abundances
- Short Name:
- J/A+A/622/A191
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We seek to provide abundances of a large set of light and neutron-capture elements homogeneously analyzed that cover a wide range of metallicity to constrain globular cluster (GC) formation and evolution models. We analyzed a large sample of 885 GCs giants from the SDSS~IV-Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. We used the Cannon results to separate the red giant branch and asymptotic giant branch stars, not only allowing for a refinement of surface gravity from isochrones, but also providing an independent H-band spectroscopic method to distinguish stellar evolutionary status in clusters. We then used the Brussels Automatic Code for Characterizing High accUracy Spectra (BACCHUS) to derive metallicity, microturbulence, macroturbulence, many light-element abundances, and the neutron-capture elements Nd and Ce for the first time from the APOGEE GCs data. Our independent analysis helped us to diagnose issues regarding the standard analysis of the APOGEE DR14 for low-metallicity GC stars. Furthermore, while we confirm most of the known correlations and anticorrelation trends (Na-O, Mg-Al, C-N), we discover that some stars within our most metal-poor clusters show an extreme Mg depletion and some Si enhancement. At the same time, these stars show some relative Al depletion, displaying a turnover in the Mg-Al diagram. These stars suggest that Al has been partially depleted in their progenitors by very hot proton-capture nucleosynthetic processes. Furthermore, we attempted to quantitatively correlate the spread of Al abundances with the global properties of GCs. We find an anticorrelation of the Al spread against clusters metallicity and luminosity, but the data do not allow us to find clear evidence of a dependence of N against metallicity in the more metal-poor clusters. Large and homogeneously analyzed samples from ongoing spectroscopic surveys unveil unseen chemical details for many clusters, including a turnover in the Mg-Al anticorrelation, thus yielding new constrains for GCs formation/evolution models.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/245/5
- Title:
- Globular cluster intrinsic iron abundance spreads
- Short Name:
- J/ApJS/245/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an up-to-date catalog of intrinsic iron abundance spreads in the 55 Milky Way globular clusters (GCs) for which sufficiently precise spectroscopic measurements are available. Our method combines multiple data sets when possible to improve the statistics, taking into account the fact that different methods and instruments can lead to systematically offset metallicities. Only high spectral resolution (R>14000) studies that measure the equivalent widths of individual iron lines are found to have uncertainties on the metallicities of the individual stars that can be calibrated sufficiently well for the intrinsic dispersion to be separated cleanly from a random measurement error. The median intrinsic iron spread is found to be 0.045dex, which is small but unambiguously measured to be nonzero in most cases. There is large variation between clusters, but more luminous GCs, above 10^5^L_{sun}_, have increasingly large iron spreads on average; no trend between the iron spread and metallicity is found.
- ID:
- ivo://CDS.VizieR/J/AZh/96/267
- Title:
- Globular clusters abundances and kinematics
- Short Name:
- J/AZh/96/267
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- For the catalog, we compiled the abundances of 28 chemical elements: alpha-elements (O, Mg, Si, Ca, Ti), carbon, iron-peak elements(Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), slow and rapid neutron-capture elements (Sr, Y, Zr, Mo, Ba, La, Ce, Nd, Eu, Dy) and three odd-Z elements(Na, Al, K) in the stars of 69 globular clusters. The data are taken from 101 papers published from 1986 to 2018. The abundances of chemical elements in stars of the clusters in almost all the used papers are determined from high-resolution spectra obtained mainly for the atmospheres of red giants. The spectra are analyzed with the local thermodynamic equilibrium approximation.
- ID:
- ivo://CDS.VizieR/J/ApJ/682/199
- Title:
- Globulars with X-ray sources in NGC 5128
- Short Name:
- J/ApJ/682/199
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We detect 353 X-ray point sources, mostly low-mass X-ray binaries (LMXBs), in four Chandra observations of Centaurus A (NGC 5128), the nearest giant early-type galaxy, and correlate this point-source population with the largest available ensemble of confirmed and likely globular clusters (GCs) associated with this galaxy. Of the X-ray sources, 31 are coincident with 30 GCs that are confirmed members of the galaxy by radial velocity measurement (two X-ray sources match one GC within our search radius), while one X-ray source coincides with a GC resolved by Hubble Space Telescope (HST) images. Another 36 X-ray point sources match probable, but spectroscopically unconfirmed, GC candidates.
- ID:
- ivo://CDS.VizieR/J/A+A/593/A28
- Title:
- Halo metal-poor stars chemical data
- Short Name:
- J/A+A/593/A28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an analysis of 107 extremely metal-poor (EMP) stars with metallicities lower than [Fe/H]=-3.0, identified in medium-resolution spectra in the Sloan Digital Sky Survey (SDSS). Our analysis provides estimates of the stellar effective temperatures and surface gravities, as well as iron, calcium, and magnesium abundances. We followed the same method as in previous papers of this series. The method is based on comparisons of the observed spectra with synthetic spectra. The abundances of Fe, Ca, and Mg were determined by fitting spectral regions that are dominated by lines of each element. In addition, we present a technique to determine upper limits for elements whose features are not detected in a given spectrum. We also analyzed our sample with the SEGUE stellar parameter pipeline to obtain additional determinations of the atmospheric parameters and iron and alpha-element abundances, which we then compare with ours. In addition, we used these parameters to infer [C/Fe] ratios. Ca is typically the only element in these spectra with a moderate to low signal-to-noise ratio and medium resolution in this metallicity regime with lines that are sufficiently strong to reliably measure its abundance. Fe and Mg exhibit weaker features that in most cases only provide upper limits. We measured [Ca/Fe] and [Mg/Fe] for EMP stars in the SDSS spectra and conclude that most of the stars exhibit the typical enhancement level for alpha-elements, ~+0.4, although some stars for which only [Fe/H] upper limits could be estimated indicate higher [alpha/Fe] ratios. We also find that 26% of the stars in our sample can be classified as carbon-enhanced metal-poor (CEMP) stars and that the frequency of CEMP stars also increases with decreasing metallicity, as has been reported for previous samples. We identify a rare, bright (g=11.90) EMP star, SDSS J134144.61+474128.6, with [Fe/H]=-3.27, [C/Fe]=+0.95, and elevated magnesium ([Mg/Fe]=+0.62), an abundance pattern typical of CEMP-no stars.
- ID:
- ivo://CDS.VizieR/J/A+A/534/A136
- Title:
- Halo red giants from the SEGUE survey
- Short Name:
- J/A+A/534/A136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic search for halo field stars that originally formed in globular clusters. Using moderate-resolution SDSS-III/SEGUE-2 spectra of 561 red giants with typical halo metallicities (-1.8<=[Fe/H]<=-1.0), we identify 16 stars, 3% of the sample, with CN and CH bandstrength behavior indicating depleted carbon and enhanced nitrogen abundances relative to the rest of the data set. Since globular clusters are the only environment known in which stars form with this pattern of atypical light-element abundances, we claim that these stars are second-generation globular cluster stars that have been lost to the halo field via normal cluster mass-loss processes.
- ID:
- ivo://CDS.VizieR/J/ApJ/698/865
- Title:
- Halo streams in the SDSS-DR7
- Short Name:
- J/ApJ/698/865
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have detected stellar halo streams in the solar neighborhood using data from the seventh public data release of the Sloan Digital Sky Survey (SDSS), which includes the directed stellar program Sloan Extension For Galactic Understanding and Exploration (SEGUE). In order to derive distances to each star, we used the metallicity-dependent photometric parallax relation from Ivezic et al. (2008ApJ...684..287I). Our final sample consists of 22321 nearby (d<=2kpc), metal-poor ([Fe/H]<=-0.5) main-sequence stars with six-dimensional estimates of position and space velocity (r{vec},{nu}{vec}). We characterize the orbits of these stars through suitable kinematic proxies for their "effective" integrals of motion, angular momentum, eccentricity, and orbital polar angle and compare the observed distribution to expectations from a smooth distribution in four [Fe/H] bins. The metallicities provide an additional dimension in parameter space that is well suited to distinguish tidal streams from those of dynamical origin. On this basis, we identify at least five significant "phase-space overdensities" of stars on very similar orbits in the solar neighborhood to which we can assign unambiguously peaked [Fe/H] distributions. Three of them have been identified previously, including the halo stream discovered by Helmi et al. (1999MNRAS.307..495H) at a significance level of {sigma}=12.0. In addition, we find at least two new genuine halo streams, judged by their kinematics and [Fe/H], at {sigma}=2.9 and 4.8, respectively.
- ID:
- ivo://CDS.VizieR/J/MNRAS/506/3079
- Title:
- Halpha and other SFR indicators
- Short Name:
- J/MNRAS/506/3079
- Date:
- 18 Jan 2022 13:46:29
- Publisher:
- CDS
- Description:
- We present new H{alpha} photometry for the Star Formation Reference Survey (SFRS), a representative sample of star-forming galaxies in the local Universe. Combining these data with the panchromatic coverage of the SFRS, we provide calibrations of H{alpha}-based star-formation rates (SFRs) with and without correction for the contribution of [NII] emission. We consider the effect of extinction corrections based on the Balmer decrement, infrared excess, and spectral energy distribution (SED) fits. We compare the SFR estimates derived from SED fits, polycyclic aromatic hydrocarbons, hybrid indicators such as 24um+H{alpha}, 8um+H{alpha}, FIR+FUV, and H{alpha} emission for a sample of purely star-forming galaxies. We provide a new calibration for 1.4GHz-based SFRs by comparing to the H{alpha} emission, and we measure a dependence of the radio-to-H{alpha} emission ratio based on galaxy stellar mass. Active galactic nuclei introduce biases in the calibrations of different SFR indicators but have only a minimal effect on the inferred SFR densities from galaxy surveys. Finally, we quantify the correlation between galaxy metallicity and extinction.
- ID:
- ivo://CDS.VizieR/J/ApJ/778/56
- Title:
- Hamburg/ESO Survey extremely metal-poor stars
- Short Name:
- J/ApJ/778/56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From detailed abundance analysis of >100 Hamburg/ESO candidate extremely metal-poor (EMP) stars we find 45 with [Fe/H]<-3.0dex. We identify a heretofore unidentified group: Ca-deficient stars with sub-solar [Ca/Fe] ratios and the lowest neutron-capture abundances; the Ca-deficient group comprises ~10% of the sample, excluding Carbon stars. Our radial velocity distribution shows that the carbon-enhanced stars with no s-process enhancements, CEMP-no, and which do not show C_2_ bands are not preferentially binary systems. Ignoring Carbon stars, approximately 15% of our sample are strong (>=5{sigma}) outliers in one or more elements between Mg and Ni; this rises to ~19% if very strong (>=10{sigma}) outliers for Sr and Ba are included. Examples include: HE0305-0554 with the lowest [Ba/H] known; HE1012-1540 and HE2323-0256, two (non-velocity variable) C-rich stars with very strong [Mg,Al/Fe] enhancements; and HE1226-1149, an extremely r-process rich star.
- ID:
- ivo://CDS.VizieR/J/ApJ/878/134
- Title:
- HARPS and X-shooter spectra of Southern M dwarfs
- Short Name:
- J/ApJ/878/134
- Date:
- 25 Oct 2021 00:49:19
- Publisher:
- CDS
- Description:
- We present the homogeneous analysis of a sample of Southern early-type M dwarfs in the solar neighborhood (d<60pc). We used the MCAL technique to derive the effective temperature Teff, metallicity [Fe/H], and activity index i_a_(H_alpha_) of 420 M stars using HARPS spectra. The effective temperature Teff, surface gravity logg, metallicity [Fe/H], and projected rotational velocity V_rot_sini of 153 M0-M6 dwarfs were determined by fitting the observed intermediate-resolution spectra from the VIS arm of VLT/X-shooter with a grid of BT-Settl stellar atmosphere models. We estimated the typical uncertainties of the fit with X-shooter spectra by varying region-to-region results by {sigma}T_eff_~50K, {sigma}logg~0.2, and {sigma}[Fe/H]~0.2dex. Photometric verification of Teff for the 295 stars from the HARPS sample and the 61 stars from the X-shooter sample is also provided. We compared our results from different methods to estimate absolute uncertainty in determining the physical properties of M dwarfs.
