COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                        Number 2714

                                            Konkoly Observatory
                                            Budapest
                                            25 April 1985

                                            HU ISSN 0374 - 0676


                ON THE CYCLE-LENGTH OF RZ LEONIS


  According to Mattei (1985) and Christiani et al. (1985) RZ Leo, which
has undergone a nova-like outburst in 1918, erupted again in the last days
of 1984; its spectral behaviour suggests a membership of the WZ Sagittae 
subclass of dwarf novae. If this classification is accurate, then the object is
the dwarf nova with the largest observed interval of 66 years between outbursts.
For understanding the physics of the WZ Sagittae phenomenon the true cycle-
length of RZ Leo is of great interest. To find an estimate, altogether 1461
plates of the Sonneberg sky patrol, taken by H. Huth and predecessors, of the
fields alpha= 11h, delta= -4deg, 0deg, and +10deg and alpha= 12h, delta= 
-4deg, 0deg, and +10deg were
inspected for eruptions. The time covered is from 1928 to 1984, with only
1 plate in 1928 and 3 plates in 1938. The limiting magnitudes of the plates
are about 12mag to 14mag. But, being in the vicinity of a relatively bright star,
RZ Leo could be followed up only to the brightness of 13m.
  In this time interval no certain outburst could be observed. On some plates
there are impressions at the very plate limit, their reality, however, cannot
be guaranteed. The dates of the plates with a suspected eruption are as follows:

Date             JD            Magnitude   Remarks
1934 Feb.   14   2427483.541   12??        1
1935 Mar.   25   2427887.345   12::
1940 Apr.    6   2429726.432   13::?       2
1950 Mar.   20   2433361.487   13::?       3
1952 Apr.   16   2434119.426   13??        1
     Apr.   17   2434120.417   13:?        4
1959 Feb.    5   2436605.556   13          5
1967 Feb.    7   2439529.611   13.5        6
1976 Mar.    1   2442839.528  [13
     Mar.    2   2442840.475   13??        1
                      40.475   13:         7
Remarks
1 very questionable
2 April 7 invisible  [13mag    
3 March 23 invisible [13mag
4 April 18 and 19 invisible [13mag       



Remarks

5 Probably not real (not exactly at the position of RZ Leo)
6 Probably plate fault
7 On two plates of February 29 invisible [12mag and on two plates of March 3
 invisible [13mag

  As can be seen from the table the only observations likely to be real are
those from 1935 March 25, 1952 Apr. 17, and 1976 March 2. Provided those 3
dates are positive observations of RZ Leo, then from 1928 to 1984 there
occurred 3 eruptions. Taking into account that no plates exist from the months
June to September and making the assumption that half of the eruptions could
not be detected on account of bad weather or moonlight (so, for example, the
eruption of 1984 could not be followed up on Sonneberg plates), one may
conclude that the cycle-length of RZ Leo could be as short as 6 years!
  To sum up, it can be said that the cycle-length of RZ Leo must be somewhere
between 6 and 66 years. The true value of the cycle-length will probably be
near the smaller limit because of the relatively small brightness amplitude
of about 6 mag.
  The table given above is to prompt observers having access to plate 
collections to confirm the suspected outbursts and search for further ones.




                         G.A. RICHTER

                         Zentralinstitut fur Astrophysik
                         der Akademie der Wissenschaften
                         der DDR
                         DDR-6400 Sonneberg, Sternwarte





References:

Mattei, J. (1985) IAU Circ. No. 4026 [BIBCODE 1985IAUC.4026....1M ]
Christiani, S., Duerbeck, H.W., and Seitter, W.C. (1985) IAU Circ. No. 4027 [BIBCODE 1985IAUC.4027....2C ]