Determination of the superoutburst cycle lengths of 206 SU UMa type dwarf novae

TL;DR

This study significantly expands the dataset of superoutburst cycle lengths for SU UMa dwarf novae, providing new statistical insights and identifying long-cycle stars, thereby enhancing understanding of their outburst behaviors.

Contribution

It introduces new Cso measurements for 206 SU UMa stars, increasing the known data by nearly fourfold and exploring long-cycle stars up to 4590 days, with implications for classification and future research.

Findings

Distribution peaks around 270 days

Long cycles (>450 days) are more common than previously known

Superoutburst timings show about ±7% deviation from linear ephemeris

Abstract

SU UMa stars are characterized by "superoutbursts" which are brighter at maximum light and which last much longer than the more frequent "ordinary" outbursts of these dwarf novae. Although there are now more than 1180 SU UMa type dwarf novae catalogued, our knowledge on their superoutburst cycle length Cso was hitherto limited to about 6$\%$ of the entire sample of known SU UMa stars. Using public data bases we have determined new Cso values for a total of 206 additional SU UMa stars in the range 17 d $<$ Cso $<$ 4590 d (including some ER UMa and WZ Sge type representants) within total time intervals between 2 and 57 years, and with an estimated uncertainty of $\pm$11$\%$. This way, we are increasing our present knowledge of Cso values by a factor $\sim$3.8. Its distribution is characterized by a broad maximum around Cso $\approx$ 270 days, and slowly decreasing numbers till Cso $\approx$ 800 d. The domain Cso $>$ 450 d was unexplored until now; we add here 106 cases ($\sim$51$\%$ of our total sample) in this range of long cycles, implying a better statistical basis for future studies of their distribution. Our sample contains 16 known WZ Sge stars, and we propose WZ Sge membership for 5 others hitherto classified as ordinary SU UMa stars. Individual superoutburst timings deviate in average about $\pm$7$\%$ of the cycle length from their overall linear ephemeris, conrming a pronounced quasi-periodic repeatability of superoutbursts. All relevant parameters are listed with their errors, and a table with individual superoutburst epochs of our targets is given, enabling future researchers to combine our results with other (past or future) observations.