734 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
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 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
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
A precessing jet model for the PN K 3-35: simulated radio-continuum emission
The bipolar morphology of the planetary nebula (PN) K 3-35 observed in
radio-continuum images was modelled with 3D hydrodynamic simulations with the
adaptive grid code yguazu-a. We find that the observed morphology of this PN
can be reproduced considering a precessing jet evolving in a dense AGB
circumstellar medium, given by a mass loss rate
\dot{M}_{csm}=5x10^{-5}M_{\odot}/yr and a terminal velocity v_{w}=10 km/s.
Synthetic thermal radio-continuum maps were generated from numerical results
for several frequencies. Comparing the maps and the total fluxes obtained from
the simulations with the observational results, we find that a model of
precessing dense jets, where each jet injects material into the surrounding CSM
at a rate \dot{M}_j=2.8x10^{-4} {M_{\odot}/yr (equivalent to a density of
8x10^{4} {cm}^{-3}, a velocity of 1500 km/s, a precession period of 100 yr, and
a semi-aperture precession angle of 20 degrees agrees well with the
observations.Comment: 6 pages, 4 figures, accepted to MNRA
Filaments in Galactic Winds Driven by Young Stellar Clusters
The starburst galaxy M82 shows a system of H-emitting filaments which
extend to each side of the galactic disk. We model these filaments as the
result of the interaction between the winds from a distribution of Super
Stellar Clusters (SSCs). We first derive the condition necessary for producing
a radiative interaction between the cluster winds (a condition which is met by
the SSC distribution of M82). We then compute 3D simulations for SSC wind
distributions which satisfy the condition for a radiative interaction, and also
for distributions which do not satisfy this condition. We find that the highly
radiative models, that result from the interaction of high metallicity cluster
winds, produce a structure of H emitting filaments, which qualitatively
agrees with the observations of the M82, while the non-radiative SSC wind
interaction models do not produce filamentary structures. Therefore, our
criterion for radiative interactions (which depends on the mass loss rate and
the terminal velocity of the SSC winds, and the mean separation between SSCs)
can be used to predict whether or not an observed galaxy should have associated
H emitting filaments.Comment: 10 pages, 6 Figures. ApJ Accepted, August 7, 200
PENGARUH DISIPLIN KERJA DAN MOTIVASI KERJA TERHADAP KINERJA KARYAWAN PADA PT. JASA ANGKASA SEMESTA SURABAYA
Sumber daya manusia memiliki peran yang penting baik secara perorangan
ataupun kelompok, dan sumber daya manusia merupakan salah satu penggerak
utama atas kelancaran jalannya kegiatan sebuah organisasi. Berdasarkan data
menurunnya hasil kinerja karyawan pada tahun 2016 dari target yang diberikan
oleh perusahaan, diketahui karena kurangnya disiplin dan motivasi kerja yang
dianggap kurang menyeluruh oleh karyawan. Penelitian ini bertujuan untuk
mengetahui pengaruh disiplin kerja dan motivasi kerja terhadap kinerja karyawan
pada PT. Jasa Angkasa Semesta Surabaya.
Sampel yang digunakan dalam penelitian ini adalah semua karyawan yang
bekerja di PT. Jasa Angkasa Semesta Surabaya yang berjumlah 60 orang. Teknik
penentuan sampel yang digunakan yaitu teknik sampel jenuh yang artinya teknik
penentuan sampel dengan menggunakan semua anggota populasi. Teknik analis
yang digunakan dalam penelitian ini adalah Partial Least Square (PLS).
Berdasarkan hasil penelitian menyimpulkan bahwa Disiplin Kerja dan
Motivasi Kerja yang tinggi mampu meningkatkan Kinerja Karyawan pada PT.
Jasa Angkasa Semesta di Surabaya.
Keyword : Disiplin Kerja, Motivasi Kerja, dan Kinerja Karyawa
Time-dependent ejection velocity model for the outflow of Hen 3--1475
We present 2D axisymmetric and 3D numerical simulations of the
proto-planetary nebula Hen 3-1475, which is characterized by a remarkably
highly collimated optical jet, formed by a string of shock-excited knots along
the axis of the nebula. It has recently been suggested that the kinematical and
morphological properties of the Hen 3-1475 jet could be the result of an
ejection variability of the central source (Riera et al. 2003). The
observations suggest a periodic variability of the ejection velocity
superimposed on a smoothly increasing ejection velocity ramp. From our
numerical simulations, we have obtained intensity maps (for different optical
emission lines) and position-velocity diagrams, in order to make a direct
comparison with the HST observations of this object. Our numerical study allows
us to conclude that a model of a precessing jet with a time-dependent ejection
velocity, which is propagating into an ISM previously perturbed by an AGB wind,
can succesfully explain both the morphological and the kinematical
characteristics of this proto-planetary nebula.Comment: Astronomy and Astrophysics (accepted) (8 figures
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