COMMISSION 27 OF THE I.A.U. INFORMATION BULLETIN ON VARIABLE STARS Number 1265 Konkoly Observatory Budapest 1977 April 15 INTERMEDIATE BAND LIGHT CURVES FOR FIVE SOUTHERN HD STARS Introduction: In the course of obtaining intermediate band photoelectric light curves for 16 southern Wolf-Rayet stars during a run in Feb/March 1975, seven of the 26 comparison stars used were found to be low amplitude variable stars. A search of the literature at the end of 1975 revealed that only one of these seven stars was previously known to be variable (HD 93206 = Var. No. 6797 in Carina). Two of the seven stars have been discussed elsewhere (HD 5836,0 = Eta CMa: Moffat, 1977; HD 114911 = Eta Mus: Moffat and Seggewiss, 1977). This communication presents the photometric results for the remaining five stars (listed in Table 1) along with their respective comparison stars. These comparison stars are of constant magnitude within the attained observational accuracy, as verified by intercomparison of magnitudes obtained during the same nights. The Observations Measurements were obtained, normally one per night, over an interval of 37 days. A diaphragm of diameter 18" was normally used in the one channel dry-ice cooled photometer attached to the 61 cm Bochum telescope located on La Silla, Chile. The filters used are listed in Table 2: they were chosen to isolate certain features (emission line or continuum) in the spectra of Wolf-Rayet stars. Integration times ranged from 30 to 60 sec per filter depending on the magnitude. The air mass was always <1.5 but normally <~1.2 for all observations. The internal r.m.s. deviation of one observation was normally +-0.003m increasing to +-0.006m for the fainter stars. The r.m.s. scatter after systematic correction for the light curve was usually +-0.007m for one data point, which comprises the difference in magnitude or colour between 2 stars. This value increased to +-0.015m for the faintest magnitudes. UBV photometry (on observation for each star) obtained with the same telescope is also listed in Table 1. These data are subject to variability but still give a good indication and check on the spectral type. A journal of magnitudes (in F3 or F4) is given in Table 3 for 4 of the 5 variable stars; data for HD 96829 are excluded from the Table because no period was found for this low amplitude variable. Using all the magnitude information in turn, periods were searched for the remaining 4 periodic variables using the method of Lafler and Kinman.(1965). The light curves resulting from the most likely periods so obtained are plotted for these 4 stars along with HD 96829 in Figs. 1-5. In Table 4 is presented a resume of some parameters for each of the 5 variable stars. Brief Description of Individual Stars (1) HD 86441 This star was always measured with a near, faint, visual companion in a diaphragm of diameter 28". Being 5 magnitudes fainter than HD 86441, the companion is not likely to be responsible for the magnitude variation. The best period is P = 5.73 days; the light curve with period 2P also shows 2 minima but has other bumps making it unnecessarily complicated. Other alias periods shorter than that corresponding to the Nyquist frequency (~0.5 day^-1) produce even less plausible looking light curves. It appears that HD 86441 is an eclipsing binary with distortion, implying that the radii of the stars may be larger than that estimated for normal dwarfs in Table 4. (2) HD 93206 At the time of observation, the author was unaware of the eclipsing nature of this star as noted by Walker & Marino (1972) who derived a period of 6.000 +- 0.007 days from 51 observations spread over 10 months. The present data (34 observations spread over 37 nights) yield the best median period of 5.98 days which is so close to an integral number of days, that the light curve is rather ill determined. However, since colour variations appear to be negligible we can combine the previous V data with the present F3 data. On this basis we were able to sketch in the light curve with some confidence in Fig.2. All data together yield an improved period of 5.986 +- 0.001 days. The only other possible period, 6.011 days, although compatible with the previous observations, appears to be inferior for the present observations. (3) HD 96829 Only a slow variation of Delta m=~0.02m over 36 days has been observed for this star with no indication of a period. (4) HD 115599 Any other periods besides 0.6755 days (e.q. its aliases) produce more complex, implausible light curves. With amplitude increasing from 0.07m in the red (F3) to 0.14m in the blue (F1), this star appears to be a pulsating variable, probably of the short period Cepheid type or, if population II, of the RR Lyrae type. (5) HD 152235 Both this star and its comparison star HD 152003 are likely members of the O type cluster in Scorpius NGC 6231 or of its surrounding association Sco OB1. Neither of them is mentioned in the work on spectroscopic orbits of luminous stars in NGC 6231 by Hill et al. (1974). The best period given here (2.63d) is only marginally better than the period 6.20 or 6.85 days which also yield simple, single-minimum light curves. It is also not possible to exclude periods of double these lengths, having 2 minima per cycle. The period 2.63d is close to the critical period for contact (cf. Table 4), assuming both stars to be moderate supergiants. The relatively large residual scatter in the light curve may be a consequence of this. Final Remarks From the 36 originally chosen comparison stars, all the 7 variable stars detected have small amplitudes - less than ~0.1 mag., which is small enough to have escaped previous discovery by photographic techniques. This high yield of variables in interesting in itself since the 26 stars were chosen without bias. Four of the seven variables appear to show low-inclination eclipses (or ellipsoidal variations) in the light curves. Since most binaries will have inclined orbital planes which are non conducive to yielding eclipses, this lends support to the commonly accepted hypothesis that a large fraction of all stars are binaries. Acknowledgements This work was carried out while I was at the Ruhr University, Bochum, F.R. Germany. I wish to express my gratitude to the director, Th. Schmidt-Kaler, for generous allotment of observing time and to the Deutsche Forschungsgemeinschaft for its grant of the telescope and equipment. Table 1: Stars observed HD Sp.(HD) V B-V U-B Sp.(UBV) 86441** variable B9 7.49 -0.02 -0.55 B9(V), B8(Ib) 86199 comparison B9 6.76 -0.14 -0.48 B6(V) 93206 variable B0 Ib:* 6.32 0.14 -0.83 OB 93222 comparison O7* 8.10 0.05 -0.90 OB 96829 variable B3III* 7.32 0.24 -0.66 B1(III) 96970 comparison A0 8.20 0.19 0.18 A 115599 variable A2 9.00 0.21 -0.18 B7(V) 115996 comparison G5 8.61 0.66 0.15 G 152235 variable B0.5 Ia* 6.34 0.54 -0.48 OB 152003 comparison B0 I* 7.05 0.39 -0.63 OB * Sp from LSS catalogue (Stephenson and Sanduleak, 1971). ** observed with a near faint companion star (V=12.55, B-V=0.46, U-B=0.33). Table 2: Filters Designation (lambda) Half-width mean terr. extinction coeff. F1 3635 A 70 A 0.485 mag/air mass F2 4680 130 0.183 F3 5170 190 0.139 F4 5640 110 0.115 Table 3: Magnitudes [m(var) - m(comp)] and times of four variable stars (1) HD 86441 (2) HD 93206 J.D. m(F4) J.D. m(F3) -2442400 -2442400 47.6906 0.737 47.8087 -1.817 48.6072 0.755 48.6955 -1.616 49.6708 0.753 49.7560 -1.821 51.6420 0.839 51.7198 -1.668 52.6807 0.782 52.7250 -1.834 53.6559 0.749 53.7069 -1.820 54.6859 0.776 54.7713 -1.605 55.7063 0.751 55.7755 -1.838 57.7380 0.837 56.7589 -1.848 58.7275 0.735 57.7805 -1.657 59.7537 0.771 58.7669 -1.826 60.7244 0.773 59.7931 -1.811 61.7166 0.767 60.7655 -1.621 62.6245 0.834 61.7327 -1.820 63.5962 0.824 62.6676 -1.837 64.5827 0.739 63.6442 -1.656 65.5577 0.767 64.6271 -1.837 66.5998 0.778 65.6346 -1.827 67.7167 0.794 66.7306 -1.638 68.7558 0.841 67.7629 -1.837 69.7490 0.781 68.7984 -1.851 70.6335 0.741 69.7645 -1.683 71.5521 0.776 70.7654 -1.840 72.6254 0.764 71.5971 -1.827 73.5948 0.780 72.6416 -1.613 74.6367 0.831 73.6116 -1.806 75.6747 0.777 74.6768 -1.850 77.5864 0.843 75.6886 -1.657 78.6825 0.729 77.6558 -1.830 80.7531 0.811 78.6982 -1.619 81.6655 0.746 80.7690 -1.836 82.6576 0.782 81.7655 -1.680 83.6703 0.790 82.7046 -1.845 84.6526 0.755 84.6981 -1.617 (3) HD 115599 (4) HD 152235 J.D. m(F3) J.D. m(F3) -2442400 -2442400 48.7842 0.305 48.8680 -0.617 49.8589 0.263 52.8451 -0.647 53.8254 0.259 53.8662 -0.637 54.8536 0.332 54.8805 -0.637 55.8355 0.260 55.8845 -0.667 56.8256 0.326 56.8855 -0.623 57.8514 0.274 57.8796 -0.684 58.8324 0.335 58.8592 -0.710 59.8556 0.289 59.8819 -0.656 60.8345 0.346 60.8872 -0.637 62.8594 0.330 61.8852 -0.642 63.7785 0.318 62.8909 -0.674 66.8004 0.284 63.8775 -0.636 68.8753 0.332 64.8882 -0.637 70.8584 0.300 65.8792 -0.682 71.8456 0.313 66.8920 -0.645 79.8127 0.321 67.8944 -0.638 84.8034 0.295 68.8947 -0.667 69.8758 -0.614 70.8993 -0.664 71.8840 -0.658 72.8986 -0.651 73.8947 -0.642 74.8965 -0.597 75.8927 -0.577 78.8912 -0.668 83.9057 -0.647 Table 4: Parameters of the Variable Stars J.D.-2442400 Depth HD Periods R1+R2 m1+m2 P_min* P* T_o* prim.. sec. Type Searched 86441 0.8d-25d 7 Rsun 10 Msun 0.7d 5d73+-0.04d 68.79+-0.05 0.10m 0.05m eclipsing 93206 1.8-15 30 60 2.4 5.98+-(0.10) 72.64+-0.10 0.09 .07 eclipsing 96829 ---- -- -- --- ---- - Deltam~0.02m in 36d ? 115599 0.4-15 5 6 0.5 0.6755+-0.0005 60.89+-0.03 0.07m - Cepheid? 152235 0.4-20 30 60 2.9 2.63+-0.05 69.86+-0.10 0.05 - eclipsing? * P_min = minimum period of a binary with estimated sum of radii (R1+R2) and masses (m1+m2) using Kepler's third law. P = most likely period based on the present data T_0 = epoch of primary minimum (phase zero). [FIGURE 1] Fig. 1 Light curve of HD 86441 [FIGURE 2] Fig. 2 Light curve of HD 93206 [FIGURE 3] Fig. 3 Light curve of HD 96829 [FIGURE 4] Fig. 4 Light curve of HD 115599 [FIGURE 5] Fig. 5 Light curve of HD 152235 A.F.J. MOFFAT Departement de Physique University de Montreal Montreal, P.Q., H3C 3J7 Canada References: Hill, G., Crawford, D.L, Barnes, J.V. 1974, Astron. J., 79, 1271 [BIBCODE 1974AJ.....79.1271H ] Lafler,.J., Kinman, T.D. 1965, Astrophys. J. Sup., 11, 216. [BIBCODE 1965ApJS...11..216L ] Moffat, A.F.J. 1977, Astron. Astrophys., in press. Moffat, A.F.J. and Seggewiss, W. 1977, Astron. Astrophys., 54, 607. [BIBCODE 1977A&A....54..607M ] Stephenson, C.B., and Sanduleak, N. 1971 Publ. Warner & Swasey Obs., 1, No. 1. [BIBCODE 1971PW&SO...1a...1S ] Walker, W.S.G., and Marino, B.F. 1972, I.A.U. Bull. Var. St., No. 681. [IBVS No. 681]