DO Dra: Transient Periodic Oscillations at the Suboutburst state of the Magnetic Dwarf Nova

ATel #12527; Ivan L. Andronov (Odessa National Maritime University, Ukraine), Lewis M. Cook, Donna Gholson Cook (CBA Concord, USA)
on 24 Feb 2019; 00:48 UT
Credential Certification: Ivan L.Andronov (tt_ari@ukr.net)

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We report on a detection of the "sub-outburst" state (14.2-14.7 "clear" V) of the outbursting intermediate polar (or a magnetic dwarf nova) DO Dra. The object has changed its luminosity state to a "super-low" ( http://adsabs.harvard.edu/abs/2017ATel10477....1B ) luminosity state and was found at a "sub-low" state last autumn ( http://adsabs.harvard.edu/abs/2018RNAAS...2d.197A ). Previously there was a low state ~15.2 interrupted by short outbursts to ~10-11 . A new type of variability - TPO ("Transient Periodic Oscillations" were detected with rapidly-decreasing frequency from 86 to 47 cycles/day at a magnitude 14.27-14.13 (http://adsabs.harvard.edu/abs/2008A%26A...486..855A). Quasi-periodic oscillations with 18-48 cycles/day were apparently present (http://adsabs.harvard.edu/abs/2017JASS...34...37H). We report on the analysis of the "clear" V (CV) observations obtained on February 22, 2019 by Lewis M.Cook and Donna Cook at the private CBA Concord observatory, USA. The original data are available at the site http://aavso.org . The light curve and its approximations with a two-period model and a "running parabola" fit (http://adsabs.harvard.edu/abs/1997A%26AS..125..207A, realized in the program MAVKA, http://adsabs.harvard.edu/abs/2018arXiv181206949A ) are shown at http://uavso.org.ua/stars/DO_Dra190222-2sin.jpg. The periodograms (http://adsabs.harvard.edu/abs/1994OAP.....7...49A) for the original and detrended data are shown at http://uavso.org.ua/stars/DO_Dra190222-periodogram.jpg. The longer period after corrections is P1=0.0731(16) days, which is approximately half of the orbital period (or possible negative superhump) period. The semi-amplitude is R1=0.088(6) mag and the initial epoch for the maximum brightness is T01=2458536.91247(82). For the shorter period, P2=0.01225(9) days, R2=0.036(6), T02=2458536.94742(33). The optimal value of the filter half-wifth for the "running parabola" fit is 0.0027d, the corresponding curve shows drastic changes in the cycle length (however, within the range of "transient periodic oscillations"). However, the 2-sine fit seems to be reasonable, except few cases of maximum instead of minimum and vice versa. International monitoring was carried out according to the "Inter-longitude astronomy" (ILA) campaign (http://adsabs.harvard.edu/abs/2017ASPC..511...43A). Further observations are required to check the stability/variations of the TPO at this stage of activity.