"TNOs are Cool'': A survey of the trans‐Neptunian region XII. Thermal light curves of Haumea, 2003 VS2 and 2003 AZ(84) with Herschel/PACS

P. Santos‐sanz , E. Lellouch (1) , O. Groussin , P. Lacerda , T. G. Mueller , J. L. Ortiz , C. Kiss , E. Vilenius , J. Stansberry , R. Duffard , S. Fornasier (1) , L. Jorda (2) , A. Thirouin

1 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
2 LAM - Laboratoire d'Astrophysique de Marseille

Context. Time series observations of the dwarf planet Haumea and the Plutinos 2003 VS2 and 2003 AZ(84) with Herschel/PACS are presented in this work. Thermal emission of these trans‐Neptunian objects (TNOs) were acquired as part of the ``TNOs are Cool'' Herschel Space Observatory key programme. Aims. We search for the thermal light curves at 100 and 160 mu m of Haumea and 2003 AZ(84), and at 70 and 160 mu m for 2003 VS2 by means of photometric analysis of the PACS data. The goal of this work is to use these thermal light curves to obtain physical and thermophysical properties of these icy Solar System bodies. Methods. When a thermal light curve is detected, it is possible to derive or constrain the object thermal inertia, phase integral and/or surface roughness with thermophysical modeling. Results. Haumea's thermal light curve is clearly detected at 100 and 160 mu m. The effect of the reported dark spot is apparent at 100 mu m. Different thermophysical models were applied to these light curves, varying the thermophysical properties of the surface within and outside the spot. Although no model gives a perfect fit to the thermal observations, results imply an extremely low thermal inertia (<0.5 J m(‐2) s(‐1/2) K‐1, hereafter MKS) and a high phase integral (>0.73) for Haumea's surface. We note that the dark spot region appears to be only weakly different from the rest of the object, with modest changes in thermal inertia and/or phase integral. The thermal light curve of 2003 VS2 is not firmly detected at 70 mu m and at 160 mu m but a thermal inertia of (2 +/‐ 0.5) MKS can be derived from these data. The thermal light curve of 2003 AZ(84) is not firmly detected at 100 mu m. We apply a thermophysical model to the mean thermal fluxes and to all the Herschel/PACS and Spitzer/MIPS thermal data of 2003 AZ(84), obtaining a close to pole‐on orientation as the most likely for this TNO. Conclusions. For the three TNOs, the thermal inertias derived from light curve analyses or from the thermophysical analysis of the mean thermal fluxes confirm the generally small or very small surface thermal inertias of the TNO population, which is consistent with a statistical mean value Gamma(mean) = 2.5 +/‐ 0.5 MKS.

Domaines: Astrophysique [astro-ph]

P. Santos‐sanz, E. Lellouch, O. Groussin, P. Lacerda, T. G. Mueller, et al.. "TNOs are Cool'': A survey of the trans‐Neptunian region XII. Thermal light curves of Haumea, 2003 VS2 and 2003 AZ(84) with Herschel/PACS. Astronomy and Astrophysics - A&A, 2017, 604, ⟨10.1051/0004-6361/201630354⟩. ⟨hal-01678514⟩