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Register a new userAn ALMA Disk Mass for the Candidate Protoplanetary Companion to FW Tau
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We present ALMA observations of the FW Tau system, a close binary pair of M5 stars with a wide-orbit (300 AU projected separation) substellar companion. The companion is extremely faint and red in the optical and near-infrared, but boasts a weak far-infrared excess and optical/near-infrared emission lines indicative of a primordial accretion disk of gas and dust. The component-resolved 1.3 mm continuum emission is found to be associated only with the companion, with a flux (1.78 +/- 0.03 mJy) that indicates a dust mass of 1-2 M_Earth. While this mass reservoir is insufficient to form a giant planet, it is more than sufficient to produce an analog of the Kepler-42 exoplanetary system or the Galilean satellites. The mass and geometry of the disk-bearing FW Tau companion remains unclear. Near-infrared spectroscopy shows deep water bands that indicate a spectral type later than M5, but substantial veiling prevents a more accurate determination of the effective temperature (and hence mass). Both a disk-bearing planetary-mass companion seen in direct light or a brown dwarf tertiary viewed in light scattered by an edge-on disk or envelope remain possibilities.
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We report the discovery of three planetary-mass companions (M = 6--20 $M_{Jup}$) in wide orbits ($rho sim$ 150--300 AU) around the young stars FW Tau (Taurus-Auriga), ROXs 12 (Ophiuchus), and ROXs 42B (Ophiuchus). All three wide planetary-mass companions (PMCs) were reported as candidate companions in previous binary survey programs, but then were neglected for $>$10 years. We therefore obtained followup observations which demonstrate that each candidate is comoving with its host star. Based on the absolute $M_{K}$ magnitudes, we infer masses (from hot-start evolutionary models) and projected separations of 10 $pm$ 4 $M_{Jup}$ and 330 $pm$ 30 AU for FW Tau b, 16 $pm$ 4 $M_{Jup}$ and 210 $pm$ 20 AU for ROXs 12 b, and 10 $pm$ 4 $M_{Jup}$ and 140 $pm$ 10 AU for ROXs 42B b. We also present similar observations for ten other candidates which show that they are unassociated field stars, as well as multicolor JHKL near-infrared photometry for our new PMCs and for five previously-identified substellar or planetary-mass companions. The NIR photometry for our sample of eight known and new companions generally parallels the properties of free-floating low-mass brown dwarfs in these star-forming regions. However, 5 of the 7 objects with M $<$ 30 $M_{Jup}$ are redder in K-L than the distribution of young free-floating counterparts of similar J-K. We speculate that this distinction could indicate a structural difference in circum-planetary disks, perhaps tied to higher disk mass since at least two of the objects in our sample are known to be accreting more vigorously than typical free-floating counterparts.
Using the Atacama Large Millimeter/submillimeter Array (ALMA), we observed the young Herbig star HD 100546, host to a prominent disk with a deep, wide gap in the dust. The high-resolution 1.3 mm continuum observation reveals fine radial and azimuthal substructures in the form of a complex maze of ridges and trenches sculpting a dust ring. The $^{12}$CO(2-1) channel maps are modulated by wiggles or kinks that deviate from Keplerian kinematics particularly over the continuum ring, where deviations span 90$^circ$ in azimuth, covering 5 km s$^{-1}$. The most pronounced wiggle resembles the imprint of an embedded massive planet of at least 5 M$_{rm Jup}$ predicted from previous hydrodynamical simulations (Perez, Casassus, & Benitez-Llambay 2018). Such planet is expected to open a deep gap in both gas and dust density fields within a few orbital timescales, yet the kinematic wiggles lie near ridges in the continuum. The lesser strength of the wiggles in the $^{13}$CO and C$^{18}$O isotopologues show that the kinematic signature weakens at lower disk heights, and suggests qualitatively that it is due to vertical flows in the disk surface. Within the gap, the velocity field transitions from Keplerian to strongly non-Keplerian via a twist in position angle, suggesting the presence of another perturber and/or an inner warp. We also present VLT/SPHERE sparse aperture masking data which recovers scattered light emission from the gaps edges but shows no evidence for signal within the gap, discarding a stellar binary origin for its opening.
We report an analysis of the dust disk around DM~Tau, newly observed with the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.3 mm. The ALMA observations with high sensitivity (8.4~$mu$Jy/beam) and high angular resolution (35~mas, 5.1~au) detect two asymmetries on the ring at $rsim$20~au. They could be two vortices in early evolution, the destruction of a large scale vortex, or double continuum emission peaks with different dust sizes. We also found millimeter emissions with $sim$50~$mu$Jy (a lower limit dust mass of 0.3~$M_{rm Moon}$) inside the 3-au ring. To characterize these emissions, we modeled the spectral energy distribution (SED) of DM~Tau using a Monte Carlo radiative transfer code. We found that an additional ring at $r=$ 1~au could explain both the DM~Tau SED and the central point source. The disk midplane temperature at the 1-au ring calculated in our modeling is less than the typical water sublimation temperature of 150~K, prompting the possibility of forming small icy planets there.
We aim at estimating the dust scale height of protoplanetary disks from millimeter continuum observations. First, we present a general expression of intensity of a ring in a protoplanetary disk, and show that we can constrain the dust scale height by the azimuthal intensity variation. Then, we apply the presented methodology to the two distinct rings at 68 au and at 100 au of the protoplanetary disk around HD 163296. We constrain the dust scale height by comparing the DSHARP high-resolution millimeter dust continuum image with radiative transfer simulations using RADMC-3D. We find that h_d/h_g > 0.84 at the inner ring and h_d/h_g < 0.11 at the outer ring with the 3 sigma uncertainties, where h_d is the dust scale height and h_g is the gas scale height. This indicates that the dust is flared at the inner ring and settled at the outer ring. We further constrain the ratio of turbulence parameter alpha to gas-to-dust-coupling parameter St from the derived dust scale height; alpha/St > 2.4 at the inner ring, and alpha/St < 1.1*10^{-2} at the outer ring. This result shows that the turbulence is stronger or the dust is smaller at the inner ring than at the outer ring.
Astrometric observations of the M9 dwarf TVLM 513$-$46546 taken with the VLBA reveal an astrometric signature consistent with a period of 221 $pm$ 5 days. The orbital fit implies that the companion has a mass m$_{p}$ = 0.35$-$0.42 $M_{J}$, a circular orbit ($e simeq 0$), a semi-major axis a = 0.28$-$0.31 AU and an inclination angle i = 71$-$88$^circ$. The detected companion, TVLM~513$b$, is one of the few giant-mass planets found associated to UCDs. The presence of a Saturn-like planet on a circular orbit, 0.3 AU from a 0.06$-$0.08 $M_odot$ star, represents a challenge to planet formation theory. This is the first astrometric detection of a planet at radio wavelengths.
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