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Astron. Astrophys. 323, 881-885 (1997)

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1. Introduction

Bidelman & MacConnell (1973) have classified HD 137509 (= CPD [FORMULA]) as a peculiar A star of the Si type. Cowley & Houk (1975) stressed the interesting character of this star, of spectral type near B9, which is rich in Si, Fe, Cr, and Ti, and deficient in He. HD 137509 is also extremely peculiar in photometry, both in the Geneva system: [FORMULA] (Hauck & North 1982), and according to Maitzen's peculiarity index: [FORMULA] (Maitzen & Vogt 1983). Pedersen (1979) found some hint of spectrum variability and suggested that the star should be included in future programmes to study this aspect more in detail. The photometric variability of HD 137509 has first been reported by Lodén & Sundman (1989) from the consideration of 10 photometric measurements in the UBV system. A first attempt to determine the rotation period was made by Mathys (1991), from 9 determinations of the mean longitudinal magnetic field [FORMULA] and of the crossover [FORMULA] (see Mathys 1995a for the definition of the latter). Not surprisingly, given the small number of measurements, this attempt was plagued by severe ambiguities. The latter could be resolved by considering simultaneously the magnetic data of Mathys (1991), two additional determinations of the longitudinal field of Bohlender et al. (1993), and 36 photometric measurements in the Geneva seven-colour system. This had allowed us to establish unequivocally that HD 137509 rotates with a period [FORMULA]  d (Lanz & Mathys 1991).

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© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998