COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 2832

                                          Konkoly Observatory
                                          Budapest
                                          11 December 1985

                                          HU ISSN 0374 - 0676



       HT CASSIOPEIAE AS AN SU URSAE MAJORIS TYPE DWARF NOVA


  In the existing catalogues (P.N. Kholopov et al., GCVS 4th ed., 1985;
H. Ritter, Garching MPA 106, 1983; R.F. Webbink, Urbana IAP 6, 1984) HT Cas
is listed as one of the very few SS Cygni type dwarf novae (sometimes also
called U Geminorum stars in the narrower sense) with orbital periods shorter
than two hours. Most of the dwarf novae in this period domain are SU Ursae
Majoris variables, in general exhibiting "supermaxima" from time to time,
which can be distinguished from the ordinary maxima by their greater 
brightness and longer duration.
  In order to clarify the nature of HT Cas I checked a sample of about
1000 Sonneberg sky patrol plates taken between 1949.0 and 1985.0 mainly by
P. Ahnert and H. Huth of fields centred at 0h +60deg (65deg), Gamma Cas, and
1h +60deg (65deg).
  The brightness of what now maybe classified as "normal" eruptions of the
star was reported as being only slightly higher than 14.0m (J.S. Glasby,
The Dwarf Novae, p.177, 1970; C. Hoffmeister, Veroff. Sternw. Sonneberg, 1,
p.61, 1947), and a cycle length for these maxima of 30 to 35 days was clearly
visible (Glasby, l.c.). From the very beginning it was therefore obvious
that on our plate material we would be able to detect only "supermaxima"
(if present at all), the threshold of good-quality exposures being 14.2m at
the position of the variable.
  Altogether 905 suitable plates yielded 16 cases when the star was brighter
than or equal to 12.8 pg (system of Bergedorfer Spektraldurchmusterung of
SA 8). These observations belong to eight eruptions. We conclude that in this
way we have discovered "supermaxima" of the star. None of these maxima are,
to the best of my knowledge, identical with findings reported by the AAVSO,
AFOEV, or SUAA. On the other hand, three outbursts brighter than 13.0 vis.
not present in our material have been found by the observers of these organizations.
J. Patterson (Astrophys.J.Suppl., 45, 517, 1981) measured one further
bright maximum accidentally; the outburst of January 1985 (J. Mattei et al.,



IAU Circ., Nos. 4027 and 4037, 1985) is outside    the time interval covered
by the inspected plates.
   The supermaximum of October 1959 lasted L= 9 days at least (visibility
above the plate limit), that of January 1985 about 10 days, but much shorter
eruptions of this kind also seem to occur (L <=3 days: July 1963).
   It should be noted that on many a good plate faint traces at the position
of the star can be perceived, caused by the combined light of HT Cas at or
near normal maximum (14m) and a star 14.6m just to the south of the variable.
These observations were of course ignored.

   The mean cycle length C of the supermaxima can be evaluated in various
ways (W. Wenzel, G.A. Richter, Astron. Nachr., in press, 1986):
i) by Poisson distribution of bright observations independently recorded,
ii) by means of the (known or estimated) mean duration of the outbursts, or
   by averaging the observed outburst interval with (iii) or without (iv)
   taking into account sun and moon gaps.
   Clearly the last method (iv) yields the largest value for C. From the
procedures  i)-iii) follows

      C (supermaxima) =~ 430d . . . 660d

where values near the lower one are more trustworthy.
   A listing of all supermaxima known up to now and some further details
will be given in a forthcoming issue of Mitteil. Verand. Sterne Sonneberg.






                             W. WENZEL
                         Sternwarte Sonneberg
                      Zentralinstitut fur Astrophysik
                      der Akademie der Wissenschaften
                              der DDR