Ultraviolet observations of the hydrogen-deficient variable star MV sagittarii |
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| Authors: | N Kameswara Rao K Nandy |
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| Institution: | (1) Indian Institute of Astrophysics, 560034 Bangalore;(2) Royal Observatory, Edinburgh, UK |
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| Abstract: | IUE observations of the hydrogen-deficient irregular variable star MV Sgr obtained in 1980 June-October and also in 1979 November
are discussed. These observations show a prominent λ 2200 absorption feature. A value ofE(B — V) = 0.55 is deduced from the strength of λ 2200 band assuming that this absorption is caused by interstellar medium. The dereddened
continuum obtained at different times can be fitted to a theoretical energy distribution of a helium star model with Teff = 18000 K and log g = 2.5, similar to that of BD + 10‡ 2179. This theoretical energy distribution, after applying interstellar extinction, givesV = 12.7 mag, agreeing with the observed visual magnitude of ≃ 13 in 1979 November and 1980 June-October. Even though there
was no change in the continuum flux, the ultraviolet line-spectrum shows variations. The IUE spectra of 1980 October show
enhanced (circumstellar) absorption lines of Fe II, Si II, O I, C I and others along with the absorption lines of a B star.
In view of the similarity of the spectroscopic phenomena of MV Sgr with that of α Sco system, a model is proposed in which
a cool companion star, surrounded by dust, occasionally blows gas towards the hotter hydrogen-poor B star. This model explains
the irregular light variations and the spectroscopic phenomena.
Based on observations obtained with IUE satellite at the Villafranca Satellite Tracking Station of the European Space Agency. |
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| Keywords: | variable stars ultraviolet spectra circumstellar dust |
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