# A New Class of Brown Dwarf?

Although the image below isn’t particularly striking, do focus in on it for a moment. You’re looking at what astronomers now consider the coldest brown dwarf yet to be found. Look just down from the top of the image and just left of center for the unusually red pinpoint. This is CFBDS J005910.83-011401.3, thankfully abbreviated CFBDS0059. A science fiction writer with brown dwarf credentials (Karl Schroeder is just the guy) could think of a more poetic name and set up a story around such a place.

Image: Three-color image of the star field in which the brown dwarf has been discovered. The brown dwarf is the very red object seen at the top left of the image. This image illustrates how very different is the color of this object compared to the other cold stars around. Image copyright Canada-France-Brown-Dwarf-Survey 2008.

As interesting stars go, CFBDS0059 isn’t all that far away, some forty light years. Massing between 15-30 Jupiter masses, it’s typical of brown dwarfs in at least one sense, not being able to sustain thermonuclear reactions. It’s also unusually like a giant planet, more so than other known classes of brown dwarfs, not only because of temperatures in the range of 350 degrees Celsius but also because of the presence of ammonia, hitherto undetected in brown dwarf near-infrared spectra.

By contrast, L dwarfs have temperatures in the range of 1200 to 2000 degrees Celsius, while the cooler T dwarfs (both of these are considered brown dwarf classes) come in at under 1200 Celsius. Are we looking at a new class of brown dwarfs in CFBDS0059? They would offer an unusual chance to fill in the gap between giant planets and stars. The most significant aspect of a find like this one is the chance to study a cold brown dwarf in relation to exoplanets we cannot directly observe. This ‘almost planet,’ not swamped by light from a parent star, may help us tune up our models for working with distant planetary atmospheres.

And other cool brown dwarfs fitting the proposed spectral class Y are likely to be found. The same team points to ULAS0034 as an example, and the paper on this work notes “We therefore expect to ﬁnd another few similarly cool objects, and hopefully one signiﬁcantly cooler…” The paper is Delorme et al., “CFBDS J005910.90-011401.3: reaching the T-Y Brown Dwarf transition?” accepted by Astronomy & Astrophysics and available online.

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• Adam April 11, 2008, 7:30

Hi Paul

Brown dwarfs fascinate me because there could be one closer to us than Alpha Centauri – but I wonder how much closer? Do you have any data in that regard, as to the limits of previous all-sky surveys like the IRAS mission and that sort of thing?

• Administrator April 11, 2008, 7:48

Adam, I’ve also been curious about the possibilities of a brown dwarf closer than the Centauri stars. Finding another star maybe a light year out would surely be a boost to our thinking about interstellar missions. I don’t have a good read on how (un)likely this may be based on current all-sky surveys, but let me look around, as it’s been on my mind for some time.

• dad2059 April 11, 2008, 9:33

I don’t know as much about this stuff as you guys, but it would seem to me that in order to detect nearby brown dwarfs, a targetted search between our immediate light cone out to almost Proxima looking for gravity anomalies or infrared signatures beyond the Kuiper Belt. Hell, there could be one lurking amongst the Kuiper Belt objects! Astronomers have already discovered planet-sized bodies there haven’t they?

Discoveries of one, maybe two brown dwarfs between here and Proxima would certainly be a boost to say the least Paul!

• george scaglione April 11, 2008, 13:18

dad, iwon’t comment too much on your ideas above but when it comes to the kuiper belt and or oort cloud i just can’t wait to have a look myself.but i have it on good authority,dr michio kakau’s latest book that : antimatter spacecraft engines may be possible in as “short” a time as this century or next ! in that same vein i see in a “short” time we can easily have pretty much bases from earth orbit to the moon to mars to the orbits of jupiter and saturn.let me go out on a limb and predict the first manned starshipfor about 2175 ! what do you say,dad,jim,paul,ljk…everybody!? your friend george

• ljk April 11, 2008, 13:20

Twenty-three new ultra-cool subdwarfs from the Sloan Digital Sky Survey

Authors: Sebastien Lepine, Ralf-Dieter Scholz

(Submitted on 10 Apr 2008)

Abstract: A search of the Sloan Digital Sky Survey spectroscopic database has turned up 23 new ultra-cool subdwarfs, low-mass metal-poor stars of spectral subtype M 7.0 or later. Spectra from these red objects all show strong molecular bands of CaH but relatively weak bands of TiO, indicative of a cool, metal-poor atmosphere.

Five of the stars are formally classified as M subdwarfs (sdM7.0-sdM8.5), thirteen as more metal-poor extreme subdwarfs (esdM7.0-esdM8.5), and five as extremely metal-poor ultra subdwarfs (usdM7.0-usdM8.0). In the [H_r,r-z] reduced proper motion diagram, the subdwarfs clearly populate the locus of low-luminosity stars with halo kinematics (Population II).

These new discoveries more than double the census of spectroscopically confirmed ultra-cool subdwarfs. It is shown that the stars stand out remarkably in the [g-r,r-i] color-color space. A proposed color and proper motion selection scheme is expected to be extremely efficient in identifying more of these old, very low-mass stars in the vicinity of the Sun.

Comments: 4 pages, submitted to the Astrophysical Journal Letters

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0804.1731v1 [astro-ph]

Submission history

From: Sebastien Lepine [view email]

[v1] Thu, 10 Apr 2008 15:23:24 GMT (219kb)

http://arxiv.org/abs/0804.1731

• David April 11, 2008, 14:16

I recall reading somewhere, sorry can’t recall the reference, that there is a
significant chance (say few tens of percent) of there being a brown dwarf closer to us then Proxima Centaurus. The low resolution of the IRAS data is often a problem, the best is the 12 micron data and that is a couple of tens of of arcseconds which means that often there is confusion in which the one source may actually be two that are sufficiently close that they seem to overlap. This is particularly true in the galactic plane.

In any case one needs data at other wavelengths because one would be looking for objects which have certain colours and that can be done only by comparing the fluxes at different wavelengths. Most of the brown dwarfs have been discovered using 2MASS data which are images taken by two 53 inch telescopes at three near IR wavelengths.

There are no brown dwarfs in the Kuiper Belt for one would be visible to the naked eye, even one as cold as the one discussed in the article which is still radiating about 100 times more light than Jupiter.

• philw1776 April 11, 2008, 15:09

Here’s a look at the WISE survey expectations in regard to finding nearby Brownies…

http://www.haydenplanetarium.org/universe/products/wise/

• Administrator April 11, 2008, 15:24

philw, I also note this from the WISE site:

“WISE will determine how common these objects are in our own Solar neighborhood, allowing us to measure the efficiency of the star formation process at its lowest masses. WISE will also allow us to determine if star formation has a cut-off mass below which formation is inhibited. At the moment, we believe that brown dwarfs are as prevalent as stars. Because brown dwarfs are so common, it is likely that the closest “star” to the Sun is not Proxima Centauri but some hitherto undiscovered brown dwarf that will be imaged successfully for the first time by WISE.”

http://wise.ssl.berkeley.edu/index.html

• Administrator April 11, 2008, 15:42

David, I think we’re talking about the same reference, and I can’t find it either, but I do recall the odds on a nearby brown dwarf being calculated therein. Didn’t realize about the significance of the 2MASS data in the brown dwarf hunt — thanks.

• andy April 11, 2008, 15:56

Anyone interested in brown dwarf stars may want to check out the Brown Dwarf and Extra-Solar Giant Planet Calculator, which uses an evolutionary model to calculate the expected temperature, surface gravity, radius and luminosity of a brown dwarf given its mass and age.

• David April 11, 2008, 19:01

http://www.ucm.es/info/Astrof/recopilaciones/enanasmarrones.html

Has a lot of good links to brown dwarf related websites, including “dwarf archives” which is an on-line catalog.

• Adam April 11, 2008, 21:52

Hi andy

Had forgotten about that one. Shame modelling the visible luminosity is so challenging – the luminosity the calculator produces is bolometric, and so not very useful for figuring out the apparent brightness of brown dwarfs at low temperatures, unless we’re using an IR telescope. Perhaps an orbital T-ray observatory will open up vistas as yet unsuspected?

• dad2059 April 12, 2008, 9:25

Hi George and all.

No, I’m not going to go into the ‘Nibiru’ thing here because this isn’t the forum for it.

You say a brown dwarf would even be visible out in our Kuiper Belt? Okay, I’ll go with that. It should be large and hot enough to detect I should think.

But we don’t know how far the Kuiper Belt extends out to yet. Estimates vary from 55 to 100 AU. And we have no idea where that boundry ends and where the Oort Cloud starts. A brown dwarf could very well inhabit the outer Oort Cloud, 50,000 AU to one light-year out.

The New Horizons Pluto probe should give us a good look in eight years when it makes it’s fly-by. It’ll be our first chance to estimate the true size of the Kuiper Belt.

Hopefully it’ll be the first of many.

• george scaglione April 12, 2008, 12:53

dad,yes new horizons should go into the kuiper belt ,heck there are those that say that pluto itself is the nearest of the belt objects ! but as to how big the belt is? i think new horizons would take a loooooong time to answer that question! but at least we will have a probe out there. also…as to the oort cloud,i think i heard that it goes a good part of the way to the nearest star.anybody feel free to correct me if i am wrong but i think a minimum of 2 light years or so.anyhow,thats all for now,thanks dad and all your friend george

• James M. Essig April 14, 2008, 22:20

Hi George and other Folks;

The mere fact that we seem to be finding more and more brown dwarfs among their various theoretical and discovered spectral classes causes me to think, WOW! what a great supply of hydrogen and helium for future interstellar transporation and dailly living infrastructure wherein the fuel would be much more easily accessed than say fuel that would be obtained from main-sequence atars. Going into the gravity well of a star and remaining in close proximity to the star is going to be difficult in terms of collecting fusion fuel.

Take for instance extracting fuel from a sun-like star. At a blackbody approximation surface temperature of 5,800 K, the total integrated spectral radiance near the surface of the star is going to be about 16 times greater than that of an oxy-acetyline blow torch as 2,900 K. In the environment of a 58,000 K surface temperature Blue Supergiant Star, the integrated spectral radiance is going to be 160,000 times greater than that of the blow torch. Add the much higher temperatures that can exist within the plasma of the corona sphere of stars and the extreme temperatures of the plasma of solar or should I say stellar flares and promenances, and extracting stellar gas directly from the surfaces or atmospheres of stars becomes vary difficult.

Thanks;

• ljk May 9, 2008, 10:54

Chromospheric Activity, Rotation, and Rotational Braking in M and L Dwarfs

Authors: Ansgar Reiners, Gibor Basri

(Submitted on 7 May 2008)

Abstract: We present results from a high-resolution spectroscopic survey of 45 L dwarfs, which includes both very low-mass stars and brown dwarfs. Our spectra allow us to derive a significant number of new rotational velocities, and discover a slowly rotating (in projected velocity) L dwarf that allows more accurate measurement of spectroscopic rotations for these objects. We measure chromospheric activity (and often its variability) through the H$\alpha$ emission line.

Our primary new result is good evidence that magnetic braking dominates the angular momentum evolution of even brown dwarfs, although spindown times appear to increase as mass decreases. We confirm that activity decreases as effective temperature decreases, though a larger fraction of L dwarfs are active than has previously been reported. Essentially all active objects are also variable.

We confirm the lack of a rotation-activity connection for L dwarfs. We find a minimum limit for rotational velocities that increases with later spectral types, rising from near zero in older mid-M stars to more than 20 km s$^{-1}$ for mid-L objects. There is strong evidence that all L dwarfs are rapid rotators.

We derive a braking law that depends on mass which can explain all the rotational results and provides an age dependence for the angular momentum evolution. It is not clear why its behavior is different than for stars which are not fully convective.

Comments: 19 pages, accepted for publication in ApJ

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0805.1059v1 [astro-ph]

Submission history

From: Ansgar Reiners [view email]

[v1] Wed, 7 May 2008 20:02:28 GMT (148kb)

http://arxiv.org/abs/0805.1059

• ljk May 29, 2008, 12:50

Confirmation of the Electron Cyclotron Maser Instability as the Dominant Source of Radio Emission from Very Low Mass Stars and Brown Dwarfs

Authors: G. Hallinan, A. Antonova, J.G. Doyle, S. Bourke, C. Lane, A. Golden

(Submitted on 26 May 2008)

Abstract: We report on radio observations of the M8.5 dwarf LSR J1835+3259 and the L3.5 dwarf 2MASS J00361617+1821104, which provide the strongest evidence to date that the electron cyclotron maser instability is the dominant mechanism producing radio emission in the magnetospheres of ultracool dwarfs. As has previously been reported for the M9 dwarf TVLM 513-46546, periodic pulses of 100% circularly polarized, coherent radio emission are detected from both dwarfs with periods of 2.84 +/- 0.01 and 3.08 +/- 0.05 hours respectively for LSR J1835+3259 and 2MASS J00361617+1821104.

Importantly, periodic unpolarized radio emission is also detected from 2MASS J00361617+1821104, and brightness temperature limitations rule out gyrosynchrotron radiation as a source of this radio emission. The unpolarized emission from this and other ultracool dwarfs is also attributed to electron cyclotron maser emission, which has become depolarized on traversing the ultracool dwarf magnetosphere, possibly due to propagations effects such as scattering.

Based on available v sin i data in the literature and rotation periods derived from the periodic radio data for the three confirmed sources of electron cyclotron maser emission, TVLM 513-46546, LSR J1835+3259 and 2MASS J00361617+1821104, we determine that the rotation axes of all three dwarfs are close to perpendicular to our line of sight. This suggests a possible geometrical selection effect due to the inherent directivity of electron cyclotron maser emission, that may account for the previously reported relationship between radio activity and v sin i observed for ultracool dwarfs. We also determine the radius of the dwarf LSR J1835+3259 to be > 0.117 +/- 0.012 R_Sol. (abridged)

Comments: 11 pages, 2 tables, 4 figures, accepted for publication in ApJ

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0805.4010v1 [astro-ph]

Submission history

From: Gregg Hallinan [view email]

[v1] Mon, 26 May 2008 21:11:24 GMT (780kb)

http://arxiv.org/abs/0805.4010

• ljk June 10, 2008, 13:37

Discovery of Two Nearby, Peculiar L Dwarfs from the 2MASS Proper Motion Survey: Young or Metal-Rich?

Authors: Dagny L. Looper (1), J. Davy Kirkpatrick (2), Roc M. Cutri (2), Travis Barman (3), Adam J. Burgasser (4), Michael C. Cushing (1,5), Thomas Roellig (6), Mark R. McGovern (7), Ian S. McLean (8), Emily Rice (8), Brandon J. Swift (5), Steven D. Schurr (2) (1. Institute for Astronomy/UH, Caltech/IPAC, 3. Lowell Observatory, 4. MIT, 5. Steward Observatory/UA, 6. NASA AMES, 7. Antelope Valley College, 8. UCLA)

(Submitted on 5 Jun 2008)

Abstract: We present the discovery of two nearby L dwarfs from our 2MASS proper motion search, which uses multi-epoch 2MASS observations covering ~4700 square degrees of sky. 2MASS J18212815+1414010 and 2MASS J21481628+4003593 were overlooked by earlier surveys due to their faint optical magnitudes and their proximity to the Galactic Plane (10 degrees < |b| < 15 degrees).

Assuming that both dwarfs are single, we derive spectrophotometric distances of ~10 pc, thus increasing the number of known L dwarfs within 10 pc to 10.

In the near-infrared, 2MASS J21481628+4003593 shows a triangular-shaped H-band spectrum, strong CO absorption, and a markedly red J-Ks color (2.38+/-0.06) for its L6 optical spectral type. 2MASS J18212815+1414010 also shows a triangular-shaped H-band spectrum and a slightly red J-Ks color (1.78+/-0.05) for its L4.5 optical spectral type. Both objects show strong silicate absorption at 9-11 microns. Cumulatively, these features imply an unusually dusty photosphere for both of these objects.

We examine several scenarios to explain the underlying cause for their enhanced dust content and find that a metal-rich atmosphere or a low-surface gravity are consistent with these results. 2MASS J18212815+1414010 may be young (and therefore have a low-surface gravity) based on its low tangential velocity of 10 km/s. On the other hand, 2MASS J21481628+4003593 has a high tangential velocity of 62 km/s and is therefore likely old. Hence, high metallicity and low-surface gravity may lead to similar effects.

Comments: 9 pages, 4 tables, 13 figures. Accepted to ApJ

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0806.1059v1 [astro-ph]

Submission history

From: Dagny Looper [view email]

[v1] Thu, 5 Jun 2008 21:16:29 GMT (543kb)

http://arxiv.org/abs/0806.1059

• What about Brown Dwarfs as colonization targets? Assuming they had Moons/Planets surrounding them, and radiated heat, how hard?

Not discounting the concept of colonizing the Brown Dwarf itself.