[vsnet-outburst 22295] ASASSN-18ey: emergence of superhumps

[Taichi Kato]

ASASSN-18ey: emergence of superhumps

   We have been following this object since the discovery,
and the (most likely) superhump signal finally emerged.
The current period is 0.6987(4) d (from O-C analysis,
a PDM analysis gave a slightly longer period).
This variation have a mean amplitude of 0.3 mag, which
is unexpected for an X-ray transient since the reprocessed
light is expected to overwhelm the accretion luminosity
in the outer part of the disk.  This variation became
prominent around on June 4.  This variation is the same
as the one reported in ATEL 11756.
The signal could be traced back to May 21 (with a small
ampliude).  An analysis of the earlier part of the outburst
yielded a period of 0.69744(4) d.  If the current variation
is indeed of superhumps, this period may be the orbital one.
Further observation will clarify the more accurate period
and may enable identification of the true orbital period.

   The object took about 90 d to develop (likely) superhumps.
Around this time, the system slightly brightened from
the declining trend.  This delay of superhump appearance
is similar to about 100 d in V518 Per (GRO J0422+32).
http://adsabs.harvard.edu/abs/1995PASJ...47...31K
The appearance of (likely superhumps) indeed agrees with
the X-ray minimum. cf.
https://swift.gsfc.nasa.gov/results/transients/weak/MAXIJ1820p070/
There is some suggestion from the theoretical side:
http://adsabs.harvard.edu/abs/1994ApJ...435..748I

Contributed observers (in our observer's code):

         (scatter) (N obs)
 RIT   CV  0.046 23144
 HaC    V  0.066 15037
 HaC   CV  0.070 12873
 BSM   CV  0.034 10985
 LCO    V  0.070 4990
 Trt   CV  0.064 4014
 Ioh    V  0.052 3813
 Van   CV  0.032 3764
 Van    C  0.052 3550
 Kis    V  0.056 3471
 RIT    C  0.063 2452
 DPV    C  0.058 2260
 LCO   CV  0.068 2185
 COO   CV  0.027 1495
 DPV    V  0.089 1407
 deM    C  0.068 1108
 HaC    I  0.088  859
 Kis    C  0.056  497
 Van    V  0.025  466
 Ioh    C  0.042   78