Spitzer space telescope spectral observations of AGB stars in the Fornax dwarf spheroidal galaxy

Matsuura, M ORCID: https://orcid.org/0000-0002-5529-5593, Zijlstra, A. A, Bernard-Salas, J, Menzies, J. W, Sloan, G. C, Whitelock, P. A, Wood, P. R, Cioni, M.-R. L, Feast, M. W, Lagadec, E, Van Loon, J. Th, Groenewegen, M. A. T and Harris, G. J 2007. Spitzer space telescope spectral observations of AGB stars in the Fornax dwarf spheroidal galaxy. Monthly Notices of the Royal Astronomical Society 382 (4) , pp. 1889-1900. 10.1111/j.1365-2966.2007.12501.x

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Abstract

We have observed five carbon-rich asymptotic giant branch (AGB) stars in the Fornax dwarf spheroidal (dSph) galaxy, using the Infrared Spectrometer on board the Spitzer Space Telescope. The stars were selected from a near-infrared survey of Fornax and include the three reddest stars, with presumably the highest mass-loss rates, in that galaxy. Such carbon stars probably belong to the intermediate-age population (2-8Gyr old and metallicity of [Fe/H] ~ -1) of Fornax. The primary aim of this paper is to investigate mass-loss rate, as a function of luminosity and metallicity, by comparing AGB stars in several galaxies with different metallicities. The spectra of three stars are fitted with a radiative transfer model. We find that mass-loss rates of these three stars are 4-7 × 10^-6M_solaryr^-1. The other two stars have mass-loss rates below 1.3 × 10^-6M_solaryr^-1. We find no evidence that these rates depend on metallicity, although we do suggest that the gas-to-dust ratio could be higher than at solar metallicity, in the range 240 to 800. The C₂H₂ bands are stronger at lower metallicity because of the higher C/O ratio. In contrast, the SiC fraction is reduced at low metallicity due to low silicon abundance. The total mass-loss rate from all known carbon-rich AGB stars into the interstellar medium (ISM) of this galaxy is of the order of 2 × 10^-5M_solaryr^-1. This is much lower than that of the dwarf irregular galaxy Wolf Lundmark Melotte (WLM), which has a similar visual luminosity and metallicity. The difference is attributed to the younger stellar population of WLM. The suppressed gas-return rate to the ISM accentuates the difference between the relatively gas-rich dwarf irregular and the gas-poor dSph galaxies. Our study will be useful to constrain gas and dust recycling processes in low-metallicity galaxies....

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Publisher:	Oxford University Press
ISSN:	0035-8711
Date of Acceptance:	19 September 2007
Last Modified:	23 May 2024 13:30
URI:	https://orca.cardiff.ac.uk/id/eprint/168092

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