observations of the first known transiting planet, HD209458.
The solid line in the lower panel is a model and the dashed
lines illustrate a variation of the planet diameter by 10%.
The upper panel illustrates a reference star near HD209458 and
shows that, for this particular observation, we achieve an RMS
variation of 0.003 magnitudes.
Our team is
searching for new planets orbiting nearby stars using our very own
Automated Patrol Telescope. On about 30% of the clear nights at
Siding Spring Observatory (near Coonabarabran in northern NSW) we
observe a patch of sky near the plane of the Galaxy. In each image
we take, we can measure the brightness of thousands of stars. Using
a new observing technique developed by Michael Ashley, and data
processing software from our collaborator, Mike Irwin at Cambridge,
we can make these measurements with a precision that is currently
unrivaled by any similar projects being developed elsewhere.
If one of our
target stars hosts a planet in an orbit that is edge-on to our line
of sight, the planet will periodically eclipse (transit) the star.
We can detect this as a slight dip in the apparent brightness of
the star. In favourable cases, the depth of this dip is considerably
greater than our measurement error, and a significant detection
can be made. Such a detection yields the planetary orbital period
and size of the planet. However, other systems, such as binary stars,
can mimic a planetary transit. However, follow-up spectroscopic
observations (measuring periodic changes in the star’s radial
velocity) can determine the orbiting object’s mass, and thus
confirm whether or not it is a planet.
Hidas, John Webb and Michael Ashley