1999A&A...345...49B

We present results of a long-term variability campaign on the Seyfert 1 galaxy Markarian 110. Mkn 110 is a narrow-line Seyfert 1 object hosted in a morphological peculiar galaxy. We monitored the optical continuum and the line intensities as well as their profiles over a time interval of nearly ten years. The continuum and the Balmer lines varied by a factor of 2 to 5 within two years. The HeIIλ4686 line showed exceptional intensity variations of a factor of eight. We detected an additional independent very broad-line region in high intensity stages of the Balmer and HeII lines. The CCF analysis of the HeII line indicates that this very broad-line region originates at a distance of 9 light days only from the central ionizing source.