149 research outputs found
Super stellar clusters with a bimodal hydrodynamic solution: an Approximate Analytic Approach
We look for a simple analytic model to distinguish between stellar clusters
undergoing a bimodal hydrodynamic solution from those able to drive only a
stationary wind. Clusters in the bimodal regime undergo strong radiative
cooling within their densest inner regions, which results in the accumulation
of the matter injected by supernovae and stellar winds and eventually in the
formation of further stellar generations, while their outer regions sustain a
stationary wind. The analytic formulae are derived from the basic hydrodynamic
equations. Our main assumption, that the density at the star cluster surface
scales almost linearly with that at the stagnation radius, is based on results
from semi-analytic and full numerical calculations. The analytic formulation
allows for the determination of the threshold mechanical luminosity that
separates clusters evolving in either of the two solutions. It is possible to
fix the stagnation radius by simple analytic expressions and thus to determine
the fractions of the deposited matter that clusters evolving in the bimodal
regime blow out as a wind or recycle into further stellar generations.Comment: 5 pages, 4 figures, accepted by A&
WINDS DRIVEN BY MASSIVE STAR CLUSTERS
Abstract Here I discuss the X-ray emission resulting from the interaction of star cluster winds with the surrounding medium. I demonstrate that X-ray emission from the free wind region dominates the total bubble X-ray luminosity if the central star cluster is sufficiently young, massive and compact. I also prove that strong radiative cooling is a crucial ingredient which defines the physical properties and observational manifestations of gaseous outflows generated within such clusters. It may modify drastically the distribution of temperature if the rate of injected energy approaches a critical value. I also show that the stationary wind solution does not exist whenever the energy radiated away at the star cluster center exceeds 30% of the energy deposition rate. This implies that stationary star cluster winds may evolve either in the quasi-adiabatic or in the strongly radiative regimes. I then compare our model to the winds from Arches cluster and NGC4303 central cluster and demonstrate that Arches cluster wind evolves in a quasi-adiabatic regime whereas the NGC4303 cluster wind seems to be strongly affected by the radiative cooling
The algorithm of forecasting of the oil well intervention effect
The paper reviews stages of oil well intervention effect forecasting. The proposed algorithm based on regression equation solution automates the process of oil well intervention effect forecasting. An assessment of the hydraulic fracturing effect was provided as a validation of the algorithm. According to assessments results, the suggested regression algorithm allows a 1.87-time decrease of an estimation error according to the error of central tendency
ALMA CO(3-2) Observations of Star-Forming Filaments in a Gas-Poor Dwarf Spheroidal Galaxy
We report ALMA observations of CO(3-2) and CO(3-2) in the
gas-poor dwarf galaxy NGC 5253. These 0.3"(5.5 pc) resolution images reveal
small, dense molecular gas clouds that are located in kinematically distinct,
extended filaments. Some of the filaments appear to be falling into the galaxy
and may be fueling its current star formation. The most intense CO(3-2)
emission comes from the central 100 pc region centered on the luminous
radio-infrared HII region known as the supernebula. The CO(3-2) clumps within
the starburst region are anti-correlated with H on 5 pc scales,
but are well-correlated with radio free-free emission. Cloud D1, which
enshrouds the supernebula, has a high CO/CO ratio, as does
another cloud within the central 100 pc starburst region, possibly because the
clouds are hot. CO(3-2) emission alone does not allow determination of cloud
masses as molecular gas temperature and column density are degenerate at the
observed brightness, unless combined with other lines such as CO.Comment: 7 pages, 5 figures, Accepted to Ap
Supernova Remnant in a Stratified Medium: Explicit, Analytical Approximations for Adiabatic Expansion and Radiative Cooling
We propose simple, explicit, analytical approximations for the kinematics of
an adiabatic blast wave propagating in an exponentially stratified ambient
medium, and for the onset of radiative cooling, which ends the adiabatic era.
Our method, based on the Kompaneets implicit solution and the Kahn
approximation for the radiative cooling coefficient, gives straightforward
estimates for the size, expansion velocity, and progression of cooling times
over the surface, when applied to supernova remnants (SNRs). The remnant shape
is remarkably close to spherical for moderate density gradients, but even a
small gradient in ambient density causes the cooling time to vary substantially
over the remnant's surface, so that for a considerable period there will be a
cold dense expanding shell covering only a part of the remnant. Our
approximation provides an effective tool for identifying the approximate
parameters when planning 2-dimensional numerical models of SNRs, the example of
W44 being given in a subsequent paper.Comment: ApJ accepted, 11 pages, 2 figures embedded, aas style with
ecmatex.sty and lscape.sty package
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