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UKIRT Astronomers Discover Local Star's Cool Companion EMBARGOED UNTIL 1201 HST (4/19)/1901 ET (4/19)/0001 BST (4/20)/0101 CET (4/20):

Issued by: Dr. Robert Massey, Press Officer
Royal Astronomical Society
Desk: +44 (0)20 7734 3307 / 4582
Cell: +44 (0)794 124 8035

Issued by: Inge Heyer, Science Outreach Specialist
Joint Astronomy Centre
Desk: +1 808 969 6524

Images, notes, and contact details appear below.

20 April 2009

UKIRT Astronomers Discover Local Star's Cool Companion

An international team, led by astronomers at the University of Hertfordshire in the UK, have discovered one of the coolest sub-stellar bodies ever found outside our own solar system, orbiting the red dwarf star Wolf 940, some 40 light years from Earth.

"Although it has a temperature of 300 degrees celcius, which is almost hot enough to melt lead, temperature is relative when you study this sort of thing, and this object is very cool by stellar standards. In fact, this is the first time we've been able to study an object as cool as this in such detail", says Dr Ben Burningham, of the University of Hertfordshire, "the fact that it is orbiting a star makes it extra special".

The object is thought to have formed like a star, but has ended up looking more like Jupiter. It is roughly the same size, despite being between 20 and 30 times as heavy, and when the infrared spectral "fingerprints" of the two objects are compared, their resemblance is striking.

The new object orbits its star at about 440 times the distance at which the Earth orbits the sun. At such a wide distance, it takes about 18,000 years to complete a single orbit.

Too small to be stars, so-called "brown dwarfs" have masses lower than stars but larger than gas giant planets like Jupiter. Due to their low temperature these objects are very faint in visible light, and are detected by their glow at infrared wavelengths.

Modelling the atmospheres of cool brown dwarfs is a complex task, but it is key to understanding what we see when we look at planets that orbit other stars. Models of emitted light from such objects, which are dominated by absorption due to water and methane gas, are sensitive to assumptions about their age and chemical make-up.

In most cases astronomers don't initially know much about the age and composition of brown dwarfs and this can make it hard to tell where the models are right, and where they are going wrong.

"What's so exciting in this case, is that we can use what we know about the primary star to find out about the properties of the brown dwarf, and that makes it an extremely useful find", explains Dr Burningham, "you can think of it as a Rosetta Stone for decrypting what the light from such cool objects is telling us".

The object has been named Wolf 940B, after the red dwarf star that it orbits, which was first catalogued by the pioneering German astronomer Max Wolf ninety years ago.

"Red dwarfs are the most populous stars in the Galaxy, and systems like this may be more common than we know" says Dr David Pinfield of the University of Hertfordshire, "As the generation of ongoing large scale surveys continues, we may discover a pack of Wolf-940B-like objects in our solar back yard."

Wolf 940B was initially discovered as part of a major infrared sky survey - the UKIRT Infrared Deep Sky Survey (UKIDSS) which is being carried out using the United Kingdom Infrared Telescope (UKIRT) on Mauna Kea in Hawaii.

The object was found as part of a wider effort to find the coolest and least luminous bodies in our local Galactic neighbourhood, but it was then found to be a companion to the nearby red dwarf Wolf 940 through its common motion across the sky. The data used to confirm the discovery were obtained using telescopes in Chile, the Canary Islands and Hawaii.

Its temperature was then confirmed using data from the Gemini-North telescope on Mauna Kea. The team's findings will soon be published in the Monthly Notices of the Royal Astronomical Society.

Following its discovery with ground based telescopes, Wolf 940B, has since been observed by the NASA's Spitzer Space Telescope, and the findings from those observations will be published later this year.

"This object is going to continue to provide insights into the processes of cool brown dwarf, and warm planetary atmospheres for some time to come", says Dr Sandy Leggett, of the Gemini Observatory, "finding it was just the first step".

Dr Burningham will present this result at the European Week of Astronomy and Space Science (NAM 2009) at the University of Hertfordshire today.


A comparison of the Wolf 940B spectrum and that of Jupiter.

UKIRT UKIDSS image of Wolf 940A and Wolf 940B. Credit: UKIRT/JAC.

The Wide Field Camera (long black tube) on the United Kingdom Infrared Telescope on Mauna Kea, Hawaii. Credit: UKIRT/JAC.

The United Kingdom Infrared Telescope on Mauna Kea, Hawaii. Credit: UKIRT/JAC.

Notes for Editors

Light Year

One light year is about 10 million million kilometres or 6 million million miles.

Infrared Light

Infrared wavelengths are longer wavelengths than light waves. They are typically measured in microns, also called micrometres. One micron is one millionth of a metre, one 10000th of a centimetre, or one 25000th of an inch.


The world's largest telescope dedicated solely to infrared astronomy, the 3.8-metre (12.5-foot) UK Infrared Telescope (UKIRT) is sited near the summit of Mauna Kea, Hawaii, at an altitude of 4194 metres (13760 feet) above sea level. It is operated by the Joint Astronomy Centre in Hilo, Hawaii, on behalf of the UK Science and Technology Facilities Council. UKIRT's technical innovation and privileged position on the high, dry Mauna Kea site have placed it at the forefront of infrared astronomy since its opening in 1979. UKIRT is currently engaged in a world-leading infrared sky survey as well as the type of innovative individual programmes described in this press release. More about the UK Infrared Telescope:

Gemini Observatory

The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located at Mauna Kea, Hawai'i (Gemini North) and the other telescope at Cerro Pachon in central Chile (Gemini South), and hence provide full coverage of both hemispheres of the sky. Both telescopes incorporate new technologies that allow large, relatively thin mirrors under active control to collect and focus both optical and infrared radiation from space. More about Gemini Observatory:


Royal Astronomical Society of the United Kingdom.


The RAS National Astronomy Meeting (NAM 2009) is hosted by the University of Hertfordshire. It is principally sponsored by the RAS and the Science and Technology Facilities Council (STFC). The European Week of Astronomy & Space Science incorporates both the 2009 NAM and 2009 JENAM.

Science and Technology Facilities Council

The Science and Technology Facilities Council is an independent, non-departmental public body of the Office of Science and Innovation which itself is part of the Department of Innovation, Universities and Skills. It was formed as a new Research Council on 1 April 2007 through a merger of the Council for the Central Laboratory of the Research Councils (CCLRC) and the Particle Physics and Astronomy Research Council (PPARC) and the transfer of responsibility for nuclear physics from the Engineering and Physical Sciences Research Council (EPSRC). We are one of seven national research councils in the UK. The Science and Technology Facilities Council is government funded and provides research grants and studentships to scientists in British universities, gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Organisation for Nuclear Research, CERN, the European Space Agency and the European Southern Observatory. It also contributes money for the UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh and the MERLIN/VLBI National Facility.

Media Contacts

Please note that it is best to contact these individuals by email.
  • Inge Heyer, Science Outreach Specialist
    Joint Astronomy Centre
    Desk: +1 808 969 6524
    Fax: +1 808 961 6516
  • Julia Maddock, Senior Press Officer
    Science and Technology Facilities Council
    Desk: +44 (0)1793 442094
    Fax: +44 (0)1793 442002
  • Peter Michaud, Public Information Outreach Manager
    Gemini Observatory
    Desk: 808-974-2510
    Cell: 808-937-0845
  • Dr Robert Massey, Press and Policy Officer
    Royal Astronomical Society
    Desk: +44 (0)20 7734 3307
    Cell: +44 (0)794 124 8035
  • Anita Heward, Press Officer
    Royal Astronomical Society
    Cell: +44 (0)7756 034 243

Science Contacts

Please note that it is best to contact these individuals by email.
  • Dr Ben Burningham
    University of Hertfordshire
    Desk: +44 (0) 1707 286435
    Cell: +44 (0) 7815 122383 (mobile)
  • Dr Andy Adamson
    Joint Astronomy Centre
    Desk: +1 808 969 6511
  • Dr Sandy Leggett
    Gemini Observatory
    Tel: 808-974-2604
  • Dr David Pinfield
    University of Hertfordshire
    Desk: +44 (0)1707 284171
  • Prof. Gary Davis
    Joint Astronomy Centre
    Desk: +1 808 969 6504


This press release refers to a paper to be published in The Monthly Notices of the Royal Astronomical Society (MNRAS)
"The discovery of an M4+T8.5 binary system"
astro-ph: arXiv:0902.181

Web links

Joint Astronomy Centre - UKIRT
Joint Astronomy Centre - UKIRT - WFCAM
Joint Astronomy Centre Press Room
Gemini Observatory
NAM 2009
Royal Astronomical Society
Science and Technology Facilities Council
This press release
Contact: JAC outreach. Updated: Sun Apr 19 07:09:24 HST 2009

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