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Active Stars and He I 10830 A, the EUV Connection

Active Stars and He I 10830 A, the EUV Connection

Publication date: 02 September 2005

Authors: Sanz-Forcada, J., et al.

Journal: High Resolution Infrared Spectroscopy in Astronomy
Volume: 1
Page: 256
Year: 2005

Copyright: Springer-Verlag/ESO

We present a relation between EUV flux and strength of the He I 10830 A line in active cool stars. The metastable lower level of the Helium 10830 line is believed to be populated by recombination following photoionization of neutral Helium present in the upper chromosphere. The EUV flux radiated in the corona (the ionization edge of He I is at 24.58 eV, or 504.27 A) is responsible for the photoionization. For the first time, we have measured the EUV flux in active stars directly using the Extreme Ultraviolet Explorer (EUVE) to verify a relation to the strength of the He I absorption, measured with the SOFIN echelle spectrograph (R~170000) on the Nordic Optical Telescope. The He I absorption increases with the EUV flux, displaying two different relations, one for subgiants and dwarfs, and another one for giants, which has stronger absorption. The presence of emission and chromospheric acceleration observed in the He 10830 line profiles will be also discussed.

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