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Physical Studies of Asteroids C 4. Conclusions metry of the nuelear region of NGC 4594 Jarvis, B.J., Oubath, P.: 1988, Astron. Astro­ in good seeing are urgently needed to phys., in press. The major new finding of this study is put new eonstraints on this problem. Kormendy, J.: 1988, Astrophys. J 325, 128. the diseovery of a large mass eoneen­ Kormendy, J., Illingworth, G.: 1982, Astro­ tration at the eentre of NGC 4594. Our phys. J, 256, 460, KI. strongest evidenee is the deteetion of a Acknowledgements Sargent, W. L. W., Young, P.J., Boksenberg, sharp rise in the observed veloeity dis­ A., Shortridge, K., Lynds, C. R., Hartwick, We gratefully aeknowledge the ESO O.A.: 1978, Astrophys. J 221, 731. persion of at least 59 km S-1 within the teleseope time that has been alloeated Schechter, P. L.: 1983, Astron. J Supp. 52, eentral 3':5, although this is probably a to this projeet. 425. lower limit. Under the assumption of Schweizer, F.: 1978, Astrophys. J 220, 98. spherieal symmetry and an isotropie Whitmore, B. C., Kirshner, R. P., Schechter, veloeity distribution, the mass eontained References P. L.: 1979, Astrophys. J 234, 68. within r = 3':5 of the eentre of NGC 4594 Burkhead, M. S.: 1986, Astron. J 91, 777. Williams, T. B.: 1977, Astrophys. J. 214, 685. is M = 1.3 x 109 MG' Higher spatial Dressler, A., Richstone, 0.0.: 1987, Astro- resolution kinematie and surfaee photo- phys. J 324, 701. Physical Studies of Asteroids C. -I. LAGERKVIST, G. HAHN, M. LlNOGREN and P. MAGNUSSON, Astronomiska Observatoriet, Uppsala, Sweden Introduction lar, may be tested against the wealth of sion of the full photometrie information Photometrie and speetroseopie ob­ spin rates that have been obtained from to interpretable constraints on shape servations of asteroids give important photometry. If observations of an object and albedo variegation. information on the physieal properties of are earried out at several oppositions, The M-type asteroids have attraeted these bodies and inerease our under­ the differing viewing geometry gives special attention from us in Uppsala standing of the origin and evolution of three-dimensional information wh ich sinee they seem to have different rota­ the asteroids. The 50-em, 1-m and enables us to derive the axis and sense tional properties from asteroids of other 1.5-m teleseopes and the Sehmidt tele­ of rotation (6). Sueh pole information is types (1, 5). In this report only the varia­ seope at ESO, Chile, have for almost ten of importance in the interpretation of tion of spin rate with the mean distanee years been used by us for sueh obser­ most physical observations of asteroids from the sun will be discussed briefly. vations. These observations have so far (e. g. radar, infrared, ete.) as soon as Figure 1 shows this variation for as­ resulted in more than 20 seientifie pa­ the "spherical-featureless-nonrotating­ teroids of type Sand C. We use only pers. Referenees to these may be found model" is abandoned. One goal with data for asteroids smaller than 140 km in (1). Here only a short summary of these observations is to obtain an inver- in diameter sinee larger objeets show a these results will be given. Spin Properties of Asteroids Spin Rote The ESO 50-em teleseope has been 3 used for UBV and UBVRI photometry of asteroids with the intention of deriving 3/1 512 lighteurves and broadband eolours. 2.8 These lighteurves give information about spin rates, and the lighteurve am­ plitudes give a hint of the asteroidal 2.6 shapes. The study of eolours and mag­ nitudes as a funetion of solar phase 2.4· S Asteroids angle (phase eurve) give important eon­ straints to the light seattering properties of the surfaee material. One night or a 2.2 few eonseeutive nights of observations usually give a full eoverage over all rota­ ..' tional phases and enable an unambig­ 2 \i\ ous eonstruetion of a eomposite light­ eurve. The amplitude of this eurve, 1.8 whieh ean amount to several tenths of a magnitude, gives important statistical information on asteroid shapes and al­ 1.6 bedo variegation (1, 4). Scenarios for the 2.3 2.4 25 26 27 2.8 29 3 3.1 3.2 collisional evolution of the asteroid belt Mean Distonce in general, and asteroid dynamieal Figure 1: Running mean of spin rate (rev.lday) versus mean distance from the sun (AU) for S families and other subelasses in particu- and C asteroids. The bin sizes are 15 and 10 objects, respectively. 21 0.70 shows a steep rise of spin rate towards the inner edge of the main asteroid belt 0.65 and a minimum (though statistieally un­ eertain) near the 3 : 1 Kirkwood gap at Type 0.60 2.5 AU. Possibly a seeond minimum may be present at 2.8 AU where the 0.55 • NEr:l 5 : 2 resonanee gap is loeated. The gen­ .1943 J eral trend for the C-type asteroids o seems to be the same but more data are 0.50 Comees I needed to eonfirm these findings. Both ~ 1627 2368. data on small asteroids, asteroids at the 0.45 1862 • 1986 DA ...., 43'f resonanees, and data for distant as­ .1685 SC Nl teroids are desireable and will hopefully O. 40 2201 :. 0 - AR • • • RIO c· S be obtained in the near future. 1915 1866 j HO KK .2100 0.35 OSB --< 1036• .1979 VA JHK Photometry 0.30 Broadband photometry gives eolour 3200 indices wh ich may be used for dividing 0.25 • asteroids into different taxonomie elasses. An extension of the elassifiea­ tion eriteria into the infrared region of the -0. 10 0.00 O. 10 O. 30 speetrum is important sinee several ab­ H - K sorption features that are eharaeteristie Figure 2: JHK c%urs in magnitudes tor Near-Earth asteroids and comets. (G2: Gehre/s 2, SG: for the various taxonomie types are pre­ Swift-Gehre/s, H.: Howell, B: Baweil, SB: S/aughter-Burnham, KK: Kearns-Kwee, R 1: Rein­ sent at these wavelengths. JHK obser­ muth 1, S: Shoemaker, N1: Neujmin 1, AR: Arend-Rigaux). vations of asteroids give thus a possibil­ ity to improve the definition of the tax­ onomie types and to look for interesting strong eorrelation between spin-rate C-type asteroids and 55 S asteroids absorption features. The 1-m teleseope and size (1). The running means of spin with weil determined periods. There is a was used during 1984-1986 to obtain rate has been plotted using data for 36 peeuliar trend for the S group whieh JHK eolours for 74 main belt asteroids 37 Fides 1.9 Date ROlational wavelenfh 1.8 phase range () 1.7 March 71986 0.00 4000 -7200 March 71986 050 4000 -7200 1.6 March 81986 0.18 4000 -7200 March 91986 0.45 5900 - 8900 1.5 March 10 1986 0.70 5900 - 8900 March 10 1986 0.22 5900 - 8900 1. 4 March 10 1986 0.44 5900 - 8900 March 111986 0.95 4000 -7300 1. 3 March 11 1986 0.21 4000 -7300 March 111986 0.61 4000 -7300 QJ 1. 2 u C 1. l (0 -' u 1.0 QJ '- O. 9 QJ 0::: 0.8 0.7 0.5 0.5 0.4 O. 3 0.2 O. 1 4000 5000 6000 7000 8000 9000 Wavelength in Rngstroms Figure 3: lOS spectra tor asteroid 37 Fides. 22 and 3 Apollo asteroids. Combined with previously published observations this gives a total sampie of 151 asteroids with known JHK colours (2). Here we discuss only the results concerning the Apollo asteroids. Figure 2 shows J-H versus H-K for near-Earth asteroids and for comets. From the figure may be seen that there is a large spread in the JHK colours for these asteroids, maybe re­ flecting a variety of surface materials and different origins. Almost half the ob­ jects fall into the S-type domain wh ich long seemed to be the dominating type among this kind of asteroids. The as­ teroids 1627 Ivar, 2368 Beltrovata and 1986 DA have almost identical JHK col­ ours and lie in the part of the diagram where D-type asteroids and comets are found. These results are even more evident for the asteroids 2100 Ra­ Shalom and 1979 VA rendering them candidates for being extinct cometary nuclei. lOS Spectra of Asteroids Spectra of asteroids give important contributions to the knowledge about Figure 4: The first pieture of asteroid 2100 Ra-Shalom was taken with the ESO Sehmidt teleseope on Oelober 2, 1975 (see also the Messenger No. 15, page 17). During the 60-min the composition of the surfaces of the exposure, it moved more than 5 areminutes. By eoineidenee, it was seen in front of the asteroids and a possibility to study al­ Seulptor dwarf galaxy. bedo variegations. IDS and Reticon spectra were obtained with the ESO 1.5-m telescope during 1985-1986 and a total of 148 spectra of 45 asteroids were obtained. Additional CCD spectra References have also been obtained. The spectral teroids (7) there are still many interesting (1) Lagerkvist, C.-I., Hahn, G., Magnusson, range was normally 3800-9000 Aand a questions that are not settled yet. We P., Rickman, H.: 1987, "Physical studies typical resolution was 172 Nmm. The still lack data on small asteroids to draw of asteroids XVI: photoelectric photome­ intention was to cover as many asteroid conclusions about spin properties of try of 17 asteroids", Astron. Astrophys. types as possible in order to make it these asteroids. Outer-belt asteroids Suppl.
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