1,058 research outputs found
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
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
Multidimensional Hydrodynamical Simulations of radiative cooling SNRs-clouds interactions: an application to Starburst Environments
In this work we are interested to study the by-products of SNR-clouds in a
starburst (SB) system. These interactions can have an important role in the
recycling of matter from the clouds to the ISM and vice-versa. In the present
work, we have focused our attention on the global effects of the interactions
between clouds and SN shock waves in the ISM of SB environments, and performed
3-D radiative cooling hydrodynamical simulations with the adaptive YGUAZU grid
code. We have also considered the effects of the photo-evaporation due to the
presence of a high number of UV photons from hot stars and supernovae (SNe).
The results have shown that, in the presence of radiative cooling, instead of
an efficient gas mixing with the diffuse ISM, the interactions cause the
fragmentation of the clouds into smaller ones. The results have also revealed
that the SNR-clouds interactions are less efficient at producing substantial
mass loss from the clouds to the diffuse ISM than mechanisms such as the
photo-evaporation caused by the UV flux from the hot stars.Comment: 15 pages, 25 figures. Figures with higher resolution at the page:
http://www.astro.iag.usp.br/~dalpino/ Astronomy & Astrophysics accepte
The precession of the giant HH34 outflow: a possible jet deceleration mechanism
The giant jets represent a fundamental trace of the historical evolution of
the outflow activity over timescales which are comparable to the accretion time
of the outflow sources in their main protostellar phase. The study of such huge
jets provides the possibility of retrieving important elements related to the
life of the outflow sources. In this paper, we study the role of precession
(combined with jet velocity-variability and the resulting enhanced interaction
with the surrounding environment) as a deceleration mechanism for giant jets
using a numerical approach. We obtain predictions of H alpha intensity maps and
position-velocity diagrams from 3D simulations of the giant HH 34 jet
(including an appropriate ejection velocity time-variability and a precession
of the outflow axis), and we compare them with previously published
observations of this object. Our simulations represent a step forward from
previous numerical studies of HH objects, in that the use of a 7-level, binary
adaptive grid has allowed us to compute models which appropiately cover all
relevant scales of a giant jet, from the ~ 100 AU jet radius close to the
source to the ~ 1 pc length of the outflow. A good qualitative and quantitative
agreement is found between the model predictions and the observations.
Moreover, we show that a critical parameter for obtaining a better or worse
agreement with the observations is the ratio rho_j/rho_a between the jet and
the environmental densities. The implications of this result in the context of
the current star formation models are discussed (ABRIDGED).Comment: 19 pages, 8 eps figs.,uses aaspp4; accepted by the Ap
The X-ray Luminosities of HH Objects
The recent detection of X-ray emission from HH 2 and HH 154 with the Chandra
and XMM-Newton satellites (respectively) have opened up an interesting, new
observational possibility in the field of Herbig-Haro objects. In order to be
able to plan further X-ray observations of other HH objects, it is now of
interest to be able to estimate their X-ray luminosities in order to choose
which objects to observe. This paper describes a simple, analytic model for
predicting the X-ray luminosity of a bow shock from the parameters of the flow
(i.e., the size of the bow shock, its velocity, and the pre-shock density). The
accuracy of the analytic model is analyzed through a comparison with the
predictions obtained from axisymmetric, gasdynamic simulations of the leading
working surface of an HH jet. We find that our analytic model reproduces the
observed X-ray luminosities of HH 2 and HH 154, and we propose that HH~80/81 is
a good candidate for future observations with Chandra.Comment: 10 pages (8 text, 2 figures
ANALISIS PENGARUH CURRENT RATIO, SIZE, DEBT TO EQUITY RATIO, DAN TOTAL ASSET TURNOVER TERHADAP DIVIDEND YIELD DENGAN RETURN ON ASSET SEBAGAI VARIABEL INTERVENING (Studi Kasus Pada Perusahaan Manufaktur yang Terdaftar di Bursa Efek Indonesia Tahun 2010-2014)
Financial performance has become one of the most important issues for investors before they investing their fund inside the company. There is so many factors affect the financial performance and affect their decisions. Therefore, this study examines the effect of Current Ratio (CR), Firm’s Size (TA), Debt To Equity Ratio (DER), and Total Asset Turnover (TATO) of the Dividend Yield with the Return On Assets (ROA) used as intervening variable.
The sample used in this research consists of 25 manufacturing companies listed on the Indonesian Stock Exchange (IDX) 2010-2014. This study used the purposive sampling methods. Data obtained from the Indonesian Capital Market Directory (ICMD) and Annual Report. Data analysis method used is multiple linear regression analysis and also path analyisis for analyze the indirect effect of independent variables.
The result indicates that CR, and TATO has significant positive effect on ROA, while DER has significant negative effect on ROA, while Size is the only one variable that has no effect on ROA. In the second regression, the result indicates that ROA, Size, and TATO has significant positive effect on Dividend Yield, while CR and DER has significant negative effect. More further, path analysis result indicates that CR and TATO has significant positive effect on Dividend Yield through intervening variables (ROA) while Size and DER has no significant effect on Dividend Yield through intervening variables (ROA)
Star formation triggered by SN explosions: an application to the stellar association of Pictoris
In the present study, considering the physical conditions that are relevant
in interactions between supernova remnants (SNRs) and dense molecular clouds
for triggering star formation we have built a diagram of SNR radius versus
cloud density in which the constraints above delineate a shaded zone where star
formation is allowed. We have also performed fully 3-D radiatively cooling
numerical simulations of the impact between SNRs and clouds under different
initial conditions in order to follow the initial steps of these interactions.
We determine the conditions that may lead either to cloud collapse and star
formation or to complete cloud destruction and find that the numerical results
are consistent with those of the SNR-cloud density diagram. Finally, we have
applied the results above to the Pictoris stellar association which is
composed of low mass Post-T Tauri stars with an age of 11 Myr. It has been
recently suggested that its formation could have been triggered by the shock
wave produced by a SN explosion localized at a distance of about 62 pc that may
have occurred either in the Lower Centaurus Crux (LCC) or in the Upper
Centaurus Lupus (UCL) which are both nearby older subgroups of that association
(Ortega and co-workers). Using the results of the analysis above we have shown
that the suggested origin for the young association at the proposed distance is
plausible only for a very restricted range of initial conditions for the parent
molecular cloud, i.e., a cloud with a radius of the order of 10 pc and density
of the order of 20 cm and a temperature of the order of 50100 K.Comment: 9 pages, 10 figures, to appear in MNRA
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