Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 407, Issue 2, Pages 734-748Publisher
WILEY-BLACKWELL PUBLISHING, INC
DOI: 10.1111/j.1365-2966.2010.16960.x
Keywords
stars: early-type; stars: evolution; stars: mass-loss; stars: winds; outflows
Categories
Funding
- Fondecyt [1070705]
- Chilean Center for Astrophysics FONDAP [15010003]
- BASAL Centro de Astrofisica y Tecnologias Afines (CATA) [PFB-06/2007]
- NASA [NNX07AC75G]
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We present the results of a spectroscopic investigation of two novel variable bright blue stars in the SMC, OGLE004336.91-732637.7 (SMC-SC3) and the periodically occulted star OGLE004633.76-731204.3 (SMC-SC4), whose photometric properties were reported by Mennickent et al. (2010). High-resolution spectra in the optical and far-UV show that both objects are actually A + B type binaries. Three spectra of SMC-SC4 show radial velocity variations, consistent with the photometric period of 184.26 d found in Mennickent et al. 2010. The optical spectra of the metallic lines in both systems show combined absorption and emission components that imply that they are formed in a flattened envelope. A comparison of the radial velocity variations in SMC-SC4 and the separation of the V and R emission components in the H alpha emission profile indicate that this envelope, and probably also the envelope around SMC-SC3, is a circumbinary disc with a characteristic orbital radius some three times the radius of the binary system. The optical spectra of SMC-SC3 and SMC-SC4 show, respectively, He i emission lines and discrete blue absorption components (BACs) in metallic lines. The high excitations of the He i lines in the SMC-SC3 spectrum and the complicated variations of Fe ii emission and absorption components with orbital phase in the spectrum of SMC-SC4 suggests that shocks occur between the winds and various static regions of the stars' corotating binary-disc complexes. We suggest that BACs arise from wind shocks from the A star impacting the circumbinary disc and a stream of former wind-efflux from the B star accreting on to the A star. The latter picture is broadly similar to mass transfer occurring in the more evolved (but less massive) algol (B/A + K) systems, except that we envision transfer occurring in the other direction and not through the inner Lagrangian point. Accordingly, we dub these objects prototype of a small group of Magellanic Cloud wind-interacting A + B binaries.
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