"TNOs are Cool": A survey of the trans-Neptunian region. XII. Thermal light curves of Haumea, 2003 VS2 and 2003 AZ84 with Herschel/PACS

P. Santos-Sanz, E. Lellouch, O. Groussin, P. Lacerda, T. G. Müller, Jose-Luis Ortiz, C. Kiss, Esa Vilenius, J. Stansberry, R. Duffard, Sonia Fornasier, L. Jorda, A. Thirouin

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Abstract

Context. Time series observations of the dwarf planet Haumea and thePlutinos 2003 VS2 and 2003 AZ84 with Herschel/PACSare presented in this work. Thermal emission of these trans-Neptunianobjects (TNOs) were acquired as part of the "TNOs are Cool" HerschelSpace Observatory key programme.

Aims: We search for the thermallight curves at 100 and 160 μm of Haumea and 2003 AZ84,and at 70 and 160 μm for 2003 VS2 by means of photometricanalysis of the PACS data. The goal of this work is to use these thermallight curves to obtain physical and thermophysical properties of theseicy Solar System bodies.

Methods: When a thermal light curve isdetected, it is possible to derive or constrain the object thermalinertia, phase integral and/or surface roughness with thermophysicalmodeling.

Results: Haumea's thermal light curve is clearlydetected at 100 and 160 μm. The effect of the reported dark spot isapparent at 100 μm. Different thermophysical models were applied tothese light curves, varying the thermophysical properties of the surfacewithin and outside the spot. Although no model gives a perfect fit tothe thermal observations, results imply an extremely low thermal inertia(0.73) for Haumea's surface. We notethat the dark spot region appears to be only weakly different from therest of the object, with modest changes in thermal inertia and/or phaseintegral. The thermal light curve of 2003 VS2 is not firmlydetected at 70 μm and at 160 μm but a thermal inertia of (2± 0.5) MKS can be derived from these data. The thermal lightcurve of 2003 AZ84 is not firmly detected at 100 μm. Weapply a thermophysical model to the mean thermal fluxes and to all theHerschel/PACS and Spitzer/MIPS thermal data of 2003 AZ84,obtaining a close to pole-on orientation as the most likely for thisTNO.

Conclusions: For the three TNOs, the thermal inertiasderived from light curve analyses or from the thermophysical analysis ofthe mean thermal fluxes confirm the generally small or very smallsurface thermal inertias of the TNO population, which is consistent witha statistical mean value Γmean = 2.5 ± 0.5 MKS.Herschel is an ESA space observatory with science instruments providedby European-led Principal Investigator consortia and with importantparticipation from NASA. PACS: The Photodetector Array Camera andSpectrometer is one of Herschel's instruments.
Original languageEnglish
Article numberA95
Number of pages19
JournalAstronomy & Astrophysics
Volume604
DOIs
Publication statusPublished - 14 Aug 2017

Keywords

  • Kuiper belt objects: individual: Haumea
  • Kuiper belt objects: individual: 2003 VS2
  • Kuiper belt objects: individual: 2003 AZ84
  • submillimeter: planetary systems
  • techniques: photometric
  • infrared: planetary systems

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