Speaker
Description
An accretion disk plays a crucial role in various astrophysical phenomena. Dwarf nova (DN) outbursts in an accreting white dwarf binary provide the simplest laboratory for the time-dependent behavior of accretion disks. Most energetic DN outbursts (superoutbursts) are accompanied by small modulations known as superhumps, which change their periods and profiles over a superoutburst. Despite numerous works using ground-based telescopes, coverage of the rapid evolution in light curves and superhumps remain incomplete, which is crucial for a time-dependent model of accretion disks. Here we present the first 10 TESS examples of DN superoutbursts in systems with the shortest orbital periods and longest outburst cycles, so-called WZ Sge-type DNe. TESS provides uniform and precise photometry over month-long baselines, which is advantageous to trace the rapid rise of the outburst and changes in superhumps. We obtained the orbital periods and mass ratios of our samples by determining the superhump period and its evolution. We measured the rise timescale of these outbursts as 0.1-0.3 d mag$^{-1}$. This agrees with the models, which predict that an outburst is first triggered at the outer disk. Moreover, two samples show the broken powerlaw rise, previously found in only one WZ Sge-type DN observed by Kepler. This phenomenon presumably corresponds to the onset of the heating wave propagating through the disk. We did not detect any orbital modulation in the early rise of the outburst. This non-detection of orbital humps in V748 Hya constrains the corresponding mass transfer rate to be below ≃ 1 × 10$^{16}$ g s$^{−1}$, disfavoring an enhancement of a mass transfer rate by an order of magnitude or larger, even if such an enhancement occurs. Overall, these results support the thermal-tidal instability model of DN superoutbursts.
| Stream | Science or Engineering |
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