COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1388 Konkoly Observatory Budapest 1978 February 13 THE BEAT PERIOD OF CY AQUARII In order to clear up the puzzling problem of the beat phenomenon of the RRs variable CY Aqr (cf. papers of Elst (1972), Fitch (1973), Geyer and Hoffmann (1975), Percy (1975)) we organized a campaign of observation from 17 to 27 August 1976. More than 4000 visual estimates were performed by a team of seven observers using 8 inch-reflectors (A. Figer, J.F. Le Borgne, A. Marot, Ph. Ralincourt, C. Romoli, A. Royer, G. Troispoux). Table 1 lists the 40 means of the times of the maxima observed by several observers. The number n of observers is given in column 2. The O-C values in the third column refer to the G.C.V.S. (1976) ephemeris, i.e.: Max = J.D.hel. 2441959.4018 + 0.061038354d E We find a standard deviation of the 191 individual determinations between 0.0012 and 0.0026 day, varying with the concerned observer. Thus a weighting by 1/sigma^2 has been applied in the calculation of the mean times. The final standard deviation of each mean time of maximum is given in the last column. Using a least squares procedure we find a solution explaining the observations, the beat period being:(3.575 +- 0.025)P_0 (P_0:fundamental period of light variations of CY Aqr). The resulting ratio P_1/P_0 of the first overtone to the fundamental would be 0.720 or 0.781. An ephemeris for the beat phenomenon is derived: Max (O-C) = J.D.hel. 2443013.298 + 0.2182d E +-.025 +-.0015 The mean curve of Figure 1 shows the variation of the O-C with phase of the beat period. Each dot represents a mean of several values taken from Table 1. A close inspection of the photoelectric series by Zissell (1968) or Geyer and Hoffmann (1975) does not allow the rejection Table 1 Maxima of CY Aquarii J.D. hel. n O - C sigma J.D. hel. n O - C sigma 2400000+ 2400000+ 43008.4110 5 +.0041 .0007 43012.4971 6 +.0006 .0007 .4742 6 +.0062 .0007 .5573 5 -.0003 .0007 .5308 6 +.0018 .0007 .6185 3 -.0001 .0008 .5915 6 +.0014 .0006 43014.5121 7 +.0013 .0006 43009.3870 4 +.0034 .0008 .5732 7 +.0014 .0006 .4461 4 +.0015 .0008 .6326 6 -.0003 .0006 .5065 3 +.0009 .0011 43015.4880 5 +.0006 .0006 .5679 4 +.0012 .0008 43016.4644 3 +.0004 .0009 .6309 4 +.0032 .0008 .5256 4 +.0006 .0007 43010.3616 5 +.0014 .0007 .5906 2 +.0045 .0011 .4233 5 +.0021 .0007 43017.3802 5 +.0006 .0007 .4838 4 +.0015 .0008 .4416 7 +.0010 .0006 .5440 4 +.0007 .0007 .5012 6 -.0005 .0006 .6047 4 +.0004 .0007 .5618 6 -.0009 .0007 43011.3971 5 -.0007 .0007 .6243 4 +.0006 .0007 .4578 5 -.0011 .0007 43018.3583 4 +.0021 .0007 .5208 5 +.0009 .0007 .4184 2 +.0012 .0009 .5832 5 +.0023 .0007 .4788 4 +.0005 .0007 .6412 7 -.0008 .0006 .5420 4 +.0027 .0007 43012.4361 6 +.0006 .0006 .6004 4 +.0000 .0007 of the proposed 0.218 day beat period. [FIGURE 1] Fig. 1 - Variation of the O-C with phase of the beat period. A. FIGER GEOS 12 rue Bezout F-75014 Paris References: Elst, E.W.,1972, Astron. Astrophys. 17, 148 [BIBCODE 1972A&A....17..148E ] Fitch, W.S., 1973, Astron. Astrophys. 27, 161 [BIBCODE 1973A&A....27..161F ] Geyer, E.H., Hoffmann, M., 1975, Astron.Astrophys.Suppl. 21, 177. [BIBCODE 1975A&AS...21..177G ] Kukarkin et al., Third Supplement to the Third Edition of the General Catalogue of Variable Stars, Moscow, 1976 Percy, J.R., 1975, Astron. Astrophys. 43, 469 [BIBCODE 1975A&A....43..469P ] Zissell, R., 1968, Astron.J. 73, 696 [BIBCODE 1968AJ.....73..696Z ]