S. Cabrit

Dust properties of protoplanetary disks in the Taurus-Auriga star forming region from millimeter wavelengths

We present the most sensitive 3 mm-survey to date of protoplanetary disks carried out in the Taurus-Auriga star forming region (average rms of about 0.3 mJy), using the IRAM PdBI. With our high detection rate of 17/19 we provide the first detections at wavelengths longer than about 1 mm for 12 sources. This enables us to statistically study the mm SED slopes and dust properties of faint disks and compare them to brighter disks using a uniform analysis method. With these new data and literature measurements at sub-millimeter and millimeter wavelengths, we analyze the dust properties of a sample of 21 isolated disks around T Tauri stars in the Taurus-Auriga star forming region. Together with the information about the disks’ spatial extension from sub/mm-mm interferometric studies, we derive from the observed sub-mm/mm spectral energy distribution constraints on the dust opacity law at these wavelengths, using two-layer flared disk models and a self-consistent dust model that properly takes into account the variation of the dust opacity with grain growth. We find evidence for the presence of dust particles in the disk midplane that have grown to sizes as large as at least 1 millimeter in all the disks of our sample, confirming what was previously observed on smaller brighter objects. This indicates that the dust coagulation from ISM dust to mm-sized grains is a very fast process in protoplanetary disks, which appears to occur before a young stellar object enters the class II evolutionary stage. The amount of these large grains in the disk outer regions is also found to be stationary throughout the whole class II evolutionary stage, which indicates that mechanisms slowing down the dust inward migration play an important role in the Taurus-Auriga protoplanetary disks. Another result is that the spectral index between 1 and 3 mm for the six faintest disks in our sample is on average smaller than for the brighter disks, indicating either that these fainter yet unmapped disks are spatially much less extended than the brighter spatially resolved disks, or that fainter disks have typically larger dust grains in their outer regions. Considering that these fainter disks are more representative of the bulk of the disk population than the brighter ones, this may have important consequences for the theories of planetesimal formation and disk formation and evolution. Finally, we investigate the relations between the derived dust properties, namely dust mass and grain growth, and the properties of the central star, like its mass, age and mass accretion rate.

Water in star-forming regions with Herschel (WISH): II. Evolution of 557 GHz 110-101 emission in low-mass protostars

Context. Water is a key tracer of dynamics and chemistry in low-mass star-forming regions, but spectrally resolved observations have so far been limited in sensitivity and angular resolution, and only data from the brightest low-mass protostars have been published. Aims. The first systematic survey of spectrally resolved water emission in 29 low-mass (L 10 km s(-1)). The water abundance in the outer cold envelope is low, greater than or similar to 10(-10). The different H2O profile components show a clear evolutionary trend: in the younger Class 0 sources the emission is dominated by outflow components originating inside an infalling envelope. When large-scale infall diminishes during the Class I phase, the outflow weakens and H2O emission all but disappears.

Herschel observations of EXtra-Ordinary Sources (HEXOS):The present and future of spectral surveys with Herschel/HIFI

We present initial results from the Herschel GT key program: Herschel observations of EXtra-Ordinary Sources (HEXOS) and outline the promise and potential of spectral surveys with Herschel/HIFI. The HIFI instrument offers unprecedented sensitivity, as well as continuous spectral coverage across the gaps imposed by the atmosphere, opening up a largely unexplored wavelength regime to high-resolution spectroscopy. We show the spectrum of Orion KL between 480 and 560 GHz and from 1.06 to 1.115 THz. From these data, we confirm that HIFI separately measures the dust continuum and spectrally resolves emission lines in Orion KL. Based on this capability we demonstrate that the line contribution to the broad-band continuum in this molecule-rich source is ~20-40% below 1 THz and declines to a few percent at higher frequencies. We also tentatively identify multiple transitions of HD18O in the spectra. The first detection of this rare isotopologue in the interstellar medium suggests that HDO emission is optically thick in the Orion hot core with HDO/H2O ~ 0.02. We discuss the implications of this detection for the water D/H ratio in hot cores. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Figure 2 (page 6) is also available in electronic form at http://www.aanda.org

Herschel spectral surveys of star-forming regions - Overview of the 555–636 GHz range

High resolution line spectra of star-forming regions are mines of information: they provide unique clues to reconstruct the chemical, dynamical, and physical structure of the observed source. We present the first results from the Herschel key project “Chemical HErschel Surveys of Star forming regions”, CHESS. We report and discuss observations towards five CHESS targets, one outflow shock spot and four protostars with luminosities bewteen 20 and 2 × 105 L_ȯ: L1157-B1, IRAS 16293-2422, OMC2-FIR4, AFGL 2591, and NGC 6334I. The observations were obtained with the heterodyne spectrometer HIFI on board Herschel, with a spectral resolution of 1 MHz. They cover the frequency range 555-636 GHz, a range largely unexplored before the launch of the Herschel satellite. A comparison of the five spectra highlights spectacular differences in the five sources, for example in the density of methanol lines, or the presence/absence of lines from S-bearing molecules or deuterated species. We discuss how these differences can be attributed to the different star-forming mass or evolutionary status. Herschel is an ESA space observatory with science instruments provided by European-led principal Investigator consortia and with important participation from NASA.Figures [see full textsee full text]-[see full textsee full text] and Tables 3, 4 (pages 6 to 8) are only available in electronic form at http://www.aanda.org

A highly-collimated SiO jet in the HH212 protostellar outflow

Context: In young stars, jets are believed to play a role in removing angular momentum from the circumstellar disk, allowing accretion onto the central star. Recent results suggest that in earlier phases of star formation, SiO might trace the primary jet launched close to the protostar, but further observations are required in order to reveal the properties of this molecular component. Aims: We wish to exploit the combination of high angular and spectral resolution provided by millimetre interferometry to investigate the collimation and kinematics of molecular protostellar jets, and their angular momentum content. Methods: We mapped the inner 40 arcsec of the HH212 Class 0 outflow in SiO(2-1), SiO(5-4) and continuum using the Plateau de Bure interferometer in its extended configurations. The unprecedented angular resolution (down to 0.34 arcsec) allows accurate comparison with a new, deep H2 image obtained at the VLT. Results: The SiO emission is confined to a highly-collimated bipolar jet (width ~0.35 arcsec close to the protostar) along the outflow axis. The jet can be traced down to within 500 AU of the protostar, in a region that is heavily obscured in H2 images. Where both species are detected, SiO shows the same overall kinematics and structure as H2, indicating that both molecules are tracing the same material. Transverse cuts reveal no velocity gradient compatible with jet rotation above 1 km s-1, in contrast to previous claims based on H2 spectra. The central continuum peak is unresolved and close to optically thick, suggesting an edge-on disk with diameter ≤117 AU. Conclusions: .SiO proves to be a powerful tracer of molecular jets in Class 0 sources, in particular of their obscured innermost regions. The very small blue/red overlap in the SiO outflow lobes, despite the nearly edge-on view to HH212, further implies that the high-velocity SiO gas is not tracing a wide-angle wind but is already confined to a flow inside a narrow cone of half-opening angle <6° at ≤500 AU from the protostar. The broad SiO line widths and the transverse velocity gradients both appear significantly affected by internal bowshocks, and should thus be interpreted with caution.

L183 (L134N) revisited. III. The gas depletion

We present a detailed study of the gas depletion in L183 (= L134N) for a set of important species, namely, CO, CS, SO, N_2H+ and NH_3. We show that all these species are depleted at some level. This level seems to depend mostly on a density threshold rather than on dust opacity. Therefore UV shielding would not be a main factor in the triggering of depletion. Our data suggest that CO, CS and SO depletion happen at densities of ˜3 × 104 cm-3, while N_2H+b and NH_3 seem to deplete at densities close to 106 cm-3. The latter result is consistent with the Bergin & Langer (\cite{Bergin97}, ApJ, 486, 316) polar (H_2O) ice case but not with the more recent models of Aikawa et al. (\cite{Aikawa03}, ApJ, 593, 906). CS depletion occurs much below its (J:2-1)b critical density, (7 × 105 cm-3) and therefore makes this species unsuitable to study the density structure of many dark cloud cores. Based on observations made with the CFHT, the Iram 30-m and the ARO 12-m (formerly NRAO 12-m). Appendix A is only available in electronic form at http://www.edpsciences.org

PdBI sub-arcsecond study of the SiO microjet in HH212. Origin and collimation of class 0 jets

Context: The bipolar HH 212 outflow has been mapped in SiO using the extended configuration of the Plateau de Bure Interferometer (PdBI), revealing a highly collimated SiO jet closely associated with the H2 jet component. Aims: We study at unprecedented resolution (0.34 farcsec across the jet axis) the properties of the innermost SiO “microjet” within 1000 AU of this young Class 0 source, to compare it with atomic microjets from more evolved sources and to constrain its origin. Methods: The SiO channel maps are used to investigate the microjet collimation and velocity structure. A large velocity gradient analysis is applied to SiO (2-1), (5-4) and (8-7) data from the PdBI and the Submillimeter Array to constrain the SiO opacity and abundance. Results: The HH212 Class 0 microjet shows striking similarities in collimation and energetic budget with atomic microjets from T Tauri sources. Furthermore, the SiO lines appear optically thick, unlike what is generally assumed. We infer Tk ≃ 50-500 K and an SiO/H2 abundance ≥4 × 10-8-6 × 10-5 for n(H_2) = 10^7-105 cm-3, i.e. 0.05-90% of the elemental silicon. Conclusions: This similar jet width, regardless of the presence of a dense envelope, definitely rules out jet collimation by external pressure, and favors a common MHD self-collimation (and possibly acceleration) process at all stages of star formation. We propose that the more abundant SiO in Class 0 jets could mainly result from rapid (≤25 yrs) molecular synthesis at high jet densities.

First results from the CALYPSO IRAM-PdBI survey - II. Resolving the hot corino in the Class 0 protostar NGC 1333-IRAS2A

We investigate the origin of complex organic molecules (COMs) in the gas phase around the low-mass Class~0 protostar NGC1333-IRAS2A, to determine if the COM emission lines trace an embedded disk, shocks from the protostellar jet, or the warm inner parts of the protostellar envelope. In the framework of the CALYPSO (Continuum And Lines in Young ProtoStellar Objects) IRAM Plateau de Bure survey, we obtained large bandwidth spectra at sub-arcsecond resolution towards NGC 1333-IRAS2A. We identify the emission lines towards the central protostar and perform Gaussian fits to constrain the size of the emitting region for each of these lines, tracing various physical conditions and scales. The emission of numerous COMs such as methanol, ethylene glycol, and methyl formate is spatially resolved by our observations. This allows us to measure, for the first time, the size of the COM emission inside the protostellar envelope, finding that it originates from a region of radius 40-100 AU, centered on the NGC 1333-IRAS2A protostellar object. Our analysis shows no preferential elongation of the COM emission along the jet axis, and therefore does not support the hypothesis that COM emission arises from shocked envelope material at the base of the jet. Down to similar sizes, the dust continuum emission is well reproduced with a single envelope model, and therefore does not favor the hypothesis that COM emission arises from the thermal sublimation of grains embedded in a circumstellar disk. Finally, the typical scale

Nitrogen hydrides in the cold envelope of IRAS 16293-2422

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POISSON project - I. Emission lines as accretion tracers in young stellar objects: results from observations of Chamaeleon I and II sources

60 AU observed for COM emission is consistent with the size of the inner envelope where