Barucci, M. A.M. A.BarucciDalle Ore, C. M.C. M.Dalle OrePERNA, DavideDavidePERNACruikshank, D. P.D. P.CruikshankDoressoundiram, A.A.DoressoundiramAlvarez-Candal, A.A.Alvarez-CandalDOTTO, ElisabettaElisabettaDOTTONitschelm, C.C.Nitschelm2020-12-212020-12-2120150004-6361http://hdl.handle.net/20.500.12386/29032Based on observations carried out at the European Southern Observatory (ESO), Chile (programme 091.C-0057). The project is supported by the French Planetology National Programme (INSU-PNP). C.M.D.O. acknowledges support from the Outer Planets Research grant NASA NNX12AM75G. A.A.C. acknowledges financial support from CNPq and FAPERJ through diverse grants.<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).STAMPAenArticle10.1051/0004-6361/2015261192-s2.0-84948978531000366936800107https://www.aanda.org/articles/aa/full_html/2015/12/aa26119-15/aa26119-15.html2015A&A...584A.107BFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation::PE9_6 Stars and stellar systems