Asteroid Occultations & Light-curve Inversion models

This is based on a paper published in ICARUS this year, with the following authors: Josef Durech, Mikko Kaasalainen, David Herald, David Dunham, Brad Timerson, Josef Hanus, Eric Frappa, John Talbot, Tsutomu Hayamizu, Brian D. Warner, Frederick Pilcher, Adrian Galad

Asteroidal occultations…. Give dimensions of an asteroid (at about 1-km accuracy) as oriented at the time of the occultation

(135) Hertha 2008 Dec 11

(234) Barbara 2009 Nov 21

However occultations only give a single snap-shot However occultations only give a single snap-shot. Difficult to get a full 3-D picture of an asteroid

Light curve analysis

Irregular shape causes rotational light curve variation When polar axis is inclined to the ecliptic, the parts of the asteroid that are ‘visible’ varies, depending on location in orbit Can model the shape of the asteroid using the differing light curves – called ‘inversion models’

Requires accurate measurement of the rotation period, and determination of the direction of the axis of rotation The model gives a shape for the asteroid, but not its size Most models currently are limited to convex surfaces Sometimes more than one model fits the available data

[break to demo 3-D model]

Combining Occultations with inversion models If the 3-D model is generated for the orientation at the time of an occultation, it can be matched. Matching: Puts a definite scale to the 3-D model Discriminates between different models

Very recent example : (516) Amherstia 2011 Apr 18

(516) Amherstia 2011 Apr 18 #1

(516) Amherstia 2011 Apr 18 #2

Hertha against shape model

(3) Juno

5 Astraea

17 Thetis

88 Thisbe

372 Palma

925 Alphonsina