Detection of CN emission from (2060) Chiron

Spectrophotometric observations of (2060) Chiron were obtained. Their primary goal was to look for the subtle differences in color between Chiron and its surrounding coma, and to search for possible absorption or emission features in Chiron's spectrum. The presence of the CN(0-0) emission band was identified. It proves Chiron's cometary nature and breaks the record heliocentric distance for cometary gaseous emission

Studies of asteroids, comets, and Jupiter's outer satellites

The work comprises observational, theoretical, and computational research on asteroids, together with a smaller effort concerning the astrometry of comets and Jupiter's satellites JVI through JXIII. Two principal areas of research, centering on astrometry and photometry, are interrelated in their aim to study the overall structure of the asteroid belt and the physical and orbital properties of individual asteroids. About 2000 accurate photographic positions of asteroids and comets, including a number from the Lowell, Palomar, and Goethe-Link archival plate collections, the last of which was donated to us last winter by Indiana University were measured and published. Charge coupled device (CCD) astrometry of 36 faint targets was undertaken, including 4 comets; JVI, JVII, JVIII, JLX, JXI, and JXII; and 26 asteroids, most of which are Earth-approachers. A deep, bias-correctable asteroid survey (LUKAS), the aim of which is to determine the true spatial distribution of asteroids down to subkilometer diameters was started. A series of eight plates at the UK Schmidt telescope that contain images of asteroids as faint as V approximately 22 mag was obtained. Analysis of microdensitometric scans of two plates has shown that about 98 percent of the asteroid images could be identified completely automatically

Studies of asteroids, comets, and Jupiter's outer satellites

Observational, theoretical, and computational research was performed, mainly on asteroids. Two principal areas of research, centering on astrometry and photometry, are interrelated in their aim to study the overall structure of the asteroid belt and the physical and orbital properties of individual asteroids. Two highlights are: detection of CN emission from Chiron; and realization that 1990 MB is the first known Trojan type asteroid of a planet other than Jupiter. A new method of asteroid orbital error analysis, based on Bayesian theory, was developed

Asteroid orbital error analysis: Theory and application

We present a rigorous Bayesian theory for asteroid orbital error estimation in which the probability density of the orbital elements is derived from the noise statistics of the observations. For Gaussian noise in a linearized approximation the probability density is also Gaussian, and the errors of the orbital elements at a given epoch are fully described by the covariance matrix. The law of error propagation can then be applied to calculate past and future positional uncertainty ellipsoids (Cappellari et al. 1976, Yeomans et al. 1987, Whipple et al. 1991). To our knowledge, this is the first time a Bayesian approach has been formulated for orbital element estimation. In contrast to the classical Fisherian school of statistics, the Bayesian school allows a priori information to be formally present in the final estimation. However, Bayesian estimation does give the same results as Fisherian estimation when no priori information is assumed (Lehtinen 1988, and reference therein)

The 2060 Chiron: CCD photometry

R-band CCD photometry of 2060 was carried out on nine nights in Nov. and Dec. 1986. The rotation period is 5.9181 + or - 0.0003 hr and the peak to peak lightcurve amplitude is 0.088 + or - 0.0003 mag. Photometric parameters are H sub R = 6.24 + or - 0.02 mag and G sub R = + or - 0.15, though formal errors may not be realistic. The lightcurve has two pairs of extrema, but its asymmetry, as evidenced by the presence of significant odd Fourier harmonics, suggests macroscopic surface irregularities and/or the presence of some large scale albedo variegation. The observational rms residual is + or - 0.015 mag. On time scales from minutes to days there is no evidence for nonperiodic (cometary) brightness changes at the level of a few millimagnitudes

Chiron: Evidence for historic cometary activity

The non-asteroidal brightening of (2060) Chiron, first noted by Tholen in 1988 is now ascribed to cometary activity. Photometry since 1988 has revealed a broad surge in brightness that peaked in 1989 about 1.0 mag above the brightness in the mid-1980s. The surge is evidently due to sporatic formation of dust coma, which is itself driven by the presence of extremely volatile ices at or near the surface. CN emission was recently reported. Since Chiron is now nearing perihelion, there is interest in determining whether it has exhibited anomalous brightening in the past, particularly at greater heliocentric distances. Photographic plates dating back to 1895 are known to contain images of Chiron. Using some of these archival material, the initial results are presented for a project to determine Chiron's brightness history over orbital timescales. A particularly homogeneous and high-quality set of plates taken prior to and around the time of Chiron's discovery in Oct. 1977 at the 1.2 m Oschin Schmidt telescope at Mt. Palomar Observatory were examined. Images of Chiron were identified and digitized using a PDS microdensitometer, and images of field stars around Chiron were both similarly digitized and photometrically calibrated using recently acquired B and V band CCD frames. As a result of the present work, eleven new data, including estimated errors, were added between 1969 and 1977. The implications that Chiron can be active at any heliocentric distance in its present orbit suggest that the active volatile is either N2, CH4, or CO, and that a substantial degree of mantling may have developed. Further historical data is presented, the error bars discussed, and possible mechanisms suggested for the observed activity

The 1990 MB: The first Mars Trojan

Asteroid 1990 MB was discovered by D. H. Levy and H. E. Holt during the course of the Mars and Earth Crossing Asteroid and Comet Survey. An orbit based on a 9 day arc and the asteroid's location near Mars' L5 (trailing Lagrangean) longitude led E. Boswell to speculate that it might be in 1:1 resonance with Mars, analogous to the Trojan asteroids of Jupiter. Subsequent observations strengthened the possibility, and later calculations confirmed it. Thus 1990 MB is the first known asteroid in 1:1 resonance with a planet other than Jupiter. The existence of 1990 MB (a small body most likely between 2 and 4 km in diameter) provides remarkable confirmation of computer simulations. These self consistent n-body simulations demonstrated this sort of stability for Trojans of all the terrestrial planets over at least a 2 million year time base. The discovery of 1990 MB suggests that others of similar or smaller diameter may be found. Using hypothetical populations of Mars Trojans, their possible sky plane distributions were modeled as a first step in undertaking a systematic observational search of Mars' L4 and L5 libration regions

Evidence for Distinct Components of the Galactic Stellar Halo from 838 RR Lyrae Stars Discovered in the LONEOS-I Survey

We present 838 ab-type RR Lyrae stars from the Lowell Observatory Near Earth Objects Survey Phase I (LONEOS-I). These objects cover 1430 deg^2 and span distances ranging from 3-30 kpc from the Galactic Center. Object selection is based on phased, photometric data with 28-50 epochs. We use this large sample to explore the bulk properties of the stellar halo, including the spatial distribution. The period-amplitude distribution of this sample shows that the majority of these RR Lyrae stars resemble Oosterhoff type I, but there is a significant fraction (26 %) which have longer periods and appear to be Oosterhoff type II. We find that the radial distributions of these two populations have significantly different profiles (rho_{OoI} ~ R^(-2.26 +- 0.07) and rho_{OoII} ~ R^(-2.88 +- 0.11). This suggests that the stellar halo was formed by at least two distinct accretion processes and supports dual-halo models.Comment: 18 pages, 28 figures, apjemulated, minor corrections and clarifications. Accepted to ApJ on Jan 21, 200

LSST: Comprehensive NEO Detection, Characterization, and Orbits

(Abridged) The Large Synoptic Survey Telescope (LSST) is currently by far the most ambitious proposed ground-based optical survey. Solar System mapping is one of the four key scientific design drivers, with emphasis on efficient Near-Earth Object (NEO) and Potentially Hazardous Asteroid (PHA) detection, orbit determination, and characterization. In a continuous observing campaign of pairs of 15 second exposures of its 3,200 megapixel camera, LSST will cover the entire available sky every three nights in two photometric bands to a depth of V=25 per visit (two exposures), with exquisitely accurate astrometry and photometry. Over the proposed survey lifetime of 10 years, each sky location would be visited about 1000 times. The baseline design satisfies strong constraints on the cadence of observations mandated by PHAs such as closely spaced pairs of observations to link different detections and short exposures to avoid trailing losses. Equally important, due to frequent repeat visits LSST will effectively provide its own follow-up to derive orbits for detected moving objects. Detailed modeling of LSST operations, incorporating real historical weather and seeing data from LSST site at Cerro Pachon, shows that LSST using its baseline design cadence could find 90% of the PHAs with diameters larger than 250 m, and 75% of those greater than 140 m within ten years. However, by optimizing sky coverage, the ongoing simulations suggest that the LSST system, with its first light in 2013, can reach the Congressional mandate of cataloging 90% of PHAs larger than 140m by 2020.Comment: 10 pages, color figures, presented at IAU Symposium 23