Ultra-cool companion helps reveal giant planets

[David]

http://www.ras.org.uk/news-and-press/219-news-2012/2121-ultra-cool-companion-helps-reveal-giant-planets


Ultra-cool companion helps reveal giant planets
Last Updated on Thursday, 10 May 2012 09:29

An international team of astronomers led by David Pinfield of the
University of Hertfordshire has found a brown dwarf that is more than
99% hydrogen and helium. Described as ultra-cool, it has a temperature
of just 400 degrees Celsius and its discovery could be a key step
forward in helping astronomers distinguish between brown dwarfs and
giant planets. The researchers publish their work in the journal
Monthly Notices of the Royal Astronomical Society.

This artist’s impression shows BD+01 2920B in the foreground (on the
right hand side), with its host star in the background. The colour and
banded atmosphere of the brown dwarf result from atmospheric gases and
turbulence (click the image for a high-resolution version). Credit: J.
Pinfield, for the RoPACS network at the University of Hertfordshire.
Brown dwarfs are star-like objects with insufficient mass to ignite
hydrogen fusion in their cores. Over time they cool to temperatures of
just a few hundred degrees. Formed like stars from the collapse of a
giant molecular cloud a few hundred light years across, brown dwarfs
in binary systems such as this have the same atmospheric chemistry as
their host star.
In contrast, giant planets form with a more diverse chemistry. Those
in our own solar system first formed as large solid cores, which then
accreted gas from the disk around them. This led to a different
chemistry in their outer layers. For example, when the Galileo
spacecraft entered Jupiter's atmosphere in 1995, it found the
proportion of heavier elements (astronomers call these 'metals') to be
three times higher than in the Sun. Such differences allow astronomers
to discriminate between planets and brown dwarfs and reveal their
formation mechanisms.
Dr Pinfield and his team detected the brown dwarf using data from the
Wide-field Infrared Explorer (WISE) satellite, the UK Infrared
Telescope (UKIRT) in Hawaii and the Visible and Infrared Survey
Telescope for Astronomy (VISTA) in Chile. He carried out this work as
part of his European (FP7) Initial Training Network RoPACS which
studies planets around cool stars.
The newly discovered object, known as BD+01 2920B, is about 35 times
more massive than Jupiter. It orbits its host star at a distance of
390 billion km or about 2600 times the average distance from the Earth
to the Sun.
Searches for planets around other stars find many possible planets
through the gravitational pull of the candidate objects on the stars
they orbit as well as direct imaging using the latest (and future)
optical technology on the largest telescopes. The problem is that
compact brown dwarfs share many characteristics with giant planets, so
astronomers struggle to confirm the nature of what they detect.
The new work has been made possible by combining data from ground- and
space-based surveys, says Dr Pinfield. "Surveys from telescopes like
VISTA and UKIRT and orbiting observatories like WISE are giving us an
unprecedented view of 'ultra-cool' bodies in our neighbourhood."
'By finding these rare objects in orbit around nearby stars, we get a
handle on the bigger picture; that we live in a galaxy where both
giant planets and brown dwarfs are commonplace."