COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3587 Konkoly Observatory Budapest 5 April 1991 HU ISSN 0374 - 0676 BV OBSERVATIONS OF THE OCT. 1990 ECLIPSE OF 22 Vul INTRODUCTION Zeta Aurigae eclipsing binaries consist of a K or M giant and a B main sequence star. Around the times of the eclipse contacts, the B star shines through the outer atmosphere and inner stellar wind of the giant, producing absorption features. Because the B star is small, these binaries offer a unique opportunity to spatially resolve the density, velocity structure, composition, and ionization state of the near environment of the giant star. Unfortunately, the typically large orbits mean that orbital inclinations must lie quite close to 90deg for there to be eclipses, and the frequency of the eclipses will be low. There are presently only 9 such systems known; Zeta Aurigae itself, Epsilon Aurigae, VV Cep, 31 and 32 Cyg, and four recent discoveries; Tau Persei (Ake, et al. 1986), HR 6902 (Griffin and Griffin, 1986), HR 2554 (Ake and Parsons, 1987), and 22 Vul (Parsons and Ake, 1983). The number is expected to grow with the ongoing systematic search conducted by the Griffins (Griffin, et al. 1990). 22 Vul was discovered to be a Zeta Aurigae system in 1983 (Parsons and Ake 1983) and is especially interesting, having the latest hot component (B9) and the earliest cool component (G3 Ib-II) of the class, as well as the shortest period (249 days). Ake, Parsons, and Kondo (1985) performed a preliminary analysis of the star, and found some uncertainties which could be clarified by more photometry. For example, combined ground- based and IUE fluxes are difficult to fit with a standard color and the standard reddening law. Also, the hot component is quite faint and only an upper limit on its luminosity class is known. While mass transfer effects appear not to be important, the UV spectrum is similar to some interacting binaries, and P Cygni-type line profiles show the entire region surrounding the stars is filled with a cool gas. It may be that 22 Vul is in the brief phase before or after the supercritical mass flow stage presently observed in Beta Lyrae (Ake, Parsons, and Kondo 1985). In order to make further progress, the relative sizes, shapes, brightnesses, and positioning of the stars must be measured more accurately. This requires good photometry, especially around the time of the eclipse contacts. Towards this end, Cabrillo Observatory undertook BVR observations of 22 Vul during its October 1990 primary eclipse. [FIGURE 1] Figure 1. Differential B magnitude relative to 24 Vul [FIGURE 2] Figure 2. Differential V magnitude relative to 24 Vul Table 1. V and B-V magnitudes for each observation Hel. JD JD(V) V JD(B-V) B-V 2448174+ 0.72053 5.195 0.72010 1.040 2448174+ 0.72233 5.197 0.72206 1.018 2448174+ 0.72485 5.192 0.72453 1.040 2448175+ 0.71624 5.194 0.71596 1.061 2448175+ 0.71834 5.204 0.71799 1.057 2448175+ 0.72042 5.208 0.72013 1.041 2448176+ 0.67280 5.194 0.67271 1.037 2448176+ 0.67525 5.191 0.67485 1.042 2448176+ 0.67763 5.185 0.67727 1.057 2448179+ 0.63339 5.217 0.63306 1.149 2448179+ 0.63514 5.232 0.63486 1.109 2448179+ 0.63720 5.248 0.63691 1.120 2448179+ 0.63339 5.217 0.63306 1.149 2448179+ 0.63514 5.232 0.63486 1.109 2448179+ 0.63720 5.248 0.63691 1.120 2448181+ 0.63889 5.247 0.63853 1.138 2448181+ 0.64069 5.252 0.64043 1.110 2448181+ 0.64287 5.251 0.64249 1.132 2448181+ 0.65001 5.249 0.64975 1.127 2448181+ 0.65194 5.264 0.65162 1.121 2448184+ 0.76111 5.249 0.76081 1.125 2448184+ 0.76355 5.239 0.76313 1.134 2448184+ 0.76551 5.245 0.76521 1.111 2448186+ 0.64076 5.251 0.64049 1.131 2448186+ 0.64285 5.248 0.64256 1.133 2448186+ 0.64472 5.251 0.64439 1.124 2448186+ 0.65139 5.249 0.65110 1.128 2448186+ 0.65341 5.253 0.65304 1.119 2448186+ 0.65524 5.228 0.65694 1.153 2448186+ 0.64076 5.251 0.64049 1.131 2448186+ 0.64285 5.248 0.64256 1.133 2448186+ 0.64472 5.251 0.64439 1.124 2448186+ 0.65139 5.249 0.65110 1.128 2448186+ 0.65341 5.253 0.65306 1.119 2448186+ 0.65524 5.228 0.65494 1.153 2448187+ 0.68576 5.245 0.69530 1.150 2448187+ 0.69715 5.244 0.69681 1.139 2448187+ 0.69866 5.255 0.69826 1.137 2448187+ 0.70005 5.258 0.69970 1.119 2448187+ 0.70144 5.250 0.70111 1.135 2448188+ 0.62083 5.245 0.62057 1.138 2448188+ 0.62208 5.255 0.62181 1.122 2448188+ 0.62492 5.252 0.62464 1.124 2448188+ 0.62617 5.253 0.62590 1.125 2448188+ 0.62743 5.263 0.62715 1.112 2448189+ 0.68757 5.225 0.68715 1.111 2448189+ 0.68925 5.210 0.68883 1.099 2448189+ 0.69071 5.207 0.69035 1.104 2448189+ 0.69212 5.212 0.69174 1.088 2448189+ 0.69362 5.207 0.69319 1.091 2448191+ 0.62045 5.208 0.62016 1.030 2448191+ 0.62484 5.190 0.62456 1.060 2448191+ 0.62604 5.186 0.62573 1.044 2448191+ 0.63108 5.188 0.63079 1.044 2448191+ 0.63404 5.201 0.63376 4.045 2448191+ 0.63970 5.200 0.63942 1.052 2448191+ 0.64091 5.198 0.64063 1.052 2448191+ 0.64645 5.199 0.64611 1.061 2448191+ 0.64770 5.212 0.66740 1.033 2448192+ 0.76366 5.188 0.76339 1.052 2448192+ 0.76498 5.197 0.76472 1.055 2448192+ 0.77013 5.199 0.76986 1.039 2448192+ 0.77141 5.207 0.77115 1.012 2448193+ 0.63126 5.195 0.63100 1.035 2448193+ 0.63249 5.187 0.63222 1.045 2448193+ 0.63561 5.196 0.63536 1.076 2448193+ 0.63794 5.184 0.63767 1.072 2448194+ 0.73278 5.205 0.73204 0.992 2448194+ 0.73398 5.195 0.73372 1.040 2448194+ 0.73530 5.201 0.73501 1.043 2448194+ 0.74000 5.199 0.73973 1.034 2448194+ 0.74131 5.201 0.74102 1.041 2448194+ 0.74259 5.223 0.74230 0.996 2448194+ 0.74411 5.203 0.74383 1.021 2448197+ 0.66649 5.197 0.66583 1.078 2448197+ 0.66815 5.204 0.66767 1.043 2448197+ 0.67016 5.204 0.66949 1.037 2448197+ 0.67292 5.198 0.67234 1.041 2448197+ 0.67525 5.193 0.67464 1.035 2448198+ 0.60889 5.197 0.60844 1.047 2448198+ 0.61036 5.196 0.61005 1.064 2448198+ 0.61191 5.201 0.61161 1.042 2448198+ 0.61321 5.193 0.61291 1.068 2448198+ 0.61450 5.190 0.61424 1.070 2448204+ 0.67745 5.207 0.67705 1.060 2448204+ 0.67920 5.202 0.67874 1.064 2448204+ 0.68117 5.212 0.68078 1.042 2448204+ 0.68257 5.218 0.68228 1.022 2448204+ 0.68477 5.204 0.68404 1.048 2448206+ 0.60213 5.200 0.60184 1.049 2448206+ 0.60350 5.199 0.60314 1.049 2448206+ 0.60487 5.196 0.60455 1.050 OBSERVATIONS Cabrillo College Observatory has a 0.25m Schmidt-Cassegrain with a PC controlling an Optec SSP-3A photometer equipped with Johnson-Cousins BVRI filters. We use the RPHOT data acquisition and reduction software package (Nolthenius 1990). Each clear night in October and early November 1990, the star was observed with the following sequence; sky - comparison - variable - variable - variable - comparison - sky. Each night, from three to 12 observations were made of the variable star. Each observation consisted of 4 to 8 consecutive 10-second integrations in each of the filters B, V, and R. The comparison star was 24 Vul = HR 7753. Figure 1 shows the light curve in B, with each night's data averaged to a single point. Unfortunately, most of the critical periods of ingress and egress were spoiled by clouds. Figure 2 shows the V light curve. All magnitudes are differential with respect to 24 Vul, whose B=5.32 and B-V=0.95. Table 1 shows the V and B-V for each observation. RESULTS The eclipse depth is 0.150 +- 0.007 in B, and 0.051 +- 0.007 in V; in good agreement with the Parsons, Ake, and Hopkins (1985) values of 0.136 and 0.052, respectively. From the single ingress and egress observations, the time of mid-eclipse is found to be JD 2448184.94 +-.1. Combining this with the well- observed eclipse of August 1984 (Parsons, Ake, and Hopkins 1985) gives a photometric period of 249.1828 +-.01 days. The duration of totality is not well determined, but is at least 8.8 days, and less than 10.0 days, with no significant difference between the durations in B and V. With this further refinement in the photometric period, it should be possible to better target the brief and critical partial phases during subsequent eclipses. RICHARD NOLTHENIUS Dept. of Astronomy Cabrillo College Aptos, CA 95003 email ucscc\!cabuucp\!rickn REFERENCES: Ake, T.B., Barksdale, W.S., Fried, R.E., Hopkins, J.L., Fekel, F.C., Hall, D. S., Landis, H.J., and Louth, H., 1986, Inf. Bull. Var. Stars No. 2847. Ake, T.B., and Parsons, S.B., 1987, Inf. Bull. Var. Stars No. 3002. Ake, T.B., Parsons, S.B., and Kondo, Y., 1985, Ap. J. 298, 772. [BIBCODE 1985ApJ...298..772A ] Griffin, R.E.M., Griffin, R.F., Schroder, K.-P., and Reimers, D., 1990, Astron. Astrophys. 234, 284. [BIBCODE 1990A&A...234..284G ] Griffin, R. and Griffin, R., 1986, J. Astrophys. Astron. 7, 195. [BIBCODE 1986JApA....7..195G ] Parsons, S.B., and Ake, T.B., 1983, Inf. Bull. Var. Stars No. 2334. Parsons, S.B., Ake, T.B., and Hopkins, J.L., 1985, P.A.S.P. 97, 725. [BIBCODE 1985PASP...97..725P ] Nolthenius, R.A., 1990, in "Proceedings of the Conference on Robotic Observatories", Astronomical Society of the Pacific, Conference Series, Boston Univ., Fairborn Press