COMMISSION 27 OF THE I.A.U. INFORMATION BULLETIN ON VARIABLE STARS Number 1432 Konkoly Observatory Budapest 1978 June 8 PHOTOELECTRIC PHOTOMETRY OF SIGMA GEMINORUM AND HR 4665 Hall (1976) has characterized the group of binary stars with periods longer than two weeks and with G-K spectra displaying CaII in emission as being related to such well known eclipsing binaries as RS Canum Venaticorum and AR Lacertae. Two recently discovered members of this group are Sigma Geminorum and HR 4665. Although both of these systems are binaries, neither displays eclipses. During the present year this investigator has observed these systems, both at Kitt Peak National Observatory and at the Kutztown State College Observatory. Sigma Geminorum is a single-lined spectroscopic binary, one of whose components is of spectral type K1 III. The orbital period was determined by Harper (1935) as 19.603 days. Observations were made by me with the 40-cm telescope no. 4 of KPNO during January, 1978. An RCA 1P21 photomultiplier, refrigerated with dry ice, was used together with a pulse-counting photometer. Observations were made with an intermediate-band y-filter. The observations at Kutztown State College were made with a 46-cm Cassegrain reflector from February to May, 1978. The photomultiplier was an unrefrigerated EMI 6256 SA (S-13 surface), and the observations were measured with a strip-chart recorder. Observations were made with a standard-band V-filter, but the KPNO and KSC observations were found to be similar enough to allow them to be combined together without using transformation equations. The comparison star used was HR 2896 (K0 III). As a check star Iota Geminorum (K0 III) was used. The magnitude difference (iota Gem - HR 2896 ) was found to be -1.558 with +- 0m.003 as a mean residual for the KPNO observations, and -1.548 with +- 0m.011 as a mean residual for the KSC observations. Each observation of sigma Gem is the mean of two individual readings. The phases of these observations have been calculated by the ephemeris given by Hall (1977a) Hel. JD = 2418967.33 + 19d.603 E. The observations are as follow: KPNO - Hel. JD Phase sigma Gem - HR 2896 2443508.675 0.918 -1.110 10.816 0.027 1.080 11.782 0.076 1.060 12.843 0.130 1.063 15.923 0.287 1.142 16.846 0.334 1.170 21.659 0.580 1.153 22.727 0.634 1.149 KSC 2443563.569 0.718 -1.133 567.562 0.922 1.097 574.536 0.278 1.111 578.721 0.491 1.141 597.650 0.457 1.123 607.657 0.967 1.048 613.603 0.271 1.131 621.605 0.679 1.181 623.571 0.779 1.149 627.569 0.983 1.057 629.565 0.085 1.046 These observations are shown plotted in Figure 1. This figure resembles the one published by Hall, but the amplitude which I find is larger than that reported by him. The amplitude of the light variation is about 0m.12, and minimum light occurs between 0.00 and 0.10 phase according to the ephemeris used. HR 4665 was reported to be variable by Hall (1977b). It is a double-lined spectroscopic binary, both components having spectral types of about K0 with CaII in emission. The orbital period has not yet been determined, but evidence indicates that it differs from the period of the light variation. Observations were made using the same equipment as was used for Sigma Gem. The only difference was that a standard V-filter was used for the KPNO observations instead of an intermediate- band y-filter. The comparison star chosen was HR 4659(K2 III). HR 4740 (G8 III) was used as a check star. For the KPNO observations the mean magnitude difference (HR 4740 - HR 4659) was found to be +0.616 with a mean residual of +-0m.009. For the KSC observations these values were +0.600 and +-0m009, respectively. The observations of HR 4665 are as follows: KPNO - Hel. JD HR 4665-HR 4659 2443511.001 +0.486 16.046 0.506 17.060 0.505 KSC 2443567.655 +0.418 574.769 0.476 578.735 0.484 597.669 0.560 607.681 0.580 612.584 0.556 613.634 0.527 621.631 0.457 623.585 0.434 627.614 0.426 629.589 0.441 648.587 0.509 650.669 0.502 Each of these observations is the mean of two individual readings. The KSC observations are shown plotted in Figure 2. These indicate an amplitude of about 0m.15. Hall has stated that the photometric period of HR 4665 is in the range 60 to 70 days. My observations confirm this period, but allow it to be refined. Hall's light curve shows a maximum at ca. JD 2443304 and a minimum at ca. JD 2443350. Figure 2 shows a maximum at ca. JD 2443626 and a minimum at ca. JD 2443605. Both of these intervals indicate a period of 64 days. Additional observations of HR 4665 will enable its period to be more precisely determined. The apparent difference between the spectroscopic and photometric periods remains to be verified. This investigator wishes to thank Dr. D.S. Hall of Vanderbilt University for suggesting the need for observations of these two systems to me. CARLSON R. CHAMBLISS Dept. of Physical Sciences Kutztown State College Kutztown, Pa. USA 19530 References: Hall, D.S. 1976, I.A.U. Colloq. no. 29, part I. 287. [BIBCODE 1976ASSL...60..287H ] Hall, D.S. 1977a, Inf. Bull. on Var. Stars no 1328. Hall, D.S. 1977b, Inf. Bull. on Var. Stars no 1352. Harper, W.E. 1935, Pub. D.A.O. 6, 224. [BIBCODE 1935PDAO....6..207H ] [FIGURE 1] [FIGURE 2]