The photometric lightcurve and phase curve of an asteroid refer to the dependences of the asteroid’s disk-integrated brightness on time and on the phase angle (the Sun-Object-Observer angle), respectively. They depend on the shape and rotation state of the asteroid, as well as the surface scattering properties. It follows that the shape, rotation state, and scattering properties can be estimated from the observations, to an extent allowed by the data available. We study the feasibility of retrieving phase curve parameters via statistical lightcurve inversion from the sparse asteroid photometry available from Gaia Data Release 2. We utilize triaxial Lommel-Seeliger ellipsoids as well as convex and non-convex shapes. With the help of the H, G1, G2 photometric function, we devise a surface scattering phase function that gives rise to realistic disk-integrated phase curves. This allows us to derive so-called proper phase curve parameters that allow for photometric classification of asteroids.

Asteroid proper phase curves from Gaia photometry

An asteroid's lightcurve, i.e., its observed diskintegrated brightness as a function of time, depends on the shape and spin state of the asteroid, as well as its surface scattering properties. It follows that these properties can be estimated from the observations, to an extent allowed by a given data set. The phase curve of the asteroid refers to the dependence of diskintegrated brightness on the phase angle (the SunObject-Observer angle). In the present work, we study reference phase curves that are extrapolated to equatorial illumination and observation of the given asteroid. We show that the reference phase curves, with realistic error bars, can be efficiently derived through statistical lightcurve inversion. These phase curves can have substantial value in asteroid taxonomy.

O. Wilkman

Papers

Asteroid lightcurve inversion with Bayesian inference: Reference phase curves