COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3163 Konkoly Observatory Budapest 22 March 1988 HU ISSN 0374-0676 HY PAVONIS: PHOTOELECTRIC TIMES OF MINIMUM AND IMPROVED PERIOD The variability of the short period eclipsing system HY Pavonis (alpha = 20h 18m06s, delta = -73d51.8', 1950.0) was detected by Hoffmeister (1963) who suggested that it was an Algol-type eclipsing binary. Gessner and Meinunger (1974) obtained a photographic light curve with an amplitude of the order of 0.9 magnitudes. They found that the depths of both minima were almost equal so that they classified this star as a W UMa-type eclipsing binary. From their photographic observations 12 times of minimum were determined which yielded the following ephemeris; Min I = Hel. J.D. 2436730.4586 + 0.351653d E (1) +/-0.0044 +/-0.000027 As no photoelectric data of this eleventh magnitude star have been published so far, we decided to include it in our short-period-eclipsing-binary observational program. In this note we present 16 new photoelectric times of minimum obtained at El Leoncito (San Juan, Argentina) and at Bosque Alegre (Cordoba, Argentina) stations during the 1987 observing seasons. The observations carried out at El Leoncito were performed by means of a 76 cm reflector telescope, an RCA 34031(A) photomultiplier refrigerated by Peltier effect and photon-counting electronics. At Bosque Alegre the observations were realized with a conventional design photometer and an RCA 1P21 photomultiplier refrigerated with dry ice attached to the 154 cm reflector. In both observatories standard BV filters were employed. The measurements were made differentially with respect to the comparison star designated as number 1 in our finding chart (Figure 1). All observations have been corrected for first and second order differential extinction. The comparison star is located approximately 5 minutes of arc south-west from HY Pav and consequently the corrections for differential extinction were small. Table I. Photoelectric times of minimum light of HY Pavonis Min JD hel. E O-C 2440000.+ I 6972.8229 0.0 0.00139 I 6972.8224 0.0 0.00094 I 6973.8762 3.0 -0.00024 I 6973.8762 3.0 -0.00030 I 7002.7128 85.0 0.00060 I 7002.7107 85.0 -0.00149 II 7002.8863 85.5 -0.00178 II 7002.5866 85.5 -0.00141 I 7008.6904 102.0 0.00006 I 7008.6897 102.0 -0.00064 I 7009.7454 105.0 0.00006 I 7009.7452 105.0 -0.00011 I 7022.7576 142.0 0.00107 I 7022.7590 142.0 0.00296 II 7023.6354 144.5 -0.00029 II 7023.6354 144.5 -0.00030 [FIGURE 1] Figure 1. Finding chart of HY Pavonis [FIGURE 2] Figure 2. V light curve of the eclipsing binary HY Pavonis From 735 observations for each [BV) passband we derived 16 times of minimum light. The bisection-of-chords method was used to determine 12 times of primary minimum and 4 of the secondary one. A linear least square solution using our photometric data yields the following updated ephemeris: Min I = Hel. J.D. 2446972.82149 + 0.3516555d E (2) +/-0.00027 +/-0.0000027 Table I lists the 16 times of minimum light reported in this note. The last two columns give the epoch number and the (O-C) residuals calculated from equation (2). Within the precision of the ephemeris determinations no variability of the period of the system can be asserted. Although the light curve of the system (Figure 2) has not been completed yet, it shows the typical configuration of the W UMa-type systems. The difference between minima is about 0.15 magnitudes. The maxima clearly show the variation due to the deformation and reflection effects of the components. This system will be observed again during the next observing season in order to complete the light curves and analyze them by means of a synthetic method of solutions. We are very grateful to the Director of the Felix Aguilar Observatory (San Juan) for granting the running time at El Leoncito Observatory. The assistance of J. Laborde, J.R. Puerta and J. Ahumada during the observations carried out at Bosque Alegre (Cordoba) is also gratefully acknowledged. This work was partially supported by the Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) of Argentina. E. LAPASSET, M. GOMEZ Observatorio Astronomico Universidad Nacional de Cordoba Laprida 854, 5000 Cordoba Argentina References: Hoffmeister, C., 1963, Veroffentlichungen der Sternwarte zu Sonneberg, Band 6, Heft 1, p. 50 [BIBCODE 1963VeSon...6....1H ] Gessner, H., Meinunger, I., 1974, Veroffentlichungen der Sternwarte zu Sonneberg, Band 6, Heft 5, p. 318 [BIBCODE 1974VeSon...5..249G ]