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In 2017, the next generation Very Large Array (ngVLA) Science Advisory Council, together with the international astronomy community, developed a set of five Key Science Goals (KSGs) to inform, prioritize and refine the technical capabilities of a future radio telescope array for high angular resolution operation from 1.2 - 116 GHz with 10 times the sensitivity of the Jansky VLA and ALMA. The resulting KSGs, which require observations at centimeter and millimeter wavelengths that cannot be achieved by any other facility, represent a small subset of the broad range of astrophysical problems that the ngVLA will be able address. This document presents an update to the original ngVLA KSGs, taking account of new results and progress in the 7+ years since their initial presentation, again drawing on the expertise of the ngVLA Science Advisory Council and the broader community in the ngVLA Science Working Groups. As the design of the ngVLA has also matured substantially in this period, this document also briefly addresses initial expectations for ngVLA data products and processing that will be needed to achieve the KSGs. The original ngVLA KSGs endure as outstanding problems of high priority. In brief, they are: (1) Unveiling the Formation of Solar System Analogues; (2) Probing the Initial Conditions for Planetary Systems and Life with Astrochemistry; (3) Charting the Assembly, Structure, and Evolution of Galaxies from the First Billion Years to the Present; (4) Science at the Extremes: Pulsars as Laboratories for Fundamental Physics; (5) Understanding the Formation and Evolution of Stellar and Supermassive Black Holes in the Era of Multi-Messenger Astronomy., Comment: 29 pages, 9 figures, ngVLA memo 125. arXiv admin note: text overlap with arXiv:1711.09960

Synthesized beam (PSF) synthetic observations with and without the antennas in Mexico are analyzed. For a simple continuum observing setup, we generated visibility files and their associated PSF images for a grid of parameters (robust weighting, tapering, and declination). The tests were done for both the MID and MID+Spiral+Core configurations and their cropped versions without antennas in Mexico. We show that the performance of the Array, in terms of the beam properties, is in general significantly better when both the MID array antennas are present in Northern Mexico and observations target southern sources. At a declination of -40 deg, there are increments in the ellipticity of at least ~1.3X and 1.2X for a tapering of 3.0 and 4.0 mas, if the antennas in Mexico are not included. For the parameter space tested, the changes in ellipticity of the MID and MID+Spiral+Core configurations differ by ~10%. Larger tapering values help to reduce the ellipticity for cropped configurations at all declinations, but it will impose more constraints in terms of angular resolution., Comment: 10 pages, 8 figures

We investigate the planetary migration of low-mass planets ($M_p\in[1,15]M_\oplus$, here $M_\oplus$ is the Earth mass) in a gaseous disc containing a previously formed gap. We perform high-resolution 3D simulations with the FARGO3D code. To create the gap in the surface density of the disc, we use a radial viscosity profile with a bump, which is maintained during the entire simulation time. We find that when the gap is sufficiently deep, the spiral waves excited by the planet trigger the Rossby wave instability, forming cyclonic (underdense) vortices at the edges of the gap. When the planet approaches the gap, it interacts with the vortices, which produce a complex flow structure around the planet. Remarkably, we find a widening of the horseshoe region of the planet produced by the vortex at the outer edge of the gap, which depending on the mass of the planet differs by at least a factor of two with respect to the standard horseshoe width. This inevitably leads to an increase in the corotation torque on the planet and produces an efficient trap to halt its inward migration. In some cases, the planet becomes locked in corotation with the outer vortex. Under this scenario, our results could explain why low-mass planets do not fall towards the central star within the lifetime of the protoplanetary disc. Lastly, the development of these vortices produces an asymmetric temporal evolution of the gap, which could explain the structures observed in some protoplanetary discs., Comment: 17 pages, 20 figures, accepted for publication in MNRAS

Aims. To comprehend the efficiency of dust evolution within protoplanetary disks, it is crucial to conduct studies of these disks using high-resolution observations at multiple wavelengths with the Atacama Large Millimeter/submillimeter Array (ALMA). Methods. In this work, we present high-frequency ALMA observations of the HL Tau disk using its Band 9 centered at a wavelength of 0.45 mm. These observations achieve the highest angular resolution in a protoplanetary disk to date, 12 milliarcseconds (mas), allowing the study of the dust emission at scales of 2 au. We use these data to extend the previously published multi-wavelength analysis of the HL Tau disk. Results. Our new 0.45 mm data traces mainly optically thick emission, providing a tight constraint to the dust temperature profile. We derive maximum particle sizes of $\sim$1 cm from the inner disk to $\sim$60 au. Beyond this radius, we find particles between 300 $\mu$m and 1 mm. Moreover, an intriguing asymmetry is observed at 32 au in the northeast inner part of the HL Tau disk at 0.45 mm. We propose that this asymmetry is the outcome of a combination of factors including the optically thick nature of the emission, the orientation of the disk, and a relatively large dust scale height of the grains. To validate this, we conducted a series of radiative transfer models using the RADMC-3D software. If this scenario is correct, our measured dust mass within 32 au would suggest a dust scale height H/R> 0.08 for the inner disk. Finally, the unprecedented resolution allowed us to probe for the first time the dust emission down to a few au scales. We observed an increase in brightness temperature inside the estimated water snowline and speculate whether it could indicate the presence of a traffic jam effect in the inner disk. Abridge, Comment: Accepted for publication in A&A, 13 pages, 8 figures

Polarized (sub)millimeter emission from dust grains in circumstellar disks was initially thought to be due to grains aligned with the magnetic field. However, higher resolution multi-wavelength observations along with improved models found that this polarization is dominated by self-scattering at shorter wavelengths (e.g., 870 $\mu$m) and by grains aligned with something other than magnetic fields at longer wavelengths (e.g., 3 mm). Nevertheless, the polarization signal is expected to depend on the underlying substructure, and observations hitherto have been unable to resolve polarization in multiple rings and gaps. HL Tau, a protoplanetary disk located 147.3 $\pm$ 0.5 pc away, is the brightest Class I or Class II disk at millimeter/submillimeter wavelengths. Here we show deep, high-resolution 870 $\mu$m polarization observations of HL Tau, resolving polarization in both the rings and gaps. We find that the gaps have polarization angles with a significant azimuthal component and a higher polarization fraction than the rings. Our models show that the disk polarization is due to both scattering and emission from aligned effectively prolate grains. The intrinsic polarization of aligned dust grains is likely over 10%, which is much higher than what was expected in low resolution observations (~1%). Asymmetries and dust features are revealed in the polarization observations that are not seen in non-polarimetric observations., Comment: Published in Nature

Recent laboratory experiments have revealed that destructive collisions of icy dust particles may occur at much lower velocities than previously believed. These low fragmentation velocities push down the maximum grain size in collisional growth models. Motivated by the smooth radial distribution of pebble sizes inferred from ALMA/VLA multi-wavelength continuum analysis, we propose a concise model to explain this feature and aim to constrain the turbulence level at the midplane of protoplanetary disks. Our approach is built on the assumption that the fragmentation threshold is the primary barrier limiting pebble growth within pressure maxima. Consequently, the grain size at the ring location can provide direct insights into the turbulent velocity governing pebble collisions and, by extension, the turbulence level at the disk midplane. We validate this method using the Dustpy code, which simulates dust transport and coagulation. We apply our method to 7 disks, TW Hya, IM Lup, GM Aur, AS 209, HL Tau, HD 163296, and MWC 480, for which grain sizes have been measured from multi-wavelength continuum analysis. A common feature emerges from our analysis, with an overall low turbulence coefficient of $\alpha\sim10^{-4}$ observed in five out of seven disks when taking fragmentation velocity $v_{\rm frag} = 1{\rm \,m\,s}^{-1}$. A higher fragmentation velocity would imply a turbulence coefficient significantly larger than the current observational constraints. IM Lup stands out with a relatively higher coefficient of $10^{-3}$. Notably, HL Tau exhibits an increasing trend in $\alpha$ with distance, which supports enhanced turbulence at its outer disk region, possibly associated with the infalling streamer onto HL~Tau. The current (sub)mm pebble size constrained in disks implies low levels of turbulence, as well as fragile pebbles consistent with recent laboratory measurements., Comment: 11 pages, 8 figures, 2 tables, Accepted for publication in A&A

We have carried out ALMA observations of the massive star-forming region W75N(B), which contains the massive protostars VLA1, VLA2, and VLA3. Particularly, VLA2 is an enigmatic protostar associated with a wind-driven H$_2$O maser shell, which has evolved from an almost isotropic outflow to a collimated one in just 20 years. The shell expansion seemed to be halted by an obstacle located to the northeast of VLA2. Here we present our findings from observing the 1.3 mm continuum and H$_2$CO and SiO emission lines. Within a region of $\sim 30"$ ($\sim 39,000$ au) diameter, we have detected 40 compact mm-continuum sources, three of them coinciding with VLA1, VLA2, and VLA3. While the H$_2$CO emission is mainly distributed in a fragmented structure around the three massive protostars, but without any of the main H$_2$CO clumps spatially coinciding with them, the SiO is highly concentrated on VLA2, indicating the presence of very strong shocks generated near this protostar. The SiO emission is clearly resolved into an elongated structure ($\sim 0.6"\times0.3"$; $\sim 780$ au$\times$390 au) perpendicular to the major axis of the wind-driven maser shell. The structure and kinematics of the SiO emission are consistent with a toroid and a wide-angle outflow surrounding a central mass of $\sim 10$ M$_{\odot}$, thus supporting previous theoretical predictions regarding the evolution of the outflow. Additionally, we have identified the expected location and estimated the gas density of the obstacle that is hindering the expansion of the maser shell., Comment: To be published in The Astrophysical Journal Letters. Sixteen pages, seven figures. Updated metadata

Polarization is a unique tool to study the properties of dust grains of protoplanetary disks and detail the initial conditions of planet formation. Polarization around HL Tau was previously imaged using the Atacama Large Millimeter/submillimeter Array (ALMA) at Bands 3 (3.1 mm), 6 (1.3 mm), and 7 (0.87 mm), showing that the polarization orientation changes across wavelength $\lambda$. The polarization morphology at Band 7 is predominantly parallel to the disk minor axis but appears azimuthally oriented at Band 3, with the morphology at Band 6 in between the two. We present new ~0.2" (29 au) polarization observations at Q-Band (7.0 mm) using the Karl G. Jansky Very Large Array (VLA) and at Bands 4 (2.1 mm), 5 (1.5 mm), and 7 using ALMA, consolidating HL Tau's position as the protoplanetary disk with the most complete wavelength coverage in dust polarization. The polarization patterns at Bands 4 and 5 continue to follow the morphological transition with wavelength previously identified in Bands 3, 6, and 7. Based on the azimuthal variation, we decompose the polarization into contributions from scattering ($s$) and thermal emission ($t$). We find that $s$ decreases slowly with increasing $\lambda$, and $t$ increases more rapidly with $\lambda$ which are expected from optical depth effects of toroidally aligned, scattering prolate grains. The relatively weak $\lambda$ dependence of $s$ is consistent with large, porous grains. The sparse polarization detections from the Q-band image are also consistent with toroidally aligned prolate grains., Comment: 22 pages, 13 figures, submitted to MNRAS

Dust particle sizes constrained from dust continuum and polarization observations by radio interferometry are inconsistent by at least an order of magnitude. Motivated by porous dust observed in small Solar System bodies (e.g., from the Rosetta mission), we explore how the dust particle's porosity affects the estimated particle sizes from these two methods. Porous particles have lower refractive indices, which affect both opacity and polarization fraction. With weaker Mie interference patterns, the porous particles have lower opacity at mm wavelengths than the compact particles if the particle size exceeds several hundred microns. Consequently, the inferred dust mass using porous particles can be up to a factor of six higher. The most significant difference between compact and porous particles is their scattering properties. The porous particles have a wider range of particle sizes with high linear polarization from dust self-scattering, allowing mm-cm-sized particles to explain polarization observations. With a Bayesian approach, we use porous particles to fit HL Tau disk's multi-wavelength continuum and mm-polarization observations from ALMA and VLA. The moderately porous particles with sizes from 1 mm-1 m can explain both continuum and polarization observations, especially in the region between 20-60 au. If the particles in HL Tau are porous, the porosity should be from 70% to 97% from current polarization observations. We also predict that future observations of the self-scattering linear polarization at longer wavelengths (e.g., ALMA B1 and ngVLA) have the potential to further constrain the particle's porosity and size., Comment: 39 pages, 18 figures, 1 table, accepted to be published in The Astrophysical Journal

Forbidden emission lines in protoplanetary disks are a key diagnostic in studies of the evolution of the disk and the host star. We report spatially resolved emission lines, [OI] 6300, 6363, [NII] 6548, 6583, H$\alpha$, and [SII] 6716, 6730 Angstrom that are believed to be associated with jets and magnetically driven winds in the inner disks. Observations were carried out with the optical integral field spectrograph of the Multi Unit Spectroscopic Explorer (MUSE), at the Very Large Telescope (VLT). With a resolution of 0.025 X 0.025 arcsec$^{2}$, we aim to derive the position angle of the outflow/jet (PA$_{outflow/jet}$) that is connected with the inner disk. The forbidden emission lines analyzed here have their origin at the inner parts of the protoplanetary disk. From the maximum intensity emission along the outflow/jet in DL Tau, CI Tau, DS Tau, IP Tau, and IM Lup, we were able to reliably measure the PA$_{outflow/jet}$ for most of the identified lines. We found that our estimates agree with PA$_{dust}$ for most of the disks. These estimates depend on the signal-to-noise level and the collimation of the outflow (jet). The outflows/jets in CIDA 9, GO Tau, and GW Lup are too compact for a PA$_{outflow/jet}$ to be estimated. Based on our kinematics analysis, we confirm that DL Tau and CI Tau host a strong outflow/jet with line-of-sight velocities much greater than 100 km s$^{-1}$, whereas DS Tau, IP Tau, and IM Lup velocities are lower and their structures encompass low-velocity components to be more associated with winds. Our estimates for the mass-loss rate, $\dot{M}_{{loss}}$, range between (1.1-6.5)X10$^{-7}$-10$^{-8}$ $M_{\odot}$ yr$^{-1}$ for the disk-outflow/jet systems analyzed here. The outflow/jet systems analyzed here are aligned within around 1 degree between the inner and outer disk. Further observations are needed to confirm a potential misalignment in IM Lup., Comment: Accepted on December 19 2022

We present ALMA observations with a 800 au resolution and radiative-transfer modelling of the inner part ($r\approx6000$ au) of the ionized accretion flow around a compact star cluster in formation at the center of the luminous ultra-compact (UC) HII region G10.6-0.4. We modeled the flow with an ionized Keplerian disk with and without radial motions in its outer part, or with an external Ulrich envelope. The MCMC fits to the data give total stellar masses $M_\star$ from 120 to $200~M_\odot$, with much smaller ionized-gas masses $M_\mathrm{ion-gas} = 0.2$ to $0.25~M_\odot$. The stellar mass is distributed within the gravitational radius $R_g\approx 1000$ to 1500 au, where the ionized gas is bound. The viewing inclination angle from the face-on orientation is $i = 49$ to $56~\deg$. Radial motions at radii $r > R_g$ converge to $v_{r,0} \approx 8.7$ km/s, or about the speed of sound of ionized gas, indicating that this gas is marginally unbound at most. From additional constraints on the ionizing-photon rate and far-IR luminosity of the region, we conclude that the stellar cluster consists of a few massive stars with $M_\mathrm{star} = 32$ to $60~M_\odot$, or one star in this range of masses accompanied by a population of lower-mass stars. Any active accretion of ionized gas onto the massive (proto)stars is residual. The inferred cluster density is very large, comparable to that reported at similar scales in the Galactic Center. Stellar interactions are likely to occur within the next Myr., Comment: Accepted to ApJ Letters, December 7 2022

We report new VLA and e-MERLIN high resolution and sensitivity images of the Triple Radio continuum Source in the Serpens star forming region. These observations allowed us to perform a deep multi-frequency, multi-epoch study by exploring the innermost regions (<~100 au) of an intermediate-mass YSO for the first time, with a physical resolution of ~15 au. The kinematic analysis of knots recently ejected by the protostar indicates that the jet is undergoing episodic variations in velocity. In addition, our multi-frequency images reveal striking characteristics, e.g., a highly collimated ionized stream that would be launched at a radial distance of ~0.4 au from the protostar, and a narrow (~28 au wide) ionized cavity that would be excited by the interaction of a wide-angle component with the surrounding toroid of infalling material. In light of these results, we propose the scenario in which both a highly-collimated jet and a wide-angle wind coexist to be the most plausible to explain our observations, either launched by the X-wind or X- plus Disk-wind mechanism., Comment: 13 pages, 3 figures. Accepted for publication in APJL

We present unprecedented high fidelity radio images of the M87 jet. We analyzed Jansky Very Large Array (VLA) broadband, full polarization, radio data from 4 to 18 GHz. The observations were taken with the most extended configuration (A configuration), which allow the study of the emission of the jet up to kpc scales with a linear resolution $\sim$10 pc. The high sensitivity and resolution of our data allow to resolve the jet width. We confirm a double-helix morphology of the jet material between $\sim$300 pc and $\sim$1 kpc. We found a gradient of the polarization degree with a minimum at the projected axis and maxima at the jet edges, and a gradient in the Faraday depth with opposite signs at the jet edges. We also found that the behavior of the polarization properties along the wide range of frequencies is consistent with internal Faraday depolarization. All these characteristics strongly support the presence of a helical magnetic field in the M87 jet up to 1 kpc from the central black hole although the jet is most likely particle dominated at these large scales. Therefore, we propose a plausible scenario in which the helical configuration of the magnetic field has been maintained to large scales thanks to the presence of Kelvin-Helmholtz instabilities., Comment: Published on ApJL

We present VLA and ALMA observations of the close (0.3" = 90 au separation) protobinary system SVS 13. We detect two small circumstellar disks (radii $\sim$12 and $\sim$9 au in dust, and $\sim$30 au in gas) with masses of $\sim$0.004-0.009 $M_{sun}$ for VLA 4A (the western component) and $\sim$0.009-0.030 $M_{sun}$ for VLA 4B (the eastern component). A circumbinary disk with prominent spiral arms extending $\sim$500 au and a mass of $\sim$0.052 $M_{sun}$ appears to be in the earliest stages of formation. The dust emission is more compact and with a very high optical depth toward VLA 4B, while toward VLA 4A the dust column density is lower, allowing the detection of stronger molecular transitions. We infer rotational temperatures of $\sim$140 K, on scales of $\sim$30 au, across the whole source, and a rich chemistry. Molecular transitions typical of hot corinos are detected toward both protostars, being stronger toward VLA 4A, with several ethylene glycol transitions detected only toward this source. There are clear velocity gradients, that we interpret in terms of infall plus rotation of the circumbinary disk, and purely rotation of the circumstellar disk of VLA 4A. We measured orbital proper motions and determined a total stellar mass of 1 $M_{sun}$. From the molecular kinematics we infer the geometry and orientation of the system, and stellar masses of $\sim$0.26 $M_{sun}$ for VLA 4A and $\sim$0.60 $M_{sun}$ for VLA 4B., Comment: 59 pages, 28 Figures, 14 Tables, accepted by The Astrophysical Journal. Includes changes after the ApJ proof corrections

One of the most important questions in the field of planet formation is how mm-cm sized dust particles overcome the radial drift and fragmentation barriers to form kilometer-sized planetesimals. ALMA observations of protoplanetary disks, in particular transition disks or disks with clear signs of substructures, can provide new constraints on theories of grain growth and planetesimal formation and therefore represent one possibility to progress on this issue. We here present ALMA band 4 (2.1 mm) observations of the transition disk system Sz 91 and combine them with previously obtained band 6 (1.3 mm) and 7 (0.9 mm) observations. Sz 91 with its well defined mm-ring, more extended gas disk, and evidence of smaller dust particles close to the star, is a clear case of dust filtering and the accumulation of mm sized particles in a gas pressure bump. We computed the spectral index (nearly constant at $\sim$3.34), optical depth (marginally optically thick), and maximum grain size ($\sim\,0.61$ mm) in the dust ring from the multi-wavelength ALMA observations and compared the results with recently published simulations of grain growth in disk substructures. Our observational results are in very good agreement with the predictions of models for grain growth in dust rings that include fragmentation and planetesimal formation through the streaming instability., Comment: Accepted for publication in the ApJ 19 pages, 13 figures

Protostellar jets have a fundamental role at the earliest evolution of protostars of all masses. In the case of low-mass (<8 Msun) protostars, strong observational evidence exists that the launching and collimation is due to the X- and/or disk-wind mechanisms. In these models, it is the protostar/disk system that creates all the necessary conditions to launch and collimate the jets near the protostar via strong magnetic fields. The origin of jets from more massive protostars has been investigated much less, in part because of the difficulty of resolving the collimation zone in these more distant objects. Here we present the highest angular resolution observations of a jet powered by a massive protostar, the Cep A HW2 radio jet. We imaged the radio emission at projected distances of only ~20 au from the protostar, resolving the innermost 100 au of a massive protostellar jet for the first time. The morphology of the radio jet emission in this massive object is very different than what is usually observed in jets from low-mass protostars. We found that the outflowing material in HW2 has two components: a wide-angle wind launched from the protostar/disk system, and a highly collimated jet starting at 20-30 au from the protostar. We discuss two possible scenarios: an extension of the classical disk-wind to a massive protostar, or external collimation of a wide-angle wind. These results have important consequences for our understanding of how stars of different masses are formed., Comment: Accepted for publication in ApJ Letters

The polarimetric observations on the protoplanetary disk around HL Tau have shown the scattering-induced polarization at ALMA Band 7, which indicates that the maximum dust size is $\sim 100~{\rm \mu m}$, while the Spectral Energy Distribution (SED) has suggested that the maximum dust size is $\sim$ mm. To solve the contradiction, we investigate the impact of differential settling of dust grains on the SED and polarization. If the disk is optically thick, longer observing wavelength traces more interior layer which would be dominated by larger grains. We find that, the SED of the center part of the HL Tau disk can be explained with mm-sized grains for a broad range of turbulence strength, while $160~{\rm \mu m}$-sized grains can explain barely only if the turbulence strength parameter $\alpha_{\rm t}$ is lower than $10^{-5}$. We also find that the observed polarization fraction can be potentially explained with the maximum dust size of $1~{\rm mm}$ if $\alpha_{\rm t}\lesssim10^{-5}$, although models with $160~{\rm \mu m}$-sized grains are also acceptable. However, if the maximum dust size is $\sim3~{\rm mm}$, the simulated polarization fraction is too low to explain the observations even if the turbulence strength is extremely small, indicating the maximum dust size of $\lesssim1$ mm. The degeneracy between 100 ${\rm \mu m}$-sized and mm-sized grains can be solved by improving the ALMA calibration accuracy or polarimetric observations at (sub-)cm wavelengths., Comment: 13 pages, 11 figures. Accepted for publication in ApJ

We present Atacama Large Millimeter Array (ALMA) observations of TW Hya at 3.1 mm with $\sim50$ milliarcsecond resolution. These new data were combined with archival high angular resolution ALMA observations at 0.87 mm, 1.3 mm, and 2.1 mm. We analyze these multi-wavelength data to infer a disk radial profile of the dust surface density, maximum particle size, and slope of the particle size distribution. Most previously known annular substructures in the disk of TW Hya are resolved at the four wavelengths. Inside the inner 3 au cavity, the 2.1 mm and 3.1 mm images show a compact source of free-free emission, likely associated with an ionized jet. Our multi-wavelength analysis of the dust emission shows that the maximum particle size in the disk of TW Hya is $>1$ mm. The inner 20 au are completely optically thick at all four bands, which results in the data tracing different disk heights at different wavelengths. Coupled with the effects of dust settling, this prevents the derivation of accurate density and grain size estimates in these regions. At $r>20$ au, we find evidence of the accumulation of large dust particle at the position of the bright rings, indicating that these are working as dust traps. The total dust mass in the disk is between 250 and 330 $M_{\oplus}$, which represents a gas-to-dust mass ratio between 50 and 70. Our mass measurement is a factor of 4.5-5.9 higher than the mass that one would estimate using the typical assumptions of large demographic surveys. Our results indicate that the ring substructures in TW Hya are ideal locations to trigger the streaming instability and form new generations of planetesimals., Comment: 22 pages, 17 figures, accepted for publication in A&A. Language edited version

Wolf-Rayet (WR) stars are evolved massive stars, presumably on their way to becoming supernova. They are characterized by high luminosities and fast and dense stellar winds. We have detected signs of a radio continuum pinwheel associated with WR147, a nitrogen-rich WR star with spectral subtype WN8. These structures are known around a handful of late-type carbon-rich WR stars with massive companions were the dust formed at the zone where the two winds collide produces a plume of dense gas and dust that is carried out with the WR wind. As the binary system rotates, an Archimedean spiral detectable in the infrared is formed. The resulting pinwheel contains information on wind speeds, wind-momentum ratio and orbital parameters. However, WR147 is a WN star and the formation of dust is unlikely so a different emission mechanism must be at work. Our analysis of the data suggests that in this case the emission is dominantly of non-thermal nature (synchrotron), although we cannot exclude that some clumps could be brighter in free-free emission. It is possible that the pinwheels associated with WN stars will be detectable only as non-thermal emitters at radio wavelengths. From the characteristics of the pinwheel we estimate a period of 1.7 years for the binary system (the WN8 star and a companion yet undetected directly) responsible for the pinwheel., Comment: 9 pages, 3 figures, To appear in The Astrophysical Journal Letters

We model the ALMA and VLA millimeter radial profiles of the disk around HL Tau to constrain the properties of the dust grains. We adopt the disk evolutionary models of Lynden-Bell \& Pringle and calculate their temperature and density structure and emission. These disks are heated by the internal viscosity and irradiated by the central star and a warm envelope. We consider a dust size distribution $n(a) da \propto a^{-3.5} da $, and vary the maximum grain size in the atmosphere and the midplane, $a_{\rm max}=100\ \mu$m, 1 mm, and 1cm. We also include dust settling and vary the dust-to-gas mass ratio from 1 to 9 times the ISM value. We find that the models that can fit the observed level of emission along the profiles at all wavelengths have an atmosphere with a maximum grain size $a_{\rm max} = 100 \ \mu$m, and a midplane with $a_{\rm max}=1$ cm. The disk substructure, with a deficit of emission in the gaps, can be due to dust properties in these regions that are different from those in the rings. We test an opacity effect (different $a_{\rm max}$) and a dust mass deficit (smaller dust-to-gas mass ratio) in the gaps. We find that the emission profiles are better reproduced by models with a dust deficit in the gaps, although a combined effect is also possible. These models have a global dust-to-gas mass ratio twice the ISM value, needed to reach the level of emission of the 7.8 mm VLA profile., Comment: 17 pages, 11 figures

Understanding planet formation requires to discern how dust grows in protoplanetary disks. An important parameter to measure in disks is the maximum dust grain size present. This is usually estimated through measurements of the dust opacity at different millimeter wavelengths assuming optically thin emission and dust opacity dominated by absorption. However, ALMA observations have shown that these assumptions might not be correct in the case of protoplanetary disks, leading to overestimation of particle sizes and to underestimation of the disk's mass. Here, we present an analysis of high quality ALMA and VLA images of the HL Tau protoplanetary disk, covering a wide range of wavelengths, from 0.8 mm to 1 cm, and with a physical resolution of $\sim$7.35 au. We describe a procedure to analyze a set of millimeter images without any assumption about the optical depth of the emission, and including the effects of absorption and scattering in the dust opacity. This procedure allows us to obtain the dust temperature, the dust surface density and the maximum particle size at each radius. In the HL Tau disk, we found that particles have already grown up to a few millimeters in size. We detect differences in the dust properties between dark and bright rings, with dark rings containing low dust density and small dust particles. Different features in the HL Tau disk seem to have different origins. Planet-disk interactions can explain substructure at the external half of the disk, but the internal rings seem to be associated to the presence of snow lines of several molecules.

We present a detailed multi-wavelength characterization of the multi-ring disk of HD 169142. We report new ALMA observations at 3 mm and analyze them together with archival 0.89 and 1.3 mm data. Our observations resolve three out of the four rings in the disk previously seen in high-resolution ALMA data. A simple parametric model is used to estimate the radial profile of the dust optical depth, temperature, density, and particle size distribution. We find that the multiple ring features of the disk are produced by annular accumulations of large particles, probably associated with gas pressure bumps. Our model indicates that the maximum dust grain size in the rings is $\sim1$ cm, with slightly flatter power-law size distributions than the ISM-like size distribution ($p\sim3.5$) found in the gaps. In particular, the inner ring ($\sim26$ au) is associated with a strong and narrow buildup of dust particles that could harbor the necessary conditions to trigger the streaming instability. According to our analysis, the snowlines of the most important volatiles do not coincide with the observed substructures. We explore different ring formation mechanisms and find that planet-disk interactions are the most likely scenario to explain the main features of HD 169142. Overall, our multi-wavelength analysis provides some of the first unambiguous evidence of the presence of radial dust traps in the rings of HD 169142. A similar analysis in a larger sample of disks could provide key insights on the impact that disk substructures have on the dust evolution and planet formation processes., Comment: 19 pages, 8 figures, accepted for publication in ApJ

We study dust concentration in axisymmetric gas rings in protoplanetary disks. Given the gas surface density, we derived an analytical total dust surface density by taking into account the differential concentration of all the grain sizes. This model allows us to predict the local dust-to-gas mass ratio and the slope of the particle size distribution, as a function of radius. We test this analytical model comparing it with a 3D magneto-hydrodynamical simulation of dust evolution in an accretion disk. The model is also applied to the disk around HD 169142. By fitting the disk continuum observations simultaneously at $\lambda = 0.87$, 1.3, 3.0 mm, we obtain a global dust-to-gas mass ratio $\epsilon_{\rm global} = 1.05 \times 10^{-2}$ and a viscosity coefficient $\alpha = 1.35 \times 10^{-2}$. This model can be easily implemented in numerical simulations of accretion disks.

Polarized dust emission outside of disks reveal the magnetic field morphology of molecular clouds. Within disks, however, polarized dust emission can arise from very different mechanisms (e.g., self-scattering), and each of them are useful for constraining physical properties in the disk. For example, these mechanisms allow us to constrain the disk grain size distributions and grain/disk geometries, independent from current methods of measuring these parameters. To accurately model these features and disentangle the various polarization mechanisms, multiwavelength observations at very high resolution and sensitivity are required. With significant upgrades to current interferometric facilities, we can understand how grains evolve in disks during the planet formation process., Comment: Science white paper submitted to the Astro2020 Decadal Survey

We present an analysis of radio (Karl G. Jansky Very Large Array (VLA)), optical (HST), and X-ray (Chandra and XMM-Newton) observations and archival data of the Herbig-Haro objects HH 80 and HH 81 in the context of jet-cloud interactions. Our radio images are the highest angular resolution to date of these objects, allowing to spatially resolve the knots and compare the regions emitting in the different spectral ranges. We found that soft X-ray thermal emission is located ahead of the non-thermal radio peak. This result is consistent with a radiative forward shock that heats the shocked gas up to 10 6 K, and an adiabatic reverse shock able to accelerate particles and produce synchrotron radiation detectable at radio frequencies. These high angular resolution radio images also reveal a bow shock structure in the case of HH 80N, being the first time this morphology is detected in a Herbig-Haro object at these frequencies., Comment: 12 pages, 5 figures. Published in MNRAS. Corrected typo in author's name

Terrestrial planets and the cores of giant planets are thought to be built by the collisional agglomeration of solids spanning over 20 orders of magnitude in size within a few million years. However, there is tension between this basic picture of planet formation and standard theoretical assumptions associated with the migration of "pebbles" ($\sim$mm/cm-sized particles) in gas-rich disks and the presumably much longer timescales necessary to assemble ($\sim$km-scale) "planetesimals". To confront these potential theoretical discrepancies with observational constraints, the ideal tracer of the solids concentrated in protoplanetary disk substructures is the 30-100 GHz continuum, which strikes the best balance in sensitivity (emission still bright), optical depth (low enough to reliably estimate densities), and angular resolution (high enough to resolve fine-scale features at disk radii as small as 1 au). With its combination of sensitivity, frequency coverage, and angular resolution, the next-generation VLA will be the only facility that has the capabilities to open up this new window into the physics of planetesimal formation., Comment: To be published in the ASP Monograph Series, Science with a Next-Generation VLA, ed. E. J. Murphy (ASP, San Francisco, CA)

In this paper we explore the effects of self-obscuration in protostellar disks with a radially decreasing temperature gradient and a colder midplane. We are motivated by recent reports of resolved dark lanes (`hamburgers') and (sub)mm spectral indices systematically below the ISM value for optically thin dust $\alpha_{\rm ISM} =3.7$. We explore several model grids, scaling disk mass and varying inclination angle $i$ and observing frequency $\nu$ from the VLA Ka band ($\sim 37$ GHz) to ALMA Band 8 ($\sim 405$ GHz). We also consider the effects of decreasing the index of the (sub-)mm dust opacity power law $\beta$ from 1.7 to 1. We find that a distribution of disk masses in the range $M_{\rm disk} = 0.01-2~M_\odot$ is needed to reproduce the observed distribution of spectral indices, and that assuming a fixed $\beta =1.7$ gives better results than $\beta=1$. A wide distribution of disk masses is also needed to produce some cases with $\alpha <2$, as reported for some sources in the literature. Such extremely low spectral indices arise naturally when the selected observing frequencies sample the appropriate change in the temperature structure of the optically thick model disk. Our results show that protostellar disk masses could often be underestimated by $> \times10$, and are consistent with recent hydrodynamical simulations. Although we do not rule out the possibility of some grain growth occurring within the short protostellar timescales, we conclude that self-obscuration needs to be taken into account., Comment: Accepted to The Astrophysical Journal Supplement

Our understanding of protoplanetary disks is rapidly departing from the classical view of a smooth, axisymmetric disk. This is in part thanks to the high angular resolution that (sub)mm observations can provide. Here we present the combined results of ALMA (0.9 mm) and VLA (7 mm) dust continuum observations toward the protoplanetary disk around the solar analogue GM Aur. Both images clearly resolve the $\sim$35 au inner cavity. The ALMA observations also reveal a fainter disk that extends up to $\sim250$ au. We model our observations using two approaches: an analytical fit to the observed deprojected visibilities, and a physical disk model that fits the SED as well as the VLA and ALMA observations. Despite not being evident in the deconvolved images, the VLA and ALMA visibilities can only be fitted with two bright rings of radii $\sim$40 and $\sim$80 au. Our physical model indicates that this morphology is the result of an accumulation or trapping of large dust grains, probably due to the presence of two pressure bumps in the disk. Even though alternative mechanisms cannot be discarded, the multiple rings suggest that forming planets may have cleared at least two gaps in the disk. Finally, our analysis suggests that the inner cavity might display different sizes at 0.9 mm and 7 mm. This discrepancy could be caused by the presence of free-free emission close to the star at 7 mm, or by a more compact accumulation of the large dust grains at the edge of the cavity., Comment: 18 pages, 8 figures, accepted for publication in ApJ

In this contribution we explore the new science that a Next Generation Very Large Array (ngVLA) would be able to perform on the topics of the youngest HII regions and (proto)stellar jets. Free-free continuum and radio recombination line (RRL) emission are often the only way of peering into the dense envelopes surrounding (proto)stars of all masses, and trace their initial feedback in the form of `radio jets', `hypercompact HII regions', or photoevaporating, partially-ionized flows. Properly disentangling free-free from dust emission is also mandatory in studies of protoplanetary and accretion disks. Current VLA research has reached an impasse in which a population of faint ionized radio sources, probably corresponding to the above mentioned objects, is detected, but their nature is mostly unknown. The ngVLA would allow us to resolve the density structure and kinematics of such sources, revolutionizing our knowledge of star formation across the entire stellar-mass spectrum., Comment: An ngVLA Science Book chapter. v2 includes a few modifications in references

Jets and outflows are ubiquitous in the process of formation of stars since outflow is intimately associated with accretion. Free-free (thermal) radio continuum emission is associated with these jets. This emission is relatively weak and compact, and sensitive radio interferometers are required to study it. Observations in the cm range are most useful to trace the base of the ionized jets, close to the central protostar, where optical or near-IR imaging is made difficult by the high extinction present. Radio recombination lines in jets (in combination with proper motions) should provide their 3D kinematics at very small scale. Future instruments such as the Square Kilometre Array (SKA) and the Next Generation Very Large Array (ngVLA) will be crucial to perform this kind of sensitive observations. Thermal jets are associated with both high and low mass protostars and possibly even with substellar objects. The ionizing mechanism of these radio jets appears to be related to shocks in the associated outflows, as suggested by the observed correlation between the cm luminosity and the outflow momentum rate. Some protostellar jets show indications of non-thermal emission in their lobes. Linearly polarized synchrotron emission has been found in the jet of HH 80-81, allowing one to map the jet magnetic field, a key ingredient to determine the collimation and ejection mechanisms. As only a fraction of the emission is polarized, very sensitive observations such as those that will be feasible with the interferometers previously mentioned are required to perform studies in a large sample of sources. Jets are present in many kinds of astrophysical scenarios. Characterizing radio jets in young stars, where thermal emission allows one to determine their physical conditions, would also be useful in understanding acceleration and collimation mechanisms in all kinds of astrophysical jets., Comment: 50 pages, 11 figures, invited review article for The Astronomy and Astrophysics Review

The magnetic field plays an important role in every stage of the star-formation process from the collapse of the initial protostellar core to the star's arrival on the main sequence. Consequently, the goal of this science case is to explore a wide range of magnetic phenomena that can be investigated using the polarization capabilities of the Next Generation Very Large Array (ngVLA). These include (1) magnetic fields in protostellar cores via polarized emission from aligned dust grains, including in regions optically thick at wavelengths observable by the Atacama Large Millimeter/submillimeter Array (ALMA); (2) magnetic fields in both protostellar cores and molecular outflows via spectral-line polarization from the Zeeman and Goldreich-Kylafis effects; (3) magnetic fields in protostellar jets via polarized synchrotron emission; and (4) gyrosynchrotron emission from magnetospheres around low-mass stars., Comment: 14 pages, 2 figures. An ngVLA Science Book chapter

We present broadband polarimetric observations of a sample of high Faraday rotation measure (RM) AGN using the VLA telescope from 1 to 2 GHz, and 4 to 12 GHz. The sample (14 sources) consists of compact sources (linear resolution smaller than ~ 5 kpc) that are unpolarized at 1.4 GHz in the NVSS. Total intensity data have been modelled using combination of synchrotron components, revealing complex structure in their radio spectra. Depolarization modelling, through the so called qu-fitting, have been performed on the polarized data using an equation that attempts to simplify the process of fitting many different depolarization models that we can divide into two major categories: External Depolarization and Internal Depolarization models. Understanding which of the two mechanisms are the most representative, would help the qualitative understanding of the AGN jet environment, whether it is embedded in a dense external magnetoionic medium or if it is the jet-wind that causes the high RM and strong depolarization. This could help to probe the jet magnetic field geometry (e.g. helical or otherwise). This new high-sensitivity data, shows a complicated behaviour in the total intensity and polarization radio spectrum of individual sources. We observed the presence of several synchrotron components and Faraday components in their total intensity and polarized spectra. For the majority of our targets, (12 sources) the depolarization seems to be caused by a turbulent magnetic field. Thus, our main selection criteria (lack of polarization at 1.4 GHz in the NVSS), results in a sample of sources with very large RMs and depolarization due to turbulent magnetic fields local to the source. We show how the new qu-fitting technique can be used to probe the magnetised radio source environment and to spectrally resolve the polarized components of unresolved radio sources., Comment: Accepted by A&A, Previous ArXiv version the Fig.3 on pag. 8 had problem during printing stage. I uploaded this new version with a different format of those plots

Radio emission from protostellar jets is usually dominated by free-free emission from thermal electrons. However, in some cases, it has been proposed that non-thermal emission could also be present. This additional contribution from non-thermal emission has been inferred through negative spectral indices at centimeter wavelengths in some regions of the radio jets. In the case of HH 80-81, one of the most powerful protostellar jets known, linearly polarized emission has also been detected, revealing that the non-thermal emission is of synchrotron nature from a population of relativistic particles in the jet. This result implies that an acceleration mechanism should be taking place in some parts of the jet. Here, we present new high sensitivity and high angular resolution radio observations at several wavelengths (in the 3-20 cm range) of the HH80-81 radio jet. These new observations represent an improvement in sensitivity and angular resolution by a factor of $\sim$10 with respect to previous observations. This allows us to resolve the morphology of the radio jet, and to study the different emission mechanisms involved through spectral index maps. We conclude that synchrotron emission in this jet arises from an extended component detected at low frequencies and from the termination points of the jet, where strong shocks against the ambient medium can produce efficient particle acceleration., Comment: 28 pages, 7 figures, and 3 tables. Accepted for publication in ApJ

Young stellar objects (YSOs) may undergo periods of active accretion (outbursts), during which the protostellar accretion rate is temporarily enhanced by a few orders of magnitude. Whether or not these accretion outburst YSOs possess similar dust/gas reservoirs to each other, and whether or not their dust/gas reservoirs are similar as quiescent YSOs, are issues not yet clarified. The aim of this work is to characterize the millimeter thermal dust emission properties of a statistically significant sample of long and short duration accretion outburst YSOs (i.e., FUors and EXors) and the spectroscopically identified candidates of accretion outbursting YSOs (i.e., FUor-like objects). We have carried out extensive Submillimeter Array (SMA) observations mostly at $\sim$225 GHz (1.33 mm) and $\sim$272 GHz (1.10 mm), from 2008 to 2017. We covered accretion outburst YSOs located at $<$1 kpc distances from the solar system. We analyze all the existing SMA data of such objects, both published and unpublished, in a coherent way to present a millimeter interferometric database of 29 objects. We obtained 21 detections at $>$3-$\sigma$ significance. Detected sources except for the two cases of V883 Ori and NGC 2071 MM3 were observed with $\sim$1$"$ angular resolution. Overall our observed targets show a systematically higher millimeter luminosity distribution than those of the $M_{*}>$0.3 $M_{\odot}$ Class II YSOs in the nearby ($\lesssim$400 pc) low-mass star-forming molecular clouds (e.g., Taurus, Lupus, Upp Scorpio, and Chameleon I). In addition, at 1 mm our observed confirmed binaries or triple-system sources are systematically fainter than the rest of the sources even though their 1 mm fluxes are broadly distributed. We may have detected $\sim$30-60\% millimeter flux variability from V2494 Cyg and V2495 Cyg, from the observations separated by $\sim$1 year., Comment: 23 pages, 17 figures, accepted to A&A

Planets are born in protostellar disks, which are now observed with enough resolution to address questions about internal gas flows. Candidates for driving the flows include magnetic forces, but ionization state estimates suggest much of the gas mass decouples from magnetic fields. Thus, hydrodynamical instabilities could play a major role. We investigate disk dynamics under conditions typical for a T Tauri system, using global 3D radiation hydrodynamics simulations with embedded particles and a resolution of 70 cells per scale height. Stellar irradiation heating is included with realistic dust opacities. The disk starts in joint radiative balance and hydrostatic equilibrium. The vertical shear instability (VSI) develops into turbulence that persists up to at least 1600 inner orbits (143 outer orbits). Turbulent speeds are a few percent of the local sound speed at the midplane, increasing to 20%, or 100 m/s, in the corona. These are consistent with recent upper limits on turbulent speeds from optically thin and thick molecular line observations of TW Hya and HD 163296. The predominantly vertical motions induced by the VSI efficiently lift particles upwards. Grains 0.1 and 1 mm in size achieve scale heights greater than expected in isotropic turbulence. We conclude that while kinematic constraints from molecular line emission do not directly discriminate between magnetic and nonmagnetic disk models, the small dust scale heights measured in HL Tau and HD 163296 favor turbulent magnetic models, which reach lower ratios of the vertical kinetic energy density to the accretion stress., Comment: Accepted for ApJ

We conducted a detailed radiative transfer modeling of the dust emission from the circumstellar disk around HL Tau. The goal of our study is to derive the surface density profile of the inner disk and its structure. In addition to the Atacama Large Millimeter/submillimeter Array images at Band 3 (2.9mm), Band 6 (1.3mm), and Band 7 (0.87mm), the most recent Karl G. Jansky Very Large Array (VLA) observations at 7mm were included in the analysis. A simulated annealing algorithm was invoked to search for the optimum model. The radiative transfer analysis demonstrates that most radial components (i.e., >6AU) of the disk become optically thin at a wavelength of 7mm, which allows us to constrain, for the first time, the dust density distribution in the inner region of the disk. We found that a homogeneous grain size distribution is not sufficient to explain the observed images at different wavelengths simultaneously, while models with a shallower grain size distribution in the inner disk work well. We found clear evidence that larger grains are trapped in the first bright ring. Our results imply that dust evolution has already taken place in the disk at a relatively young (i.e., ~1Myr) age. We compared the midplane temperature distribution, optical depth, and properties of various dust rings with those reported previously. Using the Toomre parameter, we briefly discussed the gravitational instability as a potential mechanism for the origin of the dust clump detected in the first bright ring via the VLA observations., Comment: Accepted for publication in A&A (10 pages)

We carried out multiwavelength (0.7-5 cm), multiepoch (1994-2015) Very Large Array (VLA) observations toward the region enclosing the bright far-IR sources FIR 3 (HOPS 370) and FIR 4 (HOPS 108) in OMC-2. We report the detection of 10 radio sources, seven of them identified as young stellar objects. We image a well-collimated radio jet with a thermal free-free core (VLA 11) associated with the Class I intermediate-mass protostar HOPS 370. The jet presents several knots (VLA 12N, 12C, 12S) of non-thermal radio emission (likely synchrotron from shock-accelerated relativistic electrons) at distances of ~7,500-12,500 au from the protostar, in a region where other shock tracers have been previously identified. These knots are moving away from the HOPS 370 protostar at ~ 100 km/s. The Class 0 protostar HOPS 108, which itself is detected as an independent, kinematically decoupled radio source, falls in the path of these non-thermal radio knots. These results favor the previously proposed scenario where the formation of HOPS 108 has been triggered by the impact of the HOPS 370 outflow with a dense clump. However, HOPS 108 presents a large proper motion velocity of ~ 30 km/s, similar to that of other runaway stars in Orion, whose origin would be puzzling within this scenario. Alternatively, an apparent proper motion could result because of changes in the position of the centroid of the source due to blending with nearby extended emission, variations in the source shape, and /or opacity effects., Comment: 16 pages, 4 figures, accepted for publication in The Astrophysical Journal

We report Very Large Array observations at 7 mm, 9 mm, and 3 cm toward the pre-transitional disk of the Herbig Ae star HD 169142. These observations have allowed us to study the mm emission of this disk with the highest angular resolution so far ($0\rlap."12\times0\rlap."09$, or 14 au$\times$11 au, at 7 mm). Our 7 and 9 mm images show a narrow ring of emission at a radius of $\sim25$ au tracing the outer edge of the inner gap. This ring presents an asymmetric morphology that could be produced by dynamical interactions between the disk and forming planets. Additionally, the azimuthally averaged radial intensity profiles of the 7 and 9 mm images confirm the presence of the previously reported gap at $\sim45$ au, and reveal a new gap at $\sim85$ au. We analyzed archival DCO$^+$(3-2) and C$^{18}$O(2-1) ALMA observations, showing that the CO snowline is located very close to this third outer gap. This suggests that growth and accumulation of large dust grains close to the CO snowline could be the mechanism responsible for this proposed outer gap. Finally, a compact source of emission is detected at 7 mm, 9 mm, and 3 cm toward the center of the disk. Its flux density and spectral index indicate that it is dominated by free-free emission from ionized gas, which could be associated with either the photoionization of the inner disk, an independent object, or an ionized jet., Comment: 12 pages, 6 figures, accepted for publication in ApJ

We resolved FU Ori at 29-37 GHz using the JVLA with $\sim$0$''$.07 resolution, and performed the complementary JVLA 8-10 GHz observations, the SMA 224 GHz and 272 GHz observations, and compared with archival ALMA 346 GHz observations to obtain the SEDs. Our 8-10 GHz observations do not find evidence for the presence of thermal radio jets, and constrain the radio jet/wind flux to at least 90 times lower than the expected value from the previously reported bolometric luminosity-radio luminosity correlation. The emission at $>$29 GHz may be dominated by the two spatially unresolved sources, which are located immediately around FU Ori and its companion FU Ori S, respectively. Their deconvolved radii at 33 GHz are only a few au. The 8-346 GHz SEDs of FU Ori and FU Ori S cannot be fit by constant spectral indices (over frequency). The more sophisticated models for SEDs suggest that the $>$29 GHz emission is contributed by a combination of free-free emission from ionized gas, and thermal emission from optically thick and optically thin dust components. We hypothesize that dust in the innermost parts of the disks ($\lesssim$0.1 au) has been sublimated, and thus the disks are no more well shielded against the ionizing photons. The estimated overall gas and dust mass based on SED modeling, can be as high as a fraction of a solar mass, which is adequate for developing disk gravitational instability. Our present explanation for the observational data is that the massive inflow of gas and dust due to disk gravitational instability or interaction with a companion/intruder, was piled up at the few au scale due to the development of a deadzone with negligible ionization. The piled up material subsequently triggered the thermal and the MRI instabilities when the ionization fraction in the inner sub-au scale region exceeded a threshold value, leading to the high protostellar accretion rate., Comment: 10 pages, 4 figures, referee reported received and replied

We present preliminary results of JVLA wideband full polarization observations of a sample of Active Galactic Nuclei (AGN) with very high Rotation Measure (RM) values, a sign of extreme environment. Polarization properties show a complex behaviour such that the polarization angle (PA) and fractional polarization (fp) change dramatically within the wide band. The measured RM is not constant within the wide band. Its complex behaviour reflects the complexity of the medium with the presence of several Faraday components. The depolarization has been studied by modelling the variations of the Stokes parameters Q and U together with the polarization parameters (PA and fp) with wavelength using combinations of the simplest existing depolarization models. With this JVLA study we could spectrally resolve multiple polarized components of unresolved AGN. These preliminary results reveal the complexity of these objects, but improvements to the depolarization modelling are needed to better understand the polarization structure of these sources., Comment: Conference proceeding accepted to be published in Galaxies jurnal

Photoevaporation is probably the main agent for gas dispersal during the last stages of protoplanetary disk evolution. However, the overall mass loss rate in the photoevaporative wind and its driving mechanism are still not well understood. Here we report multi-configuration Very Large Array observations at 0.7, 3, and 5 cm towards the transitional disk of GM Aur. Our radio continuum observations allow us to image and spatially resolve, for the first time, the three main components at work in this stage of the disk evolution: the disk of dust, the ionized radio jet perpendicular to it, and the photoevaporative wind arising from the disk. The mass loss rate inferred from the flux density of the radio jet is consistent with the ratio between ejection and accretion rates found in younger objects, suggesting that transitional disks can power collimated ejections of material apparently following the same physical mechanisms as much younger protostars. Our results indicate that extreme-UV (EUV) radiation is the main ionizing mechanism of the photoevaporative wind traced by the free-free emission. The required low EUV photon luminosity of $\sim6\times10^{40}$ s$^{-1}$ would produce a photoevaporation rate of only $\dot{M}_{\rm w,EUV}\simeq1.3\times10^{-10}~M_{\odot}$ yr$^{-1}$. Therefore, other mechanisms are required to disperse the disk in the timescale imposed by observations., Comment: 20 pages, 3 figures, accepted for publication in ApJ

We report the discovery of a dwarf protoplanetary disk around the star XZ Tau B that shows all the features of a classical transitional disk but on a much smaller scale. The disk has been imaged with the Atacama Large Millimeter/Submillimeter Array (ALMA), revealing that its dust emission has a quite small radius of ~ 3.4 au and presents a central cavity of ~ 1.3 au in radius that we attribute to clearing by a compact system of orbiting (proto)planets. Given the very small radii involved, evolution is expected to be much faster in this disk (observable changes in a few months) than in classical disks (observable changes requiring decades) and easy to monitor with observations in the near future. From our modeling we estimate that the mass of the disk is large enough to form a compact planetary system., Comment: To appear in ApJL, 15 pages

We report ALMA observations of a one-sided, high-velocity ($\sim$80 km s$^{-1}$) CO($J = 2 \rightarrow 1$) jet powered by the intermediate-mass protostellar source Serpens SMM1-a. The highly collimated molecular jet is flanked at the base by a wide-angle cavity; the walls of the cavity can be seen in both 4 cm free-free emission detected by the VLA and 1.3 mm thermal dust emission detected by ALMA. This is the first time that ionization of an outflow cavity has been directly detected via free-free emission in a very young, embedded Class 0 protostellar source that is still powering a molecular jet. The cavity walls are ionized either by UV photons escaping from the accreting protostellar source, or by the precessing molecular jet impacting the walls. These observations suggest that ionized outflow cavities may be common in Class 0 protostellar sources, shedding further light on the radiation, outflow, and jet environments in the youngest, most embedded forming stars., Comment: 6 pages, 4 figures, accepted for publication in the Astrophysical Journal Letters

The first long-baseline ALMA campaign resolved the disk around the young star HL Tau into a number of axisymmetric bright and dark rings. Despite the very young age of HL Tau these structures have been interpreted as signatures for the presence of (proto)planets. The ALMA images triggered numerous theoretical studies based on disk-planet interactions, magnetically driven disk structures, and grain evolution. Of special interest are the inner parts of disks, where terrestrial planets are expected to form. However, the emission from these regions in HL Tau turned out to be optically thick at all ALMA wavelengths, preventing the derivation of surface density profiles and grain size distributions. Here, we present the most sensitive images of HL Tau obtained to date with the Karl G. Jansky Very Large Array at 7.0 mm wavelength with a spatial resolution comparable to the ALMA images. At this long wavelength the dust emission from HL Tau is optically thin, allowing a comprehensive study of the inner disk. We obtain a total disk dust mass of 0.001 - 0.003 Msun, depending on the assumed opacity and disk temperature. Our optically thin data also indicate fast grain growth, fragmentation, and formation of dense clumps in the inner densest parts of the disk. Our results suggest that the HL Tau disk may be actually in a very early stage of planetary formation, with planets not already formed in the gaps but in the process of future formation in the bright rings., Comment: Accepted by The Astrophysical Journal Letters

We report new Karl G. Jansky Very Large Array (JVLA), 0$"$.5 angular resolution observations of linearly polarized continuum emission at 6.9 mm, towards the Class 0 young stellar object (YSO) NGC1333 IRAS4A. This target source is a collapsing dense molecular core, which was resolved at short wavelengths to have hourglass shaped B-field configuration. We compare these 6.9 mm observations with previous polarization Submillimeter Array (SMA) observations at 0.88 mm, which have comparable angular resolution ($\sim$0$"$7). We found that at the same resolution, the observed polarization position angles at 6.9 mm are slightly deviated from those observed at 0.88 mm. Due to the lower optical depth of the emission at 6.9 mm, and the potential effect of dust grain growth, the new JVLA observations are likely probing B-field alignments in regions interior to those sampled by the previous polarization observations at higher frequencies. Our understanding can be improved by more sensitive observations, and observations for the more extended spatial scales., Comment: 10 pages, 6 figures. Submitted to ApJ

We report Submillimeter Array (SMA) 1.3 mm high angular resolution observations towards the four EXor type outbursting young stellar objects (YSOs) VY Tau, V1118 Ori, V1143 Ori, and NY Ori. The data mostly show low dust masses $M_{dust}$ in the associated circumstellar disks. Among the sources, NY Ori possesses a relatively massive disk with $M_{dust} \sim 9 \times 10^{-4}$ $M_{\odot}$. V1118 Ori has a marginal detection equivalent to $M_{dust} \sim 6 \times 10^{-5}$ $M_{\odot}$. V1143 Ori has a non-detection also equivalent to $M_{dust} < 6 \times 10^{-5}$ $M_{\odot}$. For the nearest source VY Tau, we get a surprising non-detection which provides a stringent upper limit $M_{dust} < 6 \times 10^{-6}$ $M_{\odot}$. We interpret our findings as suggesting that the gas and dust reservoirs that feed the short duration, repetitive optical outbursts seen in some EXors may be limited to the small scale, innermost region of their circumstellar disks. This hot dust may have escaped our detection limits. Follow-up, more sensitive millimeter observations are needed to improve our understanding of the triggering mechanisms of EXor type outbursts., Comment: 6 pages, 1 figure, accepted to ApJL

While most protostellar jets present free-free emission at radio wavelengths, synchrotron emission has been also proposed to be present in a handful of these objects. The presence of non-thermal emission has been inferred by negative spectral indices at centimeter wavelengths. In one case (the HH 80-81 jet arising from a massive protostar), its synchrotron nature was confirmed by the detection of linearly polarized radio emission. One of the main consequences of these results is that synchrotron emission implies the presence of relativistic particles among the non-relativistic material of these jets. Therefore, an acceleration mechanism should be taking place. The most probable scenario is that particles are accelerated when the jets strongly impact against the dense envelope surrounding the protostar. Here, we present an analysis of radio observations obtained with the Very Large Array of the Triple Radio Source in the Serpens star-forming region. This object is known to be a radio jet arising from an intermediate-mass protostar. It is also one of the first protostellar jets where the presence of non-thermal emission was proposed. We analysed the dynamics of the jet as well as the nature of the emission and discuss these issues in the context of the physical parameters of the jet and the particle acceleration phenomenon., Comment: Astrophysical Journal (in press). 24 pages (9 figures). Contact: Adriana Rodr\'iguez-Kamenetzky (adrianark@gmail.com)

We report here the study, in the radio band, of a sample of candidates of high Rotation Measure (RM). The point-like objects (at kpc scale) were selected by choosing unpolarised sources from the NVSS which show significant linear polarisation at 10.45 GHz. Assuming in-band depolarisation, this feature suggests the presence of a very dense medium surrounding them in a combination of a strong magnetic field. Further single-dish observations were performed with the 100-m Effelsberg telescope to characterise the SEDs of the sample and to well determine their RM in the 11 to 2 cm wavelength range. Besides, a wideband (L, S, C and X band ) full polarisation observational campaign was performed at the JVLA facility. It allows us to analyse the in-band RM for the most extreme objects. Some Effelsberg results and analysis, and preliminary JVLA results are presented. The observations reveal that sources with young, newly growing, radio components at high frequency (i.e. GPS and HFP sources) are characterised by a really dense and/or a magnetised medium that strongly rotates the polarisation angle at the different frequencies, leading to a high-RM., Comment: Paper accepted to by published on Astronomische Nachrichten Journal. arXiv admin note: text overlap with arXiv:1510.01136

(abridged) The HH 80/81/80N jet extends from the HH 80 object to the recently discovered Source 34 and has a total projected jet size of 10.3 pc, constituting the largest collimated radio-jet system known so far. It is powered by IRAS 18162-2048 associated with a massive young stellar object. We report 6 cm JVLA observations that, compared with previous 6 cm VLA observations carried out in 1989, allow us to derive proper motions of the HH 80, HH 81 and HH 80N radio knots located about 2.5 pc away in projection from the powering source. For the first time, we measure proper motions of the optically obscured HH 80N object providing evidence that HH 81, 80 and 80N are associated with the same radio-jet. We derived tangential velocities of these HH objects between 260 and 350 km/s, significantly lower than those for the radio knots of the jet close to the powering source (600-1400 km/s) derived in a previous work, suggesting that the jet material is slowing down due to a strong interaction with the ambient medium. The HH 80 and HH 80N emission at 6 cm is, at least in part, probably synchrotron radiation produced by relativistic electrons in a magnetic field of 1 mG. If these electrons are accelerated in a reverse adiabatic shock, we estimate a jet total density of $\lesssim1000$ cm$^{-3}$. All these features are consistent with a jet emanating from a high mass protostar and make evident its capability of accelerating particles up to relativistic velocities., Comment: 15 pages, 3 figures, 1 table, accepted for publication in ApJ