Solar-Stellar Connection

Abstract

During the era of the Solar Maximum Mission (SMM) observations of the Sun, significant developments were taking place in the parallel field of stellar astrophysics which led to the concept of the so-called “solar-stellar connection.” In the same way that the developments in the earlier part of this century had used solar observations, such as limb darkening, together with stellar observations, such as flux distributions and line profiles, to create the field of stellar atmospheres, the fields of stellar outer atmospheres and stellar activity developed as connections were made between the highly dynamic, highly structured phenomena of the Sun revealed by Skylab and SMM, and apparently analogous phenomena on stars. Broadly speaking, the most important concepts were: 1. The detection of X-ray-emitting coronae on many types of stars, together with the fact that such coronal emissions could vary widely for stars of identical spectral type. This played an important role in the rejection of acoustic heating mechanisms for the corona. 2. The discovery of a dividing line in the H-R diagram at which stars evolving off the main sequence seemed to abruptly lose their coronae and appeared to acquire massive stellar winds instead. 3. The establishment of relations between coronal emission and rotation of stars. 4. The establishment of age-versus-activity relations. 5. The discovery of stellar activity cycles analogous to the 11-year solar cycle. 6. The development of flux-flux relationships to see whether plages and active regions are the same on all active late-type stars and of techniques to begin to map spots and active regions on other stars. 7. The observations of the high-energy components of flares on other stars in the ultraviolet and X-ray regions. 8. The exploration of the limits of the fraction of the stellar thermonuclear power that is or can be channeled into chromospheric, coronal, or flare phenomena. This ranges from non-magnetic basal levels of chromospheric emission to extreme X-ray emission in coronae and flares.