SIMBAD references

Full disk spectroscopic observations in the near infrared region of the solar spectrum (the Sun-as-a-star) are presented for the years 1981-1993. The central depth of the He I λ10830A line shows changes following the 11-year activity cycle, and also variability following 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 λ5303 coronal emission index and 10.7cm radio flux. Thus the He I line depth may be used as an index of activity for the chromospheric and low chromospheric-coronal transition region for the Sun, observed as a star and, by inference for other late-type stars.