[Paper Review] TNOs are Cool: A Survey of the Transneptunian Region: A Herschel-PACSview of 16 Centaurs

R. Duffárd, N. Pinilla Alonso+14 more|arXiv (Cornell University)|Sep 4, 2013

Astro and Planetary SciencePhysics and Astronomy1 citations

TL;DR

This study presents a radiometric analysis of 16 Centaurs using Herschel-PACS and Spitzer-MIPS photometry to determine their sizes, albedos, and thermal properties. It finds no correlation between albedo or diameter and orbital parameters, but reveals that red Centaurs are small (mean 65 km) and moderately bright (mean albedo 8.5%), while gray objects span a wider size range and are darker (mean albedo 5.6%).

ABSTRACT

Centaurs are the transitional population between trans-Neptunian objects (TNOs) and Jupiter-family comets. For this reason it is possible to access the smaller ones, which is more difficult to do with the TNO population. The goal of this work is to characterize a set of 16 Centaurs in terms of their size, albedo, and thermal properties. We study the correlations, for a more extended sample obtained from the literature, of diameter, albedo, orbital parameters, and spectral slopes. We performed three-band photometric observations using Herschel-PACS and used a consistent method for the data reduction and aperture photometry of this sample to obtain monochromatic flux densities at 70, 100, and 160 $\mu$m. Additionally, we used Spitzer-MIPS flux densities at 24 and 70 $\mu$m when available. We also included in our Centaur sample scattered disk objects (SDOs), a dynamical family of TNOS, using results previously published by our team, and some Centaurs observed only with the Spitzer/MIPS instrument. We have determined new radiometric sizes and albedos of 16 Centaurs. The first conclusion is that the albedos of Centaur objects are not correlated with their orbital parameters. Similarly, there is no correlation between diameter and orbital parameters. Most of the objects in our sample are dark (pv < 7%) and most of them are small (D < 120km). However, there is no correlation between albedo and diameter, in particular for the group of the small objects as albedo values are homogeneously distributed between 4 to 16%. The correlation with the color of the objects showed that red objects are all small (mean diameter 65 km), while the gray ones span a wide range of sizes (mean diameter 120 km). Moreover, the gray objects tend to be darker, with a mean albedo of 5.6%, compared with a mean of 8.5% (ranging from 5 to 15%) for the red objects.

Motivation & Objective

• To characterize the size, albedo, and thermal properties of 16 Centaurs using multi-wavelength photometry.
• To investigate correlations between physical properties (diameter, albedo) and orbital parameters (perihelion, aphelion, inclination).
• To explore relationships between albedo, size, and spectral color (red vs. gray) in the Centaur population.
• To extend the sample by including scattered disk objects and previously observed Centaurs for consistency.
• To provide a homogeneous, radiometric analysis using consistent data reduction and aperture photometry techniques.

Proposed method

• Conducted three-band photometric observations at 70, 100, and 160 μm using the Herschel-PACS instrument.
• Applied consistent data reduction and aperture photometry methods across all 16 Centaurs to derive monochromatic flux densities.
• Incorporated Spitzer-MIPS flux densities at 24 and 70 μm where available for improved radiometric modeling.
• Extended the sample to include scattered disk objects (SDOs) and previously observed Centaurs from prior publications.
• Used radiometric modeling to derive physical parameters such as diameter and geometric albedo from thermal flux measurements.
• Classified objects by spectral slope (red vs. gray) and analyzed correlations with size and albedo.

Experimental results

Research questions

• RQ1 Is there a correlation between the albedo of Centaurs and their orbital parameters such as perihelion distance or inclination?
• RQ2 Does the diameter of Centaurs correlate with their orbital elements or dynamical class?
• RQ3 How do the albedo and size distributions differ between red and gray Centaurs?
• RQ4 What is the relationship between spectral color (slope) and physical properties like diameter and albedo?
• RQ5 Are small Centaurs (D < 120 km) systematically darker or brighter than larger ones?

Key findings

• No significant correlation was found between albedo and orbital parameters of Centaurs.
• No correlation was observed between diameter and orbital parameters across the sample.
• Most Centaurs are dark (geometric albedo pv < 7%) and small (diameter D < 120 km).
• Albedo values for small Centaurs (D < 120 km) are uniformly distributed between 4% and 16%, with no size-albedo trend.
• Red Centaurs have a mean diameter of 65 km and a higher mean albedo of 8.5% (range 5–15%).
• Gray Centaurs span a wider size range and are darker on average, with a mean albedo of 5.6%.