870 research outputs found
Numerical Simulations of HH 555
We present 3D gasdynamic simulations of the Herbig Haro object HH 555. HH 555
is a bipolar jet emerging from the tip of an elephant trunk entering the
Pelican Nebula from the adjacent molecular cloud. Both beams of HH 555 are
curved away from the center of the H II region. This indicates that they are
being deflected by a side-wind probably coming from a star located inside the
nebula or by the expansion of the nebula itself. HH 555 is most likely an
irradiated jet emerging from a highly embedded protostar, which has not yet
been detected.
In our simulations we vary the incident photon flux, which in one of our
models is equal to the flux coming from a star 1 pc away emitting 5x10^48
ionizing (i. e., with energies above the H Lyman limit) photons per second. An
external, plane-parallel flow (a ``side-wind'') is coming from the same
direction as the photoionizing flux. We have made four simulations, decreasing
the photon flux by a factor of 10 in each simulation. We discuss the properties
of the flow and we compute Halpha emission maps (integrated along lines of
sight).
We show that the level of the incident photon flux has an important influence
on the shape and visibility of the jet. If the flux is very high, it causes a
strong evaporation of the neutral clump, producing a photoevaporated wind
traveling in the direction opposite to the incident flow. The interaction of
the two flows creates a double shock ``working surface'' around the clump
protecting it and the jet from the external flow. The jet only starts to curve
when it penetrates through the working surface.Comment: 14 pages, 4 figures, accepted by Ap
The 3-Dimensional Structure of HH 32 from GMOS IFU Spetroscopy
We present new high resolution spectroscopic observations of the Herbig-Haro
object HH 32 from System Verification observations made with the GMOS IFU at
Gemini North Observatory. The 3D spectral data covers a 8''.7 x 5''.85 spatial
field and 4820 - 7040 Angstrom spectral region centered on the HH~32 A knot
complex. We show the position-dependent line profiles and radial velocity
channel maps of the Halpha line, as well as line ratio velocity channel maps of
[OIII]5007/Halpha, [OI]6300/Halpha, [NII]6583/Halpha, [SII](6716+6730)/Halpha
and [SII]6716/6730. We find that the line emission and the line ratios vary
significantly on spatial scales of ~1'' and over velocities of ~50 km/s. A
``3/2-D'' bow shock model is qualitatively successful at reproducing the
general features of the radial velocity channel maps, but it does not show the
same complexity as the data and it fails to reproduce the line ratios in our
high spatial resolution maps. The observations of HH 32 A show two or three
superimposed bow shocks with separations of ~3'', which we interpret as
evidence of a line of sight superposition of two or three working surfaces
located along the redshifted body of the HH 32 outflow.Comment: Accepted for Publication in the Astronomical Journal (January 2004
A latitude-dependent wind model for Mira's cometary head
We present a 3D numerical simulation of the recently discovered cometary
structure produced as Mira travels through the galactic ISM. In our simulation,
we consider that Mira ejects a steady, latitude-dependent wind, which interacts
with a homogeneous, streaming environment. The axisymmetry of the problem is
broken by the lack of alignment between the direction of the relative motion of
the environment and the polar axis of the latitude-dependent wind. With this
model, we are able to produce a cometary head with a ``double bow shock'' which
agrees well with the structure of the head of Mira's comet. We therefore
conclude that a time-dependence in the ejected wind is not required for
reproducing the observed double bow shock.Comment: 4 pages, 4 figures, accepted for publication in ApJ
A 3-mode, Variable Velocity Jet Model for HH 34
Variable ejection velocity jet models can qualitatively explain the
appearance of successive working surfaces in Herbig-Haro (HH) jets. This paper
presents an attempt to explore which features of the HH-34 jet can indeed be
reproduced by such a model. From previously published data on this object, we
find evidence for the existence of a 3-mode ejection velocity variability, and
then explore the implications of such a variability. From simple, analytic
considerations it is possible to show that the longer period modes produce a
modulation on the shorter period modes, resulting in the formation of
``trains'' of multiple knots. The knots observed close to the source of HH-34
could correspond to such a structure. Finally, a numerical simulation with the
ejection velocity variability deduced from the HH-34 data is computed. This
numerical simulation shows a quite remarkable resemblance with the observed
properties of the HH-34 jet.Comment: 28 pages LaTex, 10 postscript figure
A model of Mira's cometary head/tail entering the Local Bubble
We model the cometary structure around Mira as the interaction of an AGB wind
from Mira A, and a streaming environment. Our simulations introduce the
following new element: we assume that after 200 kyr of evolution in a dense
environment Mira entered the Local Bubble (low density coronal gas). As Mira
enters the bubble, the head of the comet expands quite rapidly, while the tail
remains well collimated for a 100 kyr timescale. The result is a
broad-head/narrow-tail structure that resembles the observed morphology of
Mira's comet. The simulations were carried out with our new adaptive grid code
WALICXE, which is described in detail.Comment: 12 pages, 8 figures (4 in color). Accepted for publication in The
Astrophysical Journa
Polarization Profiles of Scattered Emission Lines. II. Upstream Dust Scattering in the HH 1 Jet
Detailed comparisons are made between observations of scattered light
upstream of the head of the HH~1 jet and predictions of simple scattering
models. It is shown that, in order to unambiguously determine the velocity of
the head of the jet (bow shock) with respect to the upstream dust, existing
spectroscopic observations are insufficient and that spectropolarimetric
observations of the scattered light are necessary. Such an independent measure
of the bow shock velocity is important in order to test ``multiple outflow''
theories of Herbig-Haro jets. It is also shown 2that the scattering dust must
have a very forward-throwing scattering phase function
(\langle\cos\theta\rangle\msim 0.7) and slight evidence is found for a
dust-gas ratio that is higher than average.Comment: 11 pages, uuencoded compressed postscript (including 9 figures),
accepted for publication in Ap.J., IAUNAM_contrib.#34
Emission lines from rotating proto-stellar jets with variable velocity profiles. I. Three-dimensional numerical simulation of the non-magnetic case
Using the Yguazu-a three-dimensional hydrodynamic code, we have computed a
set of numerical simulations of heavy, supersonic, radiatively cooling jets
including variabilities in both the ejection direction (precession) and the jet
velocity (intermittence). In order to investigate the effects of jet rotation
on the shape of the line profiles, we also introduce an initial toroidal
rotation velocity profile, in agreement with some recent observational evidence
found in jets from T Tauri stars which seems to support the presence of a
rotation velocity pattern inside the jet beam, near the jet production region.
Since the Yguazu-a code includes an atomic/ionic network, we are able to
compute the emission coefficients for several emission lines, and we generate
line profiles for the H, [O I]6300, [S II]6716 and [N II]6548 lines. Using
initial parameters that are suitable for the DG Tau microjet, we show that the
computed radial velocity shift for the medium-velocity component of the line
profile as a function of distance from the jet axis is strikingly similar for
rotating and non-rotating jet models. These findings lead us to put forward
some caveats on the interpretation of the observed radial velocity distribution
from a few outflows from young stellar objects, and we claim that these data
should not be directly used as a doubtless confirmation of the
magnetocentrifugal wind acceleration models.Comment: 15 pages, 8 figures. Accepted to publication in Astronomy and
Astrophysic
Interaction of Infall and Winds in Young Stellar Objects
The interaction of a stellar or disk wind with a collapsing environment holds
promise for explaining a variety of outflow phenomena observed around young
stars. In this paper we present the first simulations of these interactions.
The focus here is on exploring how ram pressure balance between wind and
ambient gas and post-shock cooling affects the shape of the resulting outflows.
In our models we explore the role of ram pressure and cooling by holding the
wind speed constant and adjusting the ratio of the inflow mass flux to the wind
mass flux (Mdot_a/Mdot_w) Assuming non-spherical cloud collapse, we find that
relatively strong winds can carve out wide, conical outflow cavities and that
relatively weak winds can be strongly collimated into jet-like structures. If
the winds become weak enough, they can be cut off entirely by the infalling
environment. We identify discrepancies between results from standard snowplow
models and those presented here that have important implications for molecular
outflows. We also present mass vs. velocity curves for comparison with
observations.Comment: 35 pages, 11 figures (PNG and EPS
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