COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3306 Konkoly Observatory Budapest 16 March 1989 HU ISSN 0374 - 0676 PHOTOMETRIC VARIABILITY OF THE SPECTROSCOPIC BINARY HD 133822 The double-lined spectroscopic binary HD 133822 (V=7.7, P=17.8d ?) was investigated by Evans (1961) who derived spectral types of G5IV and a set of orbital elements according to which eclipses were not excluded. Photometric variability is reported in the Seventh Catalogue of the orbital elements of spectroscopic binary systems (Batten et al., 1978). Were the system to be found eclipsing, it would be a most interesting late subgiant system with an eccentric orbit. At the suggestion of D.M. Popper and J. Andersen, we therefore included HD 133822 in our uvby observations with the Danish 50 cm telescope on La Silla, Chile, and obtained 87 observations in each colour on 28 nights during March-May 1984 (Table I). HR 5566 (G 3-5 V, V=6.35) and HR 5699 (G 3-5 V, V=5.65) were used as comparison stars. Three unpublished CORAVEL observations from March 1984, kindly provided by J. Andersen, indicate slow rotation and confirm mass and luminosity ratios near one. When combined with Evans' data and assuming that his period is nearly correct, they lead to an improved spectroscopic ephemeris: Min at HJD 2436068.207+17.83792d*E We found no indication of eclipses but we did find the system to be variable as indicated by the scatter given in Table II. We searched the interval from 17.7 to 18.2 days to see if any period here could describe the photometric variability, but with no success whatsoever. Visual inspection of a plot of the observations versus time showed a period near 7 days. Further period searches, covering the interval 6 to 8 days, revealed that only a period of 7.07 days (or possibly twice as large) fits the photometry. If we subtract cosine curves with this period and with amplitudes as given in Table II the residual scatter is near that expected from the photometry. Figure 1 shows the light curve in b and colour index curves for (b-y) and c_1 with phases calculated from HJD 2445805.400+7.07d*E Table I: Magnitude differences HD 133822 - HR 5566 in the instrumental system -2445000 u v b y -2445000 u v b y 784.65221 1.369 1.411 1.381 1.380 805.88398 1.363 1.409 1.382 1.378 .65739 1.371 1.417 1.388 1.387 .88626 1.362 1.412 1.380 1.382 .80836 1.365 1.414 1.386 1.380 807.64186 1.381 1.433 1.400 1.398 .81086 1.374 1.417 1.387 1.383 .64413 1.372 1.433 1.399 1.392 .88521 1.372 1.420 1.388 1.386 .74016 1.391 1.430 1.405 1.397 .88808 1.369 1.419 1.389 1.384 .74240 1.389 1.431 1.409 1.399 786.89100 1.395 1.441 1.411 1.404 .79553 1.380 1.431 1.402 1.396 .89362 1.401 1.441 1.410 1.401 .84714 1.397 1.433 1.406 1.403 787.86756 1.387 1.443 1.407 1.395 .84978 1.389 1.443 1.402 1.401 .87096 1.393 1.431 1.402 1.399 .89025 1.389 1.441 1.401 1.399 .88782 1.390 1.439 1.406 1.404 .89506 1.389 1.432 1.396 1.401 .89017 1.397 1.435 1.403 1.405 811.70062 1.368 1.419 1.389 1.388 788.69388 1.390 1.438 1.401 1.401 .70316 1.376 1.416 1.390 1.392 .69654 1.395 1.439 1.404 1.402 812.72032 1.369 1.406 1.382 1.377 .76857 1.386 1.432 1.399 1.401 .72291 1.372 1.413 1.384 1.384 .77103 1.390 1.439 1.401 1.400 813.83784 1.379 1.429 1.395 1.391 792.90256 1.384 1.421 1.395 1.388 .83988 1.385 1.422 1.391 1.391 .90480 1.388 1.429 1.393 1.393 814.75051 1.390 1.442 1.417 1.408 794.74611 1.406 1.446 1.408 1.408 .75298 1.386 1.439 1.404 1.402 .74854 1.402 1.441 1.407 1.406 815.75638 1.398 1.446 1.412 1.410 795.87532 1.398 1.437 1.406 1.401 .75938 1.403 1.449 1.414 1.410 .87753 1.386 1.435 1.403 1.397 .80181 1.397 1.445 1.411 1.409 797.83582 1.375 1.410 1.382 1.383 .80407 1.414 1.450 1.410 1.410 .83855 1.372 1.407 1.385 1.381 816.77490 1.403 1.450 1.413 1.406 798.58473 1.368 1.403 1.377 1.380 .77710 1.402 1.440 1.404 1.406 .58707 1.369 1.408 1.376 1.377 .85372 1.399 1.440 1.410 1.409 .62144 1.361 1.409 1.384 1.377 .85619 1.406 1.438 1.410 1.408 .62480 1.358 1.404 1.379 1.381 817.59730 1.391 1.427 1.401 1.394 .66323 1.359 1.406 1.378 1.376 .59962 1.384 1.432 1.399 1.394 .66553 1.361 1.411 1.376 1.378 .65992 1.386 1.421 1.400 1.397 .71901 1.362 1.409 1.373 1.379 .66233 1.389 1.430 1.394 1.397 .72119 1.365 1.407 1.378 1.374 818.72079 1.371 1.416 1.388 1.387 .76507 1.359 1.407 1.376 1.378 .72298 1.376 1.412 1.393 1.390 .76722 1.352 1.409 1.377 1.379 821.57493 1.396 1.441 1.398 1.396 .82225 1.363 1.399 1.379 1.378 .57716 1.393 1.432 1.398 1.397 .82538 1.362 1.407 1.382 1.376 822.61904 1.406 1.444 1.416 1.408 799.84860 1.376 1.422 1.401 1.390 .62099 1.404 1.453 1.411 1.409 .85087 1.373 1.425 1.398 1.390 826.74817 1.361 1.411 1.387 1.381 801.89213 1.408 1.443 1.411 1.407 .75057 1.369 1.406 1.383 1.385 .89440 1.406 1.448 1.411 1.405 830.64425 1.397 1.440 1.408 1.405 803.89312 1.383 1.421 1.391 1.393 .64735 1.406 1.445 1.410 1.407 .89556 1.384 1.425 1.400 1.391 831.74469 1.380 1.419 1.397 1.390 804.85754 1.352 1.415 1.374 1.379 .74701 1.375 1.421 1.394 1.390 .86005 1.370 1.412 1.384 1.389 [FIGURE 1] Figure 1. Light and colour curves of HD 133822, assuming a period of 7.07d. If the period is doubled, observations plotted as crosses will lie in the phase interval from 0.0 to 0.5, squares from 0.5 to 1.0. We derive the following average values for the Stromgren indices: V=7.792 b-y=0.441 c_1=0.273 m_1=0.266 If we accept the spectroscopic result that the stars are indeed nearly identical all indices are compatible with the stars being main sequence stars of spectral type G6-G8 while luminosity class IV is ruled out because of the low value of the c_1 index. We find M_v=5.3, T_eff=5500 K and [Fe/H]= -0.03. This is in agreement with a recent result of Lu and Tsay (1983) who find M_v=5.4 and spectral type G6V. We suggest that the system consists of two normal main sequence stars of solar composition. For such a system eclipses would be very narrow, lasting less than 0.017 in phase (assuming Evans' period). In that case, we actually cannot completely exclude the possibility that the system is eclipsing, since the uncertainty in epoch is about 0.7 days. Table II: Photometric variability of HD 133822 residual scatter mean errors from scatter around amplitude of after subtraction comparison star mean value cosine curve of cosine curve differences y 0.011 0.013 0.004 0.002 b 0.012 0.015 0.004 0.003 v 0.014 0.018 0.005 0.003 u 0.015 0.018 0.006 0.005 Attempts have been made at fitting the spectroscopic observations to periods near 7 or 14 days, by applying changes of sign to whatever observations seemed to need it, but they have been unsuccessful. Considering the problems with component identification on the spectrograms which Evans reports, and noting the large scatter in his figure and the smooth run of the CORAVEL observations (obtained on consecutive nights), it is clear that a definitive ephemeris and radial velocity curve can be found from radial velocity spectrometer observations. Since few empirical mass and radius determinations for main sequence G stars exist, we urge observers with access to such an instrument to place the system on their observing list. The question remains what is the cause of the photometric variability reported here. Two obvious possibilities are: (1) One or both stars could be spotted and rotate (synchronously or nonsynchronously) with a period of 7.07 days, which means an equatorial rotational velocity of about 6 km/s, large enough that spots are likely to develop. (2) The variability could be related to an orbital period near 14.14 days. Note, however, that ellipsoidal deformation must be negligible, because the relative radii are on the average only about 0.03. BODIL E. HELT KAARE S. JENSEN Copenhagen University Observatory Oster Voldgade 3 DK-1350 Copenhagen K, Denmark References: Batten, A.H., Fletcher, J.M., Mann, P.J.: 1978, Publ. Dom. Astrophys. Obs. XV, No. 5. [BIBCODE 1978PDAO...15..121B ] Evans, D.S.: 1961, Royal Obs. Bull. No. 30, E 93. [BIBCODE 1961RGOB...30...93E ] Lu, P.K., Tsay, W.S.: 1983, Astron. J. 88, 1367. [BIBCODE 1983AJ.....88.1367L ]