White dwarf and ultra-cool dwarf keep their distance (Forwarded)

Royal Astronomical Society
London, U.K.

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Robert Massey
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CONTACT:

Avril Day-Jones
University of Hertfordshire
E-mail: a.c.day-jones @ herts.ac.uk

Between 17th April and 20th April, Avril Day-Jones can be contacted through
the NAM press office (see top of release for details)

PRESS INFORMATION NOTE: RAS PN 07/21 (NAM17)

EMBARGOED FOR 00:01 BST, WEDNESDAY, 18 APRIL 2007

WHITE DWARF AND ULTRA-COOL DWARF KEEP THEIR DISTANCE

Scientists from the University of Hertfordshire have discovered a rare
binary system consisting of a white dwarf, a Sun-like star that has reached
the end of its life, and an ultra-cool dwarf, which is the smallest kind of
star. To make the discovery even more unusual, the co-orbiting pair has by
far the widest separation ever detected in this type of binary system.

Avril Day-Jones, who is presenting results at the RAS National Astronomy
Meeting in Preston, said, "This is a record breaking discovery for a system
of this kind. In the other few binary cases that are known, the objects are
relatively close together. In this new system, the objects are 600 billion
kilometres apart which is hundreds of times wider."

The group from Hertfordshire believes that the two objects formed at roughly
the same time and were originally much closer together. During the
death-throes of the white dwarf's progenitor star, forces induced when gas
and dust from the star were thrown off into space caused the ultra-cool
dwarf spiral out to its remote position.

Miss Day-Jones said, "Ultra-cool dwarfs are elusive objects and we don't
know that much about them. This type of binary allows us to use our
knowledge of white dwarfs, which we understand quite well, to infer
properties of the ultra-cool dwarf, such as the temperature, surface
gravity, mass and age. We need to discover more of this type of binary
system if we want to improve our understanding of ultra-cool dwarfs."

NOTES FOR EDITORS

Royal Astronomical Society's National Astronomy Meeting

The RAS National Astronomy Meeting is the UK's premier meeting for the
astronomy, solar system and space science communities. The RAS-NAM 2007 is
hosted by the University of Central Lancashire and is joined by the UK Solar
Physics and Spring MIST meetings. It is sponsored by the Royal Astronomical
Society, the UK Science and Technology Facilities Council and the University
of Central Lancashire.

FURTHER INFORMATION

The binary system was discovered from a search of the southern hemisphere in
the 2MASS (two Micron All Sky Survey) and SuperCOSMOS archives, from the
tell-tale characteristic colours of the pair. The discovery was confirmed
with additional observations taken at the Anglo-Australian telescope in NSW
and the Very Large Telescope in Chile.

IMAGES

Images can be found at
http://www.nam2007.uclan.ac.uk/press.../20070418c.png (568KB)