[vsnet-alert 23889] Re: DDE 158 = GALEX J140934.6-384610 outburst

[Denis Denisenko d.v.denisenko@gmail.com via vsnet-alert]

On Thu, Jan 23, 2020 at 3:20 AM Taichi Kato <tkato at kusastro.kyoto-u.ac.jp>
wrote:

   I wonder if these low-luminosity outbursts are not
> true dwarf-nova outbursts, and if they may be "brightening"
> as seen as in low-Mdot, long-Porb object (and an IP) DO Dra.
>

DDE 158 does not fit into any type of CVs. Analogy with DO Dra has a right
to exist, but the differences are huge. X-ray flux, light curve pattern,
absolute magnitudes and colors are all different.

DO Dra: 0.587 cnts/s in ROSAT at 198 pc
DDE 158: <0.03 cnts/s in ROSAT at 103 pc

DDE 158 is in the ROSAT footprint, since there's a QSO 1.6 arc min from it.
X-ray luminocity is fainter by two orders of magnitude than that of DO Dra.
The accretion rate is much lower. Colors are much redder:

DO Dra: NUV-W1=3.75, BP-RP=1.27
DDE 158: NUV-W1=8.9, BP-RP=2.62

It is possible that DDE 158 has undergone the classical Nova eruption some
time ago. Extreme colors and low M_abs may be caused by the expanding
nebula. The accretion disk meanwhile is slowly recovering.

DO Dra ZTF DR2 light curve is irregular on the time scale of 500 days:
http://scan.sai.msu.ru/~denis/DODra-ZTF2-LC.gif

DDE 158 CRTS light curve remained almost stable during 3000 days:
http://scan.sai.msu.ru/~denis/DDE158-SSS_LC.gif

The outbursts with the approximate average cycle of 71 days have the
saw-toothed shape and last for a very short time, more reminescent of the
brightenings in WZ Sge-type dwarf nova SDSS J080434.20+510349.2 near
quiescence.

http://scan.sai.msu.ru/~denis/DDE158-T17-2018Aug01-14.gif

Denis Denisenko