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Rare Low State of DO Dra, the Magnetic Dwarf Nova=Outbursting Intermediate Polar

ATel #10477; Vitalii V. Breus (Odessa National Maritime University, Ukraine), Ivan L. Andronov (Odessa National Maritime University, Ukraine), Joh-Na Yoon (Chungbuk National University, Korea), Pavol Dubovsk\'y (Vihorlat Observatory Humenn\'e, Slovakia)
on 9 Jun 2017; 21:05 UT
Credential Certification: Ivan L.Andronov (tt_ari@ukr.net)

Subjects: Optical, Binary, Cataclysmic Variable, Variables

DO Dra is an exotic cataclysmic variable which shows properties either of the intermediate polars, or dwarf novae. It may represent a new subclass of "magnetic Dwarf Nova=outbursting intermediate polar". Erroneously it is sometimes called YY Dra (the name assigned in the GCVS ( Samus et al. (2017) ) to another star of an Algol type), see Andronov et al. (2007). The star showed a statistical dependence between the decay time of the outbursts and a brightness at maximum, and "transient periodic oscillations" at the descending branch. The nightly mean brightness outside eclipses was no fainter than 15.36mag. On June 8, 2017, Joh-Na Yoon (CBNU) reported that DO Dra was invisible, but the weather conditions prevented to make longer exposures. After this alert, Vitalii Breus made a run in the filter R (HJD 2457913.336-.558, totally 158 data points) using the 60-cm telescope of the Planetarium and Astronomical observatory in Hlohovec, Slovakia. The light curve shows variations from 15.82 to 16.34 with a mean of 16.095+-0.007. The second-order trigonometric polynomial fit with an orbital period of 0.16537398 (Haswell et al. 1997) shows double-humped shape with a maximum of R= 15.954+-0.013 at HJD 2457913.37965, minimum of R= 16.194+-0.015 at HJD 2457913.42045. Very unequal maxima are strange to be interpreted as the effect of ellipticity. Maybe they are due to a hot spot in the accretion disk. One may note an apparent resemblance to the "extreme direct impactor" V361 Lyr (The Andronov and Richter (1987)), however, in DO Dra, there is a weakly magnetic white dwarf, so the hot spot is to be at the edge of the accretion disk. Current unprecedented low state of DO Dra resembles low states of intermediate polars (e.g. in V1323 Her )) and Nova-Like CVs (e.g. in TT Ari )). It was never observed in DO Dra before 2008 Andronov et al. (2007), according to the AAVSO. database. However, there were 2 nightly runs obtained at the 1-m telescope VNT of the Vihorlat observatory with even lower luminosity with a nightly mean stellar magnitude 16.9 (V), so 16.1 (R), comparable to a current low state. Further monitoring is encouraged to determine details of this interesting event.