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

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. (C) 2015 Elsevier Ltd. All rights reserved.