[vsnet-alert 21188] CTCV J1940-4724 outburst and a bonus

[Denis Denisenko]

The neglected dwarf nova in Telescopium CTCV J1940-4724 is going into
outburst on the images from iTelescope.Net T32 in Siding Spring.

CTCV J1940-4724
  20170630.6832  17.065CV  T32
  20170630.6857  17.184CV  T32
  20170701.6072  14.801CV  T32  Outburst!
  20170701.6097  14.774CV  T32  Outburst!

VSX entry: https://www.aavso.org/vsx/index.php?view=detail.top&oid=477956
Range from Siding Spring Survey data: 13.2-17.5 CV
Approximate orbital period: 0.0809 d from spectroscopic observations
covering 0.11 d (less than 1.5 period!)

With a period like that CTCV J1940-4724 must be nothing but a UGSU
dwarf nova. Time-resolved photometry is requested. Recommended
Comparison and Check stars are 135 (V=13.479) and 152 from AAVSO
sequence marked on the color-combined DSS finder chart
http://scan.sai.msu.ru/~denis/J1940-4724-comp_stars.jpg (10'x10' FOV).

Bonus: there's another hot star 15' from CTCV J1940-4724 named
SSS_J194140.2-473502. SSS catalog (Drake et al., 2017, MNRAS) lists it
as a Delta Scuti variable with P=0.142769 d and range 17.7-18.0 CV.
However, it is impossibly hot in the ultraviolet to be the HADS star.
FUV=16.378, NUV=16.714 in GALEX DR5. (FUV-NUV)=-0.34 is too hot even
for CVs, rather typical of sdB stars. Hot subdwarf varying by 0.3m at
P=0.14277 d is even more interesting than the dwarf nova in outburst.

Chart showing the position of both stars:
http://scan.sai.msu.ru/~denis/J1941-4730.jpg

Please take the opportunity to investigate two poorly studied hot
variables in one field!

Denis Denisenko
Sternberg Astronomical Institute of Moscow State University