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Parametric thermohydraulic calculations for advanced pressurized water reactors with the code HADA-2
Rotationally resolved spectroscopy of (20000) Varuna in the near-infrared
Models of the escape and retention of volatiles by minor icy objects exclude
any presence of volatile ices on the surface of TNOs smaller than ~1000km in
diameter at the typical temperature in this region of the solar system, whereas
the same models show that water ice is stable on the surface of objects over a
wide range of diameters. Collisions and cometary activity have been used to
explain the process of surface refreshing of TNOs and Centaurs. These processes
can produce surface heterogeneity that can be studied by collecting information
at different rotational phases. The aims of this work are to study the surface
composition of (20000)Varuna, a TNO with a diameter ~650km and to search for
indications of rotational variability. We observed Varuna during two
consecutive nights in January 2011 with NICS@TNG obtaining a set of spectra
covering the whole rotation period of Varuna. After studying the spectra
corresponding to different rotational phases, we did not find any indication of
surface variability. In all the spectra, we detect an absorption at 2{\mu}m,
suggesting the presence of water ice on the surface. We do not detect any other
volatiles on the surface, although the S/N is not high enough to discard their
presence. Based on scattering models, we present two possible compositions
compatible with our set of data and discuss their implications in the frame of
the collisional history of the Kuiper Belt. We find that the most probable
composition for the surface of Varuna is a mixture of amorphous silicates,
complex organics, and water ice. This composition is compatible with all the
materials being primordial. However, our data can also be fitted by models
containing up to a 10% of methane ice. For an object with the characteristics
of Varuna, this volatile could not be primordial, so an event, such as an
energetic impact, would be needed to explain its presence on the surface.Comment: 6 pages, 5 figures, to be published in A&
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