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

Abstract

Since the discovery of the Kuiper belt, broadband surface colors were thoroughly studied as a first approximation to the object reflectivity spectra. Visible colors (BVRI) have proven to be a reasonable proxy for real spectra, which are rather linear in this range. In contrast, near-IR colors (JHK bands) could be misleading when absorption features of ices are present in the spectra. Although the physical and chemical information provided by colors are rather limited, broadband photometry remains the best tool for establishing the bulk surface properties of Kuiper belt objects (KBOs) and Centaurs. In this work, we explore for the first time general, recurrent effects in the study of visible colors that could affect the interpretation of the scientific results: 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 -assuming the sample is unbiased; iii) the use of partial correlations to distinguish the mutual effect of two or more (physical) parameters; and iv) the sensitivity of the "reddening line" tool to the central wavelength of the filters used. To illustrate and apply these new tools, we have compiled the visible colors and orbital parameters of about 370 objects available in the literature − assumed, by default, as unbiased samplesand carried out a traditional analysis per dynamical family. Our results show in particular 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, that is, correlations that may explain ∼25% or more of the color variability; 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 famous color-inclination correlation among classical KBOs − which no longer appears to be a strong correlation -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. It therefore is the family with the most unpredictable visible surface reflectivities.

OSSOS. V. Diffusion in the Orbit of a High-perihelion Distant Solar System Object

“…Colors similarly just redward of solar are seen for comparably sized H∼6-7 objects in other dynamically excited TNO populations (Sheppard 2010;Fraser & Brown 2012;Peixinho et al 2015;Wong & Brown 2017). The color of 2013 SY 99 implies that it has a low albedo of p=0.05±0.03 (Fraser et al 2014;Lacerda et al 2014).…”

Physical Observations of (196256) 2003 Eh1, Presumed Parent of the Quadrantid Meteoroid Stream

“…a Number of objects in the population. b The weighted mean of measurements from Peixinho et al (2015), Luu 2001 andBauer et al 2003 are included), (3) Jewitt (2005), (4) Jewitt (2002), (5) Szabó et al (2007), (see also Karlsson et al 2009), (6) Fitzsimmons et al (1994), (7) Hsieh et al (2004Hsieh et al ( , 2009Hsieh et al ( , 2010Hsieh et al ( , 2011Hsieh et al ( , 2013Hsieh et al ( , 2015, Jewitt et al (2009), (8) object into an excited rotational energy state. We estimated the timescale for rotational excitation of 2003 EH1 assuming continuous mass loss at the maximum rate allowed by our data and using the formalism described in Jewitt (1997).…”

Col-OSSOS: z-Band Photometry Reveals Three Distinct TNO Surface Types

“…TNOs, in general, have red optical colors in g-, r-, and i-bands; even the "neutral" TNO surfaces, sometimes referred to as "blue" in the literature, are slightly redder than solar. It is well accepted that the small dynamically excited TNOs and Centaurs exhibit a bimodal color distribution, with red and neutral classes (e.g., Tegler & Romanishin 1998;Peixinho et al 2003Peixinho et al , 2012Peixinho et al , 2015Tegler et al 2003Tegler et al , 2016Wong & Brown 2017).…”