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Issue A&A
Volume 386, Number 3, May II 2002
Page(s) 874 - 883
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20020210



A&A 386, 874-883 (2002)
DOI: 10.1051/0004-6361:20020210

The 3 spectrum of R Doradus observed with the ISO-SWS

N. Ryde1 and K. Eriksson2

1  Department of Astronomy, University of Texas, Austin, TX 78712-1083, USA
2  Uppsala Astronomical Observatory, Box 515, 751 20 Uppsala, Sweden
    e-mail: kjell.eriksson@astro.uu.se

(Received 25 September 2001 / Accepted 31 January 2002 )

Abstract
We have modeled the 2.6- $3.7\,\mbox{$\mu$ m}$ spectrum of the red semiregular variable R Doradus observed with the Short-Wavelength Spectrometer on board the Infrared Space Observatory. The wavelength resolution of the observations varies between $R\sim 2000$- 2500. We have calculated a synthetic spectrum using a hydrostatic model photosphere in spherical geometry. The agreement between the synthetic spectrum and the ISO observations is encouraging, especially in the wavelength region of 2.8- $3.7\,\mbox{$\mu$ m}$, suggesting that a hydrostatic model photosphere is adequate for the calculation of synthetic spectra in the near infrared for this moderately varying red giant star. However, an additional absorption component is needed at 2.6- $2.8\,\mbox{$\mu$ m}$ and this discrepancy is discussed. The spectral signatures are dominated by water vapour in the stellar photosphere, but several photospheric OH, CO, and SiO features are also present. The effective temperature and surface gravity derived for R Dor, based on the 2.6- $3.7\,\mbox{$\mu$ m}$ ISO spectrum and the modeling of it with a hydrostatic model photosphere, are $3000\pm 100\,\mbox{K}$ and $\log g = 0 \pm 1$ (cgs), respectively. The spectral region observed is found to be temperature sensitive. The effective temperature given here is slightly higher than those reported in the literature. We also discuss possible reasons for this.


Key words: stars: individual: R Dor -- stars: AGB and post-AGB -- stars: late-type -- infrared: stars

Offprint request: N. Ryde, ryde@astro.as.utexas.edu

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© ESO 2002


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