COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3505 Konkoly Observatory Budapest 16 August 1990 HU ISSN 0374 - 0676 THE POSITION OF RZ NORMAE RZ Nor was first studied by Gaposchkin (1952) and it is a typical R Coronae Borealis type variable star (i.e., an RCB star). Accurate positions of it as well as other southern RCB stars were published by Villada (1980); identification charts may be found elsewhere (Milone, 1990). Unfortunately, the position as given by Villada is incorrect (I assume responsibility for the misidentification). The reason is that we had originally identified RZ Nor correctly, but an erroneous identification was passed on to us afterwards which was accepted as correct (star 1 in Fig. 1); it is actually the position of star 1 which was published by Villada. Two plates were obtained at Córdoba with the 33-cm "Carte du Ciel" astrograph (plate scale 1 mm = 1') in 1975, June 8 (# 75016), and 1988, August 8 (# 88004) and were used here for determining the position of RZ Nor. The plates were measured with a manual Repsold machine in direct and reversed position to allow for bisection errors. Reductions were made by the least-squares method using linear terms only, and positions and proper motion from the SAO Star Catalogue were used for eleven reference stars. As this star catalogue is on the FK4 system, so are our derived positions (note that Villada's positions are on the FK3 system). Table I contains the measured (X,Y) coordinates for the reference stars (SAO Catalogue numbers in column 2) and for the stars of interest. As very little is known about the spatial motions of the RCB-stars, these (X,Y) values may be found useful in the future, when better positions and pm for the reference stars used here become available. An improved position for the present epoch could then be obtained for RZ Nor, and comparison with a future accurate position would allow a reliable pm determination. Star No. 2 in Fig. 1 is a new suspected variable. Small brightness variations seem to be present on our plates. Further details will be given elsewhere. Reductions were performed using all eleven reference stars and, alternatively, employing stars No, 1', 3', 4', 6', 7', 8' and 11'. Positions derived are for the mean epoch 1982.0 and we estimate that they are accurate to +/-0.4" in both coordinates (see Table II). TABLE I P1.#75016 P1.#88004 Reference Star No. Identification X Y X Y 1' 243858 -65.898 -41.283 -70.750 -36.923 2' 243882 -47.937 21.664 -54.328 26.412 3' 243892 -41.528 18.062 -47.831 22.987 4' 243898 -31.958 -28.957 -37.132 -23.770 5' 243935 10.651 23.562 4.149 29.774 6' 243937 10.857 13.487 4.604 19.684 7' 243942 17.114 - 3.693 11.276 2.662 8' 243956 32.175 -30.908 26.983 -24.153 9' 243971 53.816 29.007 47.180 36.266 10' 243975 57.994 -54.736 53.306 -47.433 11' 243977 61.527 20.729 55.058 28.175 RZ Nor 1.903 6.126 - 4.152 12.106 RZ Nor close 2.170 6.214 - 3.908 12.207 companion Star No. 1 1.916 2.939 - 4.062 8.936 Star No. 2 -5.084 4.841 -11.112 10.662 Plate center A0=16h28m37.13s 16h28m56.87s (1950.0) D0=-53d12'23.2" -53"15'42.7" Epoch 1975.4 1988.6 TABLE II R.A. (1950.0) Dec. RZ Nor 16h28m45.076s -53"09'11.58" RZ Nor close 16 28 45.924 -53 09 08.88 companion Star No. 1 16 28 45.100 -53 10 46.13 Star No. 2 16 28 22.005 -53 09 49.13 [FIGURE 1] Figure 1. Some details in the region around RZ Nor are shown in this Figure. A, B and C, are SAO stars number 243947, 243945 and 243942, respectively. Star No. 1 was repeatedly confused with RZ Nor (Villada, 1980; Feast and Glass, 1973 and Glass, 1978), star No. 2 is a new suspected variable star, star No. 3 is RZ Nor close companion. The separation and position angle between RZ Nor and its close companion (optical?) are: 1975.4 Rho = 8.34" , Theta = 71.8d 1988.6 Rho = 7.83" , Theta = 69.0d. Many thanks to Mr. J.J. Rodriguez for kindly instructing me in the use of the Repsold measuring machine, to Mr. Z.M. Pereyra for making available a computer program for reducing the plate measurements which with only very minor modifications was used throughout this work, and to Mr. J.E. Laborde for preparing Fig. 1. Last but not least, many thanks to Lics. Alejandra A. E. Milone and Guillermo Torres for valuable suggestions and for improving my English. A grant from CONICOR, Cordoba, Argentina, partially supporting this research is gratefully acknowledged. L.A. MILONE Obs. Astronomico Univ. Nac. De Cordoba Cordoba, Argentina References: Feast, M.W., Glass, I.S.: 1973, M.N.R.A.S., 161, 293. [BIBCODE 1973MNRAS.161..293F ] Gaposchkin, S.: 1952, Harvard College Obs. Ann., 115, 47. [BIBCODE 1952AnHar.115...47G ] Glass, I.S.: 1978, M.N.R.A.S., 185, 23. [BIBCODE 1978MNRAS.185...23G ] Milone, L.A.: 1990, Ap. and Sp. Science (in press). [BIBCODE 1990Ap&SS.172..263M ] Villada, M.M.: 1980, IBVS, No. 1748.