COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3774 Konkoly Observatory Budapest 24 September 1992 HU ISSN 0374 - 0676 THE PERIOD OF THE S-CEPHEID VARIABLE V950 Sco * The variability of HD 159654=NSV 9246=BV 547=V950 Sco was first reported by Strohmeier et al. (1964) and the preliminary clements of its light variation were obtained by Diethelm & Tjemkes (1984). The latter authors classified the star as a Cepheid variable with a period of 3.3825+/-0.015 d. On the basis of new and more accurate measurements, Mantegazza & Poretti (1992) determined the Fourier parameters of the V light curve and established that the star belongs to the class of the s-Cepheids, i.e. Cepheids which do not follow the Hertzsprung progression and pulsate in the first overtone mode. Owing to the large gap, it was not possible to relate the two available times of maximum light (HJD 2445540.43 and 2447991.097) and to refine the value of the period. New measurements of V950 Sco were performed at the ESO-50 cm telescope in April and May 1992, following the same observing technique as described by Mantegazza & Poretti (1992); the same comparison star, i.e. HD 160069, was also used. The table lists the 13 new normal points collected in that way: they are not distributed in phase as well as the previous ones, but they allow us to reliably determine a new time of maximum at HJD 2448741.454, also confirmed by a much more precise time of minimum at HJD 2448743.247. No uncertainty is left as to the fact that the last two times of maxima are separated by 222 cycles: since we can estimate that the error on a single maximum determination is 0.03 d, we obtain a period of 3.3800+/-0.0002 d. A similar value, i.e. 3.38013+/-0.00005 d, was obtained by searching for the best light curve (including the first harmonic) fitting the data. In turn, this value for the period allows us to establish that 725 cycles separate the time of maximum reported by Diethelm & Tjemkes from our first one: the least-squares linear fit calculated by using the three available maxima gives Max. = HJD 2447991.07 + 3.38019 x E and an error of 0.00005d on the period determination. Of course this linear ephemeris is valid only under the hypothesis that no abrupt change in the period has occurred since 1983. * Based on observations collected at European Southern Observatory, La Silla, Chile Hel. J.D. V 2448732.842 7.402 8734.707 7.100 8735.823 7.334 8735.920 7.357 8736.814 7.390 8736.917 7.371 8739.855 7.416 [FIGURE 1] 8743.919 7.308 8745.653 7.251 8745.792 7.292 8745.921 7.324 8746.785 7.417 8746.920 7.399 As regards the Fourier parameters, the new measurements yield values that coincide (within the error bars) with those reported by Mantegazza & Poretti (1992). By processing all the 57 normal points we obtained the light curve shown in the figure; the resulting phi_21 value, 3.70+/-0.14 rad, confirms that V950 Sco lies below the classical Hertzsprung progression in the phi_21 - P plane. E. PORETTI Osservatorio Astronomico di Brera Via E. Bianchi, 46 22055 Merate - Italy L. MANTEGAZZA Dipartimento di Fisica Nucleare e Teorica Universita di Pavia 27100 Pavia - Italy References: Diethelm R., Tjemkes S., 1984, Inf. Bull. Var. Stars No. 2503 Mantegazza L., Poretti E., 1992, A&A 261, 137 [BIBCODE 1992A&A...261..137M ] Strohmeier W., Knigge R., Ott H., 1964, Inf. Bull. Var. Stars No. 74