UKIRT UKIDSS near infrared image of SDSS1416+13AB (left panel) and the Spitzer+UKIDSS image at mid-infrared wavelengths (right panel). Image: UKIRT / Spitzer
Subaru near infared spectrum of SDSS1416+13B, taken with the IRCS spectrograph. The almost total absence of light at wavelengths between 1.7 and 2.5 microns is apparent. This causes the very blue near infrared colour. Image: Subaru
An international team, led by astronomers at the University of Hertfordshire have discovered what may be the coolest sub-stellar body ever found outside our own solar system. Using the United Kingdom Infrared Telescope (UKIRT) in Hawaii, a discovery has been made of an object which is technically known as a brown dwarf. The team's findings have been accepted for publication in the journal Monthly Notices of the Royal Astronomical Society.
What has excited astronomers are its very peculiar colours, which actually make it appear either very blue or very red, depending on which part of the spectrum is used to look at it.
The object is known as SDSS1416+13B and it is in a wide orbit around a somewhat brighter and warmer brown dwarf, SDSS1416+13A. The brighter member of the pair was detected in visible light by the Sloan Digital Sky Survey. By contrast, SDSS1416+13B is only seen in infrared light. The pair is located between 15 and 50 light years from the solar system, which is quite close in astronomical terms.
"This looks like being the fourth time in three years that the UKIRT has discovered made a record breaking discovery of the coolest known brown dwarf, with an estimated temperature not far above 200 degrees Celsius,” said Dr Philip Lucas at the University of Hertfordshire’s School of Physics, Astronomy and Mathematics.
“We have to be a bit careful about this one because its colours are so different than anything seen before that we don't really understand it yet. Even if it turns out that the low temperature is not quite record breaking, the colours are so extreme that this object will keep a lot of physicists busy trying to explain it.”
SDSS1416+13B was first noticed by Dr Ben Burningham of the University of Hertfordshire as part of a dedicated search for cool brown dwarfs in the UKIRT Infrared Deep Sky Survey (UKIDSS). The object appeared far bluer at near infrared wavelengths than any brown dwarf seen before. A near infrared spectrum taken with the Japanese Subaru Telescope in Hawaii showed that it is a type of brown dwarf called a T dwarf, which has a lot of methane in its atmosphere, but with peculiar features including a big gap at certain wavelengths.
Dr Burningham soon noticed that a previously observed brighter star (SDSS1416+13A) which appears close by in the UKIDSS discovery image was also a brown dwarf. Team member Dr Sandy Leggett, of the Gemini Observatory, then used the orbiting Spitzer Space Telescope to investigate SDSS1416+13B at longer wavelengths. She measured its colour at mid-infrared wavelengths, which are thought to be the most reliable indicator of temperature, and found that it is the reddest known brown dwarf at these wavelengths by some margin. Comparison with theoretical models of the brown dwarf atmospheres then provided a temperature estimate of about 500 Kelvin (227 degrees Celsius).
"The fact that it is a binary companion to a warmer brown dwarf that also has an unusual spectrum is helping us to fill in some gaps in our understanding", says Dr Burningham. "It seems likely that both brown dwarfs are somewhat poor in heavy elements. This can be explained if they are very old, which also fits with the very low temperature of the faint companion."
Too small to be stars, brown dwarfs have masses smaller 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. They were originally dubbed "brown dwarfs" long before any were actually discovered, to describe the idea of bodies that were cooler, fainter and redder than red dwarf stars, with the colour brown representing the mix of red and black.
CONTACTS
Dr Ben Burningham
University of Hertfordshire
Tel: +44 (0)1707 285179
Mob: +44 (0)7815 122383
E-mail: b.burningham@herts.ac.uk
Dr Sandy Leggett
Gemini Observatory
Tel: +1 808-974-2604
E-mail: sleggett@gemini.edu
Dr Philip Lucas
University of Hertfordshire
Tel: +44 (0)1707 286070
Mobile: +44 (0)7951 630957
E-mail: p.w.lucas@herts.ac.uk
Dr Andy Adamson
Joint Astronomy Centre
Tel: +1 808 969 6511
E-mail: a.adamson@jach.hawaii.edu
Prof. Gary Davis
Joint Astronomy Centre
Tel:: +1 808 969 6504
E-mail: g.davis@jach.hawaii
Dr Robert Massey
Press and Policy Officer
Royal Astronomical Society
Tel: +44 (0)20 7734 3307
Mobile: +44 (0)794 124 8035
E-mail: rm@ras.org.uk
Helene Murphy
Press Office
University of Hertfordshire
Tel: +44 (0)1707 284095
Mob: +44 (0)7951 630957
E-mail: h.1.murphy@herts.ac.uk
IMAGES AND CAPTIONS
Images are available from:
1. UKIRT UKIDSS near infrared image of SDSS1416+13AB (left panel) and the Spitzer+UKIDSS image at mid-infrared wavelengths (right panel).
2. Subaru near infared spectrum of SDSS1416+13B, taken with the IRCS spectrograph. The almost total absence of light at wavelengths between 1.7 and 2.5 microns is apparent. This causes the very blue near infrared colour.
FURTHER INFORMATION
A preprint of the paper can be found at http://xxx.soton.ac.uk/abs/1001.4393
NOTES FOR EDITORS
ROYAL ASTRONOMICAL SOCIETY
The Royal Astronomical Society (RAS), 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 3000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others. For more information see http://www.ras.org.uk
THE UNIVERSITY OF HERTFORDSHIRE
The University of Hertfordshire is an ambitious and entrepreneurial university. It offers excellence in teaching, learning and research and puts students at the heart of its activities. It is a model of a 21st century university, international, business-facing and business-like in its approach – making it distinctive in an ever changing higher education environment.
The University of Hertfordshire is one of the region’s largest employers with over 2,700 staff and a turnover of £205 m. With a student community of 23,000, including more than 2,000 international students from over eighty five countries, the University has a global network of over 160,000 alumni. For more information, please visit, http://www.herts.ac.uk
A LIGHT YEAR
One light year is the distance travelled by light in a year. It corresponds to roughly 10 thousand billion kilometres or 6 thousand billion 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.
UKIRT
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 now spends most of its time surveying the sky for the UKIDSS sky survey but it continues to undertake a variety of smaller science projects covering all areas of astronomy.
SUBARU
The Subaru telescope is Japan's premier optical-infrared telescope operated by the National Astronomical Observatory of Japan. Located on Mauna Kea on the island of Hawaii, the telescope, with an effective aperture of 8.2 m, is also one of the world's largest and most technologically advanced telescopes. Through the open use program astronomers throughout the world have access to Subaru and its excellent image quality.
SPITZER
The Spitzer Space Telescope is a space-borne, cryogenically-cooled infrared observatory capable of studying objects ranging from our Solar System to the distant reaches of the Universe. Spitzer is the final element in NASA's Great Observatories Program, and an important scientific and technical cornerstone of the Astronomical Search for Origins Program.
