Showing papers by "Lee Hartmann published in 1985"

Evolution of low-mass stars in the alpha Persei cluster.

Abstract: We present a photometric and spectroscopic study of low-mass members of the ..cap alpha.. Persei cluster. Now relative proper motions have been obtained for 4000 stars in a 1X2 x 1X2 region of the ..cap alpha.. Persei open cluster. The survey extends to Vroughly-equal16.5 mag, much fainter than the previous proper motion surveys. Optical photometry and high-dispersion spectroscopy of the possible cluster members from our survey, as well as a set of 10th to 12th magnitude stars from previous surveys, have also been obtained. The new photometry shows an apparent pre-main sequence (PMS), but we cannot yet accurately determine the PMS turn-on point. The faint stars in the cluster have positions in a V versus V-I diagram that are roughly in accord with the 5 x 10/sup 7/ yr isochrone derived by VandenBerg et al. In agreement with previous results for the Pleiades cluster, some of the late-type ..cap alpha.. Persei members are photometric variables, with periods of 1 day or less. Light curves and estimated periods are presented for six of the G and K dwarf members of the cluster. We attribute the periodic light variations to spots on the surfaces of these stars, which are carried around themore » visible hemisphere by rapid rotation. The photometric periods are consistent with rotational broadening measurements when available. Projected rotational velocities derived from the echelle spectra indicate that nearly 50% of the stars observed that are later than G2 have 25 km s/sup -1/« less

On the outer atmospheres of hybrid stars

Abstract: Deep exposures with the IUE satellite have been obtained in order to search for high-temperature emission from stars with cool winds. Iota Aur and Theta Her are confirmed as hybrid stars, and an additional hybrid object, Gamma Aql, has been discovered. The emission line fluxes of the hybrid stars are analyzed to establish the emission measure distribution and, as far as possible, the electron density. The discovery of variable, high-velocity Mg II circumstellar absorption in Gamma Aql, Theta Her, and Alpha TrA is reported. Very long exposure of the latter show that cool material is being accelerated to velocities of at least 180 km/s. These observations suggest that high-velocity mass loss is more common than previously thought.

Mass Loss in Metal Deficient Red Giants

Abstract: The occurrence and rate of mass loss from metal deficient red giant field stars have consequences for the theory of evolution of low mass stars. This paper reports several of the results from an observational and theoretical program to assess the presence and character of chromospheric line profiles and their variations, to obtain quantitative measurements of radiative losses from chromospheres, and to construct semi-empirical model chromospheres and extended atmospheres in order to provide limits on the mass loss rates.