An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer (see image 1). A stellar occultation by small bodies occurs when an object (asteroid, centaurs, or Trans-Neptunian Object) passes in front of a star (occults a star), temporarily blocking its light. An example of a stellar occultation by the dwarf planet Eris is here.
Image 1: Looking for dimmed starlight — the basic method at work in the Taiwanese-American Occultation Survey (TAOS) survey. Credit: TAOS.
Stellar occultations by small solar system bodies provide a wealth of information such as accurate diameters, albedos, shapes, detection of small satellites and atmospheres. Diameters and albedos are key parameters that have only been measured for a few Trans-Neptunian Objects and with large uncertainties.
In just three years, more than ten occultations by Trans-Neptunian Objects and Centaurs (except Pluto/Charon ones) have been detected. Results about the stellar occultation by Eris have been published in [.pdf]. The event is consistent with a spherical shape for Eris, with radius of 1,16±66km, density of 2.52±0.05 grams per cm³ and a high visible geometric albedo, p~0.96 (Image 2).
Image 2: On the left panel: Three telescopes at two sites (green dots) witnessed the event. Another observatory recorded a near-miss (blue), and several others were clouded out (red). Dashed lines show the occultation’s predicted track. and solid lines show the actual track, which reflect Eris’s smaller-than-expected diameter. On the right panel: shape model of Eris based on 2 chords. Credits: Sky and Telescope, ESO.
Results about the stellar occultation by Makemake have been published in [.pdf]. The preferred shape corresponds to an elliptical object with projected axes of 1,430±9 km and 1,502±45 km, density of 1.7±0.3 grams per cm³ and a high visible geometric albedo, p~0.77 (Image 3).
Image 3: Occultation chords obtained at five different sites plotted in the projected plane of the sky. The axis marked g indicates the north–south direction in the projected plane of the sky; f indicates the east–west direction. Units are milliarcseconds (mas). Credits: [.pdf].
Results about two stellar occultations by Quaoar have been published in [.pdf].
Evidence for ring material around centaur (2060) Chiron have been published here