# A Brown Dwarf Planet?

Although we’re beginning to realize that brown dwarfs are widespread in the galaxy, we know surprisingly little about how they form. The question has an obvious impact on planetary formation models as well, but we won’t get a good read on the answer until we’ve been able to study brown dwarfs and other very low-mass stars (VLMS) in multiple systems. Right now, relying largely on the Hubble Space Telescope and direct imaging via adaptive optics, we’re unable to detect close binaries in such systems. That leaves radial velocity techniques to do the job.

And indeed, a brown dwarf binary designated PPl 15 was found in the Pleiades in the late 90’s with these methods. But the hope of landing a large number of close brown dwarf companions has faded. So far, despite ongoing work, we still have only three brown dwarf binaries confirmed through spectroscopy. And we’re still asking planet-sized questions: Can a brown dwarf support planets at just a few AU distance?

The assumption is yes, given our growing catalog of planets around low-mass M-dwarfs, but the only planet detection thus far is 2M1207b, which was discovered in so wide an orbit (55 AU) that researchers say it presumably formed quite differently from the Solar System and planets detected by radial velocity methods in other systems. In fact, the possibility that 2M1207b is actually a brown dwarf itself, forming star-like from the collapse of a gaseous nebula, cannot be discounted.

But now we have evidence for a low-mass companion orbiting the brown dwarf candidate Cha Hα 8, a member of a nearby star-forming region called Chamaeleon I. The companion object, say V. Joergens and A. Müller (Max-Planck-Institut für Astronomie, Königstuhl) in the discovery paper, is definitely low mass, orbiting in the range of 1 AU. Unfortunately, the mass of the primary is not yet well determined, leading to a range in the possible mass of the companion from 15.6 to 19.5 Jupiter masses.

Or perhaps less massive still, as the paper notes:

The discovery of the RV companion of Cha Hα 8, which has an RV semi-amplitude of only 1.6 km s−1 , is an important step towards RV planet detections of BD/VLMS. In fact, from the uncertainty in the orbit solution, it cannot be completely excluded that the companion of Cha Hα 8 has a mass in the planetary mass regime (~13 MJup). Follow-up RV measurements monitoring the next phase of periastron (April 2011) are necessary to investigate this further.

It’s an intriguing find. As the authors point out, binary stars are thought to form in such a way that the companions are of relatively equal mass, particularly when the separation is close. The exceptions that do exist only remind us how much we have to learn about the mechanics of these systems, especially brown dwarfs. Or are we dealing not with a star but a planet forming through disk instability models, one that may well have formed further out in the system and subsequently migrated inwards?

The paper is Joergens and Müller, “16–20 MJup RV companion orbiting the brown dwarf candidate Cha Hα 81,” in press at the Astrophysical Journal Letters and available as an online preprint.

Comments on this entry are closed.

• Jyril August 6, 2007, 11:42

2M1907b has a considerable mass compared to its primary. It has also a distant orbit so it is practically impossible that it could have formed like planets form. Therefore it could be called a sub-brown dwarf, a brown dwarf -like object that can’t fuse even deuterium (and not a planet, if we require that planets must form from protoplanetary disks).

• daniel August 7, 2007, 15:14

what about the new planet TrES-4? 70% bigger that Jupiter

• ljk August 22, 2007, 10:50

arXiv:0708.2827

Date: Tue, 21 Aug 2007 12:52:34 GMT (2049kb)

Title: Brown dwarf formation by gravitational fragmentation
of massive, extended protostellar discs

Authors: Dimitris Stamatellos, David Hubber, Anthony Whitworth
(School of Physics & Astronomy, Cardiff University, UK)

Categories: astro-ph

Comments: 5 pages, accepted for publication in MNRAS Letters

We suggest that low-mass hydrogen-burning stars like the
Sun should sometimes form with massive extended discs; and
we show, by means of radiation hydrodynamic simulations, that
the outer parts of such discs (R greater than 100 AU) are likely
to fragment on a dynamical timescale (10^3 to $10^4 yr), forming low-mass companions: principally brown dwarfs (BDs), but also very low-mass hydrogen-burning stars and planetary- mass objects. A few of the BDs formed in this way remain attached to the primary star, orbiting at large radii. The majority are released into the field, by interactions amongst themselves; in so doing they acquire only a low velocity dispersion (less than 2 km/s), and therefore they usually retain small discs, capable of registering an infrared excess and sustaining accretion. Some BDs form close BD/BD binaries, and these binaries can survive ejection into the field. This BD formation mechanism appears to avoid some of the problems associated with the embryo ejection’ scenario, and to answer some of the questions not yet answered by the turbulent fragmentation’ scenario. http://arxiv.org/abs/0708.2827 , 2049kb • ljk September 7, 2007, 10:02 The potential for Earth-mass planet formation around brown dwarfs Authors: Matthew J. Payne (1), Giuseppe Lodato (2,1) ((1) Institute of Astronomy, Cambridge (2) Department of Physics and Astronomy, University of Leicester) (Submitted on 5 Sep 2007) Abstract: Recent observations point to the presence of structured dust grains in the discs surrounding young brown dwarfs, thus implying that the first stages of planet formation take place also in the sub-stellar regime. Here, we investigate the potential for planet formation around brown dwarfs and very low mass stars according to the sequential core accretion model of planet formation. We find that, for a brown dwarfs of mass 0.05M_{\odot}, our models predict a maximum planetary mass of ~5M_{\oplus}, orbiting with semi-major axis ~1AU. However, we note that the predictions for the mass – semi-major axis distribution are strongly dependent upon the models chosen for the disc surface density profiles and the assumed distribution of disc masses. In particular, if brown dwarf disc masses are of the order of a few Jupiter masses, Earth-mass planets might be relatively frequent, while if typical disc masses are only a fraction of Jupiter mass, we predict that planet formation would be extremely rare in the sub-stellar regime. As the observational constraints on disc profiles, mass dependencies and their distributions are poor in the brown dwarf regime, we advise caution in validating theoretical models only on stars similar to the Sun and emphasise the need for observational data on planetary systems around a wide range of stellar masses. We also find that, unlike the situation around solar-like stars, Type-II migration is totally absent from the planet formation process around brown dwarfs, suggesting that any future observations of planets around brown dwarfs would provide a direct measure of the role of other types of migration. Comments: 11 pages, accepted for publication in MNRAS Subjects: Astrophysics (astro-ph) Cite as: arXiv:0709.0676v1 [astro-ph] Submission history From: Matthew Payne [view email] [v1] Wed, 5 Sep 2007 15:44:29 GMT (236kb) http://arxiv.org/abs/0709.0676 • ljk October 14, 2007, 20:18 Discovery of 18 Jupiter mass RV companion orbiting the brown dwarf candidate ChaHa8 Authors: Viki Joergens, Andre Mueller (Submitted on 12 Oct 2007) Abstract: We report the discovery of a 16-20 Jupiter mass radial velocity companion around the very young (3 Myr) brown dwarf candidate ChaHa8. Based on high-resolution echelle spectra of ChaHa8 taken between 2000 and 2007 with UVES at the VLT, a companion was detected through RV variability with a semi-amplitude of 1.6 km/s. A Kepler fit to the data yields an orbital period of the companion of 1590 days and an eccentricity of e=0.49. A companion minimum mass M2sin i between 16 and 20 Jupiter masses is derived when using model-dependent mass estimates for the primary. The mass ratio M2/M1 might be as small as 0.2 and, with a probability of 87%, it is less than 0.4. ChaHa8 harbors most certainly the lowest mass companion detected so far in a close (~1 AU) orbit around a brown dwarf or very low-mass star. From the uncertainty in the orbit solution, it cannot completely be ruled out that the companion has a mass in the planetary regime. Its discovery is in any case an important step towards RV planet detections around BDs. Further, ChaHa8 is the fourth known spectroscopic brown dwarf or very low-mass binary system with an RV orbit solution and the second known very young one. Comments: Proceeding of conference ‘Extreme Solar Systems’ held on Santorini in June 2007, 4 pages, 1 figure Subjects: Astrophysics (astro-ph) Cite as: arXiv:0710.2437v1 [astro-ph] Submission history From: Viki Joergens [view email] [v1] Fri, 12 Oct 2007 11:37:17 GMT (25kb) http://arxiv.org/abs/0710.2437 • ljk November 7, 2007, 13:05 An accurate distance to 2M1207Ab Authors: C. Ducourant, R. Teixeira, G. Chauvin, G.Daigne, J.F. Le Campion, Inseok Song, B.Zuckerman (Submitted on 6 Nov 2007) Abstract: In April 2004 the first image was obtained of a planetary mass companion (now known as 2M1207 b) in orbit around a self-luminous object different from our own Sun (the young brown dwarf 2MASSW J1207334-393254, hereafter 2M1207 A). 2M1207 b probably formed via fragmentation and gravitational collapse, offering proof that such a mechanism can form bodies in the planetary mass regime. However, the predicted mass, luminosity, and radius of 2M1207 b depend on its age, distance, and other observables such as effective temperature. To refine our knowledge of the physical properties of 2M1207 b and its nature, we obtained an accurate determination of the distance to the 2M1207 A and b system by measurements of its trigonometric parallax at the milliarcsec level. With the ESO NTT/SUSI2 telescope, in 2006 we began a campaign of photometric and astrometric observations to measure the trigonometric parallax of 2M1207 A. An accurate distance ($52.4\pm 1.1$pc) to 2M1207A was measured. From distance and proper motions we derived spatial velocities fully compatible with TWA membership. With this new distance estimate, we discuss three scenarios regarding the nature of 2M1207 b: (1) a cool ($1150\pm150$K) companion of mass$4\pm1$M$_{\rm{Jup}}$, (2) a warmer ($1600\pm100$K) and heavier ($8\pm2$M$_{\rm{Jup}}$) companion occulted by an edge-on circum-secondary disk or (3) a hot protoplanet collision afterglow. Comments: 5 pages, 3 figures, accepted for publication as letter in A&A, 6/11/2007 Subjects: Astrophysics (astro-ph) Cite as: arXiv:0711.0842v1 [astro-ph] Submission history From: Christine Ducourant [view email] [v1] Tue, 6 Nov 2007 16:03:38 GMT (151kb,D) http://arxiv.org/abs/0711.0842 • ljk December 13, 2007, 10:39 Mid-infrared imaging of brown dwarfs in binary systems Authors: K. Geißler, G. Chauvin, M.F. Sterzik (Submitted on 12 Dec 2007) Abstract: Context: Brown dwarfs exhibit complex atmospheric signatures, and their properties depend sensitively on effective temperature, surface gravity, and metallicity. Several physical properties of brown dwarfs in binary systems can be well inferred from the primary, and therefore allow to better constrain their atmospheres. Aims: We want to constrain atmospheric models of brown dwarfs in binary systems using narrow-band mid-infrared photometry. Methods: High spatial resolution and sensitivity is required to resolve the components. Therefore we have obtained deep mid-infrared images of four close binary systems with brown dwarf companions using VISIR at the VLT in three narrow-band filters at 8.6, 10.5 and 11.25 micron. Results: Three brown dwarfs companions (GJ 229B, HD 130948BC and HR 7329B) were detected at 8.6micron. HD 130948BC was also observed at 10.5micron. We finally place upper flux limits for the other narrow band filters with null detections. Conclusions: Our results are in general compatible with previous observations and model expectations for these objects. For HD 130948BC, we conclude photometric variability on a significance level of 2.8sigma based on repeated observations. The bandpass around 10.5micron appears specifically well suited for variability studies, and we speculate that either inhomogeneities in the atmospheric NH3 distribution, or silicate absorption might cause its time-variability. Comments: accepted by A&A Subjects: Astrophysics (astro-ph) Cite as: arXiv:0712.1887v1 [astro-ph] Submission history From: Kerstin Gei{\ss}ler [view email] [v1] Wed, 12 Dec 2007 09:31:35 GMT (501kb,D) http://arxiv.org/abs/0712.1887 • ljk January 7, 2008, 12:09 Brown dwarfs and very low mass stars in the Hyades cluster : a dynamically evolved mass function Authors: J. Bouvier, T. T. Kendall, G. Meeus, L. Testi, E. Moraux, J.R. Stauffer, D. James, J.-C. Cuillandre, J. Irwin, M.J. McCaughrean, I. Baraffe, E. Bertin (Submitted on 4 Jan 2008) Abstract: We conducted a search for brown dwarfs (BDs) and very low mass (VLM) stars in the 625 Myr-old Hyades cluster in order to derive the cluster’s mass function across the stellar-substellar boundary. We performed a deep (I=23, z=22.5) photometric survey over 16 sq.deg. around the cluster center, followed up with K-band photometry to measure the proper motion of candidate members, and optical and near-IR spectroscopy of probable BD and VLM members. We report the discovery of the first 2 brown dwarfs in the Hyades cluster. The 2 objects have a spectral type early-T and their optical and near-IR photometry as well as their proper motion are consistent with them being cluster members. According to models, their mass is 50 Jupiter masses at an age of 625 Myr. We also report the discovery of 3 new very low mass stellar members of the cluster, and confirm the membership of 16 others. We combine these results with a list of previously known cluster members to build the present-day mass function (PDMF) of the Hyades cluster from 50 Jupiter masses to 3Mo. We find the Hyades PDMF to be strongly deficient in very low mass objects and brown dwarfs compared to the IMF of younger open clusters such as the Pleiades. We interpret this deficiency as the result of dynamical evolution over the past few 100 Myr, i.e., the preferential evaporation of low mass cluster members due to weak gravitational encounters. We thus estimate that the Hyades cluster currently hosts about 10-15 brown dwarfs, while its initial substellar population may have amounted up to 150-200 members. Comments: 16 pages Subjects: Astrophysics (astro-ph) Cite as: arXiv:0801.0670v1 [astro-ph] Submission history From: Jerome Bouvier [view email] [v1] Fri, 4 Jan 2008 12:21:59 GMT (474kb) http://arxiv.org/abs/0801.0670 • ljk January 11, 2008, 2:47 Dynamical Mass of GJ 802B: a brown dwarf in a triple system Authors: M.J. Ireland, A. Kraus, F. Martinache, J.P. Lloyd, P.G. Tuthill (Submitted on 9 Jan 2008) Abstract: We report a dynamical measurement of the mass of the brown dwarf GJ 802B using aperture-masking interferometry and astrometry. In addition, we report the discovery that GJ 802A is itself a close spectroscopic non-eclipsing binary with a 19 hour period. We find the mass of GJ 802B to be$0.063\pm0.005$M$_\sun$. GJ 802 has kinematics inconsistent with a young star and more consistent with the thick disk population, implying a system age of$\sim$10 GYr. However, model evolutionary tracks for GJ 802B predict system ages of$\sim$2 GYr, suggesting that brown dwarf evolutionary models may be underestimating luminosity for old brown dwarfs. Comments: 10 pages, 6 figures, accepted for ApJ Subjects: Astrophysics (astro-ph) Cite as: arXiv:0801.1525v1 [astro-ph] Submission history From: Michael Ireland [view email] [v1] Wed, 9 Jan 2008 22:49:47 GMT (47kb) http://arxiv.org/abs/0801.1525 • ljk January 16, 2008, 11:57 CLOUDS search for variability in brown dwarf atmospheres Authors: B. Goldman (NMSU, MPIA), M. C. Cushing (UA), M. S. Marley (Ames), É. Artigau (Gemini), K. S. Baliyan (PRL), V. J. S. Béjar (IAC), J. A. Caballero (MPIA, IAC), N. Chanover (NMSU), M. Connelley (IfA), R. Doyon (Montréal), T. Forveille (CFHT, Grenoble), S. Ganesh (PRL), C. R. Gelino (NMSU, Spitzer), H. B. Hammel (SSI), J. Holtzman (NMSU), S. Joshi (ARIES), U. C. Joshi (PRL), S. K. Leggett (JAC), M. C. Liu (IfA), E. L. Martín (IAC), V. Mohan (IUCAA), D. Nadeau (Montréal), R. Sagar (AIRES), D. Stephens (BYU), for the CLOUDS Collaboration (Submitted on 15 Jan 2008) Abstract: Context: L-type ultra-cool dwarfs and brown dwarfs have cloudy atmospheres that could host weather-like phenomena. The detection of photometric or spectral variability would provide insight into unresolved atmospheric heterogeneities, such as holes in a global cloud deck. Aims: It has been proposed that growth of heterogeneities in the global cloud deck may account for the L- to T-type transition as brown dwarf photospheres evolve from cloudy to clear conditions. Such a mechanism is compatible with variability. We searched for variability in the spectra of five L6 to T6 brown dwarfs in order to test this hypothesis. Methods: We obtained spectroscopic time series using VLT/ISAAC, over 0.99-1.13um, and IRTF/SpeX for two of our targets, in J, H and K bands. We search for statistically variable lines and correlation between those. Results: High spectral-frequency variations are seen in some objects, but these detections are marginal and need to be confirmed. We find no evidence for large amplitude variations in spectral morphology and we place firm upper limits of 2 to 3% on broad-band variability, on the time scale of a few hours. The T2 transition brown dwarf SDSS J1254-0122 shows numerous variable features, but a secure variability diagnosis would require further observations. Conclusions: Assuming that any variability arises from the rotation of patterns of large-scale clear and cloudy regions across the surface, we find that the typical physical scale of cloud cover disruption should be smaller than 5-8% of the disk area for four of our targets. The possible variations seen in SDSS J1254-0122 are not strong enough to allow us to confirm the cloud breaking hypothesis. Comments: 17 pages, 14 figures, accepted by A&A Subjects: Astrophysics (astro-ph) Cite as: arXiv:0801.2371v1 [astro-ph] Submission history From: Bertrand Goldman [view email] [v1] Tue, 15 Jan 2008 20:29:08 GMT (425kb) http://arxiv.org/abs/0801.2371 • ljk January 17, 2008, 1:28 Mapping the Shores of the Brown Dwarf Desert I.: Upper Scorpius Authors: Adam L. Kraus, Michael J. Ireland (Caltech), Frantz Martinache, James P. Lloyd (Cornell) (Submitted on 15 Jan 2008) Abstract: We present the results of a survey for stellar and substellar companions to 82 young stars in the nearby OB association Upper Scorpius. This survey used nonredundant aperture-mask interferometry to achieve typical contrast limits of DeltaK~5-6 at the diffraction limit, revealing 12 new binary companions that lay below the detection limits of traditional high-resolution imaging; we also summarize a complementary snapshot imaging survey that discovered 7 directly resolved companions. The overall frequency of binary companions (~35+5/-4% at separations of 6-435 AU) appears to be equivalent to field stars of similar mass, but companions could be more common among lower-mass stars than for the field. The companion mass function has statistically significant differences compared to several suggested mass functions for the field, and we suggest an alternate log-normal parameterization of the mass-function. Our survey limits encompass the entire brown dwarf mass range, but we only detected a single companion that might be a brown dwarf; this deficit resembles the so-called “brown dwarf desert” that has been observed by radial-velocity planet searches. Finally, our survey’s deep detection limits extend into the top of the planetary mass function, reaching 8-12 MJup for half of our sample. We have not identified any planetary companions at high confidence (greater than 99.5%), but we have identified four candidate companions at lower confidence (greater than 97.5%) that merit additional followup to confirm or disprove their existence. Comments: Accepted to ApJ; 23 pages, 7 figures, 9 tables in emulateapj format Subjects: Astrophysics (astro-ph) Cite as: arXiv:0801.2387v1 [astro-ph] Submission history From: Adam Kraus [view email] [v1] Tue, 15 Jan 2008 21:26:45 GMT (209kb) http://arxiv.org/abs/0801.2387 • ljk February 18, 2008, 17:13 New Brown Dwarf Disks in the TW Hydrae Association Authors: B. Riaz, J. E. Gizis (Submitted on 14 Feb 2008) Abstract: In our analysis of {\it Spitzer}/IRS archival data on the stellar and sub-stellar members of the TW Hydrae Association (TWA), we have discovered two new brown dwarf disks: a flat optically thick disk around SSSPM J1102-3431 (SSSPM 1102), and a transition disk around 2MASS J1139511-315921 (2M1139). The disk structure for SSSPM 1102 is found to be very similar to the known brown dwarf disk 2MASSW J1207334-393254 (2M1207), with excess emission observed at wavelengths as short as 5$\micron$. 2M1139 shows no excess emission shortward of$\sim$20$\micron$, but flares up at longer wavelengths, and is the first transition disk detected among the sub-stellar members of TWA. We also report on the {\it Spitzer}/70$\micron$observations, and the presence of a weak {\it absorption} 10$\micron$silicate feature for 2M1207. The absorption can be attributed to a close to edge-on disk at a 75$\degr$inclination. The 10$\micron$spectrum for 2M1207 shows crystalline forsterite features, with a peak in absorption near 11.3$\micron$. No silicate absorption/emission is observed towards SSSPM 1102. While only 6 out of 25 stellar members show excess emission at these mid-infrared wavelengths, {\it all} of the TWA brown dwarfs that have been observed so far with {\it Spitzer} show signs of disks around them, resulting in a disk fraction of at least 60%. This is a considerable fraction at a relatively older age of$\sim$10 Myr. A comparison with younger clusters indicates that by the age of the TWA ($\sim$10 Myr), the disk fraction for brown dwarfs has not decreased, whereas it drops by a factor of$\sim$2 for the higher mass stars. This suggests longer disk decay time scales for brown dwarfs compared to higher mass stars. Comments: 23 pages, 6 figures. Accepted in ApJ Subjects: Astrophysics (astro-ph) Cite as: arXiv:0802.2048v1 [astro-ph] Submission history From: Basmah Riaz [view email] [v1] Thu, 14 Feb 2008 16:31:02 GMT (172kb) http://arxiv.org/abs/0802.2048 • James M. Essig February 18, 2008, 23:15 Hi Folks; It occurred to me that brown dwarfs upon full formation might produce enough black body thermal emmissions to provide natural warmth for very large space habitats that might be constructed in near orbit around them. Perhaps in order to maintain the warmth generated by these bodies, a gradual supply of very long lived radio nucleids could be dropped into the brown dwarf gradually and continuosly or approximately so inorder to provide warmth. Uranium 238 is one isotope that comes to mind and it is U-238 which is believed to be largely responsible for the maintainence of the hot interior of the Earth which would have cooled billions of years ago were in not for the presence or radioactive isotopes within the Earth’s core and perhaps lower mantel. Even longer lived isotopes might extend the length time that such brown dwarfs could provide heat. Brown dwarfs either by themselves or modified with radioactive material might be ideal stellar like space colony heat providers for future humanity because these dwarfs might not be under the political juristdictions of any ETI races. Any ETI civilizations might see such brown dwarfs as unwanted or un-needed real estate. Thanks; Jim • ljk February 19, 2008, 9:24 Why would an ETI see brown dwarfs as undesirable real estate yet you say they are perfectly suitable for colonization by humanity? I am not following your logic here. • James M. Essig February 19, 2008, 10:35 Hi ljk; You make a good point. If we could utilize brown dwarfs as realestate, there is no reason why ETI with more advanced technology might not have already laid claims to and have utilized them. For some dumb reason, I overlooked this fact. Thanks; Jim • ljk March 3, 2008, 10:08 CFBDS J005910.90-011401.3: reaching the T-Y Brown Dwarf transition? Authors: Philippe Delorme (LAOG), Xavier Delfosse (LAOG, OSUG), Loic Albert (CFHT), Etienne. Artigau, Thierry Forveille (LAOG, OSUG, CFHT), Céline Reylé (LAOB), France Allard (CRAL), Derek Homeier, Annie Robin (LAOB), Chris J. Willott, Michael Liu (IfA), Trent Dupuy (IfA) (Submitted on 29 Feb 2008 (v1), last revised 3 Mar 2008 (this version, v2)) Abstract: We report the discovery of CFBDS J005910.90-011401.3 (hereafter CFBDS0059), the coolest brown dwarf identified to date. We found CFBDS0059 using i’ and z’ images from the Canada-France-Hawaii Telescope (CFHT), and present optical and near-infrared photometry, Keck laser guide star adaptive optics imaging, and a complete near-infrared spectrum, from 1.0 to 2.2$\mu$m. A side to side comparison of the near-infrared spectra of CFBDS0059 and ULAS~J003402.77-005206.7 (hereafter ULAS0034), previously the coolest known brown dwarf, indicates that CFBDS0059 is ~50+/-15K cooler. We estimate a temperature of Teff~620K and gravity of log g ~ 4.75. Evolutionary models translate these parameters into an age of 1-5 Gyr and a mass of 15-30 M_Jup. We estimate a photometric distance of ~13pc, which puts CFBDS0059 within easy reach of accurate parallax measurements. Its large proper motion suggests membership in the older population of the thin disk. The spectra of both CFBDS0059 and ULAS~J0034 shows probable absorption by a wide ammonia band on the blue side of the$H\$-band flux peak. If, as we expect, that feature deepens further for still lower effective temperatures, its appearance will become a natural breakpoint for the transition between the T spectral class and the new Y spectral type. CFBDS0059 and ULAS~J0034 would then be the first Y0 dwarfs.

Comments: 12 pages, Submitted to A\&A

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0802.4387v2 [astro-ph]

Submission history

From: Philippe Delorme [view email] [via CCSD proxy]

[v1] Fri, 29 Feb 2008 13:20:57 GMT (881kb)

[v2] Mon, 3 Mar 2008 10:34:11 GMT (737kb)

http://arxiv.org/abs/0802.4387

• ljk March 11, 2008, 0:04

The Future of Ultracool Dwarf Science with JWST

Authors: Mark S. Marley (NASA ARC), S.K. Leggett (Gemini Observatory)

(Submitted on 10 Mar 2008)

Abstract: Ultracool dwarfs exhibit a remarkably varied set of characteristics which hint at the complex physical processes acting in their atmospheres and interiors. Spectra of these objects not only depend upon their mass and effective temperature, but also their atmospheric chemistry, weather, and dynamics. As a consequence divining their mass, metallicity and age solely from their spectra has been a challenge. JWST, by illuminating spectral blind spots and observing objects with constrained masses and ages should finally unearth a sufficient number of ultracool dwarf Rosetta Stones to allow us to decipher the processes underlying the complex brown dwarf cooling sequence. In addition the spectra of objects invisible from the ground, including very low mass objects in clusters and nearby cold dwarfs from the disk population, will be seen for the first time. In combination with other ground- and space-based assets and programs, JWST will usher in a new golden era of brown dwarf science and discovery.

Comments: 23 pages, 9 figures, for publication in proceedings of “Astrophysics in the Next Decade: JWST and Concurrent Facilities”, a meeting held Sept. 24-27 in Tucson, Arizona

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0803.1476v1 [astro-ph]

Submission history

From: Mark S. Marley [view email]

[v1] Mon, 10 Mar 2008 19:23:50 GMT (2157kb,D)

http://arxiv.org/abs/0803.1476

• ljk March 17, 2008, 22:20

Structural and compositional properties of brown dwarf disks: the case of 2MASS J04442713+2512164

Authors: H. Bouy, N. Huelamo, C. Pinte, J. Olofsson, D. Barrado y Navascues, E. L. Martin, E. Pantin, J.-L. Monin, G. Basri, J.-C. Augereau, F. Menard, G. Duvert, G. Duchene, F. Marchis, A. Bayo, S. Bottinelli, B. Lefort, S. Guieu

(Submitted on 13 Mar 2008)

Abstract: In order to improve our understanding of substellar formation, we have performed a compositional and structural study of a brown dwarf disk.
We present the result of photometric, spectroscopic and imaging observations of 2MASS J04442713+2512164, a young brown dwarf (M7.25) member of the Taurus association. Our dataset, combined with results from the literature, provides a complete coverage of the spectral energy distribution from the optical to the millimeter including the first photometric measurement of a brown dwarf disk at 3.7mm, and allows us to perform a detailed analysis of the disk properties.

The target was known to have a disk. High resolution optical spectroscopy shows that it is intensely accreting, and powers a jet and an outflow. The disk structure is similar to that observed for more massive TTauri stars. Spectral decomposition models of Spitzer/IRS spectra suggest that the mid-infrared emission from the optically thin disk layers is dominated by grains with intermediate sizes (1.5micron). Crystalline silicates are significantly more abondant in the outer part and/or deeper layers of the disk, implying very efficient mixing and/or additional annealing processes. Sub-millimeter and millimeter data indicate that most of the disk mass is in large grains (>1mm)

Comments: 17 pages, 10 figures, 7 tables, accepted for A&A

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0803.2051v1 [astro-ph]

Submission history

From: Herve Bouy [view email]

[v1] Thu, 13 Mar 2008 21:00:38 GMT (313kb)

http://arxiv.org/abs/0803.2051

• ljk April 2, 2008, 7:19

Dust in Brown Dwarfs and Extra-solar Planets I. Chemical composition and spectral appearance of quasi-static cloud layers

Authors: Ch. Helling, P. Woitke, W.-F. Thi

(Submitted on 30 Mar 2008)

Abstract: We aim at understanding the formation of cloud layers in quasi-static substellar atmospheres. The time-dependent description presented in (Helling & Woitke 2006) is a kinetic model describing nucleation, growth and evaporation. It is extended to treat gravitational settling and is applied to the static-stationary case of substellar model atmospheres. From the solution for the dust moments, we determine the grain size distribution function which, together with the calculated material volume fractions, provides the basis to calculate the opacities of the composite dust grains. The cloud particles in brown dwarfs and hot giant-gas planets are found to be small in the high atmospheric layers (0.01mum), and composed of a rich mixture of all considered condensates, in particular the abundant MgSiO3[s], Mg2SiO4[s] and SiO2[s]. As the particles settle downward, they increase in size and reach several 100mum in the deepest layers. The more volatile parts of the grains evaporate and the particles stepwise purify to form composite particles of high-temperature condensates in the deeper layers, mainly Fe[s] and Al2O3[s]. The gas phase abundances of the elements involved in the dust formation process vary by orders of magnitudes throughout the atmosphere. The grain size distribution is found to be relatively broad in the upper atmospheric layers but often strongly peaked in the deeper layers. The spectral appearance of the cloud layers in the mid IR (7-20mum) is close to a grey body with only weak broad features on a few percent level, mainly caused by MgSiO3[s], and Mg2SiO4[s]. Our models predict that the gas phase depletion is much weaker as compared to phase-equilibrium calculations in the high atmospheric layers. [abridged]

Comments: 16 pages, 9 Figures. A&A accepted

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0803.4315v1 [astro-ph]

Submission history

From: Christiane Helling [view email]

[v1] Sun, 30 Mar 2008 12:05:48 GMT (242kb)

http://arxiv.org/abs/0803.4315

• ljk May 27, 2008, 14:33

New Low-Mass Stars and Brown Dwarfs with Disks in the Chamaeleon I Star-Forming Region

Authors: K. L. Luhman, A. A. Muench

(Submitted on 23 May 2008)

Abstract: We have used images obtained with the Infrared Array Camera and the Multiband Imaging Photometer onboard the Spitzer Space Telescope to search for low-mass stars and brown dwarfs with circumstellar disks in the Chamaeleon I star-forming region. Through optical spectroscopy of sources with red colors in these data, we have identified seven new disk-bearing members of the cluster.

Three of these objects are probably brown dwarfs according to their spectral types (M8, M8.5, M8-L0). Three of the other new members may have edge-on disks based on the shapes of their infrared spectral energy distributions. One of the possible edge-on systems has a steeply rising slope from 4.5 to 24um, indicating that it could be a class I source (star+disk+envelope) rather than a class II source (star+disk). If so, then it would be one of the least massive known class I protostars (M5.75, M~0.1 Msun).

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0805.3722v1 [astro-ph]

Submission history

From: Kevin Luhman [view email]

[v1] Fri, 23 May 2008 21:29:38 GMT (947kb)

http://arxiv.org/abs/0805.3722

• John Liband April 12, 2010, 20:49

Brown Dwarfs are stars , even though they have very low luminosity, nevertheless they are still stars, and could be fission fragments of a larger object. Are we so sure that stars are powered by nuclear fusion? This has never been proved conclusively,in fact , they could be powered by electric currents coming in from the outside, since they are,balls of plasma, not hot balls of gas!