COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3488 Konkoly Observatory Budapest 4 July 1990 HU ISSN 0374 - 0676 NEW VARIABLE STARS IN THE OPEN CLUSTER NGC 6882/5 In a research program to detect new variable stars in open clusters (Peniche and Pena, 1987) a few stars in the direction of the open cluster NGC 6882/5 (RA = 20h 9.8m, D = 26d 26', 1960) were observed. The criterion followed in the selection of the stars was that they lie within the limits of the instability strip since, according to Breger (1979), one third of the stars found there would be variable. The observations were carried out at the San Pedro Martir Observatory during the nights of September 3 and 4, 1986. The 0.84 m telescope was utilized provided with a pulse counting photomultiplier with a 1P21 cooled phototube, Johnson's V filter was used. The integration time for both sky and star measurements was of 10 s in a series of six measurements of the star and one of the sky. Table I lists the observed stars, the JD number which, in this case, follows the notation of Hoag et al. (1961), the V magnitude and the color index of each star. The last column lists the stellar spectral type that was obtained from the calibration of (B-V) given by Hoag et al. (1961) and the spectral type from Mihalas (1981). The technique followed for determining which stars were variable and which constant was through the use of differential photometry and can briefly be summarized as follows: in order to obtain the instrumental magnitude, the flux of the sky was subtracted from the average flux of the star measurements and the instrumental magnitude was derived. Light curves for each star were constructed and a mean curve was established. The stars that did not conform to the average pattern defined by two or more stars were considered to be variable and the mean curve was subtracted. A zero base-line was established by subtracting the mean amplitude variation for each star. The final results are presented in Tables II and III and shown schematically in Figures 1 and 2. The accuracy of each figure is of 0.0035d in time and 0.003 in magnitude. As can be seen from Figure 1, the amplitude of variation of star 19 is 0.034 mag. with an interval of time between two consecutive maxima being Table I Parameters of the Observed Stars ID V B-V Spectral type Comments 9 9.26 .280 A9 Constant 5 7.60 -.090 B5 Constant 19 10.23 .440 F6 Variable 25 10.49 .420 F5 Variable 8 9.18 .480 F7 Constant Table II Differential Photoelectric Photometry of Star 25 HJD V HJD V 2440000+ (mag) 2440000+ (mag) 6677.7036 .008 6678.6878 .017 6677.7127 -.007 6678.6944 .002 6677.7211 -.013 6678.7023 .003 6677.7295 .005 6678.7098 -.002 6677.7378 .001 6678.7169 .014 6677.7453 -.007 6678.7315 .014 6677.7611 -.008 6678.7382 -.004 6677.7690 .000 6678.7473 .003 6677.7857 .005 6678.7557 -.004 6677.7932 .002 6678.7694 -.004 6677.8015 -.001 6678.7795 .001 6677.8099 -.012 6678.7836 .002 6677.8174 .006 6678.7911 -.009 ó677.8253 .003 6678.7957 -.010 6677.8328 .018 6678.8073 -.015 6678.8140 -.010 6678.8215 -.007 Table III Differential Photoelectric Photometry of Star 19 HJD V HJD V 2440000+ (mag) 2440000+ (mag) 6677.7107 -.017 6678.6861 .000 6677.7194 -.008 6678.6932 -.001 6677.7279 .001 6678.7007 -.003 6677.7357 .001 6678.7153 .000 6677.7440 -.006 6678.7236 .001 6677.7599 -.010 6678.7307 .008 6677.7674 -.006 6678.7378 -.002 6677.7757 -.009 6678.7471 -.002 6677.7841 .009 6678.7544 -.003 6677.7920 -.003 6678.7682 .001 6677.8002 -.005 6678.7757 .001 6677.8086 -.001 6678.7828 .006 6677.8153 .015 6678.7898 -.009 6677.8228 .013 6678.7982 -.010 6677.8315 .014 6678.8057 -.006 6678.8132 .003 6678.8203 .002 [FIGURE 1] Figure 1. Light curve of star 25. [FIGURE 2] Figure 2. Light curve of star 19. Table IV Amplitude of Variation of the Observed Stars DeltaV DeltaV HJD2446677 HJD2446678 V5-V8 V 0.000 0.000 V25 - 0.013 0.014 V19 - 0.016 0.009 0.056d, whereas for star 25 (Figure 2), the amplitude is 0.032 mag with an estimated period of 0.053d. We might conclude that two new variable stars in the direction of the open cluster NGC 6882/5 have been found. Due to the photometric characteristics of these stars, namely, that they are within the instability strip limits, their spectral types are F6 and F5, they show low amplitude variation and short periods of pulsation, it might be concluded that these are Delta Scuti type variables. The authors would like to acknowledge the assistance of the staff at SPM, of T. Gomez at different stages, of G. Ceron for the drawings, of J. Miller for proofreading. One of us, SD, would like to thank Dr. O. Cardona for his guidance. J.H. PENA 1,2, R. PENICHE 1,2, and S.H. DIAZ-MARTINEZ 2 1 Instituto de Astronomia Universidad Nacional Autonoma de Mexico Apartado Postal 70-264, Mexico D.F. 04340 2 Instituto Nacional de Astrofisica Optica y Electronica Apartado Postal 51 y 216, 72000 Puebla, Pue. Mexico References: Breger, M.: 1979, Publ. Astron. Soc. Pac., 91, 5. [BIBCODE 1979PASP...91....5B ] Hoag, A.A., Johnson, H.L., Iriarte, B., Mitchell, R.I., Hallam, K.L. and Sharpless, S.: 1961, Publ. U.S. Naval Obs. Vol.XVII, 346. [BIBCODE 1961PUSNO..17....1H ] Mihalas, D.: 1981, Galactic Astronomy, Freeman and Co., San Francisco. [BIBCODE 1981gask.book.....M ] Peniche, R. and Pena, J.H.: 1987, Rev. Mex. de Astron. y Astrof., 14, 420. [BIBCODE 1987RMxAA..14..420P ]