Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userProto-Brown Dwarf Disks as Products of Protostellar Disk Encounters
143
0
0.0
(
0
)
Authors
Sijing Shen
Ask ChatGPT about the research
No Arabic abstract
The formation of brown dwarfs via encounters between proto-stars has been confirmed with high-resolution numerical simulations with a restricted treatment of the thermal conditions. The new results indicate that young brown dwarfs (BDs) formed this way are disk-like and often reside in multiple systems. The newly-formed proto-BDs disks are up to 18 AU in size and spin rapidly making small-scale bipolar outflows, fragmentation and the possible formation of planetary companions likely as have recently been observed for BDs. The object masses range from 2 to 73 Jupiter masses, distributed in a manner consistent with the observed sub-stellar initial mass function. The simulations usually form multiple BDs on eccentric orbits about a star. One such system was hierarchical, a BD binary in orbit around a star, which may explain recently observed hierarchical systems. One third of the BDs were unbound after a few thousand years and interactions among orbiting BDs may eject more or add to the number of binaries. Improvements over prior work include resolution down to a Jupiter mass, self-consistent models of the vertical structure of the initial disks and careful attention to avoid artificial fragmentation.
rate research
Read More
The formation of brown dwarfs (BDs) due to the fragmentation of proto-stellar disks undergoing pairwise encounters was investigated. High resolution allowed the use of realistic initial disk models where both the vertical structure and the local Jeans mass were resolved. The results show that objects with masses ranging from giant planets to low mass stars can form during such encounters from initially stable disks. The parameter space of initial spin-orbit orientations and the azimuthal angles for each disk was explored. An upper limit on the initial Toomre Q value of ~2 was found for fragmentation to occur. Depending on the initial configuration, shocks, tidal-tail structures and mass inflows were responsible for the condensation of disk gas. Retrograde disks were generally more likely to fragment. When the interaction timescale was significantly shorter than the disks dynamical timescales, the proto-stellar disks tended to be truncated without forming objects. The newly-formed objects had masses ranging from 0.9 to 127 Jupiter masses, with the majority in the BD regime. They often resided in star-BD multiples and in some cases also formed hierarchical orbiting systems. Most of them had large angular momenta and highly flattened, disk-like shapes. The objects had radii ranging from 0.1 to 10 AU. The disk gas was assumed to be locally isothermal, appropriate for the short cooling times in extended proto-stellar disks, but not for condensed objects. An additional case with explicit cooling that reduced to zero for optically thick gas was simulated to test the extremes of cooling effectiveness and it was still possible to form objects in this case. Detailed radiative transfer is expected to lengthen the internal evolution timescale for these objects, but not to alter our basic results.
We present deep HST/NICMOS observations peering through the outflow cavity of the protostellar candidate IRAS 04381+2540 in the Taurus Molecular Cloud-1. A young stellar object as central source, a jet and a very faint and close (0.6) companion are identified. The primary and the companion have similar colours, consistent with strong reddening. We argue that the companion is neither a shock-excited knot nor a background star. The colour/magnitude information predicts a substellar upper mass limit for the companion, but the final confirmation will require spectroscopic information. Because of its geometry, young age and its rare low-mass companion, this system is likely to provide a unique insight into the formation of brown dwarfs.
We report the discovery of the youngest brown dwarf with a disk at 102 pc from the Sun, WISEA~J120037.79-784508.3 (W1200-7845), via the Disk Detective citizen science project. We establish that W1200-7845 is located in the 3.7$substack{+4.6 -1.4}$ Myr-old $varepsilon$~Cha association. Its spectral energy distribution (SED) exhibits clear evidence of an infrared (IR) excess, indicative of the presence of a warm circumstellar disk. Modeling this warm disk, we find the data are best fit using a power-law description with a slope $alpha = -0.94$, which suggests it is a young, Class II type disk. Using a single blackbody disk fit, we find $T_{eff, disk} = 521 K$ and $L_{IR}/L_{*} = 0.14$. The near-infrared spectrum of W1200-7845 matches a spectral type of M6.0$gamma pm 0.5$, which corresponds to a low surface gravity object, and lacks distinctive signatures of strong Pa$beta$ or Br$gamma$ accretion. Both our SED fitting and spectral analysis indicate the source is cool ($T_{eff} = $2784-2850 K), with a mass of 42-58 $M_{Jup}$, well within the brown dwarf regime. The proximity of this young brown dwarf disk makes the system an ideal benchmark for investigating the formation and early evolution of brown dwarfs.
The onset of planet formation in protoplanetary disks is marked by the growth and crystallization of sub-micron-sized dust grains accompanied by dust settling toward the disk mid-plane. Here we present infrared spectra of disks around brown dwarfs and brown dwarf candidates. We show that all three processes occur in such cool disks in a way similar or identical to that in disks around low- and intermediate-mass stars. These results indicate that the onset of planet formation extends to disks around brown dwarfs, suggesting that planet formation is a robust process occurring in most young circumstellar disks.
The study of the properties of disks around young brown dwarfs can provide important clues on the formation of these very low-mass objects and on the possibility of forming planetary systems around them. The presence of warm dusty disks around brown dwarfs is well known, based on near- and mid-infrared studies. High angular resolution observations of the cold outer disk are limited; we used ALMA to attempt a first survey of young brown dwarfs in the $rho$-Oph star-forming region. All 17 young brown dwarfs in our sample were observed at 890 $mu $m in the continuum at $sim0.!^{primeprime}5$ angular resolution. The sensitivity of our observations was chosen to detect $sim0.5$ M$_oplus$ of dust. We detect continuum emission in 11 disks ($sim65$% of the total), and the estimated mass of dust in the detected disks ranges from $sim0.5$ to $sim6$ M$_oplus$. These disk masses imply that planet formation around brown dwarfs may be relatively rare and that the supra-Jupiter mass companions found around some brown dwarfs are probably the result of a binary system formation. We find evidence that the two brightest disks in $rho$-Oph have sharp outer edges at R<~25 AU, in contrast to disks around Taurus brown dwarfs. This difference may suggest that the different environment in $rho$-Oph may lead to significant differences in disk properties. A comparison of the M$_{disk}$/M$_ast$ ratio for brown dwarf and solar-mass systems also shows a possible deficit of mass in brown dwarfs, which could support the evidence for dynamical truncation of disks in the substellar regime. These findings are still tentative and need to be put on firmer grounds by studying the gaseous disks around brown dwarfs and by performing a more systematic and unbiased survey of the disk population around the more massive stars.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
