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Astron. Astrophys. 329, 213-218 (1998)

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A cold detached dust envelope around an oxygen-rich Mira-type AGB star R Hydrae

O. Hashimoto 1, H. Izumiura 2, D.J.M. Kester 3 and Tj.R. Bontekoe 4

1 Gunma Astronomical Observatory, 1-18-7 Ohtomo, Maebashi, Gunma 371, Japan
2 Okayama Astrophysical Observatory, National Astronomical Observatory, Kamogata, Asaguchi, Okayama 719-02, Japan
3 SRON Laboratory for Space Research Groningen, P.O.Box 800, 9700 AV Groningen, The Netherlands
4 Bontekoe Data Consultancy, Herengracht 47, 2312 LC Leiden, The Netherlands

Received 18 September 1995 / Accepted 13 June 1997

Abstract

The circumstellar structure of R Hydrae has been investigated in the IRAS survey scan data. R Hya is a late M-type Mira variable star whose IRAS LRS spectrum is classified as 15 (no feature). But, it shows a remarkable infrared excess in the IRAS photometric data, which cannot be explained by an oxygen-rich circumstellar dust envelope of a mass losing late-type star without showing a significant 10 [FORMULA] m silicate feature in the LRS spectrum.

An extended emission component around R Hya is clearly found in the 60 and 100 [FORMULA] m images produced by Pyramid Maximum Entropy (PME) image reconstruction techniques. It is also visible in the individual IRAS scan data at 25, 60 and 100 [FORMULA] m. It firmly indicates the existence of an extended circumstellar dust envelope around R Hya. The IRAS data further suggest the dust envelope being detached from the central star. The detached circumstellar dust envelope is consistent with both the featureless LRS spectrum and the red colors in the IRAS photometric data. R Hya is likely to be experiencing a cessation of mass loss which has lasted for about one hundred years, and which has made the inner boundary of the dust envelope about sixty stellar radii, far from the region which is warm enough to produce the 10 [FORMULA] m feature.

Key words: circumstellar matter – stars: AGB – stars: mass-loss – infrared: stars – stars: individual: R Hya

Send offprint requests to: O. Hashimoto

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© European Southern Observatory (ESO) 1998

Online publication: November 24, 1997
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