Volume 469, Number 1, July I 2007
|Page(s)||309 - 317|
|Published online||24 April 2007|
Hα and the Ca II H and K lines as activity proxies for late-type stars*
Instituto de Astronomía y Física del Espacio, CONICET-UBA, C.C. 67 Suc. 28 (1428) Buenos Aires, Argentina e-mail: email@example.com
2 Fellow of the CONICET
3 Member of the Carrera del Investigador Científico, CONICET
Accepted: 14 March 2007
Context.The main chromospheric activity indicator is the S index, which is the ratio of the flux in the core of the Ca II H and K lines to the continuum nearby, and is well studied for stars from F to K. Another chromospheric proxy is the Hα line, which is believed to be tightly correlated with the Ca II index.
Aims.In this work we characterize both chromospheric activity indicators, the one associated with the H and K Ca II lines and the other with Hα, for the whole range of late type stars, from F to M.
Methods.We present periodic medium-resolution echelle observations covering the complete visual range, taken at the CASLEO Argentinean Observatory over 7 years. We use a total of 917 flux-calibrated spectra for 109 stars that range from F6 to M5. We statistically study these two indicators for stars of different activity levels and spectral types.
Results.We directly derive the conversion factor that translates the known S index to flux in the Ca II cores, and extend its calibration to a wider spectral range. We investigate the relation between the activity measurements in the calcium and hydrogen lines, and found that the usual correlation observed is the product of the dependence of each flux on stellar colour, and not the product of similar activity phenomena.
Key words: stars: late-type / stars: activity / stars: chromospheres
© ESO, 2007
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.