Volume 404, Number 2, June III 2003
|Page(s)||579 - 591|
|Section||Stellar structure and evolution|
|Published online||02 June 2003|
Institut für Astronomie der Universität Wien, Türkenschanzstr. 17, 1180 Wien, Austria e-mail: email@example.com
2 Zentraler Informatikdienst der Universität Wien, Universitätsstr. 7, 1010 Wien, Austria
3 Leiden Observatory, Niels Bohrweg 2, PO Box 9513, 2330 RA Leiden, The Netherlands e-mail: firstname.lastname@example.org
4 IRAM Grenoble, 300 rue de la Piscine, Domaine Universitaire, 38406 St. Martin d'Hères Cedex, France e-mail: email@example.com
Corresponding author: E. Paunzen, firstname.lastname@example.org
Accepted: 25 February 2003
The group of λ Bootis type stars comprises late B- to early F-type, Population I objects which are basically metal weak, in particular the Fe group elements, but with the clear exception of C, N, O and S. One of the theories to explain the abundance pattern of these stars involves circumstellar or interstellar matter around the objects. Hence, we have compiled all available data from the literature of well established members of the λ Bootis group redward of 7000 Å in order to find evidence for matter around these objects. Furthermore, we present unpublished ISO as well as submillimeter continuum and CO (2–1) line measurements to complete the data set. In total, measurements for 34 (26 with data redward of 20 μm) well established λ Bootis stars are available. There is evidence for an infrared excesses in six stars (HD 31295, HD 74873, HD 110411, HD 125162, HD 198160/1 and HD 210111) and two are doubtful cases (HD 11413 and HD 192640) resulting in a percentage of 23% (excluding the two doubtful cases). Dust models for these objects show fractional dust luminosities comparable to the Vega-type stars and slightly higher dust temperatures. ISO-SWS spectroscopy for HD 125162 and HD 192640 resulted in the detection of pure stellar H i lines ruling out an active accretion disk (as found for several Herbig Ae/Be stars) around these objects. The submillimeter measurements gave only upper limits for the line and continuum fluxes.
Key words: stars: chemically peculiar / stars: early-type
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 UK) and with the participation of ISAS and NASA; and observations at the Heinrich-Hertz-Telescope (HHT, operated by the the Submillimeter Telescope Observatory).
© ESO, 2003
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