- ID:
- ivo://CDS.VizieR/J/ApJ/786/74
- Title:
- EW measurements of 6 Segue 1 red giants
- Short Name:
- J/ApJ/786/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Magellan/MIKE and Keck/HIRES high-resolution spectra of six red giant stars in the dwarf galaxy Segue 1. Including one additional Segue 1 star observed by Norris et al. (2010ApJ...722L.104N), high-resolution spectra have now been obtained for every red giant in Segue 1. Remarkably, three of these seven stars have metallicities below [Fe/H]=-3.5, suggesting that Segue 1 is the least chemically evolved galaxy known. We confirm previous medium-resolution analyses demonstrating that Segue 1 stars span a metallicity range of more than 2 dex, from [Fe/H]=-1.4 to [Fe/H]=-3.8. All of the Segue 1 stars are {alpha}-enhanced, with [{alpha}/Fe]~0.5. High {alpha}-element abundances are typical for metal-poor stars, but in every previously studied galaxy [{alpha}/Fe] declines for more metal-rich stars, which is typically interpreted as iron enrichment from supernova Ia. The absence of this signature in Segue 1 indicates that it was enriched exclusively by massive stars. Other light element abundance ratios in Segue 1, including carbon enhancement in the three most metal-poor stars, closely resemble those of metal-poor halo stars. Finally, we classify the most metal-rich star as a CH star given its large overabundances of carbon and s-process elements. The other six stars show remarkably low neutron-capture element abundances of [Sr/H]<-4.9 and [Ba/H]<-4.2, which are comparable to the lowest levels ever detected in halo stars. This suggests minimal neutron-capture enrichment, perhaps limited to a single r-process or weak s-process synthesizing event. Altogether, the chemical abundances of Segue 1 indicate no substantial chemical evolution, supporting the idea that it may be a surviving first galaxy that experienced only one burst of star formation.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/527/A18
- Title:
- EW of 6 subgiants of {omega} Cen
- Short Name:
- J/A+A/527/A18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analysed high-resolution UVES spectra of six stars belonging to the subgiant branch of {omega} Centauri, and derived abundance ratios of 19 chemical elements (namely Al, Ba, C, Ca, Co, Cr, Cu, Fe, La, Mg, Mn, N, Na, Ni, Sc, Si, Sr, Ti, and Y). A comparison with previous abundance determinations for red giants provided remarkable agreement and allowed us to identify the sub-populations to which our targets belong. We found that three targets belong to a low-metallicity population at [Fe/H]=-2.0dex, [alpha/Fe]=+0.4dex and [s/Fe]=0dex. Stars with similar characteristics were found in small amounts by past surveys of red giants. We discuss the possibility that they belong to a separate sub-population that we name VMP (very metal-poor, at most 5% of the total cluster population), which - in the self-enrichment hypothesis - is the best-candidate first stellar generation in {omega} Cen. Two of the remaining targets belong to the dominant metal-poor population (MP) at [Fe/H]=-1.7dex, and the last one to the metal-intermediate (MInt) one at [Fe/H]=-1.2dex. The existence of the newly defined VMP population could help to understand some puzzling results based on low-resolution spectroscopy (Sollima et al. 2005ApJ...634..332S , Villanova et al., 2007, Cat. J/ApJ/663/296) in their age differences determinations, because the metallicity resolution of these studies was probably not enough to detect the VMP population. The VMP could also correspond to some of the additional substructures of the subgiant-branch region found in the latest HST photometry (Bellini et al., 2010, Cat. J/AJ/140/631). After trying to correlate chemical abundances with substructures in the subgiant branch of {omega} Cen, we found that the age difference between the VMP and MP populations should be small (0+/-2Gyr), while the difference between the MP and MInt populations could be slightly larger (2+/-2Gyr).
- ID:
- ivo://CDS.VizieR/J/A+A/502/267
- Title:
- EWs of 31 giant stars of 10 open clusters
- Short Name:
- J/A+A/502/267
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Equivalent widths (EWs) of a sample of 31 giant stars of 10 open clusters. The list includes lines of NaI, MgI, SiI, CaI, ScII, TiI, VI, VII, CrI, CrII, FeI, FeII, CoI, NiI, YII, CeII, and EuII. For most of the lines, EWs were measured using PeakFit. For some Fe II lines, EWs were measured by fitting Gaussian profiles to the lines with the IRAF task SPLOT. The adopted oscillator strengths (loggfs) and excitation potentials (EP) are also listed. For the stars of the clusters NGC 2360 and NGC 2447 only the FeII EWs are given. The EWs of the remaining lines can be found in Hamdani et al. (2000, Cat. J/A+A/360/509).
- ID:
- ivo://CDS.VizieR/J/AJ/148/24
- Title:
- Extinction maps in the bulge from APOGEE
- Short Name:
- J/AJ/148/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galactic interstellar extinction maps are powerful and necessary tools for Milky Way structure and stellar population analyses, particularly toward the heavily reddened bulge and in the midplane. However, due to the difficulty of obtaining reliable extinction measures and distances for a large number of stars that are independent of these maps, tests of their accuracy and systematics have been limited. Our goal is to assess a variety of photometric stellar extinction estimates, including both two-dimensional and three-dimensional extinction maps, using independent extinction measures based on a large spectroscopic sample of stars toward the Milky Way bulge. We employ stellar atmospheric parameters derived from high-resolution H-band Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra, combined with theoretical stellar isochrones, to calculate line-of-sight extinction and distances for a sample of more than 2400 giants toward the Milky Way bulge. We compare these extinction values to those predicted by individual near-IR and near+mid-IR stellar colors, two-dimensional bulge extinction maps, and three-dimensional extinction maps. The long baseline, near+mid-IR stellar colors are, on average, the most accurate predictors of the APOGEE extinction estimates, and the two-dimensional and three-dimensional extinction maps derived from different stellar populations along different sightlines show varying degrees of reliability. We present the results of all of the comparisons and discuss reasons for the observed discrepancies. We also demonstrate how the particular stellar atmospheric models adopted can have a strong impact on this type of analysis, and discuss related caveats.
- ID:
- ivo://CDS.VizieR/J/A+A/403/1105
- Title:
- Extremely metal-poor giants equivalent widths
- Short Name:
- J/A+A/403/1105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper reports detailed abundance analyses for four extremely metal-poor (XMP) giant stars with [Fe/H]<-3.8, based on high-resolution, high- S/N spectra from the ESO VLT (Kueyen/UVES) and LTE model atmosphere calculations. The derived [{alpha}/Fe] ratios in our sample exhibit a small dispersion, confirming previous findings in the literature, i.e. a constant overabundance of the {alpha}-elements with a very small (if any) dependence on [Fe/H]. In particular, the very small scatter we determine for [Si/Fe] suggests that this element shows a constant overabundance at very low metallicity, a conclusion which could not have been derived from the widely scattered [Si/Fe] values reported in the literature for less metal-poor stars. For the iron-peak elements, our precise abundances for the four XMP stars in our sample confirm the decreasing trend of Cr and Mn with decreasing [Fe/H], as well as the increasing trend for Co and the absence of any trend for Sc and Ni. In contrast to the significant spread of the ratios [Sr/Fe] and [Ba/Fe], we find [Sr/Ba] in our sample to be roughly solar, with a much lower dispersion than previously found for stars in the range -3.5<[Fe/H]<-2.5.
- 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/MNRAS/360/1345
- Title:
- F- and G-type stars in solar neighbourhood
- Short Name:
- J/MNRAS/360/1345
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new metallicity distribution and an age-metallicity relation are presented for 437 nearby F and G turn-off and sub-giant stars selected from radial velocity data of Nidever et al. (2002, Cat. J/ApJS/141/503). Photometric metallicities are derived from uvby-H{beta} photometry, and the stellar ages from the isochrones of Bergbusch & VandenBerg (2001ApJ...556..322B) as transformed to uvby photometry using the methods of Clem et al. (2004, Cat. J/AJ/127/1227).
- ID:
- ivo://CDS.VizieR/J/ApJ/895/78
- Title:
- [Fe/H] and [{alpha}/Fe] in M31 dwarf galaxies
- Short Name:
- J/ApJ/895/78
- Date:
- 15 Mar 2022 06:34:41
- Publisher:
- CDS
- Description:
- We present chemical abundances of red giant branch (RGB) stars in the dwarf spheroidal (dSph) satellite system of Andromeda (M31), using spectral synthesis of medium-resolution (R~6000) spectra obtained with the KeckII telescope and Deep Imaging Multi-Object Spectrometer spectrograph via the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo survey. We coadd stars according to their similarity in photometric metallicity or effective temperature to obtain a signal-to-noise ratio (S/N) high enough to measure average [Fe/H] and [{alpha}/Fe] abundances. We validate our method using high S/N spectra of RGB stars in Milky Way globular clusters, as well as deep observations for a subset of the M31 dSphs in our sample. For this set of validation coadds, we compare the weighted average abundance of the individual stars with the abundance determined from the coadd. We present individual and coadded measurements of [Fe/H] and [{alpha}/Fe] for stars in 10 M31 dSphs, including the first [{alpha}/Fe] measurements for And IX, XIV, XV, and XVIII. These fainter, less massive dSphs show declining [{alpha}/Fe] relative to [Fe/H], implying an extended star formation history (SFH). In addition, these dSphs also follow the same mass-metallicity relation found in other Local Group satellites. The conclusions we infer from coadded spectra agree with those from previous measurements in brighter M31 dSphs with individual abundance measurements, as well as conclusions from photometric studies. These abundances greatly increase the number of spectroscopic measurements of the chemical composition of M31's less massive dwarf satellites, which are crucial to understanding their SFH and interaction with the M31 system.
- ID:
- ivo://CDS.VizieR/J/ApJ/875/129
- Title:
- FeI lines in NIR spectra of Arcturus & mu Leo
- Short Name:
- J/ApJ/875/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- For a detailed analysis of stellar chemical abundances, high-resolution spectra in the optical have mainly been used, while the development of near-infrared (NIR) spectrograph has opened new wavelength windows. Red giants have a large number of resolved absorption lines in both the optical and NIR wavelengths, but the characteristics of the lines in different wave passbands are not necessarily the same. We present a selection of FeI lines in the z', Y, and J bands (0.91-1.33{mu}m). On the basis of two different lists of lines in this range, the Vienna Atomic Line Database (VALD) and the catalog published by Melendez & Barbuy in 1999 (MB99; Cat. J/ApJS/124/527), we selected sufficiently strong lines that are not severely blended and compiled lists with 107 FeI lines in total (97 and 75 lines from VALD and MB99, respectively). Combining our lists with high-resolution ({lambda}/{Delta}{lambda}=28000) and high signal-to-noise (>500) spectra taken with an NIR spectrograph, WINERED, we present measurements of the iron abundances of two prototype red giants: Arcturus and {mu} Leo. A bootstrap method for determining the microturbulence and abundance together with their errors is demonstrated. The standard deviations of log{epsilon}_Fe_ values from individual FeI lines are significantly smaller when we use the lines from MB99 instead of those from VALD. With the MB99 list, we obtained {xi}=1.20+/-0.11km/s and log{epsilon}_Fe_=7.01+/-0.05dex for Arcturus, and {xi}=1.54+/-0.17km/s and log{epsilon}_Fe_=7.73+/-0.07dex for {mu} Leo. These final values show better agreements with previous values in the literature than the corresponding values we obtained with VALD.
- ID:
- ivo://CDS.VizieR/J/MNRAS/448/2749
- Title:
- 257 field giant stars spectroscopic parameters
- Short Name:
- J/MNRAS/448/2749
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The study of stellar parameters of planet-hosting stars, such as metallicity and chemical abundances, help us to understand the theory of planet formation and stellar evolution. Here, we present a catalogue of accurate stellar atmospheric parameters and iron abundances for a sample of 257 K and G field evolved stars that are being surveyed for planets using precise radial-velocity measurements as part of the Coralie programme to search for planets around giants. The analysis was done using a set of high-resolution and high-signal-to-noise Ultraviolet and Visible Echelle Spectrograph spectra. The stellar parameters were derived using Fe I and II ionization and excitation equilibrium methods. To take into account possible effects related to the choice of the lines on the derived parameters, we used three different iron line-list sets in our analysis, and the results differ among themselves by a small factor for most of stars. For those stars with previous literature parameter estimates, we found very good agreement with our own values. In the present catalogue, we are providing new precise spectroscopic measurements of effective temperature, surface gravity, microturbulence, and metallicity for 190 stars for which it has not been found or published in previous articles.
