Spitzer observations of acetylene bands in carbon-rich asymptotic giant branch stars in the Large Magellanic Cloud

Matsuura, M ORCID: https://orcid.org/0000-0002-5529-5593, Wood, P. R, Sloan, G. C, Zijlstra, A. A, Van Loon, J. Th, Groenewegen, M. A. T, Blommaert, J. A. D. L, Cioni, M.-R. L, Feast, M. W, Habing, H. J, Hony, S, Lagadec, E, Loup, C, Menzies, J. W, Waters, L. B. F. M and Whitelock, P. A 2006. Spitzer observations of acetylene bands in carbon-rich asymptotic giant branch stars in the Large Magellanic Cloud. Monthly Notices of the Royal Astronomical Society 371 (1) , pp. 415-420. 10.1111/j.1365-2966.2006.10664.x

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Abstract

We investigate the molecular bands in carbon-rich asymptotic giant branch (AGB) stars in the Large Magellanic Cloud (LMC), using the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope (SST) over the 5-38 μm range. All 26 low-resolution spectra show acetylene (C₂H₂) bands at 7 and 14 μm. The hydrogen cyanide (HCN) bands at these wavelengths are very weak or absent. This is consistent with low nitrogen abundances in the LMC. The observed 14 μm C₂H₂ band is reasonably reproduced by an excitation temperature of 500 K. There is no clear dilution of the 14 μm C₂H₂ band by circumstellar dust emission. This 14-μm band originates from molecular gas in the circumstellar envelope in these high mass-loss rate stars, in agreement with previous findings for Galactic stars. The C₂H₂column density, derived from the 13.7 μm band, shows a gas mass-loss rate in the range 3 × 10^-6 to 5 × 10^-5M_solaryr^-1. This is comparable with the total mass-loss rate of these stars estimated from the spectral energy distribution. Additionally, we compare the line strengths of the 13.7 μm C₂H₂ band of our LMC sample with those of a Galactic sample. Despite the low metallicity of the LMC, there is no clear difference in the C₂H₂ abundance among LMC and Galactic stars. This reflects the effect of the third dredge-up bringing self-produced carbon to the surface, leading to high carbon-to-oxygen ratio at low metallicity....

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Publisher:	Oxford University Press
ISSN:	0035-8711
Date of Acceptance:	7 June 2006
Last Modified:	22 May 2024 15:45
URI:	https://orca.cardiff.ac.uk/id/eprint/168102

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