[vsnet-alert 19289] Re: ASASSN-15sz

[Denis Denisenko]

This very bright CV candidate is within 1' of two suspected variables in Simbad:

38" from BV 1025 which is close to 2MASS J03553795-8226239
61" from NSV 1440 which was suspected to be 2MASS J03554166-8225318

Obviously all three objects are the same, and both 2MASS stars are
unrelated. NSV catalogue lists BV 1025 with a range of 12.6 <15.0.
Both red stars suspected to be NSV 1440 do not vary significantly
(checked in ASAS-3 photometry).

ASASSN-15sz is identical to the blue star which is also an 18-mag UV source:

USNO-B1.0 0075-0013182 (03 55 17.80 -82 26 11.8  B1=N/A R1=19.10
B2=18.48 R2=19.09 I=18.21)
GALEX J035517.7-822612 (FUV=18.29+/-0.08 NUV=18.28+/-0.06)

There were two past outbursts in ASAS-3 data. See the light curve of
ASAS 035521-8226.3:
http://www.astrouw.edu.pl/cgi-asas/asas_variable/035521-8226.3,asas3,0,0,500,0,0

October 2003 outburst:

HJD     ASAS3 Mag
--------------------
2452929.74003 13.544
2452929.77583 13.476
2452931.78030 13.726
2452932.79381 13.970
--------------------

October-November 2005 outburst with two possible rebrightenings:

HJD     ASAS3 Mag
--------------------
2453669.79731 13.492
2453670.75593 13.190
2453671.69635 13.123
2453672.77885 13.414
2453673.61843 13.545
2453673.76127 13.573
2453675.68436 13.617
2453675.76571 13.650
2453680.77555 29.999
2453699.71425 29.999
2453702.70102 14.375
2453705.69106 29.999
[10 non-detections skipped]
2453736.71319 29.999
2453739.59869 14.619
--------------------

Thus, ASASSN-15sz is a recovery of the old variable BV 1025 = NSV 1440
which was incorrectly identified with the nearby red star. Actually
this is a dwarf nova, likely SU UMa type with the possible
rebrightenings after superoutbursts and 2-year recurrence cycle.

Denis Denisenko
Sternberg Astronomical Institute of Moscow State University (SAI MSU)