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Astron. Astrophys. 326, 741-750

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He I D3 absorption and its relation to rotation and activity
in G and K dwarfs*

S.H. Saar1 and J. Huovelin2, and R.A. Osten1,3, and A.G. Shcherbakov4

1Harvard-Smithsonian Center for Astrophysics, MS 58, 60 Garden St., Cambridge, MA 02138, USA
2Observatory and Astrophysics Laboratory, P.O. Box 14 (Tähtitorninmäki), FIN-00014 University of Helsinki, Finland
3Center for Astrophysics and Space Astronomy, Campus Box 389, University of Colorado, Boulder, CO 80309, USA
4Crimean Astrophysical Observatory, Russian Academy of Sciences, Nauchny, 334413 Crimea, Ukraine

Received 28 November 1996 / Accepted 23 April 1997


We have obtained high resolution, high S/N spectra of the He I D3 line (5876 Å) for 53 stars. Combining these data with previous measurements, we investigate correlations between the flux absorbed by D3, FORMULA , rotation and other stellar activity indicators for a set of 76 G and K dwarfs. We find that FORMULA FORMULA for FORMULA 4 days. For FORMULA 4 days, FORMULA behaviour depends on spectral type, either remaining roughly constant (G stars), decreasing (K stars), or even going into emission (a few late K stars). We study correlations between D3 and chromospheric (Ca II HK), transition region (C IV 1550 Å) and coronal emission, and find, for FORMULA 4 days, FORMULA , FORMULA , and FORMULA , respectively. Thus, D3 has a response intermediate between Ca II HK and C IV in low to moderate activity stars, consistent with its formation in the upper chromosphere. Our data suggest that the maximum flux absorbed by D3 is FORMULA erg cm-2s-1 in G stars (equivalent widths FORMULA 80 mÅ), and about 40% of that value (or FORMULA 50 mÅ) in K stars, less than predicted by current theoretical models. We discuss the implications of our results for stellar activity and He I line formation, and suggest future avenues of study.

Key words: stars: activity - stars: chromospheres - stars: coronae - stars: late-type

*Based in part on observations obtained at the European Southern Observatory, La Silla, Chile, and at the Crimean Astrophysical Observatory, Nauchny, Ukraine

Send offprint requests to: S. Saar

© European Southern Observatory (ESO) 1997

Online publication: September 18, 1997
Last change: October 15, 1997