Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982a%26a...111..120q&link_type=abstract
Astronomy and Astrophysics, vol. 111, no. 1, July 1982, p. 120-124. NASA-supported research.
Astronomy and Astrophysics
Astrophysics
7
Carbon Stars, Late Stars, Stellar Envelopes, Stellar Spectra, Stellar Structure, Variable Stars, Emission Spectra, Mira Variables, Opacity, Semiregular Variable Stars, Stellar Temperature, Ultraviolet Spectra
Scientific paper
Exposures on the spectra of four late C-type stars have been made with the IUE satellite in the wavelength range of the LWR camera (1900-3200 A). Two Mira variables near maximum light and two semiregular variables were observed. Although the exposure times used, which range up to 240 min in the low-resolution mode, were more than sufficient to record the continuum and emission lines of Mg II, Fe II, and Al II in normal M stars of similar magnitude and temperature, no light was recorded. It is concluded that the far-ultraviolet continuum is strongly depressed in these cool carbon stars. The absence of UV emission lines implies either that the chromospheric lines observed in M stars require an ultraviolet flux for their excitation, or that cool carbon stars have no chromosphere at all or that the opacity source is located above even the emission-line-forming region. This opacity source, which is probably some carbon condensate since it is weak or absent in M stars while absorbing strongly in C stars, is discussed both in terms of the chromospheric interpretation of the emission lines and in terms of their shock-wave interpretation.
Cassatella Angelo
Heck Andre
Querci Francois
Querci Monique
Wing Robert F.
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