THE B AND Be STATES OF THE STAR EM CEPHEUS
- Department of Physics, Shumen University, 9700 Shumen (Bulgaria)
- Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7 (Canada)
- Institute of Astronomy and NAO, Bulgarian Academy of Sciences, Tsarigradsko shossee 72, 1784 Sofia (Bulgaria)
We present 11 yr of high-resolution, spectroscopic observations for the star EM Cep. EM Cep switches between B and Be star states, as revealed by the level of Hα emission, but spends most of its time in the B star state. EM Cep has been considered to be an eclipsing, near-contact binary of nearly equal-mass B stars in order to reproduce regular photometric variations; however, this model is problematic due to the lack of any observed Doppler shift in the spectrum. Our observations confirm that there are no apparent Doppler shifts in the wide spectral lines Hα and He i λ6678 in either the B or Be star states. The profiles of He i λ6678 typically exhibited a filled-in absorption core, but we detected weak emission in this line during the highest Be state. Given the lack of observed Doppler shifts, we model EM Cep as an isolated Be star with a variable circumstellar disk. We can reproduce the observed Hα emission profiles over the 11 yr period reasonably well with disk masses on the order of 3--10× 10{sup −11} M{sub ∗} in the Be state with the circumstellar disk seen at an inclination of 78° to the line of sight. From a disk ejection episode in 2014, we estimate a mass-loss rate of ≈3×10{sup −9} M{sub ⊙} yr{sup −1}. The derived disk density parameters are typical of those found for the classical Be stars. We therefore suggest that the EM Cep is a classical Be star and that its photometric variations are the result of β Cep or nonradial pulsations.
- OSTI ID:
- 22862897
- Journal Information:
- The Astronomical Journal (Online), Vol. 152, Issue 3; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1538-3881
- Country of Publication:
- United States
- Language:
- English
Similar Records
CSI 2264: CHARACTERIZING YOUNG STARS IN NGC 2264 WITH STOCHASTICALLY VARYING LIGHT CURVES
HST imaging of fading AGN candidates. I. Host-galaxy properties and origin of the extended gas