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INFRARED HIGH-RESOLUTION SPECTROSCOPY
OF PLUTO BY SUBARU TELESCOPE
TAKANORI SASAKI
∗
, MASATERU ISHIGURO, DAISUKE KINOSHITA
and RYOSUKE NAKAMURA
Department of Earth and Planetary Science, The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
∗
takanori@eps.s.u-tokyo.ac.jp
Here we report a infrared high-resolution spectroscopy of Pluto in the
L
band.
The spectroscopic observation was performed by the Subaru telescope with
the adaptive optics system. The spectrum is dominated by the strong and
broad absorption features of methane, but includes some additional features.
Comparing the spectrum with model calculations, we suggest that absorp-
tion features could be an indication of nonmethane hydrocarbons on Pluto's
surface.
1. Introduction
Spectroscopic observations of Pluto at visible to 2.5
µ
m have showed absorp-
tion features of solid methane and carbon monoxide diluted by nitrogen ice,
and recently intimated the existence of ethane ice on surface of Pluto.
1
,
2
Only a few groups obtained photometric observations of Pluto at 2.8-4.1
µ
m
range, where they found CH
4
ice absorption bands as well as other features
which were attributed to CO
2
and/or SO
2
ices.
1
However, the spectral res-
olution of their data was insucient confirm the existence of hydrocarbons'
ice, because of diculties deriving precise spectra at wavelengths longer
than 2.5
µ
m with increasing telluric sky brightness. In this study, we report
the additional composition of Pluto's surface from infrared spectroscopy
at 2.8-4.0
µ
m conducted at Subaru telescope with infrared camera and
spectrograph (IRCS)
3
and adaptive optics (AO).
4
We present a spectro-
scopic analysis of this observation as well as numerical modelling of the
spectra.
∗
Corresponding author.
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