Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997a%26a...326..741s&link_type=abstract
Astronomy and Astrophysics, v.326, p.741-750
Astronomy and Astrophysics
Astrophysics
28
Stars: Activity, Stars: Chromospheres, Stars: Coronae, Stars: Late-Type
Scientific paper
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, F_D3_, rotation and other stellar activity indicators for a set of 76 G and K dwarfs. We find that F_D3_{prop.to}P_rot_^-1.2^ for P_rot_>=4days. For P_rot_<4days, F_D3_ 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 1550Å) and coronal emission, and find, for P_rot_>4days, F_D3_{prop.to}{DELTA}F_HK_^1.5^, F_D3_{prop.to}F_CIV_^0.7^, and F_D3_{prop.to}F_X_^0.6^, 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 F_D3_{prop.to}T_eff_^9.3^=~2x10^5^erg/cm^2^/s in G stars (equivalent widths Wlambda_<=80mÅ), and about 40% of that value (or Wlambda_<=50mÅ) 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.
Huovelin Juhani
Osten Rachel Ann
Saar Steven H.
Shcherbakov A. G.
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