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

Royal Astronomical Society
London, U.K.

Issued by RAS Press Officers:

Robert Massey
Tel: +44 (0)20 7734 4582
AND
Anita Heward
Tel: +44 (0)1483 420 904

NATIONAL ASTRONOMY MEETING PRESS ROOM (16 - 20 APRIL ONLY):
Tel: +44 (0)1772 892 613
+44 (0)1772 892 475
+44 (0)1772 892 477

RAS Web site:
http://www.ras.org.uk/

RAS National Astronomy Meeting web site:
http://nam2007.uclan.ac.uk

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)