COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3676 Konkoly Observatory Budapest 31 October 1991 HU ISSN 0374 - 0676 MULTIPLE PERIODICITY OF delta DELPHINI Delta Scuti stars are pulsating, short period variables characterized by small amplitude in their light curves. Known stars in this group have A or F type spectra with small color indices. Delta Delphini was noticed as a variable by Eggen (1956) with a period of 0.13505d after 3 nights of observations. Eggen defined the star as a member of delta Scuti group and spectral type was given as A7 III by Slettebak (1955). Bidelman (1966) has also defined a new spectral type using delta Del as a prototype. Table 1. Coordinates of variable and comparison stars. alpha 1950 delta 1950 Sp m delta Del 20h 41m 07.4' +14d 53.6' F0 IV 4.49 - 4.38 v zeta Del 20h 32m 58.2' +14d 30' A3 V 4.68 In this paper, we present new photometry of delta Del obtained using 0.4 m reflector at the observatory of METU, which was established at the end of 1990. Observations of delta Del (HD 197461) were performed in blue and visual regions and zeta Del (HD 196180) was chosen as comparison star. Differential star-star method was followed and magnitude differences delta m=m(delta)- m(zeta) corrected for extinction in both filters were then plotted against time (heliocentric julian days). We have also included the previous observations obtained by one of us (Uyaniker, 1989) with a telescope of 20 cm. aperture using SSP-3 photometer. A multiperiod analysis was applied to all available data using the program PERIOD of Breger (1990). Light curves are given in figure 1 and the amplitude spectra for two nights are shown in figure 2. Periods obtained from the frequency analysis are displayed in table 2. Amplitude variations between maxima and minima in the light curves have been detected. It can be seen from figure 1 that delta Del is bluer at maximum than at minimum. The fundamental period obtained from old observations is 0.157 days while new observations resulted in a period of 0.148 days, both in the visual range. We have also detected, roughly, a second and a third period of 0.057 and 0.042 days, in v filter, respectively (see also table 2). Thus we have tried to represent the light curve as the sum of three Fourier terms. However, the light curves of JD 2447405 and 2448449 are affected with a fourth frequency corresponding to a range of 0.33 to 0.40 days, and are inconsistent with the periods of delta Scuti type stars. These values may be results of the tidal influence of the component star as indicated by Fullerton (1967); who also noticed a 40 day binary period, while Fitch (1975) indicated 40.58 days. Baglin et al. (1973) also put delta Del in the class of binary stars in delta Scuti variables. Observations of JD 2448438 are of poor quality, so this night was excluded from the frequency analysis. [FIGURE 1] Figure 1. Light curves of HD 197461 in both blue and visual filters. Note that solid curves indicate the fit. [FIGURE 2] Figure 2. Power spectrum analysis of the data in two filters. Corresponding dates are also labeled. Fundamental period and its harmonics indicate that P_1/P_0 ratio is about 0.4 to 0.5 for all data available. This result implies that delta Del does not hold the P_1/P_0 ~= 0.75 criterion for the radial oscillations (Breger and Bregman, 1975). Table 2. frequency fit parameters HJD filter F_1 F_2 F_3 F_4 Residual 2447392 b 8.40 - 24.21 - 0.0078 v 8.47 - 23.41 - 0.0061 2447396 b 6.73 12.36 - - 0.0085 v 5.16 - 27.00 - 0.0048 2447405 b 7.80 17.75 22.99 1.31 0.0094 v 6.36 11.59 24.34 3.03 0.0069 2448449 b 6.87 17.35 18.60 2.46 0.0094 v 6.73 17.82 22.74 5.43 0.0074 Thus we conclude that, the preliminary period range obtained above is too small to be the binary period. However this is because of the binary nature of the star. Further work is required and a detailed frequency analysis must be carried out in order to understand the reason of these variations. Continuous observations are also needed to resolve the binary period. Bülent UYANIKER and Altan BAYKAL Physics Department Middle East Technical University, 06531 Ankara, Turkey e-mail: A10380@TRMETU.BITNET ABAY @ TRMETU.BITNET References : Baglin, A., Breger, M., Chevalier, C., Hauck, B., le Contel, J.M., Sareyan, J.P. and Valtier, J.C. : 1973, A.A., 23, 221. [BIBCODE 1973A&A....23..221B ] Bidelman, W.P. : 1966, Vistas in Astronomy, 8, 53. [BIBCODE 1966VA......8...53B ] Breger, M. : 1990, Comm. in Astroseismology, No. 20. Breger, M. and Bregman, J. N. : 1975, Ap. J., 200, 343. [BIBCODE 1975ApJ...200..343B ] Eggen, O.J. : 1956, Pub. A. S. P., 68, 541. [BIBCODE 1956PASP...68..541E ] Fitch, W.S. : 1975, Multiple Periodic Variable Stars, IAU Colloquium No. 29, Budapest, p.167. [BIBCODE 1976ASSL...60..167F ] Fullerton, W. : 1967, A. J., 72, 797. [BIBCODE 1967AJ.....72..797F ] Slettebak, A. : 1955, Ap. J., 121, 653. [BIBCODE 1955ApJ...121..653S ] Uyaniker, B : 1989, Proceedings of 6th National Meeting of Astronomy and Space Sciences, Izmir, p.417.