期刊
ASTRONOMY & ASTROPHYSICS
卷 543, 期 -, 页码 -出版社
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201219520
关键词
stars: AGB and post-AGB; circumstellar matter; infrared: stars; techniques: spectroscopic
资金
- boursier F.R.I.A, Belgium
- Fund for Scientific Research of Flanders [G.0470.07]
- Fund for Scientific Research of Flanders (FWO)
- Research Council of K.U.Leuven
- Fonds de la Recherche Scientifique (FNRS)
- Royal Observatory of Belgium
- Observatoire de Geneve
- Thuringer Landessternwarte Tautenburg
- Action de recherche concerte (ARC) from the Direction generale de l'Enseignement non obligatoire et de la Recherche scientifique -Direction de la recherche scientifique - Communaute francaise de Belgique
We report on the discovery of an infrared emission band in the Spitzer spectrum of the S-type AGB star NP Aurigae that is caused by TiO molecules in the circumstellar environment. We modeled the observed emission to derive the temperature of the TiO molecules (approximate to 600K), an upper limit on the column density (approximate to 10(17.25) cm(-2)) and a lower limit on the spatial extent of the layer that contains these molecules. (approximate to 4.6 R-*). This is the first time that this TiO emission band is observed. A search for similar emission features in the sample of S-type stars yielded two additional candidates. However, owing to the additional dust emission, the identification is less stringent. By comparing the stellar characteristics of NP Aur to those of the other stars in our sample, we find that all stars with TiO emission show large-amplitude pulsations, s-process enrichment, and a low C/O ratio. These characteristics might be necessary requirements for a star to show TiO in emission, but they are not sufficient.
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