AT 2018fdx: TESS Photometry During the Superoutburst of a SU UMa Type Dwarf Nova
ATel #12292; R. Ridden-Harper, H. Abbot, B. E. Tucker (ANU), P. Garnavich, C. Littlefield (Notre Dame), A. Rest (STScI)
on 13 Dec 2018; 20:22 UT
Credential Certification: Peter Garnavich (pgarnavi@gmail.com)
Subjects: Optical, Cataclysmic Variable, Transient, Variables
The transient AT 2018fdx (ASASSN-18sk; ATel 11964, 11967) was detected by the Transiting Exoplanet Survey Satellite (TESS) during observations of Sector 1. Preliminary photometry was extracted using a 9-pixel aperture with the transient well separated from the brighter stars in the field. With a 30-minute cadence, the photometry reveals a complex light curve consistent with a dwarf nova (DN) outburst. The transient is first detected on BJD2458345.1 and reaches an initial peak 1.1 days later. The star then fades by 1.7 mag over 4 days before rising again to a second, brighter maximum on BJD2458351.5. Rapid variability is seen beginning near the time of the second maximum. Observations of Sector 1 ended 1.6 days after the time of the second peak.
The initial peak is consistent with a normal DN outburst which has nearly faded away before a superoutburst begins. The rapid variability around the second peak is likely due to superhump oscillations and we conclude that
AT2018fdx is an SU UMa type DN. A power spectrum of the oscillations over the first 3 days of the superoutburst gives a superhump period of 2.10 hours. A light curve phased on that period shows that the superhumps have a total amplitude of 0.3 mag.
