"First Results from the TaiwaneseAmerican Occultation Survey TAOS

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"First Results from the Taiwanese-American
Occultation Survey (TAOS) Z. W. Zhang,...M. J.
Lehner, ...J. H Wang, ...S. K. King, T. Lee,
...S. Y. Wang , C. Y. Wen Institute of Astronomy
and Astrophysics Astrophysical Journal 685
L157L160 (2008)
The Taiwanese-American Occultation Survey (TAOS)
project is a unique system in the world dedicated
to a systematic study of the small objects in the
outer Solar System. With multi-telescopes in
monitoring stellar brightness of hundreds of
stars at 5 Hz rate, a possible change in the
brightness of a distant star, which might be an
occultation by a foreground Kuiper belt objects
(KBOs) can be detected. Coincide detection of the
brightness change of all telescopes effectively
rejects false positives and the total number of
KBOs can be estimated. More than a thousand of
KBOs have been identified so far. However, they
are too far from the Sun that the light reflected
back is too weak to be detectable for the smaller
ones. With the technology of stellar occultation,
the TAOS project is capable of sensing a distant
KBO down to a size smaller than one kilometer,
which cannot be seen directly by any telescopes
on the Earth. TAOS is a collaboration made up
of Institute of Astronomy and Astrophysics,
National Central University, the
Harvard-Smithsonian Center for Astrophysics, and
Yonsei University in Korea. Four 50-cm telescopes
were installed at the Lulin Observatory. The data
first released was taken from 2005 to 2006, which
includes seven billion of brightness
measurements, shows no statistically significant
event. We are thus able to place the strongest
upper bound to date on the number of KBOs with
0.5 km gt D gt 28 km. This new limit is three
orders of magnitude smaller than the most
recently published limits. It indicates that the
number of small objects in the outer Solar System
is not that much as was predicted in some
theories. That, in turn, provides an important
clue to the formation of the Solar System and its
evolution in the early stage.
Figure 1. The TAOS telescopes at Lulin
observatory.
Figure 3. TAOS images (two telescopes) of the
occultation of HIP050525 (mv8.46mag) by the
asteroid (1723) Klemola (mv15.7magD31km).
Figure 2. TAOS upper limit to the KBO size
spectrum (solid line) assuming a power-law
distribution.