COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1091 Konkoly Observatory Budapest 1976 February 2 VZ Dor IS VW Dor In the course of an extensive photoelectric observing programme of southern cepheids, I have observed a star indicated as VZ Dor at the chart position given by Schoffel (1). The star is fainter than expected, varying from 11.2 to 12.1 in V, and does not satisfy Schoffel's period of 1.3338 days. According to GCVS (2) an RR Lyrae of 12th magnitude, VW Dor, is 2' north of VZ Dor. The star marked VZ Dor on Schoffel's chart occupies the same position as VW Dor in the Hodge-Wright Atlas (3). This atlas does not mention VZ Dor. The brighter star at the expected relative position for VZ Dor was also observed and found to be non-variable (V=10.32, B-V=0.53). Thus VW Dor and VZ Dor are apparently the same star. The reciprocals of the periods of VZ Dor and VW Dor (0.7497 and 1.7527) differ by nearly an integer. Wrong periods are often found for variables which are only observed once a night. See e.g. Dean (4). Schoffel gives epochs of maxima; these satisfy both his period and the period of 0.57056 days given by McKibben Nail (5) for VW Dor (HV12250). (Table 2). The data observed at SAAO (Table 1) satisfies only McKibben Nail's period (Figure). This occurs since several observations were made twice a night, in order to avoid ambiguities in the period. Thus the period of VZ Dor alias VW Dor is 0.57056 days. J.F. DEAN South African Astronomical Observatory,South Africa References: 1. Schoffel, E., IBVS No. 118, 1965 2. General Catalogue of Variable Stars, B.V. Kukarkin et al, Moscow 1969 3. The Large Magellanic Cloud, P.W. Hodge and F.W. Wright, SAO Publ. 1966 [BIBCODE 1967SAOP.4699....1H ] 4. Dean, J.F. IBVS No. 902, 1974 5. McKibben Nail, V., H.B.No. 921, 1952 [BIBCODE 1952BHarO.921....1M ] [FIGURE 1] [FIGURE 2] Light curve of VW Dor. SAAO data. Phase relative to 2440000. Table 1: Observations of VW Dor at SAAO ---------------------------------------------------- H.J.D. phi_1.33 phi_0.57 V B-V V-I ---------------------------------------------------- 2442465.385 .39 .99 11.21 .19 .36 465.455 .44 .12 11.49 .29 .47 473.362 .37 .97 11.22 .20 .35 474.339 .10 .69 12.11 .49 .74 708.471 .64 .04 11.32 .22 .39 708.575 .72 .22 11.71 .39 712.487 .65 .08 11.41 .26 712.592 .73 .26 11.80 .38 .58 ---------------------------------------------------- Table 2: Schoffel's Epochs of Maxima ---------------------------------------------------- EPOCH PHASE RELATIVE TO FIRST MAXIMUM P = 1.3338 P = 0.57056 ---------------------------------------------------- 2438379.453 0 0 707.550 .99 .04 739.506 .95 .05 798.279 .01 .06 810.272 0 .08 ---------------------------------------------------