- ID:
- ivo://CDS.VizieR/J/A+A/533/A134
- Title:
- Abundances of microlensed stars in the Bulge
- Short Name:
- J/A+A/533/A134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform a detailed elemental abundance analysis of dwarf stars in the Galactic bulge, based on high-resolution spectra that were obtained while the stars were optically magnified during gravitational microlensing events. The analysis method is the same as for a large sample of F and G dwarf stars in the Solar neighbourhood, enabling a fully differential comparison between the Bulge and the local stellar populations in the Galactic disc.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/512/A41
- Title:
- Abundances of microlensed stars in the Bulge
- Short Name:
- J/A+A/512/A41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform a detailed elemental abundance analysis of dwarf stars in the Galactic bulge, based on high-resolution spectra that were obtained while the stars were optically magnified during gravitational microlensing events. The analysis method is the same as for a large sample of F and G dwarf stars in the Solar neighbourhood, enabling a fully differential comparison between the Bulge and the local stellar populations in the Galactic disc.
- ID:
- ivo://CDS.VizieR/J/ApJ/857/74
- Title:
- Abundances of 7 new member stars in Tucana II
- Short Name:
- J/ApJ/857/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present chemical abundance measurements for seven stars with metallicities ranging from [Fe/H]=-3.3 to [Fe/H]=-2.4 in the TucanaII ultra-faint dwarf galaxy (UFD), based on high-resolution spectra obtained with the MIKE spectrograph on the 6.5m Magellan-Clay Telescope. For three stars, we present detailed chemical abundances for the first time. Of those, two stars are newly discovered members of Tucana II and were selected as probable members from deep narrowband photometry of the Tucana II UFD taken with the SkyMapper telescope. This result demonstrates the potential for photometrically identifying members of dwarf galaxy systems based on chemical composition. One new star was selected from the membership catalog of Walker+ (2016, J/ApJ/819/53). The other four stars in our sample have been reanalyzed, following additional observations. Overall, six stars have chemical abundances that are characteristic of the UFD stellar population. The seventh star shows chemical abundances that are discrepant from the other Tucana II members and an atypical, higher strontium abundance than what is expected for typical UFD stars. While unlikely, its strontium abundance raises the possibility that it may be a foreground metal-poor halo star with the same systemic velocity as Tucana II. If we were to exclude this star, Tucana II would satisfy the criteria to be a surviving first galaxy. Otherwise, this star implies that Tucana II has likely experienced somewhat extended chemical evolution.
- ID:
- ivo://CDS.VizieR/J/AJ/140/1694
- Title:
- Abundances of non-variable red and blue HB stars
- Short Name:
- J/AJ/140/1694
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new detailed abundance study of field red horizontal branch (RHB) and blue horizontal branch (BHB) non-variable stars. High resolution and high signal-to-noise ratio echelle spectra of 11 RHB and 12 BHB were obtained with the McDonald 2.7m telescope, and the RHB sample was augmented by reanalysis of spectra of 25 stars from a recent survey. We derived stellar atmospheric parameters based on spectroscopic constraints and computed relative abundance ratios for 24 species of 19 elements.
- ID:
- ivo://CDS.VizieR/J/ApJ/763/61
- Title:
- Abundances of 7 red giant members of BootesI
- Short Name:
- J/ApJ/763/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a double-blind analysis of high-dispersion spectra of seven red giant members of the Bootes I ultrafaint dwarf spheroidal galaxy, complemented with re-analysis of a similar spectrum of an eighth-member star. The stars cover [Fe/H] from -3.7 to -1.9 and include a CEMP-no star with [Fe/H]=-3.33. We conclude from our chemical abundance data that Bootes I has evolved as a self-enriching star-forming system, from essentially primordial initial abundances. This allows us uniquely to investigate the place of CEMP-no stars in a chemically evolving system, in addition to limiting the timescale of star formation. The elemental abundances are formally consistent with a halo-like distribution, with enhanced mean [{alpha}/Fe] and small scatter about the mean. This is in accord with the high-mass stellar initial mass function in this low-stellar-density, low-metallicity system being indistinguishable from the present-day solar neighborhood value. There is a non-significant hint of a decline in [{alpha}/Fe] with [Fe/H]; together with the low scatter, this requires low star formation rates, allowing time for supernova ejecta to be mixed over the large spatial scales of interest. One star has very high [Ti/Fe], but we do not confirm a previously published high value of [Mg/Fe] for another star. We discuss the existence of CEMP-no stars, and the absence of any stars with lower CEMP-no enhancements at higher [Fe/H], a situation that is consistent with knowledge of CEMP-no stars in the Galactic field. We show that this observation requires there be two enrichment paths at very low metallicities: CEMP-no and "carbon-normal."
- ID:
- ivo://CDS.VizieR/J/MNRAS/463/580
- Title:
- Abundances of red giants in NGC6940
- Short Name:
- J/MNRAS/463/580
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the high-resolution (R~=60000), high signal-to-noise ratio (S/N~=120) spectroscopic analysis of 12 red giant members of the Galactic open cluster NGC 6940. We applied Yonsei-Yale isochrones to the colour-magnitude diagram, which suggested an age of 1.1Gyr for the cluster with a turn-off mass of 2 M_{sun}_. Atmospheric parameters (T_eff_, logg, [Fe/H], and {xi}_t_) were determined via equivalent widths of FeI, FeII, TiI, and TiII lines. Calculated mean metallicity of the cluster is <[Fe/H]>=0.04+/-0.02. We derived abundances of {alpha} (Mg, Si, Ca), Fe-group (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), and n-capture (Y, La, Nd, Eu) elements to be about solar. Light odd-Z elements Na and Al are slightly enhanced in MMU 108 and MMU 152 by ~0.34 and ~0.16dex, respectively. Abundances of light elements Li, C, N, O, and ^12^C/^13^C ratios were derived from spectrum syntheses of the LiI resonance doublet at 6707{AA}, [OI] line at 6300{AA}, C_2_ Swan bandheads at 5164 and 5635{AA}, and strong ^12,13^CN system lines in the 7995-8040{AA} region. Most carbon isotopic ratios are similar to those found in other solar-metallicity giants, but MMU 152 has an unusual value of ^12^C/^13^C=6. Evaluation of the LiCNO abundances and ^12^C/^13^C ratios along with the present theoretical models suggests that all the red giants in our sample are core-helium-burning clump stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/446/3562
- Title:
- Abundances of red giants in NGC752
- Short Name:
- J/MNRAS/446/3562
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present detailed chemical compositions of 10 red giant star members of the Galactic (open) cluster NGC 752, derived from high-resolution (R~60000), high signal-to-noise (S/N>=140) spectra. We confirmed cluster memberships by measuring the stellar radial velocities, and by deriving model atmosphere parameters (Teff, logg, [Fe/H] and {xi}t) from equivalent widths of FeI, FeII, TiI, and TiII lines. The metallicity we obtained for NGC 752 ([Fe/H]=-0.02+/-0.05) is in good agreement with previous studies. We derived abundances of alpha (Mg, Si, Ca), light odd-Z (Na, Al), Fe-group (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), n-capture (Y, La, Nd, Eu), and p-capture (Li, C, N, O) species for each star. Furthermore, we also derived abundances of the LiCNO p-capture element group and carbon isotopic ratios, using synthetic spectrum analyses of the LiI 6707{AA} resonance doublet, the [OI] line at 6300{AA}, the CH G-band features near 4311 and 4325{AA}, the C_2_ bandheads at 5160 and 563{AA}, and ^12,13^CN red system lines in the 7995-8040{AA} region. By applying recent isochrones to NGC 752 photometry, and comparing the colour-magnitude diagram information to our Li abundances and 12C/13C ratios, we suggest that the 10 observed red giants can be separated into three first-ascent, six red-clump and one red horizontal branch star.
- ID:
- ivo://CDS.VizieR/J/A+A/455/271
- Title:
- Abundances of red giants in NGC 6441
- Short Name:
- J/A+A/455/271
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of the present work is to determine accurate metallicities for a group of red giant branch stars in the field of the bulge Globular Cluster NGC 6441. This is the third paper in a series resulting from a large project aimed at determining the extent of the Na-O anticorrelation among Globular Cluster stars and exploring its relationship with HB morphology. We present an LTE abundance analysis of these objects, based on data gathered with the FLAMES fiber facility and the UVES spectrograph at VLT2. Results. Five of the thirteen stars observed are members of the cluster. The average Fe abundance for these five stars is [Fe/H]=-0.39+/-0.04+/-0.05dex, where the first error bar includes the uncertainties related to star-to-star random errors, and the second one the systematic effects related to the various assumptions made in the analysis.The overall abundance pattern is quite typical of Globular Clusters, with an excess of the alpha-elements and of Eu. There is evidence that the stars of NGC 6441 are enriched in Na and Al, while they have been depleted of O and Mg by H-burning at high temperatures, analogous with extensive observations of other Globular Clusters: in particular, one star is clearly Na and Al-rich and O and Mg-poor. We also obtained quite high V abundances, but it is possible that this is an artifact of the analysis, since similar high V abundances are also derived for the field stars. These last are all more metal-rich than NGC 6441 and probably belong to the bulge population bulge.
- ID:
- ivo://CDS.VizieR/J/A+A/464/953
- Title:
- Abundances of red giants in NGC 6441
- Short Name:
- J/A+A/464/953
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of FLAMES-Giraffe spectra for several bright giants in NGC 6441, to investigate the presence and extent of the Na-O anticorrelation in this anomalous globular cluster. The field of NGC 6441 is very crowded, with severe contamination by foreground (mainly bulge) field stars. Appropriate membership criteria were devised to identify a group of 25 likely cluster members among the about 130 stars observed. Combined with the UVES data obtained with the same observations (Gratton et al., 2006, Cat. <J/A+A/455/271>), high dispersion abundance analyses are now available for a total of 30 stars in NGC 6441, 29 of them having data for both O and Na. The spectra were analyzed by a standard line analysis procedure; care was taken to minimize the impact of the differential interstellar reddening throughout the cluster, and to extract reliable information from crowded, and moderately high S/N (30-70), moderately high resolution (R~23000) spectra.
- 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.
