[vsnet-alert 18792] New CV DDE 36 = 1RXS J202427.7+331629 36' from V404 Cyg

[Denis Denisenko]

I have serendipitously discovered another CV within 6" of the faint
ROSAT source 1RXS J202427.7+331629 (flux=0.0210+/-0.0066 cnts/s
HR1=1.00+/-0.33 HR2=0.31+/-0.31) with a 16" error circle in 1RXS.
Actually I was checking the default 15'x15' DSS plate finder field of
_another_ X-ray source with HR1=1.00 HR2=1.00 (see [vsnet-alert 18771]
for the description of idea which keeps on being fruitful), namely
J202435.9+332044. Nothing obvious was found near the plate center, but
a large-amplitude variable with a distinct proper motion appeared
~4.5' to the south of center and only ~1.5' S of red variable VSX
J202430.0+331759 = IRAS 20225+3308 = NSVS 8503179. There are two faint
X-ray sources 4.5' from each other, and the southern one shows an
obvious variability.

The star was in outburst on 1989-06-30 and 1989-07-06 blue plates and
at quiescence on other 10 DSS images. The animation of 1951 and 1989
POSS plates shows the variability and notable proper motion (about 2"
in 38 years): http://hea.iki.rssi.ru/~denis/DDE36-POSS-Blue-anim.gif

The new variable is:

1RXS J202427.7+331629 (flux=0.0210+/-0.0066 cnts/s HR1=1.00+/-0.33
HR2=0.31+/-0.31)
USNO-B1.0 1232-0517211 (20 24 27.832 +33 16 35.24  B1=19.04 B2=17.43)
2MASS J20242785+3316333 (J=15.283+/-0.047 H=15.042+/-0.09 K=N/A)

Color-combined DSS finder chart:
http://hea.iki.rssi.ru/~denis/J2024+3316-BRIR5x5.jpg (2x zoom).

The INT Photometric H-Alpha Survey has the star at quiescence as IPHAS
J202427.84+331633.1 (20 24 27.84 +33 16 33.1 rmag=20.41+/-0.05) with
no detection in H-alpha and i band.

Proper motion in PPMXL: 20 24 27.854 +33 16 33.43 pmRA=5.0 pmDE=-57.6
B1=19.04 B2=17.43. I note that pmRA may be wrong: from the plate
inspection it should have the negative sign. pmDE looks good. With
0.06"/yr this variable is among Top 30 highest proper motion CVs. If
quiescent M is about 11, then the distance is ~400 pc (M-m=8) and the
tangential velocity - about 110 km/s.

Another remarkable thing about the new variable is that DDE 36 resides
within 36' from V404 Cyg, so it may fall inside the FOV of some
telescopes observing its current outburst!

I have submitted the new variable to AAVSO VSX as DDE 36. It is
awaiting the approval by VSX Admin.

Denis Denisenko
Sternberg Astronomical Institute of Moscow State University