講演者  : Prof. Philippe Lamy
          (Laboratoire d'Astrophysique de　Marseille, France)
タイトル: A Portrait of Asteroid 2867 Steins 
          - a target of the Rosetta Mission from Visible and 
 	    Infrared Observations -
        
  日時  : 2007年03月29日（木）15:00-16:30
  場所  : 自然科学3号館6階セミナー室 609号室







 I will present the results of a coordinated campaign of visible and
infrared observations aimed at fostering our knowledge of asteroid
2867 Steins in preparation of its flyby by the Rosetta spacecraft in
Sept. 2008, on its way to comet 67P/Churyumov-Gerasimenko. Our data
set includes 22 visible light curves and 14 infrared spectra. Twenty
one light curves were obtained with various ground-based
observatories and an additional one, with the narrow angle camera
(NAC) of the OSIRIS scientific camera aboard Rosetta that
continuously monitored 2867 Steins over 24 hr in March 2006.




 Simultaneous inversion of the 22 light curves allows to generate a
three-dimensional shape model of 2867 Steins with axial ratios a/b =
1.17 and b/c = 1.24, to determine its rotational period (6.0486 ア
0.0004 hr) and the direction of its rotational axis. The infrared
spectra were obtained with the low resolution mode of the Spitzer
space telescope IRS; they extend from 5 to 35 microns and sample the
rotational light curve with a temporal resolution of 30 min. Analysis
using a standard thermal model yield an equivalent diameter of
approximately 5 km, an albedo in the range of 0.35 and a thermal
inertia in the range 100 - 300 SI. 2867 Steins is then classified as
an E-type asteroid, a class of differentiated bodies which
experienced significant heating episodes.