Bibcode
Pravec, Petr; Vokrouhlicky, D.; Polishook, D.; Harris, A. W.; Galad, A.; Vaduvescu, O.; Pozo, F.; Barr, A.; Longa, P.; Colas, F.; Marchis, F.; Macomber, B.; Pollock, J.; Pray, D. P.
Referencia bibliográfica
American Astronomical Society, DPS meeting #41, #56.06
Advertised on:
9
2009
Número de citas
0
Número de citas referidas
0
Descripción
A population of small main-belt asteroids residing on closely similar
orbits was revealed by Vokrouhlicky and Nesvorny (2008, Astron. J. 136,
280-290). We have estimated statistical significances of individual
pairs (Pravec and Vokrouhlicky 2009, Icarus, in press) and started a
photometry observing program to characterize their spin properties.
Observations of 20 primaries (larger members of asteroid pairs) reveal
that primaries of pairs with small secondaries rotate rapidly, while
primaries of pairs with large secondaries show significantly slower
rotations. Specifically, eight observed primaries of pairs with the
secondary-to-primary size ratio D2/D1 < 0.4
(estimated from the difference between absolute magnitudes of pair
members Delta H > 2.0) show primary rotation periods from 2.5 to 4.4
h, while primaries of pairs with D2/D1 between 0.4
and 0.7 show slower rotations with median period of 7.2 h. The observed
distribution of primary spin rates is consistent with a proposed
formation mechanism of asteroid pairs by a rotational fission of the
parent body or a gentle split of a binary pair. The correlation between
the primary spin and the secondary-to-primary size ratio suggests that a
part of the primary rotational angular momentum is transferred to the
relative motion of the system's components during separation. For
smaller secondaries, an insignificant fraction of the primary's angular
momentum is needed to split the pair; above the largest size ratio (
0.7) there is insufficient spin energy to effect an escape of a pair and
it must remain bound.
This work was supported by the Grant Agency of the Czech Republic, Grant
205/09/1107.