Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.5602h&link_type=abstract
American Astronomical Society, DPS meeting #41, #56.02
Astronomy and Astrophysics
Astronomy
Scientific paper
The Flora asteroid family's size and location on the inner edge of the main belt make it a likely source of NEOs and asteroid-planet collisions; however, reliable determination of Flora membership is inhibited by the family's age and the presence of a large background. We discovered a significant correlation between semimajor axis and asteroid diameter that we interpreted as the prograde spinning remnants of a single collision, disturbed over time by the Yarkovsky effect (Molnar and Haegert 2008, BAAS, 40, 286). The tightness of the correlation requires nearly uniform obliquities among the Floras. We suggested the single-collision model might be tested by an observational survey of Flora obliquities.
The present survey is designed to perform this test. We defined two samples: 1) a Flora-enriched sample of asteroids along the density enhancement in semimajor axis-diameter space, and 2) a control sample of asteroids offset from the enhancement on either side. While a collision is not expected to result in a uniform obliquity distribution, this correlation can also be produced by a uniform time-average obliquity, which we will show is theoretically plausible. We used a time-efficient modification of the epoch method to determine prograde/retrograde spin sense.
We present the spin axis results for ten Flora-enriched sample asteroids (three determined by us, six independently measured by Durech et al. 2009, and one observed by spacecraft). All ten have prograde spin sense. We also present the results for seven asteroids from our control sample; two of these have prograde spin sense and five have retrograde. The presence of retrograde asteroids in the control sample establishes the significance of our prograde Flora result, strongly confirming our model. Their abundance is consistent with an accumulated segregation due to Yarkovsky drift among the background asteroids.
Funded by a Kuiper endowment and a Calvin Research Fellowship.
Haegert Melissa J.
Molnar Larry A.
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