The Extremely Active Single Giant 1E 1751+7046 = ET Draconis Revised Properties And A Reevaluation of Its Evolutionary Status.

New spectroscopic observations have resulted in significant revisions to several of the orginally published properties of the X-ray bright, chromospherically active star 1E 1751+7046: the spectral classification has been revised from K5 IV to K0 III, v sin i from 30--40 km s-1 to 23 km s-1, and the reported nondetection of the Li I 6707 A line to a significant log epsilon (Li) = 1.8. Chromospheric and transition region surface fluxes from IUE observations and the coronal surface flux from earlier Einstein data are close to saturation levels, and comparable only to very active binaries, pre--main-sequence stars, and FK Comae itself. IUE observations also recorded a flare. Fifteen new radial velocity measurements show no evidence for a companion and are consistent with intermediate or young disk membership. On the other hand, we show the star to be located about 250 pc above the galactic plane, suggesting an intermediate or old disk object. The new spectral class (Teff) and limits on the luminosity indicate that 1E 1751+7046 is a low-mass star on its first ascent of the giant branch. Photometry from the Four College Consortium Automatic Photometry Telescope is consistent with the recently published photometric period of 13.98 days, and the light curve is well fitted by a model consisting of two large spots at latitudes of ~30 deg and ~50 deg. There are currently only two possible evolutionary scenarios for this anomalous star: (a) coalescence from a progenitor W UMa--type contact binary; or (b) the dredge-up of both angular momentum and nuclear processed material in a low-mass (~1--2.5 Msun) giant. A space motion, obtainable once a parallax and proper motion are available from Hipparcos, may resolve the age (old disk-young disk) uncertainty: young disk motions would favor the angular momentum transfer scenario. There is no current theory that can account for the observed lithium abundance.

Main Author: Ambruster, Carol W.
Other Authors: Fekel, Francis C., Guinan, Edward F., Hrivnak, Bruce J.
Language: English
Published: 1996
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