ZAMS Stars in Our Own Backyard: IUE and Coude Feed Observations of Solar Neighborhood, Pleiades-Age K Dwarfs

Details ZAMS Stars in Our Own Backyard: IUE and Coude Feed Observations of Solar Neighborhood, Pleiades-Age K Dwarfs ZAMS Stars in Our Own Backyard: IUE and Coude Feed Observations of Solar Neighborhood, Pleiades-Age K Dwarfs

Dec 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.5108a&link_type=abstract

American Astronomical Society, 181st AAS Meeting, #51.08; Bulletin of the American Astronomical Society, Vol. 24, p.1206

Astronomy and Astrophysics

Astronomy

Scientific paper

The nearest cluster Zero Age Main Sequence (ZAMS) K dwarfs are in the Pleiades (age 7times 10(7) yr). Because high temperature emissions, i.e., transition region (TR) and corona, are relatively strongest for the youngest stars, ultraviolet observations of this critical evolutionary stage would establish the level of 10(5) K (TR) emission at the onset of core hydrogen burning. Unfortunately, the Pleiades K dwarfs are too faint for IUE, and will be difficult even with HST. We have recently isolated a tiny, but homogeneous group of solar neighborhood, Pleiades-age, K dwarfs. All five stars are: single, between spectral types K0-K2 V, have very high Li abundances, and young disk space motions. The only variable is rotation rate (1.66 d < P < 5.36 d). We have obtained IUE spectra and simultaneous/contemporaneous KPNO coude feed spectroscopy at several phases of the rotation period for three of these stars, and have requested time for similar observations of the final two. So far, some 100 IUE spectra have been used for this study. We report on several results to date: 1) TR and chromospheric surface fluxes, as well as chromospheric/TR flux ratios, are intermediate between main sequence values and pre-main sequence stars, 2) high TR and chromospheric fluxes imply surfaces largely covered by active regions similar to the most active solar regions; 3) variability in high temperature (TR) plasma is greatest for the star with the shortest rotation period. Emission measure modelling is in progress, and results will be presented.

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