We present Atacama Large Millimeter/sub-millimeter Array Cycle 1 observations of the HH 46/47 molecular outflow using combined 12 m array and Atacama Compact Array observations. The improved angular ...resolution and sensitivity of our multi-line maps reveal structures that help us study the entrainment process in much more detail and allow us to obtain more precise estimates of outflow properties than in previous observations. We use {sup 13}CO (1–0) and C{sup 18}O (1–0) emission to correct for the {sup 12}CO (1–0) optical depth to accurately estimate the outflow mass, momentum, and kinetic energy. This correction increases the estimates of the mass, momentum, and kinetic energy by factors of about 9, 5, and 2, respectively, with respect to estimates assuming optically thin emission. The new {sup 13}CO and C{sup 18}O data also allow us to trace denser and slower outflow material than that traced by the {sup 12}CO maps, and they reveal an outflow cavity wall at very low velocities (as low as 0.2 km s{sup −1} with respect to the core’s central velocity). Adding the slower material traced only by {sup 13}CO and C{sup 18}O, there is another factor of three increase in the mass estimate and 50% increase in the momentum estimate. The estimated outflow properties indicate that the outflow is capable of dispersing the parent core within the typical lifetime of the embedded phase of a low-mass protostar and that it is responsible for a core-to-star efficiency of 1/4 to 1/3. We find that the outflow cavity wall is composed of multiple shells associated with a series of jet bow-shock events. Within about 3000 au of the protostar the {sup 13}CO and C{sup 18}O emission trace a circumstellar envelope with both rotation and infall motions, which we compare with a simple analytic model. The CS (2–1) emission reveals tentative evidence of a slowly moving rotating outflow, which we suggest is entrained not only poloidally but also toroidally by a disk wind that is launched from relatively large radii from the source.
We present new results from the DisksatEVLA program for two young stars: CY Tau and DoAr 25. We trace continuum emission arising from their circusmtellar disks from spatially resolved observations, ...down to tens of AU scales, at lambda = 0.9, 2.8, 8.0, 9.8 mm for DoAr 25 and at lambda = 1.3, 2.8, 7.1 mm for CY Tau. Additionally, we constrain the amount of emission whose origin is different from thermal dust emission from 5 cm observations. Directly from interferometric data, we find that observations at 7 mm and 1 cm trace emission from a compact disk while millimeter-wave observations trace an extended disk structure. From a physical disk model, where we characterize the disk structure of CY Tau and DoAr 25 at wavelengths shorter than 5 cm, we find that (1) dust continuum emission is optically thin at the observed wavelengths and over the spatial scales studied, (2) a constant value of the dust opacity is not warranted by our observations, and (3) a high-significance radial gradient of the dust opacity spectral index, beta , is consistent with the observed dust emission in both disks, with low- beta in the inner disk and high- beta in the outer disk. Assuming that changes in dust properties arise solely due to changes in the maximum particle size ( alpha sub(max)), we constrain radial variations of alpha sub(max) in both disks, from cm-sized particles in the inner disk (R < 40 AU) to millimeter sizes in the outer disk (R > 80 AU). These observational constraints agree with theoretical predictions of the radial-drift barrier, however, fragmentation of dust grains could explain our alpha sub(max)(R) constraints if these disks have lower turbulence and/or if dust can survive high-velocity collisions.
We present high spatial resolution observations of the continuum emission from the young multiple star system UZ Tau at frequencies from 6 to 340 GHz. To quantify the spatial variation of dust ...emission in the UZ Tau E circumbinary disk, the observed interferometric visibilities are modeled with a simple parametric prescription for the radial surface brightnesses at each frequency. We find evidence that the spectrum steepens with radius in the disk, manifested as a positive correlation between the observing frequency and the radius that encircles a fixed fraction of the emission (\(R_{eff} \propto \nu^{0.34 \pm 0.08}\)). The origins of this size--frequency relation are explored in the context of a theoretical framework for the growth and migration of disk solids. While that framework can reproduce a similar size--frequency relation, it predicts a steeper spectrum than is observed. Moreover, it comes closest to matching the data only on timescales much shorter (\(\le 1\) Myr) than the putative UZ Tau age (~2-3 Myr). These discrepancies are the direct consequences of the rapid radial drift rates predicted by models of dust evolution in a smooth gas disk. One way to mitigate that efficiency problem is to invoke small-scale gas pressure modulations that locally concentrate drifting solids. If such particle traps reach high continuum optical depths at 30-340 GHz with a ~30-60% filling fraction in the inner disk (\(r \lesssim20\) au), they can also explain the observed spatial gradient in the UZ Tau E disk spectrum.
Massive star formation occurs in giant molecular clouds (GMCs); an understanding of the evolution of GMCs is a prerequisite to develop theories of star formation and galaxy evolution. We report the ...highest-fidelity observations of the grand-design spiral galaxy M51 in carbon monoxide (CO) emission, revealing the evolution of GMCs vis-a-vis the large-scale galactic structure and dynamics. The most massive GMCs (giant molecular associations (GMAs)) are first assembled and then broken up as the gas flow through the spiral arms. The GMAs and their H{sub 2} molecules are not fully dissociated into atomic gas as predicted in stellar feedback scenarios, but are fragmented into smaller GMCs upon leaving the spiral arms. The remnants of GMAs are detected as the chains of GMCs that emerge from the spiral arms into interarm regions. The kinematic shear within the spiral arms is sufficient to unbind the GMAs against self-gravity. We conclude that the evolution of GMCs is driven by large-scale galactic dynamics-their coagulation into GMAs is due to spiral arm streaming motions upon entering the arms, followed by fragmentation due to shear as they leave the arms on the downstream side. In M51, the majority of the gas remains molecular from arm entry through the interarm region and into the next spiral arm passage.
During star formation, the accretion disk drives fast MHD winds which usually contain two components, a collimated jet and a radially distributed wide-angle wind. These winds entrain the surrounding ...ambient gas producing molecular outflows. We report recent observation of 12CO (2-1) emission of the HH 46/47 molecular outflow by the Atacama Large Millimeter/sub-millimeter Array, in which we identify multiple wide-angle outflowing shell structures in both the blue and red-shifted outflow lobes. These shells are highly coherent in position-position-velocity space, extending to >40-50 km/s in velocity and 10^4 au in space with well defined morphology and kinematics. We suggest these outflowing shells are the result of the entrainment of ambient gas by a series of outbursts from an intermittent wide-angle wind. Episodic outbursts in collimated jets are commonly observed, yet detection of a similar behavior in wide-angle winds has been elusive. Here we show clear evidence that the wide-angle component of the HH 46/47 protostellar outflows experiences similar variability seen in the collimated component.
The Vega planetary system hosts the archetype of extrasolar Kuiper belts, and is rich in dust from the sub-au region out to 100's of au, suggesting intense dynamical activity. We present ALMA mm ...observations that detect and resolve the outer dust belt from the star for the first time. The interferometric visibilities show that the belt can be fit by a Gaussian model or by power-law models with a steep inner edge (at 60-80 au). The belt is very broad, extending out to at least 150-200 au. We strongly detect the star and set a stringent upper limit to warm dust emission previously detected in the infrared. We discuss three scenarios that could explain the architecture of Vega's planetary system, including the new {ALMA} constraints: no outer planets, a chain of low-mass planets, and a single giant planet. The planet-less scenario is only feasible if the outer belt was born with the observed sharp inner edge. If instead the inner edge is currently being truncated by a planet, then the planet must be \(\gtrsim\)6 M\(_{\oplus}\) and at \(\lesssim71\) au to have cleared its chaotic zone within the system age. In the planet chain scenario, outward planet migration and inward scattering of planetesimals could produce the hot and warm dust observed in the inner regions of the system. In the single giant planet scenario, an asteroid belt could be responsible for the warm dust, and mean motion resonances with the planet could put asteroids on star-grazing orbits, producing the hot dust.
Construction and commissioning of the Atacama Large Millimeter/Submillimeter Array (ALMA) is progressing rapidly. Even with a fraction of the total number of antennas to be located at the Array ...Operations Site (AOS) in northern Chile in place, ALMA is the most powerful millimeter/submillimeter interferometer in the world. In this paper I report on the progress of array commissioning and science verification (CSV). I summarize the current performance of the array including noise temperatures, calibration accuracy and available observing modes. At the time of presentation of this paper, ALMA science verification observations will likely be available to the public. I will present the results and comparison data as well as update and detail the array status.
The combination of high resolution and sensitivity offered by ALMA is revolutionizing our understanding of protoplanetary discs, as their bulk gas and dust distributions can be studied independently. ...In this paper we present resolved ALMA observations of the continuum emission (\(\lambda=1.3\) mm) and CO isotopologues (\(^{12}\)CO, \(^{13}\)CO, C\(^{18}\)O \(J=2-1\)) integrated intensity from the disc around the nearby (\(d = 162\) pc), intermediate mass (\(M_{\star}=1.67\,M_{\odot}\)) pre-main-sequence star CQ Tau. The data show an inner depression in continuum, and in both \(^{13}\)CO and C\(^{18}\)O emission. We employ a thermo-chemical model of the disc reproducing both continuum and gas radial intensity profiles, together with the disc SED. The models show that a gas inner cavity with size between 15 and 25 au is needed to reproduce the data with a density depletion factor between \(\sim 10^{-1}\) and \(\sim 10^{-3}\). The radial profile of the distinct cavity in the dust continuum is described by a Gaussian ring centered at \(R_{\rm dust}=53\,\)au and with a width of \(\sigma=13\,\)au. Three dimensional gas and dust numerical simulations of a disc with an embedded planet at a separation from the central star of \(\sim20\,\)au and with a mass of \(\sim 6\textrm{-} 9\,M_{\rm Jup}\) reproduce qualitatively the gas and dust profiles of the CQ Tau disc. However, a one planet model appears not to be able to reproduce the dust Gaussian density profile predicted using the thermo-chemical modeling.
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