Asteroid absolute magnitudes and phase curve parameters from Gaia photometry

Abstract

Aims. We perform light curve inversion for 491 asteroids to retrieve phase curve parameters, rotation periods, pole longitudes and latitudes, and convex and triaxial ellipsoid shapes by using the sparse photometric observations from Gaia Data Release 2 and the dense ground-based observations from the DAMIT database. We develop a method for the derivation of reference absolute magnitudes and phase curves from the Gaia data, allowing for comparative studies involving hundreds of asteroids. Methods. For both general convex shapes and ellipsoid shapes, we computed least-squares solutions using either the Levenberg-Marquardt optimization algorithm or the Nelder-Mead downhill simplex method. Virtual observations were generated by adding Gaussian random errors to the observations, and, later on, a Markov chain Monte Carlo method was applied to sample the spin, shape, and scattering parameters. Absolute magnitude and phase curve retrieval was developed for the reference geometry of equatorial illumination and observations based on model magnitudes averaged over rotational phase. Results. The derived photometric slope values showed wide variations within each assumed Tholen class. The computed Gaia G-band absolute magnitudes matched notably well with the V-band absolute magnitudes retrieved from the Jet Propulsion Laboratory Small-Body Database. Finally, the reference phase curves were well fitted with the H, G1, G2 phase function. The resulting G1, G2 distribution differed, in an intriguing way, from the G1, G2 distribution that is based on the phase curves corresponding to light curve brightness maxima.

Asteroid Photometric Phase Functions From Bayesian Lightcurve Inversion

“…In the field of asteroid photometry, in particular, significant progress has been made recently in what concerns the capability of obtaining efficient processing and reliable interpretation of sparse photometric data. Martikainen et al (2021) carried out an analysis of photometric data combined from ground-based lightcurves and observations published in Gaia Data Release 2 (DR2) in order to invert the data for reliable estimates of shape, rotational properties, and phase curves for a large number of objects belonging to a variety of asteroid taxonomic classes. They derived photometric phase curve slopes, rates of brightness change on the magnitude scale, for more than 300 asteroids in the so-called reference geometry of equatorial illumination and observation (Kaasalainen et al, 2001).…”

“…They derived photometric phase curve slopes, rates of brightness change on the magnitude scale, for more than 300 asteroids in the so-called reference geometry of equatorial illumination and observation (Kaasalainen et al, 2001). Expanding on the study in Muinonen et al (2020), Martikainen et al (2021) provided unequivocal proof that the projection to similar illumination and observation conditions was needed to enable unbiased comparative studies of asteroid phase curves. It is possible to strive towards minimizing the biases by incorporating all practical geometries of illumination and observation (Oszkiewicz et al, 2011).…”

“…We extend the work by Martikainen et al (2021) by providing computational tools for the derivation of asteroid phase functions using fictitious spherical asteroids with equal surface properties. In earlier works, we have described these phase functions as being proper phase functions that describe the intrinsic properties of the surfaces.…”

The effect of aspect changes on Near-Earth Asteroid phase curves

“…Mottola et al (2020) extract the "reference phase curve" for the Lucy mission target (11351) Leucus in order to remove shape and viewing geometry effects from the results using a derived shape model from photometric light curve and occultation observations. Inversion of a large collection of ground-based and Gaia asteroid photometric data was performed by Martikainen et al (2021) to correct for aspect changes to the phase curves through: extraction of the intrinsic shape and scattering properties of the surface, simulation of the "proper phase curve", and subsequent fitting of the 𝐻, 𝐺 1 , 𝐺 2 system to the simulated data. However, large photometric light curve data sets suitable for shape estimation via inversion methods are not typically available for most near-Earth asteroids.…”

Photometry of selected outer main belt asteroids

“…Devogèle et al, 2017;Hanuš et al, 2016;Shevchenko et al, 2009). Martikainen et al (2021) using the model developed by Muinonen et al (2020) have performed modelling and have also obtained shape model, pole coordinates, and phase curve parameters from Gaia photometry for this asteroid.…”