Osservazioni nellIR termico dei corpi minori del sistema solare

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Osservazioni nellIR termico dei corpi minori del
sistema solare

• Marco Delbò
• INAF Osservatorio Astronomico di Torino

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Why thermal IR ?
Asteroids and comets are cold objects

• By measuring the thermal emission of asteroids
• Albedos and Sizes (Radiometric technique)
• Physical information such as surface roughness
  and thermal inertia

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Radiometric technique
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Thermal model
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What do we need ?
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Thermal IR multiwavelength coverage

• Allows deriving the temperature of the object
  through a thermal model fit
• A single measurements at 10?m cannot distinguish
  the two temperature distributions

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NEO size distribution
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Our level of knowledge
About 2000 NEOs discovered to-date Less than 60
objects for which we know diameter and albedo
H18 Geom. Albedo0.05 ? D1.5 km H18 Geom.
Albedo0.3 ? D0.6 km
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Asteroid size distribution

• The asteroid size distribution is uncertain for
  objects smaller than 20 30 km

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What we can do with LBT

• Next slides show example targets that we have
  observed with the Keck 1 10m telescope on Mauna
  Kea Hawaii
• LBT thermal IR sensitivity should be very close

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Some examples

• 2002 BM26
• D?0.6 km
• Keck LWS
• Unpublished results
• By R. Binzel (MIT)
• H.W. Harris (DLR)
• M. Delbo (INAF-OATo

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Goals of the project

• Origin of NEOs
• Physically based size distribution

• Correlation with spectral types
• Thermo-Physical properties
• Improve thermal models

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Preliminary results

• Increasing albedo with decreasing size
• Albedos of small objects seem higher than the
  value that one would expect from the taxonomic
  class
• FRM (i.e. very high thermal inertia) can be ruled
  out

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Increasing albedo with decreasing size

• Is this a selection effect ?
• Many low albedo observed at small sizes.
• Targets selected well below the discovery limit
• Does it applies for Main Belt Asteroids ?
• Is this due to some inadequacies in the thermal
  models we adopt?

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Access to a LBT class telescopewill help to
solve these and other related questions
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Exploiting LBT interferometric capabilities

• Simulation of the reconstuction of a asteroid
  surface temperature distribution with LBT

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Asteroid temperature distribution

• 140km _at_ 1AU

A
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LBT psf

• 8.4m PSF
• LBT PSF

P
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Asteroid temperature distribution

• 140km _at_1AU
• IA P
• R IP/(P2u)

A
I
R
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T distrib. Of 1.4km NEA _at_ 0.01AU

• Object
• Blurred
• Reconstruction

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The measured temperature distribution will help
for...
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Calibration of thermal models

• Which assume a temperature distribution up to now

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Study of the Yarkovsky thermal force
Which is due the asimmetrical thermal emission
force
Which causes a secular variation of the asteroid
orbital elements...