The circumstellar envelope of S Scuti

Details The circumstellar envelope of S Scuti The circumstellar envelope of S Scuti

Feb 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...282..115g&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 282, no. 1, p. 115-122

Astronomy and Astrophysics

Astronomy

14

Carbon Monoxide, Carbon Stars, Cosmic Dust, Infrared Astronomy, Spectral Energy Distribution, Stellar Envelopes, Stellar Evolution, Stellar Mass, Stellar Models, Color-Color Diagram, Mathematical Models, Stellar Luminosity, Stellar Temperature

Scientific paper

We fit the observed spectral energy distribution (SED) of S Sct. This star is the only carbon star with a 60 micron excess mapped in detail in CO. For a distance of 460 pc, corresponding to a luminosity of 7050 solar luminosity, the CO data show that the present-day mass loss is low and that a phase of high mass loss ended about 9000 years ago. For the modeling of the SED we assume the following mass loss history: an initial mass loss rate (dm3)/dt, followed by a phase of high mass loss (dM2)/dt lasting t2 years, followed by a present-day mass loss rate (dM1)/dt lasting t1 years. We consider both oxygen- and carbon-rich dust. The thickness of the CO shell implies a duration of the phase of high mass loss of between 350 and 1050 yr. The dust model allows values of t2 up to 104 yr for some combination of parameters, indicating that the width of the shell observed in CO and the dust emission may be different. From the SED we derive an effective stellar temperature of Teff = 2700 K and dM1/dt = 5.5 x 10-10 solar mass/yr. The parameters t1, t2, dM2/dt and dM3/dt are determined from IRAS 60 and 100 micron flux densities. Both oxygen- and carbon-rich models can be constructed that fit the SED. We predict that future (sub-)mm observations may resolve the question whether the dust which causes the 60 micron excess in carbon stars is carbon-rich or oxygen-rich. Taking into account the finite beam width of the IRAS detectors, reduces the time for stars with detached shells to describe a loop in the IRAS color-color diagram by approximately 30% compared to earlier calculations. The best estimate for the loop time is approximately 1.0 x 104 yr for oxygen-rich and approximately 1.5 x 104 yr for carbon-rich dust shells.

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