Geoscience Reference
In-Depth Information
1.8
1.6
1.4
1.2
1
0.8
0.6
0.9
1.2
1.5
1.8
2.1
2.4
Wavelength (micron)
Fig. 1. Relative spectra of 832 Karin: bottom one is the spectrum relative to the first
set, middle one is that relative to the second set, and top one is that relative to the
last set. Spectra are smoothed by running average of five data points. The top and the
bottom spectra are vertically shifted by +0.2 and by
0.2, respectively. We removed
data in the wavelength range where the telluric absorptions were strong and the error
bars are large.
−
light-curve obtained by supporting observations.
13
In comparison with the
light curve, rotational phases of Karin in our observation are 0.30-0.34 (the
first set), 0.35-0.38 (the second set), and 0.45-0.50 (the last set).
Figure 1 shows relative reflectance spectra of Karin. Bottom, middle,
and top spectra in Fig. 1 are those of the first, the second, and the last
observational sets, respectively. There is obvious difference between the top
two and bottom spectra. Near-infrared (0.9-1.4
µ
m) reflectance slope of the
bottom spectra is twice as steep as that of the top spectra. In general, major
color changes with rotation are very rarely observed on asteroids, e.g., only
a little difference in gradients of spectra at different rotational phase was
observed in Vesta.
14
The present color change of Karin would be the biggest
color change ever observed with rotational phase.
The shape of 0.88-2.5
µ
m in the first set's spectrum with a steep slope at
shorter wavelength is consistent with an S-type object. We identified which
S subclass of the classification scheme
15
,
16
can best describe the Karin
spectrum. Since the first set's spectrum of Karin has the peak position of
1
µ
m band shorter than 1.0
µ
m and has an apparent 2
µ
m band, it is placed
among the range of S(III), S(IV), and S(V) classes.
