Properties and nature of Be stars

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' Department of Physics and Astronomy, Michigan State University, E. Lansing, MI, 48824 and Affiliate Professor, Department of Astronomy, University of Washington, Seattle, WA 98195, USA e-mail: linnell@astro.washington.edu 2 Astronomical Institute of the Charles University, Faculty of Mathematics and Physics, V Holesovickach 2, 180 00 Praha 8, Czech Republic 3 Astronomical Institute, Academy of Sciences, 251 65 Ondrejov, Czech Republic e-mail: hec@sunstel. asu. cas. cz 4 Hvar Observatory, Faculty of Geodesy, Kaciceva 26, 10000 Zagreb, Croatia e-mail: hbozic (dsudar, rdomagoj)@hvar.geof. hr 5 Department of Physics and Astronomy, University of Victoria, PO Box 3055 STN CSC, Victoria, B.C., V8W 3P6, Canada e-mail: yang@uvastro.plays..uvic.ca 6 Dept. of Astronomy, University of Guanajuato, 36000 Guanajuato, GTO, Mexico Aims. We include existing photometric and spectroscopic material with new observations in a detailed study of the Be+F binary V360 Lac. Methods. We used the programs FOTEL and KOREL to derive an improved linear ephemeris and to disentangle the line profiles of both binary components and telluric lines. The BINSYN software suite (described in the paper) is used to calculate synthetic light curves and spectra to fit the UBV photometry, an IUE spectrum, blue and red ground-based spectra, and observed radial-velocity curves. Results. The observations provide evidence of circumstellar matter in the system. The system model shows that the Be primary star is critically rotating, and that the synchronously rotating secondary star fills its Roche lobe. The primary star has a mass of 7.45 M ⊙ . Radial-velocity observations establish a mass ratio of 0.163. Light curve synthesis demonstrates that the observed light curves are controlled largely by tidal distortion and irradiation of the massive primary by the less massive secondary. Synthetic spectra fit both blue and red observed spectra with the exception of spectral lines affected by circumstellar matter in the system. The synthetic spectra allow for gravity darkening and are consistent with critical rotation of the primary. Synthetic spectrum fits to a dereddened IUE spectrum produce a calculated system distance of 512 pc. This distance is 2σ beyond the Hipparcos distance.