HE-I LAMBDA-10830 ANGSTROM LINE AS AN INDICATOR OF SOLAR CHROMOSPHERIC ACTIVITY

Full disk spectroscopic observations in the near infrared region of th e solar spectrum (the Sun-as-a-star) are presented for the years 1981- 1993. The central depth of the He I lambda 10830 Angstrom line shows c hanges following the 11-year activity cycle, and also variability foll owing the rotation of the Sun. We found high correlations between the depth of the He I line and coronal indices of activity, such as Fe XIV lambda 5303 coronal emission index and 10.7 cm radio flux. Thus the H e I line depth may be used as an index of activity for the chromospher ic and low chromospheric-coronal transition region for the Sun, observ ed as a star and, by inference for other late-type stars.