COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3091 Konkoly Observatory Budapest, 30 September 1987 HU ISSN 0374 - 0676 VARIABILITY OF THE DOUBLE STAR HD 41824 AND ITS MULTIPLICITY Several measurements in the Geneva photometric system with the P7 photoelectric photometer attached to the 70 cm reflecting Swiss telescope at La Silla Observatory in Chile confirm the variability of the double star HD 41824 (HR 2162, CoD -48 2124, CPD -48 777, SAO 217708, NSV 2827). Coordinates in the New Catalogue of Suspected Variables (NSV) by Kholopov et al. (1982) for 1950.0 are: R.A.= 6h 03m 29s, Dec. = -48 27.2'. The star also figures in the Worley-Heintz (1983) catalogue of orbits of visual binary stars. Its period is 463.5 years and the present separation is 2.5". The variability of this star has been announced by Alexander (1970) indicating the amplitude of variation as 0.1 mag. The spectral type given in the Michigan Spectral Catalogue is G6V. The 43 measurements made in the Geneva photometric system (Table 1) do not allow us to propose a model of the observed fluctuations. We note variations of m = 0.05 in 0.1 day and of at least 0.1 over a longer period ( = 400 days). No periodicity has been detected. The values of colour index [B2-V1] are weakly correlated with the magnitudes [V]. The star becomes redder as it becomes fainter (see Fig. 1). The photometric measurements refer to the component stars A and B taken simultaneously. Taking into account the magnitude difference of the components A and B of about 0.3, then the interpretation of magnitudes and colours allows an estimation of the absolute luminosities and the distance (r=23 pc). The resulting photometric parallax confirms the dynamical parallax. Associated with the proper motion, this fact, combined with an estimation of the metallicity suggests that these stars belong to a relatively young population. Observations of the components of this binary have been done on two occasions with the spectrovelocimeter CORAVEL mounted on the Danish 1.5m telescope at La Silla. They show that the component B has a stable radial velocity of 14.1+-0.2 km/s and v.sin(i) estimated at 2.33+-1.66 km/s. In contrast, the velocity of the component A is variable and its lines are broader. At the present time we have the following observations: HJD 2444628.7607 Vr(A) = 12.10 km/s HJD 2444983.7813 Vr(A) = 32.22 km/s with a v.sin(i) of 7.99+-0.75 km/s Thus the component A itself is double. Further observations should be carried out to try to distinguish Aa and Ab. As there is no evidence for an eclipse, the variability of the combined system may arise if one of the three components is a "spotted star". Additional photometric measurements and radial velocities are therefore necessary. [FIGURE 1] Fig. 1. Individual measurements of HD 41824 showing colour [B2-V1] versus apparent magnitude. Unreliable measurements of weight 0 are not included. It should be noted that both components of the visual double were measured together. Table I. No Time (JD) P U-B V-B B1-B B2-B V1-B G-B Q V 24... 1 43211.534 3 1.469 .092 1.124 1.290 .850 1.117 3 6.626 2 43447.789 3 1.449 .074 1.122 1.268 .832 1.100 3 6.618 3 43568.607 3 1.466 .075 1.115 1.270 .822 1.086 3 6.629 4 45706.741 1 1.468 .071 1.126 1.270 .822 1.087 1 6.660 5 45706.758 1 1.475 .067 1.132 1.266 .819 1.080 1 6.639 6 45706.770 1 1.486 .067 1.131 1.277 .823 1.081 1 6.622 7 45706.784 1 1.479 .067 1.125 1.270 .814 1.075 1 6.633 8 45706.794 1 1.481 .071 1.126 1.283 .822 1.088 1 6.615 9 45706.804 1 1.476 .067 1.129 1.275 .816 1.082 1 6.625 10 45706.814 1 1.487 .062 1.137 1.276 .518 1.082 1 6.628 11 45706.824 1 1.469 .058 1.130 1.275 .814 1.078 1 6.624 12 45706.839 1 1.484 .061 1.130 1.273 .812 1.078 1 6.641 13 45712.806 0 1.462 .067 1.131 1.276 .816 1.084 0 6.657 14 45713.623 2 1.481 .071 1.127 1.280 .822 1.093 2 6.628 15 45719.825 1 1.506 .063 1.127 1.267 .818 1.074 0 6.592 16 45725.560 1 1.977 .064 1.124 1.259 .814 1.072 1 6.604 17 45725.585 2 1.479 .072 1.123 1.271 .825 1.084 2 6.608 18 45725.639 2 1.470 .080 1.124 1.273 .827 1.092 2 6.613 19 45725.705 2 1.468 .080 1.123 1.272 .834 1.090 2 6.616 20 45725.783 2 1.453 .075 1.131 1.271 .830 1.091 2 6.614 21 45726.717 3 1.475 .070 1.132 1.264 .817 1.087 3 6.621 22 45726.780 3 1.468 .081 1.131 1.275 .832 1.089 3 6.611 23 45727.585 2 1.487 .083 1.130 1.275 .841 1.106 2 6.607 24 45729.565 4 1.476 .074 1.129 1.270 .831 1.091 4 6.619 25 45729.718 4 1.463 .076 1.127 1.267 .827 1.087 4 6.618 26 46029.797 3 1.462 .089 1.123 1.278 .840 1.105 3 6.581 27 46047.798 3 1.455 .090 1.117 1.273 .837 1.109 3 6.571 28 46048.539 2 1.450 .071 1.124 1.268 .822 1.084 2 6.565 29 46048.578 2 1.462 .090 1.129 1.275 .833 1.106 2 6.566 30 46048.642 2 1.465 .078 1.123 1.274 .837 1.097 2 6.576 31 46048.718 2 1.470 .087 1.122 1.276 .842 1.110 2 6.559 32 46048.782 2 1.469 .083 1.120 1.265 .835 1.103 2 6.575 33 46048.846 2 1.452 .083 1.117 1.269 .833 1.099 2 6.569 34 46050.655 3 1.461 .089 1.129 1.273 .844 1.105 3 6.557 35 46063.539 3 1.460 .082 1.120 1.264 .830 1.088 3 6.568 36 46063.562 3 1.457 .088 1.119 1.272 .847 1.102 3 6.574 37 46063.635 3 1.463 .084 1.121 1.274 .845 1.107 3 6.569 38 46063.860 3 1.441 .091 1.115 1.282 .841 1.112 3 6.572 39 46067.600 3 1.467 .085 1.119 1.273 .837 1.103 3 6.571 40 46067.719 3 1.460 .091 1.125 1.280 .845 1.104 3 6.578 41 46067.824 3 1.456 .091 1.115 1.271 .839 1.103 3 6.580 42 46075.567 1 1.456 .097 1.126 1.275 .850 1.124 1 6.564 43 46076.601 3 1.451 .088 1.118 1.275 .842 1.109 3 6.562 Details on the P7 photometer can be found in Burnet and Rufener (1979), the Geneva photometric system is described by Golay (1980) and Rufener (1981), the CORAVEL technique is shown in Baranne et al. (1979). Z. KVIZ *), M. MAYOR, F. RUFENER Observatoire de Geneve CH-1290 Sauverny SWITZERLAND References: Alexander J.B. 1970, MNASSA 29, 44. [BIBCODE 1970MNSSA..29...44A ] Baranne A., Mayor M., Poncet J.-L. 1979, Vistas in Astronomy 23, 279. [BIBCODE 1979VA.....23..279B ] Burnet M., Rufener F. 1979, Astron. Astrophys. 74, 54. [BIBCODE 1979A&A....74...54B ] Golay M. 1980, Vistas in Astronomy, 24, 141. [BIBCODE 1980VA.....24..141G ] Kholopov P.N. et al. 1982, New Catalogue of Suspected Variable Stars, Nauka, Moscow 1982. [BIBCODE 1982ncss.book.....K ] Rufener F. 1981, Astron. Astrophys. Suppl. Ser. 45, 207. [BIBCODE 1981A&AS...45..207R ] Worley C.E., Heintz W.D. 1983, "Fourth Catalogue of Orbits of Visual Binary Stars", Publ. U.S. Naval Observatory, 2 Ser., 24, Part 7, Washington D.C. [BIBCODE 1983PUSNO..24g...1W ] *) On leave from: School of Physics, University of New South Wales, Kensington, N.S.W. 2033, AUSTRALIA.