Geoscience Reference
In-Depth Information
pulse laser irradiation
8
confirmed Hapke's hypothesis
9
that the reflectance
change forming S-type spectra is caused by formation of nanophase iron
particles within vapor-deposited rim around regolith particles. It was sug-
gested that the degree of space weathering can be used to discuss the age of
asteroids.
8
However, there had been no observational confirmation on the
relation between asteroid age and the degree of the surface alteration. Here,
we have an excellent target. Recently, using numerical integration of aster-
oid orbits, Nesvorny
et al.
revealed a new-born group of asteroids named
Karin cluster group,
10
which is thought to be remnants of a recent breakup
of only 5.8 million years ago.
10
In the present study, we observed the bright-
est asteroids 832 Karin in this group to consider the relation between the
asteroid age and the effect of space weathering.
In this study, we observed the brightest asteroid 832 Karin (diameter
being about 19 km, and absolute magnitude being 11.18
10
) in this group
in order to investigate whether the new asteroid really has fresh and un-
reddened surface.
2. Observations and Data Reductions
A spectroscopic observation of Karin was carried out on September 14, 2003
UT using a cooled infrared spectrograph and camera for OHS (CISCO)
11
with the 8.2-meter SUBARU telescope. The slit size was 108
×
0
.
8
in our
observation, which led no loss of light of the asteroid. The typical seeing
size was 0.3-0.4
during the observation. A nearby G2V star HIP3990 was
observed as a spectroscopic standard. In order to obtain a wide range near-
infrared spectrum, grisms named
zJ
(0.88-1.40
µ
m),
JH
(1.06-1.82
µ
m), and
wK
(1.85-2.51
µ
m) were used.
We obtained one-dimensional spectra of Karin by using the NOAO
Image reduction and analysis facility (IRAF) aperture extraction package.
We obtained OH sky emission lines frames at the end of the night to deter-
mine the linear dispersion for wavelength calibration. Relative magnitudes
were computed using aperture photometry. Then, we scaled relative spec-
tra to be consistent with each other by this photometry. For details refer
to Ref. 12.
3. Results
We observed Karin at 7:57-8:40 UT, 8:46-9:29 UT, and 10:45-11:50 UT.
The rotational period of Karin is 18.348 h, which was derived from a
