Reanalyzing the visible colors of Centaurs and KBOs: what is there and what we might be missing

Abstract

Visible colors (BVRI) are a reasonable proxy for real spectra of Centaurs and Kuiper Belt Objects, which are rather linear in this range. Colors provide limited information but remain the best tool to study the bulk surface properties. We explore recurrent effects in the study of visible colors: i) how a correlation could be missed or weakened as a result of the data error bars, ii) the "risk" of missing an existing trend because of low sampling, and the possibility of making quantified predictions on the sample size needed to detect a trend at a given significance level, iii) the use of partial correlations to distinguish the mutual effect of two or more parameters, and iv) the sensitivity of the "reddening line" tool to the central wavelength of the filters used. We have compiled the visible colors of about 370 objects available in the literature and carried out an analysis per dynamical family. Our results show how a) data error bars impose a limit on the detectable correlations regardless of sample size and that therefore, once that limit is achieved, it is important to diminish the error bars, but it is pointless to enlarge the sampling with the same or larger errors; b) almost all dynamical families still require larger samplings to ensure the detection of correlations stronger than 0.5; c) the correlation strength between (V-R) vs. (R-I) is systematically lower than the one between (B-V) vs. (V-R) and is not related with error-bar differences between these colors; d) it is statistically equivalent to use any of the different flavors of orbital excitation or collisional velocity parameters regarding the color-inclination correlation of classical KBOs whereas the inclination and Tisserand parameter relative to Neptune cannot be separated from one another; and e) classical KBOs are the only dynamical family that shows neither (B-V) vs. (V-R) nor (V-R) vs. (R-I) correlations.