THE EXTREMELY ACTIVE SINGLE GIANT 1E-1751- REVISED PROPERTIES AND A REEVALUATION OF ITS EVOLUTIONARY STATUS(7046 EQUALS ET DRACONIS )

Citation
Cw. Ambruster et al., THE EXTREMELY ACTIVE SINGLE GIANT 1E-1751- REVISED PROPERTIES AND A REEVALUATION OF ITS EVOLUTIONARY STATUS(7046 EQUALS ET DRACONIS ), The Astrophysical journal, 479(2), 1997, pp. 960-969
Citations number
64
Categorie Soggetti
Astronomy & Astrophysics
Journal title
ISSN journal
0004637X
Volume
479
Issue
2
Year of publication
1997
Part
1
Pages
960 - 969
Database
ISI
SICI code
0004-637X(1997)479:2<960:TEASG1>2.0.ZU;2-J
Abstract
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 classificatio n has been revised from K5 IV to K0 III, v sin i from 30-40 km s(-1) t o 23 km s(-1), and the reported nondetection of the Li I 6707 Angstrom line to a significant log epsilon(Li) = 1.8. Chromospheric and transi tion region surface fluxes from IUE observations and the coronal surfa ce 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 ha nd, we show the star to be located about 250 pc above the galactic pla ne, suggesting an intermediate or old disk object. The new spectral cl ass (T-eff) 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 co nsistent 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 similar to 30 degrees and similar to 50 degrees . There are currently only two possible evolutionary scenarios for thi s anomalous star: (a) coalescence from a progenitor W UMa-type contact binary; or (b) the dredge-up of both angular momentum and nuclear pro cessed material in a low-mass (similar to 1-2.5 M-.) giant. A space mo tion, obtainable once a parallax and proper motion are available from Hipparcos, may resolve the age (old disk-young disk) uncertainty: youn g disk motions would favor the angular momentum transfer scenario. The re is no current theory that can account for the observed lithium abun dance.