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Astron. Astrophys. 321, 145-150 (1997)

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1. Introduction

16 Lacertae (HR 8725 = HD 216916 = EN Lac, B2IV) is one of the best known [FORMULA] Cephei - [FORMULA] Canis Majoris star. It belongs to the Lac OB1 association (distance 600 pc, age 12 to 16 [FORMULA] 106 years, Eggen, 1975). It is a well-detached eclipsing binary of 12.09684 day period (Struve et al., 1952; Pigulski and Jerzykiewicz, 1988), so the components radii and mass ratio are rather well determined, and by a direct method, which is not common in this part of the HR diagram.

The primary, a main sequence star ([FORMULA], [FORMULA], [FORMULA]) is the [FORMULA] Cephei type variable, while the secondary ([FORMULA], [FORMULA]) could be a pre-main sequence object (Pigulski and Jerzykiewicz, 1988). The primary's rotation period - 11.7 to 14 days - is very probably synchronized with the orbital period (Balona, 1985, Chapellier et al., 1995, thereafter Paper 1).

Three close frequencies have been detected in the star's photometry (Fitch, 1969, Jarzebowski et al., 1979) and later confirmed (Garrido et al., 1983). There could exist some more frequencies in the star pulsation spectrum, apart from the three main components, but with very small amplitudes (Jerzykiewicz, 1993). Since 40 years (Fitch, 1969), significant variations in the amplitudes of the three periods have been reported. Such variations are of great interest to understand the [FORMULA] Cep pulsation and the physics underlying the mode selection. So 16 Lac deserves continuous attention: we observed it in two campaigns (1987 and 1992), and will continue to monitor it.

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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