COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1359 Konkoly Observatory Budapest 1977 November 4 B AND V PHOTOMETRY OF X PERSEI (=2U 0352 +30?) X Per was observed at Tallinn Observation Station beginning from 28 Dec. 1973 on 50 nights. The star HD 23478 (B3 IV, V=6.66m, B-V=+0.07m - Publ.of the U.S. Naval Obs.Sec.Ser.Vol.XXI, 1968) served as a comparison star and HD 23625 as a check star. All the observations were corrected for differential extinction by using the mean coefficients and transferred to the U,B,V system as described in Tartu Astrophys.Obs.Publ., 43,96, 1975. Several consecutive measurements were averaged to obtain the normal points given in the Table and plotted in the Figure. The mean-root-square error of the normal point is +-0.001m ...+-0.002m for Delta V and +-0.002m...+-0.004m for Delta(B-V). From the extreme values of extinction coefficients in the cases of the best and worst atmospheric conditions it results that the extinction corrections can differ from the mean no more than by -0.002m...+0.004m and -0.001m...+0.002m for Delta V and Delta(B-V), respectively. Therefore the real error of the normal point in both colours is about +-0.005m. Some conclusions: (1) From measurements made during four and half hours on 28 Dec. 1973 and seven hours on 10 Jan. 1974 (integrating time nearly 1 minute) no light variations were recorded, whereas the error of a single measurement in V was +-0.004m and in B +-0.006. (2) The amplitude of light variations between Dec. 1973 and March 1977 was about 0.07m in V and 0.05m in B. (3) By Sept. 1977 the brightness of X Per has risen 0.24m in V and 0.17m in B in comparison with the mean from the last 4 years. It well may be, that there has been continuous brightening since Febr. 1977. (4) Light variations are more pronounced in V than in B. (5) 29 Sept. 1975, the time of the lowest brightness, coincides with the supposed time of increasing of anomalies in emission spectrum of hydrogen on 3.Oct.+-22d (Mamatkazina, Sov.Astron. Circ., No.867, 4, 1975). Besides, only in that case consequence (4) is invalidated and the fall of brightness is accompanied by reddening of light. J.D. J.D. 2400000+ Delta V Delta(B-V) n 2400000+ Delta V Delta(B-V) n 42045.3721 -0.011 0.096 22 42728.4089 0.035 0.091 4 056.3951 -0.007 096 4 734.4170 0.033 084 5 057.2522 -0.004 099 6 757.4809 0.025 089 5 058.3582 -0.004 097 34 776.4849 0.015 102 4 059.3153 0.002 096 4 820.3155 -0.008 092 4 .4012 0.006 095 5 828.2923 0.014 073 5 060.3495 -0.003 088 5 831.3924 0.022 080 5 112.2373 -0.013 110 4 832.2735 0.010 080 5 113.2325 -0.003 098 4 836.3784 0.019 086 5 123.2475 0.004 088 2: 842.3209 0.030 072 5 449.3068 0.041 085 1: 43030.4804 0.061 070 5 450.2261 0.046 080 5 052.4582 0.054 074 5 453.2645 0.041 090 5 054.4235 0.056 074 4 455.2182 0.050 078 5: 067.4563 0.050 074 5 468.3004 0.041 090 4 068.4223 0.048 073 5 469.3207 0.053 082 4 069.4901 0.042 066 5 484.2738 0.042 086 4 133.3085 0.041 068 5 486.2878 0.031 095 4 172.2671 0.055 058 4 492.2749 0.039 097 4 189.2375 0.054 065 4 645.5328 0.044 090 5 209.2975 0.043 068 4 585.3100 0.069 104 3 232.2885 0.033 076 5 698.4050 0.058 072 3 411.4711 -0.202 153 6 705.4961 0.034 082 5 412.5524 -0.209 154 4 713.4056 0.056 074 4 413.4383 -0.208 149 5 716.4786 0.042 099 5 414.5027 -0.209 144 5 425.4809 -0.215 158 4: F. KALV W. Struve Tartu Astrophys. Obs. Tallinn Observation Station: Tahetorn, Tallinn, Estonian S.S.R. U.S.S.R. 200016 [FIGURE 1]