(50000) Quaoar: Surface composition variability

Abstract

<BR /> Aims: The goal of this work is to investigate the composition of the surface of (50000) Quaoar and its spatial variability. <BR /> Methods: We present new continuous spectra from the visible to near-IR (0.3-2.3 μm) obtained with the X-Shooter instrument at the VLT-ESO at four different epochs on the surface of Quaoar. The data represent the highest spectral resolution data ever obtained for this object and the first near-IR dataset acquired in a single exposure over the entire wavelength range. They are complemented by previously published photometric observations obtained in the near-IR (3.6, 4.5 μm) with the Spitzer Space Telescope, which provide an extra set of constraints in the model calculation. Spectral modelling was performed for the entire wavelength range by means of a code based on the Shkuratov radiative transfer formulation and of an updated value of albedo obtained from recent Herschel observations. <BR /> Results: We obtained compositional information for different observed areas that can cover about 40% of the assumed rotational period of 8.84 h. Our analysis helps to prove the presence of CH<SUB>4</SUB> and C<SUB>2</SUB>H<SUB>6</SUB>, as previously reported, along with indications of the possible presence of NH<SUB>3</SUB>·H<SUB>2</SUB>O. New evidence of N<SUB>2</SUB> is inferred from the shift in the CH<SUB>4</SUB> bands. The albedo at the two Spitzer bands suggests there may be CO diluted in N<SUB>2</SUB>, and CO<SUB>2</SUB> for one of the surface locations. <BR /> Conclusions: The spectral similarities indicate the overall homogeneity of the surface composition of one hemisphere of Quaoar, while some subtle variations are apparent when modelling. The presence of NH<SUB>3</SUB>·H<SUB>2</SUB>O would support the idea that Quaoar's surface may be relatively young. <P />Based on observations made with ESO Very Large Telescope under programme ID 091.C-0057(A).