[vsnet-chat 630] early SU UMa research (VSOLJ)

[Taichi Kato <tkato>]

  The following artcile (incomplete) was probably originally intended to
be published in the VSOLJ Bulletin for world-wide request for observing
CVs.  It might be interesting to some readers who have concerns with the
history of amateur varibale star research of this field.

  The text is dated 1988 June. 17.

Regards,
Taichi Kato
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     We have been observing the gross behavior of cataclysmic variables
and now organized an amateur association for the study of them.  We
have been appreciating your papers on cataclysmic binaries and much of
our observational program is based on them.  We are especially interested
in ultrashort orbital period CV's (i.e. SU UMa stars).  We have recently
started photographic and visual time-resolved observation of brightness
during supermaxima of well-known SU UMa stars and long outbursts of poorly
studied dwarf novae.  Limit of detection of periodic variation is about
0.1 mag.  Japanese sky condition is too poor for conventional photoelectric
high-speed photometry.  So we are planning CCD time-resolved photometry
using 0.4m reflector which has limiting magnitude of 16 or more with the
integration time less than 1 minute, which will be enough for the detection
of superhumps and eclipses of bright novalikes.  We include our recent
results (photographic/visual) on SU UMa variables.  We have detected
superhumps of well-known star T Leo, TY Psc, and SU UMa candidates such
as AQ Eri and CY UMa.  For these variables, as far as we know, time span
of observation at one place is not very long and the possibility of one-day
aliases can not always be excluded.  We would be very happy if our obser-
vation at different longitude would be of any use.
     Beside this, we have been making long-term light curves of many
dwarf novae down to 14th mag. at maximum in order to search more SU UMa
candidates.
  Our criteria are:
 1) rapid decline of brightness after the light maxima, exceeding 1 mag.
     per day.
 2) if long maxima are observed, the light declines regularly at the
     rate of 0.1-0.2 mag. per day.  Long maxima of normal SS Cyg type
     (longer than the period gap) does not usually show such behavior.

  Let us list our SU UMa candidates and other result on some variables.

  VW Vul is listed as an ultrashort orbital period CV.  During a long
maximum in the summer of 1987, our 6hr photographic photometry can not
detect variation larger than 0.1 mag.  Superhump amplitude may be smaller
than our limit of detection or the star may not be SU UMa subtype.
Another long outburst was caught in winter.  Such short interval of
supermaxima is not typical.
  During the recent outburst of U Sco, we possibly detected short-term
variation with the period about 50min, amplitude is about 0.5mag at the
mean magnitude of 12.6mag.  We are not completely sure because the quality
of the photographs are poor on account of light polution and guiding error.
It may be sporadic variation during nova outburst, but there may be some
hope that the period is related to the orbital motion assuming the secondary
is a helium white dwarf (as in GP Com etc.).  Please tell us your opinion
about this system.
  V394 CrA had no light variation at magnitude 11.0.
  About V795 Cyg, there has been little amount of information of its light
behavior.  During the outburst in 1987, no variation was detected.
Another long outburst was observed in 1988, both had characteristics of
long maxima of SS Cyg type.
  FO And is suspected as SU UMa by many authors.  Unfortunately the moon
prevented the long outburst in early 1988.
  We observed two short outbursts of DH Aql which satisfied criterion 2).
We suspect the star to be an SU UMa subtype.
  No major outbursts of KX Aql has been caught.  But our records show
bright (11.5v) and short faint outbursts.  It is possible that the star
belongs SU UMa.
  Some outbursts of FS Aur has been caught, but none of them could be
identified as supermaxima.
  TT Boo satisfies SU UMa criteria, but possible supermaxima in 1987 and
1988 were prevented by poor weather!
  In our record, one maximum of KU Cas satisfies SU UMa criteria.  Short
normal outbursts are sometimes seen.
  Recent DO Dra showed abrupt decline following the outburst, which seems
more characteristic of SU UMa.
  AQ Eri showed superhump period of 97min.  Details will be published in
the 'Variable Star Bulletin'.
  AH Eri shows frequent faint outbursts, but

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