Metal-rich carbon stars in the Sagittarius dwarf spheroidal galaxy

‘The definitive version is available at: www3.interscience.wiley.com '. Copyright Blackwell / Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2009.14736.xWe present spectroscopic observations from the Spitzer Space Telescope of six carbon-rich asymptotic giant branch (AGB) stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph) and two foreground Galactic carbon stars. The band strengths of the observed C2H2 and SiC features are very similar to those observed in Galactic AGB stars. The metallicities are estimated from an empirical relation between the acetylene optical depth and the strength of the SiC feature. The metallicities are higher than those of the Large Magellanic Cloud, and close to Galactic values. While the high metallicity could imply an age of around 1 Gyr, for the dusty AGB stars, the pulsation periods suggest ages in excess of 2 or 3 Gyr. We fit the spectra of the observed stars using the dusty radiative transfer model and determine their dust mass-loss rates to be in the range 1.0–3.3 × 10−8 M⊙ yr−1 . The two Galactic foreground carbon-rich AGB stars are located at the far side of the solar circle, beyond the Galactic Centre. One of these two stars shows the strongest SiC feature in our present Local Group sample.Peer reviewe

A Spitzer mid-infrared spectral survey of mass-losing carbon stars in the Large Magellanic Cloud

‘The definitive version is available at www.blackwell-synergy.com.’ Copyright Blackwell Publishing DOI: 10.1111/j.1365-2966.2006.10623.xPeer reviewe

DENIS and ISOGAL properties of variable star candidates in the Galactic Bulge

International audienceRepeated DENIS observations (summer 1996 & 1998) in the J (1.25 mu m) and the KS (2.15 mu m) bands are used to look for variable stars. We present two catalogues of ~ 1000 probable variables in an area of ~ 4 deg2 of the inner galactic bulge. The first one contains ~ 720 variable star candidates which show variability in J and KS while the second consists of sources only observed to be variable in KS (~ 270 sources), mainly in regions with high interstellar extinction. Using the extinction map by Schultheis et al. (\cite{Schultheis99a}), most of the variable stars are found to be above the RGB tip and thus belong to the AGB while there is a small fraction of candidates which could be below the RGB tip with rather small ``amplitudes'' of ~ 0.3-0.4 mag in KS. Our catalogue has been cross-correlated with five ISOGAL fields (total area ~ 0.5 deg2) in order to study the mid-IR properties of the LPVs. The AGB variables can be distinguished from other M-type giants by their high 7 mu m luminosities and redder K0-[7] colours. Based on a few repeated ISOCAM observations a good correlation is found between near- and mid-IR variability. This is paper no.~7 in a refereed journal based on data from the ISOGAL project. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA. Based on observations collected at the European Southern Observatory, La Silla Chil

The VMC survey – XLIV : mapping metallicity trends in the Large Magellanic Cloud using near-infrared passbands

We have derived high-spatial-resolution metallicity maps covering ∼105 deg2 across the Large Magellanic Cloud (LMC) using near-infrared passbands from the VISTA Survey of the Magellanic Clouds. We attempt to understand the metallicity distribution and gradients of the LMC up to a radius of ∼6 kpc. We identify red giant branch (RGB) stars in spatially distinct Y, (Y − Ks) colour–magnitude diagrams. In any of our selected subregions, the RGB slope is used as an indicator of the average metallicity, based on calibration to metallicity using spectroscopic data. The mean LMC metallicity is [Fe/H] = −0.42 dex (σ[Fe/H] = 0.04 dex). We find the bar to be mildly metal-rich compared with the outer disc, showing evidence of a shallow gradient in metallicity (−0.008 ± 0.001 dex kpc−1) from the galaxy’s centre to a radius of 6 kpc. Our results suggest that the LMC’s stellar bar is chemically similar to the bars found in large spiral galaxies. The LMC’s radial metallicity gradient is asymmetric. It is metal-poor and flatter towards the southwest, in the direction of the Bridge. This hints at mixing and/or distortion of the spatial metallicity distribution, presumably caused by tidal interactions between the Magellanic Clouds