Asteroid Reference Phase Functions from the ATLAS Photometry

The aim of this project is to derive reference phase functions and their parameters using data from the ATLAS survey. The reference phase function corrects for the observation geometry by removing the influence of the asteroid shape by normalizing it to a sphere. (Muinonen et al. 2020)The ATLAS survey performed photometric observations in two filters: cyan (420-650 nm) and orange (560 - 820 nm) for over 180 000 asteroids at phase angles even below 1 deg (Heinze et al. 2018). Mahlke et al. (2021) derived over 1270 000 phase curve parameters using the ATLAS photometry, but they were corresponding to different viewing geometries, so they cannot be directly compared with each other.Traditional phase curves are derived based on lightcurve brightness maximum (or mean) values at a given phase angle. When using sparse photometry (e.g., Gaia, ATLAS), the observational geometry can substantially change between observations and objects. As a result, it is challenging to compare phase curves obtained for different asteroids (even if they were observed at the same epoch). If enough photometry is available, one can account for brightness changes due to shape, rotation, and aspect changes by moving to a reference phase function, which can be directly compared with the phase functions of other objects. (Muinonen et al. 2020, Martikainen et al. 2021, Wilawer et al. 2022)We derive the reference phase functions for ~2750 asteroids with models derived by Ďurech et al. (2020) using ATLAS photometric data. As a result, for each object, we will derive two reference phase functions: one for each ATLAS filter.This work has been supported by grant No. 2017/25/B/ST9/00740 from the National Science Centre, Poland.ReferencesĎurech, J., J. Tonry, N. Erasmus, L. Denneau, A. N. Heinze, H. Flewelling, and R. Vanco. ‘Asteroid Models Reconstructed from ATLAS Photometry’. Astronomy & Astrophysics 643 (November 2020): A59. https://doi.org/10.1051/0004-6361/202037729.Heinze, A. N., J. L. Tonry, L. Denneau, H. Flewelling, B. Stalder, A. Rest, K. W. Smith, S. J. Smartt, and H. Weiland. ‘A First Catalog of Variable Stars Measured by the Asteroid Terrestrial-Impact Last Alert System (ATLAS)’. The Astronomical Journal 156, no. 5 (November 2018): 241. https://doi.org/10.3847/1538-3881/aae47f.Mahlke, Max, Benoit Carry, and Larry Denneau. ‘Asteroid Phase Curves from ATLAS Dual-Band Photometry’. Icarus 354 (January 2021): 114094. https://doi.org/10.1016/j.icarus.2020.114094.Martikainen, J., K. Muinonen, A. Penttilä, A. Cellino, and X.-B. Wang. ‘Asteroid Absolute Magnitudes and Phase Curve Parameters from Gaia Photometry’. Astronomy & Astrophysics 649 (May 2021): A98. https://doi.org/10.1051/0004-6361/202039796.Muinonen, K., J. Torppa, X.-B. Wang, A. Cellino, and A. Penttilä. ‘Asteroid Lightcurve Inversion with Bayesian Inference’. Astronomy & Astrophysics 642 (October 2020): A138. https://doi.org/10.1051/0004-6361/202038036.Wilawer, E, D Oszkiewicz, A Kryszczyńska, A Marciniak, V Shevchenko, I Belskaya, T Kwiatkowski, et al. ‘Asteroid Phase Curves Using Sparse Gaia DR2 Data and Differential Dense Light Curves’. Monthly Notices of the Royal Astronomical Society 513, no. 3 (May 2022): 3242–51. https://doi.org/10.1093/mnras/stac1008.