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

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Amplitude monitoring of the [FORMULA] Cephei star 16 Lacertae

J.P. Sareyan 1, J. Chauville 2, E. Chapellier 1 and M. Alvarez 3

1 Observatoire de la Côte d'Azur, Dept. Fresnel, B.P.229, F-06003 Nice Cedex, France
2 Observatoire de Meudon, URA 335 du CNRS, F-92195 Meudon Cedex, France
3 Observatorio Astronomico Nacional, UNAM, Apdo 877, Ensenada, B.C. 22800, Mexico

Received 20 September 1995 / Accepted 5 March 1996


Based on new observations, it is shown here that the amplitude of one of the three well known and stable short periods in the [FORMULA] Cep variable 16 Lac has changed: while the radial mode [FORMULA] = 0.16917 d is near its lower amplitude level and the amplitude variation of the non-radial mode [FORMULA] = 0.18173 d is still probably in phase with the orbital period, the amplitude of the NR mode [FORMULA] = 0.17077 d has increased progressively by a factor two in the last ten years. The observed phase of [FORMULA] shows that at least for this period, the previous ephemeris is no longer valid. Various hypotheses are proposed to account for the observed amplitudes variations.

Key words: stars: 16 Lac – stars: variable – stars: binaries: close – stars: oscillations

Send offprint requests to: J.P.Sareyan

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998