Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.2201s&link_type=abstract
American Astronomical Society, DPS meeting #40, #22.01; Bulletin of the American Astronomical Society, Vol. 40, p.425
Astronomy and Astrophysics
Astronomy
Scientific paper
Asteroid spin properties determined from observations of rotation lightcurves constrain models of evolution processes. Based on the clustered distributions of the spin vectors of ten Koronis family members (Slivan 2002, Slivan et al. 2003), Vokrouhlicky et al. (2003) suggest that YORP thermal radiation torques have acted on those 20- to 40-km outer main belt objects for 2-3 Gyr, trapping the prograde objects in a spin-orbit resonance. Better understanding of the evolution of the spin properties requires a larger spin vector sample at smaller diameters with reduced selection biases. The first part of a subsequent observational survey to complete the sample of Koronis family spin vectors down to about 20 km diameter (Slivan et al., 2008) yielded spin vectors for three more objects (Slivan et al., submitted). Preliminary pole solutions for an additional eight objects have now been determined from the most recent lightcurves recorded through 2008, for a total of 22 spin vectors in the Koronis family. The sample includes 21 of the brightest 25 Koronis members, plus one 15-km member (Vokrouhlicky et al., 2006). 15 objects are retrograde and 7 are prograde; an excess of retrograde rotators at least this large has a 7% chance of occurring in a random sample of this size from a uniform population. The larger sample exhibits a clustered distribution as before, with most of the retrograde objects having obliquities between 141-180 degrees, and most of the prograde objects having obliquities between 39-56 degrees and similar rotation periods, characteristic of the previously identified prograde spin-orbit resonance. However, several of the new spin vectors fall outside the previous clusters - two retrograde objects have smaller obliquities, and two prograde objects have longer periods and smaller obliquities. Also, a noticeable absence of fast prograde rotators persists.
Binzel Richard P.
Eckelman Laura J.
Hock Andrew N.
Kaasalainen Mikko
Klesman Alison J.
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