Mass loss, magnetic field and chemical inhomogeneities in the He-weak star HD 21699

Abstract

HD 21699 is a He-weak star whose longitudinal magnetic field ranges from − 1.3 to +1.1 kG (Brown et al. 1985). Its effective temperature, Teff = 15900 K, and its gravity, log g = 4.0, were determined by Wolff (1990) from photometry of the Balmer discontinuity and from measurements of the Hγ line. HD 21699 was reported to exhibit remarkable variations in the C IV ultraviolet resonance lines at 1548 and 1551 Å (Shore et al. 1987). These variations occur with the same period, 2d49 (Percy 1985), as the magnetic variations and the photometric variations in the optical region. Similar UV line variations could be found only in two other He-weak stars, HD 5737 and HD 79158. They were interpreted as an evidence of the occurrence of outflowing winds controlled by the magnetic field. Furthermore, Shore et al. emphasized that no lines in IUE spectra other than C IV, and possibly Si IV, show any statistically significant variation. Recently, irregular brightening of a few hundredths of magnitude, superimposed over the periodic variations, were observed in the U photometric band (Vetö 1993); their origin is currently unknown.