The mass-velocity and intensity-velocity relations in jet-driven molecular outflows

We use numerical simulations to examine the mass-velocity and intensity-velocity relations in the CO J=2-1 and H$_2$ S(1)1-0 lines for jet-driven molecular outflows. Contrary to previous expectations, we find that the mass-velocity relation for the swept-up gas is a single power-law, with a shallow slope $\simeq -1.5$ and no break to a steeper slope at high velocities. An analytic bowshock model with no post-shock mixing is shown to reproduce this behaviour very well. We show that molecular dissociation and the temperature dependence of the line emissivity are both critical in defining the shape of the line profiles at velocities above $\sim$ 20 km s$^{-1}$. In particular, the simulated CO J=2-1 intensity-velocity relation does show a break in slope, even though the underlying mass distribution does not. These predicted CO profiles are found to compare remarkably well with observations of molecular outflows, both in terms of the slopes at low and high velocities and in terms of the range of break velocities at which the change in slope occurs. Shallower slopes are predicted at high velocity in higher excitation lines, such as H$_2$ S(1)1-0. This work indicates that, in jet-driven outflows, the CO J=2-1 intensity profile reflects the slope of the underlying mass-velocity distribution only at velocities $\le$ 20 km/s, and that higher temperature tracers are required to probe the mass distribution at higher speed.Comment: 6 pages, 8 figures. Accepted for publication in Astronomy and Astrophysic

The evolution of stars in the Taurus-Auriga T association

In a recent study, individual parallaxes were determined for many stars of the Taurus-Auriga T association that are members of the same moving group. We use these new parallaxes to re-address the issue of the relationship between classical T Tauri stars (CTTSs) and weak-emission line T Tauri stars (WTTSs). With the available spectroscopic and photometric information for 72 individual stars or stellar systems among the Taurus-Auriga objects with known parallaxes, we derived reliable photospheric luminosities, mainly from the Ic magnitude of these objects. We then studied the mass and age distributions of the stellar sample, using pre-main sequence evolutionary models to determine the basic properties of the stellar sample. Statistical tests and Monte Carlo simulations were then applied to studying the properties of the two T Tauri subclasses. We find that the probability of CTTS and WTTS samples being drawn from the same parental age and mass distributions is low; CTTSs are, on average, younger than WTTSs. They are also less massive, but this is due to selection effects. The observed mass and age distributions of both T Tauri subclasses can be understood in the framework of a simple disk evolution model, assuming that the CTTSs evolve into WTTSs when their disks are fully accreted by the stars. According to this empirical model, the average disk lifetime in Taurus-Auriga is 4 10**6 (Mstar/Msun)**0.75 yr.Comment: accepted by A&A Letter

High SiO abundance in the HH212 protostellar jet

Previous SiO maps of the innermost regions of HH212 set strong constraints on the structure and origin of this jet. They rule out a fast wide-angle wind, and tentatively favor a magneto-centrifugal disk wind launched out to 0.6 AU. We aim to assess the SiO content at the base of the HH212 jet to set an independent constraint on the location of the jet launch zone with respect to the dust sublimation radius. We present the first sub-arcsecond (0"44x0"96) CO map of the HH212 jet base, obtained with the IRAM Plateau de Bure Interferometer. Combining this with previous SiO(5-4) data, we infer the CO(2-1) opacity and mass-flux in the high-velocity jet and arrive at a much tighter lower limit to the SiO abundance than possible from the (optically thick) SiO emission alone. Gas-phase SiO at high velocity contains at least 10% of the elemental silicon if the jet is dusty, and at least 40% if the jet is dust-free, if CO and SiO have similar excitation temperatures. Such a high SiO content is challenging for current chemical models of both dust-free winds and dusty interstellar shocks. Updated chemical models (equatorial dust-free winds, highly magnetized dusty shocks) and observations of higher J CO lines are required to elucidate the dust content and launch radius of the HH212 high-velocity jet.Comment: 4 pages, 2 figure

A Search for Consistent Jet and Disk Rotation Signatures in RY Tau

We present a radial velocity study of the RY Tau jet-disk system, designed to determine whether a transfer of angular momentum from disk to jet can be observed. Many recent studies report on the rotation of T Tauri disks, and on what may be a signature of T Tauri jet rotation. However, due to observational difficulties, few studies report on both disk and jet within the same system to establish if the senses of rotation match and hence can be interpreted as a transfer of angular momentum. We report a clear signature of Keplerian rotation in the RY Tau disk, based on Plateau de Bure observations. We also report on the transverse radial velocity profile of the RY Tau jet close to the star. We identify two distinct profile shapes: a v-shape which appears near jet shock positions, and a flat profile which appears between shocks. We do not detect a rotation signature above 3 sigma uncertainty in any of our transverse cuts of the jet. Nevertheless, if the jet is currently in steady-state, the errors themselves provide a valuable upper limit on the jet toroidal velocity of 10 km/s, implying a launch radius of < 0.45 AU. However, possible contamination of jet kinematics, via shocks or precession, prevents any firm constraint on the jet launch point, since most of its angular momentum could be stored in magnetic form rather than in rotation of matter.Comment: 10 pages, 7 figures, accepted by The Astrophysical Journa

Molecule survival in magnetized protostellar disk winds. II. Predicted H2O line profiles versus Herschel/HIFI observations

We investigate whether the broad wings of H2O emission identified with Herschel towards low-mass Class 0 and Class 1 protostars may be consistent with an origin in a dusty MHD disk wind, and the constraints it would set on the underlying disk properties. We present synthetic H2O line profiles predictions for a typical MHD disk wind solution with various values of disk accretion rate, stellar mass, extension of the launching area, and view angle. We compare them in terms of line shapes and intensities with the HIFI profiles observed by the WISH Key Program. We find that a dusty MHD disk wind launched from 0.2--0.6 AU AU to 3--25 AU can reproduce to a remarkable degree the observed shapes and intensities of the broad H2O component, both in the fundamental 557 GHz line and in more excited lines. Such a model also readily reproduces the observed correlation of 557 GHz line luminosity with envelope density, if the infall rate at 1000 AU is 1--3 times the disk accretion rate in the wind ejection region. It is also compatible with the typical disk size and bolometric luminosity in the observed targets. However, the narrower line profiles in Class 1 sources suggest that MHD disk winds in these sources, if present, would have to be slower and/or less water rich than in Class 0 sources. In conclusion, MHD disk winds appear as a valid (though not unique) option to consider for the origin of the broad H2O component in low-mass protostars. ALMA appears ideally suited to further test this model by searching for resolved signatures of the warm and slow wide-angle molecular wind that would be predicted.Comment: accepted for publication in A&

A pair of gigantic bipolar dust jets close to the solar system

We report the discovery of two adjacent jet candidates with a length of about 9 degrees each -- 10 times longer than the largest known jets -- detected by us on 60 and 100 micron IRAS maps, but not observed at any other wavelength. They are extremely collimated (length-to-width ratios 20--50), curved, knotty, and end in prominent bubbles. Their dust temperatures are 25 K and 30 K, respectively. Both harbour faint stars, one having a high proper motion (0.23 arcsec/yr) and being very red, suggesting a distance of about 60 pc. At this distance, the total mass of both jet candidates is about about 1 solar mass. We suspect that these gigantic (9 pc length respectively) jets are of fossil type and have a common origin, due to the decay of a system of evolved stars. They are the first examples of jets radiating in the far IR and might, because of their closeness, be of interest for further studies of the acceleration and collimation processes of astrophysical jets.Comment: 4 pages, 4 figures in reduced quality, accepted by Astronomy & Astrophysics (Letter) february 10, 2004. See http://astro.uibk.ac.at/dustjets/ for the full resolution and color version of the image

Temporal evolution of magnetic molecular shocks I. Moving grid simulations

We present time-dependent 1D simulations of multifluid magnetic shocks with chemistry resolved down to the mean free path. They are obtained with an adaptive moving grid implemented with an implicit scheme. We examine a broad range of parameters relevant to conditions in dense molecular clouds, with preshock densities between 10^3 and 10^5 cm-3, velocities between 10 and 40 km/s, and three different scalings for the transverse magnetic field: B=0,0.1,1 \mu G \sqrt{n.cm3}. We first use this study to validate the results of Chi\`eze, Pineau des For\^ets & Flower (1998), in particular the long delays necessary to obtain steady C-type shocks, and we provide evolutionary time-scales for a much greater range of parameters. We also present the first time-dependent models of dissociative shocks with a magnetic precursor, including the first models of stationary CJ shocks in molecular conditions. We find that the maximum speed for steady C-type shocks is reached before the occurrence of a sonic point in the neutral fluid, unlike previously thought. As a result, the maximum speed for C-shocks is lower than previously believed. Finally, we find a large amplitude bouncing instability in J-type fronts near the H2 dissociation limit (u ~ 25-30 km/s), driven by H2 dissociation/reformation. At higher speeds, we find an oscillatory behaviour of short period and small amplitude linked to collisional ionisation of H. Both instabilities are suppressed after some time when a magnetic field is present. In a companion paper, we use the present simulations to validate a new semi-analytical construction method for young low-velocity magnetic shocks based on truncated steady-state models.Comment: A&A in pres

Use of direct and large eddy simulations for the development of multicomponent reacting compressible turbulent boundary layer wall model

A study of multicomponent reacting channel flows with significant heat transfer and low Mach number has been performed using a set of direct and large eddy simulations. The use of LES computations was needed to analyze accurate and relevant data of such flows at a sufficient Reynolds number and reasonable computational cost. The analysis of these data will be detailed leading to the development of an analytical wall model for predicting the total shear stress and heat flux at the wall