COMMISSION 27 OF THE I.A.U. INFORMATION BULLETIN ON VARIABLE STARS Number 3234 Konkoly Observatory Budapest 8 September 1988 HU ISSN 0374 - 0676 FURTHER OBSERVATIONS, IMPROVED POSITION AND EPHEMERIS FOR THE EW TYPE SYSTEM V728 HERCULIS (BAV Mitteilungen Nr. 51) Recently, Nelson, Milone and Penfold (1988) reported on BVI photometry and spectroscopy of the short-period eclipsing binary V728 Her (= SVS 2086). They noted that the period P = 0.446250d quoted by its discoverer (Kurochkin 1977), fails to represent the observations. However, the preliminary period of P = 0.471302d obtained by Nelson et al. was still inadequate to fit the observed times of minimum. Differential UBV photometry - albeit of very poor quality - of V 728 Her had already been secured by Ciardo et al. (1985) who also suggested a longer period (around 0.4747d). To derive an adequate ephemeris for V 728 Her, we have collected all available epochs of minima from the literature (Table 1). For the photographic observations, these are epochs of faint light on photographic plates. Application of a simple least-squares period search algorithm led to a period close to that found by Nelson et al. (1988). Both the periods quoted by Kurochkin and Ciardo et al. turned out to be spurious periods caused by interference with the sidereal day and a gap of one month between successive observational series, respectively. The time span covered by photoelectric observations proved adequate to define the period with an accuracy sufficient to bridge the gap of 11 years to Kurochkin's estimates on plates obtained with the 40cm astrograph at the Krim station of the Sternberg Institute, and, subsequently, even 80 years backward in time, to the old plate collection ("S" series) of Moscow Observatory (cf. Kurochkin, 1977). To test the new ephemeris, we reobserved V 728 Her with the automatic photoelectric telescope at F. Agerer's private observatory (for a description see Agerer 1988a). The telescope used was a 0.35 m Schmidt-Cassegrain. The photometer was equipped with an EMI 97818 tube and Schott filters BG12 (1mm) + GG385(2mm) for the B and GG495(1mm) for the V colour, the size of the diaphragm was 32". The differential instrumental magnitudes have been transformed to the international UBV system. The light curve, reduced with the new period, is shown in Fig. 1. The amplitudes in B and V are 0.39m (0.38m) resp. 0.36m (0.35m); the values given in parentheses apply to minimum II which is only marginally shallower. Table 1 Observed times of minima for V728 Her, epochs and residual computed with respect to the ephemeris (1) and (2) derived in this paper No. JD helioc Min Type* Epoch (O-C)1 (O-C)2 Observer Source 1 2417796.394 II P: -61860 +0.024 N.E.Kurochkin PZP 3.212 2 40361.509 II P -13980 +0.003 3 40809.460 I P -13029 -0.002 4 40810.405 I P -13027 +0.000 5 40827.372 I P -12991 +0.001 6 41062.573 I P:: -12492 +0.031 7 41533.337 I P: -11493 -0.019 B 41567.287 I P -11421 -0.002 9 41571.292 II P -11413 -0.003 10 41957.241 II P:: -10594 -0.036 11 45882.375 I E: - 2265 -0.001 +0.0024 Ciardo et al. ASS 111.123 12 46257.7518 II E - 1469 -0.003 -0.0006 D.R. Faulkner PASP 98.691 13 46612.868 I E - 715 +0.000 +0.0011 Nelson et al. IBVS 3201 14 46613.809 I E - 713 -0.002 -0.0005 15 46949.835 I E 0 -0.002 -0.0019 16 47304.469 II E:: 752 -0.010 -0.0111 R. Diethelm BBSAG BS 17 47353.4937 B II E 856 +0.001 -0.0002 F. Agerer this paper .4937 V +0.001 -0.0002 18 47365.5121 B I E 882 +0.002 +0.0003 .5128 V +0.003 +0.0010 19 47366.4537 B I E 884 +0.001 -0.0006 .4565 V +0.004 +0.0022 20 47378.4726 B II E 909 +0.002 +0.0004 .4733 V +0.003 +0.0011 *) P denotes pg plate min.(weight 2 or 1), E photoelectric min. (weight 100 or 25). Minima marked ":" received reduced weight, while those marked "::" were discarded as outliers. The epoch given by Diethelm (1988) is based on a very small number of measurements and was therefore considered unreliable. Four epochs of minima derived from our observations are listed in Table 1; these were used to further refine the orbital period of V728 Her by the method of least squares. We give as best overall linear ephemeris, covering an interval of eighty years, Min I = 2446949.837 + 0.4712852d*E (1906-1988). (1) Instantaneous elements, computed from photoelectric minima only, are Min I = 2446949.8370+ 0.4712868d*E (1984-1988). (2) +-4 +-4 It seems that the period has been constant within 2 x 10E-5 days during the last 80 years. Contrary to the suggestion of Nelson et al. (1988), there is no need to include a quadratic term in the ephemeris formula. Although the variable is correctly identified on the chart provided by Kurochkin (1977), the position quoted in that paper (and in the GCVS) pertains to another star, much fainter and about 3 arc minutes south of V728 Her. From a Palomar Sky Survey print (PSS E-1135, +42d 17h00m) we have re- [FIGURE 1] Figure 1. Differential B and V light curves of V 728 Her. The comparison star is the star marked "a" in Fig. 2 [FIGURE 2] Figure 2. Comparison star chart, after Kurochkin (1977) determined the position of the variable through differential measurements against 11 AGK3 stars distributed within a field of 1x1 deg" around V728 as alpha (1950) =17h16m30s delta (1950) = +41d53.'8. Subsequently V728 Her could also be identified among the stars contained in the Cat. Photogr. du Ciel, Zone de Helsingfors, on Cliches 723 (No. 206), 726 (No. 100) and 730 (No. 18). For each plate we performed a standard astrometric plate reduction using reference stars taken from the AGK3 (some 30 stars per plate) and the published x, y coordinate measurements. From the measured coordinates of V728 Her we then deduced as mean position alpha (1950) =17h14m54s.76 delta (1950) = +41d56'58.5", +-2 +-2 alpha (1950) =17h16m29s.52 delta (1950) = +41d53'46".0. This is consistent with the above given approximate PSS coordinates. The epoch of the CdC position is 1892.7, that of the PSS plate is 1959.5. The tables containing the individual observations in B and V will be published separately (Agerer 1988b). F. AGERER 1 B.-C. KAMPER 1,2 D. LICHTENKNECKER 1 1, Berliner Arbeitsgemeinschaft fur Veranderliche Sterne e.V. (BAV) Munsterdamm 90, D-1000 Berlin 41 2, Astronomische Institute der Universitat Bonn Auf dem Hugel 71, D-5300 Bonn 1, F.R.G. References: Agerer, F., 1988a, BAV Rundbrief 37(2), 60. Agerer, F., 1988b, BAV Mitt. Nr. 52, in preparation. Catalogue Photographique du Ciel, Zone de Helsingfors entre "39 deg et +47 deg, Premiere Serie, Tome VI: 15h-18h, Eds. A. Donner and R. Furuhjelm, Helsingfors 1928. Ciardo, G., del Giudice, L., Nappi, D., and Santillo, L., 1985, Astrophys. Space Sci. 111, 123, [BIBCODE 1985Ap&SS.111..123C ] Diethelm, R., 1988. BBSAG Bull.88. Faulkner, D.R., 1986, Publ. Astron. Soc. Pac. 98, 690. [BIBCODE 1986PASP...98..690F ] Kurochkin, N.E., 1977, Perem. Zvezdy, Prilozh. 3, 201. [BIBCODE 1977PZP.....3..201K ] Nelson, R., Milone, E.F., and Penfold, J.E., 1988, Inf. Bull. Var. Stars No. 3201.