COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1615 Konkoly Observatory Budapest 1979 May 31 HD 200925, A NEW SHORT PERIOD VARIABLE STAR The discovery of a new variable star sometimes follows an unpredictable pattern. In our case, a search of variable stars with metallic lines (Am) of short period led us to the discovery of a new variable that had previously been considered as standard. This star, HD 200925 (BD+50d3259), of spectral type F 5 III as reported by Moore and Paddock (1950) has an m_V=8.0 and (B-V) = 0.4. It was originally taken as standard along with HD 200926 (BD+49d3455) in the search for the variability of the Am: star HD 200739 (BD+50d3256). Both, the Kukarkin catalogue of variable stars and the Mount Wilson catalogue of radial velocities do not report any variability in any of the previously mentioned stars. All the reported photoelectric observations were carried out on the 33 inch telescope at the Observatorio of San Pedro Martir Baja California, Mexico, during the nights from the 25th to the 28th of September, 1978. A 1P21 photomultiplier and the V filter of the original Johnson's photometer were employed. It was not necessary to change the amplification during the night. The method followed was suggested by Warman and has already been reported (Warman et al., 1974). It consisted of the following: the sequence, C1, V C2, C1, V was followed uninterruptedly all night, with an average spanned time between successive observations of the same star of 4 minutes. Each observation consisted of 3 integrations of 10 sec of the star followed by one 10 sec integration of the sky, that was subtracted from the average of the star integrations. The instrumental magnitude was obtained by means of the well known relation m=-2.5 log I. Table 1 shows the result of subtracting the mean of the magnitudes of the standard stars from the magnitude of the variable star. The accuracy on each observation is better than .003 mag. The time is reported in Heliocentric Julian Dates, and its precision is .001 day. These values are plotted and shown on Figure 1. The shortest night, September 27th, was interrupted by clouds. The analysis of the data showed that the behaviour of C1 and C2 during the four nights were constant with an accuracy of +-.003 mag. On the other hand, from Figure 1 it is easy to infer that the variation of HD 200925 is periodically repeated on the nights of the 25th and 28th of September. The period deduced from these two nights is close to 0.238 days. The mean amplitude is of 0.35 mag. Unfortunately the data available for the light curve of the night of the 26th do not allow us to determine a period or an amplitude, but nevertheless, its behaviour matches with the nights of the 25th and 28th so we might conclude that the period and amplitude on this night have the same values as those on the two other nights. With respect to the night of the 27th, the curve of light shows a change in magnitude of lesser amplitude that cannot be precisely determined due to interruption by clouds. Nevertheless, the period seems to be the same. On considering the nature of the variability of this star, one might infer that, if it were an eclipsing star, the lesser variation in the amplitude of the night of the 27th could be interpreted as a secondary minimum commonly presented by the W Ursae Majoris type stars. If,on the other hand, this were a pulsating star, its spectral type, (F5 III), its period (0.24), the amplitude of its variation and the shape of the curve lead us to catalogue it as a delta Scuti type star (as suggested by Payne-Gaposchkin, 1979). Unfortunately ubvy-beta photometric data do not exist for this star. However, given the spectral type we can infer (Mihalas, 1968) both the Mv and the B-V for its luminosity class (III); values of 1.0 and 0.4, respectively, were obtained. Interpolating in the B-V vs. b-y calibration (Crawford, 1966) a value of 0.23 for b-y was derived. These inferred values of Mv and b-y fix the position of this star within the limits of the instability strip, and when combined with the estimated period, their relationship TABLE I. PHOTOMETRY OF HD 200925 IN THE V FILTER Hel JD D MAG Hel JD D MAG Hel JD D MAG Hel JD D MAG Hel JD D MAG 2443700.0+ ------------------------------------------------------------------------------------ 76.8144 -0.137 77.7825 0.184 78.6908 -0.052 79.7215 -0.026 76.8207 -0.147 77.7860 0.189 78.6943 -0.057 79.7257 -0.041 76.6367 -0.052 76.8242 -0.147 77.7894 0.189 78.6978 -0.062 79.7285 -0.051 76.6408 -0.047 76.8276 -0.147 77.7929 0.189 78.7012 -0.067 79.7320 -0.061 76.6436 -0.047 76.8311 -0.152 77.7957 0.174 78.7047 -0.072 79.7083 39.000 76.6471 -0.042 76.8346 -0.152 77.7999 0.164 78.7082 -0.072 79.7389 -0.086 76.6499 -0.032 76.8374 -0.152 77.8026 0.159 78.7117 -0.072 79.7424 -0.096 76.6526 -0.022 76.8415 -0.147 77.8061 0.149 78.7151 -0.072 79.7451 -0.101 76.6561 -0.017 76.8450 -0.147 77.8096 0.134 78.7186 -0.072 79.7486 -0.106 76.6596 -0.012 76.8485 -0.147 77.8131 0.119 78.7221 -0.072 79.7528 -0.111 76.6624 -0.007 76.8512 -0.147 77.8165 0.109 78.7256 -0.067 79.7556 -0.116 76.6658 -0.002 76.8547 -0.142 77.8200 0.094 78.7283 -0.062 79.7590 -0.126 76.6686 -0.008 76.8582 -0.137 77.8235 0.079 78.7325 -0.057 79.7625 -0.131 76.6721 0.023 76.8610 -0.132 77.8269 0.054 78.7360 -0.052 79.7660 -0.136 76.6742 0.033 76.8644 -0.122 77.8304 0.039 78.7394 -0.047 79.7695 -0.141 76.6769 0.048 76.8679 -0.117 77.8346 0.024 78.7422 -0.042 79.7729 -0.146 76.6804 0.068 76.8707 -0.112 77.8381 0.009 78.7457 -0.037 79.7764 -0.151 76.6846 0.088 76.8749 -0.107 77.8415 -0.011 78.7492 -0.027 79.7799 -0.146 76.6887 0.113 76.8783 -0.097 77.8443 -0.026 78.7526 -0.022 79.7833 -0.146 76.6922 0.128 76.8818 -0.087 77.8478 -0.036 78.7554 -0.017 79.7868 -0.146 76.6950 0.143 77.8519 -0.051 78.7589 -0.012 79.7903 -0.146 76.6992 0.163 77.8554 -0.061 78.7624 -0.007 79.7938 -0.046 76.7026 0.178 77.6644 -0.151 77.8596 -0.071 79.7972 -0.141 76.7068 0.188 77.6679 -0.146 77.8631 -0.086 79.8007 -0.136 76.7103 0.198 77.6707 -0.146 77.8672 -0.101 79.6160 0.029 79.8042 -0.131 76.7137 0.203 77.6735 -0.141 77.8707 -0.116 79.6201 0.044 79.8070 -0.121 76.7172 0.203 77.6783 -0.116 77.8742 -0.131 79.6236 0.054 79.8104 -0.116 76.7200 0.198 77.6853 -0.111 77.8776 -0.136 79.6271 0.074 79.8039 -0.111 76.7235 0.193 77.6887 -0.106 77.8811 -0.136 79.6306 0.094 79.8174 -0.101 76.7269 0.188 77.6915 -0.101 77.8846 -0.146 79.6340 0.104 79.8208 -0.101 76.7297 0.183 77.6957 -0.096 77.8881 -0.151 79.6375 0.129 79.8243 -0.091 76.7332 0.173 77.7033 -0.081 77.8915 -0.161 79.6403 0.144 79.8271 -0.081 76.7367 0.163 77.7068 -0.076 77.8950 -0.171 79.6438 0.154 79.8306 -0.071 76.7401 0.148 77.7096 -0.066 79.6465 0.164 79.8333 -0.066 76.7436 0.133 77.7124 -0.061 79.6500 0.179 79.8368 -0.061 76.7471 0.123 77.7158 -0.056 78.6262 0.173 79.6535 0.189 79.8396 -0.051 76.7506 0.103 77.7186 -0.046 78.6290 0.158 79.6576 0.194 79.8424 -0.041 76.7533 0.093 77.7228 -0.041 78.6318 0.148 79.6604 0.189 79.8458 -0.036 76.7568 0.078 77.7256 -0.036 78.6353 0.133 79.6639 0.184 79.8486 -0.036 76.7603 0.068 77.7290 -0.026 78.6387 0.118 79.6667 0.184 79.8521 -0.031 76.7631 0.048 77.7325 -0.021 78.6415 0.108 79.6708 0.179 79.8556 -0.021 76.7665 0.038 77.7353 -0.011 78.6450 0.093 79.6743 0.174 79.8583 -0.016 76.7707 0.018 77.7387 -0.006 78.6485 0.083 79.6771 0.164 79.8618 -0.011 76.7742 0.003 77.7415 0.004 78.6512 0.068 79.6799 0.154 79.8333 45.000 76.7776 -0.012 77.7450 0.024 78.6540 0.058 79.6861 0.124 79.8688 -0.001 76.7804 -0.022 77.7485 0.039 78.6575 0.038 79.6896 0.109 79.8715 0.004 76.7839 -0.037 77.7519 0.059 78.6603 0.033 79.6931 0.094 79.8743 0.014 76.7881 -0.052 77.7554 0.074 78.6631 0.023 79.6958 0.084 79.8778 0.024 76.7908 -0.062 77.7582 0.094 78.6665 0.008 79.6993 0.069 79.8806 0.039 76.7943 -0.072 77.7624 0.114 78.6700 0.003 79.7021 0.059 79.8840 0.054 76.7978 -0.087 77.7658 0.129 78.6735 -0.007 79.7056 0.044 79.8875 0.074 76.8012 -0.097 77.7693 0.149 78.6769 -0.022 79.7090 0.029 79.8938 0.109 76.8047 -0.107 77.7721 0.159 78.6804 -0.027 79.7125 0.014 79.8972 0.129 76.8075 -0.122 77.7756 0.174 78.6846 -0.037 79.7153 -0.001 79.9000 0.144 76.8110 -0.127 77.7790 0.179 78.6874 -0.047 79.7188 -0.016 ------------------------------------------------------------------------------------ [FIGURE 1] is consistant with the PLCR as in Breger (1978). Perhaps the only conclusion that can be made at this time is (if this is a pulsating star) the agreement between the long observed period and the luminosity class (III). At any rate, it would be desirable to obtain more data,both photometric and spectroscopic, in order to decide between the eclipsing or pulsating nature of this star. The authors would like to thank Dr. Josef Warman for his assistance and guidance during the several stages of this work. Fruitful discussions with Drs. C. Payne-Gaposchkin and S. Gaposchkin are also acknowledged. S.F. GONZALEZ BEDOLLA and JOSE H. PENA Instituto de Astronomia Universidad Nacional Autonoma de Mexico, Apartado Postal 70-264 Mexico 20, D. F., Mexico References : Breger, M. 1978, preprint Crawford, D.L. 1966, IAU Symposium 24, 170 [BIBCODE 1966IAUS...24..170C ] Mihalas, D., 1968, Galactic Astronomy Moore, J.H. and Paddock, G.F., 1950, Astrophysical Journal, 112, 48 [BIBCODE 1950ApJ...112...48M ] Payne-Gaposchkin, C., 1979, private communication Warman, J., Malacara, Z. and Breger, M., 1974, Revista Mexicana de Astronomia y Astrofisica, 1, 143 [BIBCODE 1974RMxAA...1..143W ]