Techniques d'observation spectroscopique d'astéroïdes

3
Observing techniques
tel-00785991, version 1 - 7 Feb 2013
Observations from Earth remain the most accessible way to study the small bodies of the Solar System. In
this chapter are overviewed the observing techniques used to obtain asteroid spectra. First, the NASA IRTF
telescope and the SpeX instrument are briefly described. These instruments were used to obtain the spectra
presented in this thesis. The planning of the observations on which I was involved is shown.
The second part of the chapter present the data reduction procedure. The calibration files used for data
reduction are defined. In the end the description of the steps followed for obtaining the spectrum in its final
analyzable form is given.
While several programs (like Marco-Polo-R, Osiris-REx, Hayabusa2) are under development
for space exploration of asteroids and several others are in service (e.g. Rosetta, Dawn),
the choice of their targets is made based on strong groundbased science. However, space-probes
can only visit a very limited number of objects. For a picture of the whole asteroid population,
the study of their global properties and their diversity is required and this can be achieved by
using groundbased telescopes.
3.1 IRTF Telescope and the SpeX instrument
Several large telescopes are equipped with a spectrograph. Some examples among those supporting
research programs for planetary sciences are: the NASA InfraRed Telescope Facility
(IRTF), the European Southern Observatory (ESO) Very Large Telescope (VLT), the ESO New
Technology Telescope (NTT) and Telescopio Nazionale Galileo (TNG).
The NIR spectra presented in this thesis are obtained with NASA IRTF (Fig. 3.1a), a 3.0-
meter telescope located on the top of Mauna Kea - Hawaii. It was built initially to support
the Voyager missions, but today at least 50% of the observing time is devoted to planetary
sciences. The IRTF hosts 6 facility instruments:, SpeX (Fig. 3.1b), NSFCAM2, CSHELL,
MIRSI, Apogee, Moris. These instruments allow imaging, polarimetry, low and high resolution
spectroscopy in the near to mid infrared (0.8 - 30) µm.
SpeX - the most used instrument by planetologists from NASA IRTF telescope, is a low to
medium resolution spectrograph and imager in the (0.8-5.5) µm. It provides spectral resolutions
of R ≈ 1000 - 2000 across 0.8 - 2.4 µm, 2.0 - 4.1 µm, and 2.3 - 5.5 µm, using prism