A Deeply Eclipsing SU UMa-Type Dwarf Nova with the Shortest Orbital Period, XZ Eridani

We discovered superhumps in an eclipsing dwarf nova, XZ Eridani, during an outburst in 2003 January-February. We determined the orbital and average superhump periods to be 0.061159602 ± 0.000000044 d and 0.062808 ± 0.000017 d, respectively. Our observations thus established that XZ Eri belongs to a rare class of deeply eclipsing SU UMa-type dwarf novae. The object has the shortest orbital period among seven known objects in this class. The superhump period decreased with time during a mid-plateau phase of the superoutburst, as observed in a number of ordinary, long-period SU UMa stars. During an early phase of the superoutburst, however, the superhump period increased, as observed in several short-period systems. XZ Eri is a unique object with which we can study the evolution of accretion-disk structures through eclipses during the phase of the superhump period increase.