New Generation Ground-Based Optical/Infrared Telescopes 731
FIGURE 13 Image of the asteroid 87 Sylvia showing its two
satellites. This image was taken with the European Southern
Observatory 8-m Very Large Telescope at 2.2 micrometers with
an adaptive optics system. The cross marks the location of the
asteroid and the scale bar shown is 0.25 arcseconds. The
diameter of 87 Sylvia is about 280 km, and the diameters of the
satellites are about 7 and 14 km. The orbits of the satellites were
measured in order to determine a density of about 1.2 grams/cm^3
for 87 Sylvia—only 20% higher than the density of water. Thus
87 Sylvia is likely to have a rubble pile internal structure with
20-60% of its volume being empty. (Courtesy of F. Marchis.)
FIGURE 15 Infrared image of 2M 1207 (a brown dwarf and
planet binary system) obtained with one of the 8.2-m VLT
telescopes. The brown dwarf (white) is 100 times brighter than
the planet (red) and both are emitting heat left over from their
formation. Their masses are estimated to be 25 and 5 Jupiter
masses. In this image the infrared colors at wavelengths 3.8, 2.2,
and 1.6 microns are portrayed as red, green, and blue,
respectively. The separation of the objects in the sky is 0.78
arcseconds and this corresponds to a physical separation of
55 AU. (Courtesy Gael Chauvin / ESO).FIGURE 14 Sodium laser guide
star in use at Keck II. The laser
operates at a wavelength of 5890
Angstroms (0.589 micrometers),
and the laser light is propagated
through a smaller telescope
attached to the Keck telescope. It
excites sodium atoms in a layer in
the Earth’s atmosphere at an
altitude of 90 km. The sodium atoms
emit light at the same wavelength as
the laser and this is viewed as an
artificial star by the telescope. (This
is a long exposure photograph. The
laser guide star is barely visible with
the naked eye from this angle. The
lights of the island of Hawaii are
below the clouds. (Courtesy of
Jean-Charles Cuillandre.)