Adaptive optics imaging of a stellar occultation by Titan

Abstract

We present resolved images of the occultation of a binary star by Titan, recorded with the Palomar Observatory adaptive optics system on 20 December 2001 UT. These constitute the first resolved observations of a stellar occultation by a small body, and demonstrate several unique capabilities of diffraction-limited imaging systems for the study of planetary atmospheres. Two refracted stellar images are visible on Titan's limb throughout both events, displaying scintillations due to local density variations. Precise relative astrometry of the refracted stellar images with respect to the unnocculted component of the binary allows us to directly measure their altitude in Titan's atmosphere. Their changing positions also lead to simple demonstration of the finite oblateness of surfaces of constant pressure in Titan's mid-latitude stratosphere, consistent with the only previous measurement of Titan's zonal wind field.

Interferometric measurements of zonal winds on Titan

“…From our data, we cannot confirm that wind changes occurred between 2003 and 2004, even if leading and trailing hemispheres were observed. At 300-km altitude, our equatorial zonal wind velocity of 160 m/s is more in agreement with high latitude jets (160-230 m/s) than with the equatorial zonal wind (100-110 m/s) derived at ∼250 km from occultation measurements (Hubbard et al 1993;Bouchez et al 2003). Our value is very close to the equatorial zonal wind speed (∼180 m/s) computed with a coupled dynamicsmicrophysics model proposed by Rannou et al (2004).…”

“…These authors stated that their wind speed was accurate to an order of magnitude. In 2001, Titan's occultation by a binary star (Bouchez et al 2003) yielded similar equatorial winds with velocities of 110 ± 40 m/s at 0.8 mbar (200-km altitude). High latitude jets of 230±20 m/s and 160±40 m/s are seen at 60…”

Occultations of Astrophysical Radio Sources as Probes of Planetary Environments: A Case Study of Jupiter and Possible Applications to Exoplanets

“…At radio wavelengths, occultations of pulsars by the Sun have measured properties of the solar corona Rankin, 1972, 1973;Weisberg et al, 1976;Bird et al, 1980;Ord et al, 2007). At visible and infra-red wavelengths, occultations of stars by planets and their satellites have measured properties of their atmospheres and rings (Elliot et al, 1977;Bouchez et al, 2003;Sicardy et al, 2006Sicardy et al, , 2016Dias-Oliveira et al, 2015).…”

The 2003 November 14 occultation by Titan of TYC 1343-1865-1

“…The 28 Sgr occultation by Titan in 1989 (Sicardy et al, 1990;Hubbard et al, 1990) yielded temperature profiles for the 300 to 500 km region, the (non-spherical) shape of the stratosphere, measurements of the stratospheric zonal winds, and measurements of haze properties (Hubbard et al, 1993). Tracadas et al (2001) derived an isothermal atmospheric model from an occultation that occurred in 1995, and Bouchez et al (2003) inferred a non-spherical shape for the mid-latitude stratosphere from an occultation that occurred in 2001.…”