COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3637 Konkoly Observatory Budapest 16 July 1991 HU ISSN 0374 - 0676 CCD LIGHT CURVES OF V865 CYGNI Wachmann (1961) discovered the thirteenth magnitude W UMa variable, V865 Cygni (HBV 235) as a result of his photographic search for variables in the Cygnus star cloud. Thirty-two epochs of minimum of light and a finder chart are included in his paper. Since his observations, V865 Cyg has been neglected. The present observations of V865 Cyg were made from 16-19 June, 1990, inclusive. The RCA CCD camera system attached to the 1.07 m F/16 Hall reflector telescope was used at Lowell Observatory, Flagstaff, Arizona. The CCD local system approximated the standard Johnson-Cousins VR_cI_c photometric system and observations were transformed to determine R-I standard magnitudes. The chip was cooled with liquid Nitrogen throughout the observing interval to -130degC. Approximate coordinates of the check, comparison and the variable star are given in Table 1. Neither the check nor the comparison star are known to have a catalog identification. About 80 images in V and R and 65 in I were obtained with integration times ranging from one to five minutes. Our observations failed to cover phases 0.6 to 0.85, inclusive, but they suffice to reveal important characteristics of the system. TABLE I Star R. A. Dec. (1990.5) (1990.5) V865 Cygni 19h 27m 02.8s 33d 01'58" Comparison 19h 27m 06.2s 33d 02'46" Check 19h 27m 06.3s 33d 01'08" Four mean epochs of minimum light were determined from the observations made during two primary and two secondary eclipses. The tracing paper method was used to determine the epochs of minimum light in V, R and I on The first two nights. The bisection of chords technique was utilized to determine the primary epoch in V, R and I and the secondary epoch in V on the last night. An iterative technique based on the Hertzsprung method (1928) was used to determine the remaining epochs. The mean times of minimum light are given in Table 2. These epochs along with those by Wachmann (1961) were introduced into a least squares solution to obtain both a linear and a quadratic ephemeris. Our linear solution included only recent epochs from JD 2436000 on. The quadratic solution included all epochs except for three by Wachmann which were discordant. The improved ephemerides are: JD Hel Min. I = 2448060.8912(15) + 0.36530170(9)d * E and, JD Hel Min. I = 2448060.8912(9) + 0.3653026(2)*E - 5.4(1.2)*10^11d*E^2 TABLE 2 JD HEL. 2400000+ Minimum Cycles (O-C)_1 (O-C)_2 48060.8921 I 0.0 0.0009 0.0009 48061.8061 II 2.5 0.0016 0.0016 48062.7158 I 5.0 -0.0020 -0.0020 48062.8998 II 5.5 -0.0006 -0.0006 The linear ephemeris was used to calculate the (O-C)_1 residuals in Table 2 and the phases of the present observations. The quadratic ephemeris was used to calculate the (O-C)_2 residuals. The V, R light curves of V865 Cyg defined by the individual observations are shown in Figure 1 as normalized intensity versus phase. The light curves in Figure 1 are overlaid by our synthetic light curve solution. Our spotted solution reveals that the system is a contact binary with a mass ratio of about 0.45 and a fillout of 19 percent. The less massive component appears to undergo a brief occultation at the secondary minimum. The early analysis of this system was done by Scott Herr as part of his 1991 senior honors thesis. The final solution and hot spot parameters were determined largely by another undergraduate student, Jim Zetzl. Further details of the solution, along with a complete analysis will be discussed elsewhere. [FIGURE 1] Fig. 1 - CCD Light curves of V865 Cyg as defined by the individual normalized intensities. RONALD G. SAMEC a,b SCOTT A. HERR JAMES T. ZETZL Dept. of Physics & Astronomy J. I. Holcomb Observatory Butler University Indianapolis, IN 46208 USA TOBIAS J. KREIDL Lowell Observatory 1400 West Mars Hill Rd. Flagstaff, AZ 86001 USA a Visiting Astronomer, Lowell Observatory, Flagstaff, Arizona, USA b This research was partially supported through The AAS Small Research Grants Program by a grant from the Margaret Cullinan Wray Charitable Lead Annuity Trust and by a travel grant from the College of Liberal Arts and Sciences of Butler University. References: Wachmann, A. A. 1961, Astr., Hamburg VI(1), 25 Hertzsprung, E. 1928, Bull. Astr. Inst. Netherlands 4, 179 [BIBCODE 1928BAN.....4..172H ]