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Santiago, Chile

Walsh C.,Leiden University | Juhasz A.,Leiden University | Pinilla P.,Leiden University | Harsono D.,Leiden University | And 12 more authors.
Astrophysical Journal Letters | Year: 2014

HD 100546 is a well-studied Herbig Be star-disk system that likely hosts a close-in companion with compelling observational evidence for an embedded protoplanet at 68 AU. We present Atacama Large Millimeter/Submillimeter Array observations of the HD 100546 disk which resolve the gas and dust structure at (sub)millimeter wavelengths. The CO emission (at 345.795 GHz) originates from an extensive molecular disk (390 ± 20 AU in radius) whereas the continuum emission is more compact (230 ± 20 AU in radius), suggesting radial drift of the millimeter-sized grains. The CO emission is similar in extent to scattered light images indicating well-mixed gas and micrometer-sized grains in the disk atmosphere. Assuming azimuthal symmetry, a single-component power-law model cannot reproduce the continuum visibilities. The visibilities and images are better reproduced by a double-component model: a compact ring with a width of 21 AU centered at 26 AU and an outer ring with a width of 75 ± 3 AU centered at 190 ± 3 AU. The influence of a companion and protoplanet on the dust evolution is investigated. The companion at 10 AU facilitates the accumulation of millimeter-sized grains within a compact ring, ≈20-30 AU, by ≈10 Myr. The injection of a protoplanet at 1 Myr hastens the ring formation (≈1.2 Myr) and also triggers the development of an outer ring (≈100-200 AU). These observations provide additional evidence for the presence of a close-in companion and hint at dynamical clearing by a protoplanet in the outer disk. © 2014. The American Astronomical Society. All rights reserved.

Guzman A.E.,University of Chile | Guzman A.E.,Harvard - Smithsonian Center for Astrophysics | Garay G.,University of Chile | Rodriguez L.F.,National Autonomous University of Mexico | And 7 more authors.
Astrophysical Journal | Year: 2014

We report the detection, made using ALMA, of the 92 GHz continuum and hydrogen recombination lines (HRLs) H40α, H42α, and H50β emission toward the ionized wind associated with the high-mass young stellar object G345.4938+01.4677. This is the luminous central dominating source located in the massive and dense molecular clump associated with IRAS 16562-3959. The HRLs exhibit Voigt profiles, which is a strong signature of Stark broadening. We successfully reproduce the observed continuum and HRLs simultaneously using a simple model of a slow ionized wind in local thermodynamic equilibrium, with no need for a high-velocity component. The Lorentzian line wings imply electron densities of 5 × 107 cm-3 on average. In addition, we detect SO and SO2 emission arising from a compact (3000 AU) molecular core associated with the central young star. The molecular core exhibits a velocity gradient that is perpendicular to the jet-axis, which we interpret as evidence of rotation. The set of observations toward G345.4938+01.4677 are consistent with it being a young high-mass star associated with a slow photo-ionized wind. © 2014. The American Astronomical Society. All rights reserved..

Huelamo N.,CSIC - National Institute of Aerospace Technology | De Gregorio-Monsalvo I.,Joint ALMA Observatory JAO | De Gregorio-Monsalvo I.,European Southern Observatory | Macias E.,Institute Astrofisica Of Andalucia | And 6 more authors.
Astronomy and Astrophysics | Year: 2015

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), 13CO(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 13CO(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 Mâ- 1.5 ± 0.2 Mâ™comparable to the one estimated with evolutionary models for an age of 10 Myr. © ESO, 2015.

Merello M.,University of Chile | Merello M.,University of Texas at Austin | Bronfman L.,University of Chile | Garay G.,University of Chile | And 4 more authors.
Astrophysical Journal | Year: 2013

We report molecular line and dust continuum observations toward the high-mass star-forming region G331.5-0.1, one of the most luminous regions of massive star formation in the Milky Way, located at the tangent region of the Norma spiral arm, at a distance of 7.5 kpc. Molecular emission was mapped toward the G331.5-0.1 GMC in the CO(J = 1 → 0) and C18O(J = 1 → 0) lines with NANTEN, while its central region was mapped in CS(J = 2 → 1 and J = 5 → 4) with SEST, and in CS(J = 7 → 6) and 13CO(J = 3 → 2) with ASTE. Continuum emission mapped at 1.2 mm with SIMBA and at 0.87 mm with LABOCA reveal the presence of six compact and luminous dust clumps, making this source one of the most densely populated central regions of a GMC in the Galaxy. The dust clumps are associated with molecular gas and they have the following average properties: size of 1.6 pc, mass of 3.2 × 10 3 M ⊙, molecular hydrogen density of 3.7 × 104 cm-3, dust temperature of 32 K, and integrated luminosity of 5.7 × 105 L⊙, consistent with values found toward other massive star-forming dust clumps. The CS and 13CO spectra show the presence of two velocity components: a high-velocity component at -89 km s-1, seen toward four of the clumps, and a low-velocity component at -101 km s-1 seen toward the other two clumps. Radio continuum emission is present toward four of the molecular clumps, with spectral index estimated for two of them of 0.8 ± 0.2 and 1.2 ± 0.2. A high-velocity molecular outflow is found at the center of the brightest clump, with a line width of 26 km s-1 (FWHM) in CS(J = 7 → 6). Observations of SiO(J = 7 → 6 and J = 8 → 7), and SO(JK = 88 → 77 and JK = 87 → 76) lines provide estimates of the gas rotational temperature toward this outflow >120 K and >75 K, respectively. © 2013. The American Astronomical Society. All rights reserved.

Mathews G.S.,Leiden University | Klaassen P.D.,Leiden University | Juhasz A.,Leiden University | Harsono D.,Leiden University | And 14 more authors.
Astronomy and Astrophysics | Year: 2013

Context. The high spatial resolution and line sensitivity of the Atacama Large Millimeter/submillimeter Array (ALMA) opens the possibility of resolving emission from molecules in large samples of circumstellar disks. With an understanding of the conditions under which these molecules can have high abundance, they can be used as direct tracers of distinct physical regions. In particular, DCO+ is expected to have an enhanced abundance within a few Kelvin of the CO freezeout temperature of 19 K, making it a useful probe of the cold disk midplane. Aims. We aim to use line emission from DCO+ to directly resolve the CO "snowline" - the region at which the gas-phase CO abundance drops due to freezeout - and determine the temperature boundaries of the region of DCO+ emission in the HD 163296 disk. This will serve as a test of deuteration models based on enhanced formation of the parent molecule H2D+ and a direct probe of midplane disk structure and ionization. Methods. We compare ALMA line observations of HD 163296 to a grid of models based on the best fit physical model of Qi et al. (2011, ApJ, 740, 84). We vary the upper- and lower-limit temperatures of the region in which DCO+ is present as well as the abundance of DCO + in order to fit channel maps of the DCO+J = 5-4 line. To determine the abundance enhancement compared to the general interstellar medium, we carry out similar fitting to HCO+J = 4-3 and H 13CO+J = 4-3 observations. Results. ALMA images show centrally peaked extended emission from HCO+ and H 13CO+. DCO+ emission lies in a resolved ring from ~110 to 160 AU. The outer radius approximately corresponds to the size of the CO snowline as measured by previous lower resolution observations of CO lines in this disk. The ALMA DCO+ data now resolve and image the CO snowline directly. Conclusions. In the best fitting models, HCO+ exists in a region extending from the 19 K isotherm to the photodissociation layer with an abundance of 3 × 10-10 relative to H2. DCO+ exists within the 19-21 K region of the disk with an abundance ratio [DCO+]/[HCO+] = 0.3. This represents a factor of 104 enhancement of the DCO+ abundance within this narrow region of the HD 163296 disk. Such a high enhancement has only previously been seen in prestellar cores. The inferred abundances provide a lower limit to the ionization fraction in the midplane of the cold outer disk (â‰4 × 10-10), and suggest the utility of DCO+ as a tracer of its parent molecule H2D+. © ESO, 2013.

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