68 research outputs found
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 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 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 20 km s. 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 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 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
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
Steady Wind-blown Cavities within Infalling Rotating Envelopes:Application to the Broad Velocity Component in Young Protostars
Wind-driven outflows are observed around a broad range of accreting objects
throughout the Universe, ranging from forming low-mass stars to super-massive
black holes. We study the interaction between a central isotropic wind and an
infalling, rotating, envelope, determining the steady-state cavity shape formed
at their interface under the assumption of weak mixing. The shape of the
resulting wind-blown cavity is elongated and self-similar, with a physical size
determined by the ratio between wind ram pressure and envelope thermal
pressure. We compute the growth of a warm turbulent mixing-layer between the
shocked wind and the deflected envelope, and calculate the resultant broad line
profile, under the assumption of a linear (Couette-type) velocity profile
across the layer. We then test our model against the warm broad velocity
component observed in CO =16--15 by Herschel/HIFI in the protostar
Serpens-Main SMM1. Given independent observational constraints on the
temperature and density of the dust envelope around SMM1, we find an excellent
match to all its observed properties (line profile, momentum, temperature) and
to the SMM1 outflow cavity width for a physically reasonable set of parameters:
a ratio of wind to infall mass-flux , a wind speed km/s, an interstellar abundance of CO and H, and a turbulent
entrainment efficiency consistent with laboratory experiments. The inferred
ratio of ejection to disk accretion rate, , is in agreement with
current disk wind theories. Thus, the model provides a new framework to
reconcile the modest outflow cavity widths in protostars with the large
observed flow velocities. Being self-similar, it is applicable over a broader
range of astrophysical contexts as well.Comment: 31 pages, 21 figures, accepted to ApJ for publication (comments are
welcome
ALMA Cycle 1 Observations of the HH46/47 Molecular Outflow: Structure, Entrainment and Core Impact
We present ALMA Cycle 1 observations of the HH46/47 molecular outflow using
combined 12m array and ACA observations. The improved angular resolution and
sensitivity of our multi-line maps reveal structures that help us study the
entrainment process in much more detail and allow us to obtain more precise
estimates of outflow properties than previous observations. We use 13CO(1-0)
and C18O(1-0) emission to correct for the 12CO(1-0) optical depth to accurately
estimate the outflow mass, momentum and kinetic energy. This correction
increases the estimates of the mass, momentum and kinetic energy by factors of
about 9, 5 and 2, respectively, with respect to estimates assuming optically
thin emission. The new 13CO and C18O data also allow us to trace denser and
slower outflow material than that traced by the 12CO maps, and they reveal an
outflow cavity wall at very low velocities (as low as 0.2km/s with respect to
the cores central velocity). Adding with the slower material traced only by
13CO and C18O, there is another factor of 3 increase in the mass estimate and
50% increase in the momentum estimate. The estimated outflow properties
indicate that the outflow is capable of dispersing the parent core within the
typical lifetime of the embedded phase of a low-mass protostar, and that it is
responsible for a core-to-star efficiency of 1/4 to 1/3. We find that the
outflow cavity wall is composed of multiple shells associated with a series of
jet bow-shock events. Within about 3000AU of the protostar the 13CO and C18O
emission trace a circumstellar envelope with both rotation and infall motions,
which we compare with a simple analytic model. The CS(2-1) emission reveals
tentative evidence of a slowly-moving rotating outflow, which we suggest is
entrained not only poloidally but also toroidally by a disk wind that is
launched from relatively large radii from the source.Comment: Accepted for publication in ApJ. 26 pages, 20 figure
Small-scale properties of Class 0 protostars from the CALYPSO IRAM-PdBI survey
Because the formation of protostars is believed to be closely tied to the angular momentum problem of star formation, characterizing the properties of the youngest disks around Class 0 objects is crucial. However, not much is known on the structure of the youngest protostellar envelopes, on the small scales at which disks and multiple systems are observed around more evolved YSOs, due to a lack of comprehensive high angular resolution observations (probing 50 au, disk structures are not observed in most Class 0 protostars from our sample, which can be described by various envelope models reproducing satisfactorily the intensity distribution of the dust emission at all scales from 50 au to 5000 au
First detection of interaction between a magnetic disk wind and an episodic jet in a protostellar system
Interstellar matter and star formatio
Multiple Stellar Fly-Bys Sculpting the Circumstellar Architecture in RW Aurigae
We present high-resolution ALMA Band 6 and 7 observations of the tidally
disrupted protoplanetary disks of the RW Aurigae binary. Our observations
reveal the presence of additional tidal streams to the previously observed
tidal arm around RW Aur A. The observed configuration of tidal streams
surrounding RW Aur A and B is incompatible with a single star--disk tidal
encounter, suggesting that the RW Aurigae system has undergone multiple fly-by
interactions. We also resolve the circumstellar disks around RW Aur A and B,
with CO radii of 58 au and 38 au consistent with tidal truncation, and 2.5
times smaller dust emission radii. The disks appear misaligned by 12
or 57. Using new photometric observations from the American
Association of Variable Star Observers (AAVSO) and All Sky Automated Survey for
SuperNovae (ASAS-SN) archives, we have also identified an additional dimming
event of the primary that began in late 2017 and is currently ongoing. With
over a century of photometric observations, we are beginning to explore the
same spatial scales as ALMA
Gaps and Rings in an ALMA Survey of Disks in the Taurus Star-forming Region
Rings are the most frequently revealed substructure in ALMA dust observations of protoplanetary disks, but their origin is still hotly debated. In this paper, we identify dust substructures in 12 disks and measure their properties to investigate how they form. This subsample of disks is selected from a high-resolution () ALMA 1.33 mm survey of 32 disks in the Taurus star-forming region, which was designed to cover a wide range of sub-mm brightness and to be unbiased to previously known substructures. While axisymmetric rings and gaps are common within our sample, spiral patterns and high contrast azimuthal asymmetries are not detected. Fits of disk models to the visibilities lead to estimates of the location and shape of gaps and rings, the flux in each disk component, and the size of the disk. The dust substructures occur across a wide range of stellar mass and disk brightness. Disks with multiple rings tend to be more massive and more extended. The correlation between gap locations and widths, the intensity contrast between rings and gaps, and the separations of rings and gaps could all be explained if most gaps are opened by low-mass planets (super-Earths and Neptunes) in the condition of low disk turbulence (). The gap locations are not well correlated with the expected locations of CO and N ice lines, so
condensation fronts are unlikely to be a universal mechanism to create gaps and rings, though they may play a role in some cases.Several ERC grants
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