ASASSN-14fu: Unusual Cataclysmic Variable With Coexistence of 0.16-d Period and 0.020-0.025 d Quasiperiod During the 2014 Outburst Decline and Quiescence

ATel #6761; E. Pavlenko, K. Antonyuk, A. Sosnovskij, O. Antonyuk (CrAO), N. Katysheva, S. Shugarov (SAI, MSU; AISAS)
on 27 Nov 2014; 10:22 UT
Credential Certification: Elena Pavlenko (eppavlenko@gmail.com)

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ASASSN-14fu is an unusual hydrogen-rich cataclysmic variable (ATEL #6624) exhibited a prominent brightness variations during a 2014 outburst (VSNET-alert 17635) with preferred period of 0.0255(1) d before Aug. 20 and a period of 0.02572(1) d after Aug. 20 (VSNET-alert 17662).

We have been carried out an integral light photometry of ASASSN-14fu during 19 nights over the 2014 outburst decline and the following quiescence since August 27 up to October 30 inclusively with 2.6-m and 1.25-m telescopes of the Crimean Astrophysical Observatory and 1-m telescope of the Special Astronomical Observatory see light curve .

Observations with 1.25-m telescope during the decline and early phase of quiescence revealed an existence of a previously unknown 0.08 d periodicity together with the short-term variations around 0.020 - 0.025 d. While on Aug 27 these two signals were of comparable significance, the 0.08 d signal has got much stronger at the final stage of decline and quiescence.

One month later (Oct 27 - 30) using the 2.6-m and 1-m telescopes we confirmed the coexistence of these two signals with mean amplitude of 0.23 mag of the long period and 0.05 mag of the short one. More precise observations enabled us to suggest that the real period is 0.16 d because of significant difference between neighbor minima and maxima. We believe that this period is the orbital one with double wave for period see the data folded on the periods of 0.08d and 0.16d .

The profile of the orbital light curve contains unusually sharp both maxima that could not be produced by the ellipsoidal shape of the secondary component. The more deep minimum resembles an eclipse-like one with a small bump in the middle and lasts about 0.5 hours. Basing on the data of four nights in Oct 27 - 30 we obtained the ephemeris for the more deep minimum to be HJD = 2456958.1627(8) + 0.16009(40).

After an accurate subtraction of the orbital modulation from the October data we calculated a periodogram for residuals . It shows two groups of peaks around the 0.0234-d (f1=42.7) and 0.0205-d (f2=48.9) periods. While there is a one-day aliasing within each of group, we found an obvious relation between the groups: forb = f1-f2. There is no indication to the 0.025 d period detected during the outburst. We suggest that the short-term variation in the outburst and quiescence is a quasi-period, not superhump period. This is also supported by our assumption on a long orbital period.

The origin of the short-term variability is unclear. Future observations are needed to understand a nature of this unusual object.