A CONNECTION to STONY METEORITES? MD Hicks1, BJ Buratti1, DL Rabinowitz1, P
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Lunar and Planetary Science XXX 1719.pdf THE DEEP SPACE 1 MISSION TARGET 1992 KD: A CONNECTION TO STONY METEORITES? M. D. Hicks1, B. J. Buratti1, D. L. Rabinowitz1, P. R. Weissman1, A. Doressoundiram1, U. Fink2. 1Jet Propulsion Laboratory, Palomar Observatory-Caltech, MS 183-501, 4800 Oak Grove Drive, Pasadena CA 91109, [email protected]. 2Lunar and Planetary Laboratory, University of Arizona, Tucson AZ 85721. Introduction: Deep Space 1, the first in NASA's New through Johnson BV, Kron R and Gunn I filters (0.44, 0.54, Millennium program, was successfully launched on Oct 24 0.62, 0.80 micron). Each set of observations began with 1998 and currently scheduled to rendezvous with the near- imaging standard star fields [1] obtained over a wide range Earth asteroid 1992 KD in July of 1999. We took advantage of airmasses and stellar types though all filters. 1992 KD of the asteroid's apparition in late 1998 to obtain BVRI filter was considered a viable target once its airmass rose above photometry at a number of telescopes in order to character- 2.0. We cycled though the filters: a typical sequence would ize the physical properties of the object; its size, colors and be R-I-R-V-R-B-R. In this way, we could correct for light- rotational state. We found that the object is significantly curve effects in the color ratios. Often we were forced to smaller than originally predicted, with evidence of a high pause our observations to allow the object to move through amplitude lightcurve with a relatively long period. Though field stars, After the asteroid passed the maximum accept- the object was faint and the data somewhat noisy, the three able airmass we would again take standard star frames, nights of photometric filter observations suggest an asteroid ending our observations with bias and twilight flat field with extremely atypical colors: relatively flat spectral re- exposures as needed. flectance from the V to R filters but very deep absorptions in both the B and I filters. In this sense 1992 KD has colors The data was reduced to instrumental magnitudes using more similar to a sample of pure olivine and/or pyroxene standard techniques with IRAF and the DIGIPHOT software than to the vast majority of main-belt asteroids. packages. For each night, three separate synthetic aperture sizes were selected (typically 11,12 and 13 arcseconds in Observations and data reductions: The apparition of diameter) and an independent reduction was performed in 1992 KD in late 1998 was poorly placed for observers in the each and compared for consistency. In this way, we kept northern hemisphere. As the object moved towards opposi- track of variations in seeing, tracking errors, etc., which tion, passing though a solar elongation of 90 degrees, the could corrupt the data and can give rise to errors much asteroid was already at -11 declination and rapidly moving greater than those given by photon statistics alone. Table 2 south. Therefore, it was never possible to observe 1992 KD presents the calibrated data with the associated error esti- for periods longer than a few hours per night and always at mate used in the analysis. relatively high airmass. Table 1 summarizes the observa- tional geometry of the data presented in this abstract. Nine Table 2: Filter Photometry nights at the telescope where dedicated to this project, with useful data obtained on only four. The facilities utilized for Frame UT Time Air- Filter Mag Error this project where the 200 and 60-inch telescopes on Palo- Num . (hours) Mass mar Mountain in California and the 61-inch Catalina Station ——————————————————— telescope on Mount Bigelow near Tucson, Arizona. Nov 16 087 11.133 1.65 R 20.993 0.047 Table 1: Observational Circumstances 090 11.761 1.51 R 20.964 0.031 Date Site1 r D F 094 12.533 1.42 R 20.968 0.039 V2 (AU) (AU) (Deg) (Mag) Dec 12 ———————————————————————— 186 09.719 1.86 R 19.375 0.019 Nov 16 1998 A 2.400 2.166 24.38 20.23 187 10.071 1.77 R 19.410 0.022 Dec 12 B 2.270 1.770 24.42 19.66 188 10.463 1.70 I 19.401 0.101 Dec 13 B 2.265 1.758 24.40 19.63 189 10.850 1.65 R 19.372 0.028 Dec 23 C 2.214 1.624 23.95 19.40 192 11.958 1.65 V 19.822 0.016 ———————————————————————— 193 12.376 1.69 R 19.444 0.034 1 A: Palomar Mountain 200-inch, B:Catalina Station 61- 194 12.754 1.76 B 20.821 0.016 inch, C:Palomar Mountain 60-inch. 195 13.138 1.86 R 19.319 0.025 2 Visual magnitude as computed from the ephemeris as- suming H=15.5, G=0.15. Dec 13 292 09.439 1.95 R 19.541 0.086 All data were taken with facility CCD imaging systems 293 09.802 1.84 R 19.556 0.020 and standard filter sets. The Arizona data were taken with 294 10.042 1.78 I 19.733 0.192 Harris BVR filters and the interferometric Arizona I filter, 295 10.424 1.70 R 19.420 0.048 with central wavelengths near 0.44, 0.54, 0.63, and 0.82 296 10.807 1.66 V 19.980 0.031 micron, respectively. The Palomar data were taken 297 11.180 1.64 R 19.655 0.051 Lunar and Planetary Science XXX 1719.pdf PHOTOMETRY OF 1992 KD: M. D. Hicks et al. 298 11.567 1.64 B 20.831 0.032 Space 1 flyby, with its capability for high spatial resolution 299 12.120 1.68 R 19.522 0.024 optical imaging as well as UV and near-IR spectroscopy, 300 12.504 1.74 R 19.362 0.010 should be able to answer questions about 1992 KD's origins and composition. Dec 23 526 10.524 1.85 R 18.747 0.029 Lightcurve and Absolute Magnitude: The filter pho- 527 10.745 1.84 I 18.225 0.219 tometry can be used to investigate the rotational properties 528 10.962 1.83 R 19.720 0.058 of this asteroid. Table 4 summarizes the R-band photome- 533 11.292 1.83 V 20.118 0.085 try. For a given night’s observation there was no system- 534 11.504 1.85 R 19.781 0.205 atic variations in the lightcurve, though there was significant 535 11.706 1.87 B 21.071 0.075 night-to-night variations. This leads us to suggest that the 536 12.000 1.90 R 19.801 0.065 period is long relative to a few hours and that the amplitude 537 12.120 1.93 I 19.761 0.212 is high, perhaps greater than one magnitude, suggesting a 538 12.331 1.98 V 19.942 0.103 very elongated object. An absolute magnitude[7] of HR = 542 12.797 2.14 R 19.780 0.064 15.68 was fit to the data which minimized the misfit be- ——————————————————— tween the observed and predicted R-band magnitudes. With the V-R color listed in Table 3, this gives a new esti- Discussion: Given the photometry listed in Table 2 we mate of the absolute magnitude at the V-filter of HV=16.06, can derive reflectance colors for three of the nights of ob- consistent with an object roughly 2 km. in diameter. There servations. These colors, corrected for the solar spectrum, was insufficent phase coverage in our data set to attempt the are presented in Table 3. The most striking aspect of the fitting of a phase coefficient, a cononical value of G=0.15 color of 1992 KD is the extremely deep absorptions in both was assumed throughout. the B and the I filters. Though the error bars are quite large, the absorptions persist are present in the three sets of Table 4: R Filter Magnitudes observations. Much deeper than the typical S-Type asteroid, these absorptions are most consistent with the electronic Date Predicted1 Observed D Mag absorption features found in pure samples of olivine and ——————————————————— pryoxene[2]. These colors are closer to those of ordinary Nov 16 20.41 20.975±0.035 -0.57 chondrite and basaltic achondrites meteorites than those of Dec 12 19.84 19.384±0.047 0.46 the vast majority of main-belt asteroids. Dec 13 19.81 19.509±0.104 0.30 Dec 23 19.58 19.771±0.035 -0.19 1 Table 3: Adopted Colors ——————————————————— 1 Assuming HR =15.68, G=0.15 Date B-R V-R I-R References: [1] Landolt A. U. (1992) Astron. J., 104, —————————————————————— 340-371. [2] Gaffey M. J. et al. (1989) in Asteroids II, 98- Dec 12 0.408±0.045 0.047±0.047 0.349±0.107 127. [3] Hicks M. D. et al. (1998) Icarus, 133, 69-78. [4] Dec 13 0.290±0.109 0.104±0.108 0.558±0.218 Binzel R. P. et al. (1996) Science, 273, 946-948. [5] Rabi- Dec 23 0.268±0.082 -0.108±0.095 0.324±0.212 nowitz D. L. and Hicks M. D. (1998) DPS 20, 16.08. [6] AVG. 0.322±0.075 0.014±0.110 0.410±0.128 Binzel R. P. et al. (1998) LPSC 29, 1222B. [7] Bowell E. et —————————————————————— al.