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Astron. Astrophys. 329, 579-582 (1998)

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1. Introduction

[FORMULA] Coronae Borealis (HR 5778, HD 138749) is a well known but, relatively little studied bright Be star. Its photometric behavior is complex, alternating variability at different time scales with periods of constant brightness. Roark (1971) detected rapid variations with a periodicity of about one day and a large decrease of brightness of 0.7 mag. in the u and v bands. Significant photometric variations on a time scale of days were also reported by Papouek (1985) and by Percy et al. (1988) for 1986 and 1987. Guerrero et al. (1992) observed rapid light variations with a full amplitude of about 0.03 mag. during the period April 29 to May 8, 1989. They interpreted their light curve as a combination of a slow variation with a possible period of about 8 days and rapid variations with a period of either 0.869 or 0.459 days. The latter period was also found by Hubert et al. (1991) for the variability of the He I ([FORMULA] 4471) and Mg II ([FORMULA] 4481) line profiles, from spectra obtained during April 21-23, 1989. Finally, in the long term photometric survey conducted at the Hvar Observatory between 1972 and 1990, [FORMULA] CrB is a low-amplitude variable, just above the detection limit (Pavlovski et al. 1997).

On the other hand, Fernandes et al. (1985) found [FORMULA] CrB constant within a few hundreds of magnitude during May to July 1984. Further, Percy et al. (1988) and Percy & Attard (1992) did not detect any significant photometric variations in 1981, 1985, 1990 and 1991.

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© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997