[vsnet-alert 22999] Re: DDE 158 = GALEX J140934.6-384610

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

Dear Taichi,

Non-detection by ASAS-SN in 2018-2019 can be in part due to the change
from V to g filters. As I wrote, DDE 158 is very red (Gaia
BP-RP=2.62), and g band is blue-shifted from V band. So, the star has
a significant (g-V) color index to be determined.

This object location on the (NUV-W1) vs (W1-W2) diagram is close to
the known LARP (low accretion rate polar) MQ Dra, indeed. However, the
light curve is very unusual. In June-July 2018 the longer the interval
between the outbursts, the larger was the amplitude:
http://scan.sai.msu.ru/~denis/DDE158-T17-2018Jun01-Aug05.gif Then goes
the main outburst in early August:
http://scan.sai.msu.ru/~denis/DDE158-T17-2018Aug01-14.gif with a
narrow peak on top of the slower rise and fade.

I would be grateful if you point to the exisiting analogs. The only
similar thing I have seen is the X-ray light curve of Swift
J0243.6+6124, but on the longer time scale. The similarity principle
suggests if two processes follow the similar graphs, they are
described by the same function, but with the different parameters
(masses, orbital radius, accretion rate). The shape of the light curve
can be a key to understanding the nature of this system.

The star deserves the continuous monitoring, with the special
attention paid to the filters used (as I wrote, Clear and Luminance
make a big difference here)!

Denis Denisenko (DDE)

On Tue, Feb 12, 2019 at 7:00 AM Taichi Kato
<tkato at kusastro.kyoto-u.ac.jp> wrote:

> ASAS-SN data:
> https://asas-sn.osu.edu/light_curves/08462a7a-d2b6-4939-9716-bf348b120e5d
>
>    The object was bright in 2018 Aug., but is undetected now.
> Possibly a polar with low mass-transfer rate (or occasional
> activity)?