Astron. Astrophys. 336, 518-526 (1998)

1. Introduction

The serendipitous discovery of HD 2724 as a variable star is due to Reipurth (1981), which chose it as one of the comparison objects for his differential photometry of the eclipsing binary AG Phe. The author identified HD 2724 as a probable Scuti star and guessed a tentative period of 0^d.174 (i.e. a frequency of 5.75 d^-1). Lampens (1992) met this periodicity again analysing her excellent sequences of absolute measurement obtained at La Silla in 1984-85 by means of the UBVB₁B₂V₁G Geneva photometer. Lampens' analysis shows multiperiodic variations which are typical of the Scuti light curves: besides the above mentioned frequency, she identified unambiguously another component at 7.38 d^-1 and suggested 6.50 d^-1 and 4.34 d^-1 as two additional candidate frequencies.

HD 2724 is classified as an F2 III star in Hoffleit and Jaschek (1982). Lampens (1992) gets from her photometry T_eff = 7180^oK and M_V = 0.93. Physical parameters can be evaluated also by using the colours published by Hauck & Mermilliod (1990). Moon's & Dworetsky's (1985) grids lead us to estimate T_eff and at 7280^oK and 3.56 respectively, while Villa & Breger (1998) obtain from their still unpublished calibration, based on Canuto's & Mazzitelli's (1991) models and performed using dereddened indices, T_eff = 7216^oK and = 3.64. As to the absolute magnitude, Crawford's (1979) calibration yields M_V = 1.12, E(b-y) = 0.014 and therefore A_V = 0.060. Nevertheless, our photometric evaluations of luminosity are now to be revised owing to new astrometric data: in the Hipparcos Satellite General Catalogue (ESA, 1997), this object (HIC 2388) appears with a parallax = 7.77 .72 mas, which, taking account of the above assessed interstellar extinction, corresponds to an absolute magnitude M_V = 0.57 .20. In principle, pulsational masses could help us to adjust these calibrations. It would entail, however, a thorough knowledge of pulsational states, which today might be achieved only by combining photometry and spectroscopy in a synergetic approach (see e.g. Bossi et al., 1994, or Mantegazza et al., 1998).

In order to exploit the complementarity between photometry and spectroscopy in studying dynamical processes like stellar pulsations, we are performing for many years simultaneous observational campaigns of Scuti stars through both these techniques (Mantegazza et al., 1994; Mantegazza & Poretti, 1996). The present work on HD 2724 falls within this frame.

© European Southern Observatory (ESO) 1998

Online publication: July 20, 1998
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