F. Gueth

THE 2014 ALMA LONG BASELINE CAMPAIGN: FIRST RESULTS FROM HIGH ANGULAR RESOLUTION OBSERVATIONS TOWARD THE HL TAU REGION

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region. The continuum images at wavelengths of 2.9, 1.3, and 0.87 mm have unprecedented angular resolutions of 0. ′′ 075 (10 AU) to 0. ′′ 025 (3.5 AU), revealing an astonishing level of detail in the cir cumstellar disk surrounding the young solar analogue HL Tau, with a pattern of bright and dark rings observed at all wavelengths. By fitting ellipses to the most distinct rings, we measure precise values for the disk inclination (46.72 ◦ ± 0.05 ◦ ) and position angle (+138.02 ◦ ± 0.07 ◦ ). We obtain a high-fidelity image of the 1.0 mm spectral index (�), which ranges from � � 2.0 in the optically-thick central peak and two brightest ring s, increasing to 2.3-3.0 in the dark rings. The dark rings are not devoid of emission, and we estimate a grain emissivity index of 0.8 for the innermost dark ring and lower for subsequent dark rings, consistent with some degree of grain growth and evolution. Additional clues that the rings arise from planet formation incl ude an increase in their central offsets with radius and the presence of numerous orbital resonances. At a resolution of 35 AU, we resolve the molecular component of the disk in HCO + (1-0) which exhibits a pattern over LSR velocities from 2-12 km s -1 consistent with Keplerian motion around a �1.3M⊙ star, although complicated by absorption at low blue-shifted velocities. We also serendipitously detect and resolve the nearby protost ars XZ Tau (A/B) and LkH�358 at 2.9 mm. Subject headings: stars: individual (HL Tau, XZ Tau, LkH�358) — protoplanetary disks — stars: formation — submillimeter: planetary systems — techniques: interferometric

IRAS 05358+3543: Multiple outflows at the earliest stages of massive star formation

We present a high-angular-resolution molecular line and millimeter continuum study of the massive star formation site IRAS 05358+3543. Observations with the Plateau de Bure Interferometer in CO 1{0, SiO 2{1 and H 13 CO + 1{0 reveal at least three outflows which cannot be separated in single-dish data. Observations at millimeter and sub-millimeter wavelengths from the IRAM 30 m telescope and the CSO provide additional information on the region. The most remarkable feature is a highly collimated (collimation factor 10) and massive (>10 M) bipolar outflow of 1 pc length, which is part of a quadrupolar outflow system. The three observed molecular outflows forming the IRAS 05358+3543 outflow system resemble, in structure and collimation, those typical of low-mass star-forming regions. They might therefore, just like low-mass outflows, be explained by shock entrainment models of jets. We estimate a mass accretion rate of10 4 M/yr, sucient to overcome the radiative pressure of the central object and to build up a massive star, lending further support to the hypothesis that massive star formation occurs similarly to low-mass star formation, only with higher accretion rates and energetics. In the millimeter continuum, we nd three sources near the center of the quadrupolar outflow, each with a mass of 75{100 M. These cores are associated with a complex region of infrared reflection nebulosities and their embedded illuminating sources. The molecular line data show that SiO is found mostly in the outflows, whereas H 13 CO + traces core-like structures, though likely with varying relative abundances. Thermal CH3OH comprises both features and can be disentangled into a core-tracing component at the line center, and wing emission following the outflows. A CO line-ratio study (using data of the J = 1{0, 2{1 and 6{5 transitions) reveals local temperature gradients.

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.

Chemistry in disks. I. Deep search for N2H+ in the protoplanetary disks around LkCa 15, MWC 480, and DM Tauri

Aims.To constrain the ionization fraction in protoplanetary disks, we present new high-sensitivity interferometric observations of N2H+ in three disks surrounding DM Tau, LkCa 15, and MWC 480. Methods: We used the IRAM PdBI array to observe the N2H+ J=1-0 line and applied a ?^2-minimization technique to estimate corresponding column densities. These values are compared, together with HCO+ column densities, to results of a steady-state disk model with a vertical temperature gradient coupled to gas-grain chemistry. Results: We report two N2H+ detections for LkCa 15 and DM Tau at the 5 ? level and an upper limit for MWC 480. The column density derived from the data for LkCa 15 is much lower than previously reported. The [ N2H^+/HCO^+] ratio is on the order of 0.02-0.03. So far, HCO+ remains the most abundant observed molecular ion in disks. Conclusions: .All the observed values generally agree with the modelled column densities of disks at an evolutionary stage of a few million years (within the uncertainty limits), but the radial distribution of the molecules is not reproduced well. The low inferred concentration of N2H+ in three disks around low-mass and intermediate-mass young stars implies that this ion is not a sensitive tracer of the overall disk ionization fraction. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). Research partially supported by PCMI, the French national program for the Physics and Chemistry of the Interstellar Medium.

Massive Molecular Outflows at High Spatial Resolution

We present high spatial resolution Plateau de Bure Interferometer CO (2-1) and SiO (2-1) observations of one intermediate-mass and one high-mass star-forming region. The intermediate-mass region IRAS 20293+3952 exhibits four molecular outflows, one being as collimated as the highly collimated jetlike outflows observed in low-mass star formation sources. Furthermore, comparing the data with additional infrared H2 and centimeter observations, we see indications that the nearby ultracompact H II region triggers a shock wave interacting with the outflow. The high-mass region IRAS 19217+1651 exhibits a bipolar outflow as well, and the region is dominated by the central driving source. Adding two more sources from the literature, we compare position-velocity diagrams of the intermediate-to-high-mass sources with previous studies in the low-mass regime. We find similar kinematic signatures; some sources can be explained by jet-driven outflows, whereas others are better constrained by wind-driven models. The data also allow us to estimate accretion rates varying from a few times 10-5 M☉ yr-1 for the intermediate-mass sources to a few times 10-4 M☉ yr-1 for the high-mass source, consistent with models explaining star formation of all masses via accretion processes.

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.

Rotating molecular outflows: the young T Tauri star in CB 26 ⋆

Context: The disk-outflow connection is thought to play a key role in extracting excess angular momentum from a forming proto-star. Although jet rotation has been observed in a few objects, no rotation of molecular outflows has been unambiguously reported so far. Aims: We report new millimeter-interferometric observations of the edge-on T Tauri star - disk system in the isolated Bok globule CB 26. The aim of these observations was to study the disk-outflow relation in this 1 Myr old low-mass young stellar object. Methods: The IRAM PdBI array was used to observe 12CO(2-1) at 1.3 mm in two configurations, resulting in spectral line maps with 1.5´´ resolution. We use an empirical parameterized steady-state outflow model combined with 2-D line radiative transfer calculations and χ^2-minimization in parameter space to derive a best-fit model and constrain parameters of the outflow. Results: The data reveal a previously undiscovered collimated bipolar molecular outflow of total length ≈2000 AU, escaping perpendicular to the plane of the disk. We find peculiar kinematic signatures that suggest that the outflow is rotating with the same orientation as the disk. However, we could not ultimately exclude jet precession or two misaligned flows as possible origins of the observed peculiar velocity field. There is indirect indication that the embedded driving source is a binary system, which, together with the youth of the source, could provide a clue to the observed kinematic features of the outflow. Conclusions: CB 26 is so far the most promising source in which to study the rotation of a molecular outflow. Assuming that the outflow is rotating, we compute and compare masses, mass flux, angular momenta, and angular momentum flux of the disk and outflow and derive disk dispersal timescales of 0.5 ldots 1 Myr, comparable to the age of the system. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). Also based on observations collected at the Centro Astronomico Hispano Aleman (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut fur Astronomie and the Instituto de Astrofisica de Andalucia (CSIC). A complete set of channel maps is available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/494/147.

Methyl cyanide as tracer of bow shocks in L1157-B1

Context. L1157-mm is a low-mass protostar driving an outflow which is considered the proto-type of the so-called chemically active outflows. In particular, the blue-shifted lobe B1 stands out for its rich mm-wave spectrum.Aims. Our aim is to infer the physical conditions of the molecular gas within L1157-B1.Methods. We carried out CH3CN(8(K)-7(K)) observations at 2 mm with the IRAM Plateau de Bure Interferometer to map L1157-B1.Results. The CH3CN image shows a clumpy structure superimposed to the classical B1 arch-like shape, displaying a unique continuous structure tracing the propagation of a large bow shock. The CH3CN spatial distribution well agrees with that of CH3OH, one of the most abundant species evaporated from dust grain mantles. Thanks to the present CH3CN observations at unprecedented spatial resolution, we determine for the first time the temperature distribution of the B1 bow shock. We obtain values between 57 and 132 K, with the highest temperature at the shock apex, thus confirming the association of CH3CN with gas affected by the passage of a shock wave. The N-CH3CN column densities are similar or equal to 8-40 x 10(12) cm(-2), depending on the position, leading to CH3CN/CH3OH abundance ratios similar or equal to 0.2-1.3 x 10(-3), i.e. values on average smaller than those found in hot-corinos. This suggests that a significant amount of CH3CN is formed in the gas phase: in the shocked L1157-B1 regions the CH3CN abundance may not have reached its maximum yet.

Resolving the circumbinary dust disk surrounding HH 30

Context. The jet-disk connection is an important part of the star formation process. HH 30 is a rare and beautiful example of a system exhibiting a flared edge-on disk, an optical jet and a CO molecular outflow. A recent analysis of the jet wiggling has revealed that the central star is in reality a binary object. Therefore, the dust and gas disk observed around HH 30 is circumbinary. Aims. In this paper, we attempt to better constrain the system (disk + stars) properties, as well as the system age. Methods. We obtained very high angular resolution (∼0.4 �� ) observations in continuum at 1.3 mm with the IRAM interferometer. A standard disk model is used to fit the continuum and line data in the Fourier-plane and derive the disk properties. Results. We find that the disk of HH 30 is truncated at an inner radius 37 ± 4 AU. The simplest explanation is tidal truncation in a binary system. This confirms the binarity of the HH 30 system, which consists of two stars on a low eccentricity, 15 AU semi-major axis orbit. The jet wiggling is due to orbital motion. The mass ratio is poorly constrained. The system age may be less than 2 Myr. The disk is optically thin at 1.3 mm and the dust opacity index, β ≈ 0.4, indicates the presence of cm size grains. Conclusions. These observations confirm that HH 30, often presented as an archetypal example of the jet-disk paradigm, is a binary star, with one of the components at the origin of the optical jet. This suggests that many other objects similar to HH 30 may be unknown binary or multiple systems. These new data confirm that high angular resolution observations at millimeter wavelengths are powerful tools to unveil the inner dust disk properties. In this domain, ALMA will likely change our observational vision of these objects.

CHEMISTRY IN DISKS. VII. FIRST DETECTION OF HC3N IN PROTOPLANETARY DISKS

Molecular line emission from protoplanetary disks is a powerful tool to constrain their physical and chemical structure. Nevertheless, only a few molecules have been detected in disks so far. We take advantage of the enhanced capabilities of the IRAM 30?m telescope by using the new broadband correlator (fast Fourier Transform Spectrometer) to search for so far undetected molecules in the protoplanetary disks surrounding the T Tauri stars DM Tau, GO Tau, LkCa 15, and the Herbig Ae star MWC?480. We report the first detection of HC3N at 5? in the GO Tau and MWC 480 disks with the IRAM 30?m, and in the LkCa 15 disk (5?), using the IRAM array, with derived column densities of the order of 1012?cm?2. We also obtain stringent upper limits on CCS (N < 1.5 ? 1012 cm?3). We discuss the observational results by comparing them to column densities derived from existing chemical disk models (computed using the chemical code Nautilus) and based on previous nitrogen- and sulfur-bearing molecule observations. The observed column densities of HC3N are typically two orders of magnitude lower than the existing predictions and appear to be lower in the presence of strong UV flux, suggesting that the molecular chemistry is sensitive to the UV penetration through the disk. The CCS upper limits reinforce our model with low elemental abundance of sulfur derived from other sulfur-bearing molecules (CS, H2S, and SO).