The first results of a study of F-type MS stars using the He I D3 absorption feature at 5876 A as an indicator of stellar activity and structure are presented. The observations were obtained with the QUB echelle spectrograph at the Cassegrain focus of the 4.2 m William Herschel telescope. Seventeen F-stars of the Hyades main sequency were chosen as

IAUC 5057 available at Central Bureau for Astronomical Telegrams.

The effect of the rotation and finite size of a stellar radiation source on dust particle orbits is examined. It is found that, for dust particles substantially larger than the critical size, the general behavior is to spiral under the effect of the traditional Poynting-Robertson drag. However, when the effect of the source rotation is taken into

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Visible photometry of the RS CVn system AR Lac is presented. We find some interesting features in the light curves. Also a possible oscillation with period 1.05 hr arises from the data. A new determination of the geometrical parameters of the system is given.

The paper presents a new method for deriving stellar masses and distances using the theory of radiatively driven winds as presented by Kudritzki et al. (1989) and the stellar parameters derived from NLTE spectroscopic analysis. The procedure is illustrated with five stars observed in three open clusters. Comparison with evolutionary tracks