Enrique Macías

THE VLA VIEW OF THE HL TAU DISK: DISK MASS, GRAIN EVOLUTION, AND EARLY PLANET FORMATION

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.

AN IONIZED OUTFLOW FROM AB AUR, A HERBIG AE STAR WITH A TRANSITIONAL DISK

AB Aur is a Herbig Ae star with a transitional disk. Transitional disks present substantial dust clearing in their inner regions, most probably because of the formation of one or more planets, although other explanations are still viable. In transitional objects, accretion is found to be about an order of magnitude smaller than in classical full disks. Since accretion is believed to be correlated with outflow activity, centimeter free-free jets are expected to be present in association with these systems, at weaker levels than in classical protoplanetary (full) systems. We present new observations of the centimeter radio emission associated with the inner regions of AB Aur and conclude that the morphology, orientation, spectral index and lack of temporal variability of the centimeter source imply the presence of a collimated, ionized outflow. The radio luminosity of this radio jet is, however, about 20 times smaller than that expected for a classical system of similar bolometric luminosity. We conclude that centimeter continuum emission is present in association with stars with transitional disks, but at levels than are becoming detectable only with the upgraded radio arrays. On the other hand, assuming that the jet velocity is 300 km s

High-resolution observations of the outer disk around T Chamaeleontis: the view from ALMA

^{-1}

Imaging a Central Ionized Component, a Narrow Ring, and the CO Snowline in the Multigapped Disk of HD 169142

, we find that the ratio of mass loss rate to accretion rate in AB Aur is

IMAGING THE PHOTOEVAPORATING DISK AND RADIO JET OF GM AUR

\sim

ALMA Discovery of Dust Belts around Proxima Centauri

0.1, similar to that found for less evolved systems.

A DWARF TRANSITIONAL PROTOPLANETARY DISK AROUND XZ TAU B

Context. Transitional disks are circumstellar disks with dust gaps thought to be related in some cases to planet formation. They can shed light on the planet formation process by the analysis of their gas and dust properties. T Cha is a young star surrounded by a transitional disk with signatures of planet formation. Aims. The aim of this work is to spatially resolve the outer disk around T Cha and to derive its main properties. Methods. We have obtained high-resolution and high-sensitivity ALMA observations in the CO(3–2), 13 CO(3–2), and CS(7–6) emission lines to reveal the spatial distribution of the gaseous disk around the star. In order to study the dust within the disk we have also obtained continuum images at 850 μm from the line-free channels. Results. We have spatially resolved the outer disk around T Cha. Using the CO(3−2) emission we derive a radius of ∼230 AU. We also report the detection of the 13 CO(3−2) and the CS(7−8) molecular emissions, which show smaller radii than the CO(3−2) detection. The continuum observations at 850 μm allow the spatial resolution of the dusty disk, which shows two emission bumps separated by ∼40 AU, consistent with the presence of a dust gap in the inner regions of the disk, and an outer radius of ∼80 AU. Therefore, T Cha is surrounded by a compact dusty disk and a larger and more diffuse gaseous disk, as previously observed in other young stars. The continuum intensity profiles are different at both sides of the disk suggesting possible dust asymmetries. We derive an inclination of i( ◦ ) = 67 ± 5, and a position angle of PA( ◦ ) = 113 ± 6, for both the gas and dust disks. The comparison of the ALMA data with radiative transfer models shows that the gas and dust components can only be simultaneously reproduced when we include a tapered edge prescription for the surface density profile. The best model suggests that most of the disk mass is placed within a radius of R < 50 AU. Finally, we derive a dynamical mass for the central object of M∗ = 1.5 ± 0.2 M� , comparable to the one estimated with evolutionary models for an age of ∼10 Myr.

Herschel PACS Observations of 4–10 Myr Old Classical T Tauri Stars in Orion OB1

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.′′12×0. ′′09, or 14 au×11 au, at 7 mm). Our 7 and 9 mm images show a narrow ring of emission at a radius of ∼ 25 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 ∼ 45 au, and reveal a new gap at ∼ 85 au. We analyzed archival DCO(3-2) and CO(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.

Long-lived Protoplanetary Disks in Multiple Systems: The VLA View of HD 98800

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

Multiple Rings in the Transitional Disk of GM Aurigae Revealed by VLA and ALMA

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