Short-term variability of a sample of 29 trans-Neptunian objects and Centaurs

TL;DR

This six-year systematic study of 29 trans-Neptunian objects and Centaurs reveals smaller-than-expected photometric variability, suggests a correlation between size, shape, and rotation, and estimates average densities around 0.92 g/cm³.

Contribution

The paper provides new and reanalyzed lightcurve data for 29 objects, revealing lower variability and offering insights into their rotation and density characteristics.

Findings

Photometric variability is smaller than previously thought.

Smaller objects tend to have larger amplitudes and faster spins.

Average rotation period is around 7.5 hours, with densities near 0.92 g/cm³.

Abstract

We present results of 6 years of observations, reduced and analyzed with the same tools in a systematic way. We report completely new data for 15 objects, for 5 objects we present a new analysis of previously published results plus additional data and for 9 objects we present a new analysis of data already published. Lightcurves, possible rotation periods and photometric amplitudes are reported for all of them. The photometric variability is smaller than previously thought: the mean amplitude of our sample is 0.1mag and only around 15% of our sample has a larger variability than 0.15mag. The smaller variability than previously thought seems to be a bias of previous observations. We find a very weak trend of faster spinning objects towards smaller sizes, which appears to be consistent with the fact that the smaller objects are more collisionally evolved, but could also be a specific feature of the Centaurs, the smallest objects in our sample. We also find that the smaller the objects, the larger their amplitude, which is also consistent with the idea that small objects are more collisionally evolved and thus more deformed. Average rotation rates from our work are 7.5h for the whole sample, 7.6h for the TNOs alone and 7.3h for the Centaurs. All of them appear to be somewhat faster than what one can derive from a compilation of the scientific literature and our own results. Maxwellian fits to the rotation rate distribution give mean values of 7.5h (for the whole sample) and 7.3h (for the TNOs only). Assuming hydrostatic equilibrium we can determine densities from our sample under the additional assumption that the lightcurves are dominated by shape effects, which is likely not realistic. The resulting average density is 0.92g/cm^3 which is not far from the density constraint that one can derive from the apparent spin barrier that we observe.