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The close Be star c...
The close Be star companion of β Cephei
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Wheelwright, H. E. (author)
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Oudmaijer, R. D. (author)
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- Schnerr, R. S. (author)
- Stockholms universitet,Institutionen för astronomi,Institute for Solar Physics
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(creator_code:org_t)
- 2009
- 2009
- English.
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 497, s. 487-495
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Abstract
Subject headings
Close
- Context: The prototype of the β Cephei class of pulsating stars, β Cep, rotates relatively slowly, and yet displays episodic Hα emission. Such behaviour is typical of a rapidly rotating, classical Be star. For some time this posed a contradiction to our understanding of the Be phenomena as rapid rotation is thought to be a prerequisite for the characteristic emission phases of Be stars. Recent work has demonstrated that the Hα emission is in fact due to a close companion (separation ≈ 0.25 arcsec) of the star. This resolves the apparent enigma if this close companion is indeed a classical Be star, as has been proposed. Aims: We aim to test the hypothesis that this close companion is a valid Be star by determining properties such as its spectral type and v sin i. Methods: We employed the technique of spectroastrometry to investigate the close binary system. Using the spectroastrometric signatures observed, we split the composite binary spectra into its constituent spectra in the B band (4200-5000 Å) and R band (6200-7000 Å). Results: The spectroastrometrically split spectra allow us to estimate spectral types of the binary components. We find that the primary of the close binary system has a spectral type of B2III and the secondary a spectral type of B5Ve. From the relationship between mass and spectral type, we determine the masses of the binary components to be M_pri = 12.6 ± 3.2 Msun and M_sec = 4.4 ± 0.7 Msun respectively. The spectroastrometric data allow some constraint on the orbit, and we suggest a moderate revision to the previously determined orbit. We confirm that the primary of the system is a slow rotator (v sin i = 29+43-29 km s-1), while the secondary rotates significantly faster, at a v sin i = 230 ± 45 km s-1 Conclusions: We show that the close companion to the β Cephei primary is certainly a valid classical Be star. It has a spectral type of B5Ve and is a relatively fast rotator. We confirm that the β Cephei system does not contradict our current understanding of classical Be stars.
Subject headings
- NATURVETENSKAP -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)
- NATURAL SCIENCES -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)
Keyword
- binaries: close
- binaries: general
- stars: emission-line
- Be
- stars: individual: &beta
- Cephei
- Astronomy
- Astronomi
- Astronomy
- astronomi
Publication and Content Type
- ref (subject category)
- art (subject category)
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