Modelling the spectral energy distribution and SED variability of the Carbon Mira R Fornacis

Details Modelling the spectral energy distribution and SED variability of the Carbon Mira R Fornacis Modelling the spectral energy distribution and SED variability of the Carbon Mira R Fornacis

Mar 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999a%26a...343..466l&link_type=abstract

Astronomy and Astrophysics, v.343, p.466-476 (1999)

Astronomy and Astrophysics

Astrophysics

5

Stars: Agb And Post-Agb, Stars: Mass-Loss, Stars: Individual: R For, Stars: Carbon

Scientific paper

We have developed a new method to determine the physical properties and the local circumstances of dust shells surrounding Carbon- and Oxygen-rich stars for a given pulsation phase. The observed mid-IR dust emission feature(s), in conjunction with IRAS BB photometry and coeval optical and near-IR BB photometry, are modelled from radiative transport calculations through the dust shell using a grid of detailed synthetic model input spectra for M-S-C giants. From its application to the optical Carbon Mira R For we find that the temperature of the inner shell boundary exceeds 1000 K, ranging between 1200 K and 1400 K. The optical depth of the shell at 11.3 mu m is determined at tau_ {11 microns }=0.105 with T_eff=3200+/-200 K for the central star in the considered phase of variability. By-products of the analysis are the shell composition of 90% amorphous carbon and only 10% SiC grains with rather small average radii of 0.05+/-0.02 mu m. The dust density distribution assumes a power law of r(-2) for a steady-state wind with a geometrical thickness ranging between 10(4) and 5 10(4) times the inner boundary shell radius and with a high gas mass-loss rate of 3-4 10(-6) Msun y(-1) derived by radiation pressure onto the dust. We show that the optical and near-IR light curves are strongly affected by small changes of T_eff and of the shell optical depth with pulsation. A comparison of high resolution optical spectra of R For and medium/low resolution spectra of other carbon stars with the selected model input spectrum is also provided. Based on observations taken at UKIRT, CST, JCMT, SAAO, AAO and the IRAS Pointsource Catalogue

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