Techniques d'observation spectroscopique d'astéroïdes

126 CHAPTER 7. SPECTRAL PROPERTIES OF MAIN BELT ASTEROIDS
Relative Reflectance
1.4
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
(3623) Chaplin
0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
Wavelength [um]
(a)
Relative Reflectance
1.6
1.5
1.4
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
(3623) Chaplin
0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
Wavelength [um]
(b)
Figure 7.5: The NIR spectra of (3623) Chaplin; a) obtained in March 12, 2007; b) obtained in March 13, 2007.
The spectra are normalized to 1.25 µm.
tel-00785991, version 1 - 7 Feb 2013
Applying the Cloutis mineralogical model, the following parameters can be found: BI center
is at 0.9803±0.0111 µm, BII center is at 1.9630±0.0116 µm, and the BAR is 0.3317±
OPX
0.0036. These values imply an
OPX+OL
⋍ 0.19. The results of the model suggest a mineralogy
similar with ordinary chondrites LL subtype. It agrees with the results found from the
comparison with laboratory spectra.
This spectrum was analyzed by Birlan et al. [2011] using the modified Gaussian model
(MGM) procedure [Sunshine & Pieters, 1993]. The procedure allows the quantitative characterization
of absorption features, by simultaneous fitting of multiple Gaussian-like absorption
bands [Pieters & McFadden, 1994]. This analysis strongly indicate that the presence of both
olivine and pyroxene are necessary for reproducing the observational data of (1333) Cevenola.
The mineralogical solution corresponds to fayalitic material with the molar percentage equal
to 20±5 [Sunshine et al., 2007] and the width of these absorption bands span the same range
as presented by Sunshine & Pieters [1998]. However, the strength ratio between the M1 and
M2 olivine crystals is different from the calibration values proposed by Sunshine et al. [2007].
This imply that mineralogies with fayalitic-forsteritic components need to be completed with
other components.
7.4.2 (3623) Chaplin
(3623) Chaplin belongs to the Koronis family [Zappala et al., 1995, Mothé-Diniz et al., 2005].
The asteroid has the synodic period of 8.361±0.005 hrs, and a large amplitude in its composite
lightcurve estimated to 0.97±0.02 mag. [Birlan et al., 1996b]. However, there is no estimation
for its pole coordinates.
Two NIR spectra of the asteroid, presented in Fig 7.5a and Fig 7.5b were obtained at a
time interval of about 23 hours. The spectrum of March 12, 2007 is the result of combined