Abstract
We briefly review results of a long-term variability campaign on the Seyfert 1 galaxy Markarian 110. Furthermore, we present new results based on data taken between November 1999 and April 2000 with the Hobby-Eberly Telescope (HET). Mrk 110 was monitored every three to ten days with the HET. The He II λ 4686 line follows the continuum variations with a delay of only 5 days while the Balmer lines originate at distances over 23 light days. The intensity variations in the He II line are extremely strong. Interpreting the higher redshift of the broad HeII line component (with respect to the Balmer and narrow line components) as gravitational redshift we can estimate the central black hole mass. This value is 4 times higher than the value estimated from gas kinematics.
