H,G1,G2 photometric phase function extended to low-accuracy data

Abstract We introduce a constrained nonlinear least-squares algorithm to be used in estimating the parameters in the H , G 1 , G 2 phase function. As the algorithm works directly in the magnitude space, it will surpass the possible bias problem that may be present in the existing H , G 1 , G 2 fit procedure when applied to low-accuracy observations with large magnitude variations. With constraints on the photometric phase-curve shape parameters G 1 and G 2 , it guarantees a physically reasonable phase-curve estimate. With a new data set of 93 asteroids, we re-assess the two-parameter version of the H , G 1 , G 2 function. Finally, we introduce a one-parameter version of the phase function that can give a suggestion of the asteroids taxonomic group based only on its phase curve. A statistical model selection procedure is presented that can automatically select between the different versions of the photometric phase functions. An online tool that implements these algorithms is introduced.