COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2634


                                    Konkoly Observatory
                                    Budapest
                                    3 December 1984

                                    HU ISSN 0374 - 0676


                 AM Cas - A DWARF NOVA
             WITH A VERY SHORT CYCLE-LENGTH


   This object was discovered by Hoffmeister in 1928.
Richter (1961, Veroff. Sternw. Sonneberg 4, 431) was the first who thought
this object to be related to CN Ori, which is a well-know dwarf nova. On
account of this supposal several slit spectrograms (image converter tube with
UAGS) were gained in November 1983 during a full brightness cycle length at
the 2 meter telescope of Karl Schwarzschild Observatory Tautenburg. They fully
confirm that AM Cas is a dwarf nova belonging to the subclass Z Camelopardalis, 
with a very short cycle - length of only 9 days.
   The minimum brightness is characterized by hydrogen emission lines
(H_alpha line width about 3nm), superposed onto a blue continuum. The weak
excitation is remarkable in the spectra:  apart from the hydrogen lines only
traces of He I emissions can be established.
   During the brightness eruption a nearly featureless blue continuum can
be seen, where very weak H_alpha emissions are always present, but H_beta is 
practically missing, eventually with a possible   broad absorption.
   A more comprehensive description of the spectral behaviour a light
cycle will be given elsewhere.





                                  P. NOTNI
                            Sternwarte Babelsberg
    
                               G.A. RICHTER
                            Sternwarte Sonneberg

                        Zentralinstitut fur Astrophysik
                        der Akademie der Wissenschaften
                        der DDR