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Santiago, Chile

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Pety J.,IRAM | Pety J.,Ecole Normale Superieure de Paris | Guzman V.V.,Harvard - Smithsonian Center for Astrophysics | Guzman V.V.,Joint ALMA Observatory JAO | And 15 more authors.
Astronomy and Astrophysics | Year: 2017

Context. Molecular lines and line ratios are commonly used to infer properties of extra-galactic star forming regions. The new generation of millimeter receivers almost turns every observation into a line survey. Full exploitation of this technical advancement in extra-galactic study requires detailed bench-marking of available line diagnostics. Aims. We aim to develop the Orion B giant molecular cloud (GMC) as a local template for interpreting extra-galactic molecular line observations. Methods. We use the wide-band receiver at the IRAM-30 m to spatially and spectrally resolve the Orion B GMC. The observations cover almost 1 square degree at 26′′ resolution with a bandwidth of 32 GHz from 84 to 116 GHz in only two tunings. Among the mapped spectral lines are the, C18O, C17O, HCN, HNC, C2H, HCO+, N2H+(1-0), and, SiO, c-C3H2, CH3OH (2-1) transitions. Results. We introduce the molecular anatomy of the Orion B GMC, including relationships between line intensities and gas column density or far-UV radiation fields, and correlations between selected line and line ratios. We also obtain a dust-traced gas mass that is less than approximately one third the CO-traced mass, using the standard XCO conversion factor. The presence of over-luminous CO can be traced back to the dependence of the CO intensity on UV illumination. As a matter of fact, while most lines show some dependence on the UV radiation field, CN and C2H are the most sensitive. Moreover, dense cloud cores are almost exclusively traced by N2H+. Other traditional high-density tracers, such as HCN(1-0), are also easily detected in extended translucent regions at a typical density of ~500 H2 cm-3. In general, we find no straightforward relationship between line critical density and the fraction of the line luminosity coming from dense gas regions. Conclusions. Our initial findings demonstrate that the relationships between line (ratio) intensities and environment in GMCs are more complicated than often assumed. Sensitivity (i.e., the molecular column density), excitation, and, above all, chemistry contribute to the observed line intensity distributions, and they must be considered together when developing the next generation of extra-galactic molecular line diagnostics of mass, density, temperature, and radiation field. © 2017 ESO.

Sahai R.,Jet Propulsion Laboratory | Vlemmings W.H.T.,Chalmers University of Technology | Gledhill T.,University of Hertfordshire | Contreras C.S.,CSIC - National Institute of Aerospace Technology | And 4 more authors.
Astrophysical Journal Letters | Year: 2017

We have mapped 12CO J = 3-2 and other molecular lines from the "water fountain" bipolar pre-planetary nebula (PPN) IRAS 16342-3814 with ∼0.″35 resolution using Atacama Large Millimeter/submillimeter Array. We find (i) two very high-speed knotty, jet-like molecular outflows; (ii) a central high-density ( cm-3), expanding torus of diameter 1300 au; and (iii) the circumstellar envelope of the progenitor AGB, generated by a sudden, very large increase in the mass-loss rate to M o yr-1 in the past ∼455 years. Strong continuum emission at 0.89 mm from a central source (690 mJy), if due to thermally emitting dust, implies a substantial mass (0.017 M o) of very large (∼millimeter-sized) grains. The measured expansion ages of the above structural components imply that the torus (age ∼160 years) and the younger high-velocity outflow (age ∼110 years) were formed soon after the sharp increase in the AGB mass-loss rate. Assuming a binary model for the jets in IRAS 16342, the high momentum rate for the dominant jet-outflow in IRAS 16342 implies a high minimum accretion rate, ruling out standard Bondi-Hoyle-Lyttleton wind accretion and wind Roche-lobe overflow (RLOF) models with white-dwarf or main-sequence companions. Most likely, enhanced RLOF from the primary or accretion modes operating within common-envelope evolution are needed. © 2017. The American Astronomical Society. All rights reserved.

Yasui C.,University of Tokyo | Kobayashi N.,University of Tokyo | Tokunaga A.T.,University of Hawaii at Manoa | Saito M.,Japan National Astronomical Observatory | Saito M.,Joint ALMA Observatory JAO
Monthly Notices of the Royal Astronomical Society | Year: 2014

We derived the intermediate-mass ((1.5-7M() disc fraction (IMDF) in the near-infrared JHK photometric bands as well as in the mid-infrared (MIR) bands for young clusters in the age range of 0 to ~10 Myr. From the JHK IMDF, the lifetime of the innermost dust disc (~0.3 au; hereafter the K disc) is estimated to be ~3 Myr, suggesting a stellar mass (M*) dependence of K-disc lifetime ∝ M -0.7 ~. However, from the MIR IMDF, the lifetime of the inner disc (~5 au; hereafter the MIR disc) is estimated to be ~6.5 Myr, suggesting a very weak stellar mass dependence (∝ M -0.2 ~). The much shorter K-disc lifetime compared to the MIR-disc lifetime for intermediate-mass (IM) stars suggests that IM stars with transition discs, which have only MIR excess emission but no K-band excess emission, are more common than classical Herbig Ae/Be stars, which exhibit both. We suggest that this prominent early disappearance of the K disc for IM stars is due to dust settling/growth in the protoplanetary disc, and it could be one of the major reasons for the paucity of close-in planets around IM stars.

Merello M.,University of Chile | Merello M.,University of Texas at Austin | Bronfman L.,University of Chile | Garay G.,University of Chile | And 5 more authors.
Astrophysical Journal Letters | Year: 2013

The object of this study is one of the most energetic and luminous molecular outflows known in the Galaxy, G331.512-0.103. Observations with ALMA Band 7 (350 GHz; 0.86 mm) reveal a very compact, extremely young bipolar outflow and a more symmetric outflowing shocked shell surrounding a very small region of ionized gas. The velocities of the bipolar outflow are about 70 km s -1 on either side of the systemic velocity. The expansion velocity of the shocked shell is 24 km s-1, implying a crossing time of about 2000 yr. Along the symmetry axis of the outflow, there is a velocity feature, which could be a molecular "bullet" of high-velocity dense material. The source is one of the youngest examples of massive molecular outflow found associated with a high-mass star. © 2013. The American Astronomical Society. All rights reserved.

Garcia P.,University of Chile | Garcia P.,University of Cologne | Bronfman L.,University of Chile | Nyman L.-A.,Joint ALMA Observatory JAO | And 3 more authors.
Astrophysical Journal, Supplement Series | Year: 2014

The Columbia University-Universidad de Chile CO Survey of the southern Milky Way is used to separate the CO(1-0) emission of the fourth Galactic quadrant within the solar circle into its dominant components, giant molecular clouds (GMCs). After the subtraction of an axisymmetric model of the CO background emission in the inner southern Galaxy, 92 GMCs are identified, and for 87 of them the twofold distance ambiguity is solved. Their total molecular mass is M(H2) = 1.14 ± 0.05 × 108 M ⊙, accounting for around 40% of the molecular mass estimated from an axisymmetric analysis of the H2 volume density in the Galactic disk, M(H2)disk = 3.03 × 108 M ⊙. The large-scale spiral structure in the southern Galaxy, within the solar circle, is traced by the GMCs in our catalog; three spiral arm segments, the Centaurus, Norma, and 3 kpc expanding arm, are analyzed. After fitting a logarithmic spiral arm model to the arms, tangent directions at 310°, 330°, and 338°, respectively, are found, consistent with previous values from the literature. A complete CS(2-1) survey toward IRAS point-like sources with far-IR colors characteristic of ultracompact H II regions is used to estimate the massive star formation rate per unit H 2 mass (MSFR) and the massive star formation efficiency (ε) for GMCs. The average MSFR for GMCs is 0.41 ± 0.06 L /M⊙, and for the most massive clouds in the Norma arm it is 0.58 ± 0.09 L /M ⊙. Massive star formation efficiencies of GMCs are, on average, 3% of their available molecular mass. © 2014. The American Astronomical Society. All rights reserved.

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.

PubMed | Joint ALMA Observatory JAO, Rice University, Harvard - Smithsonian Center for Astrophysics, National institute for astrophysics and 6 more.
Type: Journal Article | Journal: Physical review letters | Year: 2016

We present Atacama Large Millimeter and Submillimeter Array observations of the protoplanetary disk around the Herbig Ae star HD 163296 that trace the spatial distribution of millimeter-sized particles and cold molecular gas on spatial scales as small as 25astronomical units (A.U.). The image of the disk recorded in the 1.3mm continuum emission reveals three dark concentric rings that indicate the presence of dust depleted gaps at about 60, 100, and 160A.U. from the central star. The maps of the ^{12}CO, ^{13}CO, and C^{18}O J=2-1 emission do not show such structures but reveal a change in the slope of the radial intensity profile across the positions of the dark rings in the continuum image. By comparing the observations with theoretical models for the disk emission, we find that the density of CO molecules is reduced inside the middle and outer dust gaps. However, in the inner ring there is no evidence of CO depletion. From the measurements of the dust and gas densities, we deduce that the gas-to-dust ratio varies across the disk and, in particular, it increases by at least a factor 5 within the inner dust gap compared to adjacent regions of the disk. The depletion of both dust and gas suggests that the middle and outer rings could be due to the gravitational torque exerted by two Saturn-mass planets orbiting at 100 and 160A.U. from the star. On the other hand, the inner dust gap could result from dust accumulation at the edge of a magnetorotational instability dead zone, or from dust opacity variations at the edge of the CO frost line. Observations of the dust emission at higher angular resolution and of molecules that probe dense gas are required to establish more precisely the origins of the dark rings observed in the HD 163296 disk.

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.

Cheetham A.,University of Sydney | Huelamo N.,CSIC - National Institute of Aerospace Technology | Lacour S.,University of Paris Descartes | De Gregorio-Monsalvo I.,Joint ALMA Observatory JAO | And 2 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2015

T Chamaeleontis is a young star surrounded by a transitional disc, and a plausible candidate for ongoing planet formation. Recently, a substellar companion candidate was reported within the disc gap of this star. However, its existence remains controversial, with the counter-hypothesis that light from a high-inclination disc may also be consistent with the observed data. The aim of this work is to investigate the origin of the observed closure phase signal to determine if it is best explained by a compact companion.We observed T Cha in the L' and Ks filters with sparse aperture masking, with seven data sets covering a period of 3 years. A consistent closure phase signal is recovered in all L' and Ks data sets. Data were fitted with a companion model and an inclined circumstellar discmodel based on known disc parameters: bothwere shown to provide an adequate fit. However, the absence of expected relative motion for an orbiting body over the 3-year time baseline spanned by the observations rules out the companion model. Applying image reconstruction techniques to each data set reveals a stationary structure consistent with forward scattering from the near edge of an inclined disc. © 2015 The Authors.

Sahai R.,Jet Propulsion Laboratory | Vlemmings W.H.T.,Chalmers University of Technology | Huggins P.J.,New York University | Nyman L.-A.,Joint ALMA Observatory JAO | And 2 more authors.
Astrophysical Journal | Year: 2013

The Boomerang Nebula is the coldest known object in the universe, and an extreme member of the class of pre-planetary nebulae, objects which represent a short-lived transitional phase between the asymptotic giant branch and planetary nebula evolutionary stages. Previous single-dish CO (J = 1-0) observations (with a 45″ beam) showed that the high-speed outflow in this object has cooled to a temperature significantly below the temperature of the cosmic background radiation. Here we report the first observations of the Boomerang Nebula with ALMA in the CO J = 2-1 and J = 1-0 lines to resolve the structure of this ultra-cold nebula. We find a central hourglass-shaped nebula surrounded by a patchy, but roughly round, cold high-velocity outflow. We compare the ALMA data with visible-light images obtained with the Hubble Space Telescope and confirm that the limb-brightened bipolar lobes seen in these data represent hollow cavities with dense walls of molecular gas and dust producing both the molecular-emission-line and scattered-light structures seen at millimeter and visible wavelengths. The large diffuse biconical shape of the nebula seen in the visible wavelength range is likely due to preferential illumination of the cold, high-velocity outflow. We find a compact source of millimeter-wave continuum in the nebular waist - these data, together with sensitive upper limits on the radio continuum using observations with ATCA, indicate the presence of a substantial mass of very large (millimeter-sized) grains in the waist of the nebula. Another unanticipated result is the detection of CO emission regions beyond the ultra-cold region which indicate the re-warming of the cold gas, most likely due to photoelectric grain heating. © 2013. The American Astronomical Society. All rights reserved..

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