COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 739 Konkoly Observatory Budapest 1972 November 16 ON THE VARIABILITY OF THE MIRA STAR UX CYGNI On two occasions the Mira variable UX Cygni has been reported to vary in brightness by more than one magnitude on time scales of one hour or less. The first report (1) described a decrease in brightness by 1.4 magnitudes within 12 minutes. The second (2) indicated an increase by 1.3 magnitudes within one hour. The first instance occurred 38 days before the 1933 visual maximum, and the second occurred 21 days before the 1944 maximum. In an attempt to refine the description of this phenomenon and to investigate the extent to which the variation persists to very short time scales, we observed UX Cygni with the high speed pulse-counting photometer at the McDonald Observatory (3). The observations were obtained on the 76-cm reflector. The detector was a specially selected Amperex 56 DVP photomultiplier, operated uncooled and generally without a spectral filter. The variable was observed With time resolutions between one and five seconds for a total of 12.5 hours on four nights. Table I gives the coverage times. Visual inspection of the data showed that no variations larger than 0.05 magnitude occurred on time scales less than two hours. Our data are not suitable for investigation of longer time scale variability, although we did observe a slow increase in brightness from night-to-night, consistent with the expected Mira-type variability. On three nights, observations were made in V of the UBV system in order to determine the date of visual maximum. From these results (Table II) we estimate the date of maximum to have been 1972 Sep 18 +- 4, which is in agreement with the AAVSO predicted date 1972 Sep 14(4). The phases in Table II were computed using the observed date of maximum and the period of 561,24 days (5). The bulk of our high speed observations refer to a time 19 +- 4, days before maximum. This is very close to one of the phases at which rapid variations had been noted previously (2). Since we observed no rapid variability, we conclude that such variations are not strictly phase dependent and/or that following a rapid variation, perhaps during the intervals when we were not monitoring the star, the variable soon recovers to a high precision the brightness it had prior to the rapid event. University of Texas at Austin Austin, Texas 78712 THOMAS J. MOFFETT THOMAS G. BARNES, III. TABLE I ----------------------------------------------------- UT DATE BEGIN (UT) END (UT) TOTAL COVERAGE ----------------------------------------------------- 1972 Aug 29 03h44m46s 04h02m01s 04 41 02 09 05 52 04h42m05s 1972 Aug 30 03 30 36 04 29 26 04 30 19 05 01 19 05 01 37 05 27 17 05 28 27 06 01 12 07 16 47 07 35 02 07 35 09 09 15 59 04 27 30 1972 Aug 31 03 07 38 03 10 33 03 21 29 03 35 24 04 38 36 05 45 16 05 46 32 06 23 37 07 39 09 08 58 09 03 19 35 1972 Sep 01 08h37m00s 08h40m45s 03m45s ------------------------------------------------ TABLE II -------------------------------------------- UT DATE JD V(mag) PHASE -------------------------------------------- 1972 Aug 29 2441558.5 11.27 0.97 1972 Oct 01 2441591.5 9.51 0.03 1972 Oct 16 2441606.5 9.98 0.05 -------------------------------------------- References: 1. Osvalds, V. 1955, Publ. Ast. Soc. Pacific, 67, 417. [BIBCODE 1955PASP...67..417O ] 2. Mayall, M. W. 1956, Jour. Roy. Ast. Soc. Canada, 50, 135. [BIBCODE 1956JRASC..50..135M ] 3. Nather, R. E. and Warner, B. 1971, Mon. Not. Roy. Ast. Soc., 152, 209. [BIBCODE 1971MNRAS.152..209N ] 4. Amer. Assoc. Var. Star Observers, Bulletin No. 35, 1972. 5. Kukarkin, B. V., Kholopov, P. N., Efremov, Yu. N., Kukarkina, N. P., Kurochkin, N. E., Medvedeva, G. I., Perova, N. B., Fedorovich, V. P., and Frolov, M. S. 1969, General Catalogue of Variable Stars (3rd ed.; Moscow: Academy of Sciences of the U.S.S.R.).