[vsnet-alert 22422] ASASSN-18su: likely dwarf nova outburst (10.0 mag) in Hydra (ATel #11968)

[Patrick Schmeer pasc1312-aavso@yahoo.de via vsnet-alert]

ASASSN-18su  (UGWZ:)

"ASAS-SN Discovery of a Very Bright (g~10.1) Transient ASASSN-18su"
http://www.astronomerstelegram.org/?read=11968

12:57:51.258  -28:30:16.82  2018-08-17.71  10.1
Discovered in images obtained on 2018-08-17.71 UT at g~10.1,
also detected at V~10.0 on 2018-08-17.97 UT; not detected
(V>18.0) in subtracted images taken on 2018-08-14.98 UT and
before. 

ASASSN-18su 20180814.985 <180V ASN
ASASSN-18su 20180817.71   101g ASN
ASASSN-18su 20180817.974  100V ASN

"No previous outbursts are detected at the position of
ASASSN-18su since ASAS-SN started observing this location
in December 2013."

Complete ASAS-SN Sky Patrol V-band light curve:
https://asas-sn.osu.edu/light_curves/c2c8b600-d005-4cf0-b2f9-6b29824f5af2

The likely progenitor is PSO J125751.372-283015.290
(RA 12 57 51.347, DEC -28 30 15.32; g= 17.97, r= 18.08 mag).

Gaia DR2 data:
G= 17.90 mag; parallax 5.5218 ± 0.1578 mas (distance
180 ± 5 pc); pmRA= -144.650, pmDE= -8.789 mas/yr.

Other designations:
WISE J125751.42-283014.9, GALEX J125751.4-283015,
1WGA J1257.8-2830, ...

Probably a large amplitude (8 mag) outburst of a WZ Sge-type
dwarf nova.

Spectroscopy, time-resolved photometry, and precise
astrometry are urgently required.

Clear skies,
Patrick