COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                         Number 974

                                      Konkoly Observatory
                                      Budapest
                                      1975 March 12


             NOVA RS OPHIUCHI AS A SEMIREGULAR VARIABLE

     In the years following its last outburst RS Ophiuchi has been
photoelectrically monitored at the Teramo Observatory and the 
magnitudes measured from 1970 to 1973 are reported in the table. As
comparison star was utilized BD -6deg4660 with the following photometric 
values
     
              V = 9m30 +- 0m.01    B-V = +- 1m.25 +- 0m.23

which were obtained by means of many transfers from several Johnson's
standard stars (Johnson and Harris, 1954)

                     Observations of RS Ophiuchi
                              in V light

Date        J.D.      V    m.e.   Date         J.D.      V    m.e.

1970                              1973
June   3 39741.466  10.68 +-0.01  April  30 41803.578  11.34 +-0.02
July  29 39767.431  10.71      1  May    10 41813.539  11.41      2
1972                               "     29 41832.431  11.09      1
June  17 41486.457  11.18      1   "     31 41834.448  11.08      1
July   3 41502.456  11.13      2  June   26 41860.400  11.56      2
 "     8 41507.374  11.26      5  July    1 41865.454  11.55      3
 "    16 41515.527  11.32      1   "     21 41885.378  11.31      1
 "    18 41517.397  11.31      2  Aug.   20 41915.416  11.62      2
Aug.   4 41534.405  11.52      1  Sept.   3 41929.341  11.23      3
 "    15 41545.413  11.43      3

     The B-V colour showed no great variations and during all the
time covered by the table remained almost constant at a value 
around +1m.2.
     It has been known for a long time that RS Ophiuchi during its
minimum stage undergoes light fluctuations ranging for the most time
from 10.5 to 11.5 but sometimes raises up to 9.7 or fades down to
12.5; these data are based essentially on visual estimates: therefore
no variation law could be detected and the fluctuations were 
classified as "irregular". The figure, where the Teramo observations of
1972 and 1973 are reported, shows the existence of a semiregular 
variation with a range of half a magnitude: in 1973 a 50 days wave is

clearly apparent; in 1972 there is an indication of a longer period
(70 days?). These fluctuations can be safely ascribed to the M type
component which has been recognized to constitute a symbiotic pair
with the hotter companion (Barbon et al., 1969).
     The photoelectric program is still in course and a wider report
on the photometric behaviour of this Nova from the 1967 outburst
onwards will be published elsewhere within a few months.
     Spectrographic observations which would be made in concomitance
with my photometric program in spring and summer 1975 would be 
extremely useful to get a suitable model for this binary system.


                           [FIGURE 1]

              V light curve of RS Ophiuci at minimum.



                                        P. TEMPESTI
                               Osservatorio astronomico di Teramo
                                    64100 Teramo, Italy


References:

Johnson. H.L., Harris, D.L. 1954, Astrophys. J. 120, 196 [BIBCODE 1954ApJ...120..196J ]
Barbon, R., Mammano, A., Rosino, L. 1969, Spectroscopic Observations
            of the Recurrent Nova RS Oph from 1959 to 1968,
            in Non-Periodic Phenomena in Variable Stars, Ed. L. Detre,
            Academic Press, Budapest. [CoKon No. 65]
	    [BIBCODE 1969CoKon..65..257B ]





                        [FROM IBVS 987]

                              ERRATA CORRIGE

     In the IBVS No.974 owing to a misprint the mean error of
the colour of the comparison star of Nova RS Ophiuchi is given
uncorrectly:
     Instead of

                 B - V = + 1m.25 +- 0m.23

must be read

                 B - V = + 1m.25 +- 0m.03




                                              P. TEMPESTI