COMMISSIONS 27 AND 42 OF THE IAU
            INFORMATION BULLETIN ON VARIABLE STARS
                        Number 3921

                                                 Konkoly Observatory
                                                 Budapest
                                                 9 August 1993

                                                 HU ISSN 0374 - 0676


               OBSERVATIONS OF ERUPTIONS OF THE TRUE
                           AK CANCRI



  Since its discovery by Morgenroth (1933) on Sonneberg plates AK Cnc = 77.1933
has remained a rather mysterious object. In the course of time the following, partly
contradictory, observational results have been reported:

-   Short period pulsational variability probable (Morgenroth, 1933),
-   U Geminorum type classification without particulars (Tsesevich, 1967),
-   visually never seen, fainter than ~ 13.6m (AFOEV, 1987, ff),
-   always visible near 13.6m(AAVSO, 1988, ff),
-   "blue star" on POSS (Vogt and Bateson, 1981; 1982),
-   "no certain emissions" and no late-type bands showing (Williams, 1983),
-   "spectral features and or red continuum indicative of a late-type secondary
    evident" (Szkody and Howell, 1991),
-   finding charts of Khruzina and Shugarov (1991) and Vogt and Bateson
    (1981; 1982) (see also Bateson and Morel, 1983) denote different objects.

 I investigated the location of the star on 95 exposures of the Sonneberg 140/700
 mm Triplet astrograph mainly taken in the years 1928 to 1934 and sporadically in
 the fifties and sixties - the discovery plates among them - and came to the following
 conclusions:

  - The finding charts of Bateson and collaborators mark the correct star,
  - the variable is indeed a cataclysmic dwarf nova,
  - the range of variability in the blue range is 12.8m to ~ 19.0m (POSS).

5 eruptions are visible on our plates:

1930 Dec.       23   13.6m pg
1931 March       8   12.8
                13   13.5
                15   13.5:
1931 Dec.       10   13.4
1932 Dec.        4   12.8
1967 Feb.       14   13.4
  
According to the statistical considerations of Wenzel and Richter (1986) the
mean cycle length should be about 100 days. My brightness scale has been linked
to the photometric sequence of the nearby M67 (Racine, 1971). Considering their
scanty nature, the observations of the AFOEV are in agreement with ours.

  This work has been supported by funds of the German Bundesministerium fur
Forschung und Technologie under contract no. 05-2S052A.


                            W. WENZEL
                            Sternwarte
                            D 96515 Sonneberg
                            Germany



References:

AAVSO, 1988, Circular no. 210 (and issues following)
AFOEV, 1987, Bulletin 40, p. 23 (and issues following)
Bateson, F. M., and Morel, M.,1983, Charts for Southern Variables, series no. 16
Khruzina, T. S., and Shugarov, C. Y., 1991, Atlas kataklizmicheskikh peremennykh
  (zvezdy tipa U Geminorum), chast' 1
Morgenroth, O., 1933, Astron. Nachr., 249, 383 [BIBCODE 1933AN....249..383M ]
Racine, R., 1971, Astrophys. J., 168, 393 [BIBCODE 1971ApJ...168..393R ]
Szkody, P., and Howell, S. B., 1991, Bull. American Astron. Soc., 23, 943 [BIBCODE 1991BAAS...23..943S ]
Tsesevich, V. P., 1967, 2. Suppl. to 2. Edit. of Gen. Catalogue of Variable Stars 
Vogt, N., and Bateson, F. M., 1981, ESO Sci. Prepr., no. 161
Vogt, N., and Bateson, F. M., 1982, Astron. Astrophys. Suppl., 48, 383 [BIBCODE 1982A&AS...48..383V ]
Wenzel, W., and Richter, G. A., 1986, Astron. Nachr., 307, 209 [BIBCODE 1986AN....307..209W ]
Williams, G., 1983, Astrophys. J. Suppl. Ser., 53, 523 [BIBCODE 1983ApJS...53..523W ]