Outburst of Micronova DDE 158 in Centaurus
ATel #11917; D. Denisenko (Sternberg Astronomical Institute, Lomonosov Moscow State University)
on 5 Aug 2018; 21:56 UT
Credential Certification: Denis Denisenko (d.v.denisenko@gmail.com)
Subjects: Optical, Cataclysmic Variable
The unusual variable DDE 158 = GALEX J140934.6-384610 is going into outburst on the images obtained with T17 instrument (0.43-m f/6.8 reflector + CCD) of iTelescope.Net observatory in Siding Spring, Australia. The recent magnitudes (unfiltered with V zero point) are listed in Table below.
Obs. Date, UT Magn.
20180801.4731 16.43
20180804.4940 16.17
20180804.4957 16.18
20180805.3948 16.11
Color-combined DSS finder chart of DDE 158 is uploaded to http://scan.sai.msu.ru/~denis/DDE158-JRIR.jpg (10'x10' FOV). The star USNO-A2.0 0450-16997190 (14 09 37.93 -38 46 50.3) located 56 arcsec SE of the variable was used as a reference star with V=15.269 (APASS DR9, Henden et al., 2016). Light curve of DDE 158 obtained with the same T17 telescope starting from June 2018 is shown at http://scan.sai.msu.ru/~denis/DDE158-T17-2018Jun01-Aug05.gif
This object was discovered with the tip of the pen based on its unprecedented (NUV-W1) color index of 8.9 (see Denisenko and Larin, 2018, arXiv:1807.04574). The position of DDE 158 on the color-color diagram of cataclysmic variables (NUV-W1) vs (W1-W2) is shown at http://scan.sai.msu.ru/~denis/DDE158-CVs-NUV-W1-W2.gif with the dark blue triangle. (FUV-NUV) value is 0.28. At the distance of 103+/-1 parsec (Gaia DR2) DDE 158 is in Top 20 nearby cataclysmic variables ranked 16th. With the absolute magnitude M=11.1 at quiescence and M=10.3 in outburst is was categorized as "micronova" because of a small outburst amplitude compared to dwarf novae. This subtype of compact binary systems has obviously a low accretion rate. T. Maccarone in Cataclysmic Variables discussion group has suggested that DDE 158 and Larin 2 are objects with the wind-fed accretion where wind circularization radius is smaller than the Roche Lobe overflow circularization radius. The tomography of spectral lines is required to verify whether the accretion disk is present before, during and after the outburst. Since the orbital period is unknown, the time-resolved photometry is also strongly encouraged. Based on the outburst recurrence time from the long-term light curves, the next chance to study this object will occur no earlier than in spring 2019.
Another thing to note is the light curve behavior of DDE 158 before the current outburst. One can detect the "pumping-up" phenomenon similar to that observed during the supercycle of ER UMa-type variables. Every next outburst in the cycle has a larger amplitude and a longer duration than the previous one (16.4m on June 11, 16.3 on June 25, 16.2 on July 14). The dip before the current outburst is clearly detected, even despite the gap in observations on July 27-31 due to bad weather in Australia. Continued monitoring of this unusual object from other longitudes is strongly recommended.
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