UK, US Astronomers: That’s One Cool Star

An international team, led by astronomers at the University of Hertfordshire in the UK, has discovered one of the coolest sub-stellar bodies ever found outside our own solar system.

The new object — dubbed Wolf 940B — orbits the red dwarf star Wolf 940, 40 light years from Earth. It’s 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, say Wolf 940B’s discoverers.

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

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 telescope’s wide field camera is the long black tube in the image at left.

The object was found as part of a wider effort to find the coolest and least luminous bodies in our local Galactic neighborhood, 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 findings are being reported at the European Week of Astronomy and Space Science (NAM 2009) at the University of Hertfordshire, and will soon be published in the Monthly Notices of the Royal Astronomical Society.

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 temperatures, these objects are very faint in visible light, and are detected by their glow at infrared wavelengths.

“Although it has a temperature of 300 degrees Celsius [572 degrees F], 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,” said Ben Burningham, of the University of Hertfordshire. “In fact, this is the first time we’ve been able to study an object as cool as this in such detail. The fact that it is orbiting a star makes it extra special.”

Modeling the atmospheres of cool brown dwarfs is a complex task, but it is key to understanding 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,” Burningham said. “You can think of it as a Rosetta Stone for decrypting what the light from such cool objects is telling us.”

Wolf 940A, the red dwarf star that is Wolf 940B’s namesake, was first catalogued by the pioneering German astronomer Max Wolf 90 years ago.

“Red dwarfs are the most populous stars in the Galaxy, and systems like this may be more common than we know” said David Pinfield, also 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.”

Source: Joint Astronomy Centre. For more information, visit: 

The UK Infrared Telescope
NAM 2009
Gemini Observatory

13 Replies to “UK, US Astronomers: That’s One Cool Star”

  1. What a chilly star! Makes me wonder if Sol has one as a binary buddy, especially since that recent study by Iorio which gives surprisingly close by minimum distances to possible Solar companions. Wonder what an all-sky survey would turn up…

  2. “but it was then found to be a companion to the nearby red dwarf Wolf 940 through its common motion across the sky.”

    Don’t all the stars move across the sky in common motion? How do you infer from common motion, that 940B is a companion to Wolf 940A?

    On a side note, it’s amazing to think that a red dwarf’s gravitational influence can extend as far as 440Au. Leaves much to be known about our own solar system.

  3. @ graal, An all-sky infrared survey already exists. The 2 Micron All Sky Survey (2MASS) was completed years ago and (like the Palomar Sky Survey) can be accessed online for free by anybody. This might be a sensible place to look for nearby IR stars (2MASS lacks the resolution for this object, its high sensitivity can see faint isolated dwarf stars and brown dwarfs). While I agree that our ‘solar neighborhood’ probably does harbor more of these cool bodies (say, within 100-200 light years) I don’t think the Sun has any unseen stellar or brown dwarf partners, especially any that are claimed to have moved through the inner solar system while in orbit. PanStarrs and LSST might help put the nail in the coffin of that theory (methinks it’s DOA, anyway). Meanwhile, the hunt for other faint cool members of our local solar neighborhood goes on.

  4. Donna, I’d like to disprove the existence of people who don’t know where not to post their prattle. If science is beyond you, simply read and grow slightly in sophistication.

  5. Can somebody answer my question please. May be a dumb one, but I’m only in high school.

    @ Peter.
    It was just of Donna’s opinion that all that is beautiful in the universe, structure, chaos, everything, was “created” by an “intelligent being”. I myself don’t believe that but that doesn’t make me more sophisticated than others. I highly doubt you possess that sophistication required to understand the origins and nature of our universe and existence. So keep your arrogance to yourself.

  6. K Says: April 20th, 2009 at 4:32 am
    “but it was then found to be a companion to the nearby red dwarf Wolf 940 through its common motion across the sky.”
    Don’t all the stars move across the sky in common motion? How do you infer from common motion, that 940B is a companion to Wolf 940A?

    “Common motion across the sky”: Not all stars adopt a common motion …..; only those which are gravitationally bound to each other in multiple systems. In which case they it is the common centre of mass which is moving through space. As with the alpha Centauri system, which consists of two stars in close orbit about their common centre of mass/gravity; and a third (Proxima) which may or may not be part of the same system (or just be passing by). The system has a single set of co-ordinates (RA, declination, distance and proper motion direction), and each component is orbiting the system centre of mass (or not!!) – if they are in orbit they are part of the system; if not they may just happen to be lying along the line-of-sight to the system. An example being the stars of the Plough (Big Dipper), where some (nearly half) of the asterism is moving in one direction and the others are moving in another direction. Over thousands of years the shape of the Plough will significantly alter because they are not “all” moving wit a common “proper motion” across the sky.

  7. Donna —

    I can think of nothing more revolting than having to believe that the great beauty of the universe was the product of an ingenious sadist who also invented the ichneumon wasp. In a universe with no Creator, we can appreciate the beauty of the Universe as an accident, instead of having to believe it was created by someone who is the moral equivalent of a man who enjoys pulling the wings off of flies.

  8. Donna should rethink how she looks at things; were it not for ” God” who created her
    she would not be here to enjoy what he has

    Wolf reminds me of a movie where a Meteor
    was so named. headed toward Earth.

    I am amazed at the find, and am sure there are more even GREATER WONDERS WAITING.

    Keep on looking, and, reporting.!

  9. Hello you carbon copies;). There is nothing like traveling from star system to start system instead of looking through a telescope… You are still at that latter stage and until you shape up we won’t give you the technology to travel to ‘places’ beyond your imagination.

    I’ve seen things…
    (long pause)
    seen things you little people
    wouldn’t believe… Attack ships
    on fire off the shoulder of Orion
    bright as magnesium… I rode on
    the back decks of a blinker and
    watched c-beams glitter in the dark
    near the Tannhauser Gate.
    all those moments… they’ll be gone like
    teardrops in the rain…

  10. Phillip, K, she’s not being arrogant, just pointing out that all the beauty in the universe indicates the glory of God who created it all.

    God is good, the “ichneumon wasp” and all death is OUR fault, not God’s, cause our representative, Adam, sinned and ate the Forbidden fruit. We would have done the same.

    If U can read all the other posts, read this too. Are these the words of a sadist or of a merciful God?

    Romans 5: 6- 12 “For when we were still without strength, in due time Christ died for the ungodly. For scarcely for a righteous man will one die; yet perhaps for a good man someone would even dare to die. But God demonstrates His own love toward us, in that while we were still sinners, Christ died for us. Much more then, having now been justified by His blood, we shall be saved from wrath through Him. For if when we were enemies we were reconciled to God through the death of His Son, much more, having been reconciled, we shall be saved by His life. And not only that, but we also rejoice in God through our Lord Jesus Christ, through whom we have now received the reconciliation. Therefore, just as through one man sin entered the world, and death through sin, and thus death spread to all men, because all sinned.”

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