Characterization of material around the centaur (2060) Chiron from a visible and near-infrared stellar occultation in 2011

Abstract

The centaur (2060) Chiron exhibits outgassing behaviour and possibly hosts a ring system. On 2011 November 29, Chiron occulted a fairly bright star (R~15 mag) as observed from the 3m NASA Infrared Telescope Facility (IRTF) on Mauna Kea and the 2-m Faulkes Telescope North (FTN) at Haleakala. Data were taken as visible wavelength images and simultaneous, low-resolution, near-infrared (NIR) spectra. Here, we present a detailed examination of the light-curve features in the optical data and an analysis of the NIR spectra. We place a lower limit on the spherical diameter of Chiron's nucleus of 160.2±1.3 km. Sharp, narrow dips were observed between 280-360 km from the centre (depending on event geometry). For a central chord and assumed ring plane, the separated features are 298.5-302 and 308-310.5 km from the nucleus, with normal optical depth ~0.5-0.9, and a gap of 9.1±1.3 km. These features are similar in equivalent depth to Chariklo's inner ring. The absence of absorbing/scattering material near the nucleus suggests that these sharp dips are more likely to be planar rings than a shell of material. The region of relatively-increased transmission is within the 1:2 spin-orbit resonance, consistent with the proposed clearing pattern for a non-axisymmetric nucleus. Characteristics of possible azimuthally incomplete features are presented, which could be transient, as well as a possible shell from ~900-1500 km: future observations are needed for confirmation. There are no significant features in the NIR light curves, nor any correlation between optical features and NIR spectral slope.

The 2017 May 20$^{\rm th}$ stellar occultation by the elongated centaur (95626) 2002 GZ$_{32}$

“…Stellar occultations by only five centaurs -Asbolus, Bienor, Chariklo, Chiron and Echeclus-have been recorded so far (Ortiz et al 2020a), and only for three of them (Chariklo, Chiron and, very recently, Bienor -Morales et al, private communication-) multi-chord 1 occultations were obtained. A ring system around the centaur Chariklo (Braga-Ribas et al 2014) and a possible similar structure -still under discussion-around the centaur Chiron (Ortiz et al 2015;Ruprecht et al 2015;Sickafoose et al 2020) have been reported from these multi-chord occultations. This highlights the relevance of observing stellar occultations by the largest centaurs: apart from determining their sizes, shapes, albedos and other physical properties with high accuracy, detecting Orbital elements -a, q, e and i-from JPL-Horizons.…”

The multichord stellar occultation by the centaur Bienor on January 11, 2019

“…During the last years, there has been a growing interest in the centaur population due to the discovery of a ring system around (10199) Chariklo (Braga-Ribas et al 2014). Also, the data of several stellar occultations by (2060) Chiron reveal features similar to those found for Chariklo; although, there is still an open debate on whether these features are attributed to rings (Ortiz et al 2015;Ruprecht et al 2015;Sickafoose et al 2020). The discovery of ring systems has opened a new branch of research to understand how these rings are formed and how they survive around these small bodies.…”

The Transition from the Kuiper Belt to the Jupiter-Family (Comets)

“…In contrast to the larger sawtooth shaped outbursts, the smaller symmetric outbursts may originate from a source region that spans a larger surface area on the nucleus which releases material over a longer period of time, perhaps a few days. Still another mechanism contributing to the changing brightness of Chiron is the presence of rings or ring arcs (also detected around Chariklo (Braga-Ribas et al 2014)), which changes the Centaur's apparent brightness as the aspect of the rings varies from open to edge-on (Sickafoose et al 2020;Fernández-Valenzuela 2022).…”