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UKIRT Instrumental in Discovery of the First Methane Dwarf Orbiting a Dying Star EMBARGOED UNTIL 23 November, 2010, 1401 HST (22 Nov)/1901 EST (22 Nov)/0001 GMT/0101 ECT:

Issued by: Inge Heyer, Public Information Officer
Joint Astronomy Centre
Email: outreach@jach.hawaii.edu
Desk: +1 808 969 6524

Images, notes, and contact details appear below.

23 November 2010

UKIRT Instrumental in Discovery of the First Methane Dwarf Orbiting a Dying Star

An international team of astronomers using the United Kingdom Infrared Telescope (UKIRT) and the Gemini Observatory on Mauna Kea have discovered a unique and exotic star system with a very cool methane-rich brown dwarf (T dwarf) and a dying white dwarf stellar remnant in orbit around each other. The system is a 'Rosetta Stone' for T dwarfs, giving scientists the first good handle on their masses and ages.

This system is the first of its type to be found. The two stars are low in mass and have a weak mutual gravitational attraction as they are separated by about 2.5 trillion km, which is about one quarter of a light year. Despite the frailty of this system, it has stayed together for billions of years, but its stars are cooling down to a dark demise. The system is about 5 billion years old and about 160 light years away from us in the constellation of Virgo.

Methane dwarfs are on the boundary between stars and planets with temperatures typically less than 1000 degrees Celsius (in comparison the Sun's surface is at 5500 degrees Celsius). Methane is a fragile molecule destroyed at warmer temperatures, so is only seen in very cool stars and giant planets like Jupiter. Neither giant planets nor T dwarfs are hot enough for the hydrogen fusion that powers the Sun to take place, so that they simply cool and fade over time. This new T dwarf has a temperature of about 1300 Kelvin (= 1030 Celsius = 1900 Fahrenheit) and a mass of about 70 Jupiters.

White dwarfs are the end state of stars similar to and including the Sun. Once such stars have exhausted the available hydrogen fuel in their cores, they expel most of their outer layers into space forming a remnant planetary nebula and leaving behind a small, dense, hot, but cooling core or white dwarf. For our Sun this process will begin about 5 billion years in the future.

"By the time our Sun 'dies' and becomes a white dwarf itself, the methane dwarf will have cooled to around room temperature, and the white dwarf will be as cool as the methane dwarf was at the start of its life", comments team leader Dr Avril Day-Jones from the Universidad de Chile.

In the newly-discovered binary, the remnant nebula has long since dissipated and all that is left is the cooling white dwarf and methane dwarf pair. This binary system is providing a crucial test of the physics of ultra-cool stellar atmospheres because the white dwarf lets us establish the age of both objects. By comparison it determines properties of the methane dwarf such as its mass, making it a kind of 'Rosetta Stone' for similar stars with complex, hazy ultra-cool atmospheres.

The two stars are today separated by at least 2.5 trillion km, but would have been closer in the past before the white dwarf was formed. Once the star that formed the white dwarf reached the end of its life and expelled its outer layers, the loss of mass weakened the gravitational pull between the stars, causing the methane dwarf to spiral outwards to create the gravitationally fragile system that we see today. But we know from the current age of the white dwarf that this system has survived for several billion years. So the new discovery shows that despite their fragility, such binaries are able to remain united even in the maelstrom of the galactic disk.

This system was discovered by an international team led by Dr Avril Day-Jones from the Universidad de Chile, with astronomers from the University of Hertfordshire (UK), and the University of Montreal (Canada). The methane dwarf was identified in the UKIRT Infrared Deep Sky Survey (UKIDSS) as part of the Large Area Survey's T-Dwarf Programme to identify the coolest objects in the galaxy. Its temperature and spectrum were measured by the Gemini North Telescope's NIRI Spectrometer in Hawaii.

The team found that the methane dwarf shares its motion across the sky with a nearby blue object catalogued as LSPM 1459+0857. They studied the blue object using the world's largest optical telescope, the European Southern Observatory's Very Large Telescope (VLT) in Chile. The new VLT observations revealed the blue object to be a cool white dwarf and companion to the methane dwarf. The objects were thus renamed LSPM 1459+0857 A and B.

"Binary systems like this provide vital information and allow us to better understand ultra-cool atmospheres and the very low-mass dwarfs and planets they enshroud" said Dr David Pinfield of the University of Hertfordshire. "The fact that these binaries survive intact for billions of years means that we could find many more lurking out there in the future."

The team, led by Dr Avril Day-Jones of the Universidad de Chile and including Dr David Pinfield of the University of Hertfordshire, will publish their results in the journal Monthly Notices of the Royal Astronomical Society.


Images

An artist's impression of the binary as it might appear from a point in space near the methane dwarf. From here the distant white dwarf would appear as a bright star, only gently illuminating its cooling companion. Credit: Andrew McDonagh.



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. This is the distance light travels in a year.

Infrared Light

Infrared wavelengths are longer wavelengths than visible 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. Visible light has wavelengths around half a micron, while the observations reported here were at wavelengths of about 2 microns. Human eyes are not sensitive to infrared light. We need specially designed cameras with detectors sensitive to infrared radiation to detect them.

Brown Dwarf (T Dwarf)

A brown dwarf is a small, faint, cool object (often called "failed" star) that, unlike the Sun and other stars, does not have sufficient mass to achieve hydrogen fusion in its core. With mostly slow gravitational contraction as an internal energy source, a brown dwarf gradually cools down as it radiates energy away into space over billions of years. Brown dwarfs exist in the mass range between about ten times that of Jupiter and one-twelfth the Sun's mass (which marks the boundary between these dwarfs and hydrogen-burning stars). The low temperatures and small sizes of brown dwarfs combine to make them both very faint and red in color. Most of their radiation is in the infrared, and therefore is not detectable to either the human eye or conventional optical detectors. Detectors sensitive to longer infrared wavelengths, such as those used at UKIRT, are capable of observing these objects in unique ways. The spectrum of a brown dwarf is characterized by large wavelength regions from which almost no light is seen because it is being absorbed by water, methane and other molecules in the object's atmosphere. The details of these absorption patterns depend sensitively on the star's temperature. The T dwarfs are brown dwarfs with the lowest temperatures.

United Kingdom Infrared Telescope (UKIRT)

One of the world's largest telescopes dedicated solely to infrared astronomy, the 3.8-metre (12.5-foot) United Kingdom 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: http://outreach.jach.hawaii.edu/articles/aboutukirt/

Wide-Field Camera (WFCAM)

The Wide-Field Camera (WFCAM) was delivered to UKIRT in late 2004 and has been in active operation since Spring 2005. In two years of operation WFCAM has taken 30 times the amount of data taken in the entire 25-year history of the telescope before its arrival.

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: http://wwww.gemini.edu

The Gemini Observatory provides the astronomical communities in each partner country with state-of-the-art astronomical facilities that allocate observing time in proportion to each country's contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the UK Science and Technology Facilities Council, the Canadian National Research Council (NRC), the Chilean Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT), the Australian Research Council (ARC), the Argentinean Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) and the Brazilian Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq). The Observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.

Science and Technology Facilities Council

The Science and Technology Facilities Council is an independent, non-departmental public body of the Department of Business, Innovation 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.

Royal Astronomical Society (RAS)

The Royal Astronomical Society (RAS, www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3500 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

European Southern Observatory (ESO)

ESO is the pre-eminent intergovernmental science and technology organisation in astronomy. It carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities for astronomy to enable important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. The ESO headquarters are located in Garching, near Munich, Germany. This is the scientific, technical and administrative centre of ESO where technical development programmes are carried out to provide the observatories with the most advanced instruments. ESO also hosts the European Coordinating Facility for the Hubble Space Telescope, a collaboration between ESA and NASA. Read more about ESO at http://www.eso.org


Media Contacts

Please note that it is best to contact these individuals by email.
  • Inge Heyer, Public Information Officer
    Joint Astronomy Centre
    Desk: +1 808 969 6524
    Email: outreach@jach.hawaii.edu
  • Robert Massey
    Royal Astronomical Society
    Desk: +44 (0)20 7734 3307 x 214
    Cell: +44 (0)794 124 8035
    Email: rm@ras.org.uk
  • Julia Maddock, Senior Press Officer
    Science and Technology Facilities Council
    Desk: +44 (0)1793 442094
    Email: julia.maddock@stfc.ac.uk

Science Contacts

Please note that it is best to contact these individuals by email.
  • Avril Day-Jones
    Universidad de Chile
    Email: adjones@das.uchile.cl
  • David Pinfield
    University of Hertfordshire
    Desk: +44 (0)1707 284171
    Cell: +44 (0)7867997931
    Email: d.j.pinfield@herts.ac.uk
  • Joana Gomes
    University of Hertfordshire
    Desk: +44 (0)1707 284603
    Cell: +44 (0)7564271176
    Email: j.gomes@herts.ac.uk
  • Dr Tom Kerr
    Joint Astronomy Centre
    Desk: +1 808 969 6570
    Email: t.kerr@jach.hawaii.edu
  • Prof. Gary Davis
    Joint Astronomy Centre
    Desk: +1 808 969 6504
    Email: g.davis@jach.hawaii.edu

Reference

This press release refers to a paper published in the Monthly Notices of the Royal Astronomical Society (MNRAS)
"Discovery of a T dwarf + white dwarf binary system"
authors: Avril Day-Jones, David Pinfield, et al.
astro-ph: arXiv: 1008.2960


Web links

Joint Astronomy Centre - UKIRT
http://www.jach.hawaii.edu/UKIRT/
Joint Astronomy Centre - UKIRT - WFCAM
http://www.jach.hawaii.edu/UKIRT/instruments/wfcam/
Joint Astronomy Centre Press Room
http://outreach.jach.hawaii.edu/pressroom/
Gemini Observatory
http://wwww.gemini.edu
Science and Technology Facilities Council
http://www.stfc.ac.uk/
RAS
http://www.ras.org.uk
ESO
http://www.eso.org
This press release
http://outreach.jach.hawaii.edu/pressroom/2010_ukirt_methane_bd/
Contact: JAC outreach. Updated: Wed Nov 24 10:20:25 HST 2010

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