ROTATION AND EMISSION-LINES IN STARS AND ACCRETION DISKS

In the accretion disks of quiescent dwarf novae, Doppler mapping studies reveal that Balmer emission lines increase sharply toward the center of the disk, with surface brightnesses scaling roughly as R-3/2 is-proportional-to OMEGA-Kep. Similarly, among chromospherically active stars the H-alpha and Ca II H and K emission cores are stronger in the more rapidly rotating stars, with surface brightnesses scaling again roughly as OMEGA-rot. Since in both cases the emission lines scale linearly with the rotation frequency, we propose that the mechanism powering the emission lines in quiescent accretion disks is the same as that in chromospherically active stars, namely the emergence of magnetic flux generated by the action of a dynamo, and its interaction with the atmosphere. If this empirical connection between disks and stars is in fact due to magnetic dynamos, the range of rotation rates available for testing dynamo theories expands from a factor of 10(3) to 10(7).