64 research outputs found
Modeling T Tauri Winds from He I 10830 Profiles
The high opacity of He I 10830 makes it an exceptionally sensitive probe of
the inner wind geometry of accreting T Tauri stars. In this line blueshifted
absorption below the continuum results from simple scattering of stellar
photons, a situation which is readily modeled without definite knowledge of the
physical conditions and recourse to multi-level radiative transfer. We present
theoretical line profiles for scattering in two possible wind geometries, a
disk wind and a wind emerging radially from the star, and compare them to
observed He I 10830 profiles from a survey of classical T Tauri stars. The
comparison indicates that subcontinuum blueshifted absorption is characteristic
of disk winds in ~30% of the stars and of stellar winds in ~40%. We further
conclude that for many stars the emission profile of helium likely arises in
stellar winds, increasing the fraction of accreting stars inferred to have
accretion-powered stellar winds to ~60%. Stars with the highest disk accretion
rates are more likely to have stellar wind than disk wind signatures and less
likely to have redshifted absorption from magnetospheric funnel flows. This
suggests the possibility that when accretion rates are high, disks can extend
closer to the star, magnetospheric accretion zones can be reduced in size and
conditions arise that favor radially outflowing stellar winds.Comment: 41 pages, 11 figures. Accepted by Astrophysical Journa
Time-Dependent MHD Shocks and Line Emission: The Case of the DG Tau Jet
The line emission from a growing number of Herbig-Haro jets can be observed
and resolved at angular distances smaller than a few arcseconds from the
central source. The interpretation of this emission is problematic, since the
simplest model of a cooling jet cannot sustain it. It has been suggested that
what one actually observes are shocked regions with a filling factor of . In this framework, up to now, comparisons with observations have been
based on stationary shock models. Here we introduce for the first time the
self-consistent dynamics of such shocks and we show that considering their
properties at different times, i.e. locations, we can reproduce observational
data of the DG Tau microjet. In particular, we can interpret the spatial
behavior of the [SII]6716/6731 and [NII]/[OI]6583/6300 line intensity ratios
adopting a set of physical parameters that yield values of mass loss rates and
magnetic fields consistent with previous estimates. We also obtain the values
of the mean ionization fraction and electron density along the jet, compare
these values with the ones derived from observations using the sulfur doublet
to constrain the electron density (e.g. Bacciotti et al. 1995).Comment: 6 pages, 3 figure
Proper motions and velocity asymmetries in the RW Aur jet
We present adaptive optics spectro-imaging observations of the RW Aur jet in
optical forbidden lines, at an angular resolution of 0.4 arcsec. Comparison
with HST data taken 2 years later shows that proper motions in the blueshifted
and redshifted lobes are in the same ratio as their radial velocities, a direct
proof that the velocity asymmetry in this jet is real and not an emissivity
effect. The inferred jet inclination to the line of sight is i = 46 +/- 3
degrees. The inner knot spacing appears best explained by time variability with
at least two modes: one irregular and asymmetric (possibly random) on
timescales of <3-10 yr, and another more regular with ~ 20 yr period. We also
report indirect evidence for correlated velocity and excitation gradients in
the redshifted lobe, possibly related to the blue/red velocity and brightness
asymmetry in this system.Comment: 4 pags, 3 figure
Numerical simulations of radiative magnetized Herbig-Haro jets: the influence of pre-ionization from X-rays on emission lines
We investigate supersonic, axisymmetric magnetohydrodynamic (MHD) jets with a
time-dependent injection velocity by numerical simulations with the PLUTO code.
Using a comprehensive set of parameters, we explore different jet
configurations in the attempt to construct models that can be directly compared
to observational data of microjets. In particular, we focus our attention on
the emitting properties of traveling knots and construct, at the same time,
accurate line intensity ratios and surface brightness maps. Direct comparison
of the resulting brightness and line intensity ratios distributions with
observational data of microjets shows that a closer match can be obtained only
when the jet material is pre-ionized to some degree. A very likely source for a
pre-ionized medium is photoionization by X-ray flux coming from the central
object.Comment: Accepted for publication in Ap
HeI 1.083 micron emission and absorption in DG Tau: line excitation in jet, hot wind, and accretion flow
We present long-slit spectroscopy and spectro-astrometry of HeI 1.083 micron
emission in the T Tauri star, DG Tau. We identify three components in the HeI
feature: (1) a blueshifted emission component atv -200 km s^-1, (2) a bright
emission component at zero-velocity with a FWZI of ~500 km s^-1, and (3) a
blueshifted absorption feature at velocities between -250 and -500 km s^-1. The
position and velocity of the blueshifted HeI emission coincide with a
high-velocity component (HVC) of the [FeII] 1.257 micron emission, which arises
from a jet within an arcsecond of the star. The presence of such a high
excitation line (excitation energy ~ 20 eV) within the jet supports the
scenario of shock heating. The bright HeI component does not show any spatial
extension, and it is likely to arise from magnetospheric accretion columns.
The blueshifted absorption shows greater velocities than that in H-alpha,
suggesting that these absorption features arise from the accelerating wind
close to the star.Comment: 10 pages including 2 figures, accepted for publication in the
Astrophysical Journal Letter
Laser Guide Star Adaptive Optics Integral Field Spectroscopy of a Tightly Collimated Bipolar Jet from the Herbig Ae star LkHa 233
We have used the integral field spectrograph OSIRIS and laser guide star
adaptive optics at Keck Observatory to obtain high angular resolution (0.06"),
moderate spectral resolution (R ~ 3800) images of the bipolar jet from the
Herbig Ae star LkHa 233, seen in near-IR [Fe II] emission at 1.600 & 1.644
microns. This jet is narrow and tightly collimated, with an opening angle of
only 9 degrees, and has an average radial velocity of ~ 100 km/s. The jet and
counterjet are asymmetric, with the red-shifted jet much clumpier than its
counterpart at the angular resolution of our observations. The observed
properties are in general similar to jets seen around T Tauri stars, though it
has a relatively large mass flux of (1.2e-7 +- 0.3e-7) M_sun/year, near the
high end of the observed mass flux range around T Tauri stars. We also
spatially resolve an inclined circumstellar disk around LkHa 233, which
obscures the star from direct view. By comparison with numerical radiative
transfer disk models, we estimate the disk midplane to be inclined i = 65 +- 5
degrees relative to the plane of the sky. Since the star is seen only in
scattered light at near-infrared wavelengths, we detect only a small fraction
of its intrinsic flux. Because previous estimates of its stellar properties did
not account for this, either LkHa 233 must be located closer than the
previously believed, or its true luminosity must be greater than previously
supposed, consistent with its being a ~4 M_sun star near the stellar birthline.Comment: Accepted for publication in the Ap
HST NICMOS Images of the HH 7/11 Outflow in NGC1333
We present near infrared images in H2 at 2.12um of the HH 7/11 outflow and
its driving source SVS 13 taken with HST NICMOS 2 camera, as well as archival
Ha and [SII] optical images obtained with the WFPC2 camera. The NICMOS high
angular resolution observations confirm the nature of a small scale jet arising
from SVS 13, and resolve a structure in the HH 7 working surface that could
correspond to Mach disk H2 emission. The H2 jet has a length of 430 AU (at a
distance of 350 pc), an aspect ratio of 2.2 and morphologically resembles the
well known DG Tau optical micro-jet. The kinematical age of the jet (approx. 10
yr) coincides with the time since the last outburst from SVS 13. If we
interpret the observed H2 flux density with molecular shock models of 20-30
km/s, then the jet has a density as high as 1.e+5 cc. The presence of this
small jet warns that contamination by H2 emission from an outflow in studies
searching for H2 in circumstellar disks is possible. At the working surface,
the smooth H2 morphology of the HH 7 bowshock indicates that the magnetic field
is strong, playing a major role in stabilizing this structure. The H2 flux
density of the Mach disk, when compared with that of the bowshock, suggests
that its emission is produced by molecular shocks of less than 20 km/s. The
WFPC2 optical images display several of the global features already inferred
from groundbased observations, like the filamentary structure in HH 8 and HH
10, which suggests a strong interaction of the outflow with its cavity. The H2
jet is not detected in {SII] or Ha, however, there is a small clump at approx.
5'' NE of SVS 13 that could be depicting the presence either of a different
outburst event or the north edge of the outflow cavity.Comment: 13 pages, 5 figures (JPEGs
3-D numerical simulations of rotating jets: The case of the DG Tau microjet
We here present results of three-dimensional Smoothed Particle hydro and
magnetohydrodynamics simulations of rotating jets, also including the effects
of radiative cooling, precession and velocity variability. Using initial
conditions and parameters which are particularly suitable for the DG Tau
microjet, we have been able to approximately reproduce its complex knotty
morphology and kinematics. We have also obtained radial velocity maps which are
in good agreement with the data obtained by Bacciotti et al., thus indicating
that their interpretation that the DG Tau microjet is rotating is correct.
Finally, we have found that a magnetic field of the order of ~ 0.5 mG is
sufficient to collimate the jet against the lateral expansion that is caused by
the centrifugal forces.Comment: 4 pages, 3 figures; Accepted for publication in A&A (letters). The
high resolution figures are avilable upon reques
Tomographic reconstruction of the three-dimensional structure of the HH30 jet
The physical parameters of Herbig-Haro jets are usually determined from
emission line ratios, obtained from spectroscopy or narrow band imaging,
assuming that the emitting region is homogeneous along the line of sight. Under
the more general hypothesis of axisymmetry, we apply tomographic reconstruction
techniques to the analysis of Herbig-Haro jets. We use data of the HH30 jet
taken by Hartigan & Morse (2007) with the Hubble space telescope using the
slitless spectroscopy technique. Using a non-parametric Tikhonov regularization
technique, we determine the volumetric emission line intensities of the
[SII]6716,6731, [OI]6300 and [NII]6583 forbidden emission lines. From our
tomographic analysis of the corresponding line ratios, we produce
"three-dimensional" images of the physical parameters. The reconstructed
density, temperature and ionization fraction present much steeper profiles than
those inferred using the assumption of homogeneity. Our technique reveals that
the reconstructed jet is much more collimated than the observed one close to
the source (a width ~ 5 AU vs. ~ 20 AU at a distance of 10 AU from the star),
while they have similar widths at larger distances. In addition, our results
show a much more fragmented and irregular jet structure than the classical
analysis, suggesting that the the ejection history of the jet from the
star-disk system has a shorter timescale component (~ some months) superimposed
on a longer, previously observed timescale (of a few years). Finally, we
discuss the possible application of the same technique to other stellar jets
and planetary nebulae.Comment: 13 pages, 9 figures, accepted by Ap
PdBI sub-arcsecond study of the SiO microjet in HH212 - Origin and collimation of Class 0 jets
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. We study at
unprecedented resolution (0.34" 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. 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. 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 T(kin) ~ 50-500 K and an SiO/H2 abundance
greater than 4 10(-8)-6 10(-5) for n(H2) = 10(7)-10(5) cm(-3), i.e. 0.05-90% of
the elemental silicon. 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 (less than 25 yrs) molecular synthesis at high
jet densities
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