COMMISSION 27 OF THE I.A.U.
         INFORMATION BULLETIN ON VARIABLE STARS
                      NUMBER 152

                                          Konkoly Observatory
                                          Budapest
                                          26 August 1966

              NOTE ON THE VARIABLE RU CAM

	In connection with the reports that the light amplitude of RU
Cam became very small during the seasons of 1965/66 (Wamsteker 1966)
it may be of interest to examine the behaviour of the variable in
earlier epochs. There are two sets of photoelectric observations of
the star, reduced to the B,V system, obtained by Eggen, Gascoigne
and Burr (1957) (between JD 2432821 and JD 2433028) and by Mitchell,
Iriarte, Steinmetz and Johnson (1964) (between JD 2437014 and
JD 2437053). V and B-V observations of this two sets against phase =
P^-1 (JD -2430000) with P = 22.134d (from the GCVS 1958) are plotted on 
figure 1 (crosses: obs. of Eggen et al., filled circles: obs. of Mitchell
et al.). The data show that between the two sets of observations there is

                        [FIGURE 1]
                        [FIGURE 2]
			[Figs. 1-2]

	a/ a phase shift;
	b/ a change of the shape of light and colour curves;
	c/ a change of amplitude of V and B-V.
	In our catalogue of photoelectric observations of cepheids
(Nikolov 1965) we have made an effort to accord the two series of
observations, assuming for the period P = 22.1711d. V and B-V against
phase, computed with this period, are plotted on figure 2.
	If this period is valid for the two sets of observation, one may
conclude that there is
	a/ a significant decrease in amplitude of B-V from 0.48m by
	   Eggen et al. to 0.30m by Mitchell et al.
	b/ a decrease of light amplitude after JD 2437045 (the three
	   observations noted by open circles).


Astronomical Observatory
University of Sofia					N. S. NIKOLOV


References
Eggen, O.J.; Gascoigne, S.C.B.; Burr, E.F., 1957. M.N. 117, 406. [BIBCODE 1957MNRAS.117..406E ]
Mitchell, R. I.; Iriarte, B.; Steinmetz, D.; Johnson, H. L., 1964 Bull.
   Obs. Tonantzintla y Tacubaya, 3, 153. [BIBCODE 1964BOTT....3..153M ]
Nikolov, N. S., 1965, Dissertation, Astr. Inst. Sternberg, Moscow.
Wamsteker, W., 1966. IBVS 128.





		CYCLIC AMPLITUDE VARIATIONS OF RU CAM

	Nikolov's preceding note and Smak's report in IBVS No 135
are based on different material. Herewith I take into consideration all
available photoelectric observations (Ref. 1-11).
	The phase shifts between different sets of observations of RU
Cam can be seen from the O-C diagram in Fig. 1. The observed photoelectric
V magnitudes of maximum and minimum light are plotted against epoch
number in Fig. 2. Both maxima and minima show cyclic variations, but
with opposite phase. The amplitude variations are primarily due to 
differences in the brightness of the minima. The broken curves in Fig. 2 
are tentative representations of the observational data with a cycle
of 84 P~5.1 years. This cycle-length is corroborated by visual observations
of amateur observers of the Danish "Astronomisk Selskab", who found very
faint minima around the epochs E = -148 and E = +20 respectively
(Edelberg, M. 1932, AN 246, 176; Nielsen, A. and Sjogren, T. 1943, 
AN 273, 270). The cycles are of very different amplitude and shape.
Secondary cycles are very common in RR Lyrae variables, and as we now
see, they may be present also in Population II Cepheids.

                        [FIGURE 3]
                        [FIGURE 4]
			[Figs. 1-2]

	If the above interpretation is correct, we may expect in the 
next months, or at latest next year, an increase of the amplitude. At
present (1966 August) the amplitude in V is only 0.08m (Ref. 11).


	Konkoly Observatory, Budapest

						L. DETRE

	References to photoelectric observations:

	1./ Eggen, O. J., Gascoigne, S. C. B. and Burr, E. J. 1957. MN
	   117, 406 [BIBCODE 1957MNRAS.117..406E ]
	2./ Lenouvel, F. et Jehoulet, D. 1953. Ann. d'Aph. 16, 139 [BIBCODE 1953AnAp...16..139L ]
	3./ Lenouvel, F. et Daguillon, J. 1954. JO 37, 137 [BIBCODE 1954JO.....37..137L ]
	4./ Lenouvel, F. et Fiogere, Cl. 1957. JO 40, 37 [BIBCODE 1957JO.....40...37L ]
	5./ Delsemme, A. H. et Delsemme-Jehoulet, D. 1958. Mem.
	   Soc. Roy. Sci. Liege, 4-e serie 20, 328.
	6./ Mitchell, R. I., Iriarte, B., Steinmetz, D., Johnson, H. L.
	   1964. Tonantzintla y Tacubaya Bol. Num. 24. [BIBCODE 1964BOTT....3..153M ]
	7./ Michalowska Smak, A., Smak, I. 1965. Acta Astr. 15. 333. [BIBCODE 1965AcA....15..333M ]
	8./ Wamsteker, W. 1966. IBVS No 128.
	9./ Smak, I. 1966 IBVS No 135.
       10./ Demers, S., Fernie, J. D. 1966. ApJ 144, 440. [BIBCODE 1966ApJ...144..440D ]
       11./ Detre, L., Szeidl, B. 1966. unp.