ZAMS K-Dwarfs



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ZAMS K-Dwarfs

Ambruster and collaborators A. Brown (U. CO) and F. Fekel (COE, TN State U.) have been granted time with the GHRS on Hubble Space Telescope for observations of all 6 solar-neighborhood, zero-age-main-sequence (ZAMS) K dwarfs which they have identified over the last 7 years. These stars all have spectral types between K0-K2 V, near-primordial lithium abundances, and all are single. The only variable is rotation rate, which varies between 8 hr and 6.9 d. The importance of the stars is that the nearest cluster ZAMS stars, the early K dwarfs in the Pleiades cluster, are too distant for spectroscopic observations of higher temperature spectral lines with IUE, EUVE, or even HST. As a result, the initial upper atmospheric temperature structure of a cool star just beginning core hydrogen burning is not known. However, chromospheric, transition region, and coronal temperature (and sometimes density) diagnostics can be obtained for the 6 local stars ( d pc) using IUE, EUVE, and now HST data, and will provide, through Volume Emission Measure modelling, the upper atmospheric structure as a function of rotation for ZAMS K dwarfs.

As of Sep 1995, IUE observations have been made of all 6 stars, and EUVE observations of 4 (one star, HD 197890 ('Speedy Mic') is too faint for EUVE and is very marginal with IUE). Simultaneous IUE, EUVE, and HST observations of HD 1405 (Pd) were made in late September 1995. HST observations of the remaining stars will take place in Cycle 5.



Astronomy
Mon Feb 26 18:11:01 EST 1996