TOWARD UNDERSTANDING THE B[e] PHENOMENON. V. NATURE AND SPECTRAL VARIATIONS OF THE MWC 728 BINARY SYSTEM
We report the results of a long-term spectroscopic monitoring of the FS CMa type object MWC 728. We found that it is a binary system with a B5 Ve (T sub(eff) = 14,000 + or - 1000 K) primary and a G8 III type (T sub(eff) ~ 5000 K) secondary. Absorption line positions of the secondary vary, with a sem...
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Veröffentlicht in: | The Astrophysical journal 2015-08, Vol.809 (2), p.1-12 |
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Sprache: | eng |
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Zusammenfassung: | We report the results of a long-term spectroscopic monitoring of the FS CMa type object MWC 728. We found that it is a binary system with a B5 Ve (T sub(eff) = 14,000 + or - 1000 K) primary and a G8 III type (T sub(eff) ~ 5000 K) secondary. Absorption line positions of the secondary vary, with a semi-amplitude of ~20 km s super(-1) and a period of 27.5 days. The system's mass function is 2.3 x 10 super(-2) M sub([middot in circle]), and its orbital plane is ~13[degrees]-15[degrees] tilted from the plane of the sky. The primary's v sin sub(i) ~ 110 km s super(-1), combined with this tilt, implies that it rotates at a nearly breakup velocity. We detected strong variations of the Balmer and He I emission-line profiles on timescales from days to years. This points to a variable stellar wind of the primary in addition to the presence of a circum-primary gaseous disk. The strength of the absorption-line spectrum, along with the optical and near infrared (IR) continuum, suggest that the primary contributes ~60% of the V-band flux, the disk contributes ~30%, and the secondary contributes ~10%. The system parameters, along with the interstellar extinction, suggest a distance of ~1 kpc, that the secondary does not fill its Roche lobe, and that the companions' mass ratio is q ~ 0.5. Overall, the observed spectral variability and the presence of a strong IR-excess are in agreement with a model of a close binary system that has undergone a non-conservative mass-transfer. |
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ISSN: | 1538-4357 0004-637X 1538-4357 |
DOI: | 10.1088/0004-637X/809/2/129 |