The sun-as-a-star solar spectrum



The Sun is the only star for which individual surface features can be observed directly. For other stars, the properties of starspots, stellar rotation, stellar flares, etc, are derived indirectly via variation of star-integrated spectral line profiles or their luminosity measurements. Solar disk-integrated and disk-resolved observations allow for investigations of the contribution of individual solar disk features to sun-as-a-star spectra. Here, we provide a brief overview of three sun-as-a-star programs, currently in operation, and describe recent improvements in observations and data reduction for the Integrated Sunlight Spectrometer (ISS), one of three instruments comprising the Synoptic Optical Long-term Investigations of the Sun (SOLIS) system. Next, we discuss studies employing sun-as-a-star observations (including Ca II K line as proxy for total unsigned magnetic flux and 2800 MHz radio flux) as well as the effects of flares on solar disk-integrated spectra. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)