Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.5011l&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #50.11; Bulletin of the American Astronomical Society, Vol. 24, p.1205
Astronomy and Astrophysics
Astronomy
Scientific paper
Analysis of the low resolution spectra obtained by IRAS has shown that the 10 microns silicate dust grain emission feature varies in M type Mira variables in phase with their optical light curves (Little-Marenin and Stencel, 1992, ASP Conf. Ser. vol 26, 591). Both the strength of the emission feature and the the 12 microns PSCII fluxes show the same dependence on time. The magnitude difference between maximum and minimum for those Miras is between 1-2 magnitudes, similar to their K magnitude variation. The strength of the emission feature varies by 20-30% during the same time interval. Of the 22 carbon star Miras with LRS spectra, 16 (70%) are listed in the point source catalog with a variability index greater than 7 indicating that the individual point source fluxes showed variablity. Among the M star Miras we also found that about 70% of the stars showed variablity. However, unlike the 10 microns silicate feature in M Miras, the strength of the SiC dust emission feature in C stars shows little if any variation in strength with time despite the variations in the 12 microns broadband fluxes of up to one magnitude, reflecting differences in the formation mechanisms between the silicate and SiC dust grains. The optical depths of the circumstellar shell in the 8-22 microns region for C stars with SiC dust grain features is usually small since this part of the spectrum can be matched with blackbody energy distributions close to the effective temperature of the star. We find that M stars with silicate features have larger optical depths since their black body temperature obtained by fitting the 8-22 microns region is typically around 600-800K.
Little Scott J.
Little-Marenin Irene R.
Staley Stephanie B.
Stencel Robert E.
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