A new study of the spectroscopic binary 7 Vul with a Be star primary

Abstract

We confirmed the binary nature of the Be star 7~Vul, derived a~more accurate spectroscopic orbit with an orbital period of (69.4212+/-0.0034) d, and improved the knowledge of the basic physical elements of the system. Analyzing available photometry and the strength of the \ha emission, we also document the long-term spectral variations of the Be primary. In addition, we confirmed rapid light changes with a~period of 0.5592 d, which is comparable to the expected rotational period of the Be primary, but note that its amplitude and possibly its period vary with time. We were able to disentangle only the He I 6678 A line of the secondary, which could support our tentative conclusion that the secondary appears to be a hot subdwarf. A search for this object in high-dispersion far-UV spectra could provide confirmation. Probable masses of the binary components are ($6\pm 1$)~Mnom \ and ($0.6\pm 0.1$)~Mnom. If the presence of a hot subdwarf is firmly confirmed, 7 Vul might be identified as a rare object with a B4-B5 primary; all Be + hot subdwarf systems found so far contain B0-B3 primaries.

arXiv comment17 pages, 23 figures, accepted for publication in Astronomy and Astrophysics

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• Newborn Be star systems observed shortly after mass transfer
• Long-term, orbital, and rapid variations of the Be star V923 Aql = HD 183656
• V907 Sco Switched to the Eclipsing Mode Again
• The Be star omicron Cas is indeed the primary of a triple system