  We present the 2005-2010 outburst history of the SUUMa-type dwarf HS
0417+7445,along with a detailed analysis of extensive time-series photometry
obtained in March 2008 during the second recorded superoutburst of the system.
The mean outburst interval is 197 \pm 59 d, with a median of 193 d. The March
2008 superoutburst was preceeded by a precursor outburst, had an amplitude of
4.2 magnitudes, and the whole event lasted about 16 days. No superhumps were
detected during the decline from the precursor outburst, and our data suggests
instead that orbital humps were present during that phase. Early superhumps
detected during the rise to the superoutburst maximum exhibited an unusually
large fractional period excess of epsilon = 0.137 (Psh = 0.0856(88) d).
Following the maximum, a linear decline in brightness followed, lasting at
least 6 days. During this decline, a stable superhump period of Psh =
0.07824(2) d was measured. Superimposed on the superhumps were orbital humps,
which allowed us to accurately measure the orbital period of HS 0417+7445, Porb
= 0.07531(8) d, which was previously only poorly estimated. The fractional
superhump period excess during the main phase of the outburst was epsilon =
0.037, which is typical for SU UMa dwarf novae with similar orbital period. Our
observations are consistent with the predictions of the thermal-tidal
instability model for the onset of superoutbursts,but a larger number of
superoutbursts with extensive time-series photometry during the early phases of
the outburst would be needed to reach a definite conclusion on the cause of
superoutbursts.
