Astronomers Discover Youngest and Lowest Mass Dwarfs

Astronomers have found three brown dwarfs with estimated masses of
less than 10 times that of Jupiter, making them among the youngest and
lowest mass sub-stellar objects detected in the solar neighborhood to
date.

The observations were made by a team of astronomers working at the
Laboratoire d’Astrophysique de l’Observatoire de Grenoble (LAOG),
France, using the Canada-France-Hawaii Telescope (CFHT). Andrew
Burgess will be presenting the discovery at the European Week of
Astronomy and Space Science at the University of Hertfordshire,
Hatfield, on Wednesday 22nd April.

The dwarfs were found in a star forming region named IC 348, which
lies almost 1000 light years from the Solar System towards the
constellation of Perseus. This cluster is approximately 3 million
years old — extremely young compared to our 4.5 billion year old Sun
— which makes it a good location in order to search for the lowest
mass brown dwarfs. The dwarfs are isolated in space, which means that
they are not orbiting a star, although they are gravitationally bound
to IC 348. Their atmospheres all show evidence of methane absorption
which was used to select and identify these young objects.

“There has been some controversy about identifying young, low mass
brown dwarfs in this region. An object of a similar mass was
discovered in 2002, but some groups have argued that it is an older,
cooler brown dwarf in the foreground coinciding with the line of
sight. The fact that we have detected three candidate low-mass dwarfs
towards IC 348 supports the finding that these really are very young
objects,” said Burgess.

The team set out to find a population of these brown dwarfs in order
to help theoreticians develop more accurate models for the
distribution of mass in a newly-formed population, from high mass
stars to brown dwarfs, which is needed to test current star formation
theories. The discovery of the dwarfs in IC 348 has allowed them to
set new limits on the lowest mass objects.

“Finding three candidate low-mass dwarfs towards IC 348 backs up
predictions for how many low-mass objects develop in a new population
of stars. Brown dwarfs cool with age and current models estimate that
their surfaces are approximately 900-1000 degrees Kelvin (about
600-700 degrees Celsius). That’s extremely cool for objects that have
just formed, which implies that they have the lowest masses of any of
this type of object that we’ve seen to date,” said Burgess.

Images can be found at:
http://www.caelumobservatory.com/gallery/n1333abtp.shtml

An annotated image showing star-forming region in IC348 can be found at:
http://www.ras.org.uk/index.php?option=com_content&task=view&id=1607