COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2870 Konkoly Observatory Budapest 25 February 1986 HU ISSN 0374 - 0676 VARIATION OF THE CP2 STAR BD+24deg3675 * The star BD+24deg3675 was found to be a CP2 star by Bidelman (1983). He classified it as a Si type by means of objective-prism plates. For this reason the star was placed on a list of CP2 stars to obtain Stromgren, Hbeta and Delta a indices (Schneider (1986)). The Delta a index was introduced by Maitzen (1976) to measure the flux depression at lambda 5200 which characterizes chemically peculiar early type (CP2) stars. The observations were carried out in August 1985 with the 1m telescope of the Wise Observatory/Israel. For details of the instrumentation and reduction see Schneider (1986). After three nights it was found that this star has the most outstanding Delta a value ever measured, but with a scatter larger than expected. This indicated variability, therefore, the observations were continued until the end of the campaign. Although no comparison star was measured the accuracy of the absolute photometry is very good. First the average of the magnitudes and the indices were calculated. Then the means was subtracted from the data and a sine fit was placed through the residuals to estimate the frequency for each channel. A mean frequency was calculated by averaging the single frequencies weighted with the deviation from the fits. This yielded a period of 7.52+-.3days. -------------- * Based on observations collected at The Florence and George Wise Observatory, Tel Aviv University, Israel. [FIGURE 1] Table I mean ampl average y : 9.941 .093 .014 b : 9.996 .158 .016 v : 10.230 .150 .023 u : 11.015 .152 .026 b-y : .54 .066 .010 m1 : .180 .074 .011 c1 : .551 .167 .020 Hbeta : 2.767 .059 .011 a : .101 .062 .010 Table II y b v u b-y m1 c1 a Hbeta J.D. phi 17 61 68 110 43 36 35 -13 -1 6302.306 .00 35 69 49 157 33 53 128 -45 7 6303.297 .13 28 54 47 118 25 32 78 -10 35 6304.256 .26 -34 -56 -49 -94 -23 30 -52 29 -21 6306.265 .53 -26 -48 -40 -88 -23 31 -56 05 -10 6306.285 .53 -39 -69 -69 -136 -31 31 -67 32 -42 6307.290 .66 -44 -88 -96 -177 -45 37 -73 22 -12 6307.328 .67 -41 -62 -54 -114 -22 30 -68 34 -15 6308.314 .80 -15 -12 -14 -31 2 4 -15 -5 -7 6309.272 .93 74 97 112 153 22 7 26 -19 25 6310.270 .06 43 58 49 104 14 23 64 -35 44 6311.262 .19 Table I gives the mean values and the amplitudes derived from the fit with the mean period. In the third column the average of the residuals after pre-whitening is listed, which is a criterion for the quality of the fit. Table II shows the residuals (mean- obs.) in millimag, Julian Date of the observations and the derived phase. The phases were calculated by using J.D. = 2446302.306 + 7.52 E In Fig.1 all residuals were plotted against the phase. Note that the m and the a index is in antiphase with the other quantities. HARTMUT SCHNEIDER Universitats-Sternwarte Geismarlandstr. 11 D-3400 Gottingen F.R.G. References : Bidelman, W.P. Astron.J. 88, 1182 (1983) [BIBCODE 1983AJ.....88.1182B ] Maitzen, H.M. Astron.Astrophys. 51, 223 (1976) [BIBCODE 1976A&A....51..223M ] Schneider, H. Astron.Astrophys. in press (1986) [BIBCODE 1986A&A...161..203S ] [From IBVS 2883] ERRATUM In Table I of the IBVS No. 2870, "Variation of the CP2 star BD+24deg3675", the amplitude in U-filter is erroneously given: instead of 0.152 one should read 0.304. H. SCHNEIDER