COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3471 Konkoly Observatory Budapest 4 June 1990 HU ISSN 0374 - 0676 B, V, R, I LIGHT CURVES OF EH HYDRAE As a part of our current study of very short period eclipsing binary systems, we have obtained complete B,V,R,I light curves of the fourteenth magnitude W UMa variable, EH Hya (HV 11665). The system was discovered by Ashbrook (1942) in her study of fifty-nine variable stars in Milky Way field #355. The finding chart for this variable is found in the atlas by Tsesevich and Kazanasmas (1971). No further references are available on this neglected system. The ephemeris given by Ashbrook is: Jd Hel Min. I = 2427870.515 + 0.29691d * E The present observations of EH Hya were made on 5 - 9 May, 1989 inclusive. The Yale 1M Ritchey-Cretien Telescope at Cerro Tololo Inter- American Observatory was used. The photometry was done in the Johnson- Cousins' system with standard B,V,R,I filters using the Automated Single Channel Aperture Photometer with a dry-ice-cooled Hamamatsu R943-02 (Ga- As) photomultiplier tube. The coordinates of the check, comparison and the variable star are given in Table I. Neither the check nor the comparison star has a catalogue identification. An average of 425 observations were obtained at each effective wavelength. TABLE 1 Star R. A. Dec. (1950) (1950) EH Hya 12h 02m 17s -32d 52' 54" Comparison 12h 02m 16s -32 50 35 Check 12h 02m 16s -32 52 20 [FIGURE 1] Fig. 1 - Light curves of EH Hya as defined by the individual observations. Five mean epochs of minimum light were determined from the observations made during three primary and two secondary eclipses. Most epochs were determined from an iterative technique based on the Hertzsprung method (1928). The bisection-of-chords method was used to determine the earliest secondary epoch in I, and the tatest primary epoch in B and V. The tracing paper method was used to obtain the latest primary epochs in R and I due to high scatter in these particular observations. The times of minimum light are given in Table II along with the epoch of Ashbrook (1942). TABLE II JD HEL. 2400000+ Minimum Cycles (O-C) 27870.515 I -66644.0 0.0000 47655.6455(6) I -7.0 -0.0007 47656.5358(3) I -4.0 -0.0012 47656.6864(11) II -3.5 0.0010 47657.5770(8) II -0.5 0.0009 47657.7246(1) I 0.0 0.0001 These times of minimum light along with a starting ephemeris consisting of the period by Ashbrook (1942) and our last epoch were introduced into a least squares solution to obtain the following ephemeris: JD Hel Min. I = 2447657.7246 + 0.29690909d * E This ephemeris was used to calculate the O-C's in Table II and the phases of the present observations. The B, V, R, and I light curves of EH Hya defined by the individual observations are shown in Figure 1 as Delta m versus phase. Preliminary analysis of the observations reveal that this system is of W-type in shallow physical contact with a difference in component temperatures of DeltaT~300 K and a small mass ratio, q ~ 0.3. Much of the preliminary analyses was done by Stephen Charlesworth as a part of his undergraduate honors thesis. Further results and a complete analysis of the observations will be published elsewhere. * RONALD G. SAMEC STEPHEN D. CHARLESWORTH Dept. of Physics & Astronomy J. I. Holcomb Observatory Butler University Indianapolis, IN 46208 USA * Visiting Astronomer, Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation. References: Ashbrook, M. D. (1942). Harvard Ann. 109, 36(8) [BIBCODE 1942AnHar.109...35A ] Hertzsprung E. (1928). Bull. Astron. Inst. Netherlands 4, 179. [BIBCODE 1928BAN.....4..178H ] Tsesevich, V. P., and Kazanasmas, M. S. (1971). Atlas of Finding Charts of Variable Stars Academy of Sciences, Ast. Obs. Odessa State Univ. [BIBCODE 1971afcv.book.....T ] [From IBVS 3523] [...] AND ERRATA FOR EH HYDRAE EH Hydrae The following table corrects Table 2 published earlier in IBVS No. 3471 (Samec and Charlesworth 1990). The former results were in error by one JD. TABLE 3 JD HEL. 2400000+ Minimum Cycles (O-C) 27870.515 II -66640.5 0.0000 47654.6455(6) I -7.0 -0.0007 47655.5358(3) I -4.0 -0.0012 47655.6864(11) II -3.5 0.0010 47656.5770(8) II -0.5 0.0009 47656.7246(1) I 0.0 0.0001 Also, the following improved ephemeris corrects the one given in the former publication: JD Hel Min. I = 2447656.7246(3) + 0.29690968(1)d*E RONALD G. SAMEC