Welcoming the New Neighbours

Posted by Steinn Sigurðsson on March 11, 2013
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I think we should take some pie over, in person.

Discovery of a Binary Brown Dwarf at 2 Parsecs from the Sun – Kevin Luhman, ApJLetters in press.

That is just over 6 light years away, making it the third closest system from the Sun, and the closest known substellar system, only the α Cen triple system, and Barnard’s Star, an old red dwarf, are closer.

Detection images for our new neighbour. The WISE discovery image is middle bottom, the Gemini image at the bottom right shows the resolved pair clearly.

Detection images for our new neighbour. The WISE discovery image is middle bottom, the Gemini image at the bottom right shows the resolved pair clearly.

This is a spectacular and somewhat surprising discovery, that something could be this close and not been spotted yet.

Schematic of the neighbourhood.

Schematic of the neighbourhood.



From PSU Press Release

The system was found by a careful search for high proper motion objects in the WISE all sky survey, using multi-epoch astrometry.
The primary is an L8 brown dwarf,confirmed with Gemini spectra, with a L9/T1 secondary in an optically resolved 3 AU (projected) orbit.
The object is WISE J104915.57-531906.1 – it is a southern hemisphere object, close to the galactic plane.

Kevin spotted the object in mid-infrared images from the WISE catalog, as a cool nearby object it is bright in the IR, but red as it is, the object is still 15th magnitude in the i band, and was immediately confirmed in archival data from the DSS, 2MASS and DENIS surveys.
Kevin was looking for just such things, as part of a very careful search for high proper motion red objects.

The reason it was not spotted before is that it is red, faint and in a crowded part of the sky.

It is a big sky out there.

The object has a clear parallax, a whopping 0.5″, natch, and a huge proper motion of about 3″ per year. It is a resolved binary, and the orbit can be reconstructed from the archival data spanning decades.


Animation of the proper motion of the system, combined from multiple archival sources.

This will be a key system for calibrating age, cooling and composition of brown dwarfs, as a spectroscopic binary with a known astrometric orbit, everything about this system can be nailed down.
It is also a prime target for searching for planetary mass companions around brown dwarfs.

Twinkle twinkle two little stars

Twinkle twinkle two little stars


From PSU Press Release

Followup observations are underway.

PSU press release

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Comments

  1. #1 Eccentric & Anomalous
    March 11, 2013

    Interesting. Can we infer anything from this discovery about the putative Nemesis companion to the Sun? Is anyone still looking for such a thing??

  2. #2 Steinn Sigurðsson
    March 11, 2013

    No, we can’t infer anything about the Nemesis/Planet X thing from this discovery.

    Yes, there are people still looking for a trans-Kuiper belt planet, I’ve played with it a little bit, some other people had papers out on it a couple of years ago. Nothing robust.

  3. #3 Omega Centauri
    March 11, 2013

    What does this say about the probable number of brown dwarfs in the galaxy? I’m presuming they may be quite common, if we have found one(two?) this close. Could they be as numerous as stars?

  4. #4 Yurgionas
    Cleveland
    March 11, 2013

    If In the Milky Way there are is some where from 100 to a 1000 red dwarfs for every star like the sun, I would think a number for the brown dwarfs would likely be near 1000 for every one star like the sun. Just a WAG.

  5. #5 Steinn Sigurðsson
    March 11, 2013

    So, in practise it seems the stellar mass function flattens at the low mass end and turns over at low masses, so there are fewer brown dwarfs per star than one would infer.
    Statistics of single objects are perilous, but the simple inference is that there ought to be a few undiscovered brown dwarfs within about 10 light years, which compares with 8 known M dwarfs within 10 light years. I don’t think we are missing any M dwarfs, so I think this is consistent – there are fewer brown dwarfs than M dwarfs, but not much fewer.

  6. #6 andy
    March 12, 2013

    It is also a prime target for searching for planetary mass companions around brown dwarfs.

    Talking of planets in nearby brown dwarf binaries, has anyone searched for planets at Epsilon Indi B yet?