COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 3440  
                    			Konkoly Observatory
                                	Budapest
                                	7 March 1990

	                                HU ISSN 0374 - 0676


       OBSERVATIONS OF THE DWARF NOVA CI GEMINORUM

  Hoffmeister (1943; 1947) described CI Geminorum as novalike 
or possibly of U Geminorum type. He could find only one
eruption on 166 plates of the time interval 1935 Nov. 1 to
1944 Feb. 24. He excluded Mira type because of the "unconspicuous" 
(not red) colour, which was later confirmed by Duerbeck
(1987), who observed the minimum state of the star on the POSS
charts. I checked the region of this variable on 129 additional
plates of the Sonneberg 40/160 cm GC astrograph, taken mainly
by G.A. Richter and G. Hacke in 70 nights of 1962.9 to 1966.7
and 1980.0 to 1989.2. On this material, supplemented by 19
good plates taken at the 17/120 cm astrograph from 1958 to
1966 in 19 nights, three additional eruptions are present:

        1963 Oct. 15   J.D. 243 8318.5    16m5 (2 plates)
        1966 Feb. 23        243 9180.4    16.5
        1986 Dec. 3         244 6768.6    14.5

Unfortunately the duration of these maxima cannot be estimated,
because suitable plates of adjacent dates are not available.
Therefore we do not know whether the eruption of February 1940
observed by Hoffmeister, when the star was brighter than 16.0 mag
for at least 16 days, was an exception or not. Because the old
paper of Hoffmeister (1947) might no longer be available in
the reader's library, Fig. 1 shows a drawing of his 
observations.
  The minimum brightness was estimated by Duerbeck on the POSS
charts as B = 18.5 mag two plates taken by Borngen and Ludwig at
the 134 cm Schmidt telescope of Tautenburg Observatory yield
B ~ 19.0 mag. An amplitude of CI Gem of 4.2 mag may therefore be
assumed.
  If the long eruption observed by Hoffmeister was a supermaximum 
of an SU Ursae Maioris variable, then the orbital period
should be around P = 1.5 h and, according to Richter and Brauer
(1989, equation 2a), the mean cycle length C1 = 111 d.


                         [FIGURE 1]


  Another extreme assumption would be that the three maxima
found on GC plates were "normal" ones, say of mean duration
Ln = 4 d +/- 2 d. The statistics (see Wenzel and Richter 1986)
then leads to a mean cycle length of

C2 = Ln x number of checked nights/number of observ. eruptions = 119 d +/- 59 d

which is in good agreement with C1.
  We conclude that CI Gem might be an SU Ursae Maioris type
dwarf nova with a cycle length of the order of 100 days. To
investigate the orbital period and the possible presence of
superhumps would be of interest.


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

References:

Duerbeck, H.W., 1987, Space Sci. Rev. 45, no. 1-2, p.58 [BIBCODE 1987SSRv...45....1D ]
Hoffmeister; C., 1943, Astron. Nachr. 274, 37 [BIBCODE 1943AN....274...36H ]
Hoffmeister, C., 1947, Veroff. Sternwarte Sonneberg 1, 107 [BIBCODE 1947VeSon...1...43A ]
Richter, G.A., Brauer, H.-J., 1989, Astron. Nachr. 310, 413 [BIBCODE 1989AN....310..413R ]
Wenzel, W., Richter, G.A., 1986, Astron. Nachr. 307, 209 [BIBCODE 1986AN....307..209W ]