- ID:
- ivo://CDS.VizieR/J/A+A/606/A71
- Title:
- dSph RGB abundance and velocities
- Short Name:
- J/A+A/606/A71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From ESO VLT/FLAMES/GIRAFFE spectra, abundance measurements of Zn have been made in ~100 individual red giant branch (RGB) stars in the Sculptor dwarf spheroidal galaxy. This is the largest sample of individual Zn abundance measurements within a stellar system beyond the Milky Way. In the observed metallicity range, -2.7<=[Fe/H]<=-0.9, the general trend of Zn abundances in Sculptor is similar to that of {alpha}-elements. That is, super-solar abundance ratios of [Zn/Fe] at low metallicities, which decrease with increasing [Fe/H], eventually reaching subsolar values. However, at the higher metallicities in Sculptor, [Fe/H]>~-1.8, we find a significant scatter, -0.8<~[Zn/Fe]<~+0.4, which is not seen in any {alpha}-element. Our results are consistent with previous observations of a limited number of stars in Sculptor and in other dwarf galaxies. These results suggest that zinc has a complex nucleosynthetic origin, behaving neither completely like an {alpha}- nor an iron-peak element.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/800/51
- Title:
- DUSTiNGS II. Metal-poor dusty AGB stars
- Short Name:
- J/ApJ/800/51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The DUSTiNGS survey (DUST in Nearby Galaxies with Spitzer) is a 3.6 and 4.5{mu}m imaging survey of 50 nearby dwarf galaxies designed to identify dust-producing asymptotic giant branch (AGB) stars and massive stars. Using two epochs, spaced approximately six months apart, we identify a total of 526 dusty variable AGB stars (sometimes called "extreme" or x-AGB stars; [3.6]-[4.5]>0.1mag). Of these, 111 are in galaxies with [Fe/H]<-1.5 and 12 are in galaxies with [Fe/H]<-2.0, making them the most metal-poor dust-producing AGB stars known. We compare these identifications to those in the literature and find that most are newly discovered large-amplitude variables, with the exception of {approx}30 stars in NGC185 and NGC147, 1 star in IC1613, and 1 star in Phoenix. The chemical abundances of the x-AGB variables are unknown, but the low metallicities suggest that they are more likely to be carbon-rich than oxygen-rich and comparisons with existing optical and near-IR photometry confirm that 70 of the x-AGB variables are confirmed or likely carbon stars. We see an increase in the pulsation amplitude with increased dust production, supporting previous studies suggesting that dust production and pulsation are linked. We find no strong evidence linking dust production with metallicity, indicating that dust can form in very metal-poor environments.
- ID:
- ivo://CDS.VizieR/J/ApJ/851/152
- Title:
- DUSTiNGS. IV. AGB spectral types with HST
- Short Name:
- J/ApJ/851/152
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The survey for DUST in Nearby Galaxies with Spitzer (DUSTiNGS) identified several candidate Asymptotic Giant Branch (AGB) stars in nearby dwarf galaxies and showed that dust can form even in very metal-poor systems (Z~0.008Z_{sun}_). Here, we present a follow-up survey with WFC3/IR on the Hubble Space Telescope (HST), using filters that are capable of distinguishing carbon-rich (C-type) stars from oxygen-rich (M-type) stars: F127M, F139M, and F153M. We include six star-forming DUSTiNGS galaxies (NGC147, IC10, Pegasus dIrr, SextansB, SextansA, and Sag DIG), all more metal-poor than the Magellanic Clouds and spanning 1dex in metallicity. We double the number of dusty AGB stars known in these galaxies and find that most are carbon rich. We also find 26 dusty M-type stars, mostly in IC 10. Given the large dust excess and tight spatial distribution of these M-type stars, they are most likely on the upper end of the AGB mass range (stars undergoing Hot Bottom Burning). Theoretical models do not predict significant dust production in metal-poor M-type stars, but we see evidence for dust excess around M-type stars even in the most metal-poor galaxies in our sample (12+log(O/H)=7.26-7.50). The low metallicities and inferred high stellar masses (up to ~10M_{sun}_) suggest that AGB stars can produce dust very early in the evolution of galaxies (~30Myr after they form), and may contribute significantly to the dust reservoirs seen in high-redshift galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/866/L1
- Title:
- Dust models & IR spectroscopy obs. of AGB stars
- Short Name:
- J/ApJ/866/L1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Many emission features remain unidentified in the infrared spectra of asymptotic giant branch (AGB) stars. In particular, features at ~11, 20, 28, and 32{mu}m have been noted in mid-infrared spectra of oxygen-rich AGB stars. Here, I present models of dust excess emission in 36 spectra of 24 AGB stars from the Short Wavelength Spectrometer on board the Infrared Space Observatory and the Infrared Spectrograph on the Spitzer Space Telescope. The models include opacities of grains composed of mixtures of various polymorphs of alumina obtained by preparing bayerite and boehmite at high temperatures, and these dust components provide satisfactory fits to the 11, 20, 28, and 32{mu}m features. Though not a direct conclusion from this study, the presence of grains of the various polymorphs of aluminas in circumstellar dust shells around AGB stars suggests that corundum may have a role in giving rise to the 13{mu}m feature.
- ID:
- ivo://CDS.VizieR/J/A+A/640/A2
- Title:
- Dwarfs & giants surface brightness-colour relations
- Short Name:
- J/A+A/640/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Surface brightness-colour relations (SBCRs) are used to derive the stellar angular diameters from photometric observations. They have various astrophysical applications, such as the distance determination of eclipsing binaries or the determination of exoplanet parameters. However, strong discrepancies between the SBCRs still exist in the literature, in particular for early and late-type stars. We aim at calibrating new SBCRs as a function of the spectral type and the luminosity class of the stars. Our purpose is also to apply homogeneous criteria for the selection of the reference stars and on the basis of an exhaustive and up-to-date list of interferometric late-type targets. We implement criteria to select measurements in the JMMC Measured Diameters Catalog (JMDC). We then apply additional criteria on the photometric measurements used to build the SBCRs, together with stellar characteristics diagnostics. We build SBCRs for F5/K7-II/III, F5/K7-IV/V, M-II/III and M-V stars, with respective RMS of {sigma}_FV_=0.0022mag, {sigma}_FV_ =0.0044mag, {sigma}_FV_=0.0046mag, and {sigma}_FV_=0.0038mag. This results in a precision on the angular diameter of 1.0%, 2.0%, 2.1% and 1.7%, respectively. These relations cover a large V-K colour range of magnitude, from 1 to 7.5. Our work demonstrates that SBCRs are significantly dependent on the spectral type and the luminosity class of the star. Through a new set of interferometric measurements, we demonstrate the critical importance of the selection criteria proposed for the calibration of SBCR. Finally, using the Gaia photometry for our samples, we obtain (G-K) SBCRs with a precision on the angular diameter between 1.1% and 2.4%. By adopting a refined and homogeneous methodology we show that the spectral type and the class of the star should be considered when applying a SBCR. This is particularly important in the context of PLATO.
- ID:
- ivo://CDS.VizieR/J/ApJ/886/10
- Title:
- Dwarfs or giants? Stellar metallicities & distances
- Short Name:
- J/ApJ/886/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new fully data-driven algorithm that uses photometric data from the Canada-France Imaging Survey (CFIS; u), Pan-STARRS 1 (PS1; griz), and Gaia (G) to discriminate between dwarf and giant stars and to estimate their distances and metallicities. The algorithm is trained and tested using the Sloan Digital Sky Survey (SDSS)/SEGUE spectroscopic data set and Gaia photometric/astrometric data set. At [Fe/H]<-1.2, the algorithm succeeds in identifying more than 70% of the giants in the training/test set, with a dwarf contamination fraction below 30% (with respect to the SDSS/SEGUE data set). The photometric metallicity estimates have uncertainties better than 0.2dex when compared with the spectroscopic measurements. The distances estimated by the algorithm are valid out to a distance of at least ~80kpc without requiring any prior on the stellar distribution and have fully independent uncertainties that take into account both random and systematic errors. These advances allow us to estimate these stellar parameters for approximately 12 million stars in the photometric data set. This will enable studies involving the chemical mapping of the distant outer disk and the stellar halo, including their kinematics using the Gaia proper motions. This type of algorithm can be applied in the southern hemisphere to the first release of LSST data, thus providing an almost complete view of the external components of our Galaxy out to at least ~80kpc. Critical to the success of these efforts will be ensuring well-defined spectroscopic training sets that sample a broad range of stellar parameters with minimal biases. A catalog containing the training/test set and all relevant parameters within the public footprint of CFIS is available online.
- ID:
- ivo://CDS.VizieR/J/ApJ/626/446
- Title:
- Effective temperature scale of FGK stars
- Short Name:
- J/ApJ/626/446
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The infrared flux method (IRFM) has been applied to a sample of 135 dwarf and 36 giant stars covering the following regions of the atmospheric parameter space: (1) the metal-rich ([Fe/H]>~0) end (consisting mostly of planet-hosting stars), (2) the cool (Teff<~5000K) metal-poor (-1<~[Fe/H]<~-3) dwarf region, and (3) the very metal-poor ([Fe/H]<~-2.5) end.
- ID:
- ivo://CDS.VizieR/J/MNRAS/371/879
- Title:
- Effective temperatures of 215 FGK giants
- Short Name:
- J/MNRAS/371/879
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present precise effective temperatures (Teff) of 215 FGK giants determined using the method of line-depth ratios. For each star, we have measured the line depths and equivalent widths of a large number of spectral lines of low and high excitation potentials and established ~100 relations between Teff and their ratios. Starting with an initial value Teff, the relations are then self-calibrated by an iterative process. Our final estimates have been compared with very accurate (1 per cent) published temperatures and show a good agreement. Using our calibrations, we derive precise temperatures for 215 giants with near-solar metallicity, from high-resolution (R=42000) and high signal-to-noise ratio (S/N=100250) echelle spectra, obtained with the ELODIE spectrometer at the Observatoire de Haute Provence (OHP).
- ID:
- ivo://CDS.VizieR/J/AN/321/277
- Title:
- Effective temperatures of K-M giants
- Short Name:
- J/AN/321/277
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A high-resolution spectroscopic survey in the 6380-6460{AA} region of 224 slowly-rotating M-K class III giants is presented. Spectral line-depth ratio are calibrated against effective temperature obtained from B-V and V-I color indices in the range 3200-7500K (M6-A9). A table of polynomial coefficients for 12 line-ratio-Teff relations can be used to derive Teff of F-M stars to within 33K (rms), and of early-F and mid-to-late M stars to within 77-106K (rms).
- ID:
- ivo://CDS.VizieR/J/AJ/135/1580
- Title:
- Element abundances in ten red giants of Car dSph
- Short Name:
- J/AJ/135/1580
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained high-resolution spectroscopy of ten red giants in the Carina dwarf spheroidal (dSph) galaxy with the ultraviolet and visual echelle spectrograph at the European Southern Observatory Very Large Telescope in order to study the detailed chemical evolution of this Galactic satellite. Here we present the abundances of O, Na, Mg, Si, Ca, Ti, and Fe.
