Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999a%26a...341l...9y&link_type=abstract
Astronomy and Astrophysics, v.341, p.L9-L12 (1999)
Astronomy and Astrophysics
Astrophysics
34
Stars: Agb And Post-Agb, Stars: Atmospheres, Stars: Circumstellar Matter, Stars: Late-Type, Stars: Mass-Loss, Infrared: Stars
Scientific paper
We report the discovery of the nu_3 band of SO_2 at 7.3 mu m in the ISO/SWS spectra of oxygen-rich AGB stars. The band is clearly detected in three stars, UX Cyg, o Cet and T Cep, and marginally detected in at least four other stars. The band is seen in absorption in UX Cyg, while it is in emission in o Cet. Seven spectra of T Cep taken at different phases show that the feature changes from emission to absorption on a time scale of twice the pulsation period. Using an LTE model, we find that the excitation temperature of SO_2 is typically 600 K, and that in T Cep the molecule occupies a region with dimensions of several stellar radii. The total number of molecules contained in this region is of order 10(47) , which requires a local gas density of at least 10(9) H_2 cm(-3) , and possibly up to 10(11) H_2 cm(-3) depending on the SO_2 abundance. The variation with phase of the T Cep spectra can be explained by photodissociation of SO_2 molecules by soft UV photons. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA. The SWS is a joint project of SRON and MPE.
Cami Jan
de Jong Teije
Onaka Takashi
Waters Laurens B. F. M.
Yamamura Issei
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