COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2747 Konkoly Observatory Budapest 13 June 1985 HU ISSN 0374 - 0676 THE ELLIPTICITY EFFECT AND A MIGRATING WAVE IN THE CHROMOSPHERICALLY ACTIVE TRIPLE SYSTEM V772 Her V772 Herculis = HD 165590 = ADS 11060 is a triple system very interesting in many respects. Important references are Morbey et al. (1977), Scarfe (1977), Batten et al. (1979), Fekel (1981), Bakos and Tremko (1982), and Stern and Skumanich (1983). From these we get the following picture. A G0V star (the spectroscopic primary) and an M1V star (spectroscopically unseen) orbit each other with a period of 0.8795d at an inclination of 77deg +/-7deg. That close pair orbits a G5V star (the spectroscopic secondary) with a period of 20.25y at an inclination of 82.7deg +/- 2.0deg. The system is very young, similar in age to the Pleiades, and emits soft x-ray radiation, with Lx= 4 x 10^30 ergs/sec. Both the G0V and the G5V stars show Ca II H and K emission in their spectra. The G5V star rotates unusually rapidly (Vsini = 18 +/- 2 km/sec) and the G0V star rotates exceedingly rapidly (Vsini = 75 5 km/sec), apparently in synchronism with the short orbital period. The long-period orbit is highly eccentric, with e = 0.958, and last underwent periastron passage in 1978. The short-period orbit undergoes shallow (DeltaV = 0.05mag) eclipses and also additional variations outside eclipse which until now have not been understood. With the 10-inch Newtonian at Fairborn Observatory (Boyd et al. 1984) V772 Her was observed differentially on 21 nights in 1984 in the UBV system, the comparison star being HR 6763 = HD 165524. The data are given in Table I. A preliminary plot, with respect to the ephemeris JD(hel.) = 2443656.6635 + 0.8794998d n (1) given by Bakos and Tremko for times of primary eclipse, indicated that V772 Her was in eclipse on two of our 21 nights, marked with a (p) in Table I. They are useful as recent timings of mid eclipse, uncertain by approximately +/- 0.01d. O-C residuals with respect to equation (1) are +0.017d and +0.003d. Next we used least squares to fit a sinusoidal light curve to the 19 differential magnitudes outside eclipse, with a range of different periods assumed. The results are shown in Table II, where the second column is the period which gives the smallest variance, the third column is the full amplitude of the wave, and the last column is the Julian date of the minimum of Table I Differential Photometry of V772 Her = HD 165590 JD(hel.) DeltaV DeltaB DeltaU note 2445970.6444 0.903m 0.293m -0.743m (p) 2445972.6468 0.812 0.247 -1.054 (f) 2445973.6602 0.843 0.250 -0.920 (f) 2445984.6088 0.860 0.245 -0.793 2445986.6221 0.854 0.217 -0.857 2445987.6157 0.824 0.203 -0.847 2445990.6117 0.870 0.257 -0.779 2445993.5999 0.842 0.215 -0.841 2445996.5891 0.886 0.292 -0.720 2445999.5812 0.837 0.227 -0.810 2446000.5977 0.832 0.216 -0.831 2446001.5774 0.812 0.186 -0.875 2446002.5815 0.877 0.262 -0.790 2446005.5663 0.838 0.235 -0.811 2446006.5701 0.857 0.229 -0.819 2446007.5695 0.909 0.272 -0.799 (p) 2446008.5688 0.836 0.221 -0.839 2446009.5720 0.867 0.261 -0.768 2446010.5621 0.883 0.271 -0.773 2446012.5612 0.849 0.239 -0.825 2446013.5601 0.853 0.231 -0.849 Table II Fourier Analysis of the Migrating Wave lambda P Delta m JD(min.) V 0.8726d 0.0489mag 2445970.428 +/-.0020 +/-.0038 +/- .009 B 0.8755 0.0598 2445970.416 +/-.0020 +/-.0044 +/-.008 U 0.8710 0.0965 2445970.420 +/-.0025 +/-.0064 +/-.007 Table III Fourier Analysis of the Ellipticity Effect lambda Delta m JD(min.) O-C V 0.0136mag 2445970.604 -0.023d +/-.0035 +/-.010 B 0.0197 2445970.593 -0.034 +/-.0033 +/-.005 U 0.0469 2445970.617 -0.017 +/-.0052 +/-.005 [FIGURE 1] Figure 1 Light curve of V772 Her in V with phase computed from equation (2). The solid curve is a sinusoidal fit of the migrating wave, with zero phase at light minimum. The two eclipse points, open circles, do not coincide here because 0.873 days is not the 0.8795-day orbital period. the wave. All 21 DeltaV values are plotted in Figure 1, where phase is computed with the ephemeris JD(hel.) = 2445970.421 + 0.873d n, (2) which is an average of our results in the three bandpasses. The solid curve is a sine wave with a full amplitude of DeltaV = 0.049mag and with its minimum at zero phase. Note that the two eclipse points do not coincide, because 0.873d is not the 0.8795d orbital period. Our Fourier analysis in the U bandpass omitted values from two consecutive nights, marked (f) in Table I, which gave extremely large residuals, both overluminous. We recall that Bakos and Tremko saw a flare on June 16, 1979 which made the system brighten by 0.125mag in U. In short-period (therefore, presumably, close) eclipsing systems one anticipates a detectable ellipticity effect. Therefore we removed the wave from our observations, using its 0.873d period and the appropriate amplitude for each bandpass, and did another Fourier analysis which allowed for a cos(2theta) variation, this time computing phase with the 0.8795d orbital period. Results are shown in Table III, where Delta m is the full amplitude of [FIGURE 2] Figure 2 The ordinate is DeltaV corrected by removing the migrating wave; phase is computed with equation (1). The solid curve is a cos 2Theta Fourier fit showing presumably the ellipticity effect, with zero phase at the conjunction corresponding to primary eclipse. In this figure the two eclipse points do coincide because here 0.8795 days is the orbital period. We see no trace of a secondary minimum. the variation, JD(min.) is the Julian date of the minimum which corresponds to conjunction with the G0V star behind, and O-C is the residual with respect to the ephemeris in equation (1). Because these times of conjunction should be logically equivalent to times of mid primary eclipse, it is not surprising that the O-C residuals are close to zero vis a vis their uncertainties. All 21 DeltaV values, with the wave removed as we discussed, are plotted in Figure 2, where phase is computed with the ephemeris in equation (1). The solid curve is the cos(2Theta) wave with a full amplitude of 0.0136. The interrupted portions allow for eclipses, which Bakos and Tremko say are approximately 2 hours in duration. Note that, because we are using the orbital period here, our two eclipse points do coincide very near zero phase. Although our phase coverage is not dense, we note no trace of a secondary eclipse around phase 0.50P. The 1978 periastron passage should have produced an interesting glitch in the O-C curve similar to that seen in QS Aquilae, another eclipsing binary in a highly eccentric long-period orbit around a third star, by Knipe (1971). From parameters in table II of Batten et al. we can estimate that the amplitude of such a glitch should have been only about 0.001d or 0.002d. The only times available to establish the course of the O-C curve before the JD 2443669.24 periastron were the two of Scarfe, closely spaced in time (Delta n = 24 cycles) and both relatively uncertain (+/-0.007d). Our recent times add little statistical weight in defining the course of the O-C curve after periastron. Therefore, unfortunately, the available data are incapable of revealing this small effect. The amplitude of the glitch Knipe saw in QS Aql, 0.07d, was considerably larger. Our finding of a migrating wave in the light curve of V772 Her explains the curious photometric behavior outside eclipse which Scarfe noticed but did not explain. The 0.75% difference between 0.8795d and 0.873d would explain why Scarfe found the variation correlated approximately but not exactly with orbital phase. Bakos and Tremko noticed similar behavior but explained certain aspects of it by imagining the M-type component a T Tauri star filling its Roche lobe, transferring matter onto the G0V star, and producing a hot spot at the point of impact. We, however, believe the 0.873d variability arises from a not-quite-synchronously rotating star whose surface is darkened unevenly by regions of starspot activity, as is virtually always the case in chromospherically active stars which show strong Ca II H and K emission in their spectra. The star responsible is surely the G0V component, because the G5V component (although it shows H and K emission also) has Doppler broadened lines which imply a rotation period of 2 or 3 days, very different from 0.873d. Note that the wavelength dependence of the Delta m values in both Table II and Table III is such as to have arisen from the G0V star, i.e., the hottest of the three in the triple system. This extremely interesting triple system would profit from more thorough photometric coverage which could yield a solution of the light curve for the geometrical parameters of the G0V + M1V system. Such photometry should cover the phases of both primary and secondary eclipse, although the latter may prove undetectable. It should dover the phases outside eclipse simultaneously, so that the photometric complication of the migrating wave can be removed before solution. And the photometry should be multicolor, to help in removing the third light contributed by the G5V star. We acknowledge support provided by N.S.F. research grant AST 84-14594. LOUIS J. BOYD RUSSELL M. GENET Fairborn Observatory 629 North 30th Street Phoenix, Arizona 85008 DOUGLAS S. HALL WILLIAM T. PERSINGER Dyer Observatory Vanderbilt University Nashville, Tennessee 37235 References: Bakos, G. A. and Tremko, J. 1982, Astrophys. Space Science Library 98, 67. [BIBCODE 1982ASSL...98...67B ] Batten, A. H., Morbey, C. L., Fekel, F. C., and Tomkin, J. 1979, P.A.S.P. 91, 304. [BIBCODE 1979PASP...91..304B ] Boyd, L. J., Genet, R. M., and Hall, D. S. 1984, I.A.P.P.P. Comm. No. 15, 20. [BIBCODE 1984IAPPP..15...20B ] Fekel, F. C. 1981, Ap.J. 246, 879. [BIBCODE 1981ApJ...246..879F ] Knipe, G. F. G. 1971, P.A.S.P. 83, 352. [BIBCODE 1971PASP...83..352K ] Morbey, C. L., Batten, A. H., Andrews, D. H., and Fisher, W. A. 1977, P.A.S.P. 89, 851. [BIBCODE 1977PASP...89..851M ] Scarfe, C. D. 1977, I.B.V.S. No. 1357. Stern, R. A. and Skumanich, A. 1983, Ap.J. 267, 232. [BIBCODE 1983ApJ...267..232S ]