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Session 45 - Eclipsing Binaries.
Display session, Thursday, January 08
Exhibit Hall,
V356 Sgr is an eclipsing, interacting binary star system composed of an A2II star and a B3V star which orbit each other with an 8.896 day period. Previous work by Popper (1954) using photographic spectra (in which the A star light dominates) determined a mass ratio of 0.388 and individual masses for the A2II and B3V star of 4.7 and 12.1 solar masses, respectively.
Utilizing 17 high dispersion IUE NEWSIPS SWP archival spectra covering most of the orbit, we have measured the radial velocity of the B3V star using lines of Si II, Si III, and Al III. Since the B3V star dominates the ultraviolet spectrum (supplying approximately 90total flux in the 1200-2000 A region), lines from the A2II star were not detectable in these spectra. The semi-amplitude for the B3V star reported by Popper (73 km/s) can be clearly ruled out by the IUE data. Formally, a velocity amplitude of 47.6 +/- 5.8 km/s for the B3V star is derived from the data, but smaller semi- amplitudes cannot be categorically ruled out. Combining the newly derived velocity amplitude for the B star with Popper's optical radial velocity measurements of the A star, we obtain a new mass ratio for the system of 0.25 and masses for the A star and the B star estimated at 2.7 and 10.7 solar masses, respectively.
The system parameters suggested by the new orbit will be discussed in the context of their impact on mass transfer models for the system. In addition, radial velocity measurements of low excitation, likely non-photospheric, Fe III absorption lines will be presented and discussed.
This work was supported in part by a NASA/University Joint Venture (JOVE) grant to SUNY Oswego.
