[vsnet-chat 433] old note on GD 552

[Taichi Kato <tkato>]

  The following artcile was intended for publication in VSOLJ Variable Star
Bulletin -- not appeared yet -- from a floppy disk dated 1989 July 30.

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Light variation of cataclysmic binary GD 552

                            Taichi Kato (Kyoto), Makoto Iida (Nagano)

Abstract: Cataclysmic binary GD 552 with an orbital period of 1.5 hours were
monitored visually from 1986 through 1988.  The star stayed between 15.5 and
16.5 most of the time.  Six small flares reaching 14.0 - 15.0 were detected.
The limits of variation were 14.0 and 16.8.  The amplitude and the light
curve more resembles a nova-like rather than an usual dwarf nova.

     GD 552 was discovered as a possible white dwarf by Giclas et al.(1970).
Stover (1985) obatained time-resolved spectra and found 1.5 hour modulation
in the profile of Balmer emission.  Short-term irregular variation of
brightness up to 0.25 magnitude was also discovered.  The star was therefore
assumed to be a cataclysmic binary with an orbital period below the period
gap.  Because no long-term variation of this star has been published, we
tried to catch possible outbursts.
     Observations were performed visually using the chart prepared by
M.Huruhata (Fig.1).  The overall light curve is given in Fig.2.  Limiting
magnitude was almost between 12.0 and 13.0 in 1986 and no britenings were
seen.  The star was observed at minimum in 1987, mostly staying between 15.5
and 16.5, with minor britenings.  Similar behavior was seen in 1988.  The
extreme values of magnitudes were 14.0 and 16.8.  Occasions brighter than
or equal to mv=15.0 are tabulated in Table 1.  No britenings resembling
superoutbursts, which are often seen in cataclysmic binaries with orbital
periods below the period gap, were detected.
     As is evident from the light curve and the table, observed brightenings
have smaller amplitude than normal dwarf novae and lasting only an order of
a day.  Such short, small-amplitude outbursts are more characteristically
seen in intermediate polars or DQ Her stars (Schwarz et al. 1988; Hellier
et al. 1989; Angelini abd Verbunt 1989).  From the observations, the star
is more likely to be classified as an nova-like rather than a true dwarf
nova.  If this classification is true, it is the first case of a nova-like
with the orbital period below the gap except quiescent novae.  Of course,
large amplitude outbursts may have been missed or did not occur in the
interval we observed.  Further observations and examination of plate
materials are encouraged.

References:
Angelini, L. and Verbunt, F., 1989, Mon. Not. R. astr. Soc. 238, 697.
Giclas, H.L., Burnham,Jr.,R., and Thomas,N.G., 1970, Lowell Obs. Bull.
       No. 153, (Vol.7, No.16, p.183).
Hellier,C., Mason, K.O., Smale, A.P., Corbet, R.H.D., O'Donoghue, D.,
       Barrett, P.E., and Warner,B., 1989, Mon. Not. R. astr. Soc. 237,1107.
Schwarz, H.E., van Amerongen, S.F., Heemskerk, M.H.M., and van Paradijs, J.,
       1988, Astr. Astrophys., 202, L16.
Stover,R.J., 1985, "Cataclysmic Variables and Low-mass X-ray Binaries"
       (Reidel), p.379.

Fig.1 Chart of GD 552.  Visual magnitudes are given.

Fig.2 Light curve of GD 552 by the members of VSOLJ.  "v" represents an upper
       limit.

Table 1.  Britenings of GD 552

   JD     magnitude
2447026   14.0
  47029   14.6
  47079   14.6
  47118   15.0
  47153   15.0
  47364   14.8

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