Photometric analysis for the slow rotating asteroid (103) Hera using convex inversion and Lommel-Seeliger ellipsoid methods

Abstract

The shapes and rotational states of main-belt asteroids are important for understanding their formation and evolution. Available photometric data of asteroids are biased due to selection effects, including the relative paucity of analyses of slowly rotating objects. In order to get photometric data of slowly rotating asteroids, an international joint observation project has been carried out since 2015 using Chinese and SARA (Southeastern Association for Research in Astronomy) telescopes. In this paper, the photometric data of one of this project targets – (103) Hera were analyzed using the convex inversion method and Lommel-Seeliger ellipsoid model. Combining existing and new photometric data, we re-calculated the shape and spin parameters for (103) Hera. Using a convex shape method, a pair of poles are derived for (103) Hera – (83.0∘,39.0∘) and (269.7∘,56.8∘) in ecliptic frame. The spin periods corresponding to these poles are very close – 23.74264 h and 23.74267 h respectively. Meanwhile, the same data were analyzed using the Lommel-Seeliger ellipsoid inversion method and a pair of pole solutions – (74.1∘,39.0∘) and (263.1∘,51.0∘) with a spin period of 23.74262 h and 23.74263 h respectively are derived. Based on the derived shape of (103) Hera, we have fitted the H, G1, G2 phase function using the calibrated data after removing effects of aspheric shape. As a result, we estimated its absolute magnitude H = 8.92 mag with two phase function parameters G1 = 0.13 and G2 = 0.45.