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1995Aj 110.1875C the Astronomical Journal THE ASTRONOMICAL JOURNAL VOLUME 110, NUMBER 4 OCTOBER 1995 110.1875C PHOTOMETRY OF AMOR ASTEROIDS 1036 GANYMEDE AND 1627 IVAR G. R Chernova and N. N. Kiselev Astrophysical Institute, Tajik Academy of Sciences, Bukhoro Strasse 22, Dushanbe 734670, Tajikistan 1995AJ Yu. N. Krugly, D. F. Lupishko, V. G. Shevchenko, and F. R Velichko Astronomical Observatory of Kharkov University, Sumskaya Strasse 35, Kharkov 310022, Ukraine Electronic mail: [email protected] R. A. Mohamed1 Department of Physics and Astronomy, Faculty of Science, University of Garyounis, P. O. Box 9480, Benghazi, Libya Electronic mail: [email protected] Received 1995 February 23; revised 1995 May 22 ABSTRACT The photometric observations of Amor asteroids 1036 Ganymede (BV bands) and 1627 Ivar (V band) were carried out on 10 nights in 1989 May-July and on 19 nights in 1990 May-August, respectively. The obtained composite light curve of Ganymede is markedly asymmetric with an amplitude 0.13 mag. By contrast, Ivar light curves are rather symmetric and show very large amplitude with considerable changes (from 1.05 to 1.4 mag). Magnitude-phase dependences obtained at phase angle ranges of a*« 10°-30° for Ganymede and o:ä*180-540 for Ivar are represented by the coefficients 0.020±0.002 and 0.024±0.002 mag deg \ respectively. © 1995 American Astronomical Society. 1. INTRODUCTION phase angle a. This table also contains the reduced magni- tude V(l,a) of the light curve extremum, notation of the This paper is a continuation of a series of the author’s extremum (see Figs. 1, and 3-5), the number of the compari- publications on the photometry of Earth-approaching aster- son star, and the site where the observations were carried out. oids (Lupishko et al. 1986; Lupishko et al. 1988; Velichko In addition, a data file containing the original observations et al. 1990; Velichko et al. 1992). can be obtained by sending the request to Yu. N. Krugly. New observations of the Amor-group asteroids 1036 Ganymede and 1627 Ivar were carried out with the 1 m reflector of Sanglok Mountain Observatory (SMO) of the 2. RESULTS Institute of Astrophysics in Dushanbe (Tajikistan) and with 2.1 1036 Ganymede the 0.7 m reflector of the Astronomical Observatory of This asteroid is the largest Earth-approaching object. Kharkov University, Ukraine (KhAO). The photoelectric Ganymede is classified as an S-type asteroid (Tholen 1989), measurements of brightness were carried out using the with albedo of 0.14-0.17 and diameter of about 38.5 km method of differential photometry in the BV bands of the standard photometric system. The precision of the measure- ments and the reduction technique of the observations are Table 1. Comparison stars. described in detail by Kayumov et al. (1989) and Velichko Comparison «le V Standard star (1991). star $19 As comparison stars nearest to the asteroid field star (at 1 15Î3878 -3°23' 11759 HD 140850 [O] KhAO) or a nearest photometrical standard star (at SMO) 2 15 30.8 - 1 30 13.04 were used. The photometrical standardization of stars was 3 15 29.0 - 0 55 10.79 4 15 25.3 - 0 13 10.80 made both on the nights when the asteroid was observed and 5 15 19.1 + 111 10.84 HD 136834 [O] after the fulfillment of the whole program of observations. 6 15 15.2 + 1 49 12.26 Ne 2,3 NGC 5904 [©] The equatorial coordinates of the comparison stars referred 7 14 56.9 + 6 08 11.43 Ne 544, 684 SAI07 [©] to the equinox 1950.0, their V magnitudes and the numbers 8 14 57.1 + 6 07 11.93 9 14 20.3 +11 52 9.47 HD 124066A [O] of the photometrical standards are given in Table 1. The co- 10 14 07.8 +13 57 12.65 ordinates of the uncatalogued stars were taken from Atlas 11 14 05.1 +14 15 12.38 Stellarum 1950.0 (Vehrenberg 1970). 12 14 55.5 +15 00 12.35 Table 2 contains the aspect data of the observed asteroids 13 13 46.3 +12 28 11.72 BD+13 2698, HD 121109 [O] for the midtime of the light curve: the ecliptic coordinates X 14 13 46.7 +12 10 9.85 15 13 49.8 +10 49 12.14 and ß, the helio- and geocentric distances r and A, and the 16 13 54.3 + 8 37 11.63 ROSS 838 [O] Note: O, Blanco et al. (1968); ©, Kazanasmas et al. (1982); Address of correspondence: Astronomical Observatory of Kharkov State ©, Moffett & Bames (1979). University, Sumskaya str. 35, Kharkov 310022, Ukraine. 1875 Astron. J. 110 (4), October 1995 0004-6256/95/110(4)/1875/4/$0.90 © 1995 Am. Astron. Soc. 1875 © American Astronomical Society • Provided by the NASA Astrophysics Data System 1876 CHERNOVA ET AL.\ 1036 GANYMEDE AND 1627 IVAR 1876 110.1875C Table 2. Aspect data and the measured magnitudes of the observed asteroids. Comp. Date r A V0(l,<x) Observatory UT AU AU mag Extr. star 1995AJ 1036 Ganymede (1989) 05 16?91 233°2 15?6 2.351 1.362 6.7 - - 1 KhAO 05 23.84 230.7 17.0 2.307 1.331 8.8 - - 2 05 25.87 230.0 17.4 2.294 1.324 9.6 10.01 M 3 05 28.89 228.9 17.9 2.275 1.317 10.9 10.02 M 4 06 02.92 227.1 18.7 2.243 1.310 13.3 10.14 M 5 06 06.88 225.8 19.3 2.218 1.308 15.2 10.14 M 6 07 07.75 219.7 22.0 2.015 1.389 27.7 10.40 M 7,8 SMO 07 08.74 219.7 22.0 2.008 1.394 28.0 10.40 M 07 09.74 219.7 22.0 2.001 1.398 28.3 10.40 M 07 10.73 219.6 22.1 1.995 1.402 28.6 10.39 M 1627 Ivor (1990) 05 01.80 208.3 24.4 1.500 0.530 17.8 13.28 Ml 9 KhAO 05 11.82 204.5 25.2 1.446 0.499 23.9 13.46 Ml 10 05 13.90 203.8 25.3 1.435 0.494 25.3 13.48 Ml 11 05 22.91 201.0 25.1 1.387 0.478 31.7 13.57 Ml 12 O - May 25.87 -0.135 05 23.88 200.8 25.0 1.382 0.476 32.4 13.63 Ml 13 B - May 28.89 -0.120 +A - Jun 6.882.92 -0.0050.000 06 15.76 199.7 22.0 1.272 0.458 46.9 13.94 Ml SMO ■x - Jul 8.747.75 0.2550.260 06 16.88 199.9 21.8 1.267 0.457 47.5 13.83 Ml 14 KhAO A0 - Jul 10.739.74 0.2450.260 06 17.83 200.1 21.6 1.263 0.457 48.0 13.09 Ml 15 06 21.77 200.9 20.8 1.246 0.455 50.1 14.09 Ml SMO Fig. 1. Composite light curve of 1036 Ganymede in 1989 May-July. The 06 22.77 201.2 20.6 1.242 0.454 50.6 14.18 Ml zero phase corresponds to JD 2447715.1967 corrected for light time. 06 22.87 201.2 20.6 1.242 0.454 50.6 14.18 Ml 16 KhAO 06 23.76 201.4 20.4 1.238 0.453 51.0 14.29 Ml SMO 06 29.88 203.5 19.1 1.215 0.449 53.9 14.21 Ml KhAO able to get the complete one-night light curve because the 07 14.75 210.8 15.4 1.167 0.436 59.4 14.76 M2 SMO asteroid opposition was in 1989 May (short nights) and at 07 15.74 211.4 15.1 1.164 0.435 59.7 14.78 M2 negative declination. 07 18.75 213.3 14.2 1.156 0.432 60.6 14.78 M2 The July observations of Ganymede were carried out in 07 19.75 213.9 14.0 1.154 0.431 60.8 14.78 M2 the standard B and V bands at SMO. Color composite light 07 22.76 216.0 13.1 1.147 0.428 61.6 14.78 M2 curve {B-V) is presented in Fig. 1 (upper part). It does not 08 12.70 233.8 5.9 1.123 0.409 64.1 14.89 M2 show noticeable changes (>±0.03 mag). The mean color Note: KhAO, Kharkov Astronomical Observatory; SMO, Sanglok Mountain Observatory. estimation is 0.877±0.015 mag at phase angle £*=28°. The obtained value is a bit greater than the one published by Lupishko et al (1988) (Æ—V=0.84±0.01 mag at a?=19°). However, this difference can be explained by the effect of (Veeder et al 1989; Kiselev et al 1994). The spectrophoto- reddening with the phase angle, which is typical for S aster- metric data point out the existence of silicates on the surface oids. of this asteroid and the absence of large scale variations of the surface mineralogical composition (Chapman & Gaffey m 1979; McFadden et al 1984; Vilas & McFadden 1992). From the analysis of the light curves it is known that the asteroid has a retrograde sense of rotation with period of 10.31 hr (Lupishko et al 1988; Hahn et al 1989).
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