اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدFeedback from Winds and Supernovae in Massive Stellar Clusters
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We simulate the effects of massive star feedback, via winds and SNe, on inhomogeneous molecular material left over from the formation of a massive stellar cluster. We use 3D hydrodynamic models with a temperature dependent average particle mass to model the separate molecular, atomic, and ionized phases. We find that the winds blow out of the molecular clump along low-density channels, and gradually ablate denser material into these. However, the dense molecular gas is surprisingly long-lived and is not immediately affected by the first star in the cluster exploding.
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We use 3D hydrodynamical models to investigate the effects of massive star feedback from winds and supernovae on inhomogeneous molecular material left over from the formation of a massive stellar cluster. We simulate the interaction of the mechanical
energy input from a cluster with 3 O-stars into a giant molecular cloud (GMC) clump containing 3240 solar masses of molecular material within a 4 pc radius. The cluster wind blows out of the molecular clump along low-density channels, into which denser clump material is entrained. We find that the densest molecular regions are surprisingly resistant to ablation by the cluster wind, in part due to shielding by other dense regions closer to the cluster. Nonetheless, molecular material is gradually removed by the cluster wind during which mass-loading factors in excess of several 100 are obtained. Because the clump is very porous, 60-75 per cent of the injected wind energy escapes the simulation domain, with the difference being radiated. After 4.4 Myr, the massive stars in our simulation begin to explode as supernovae. The highly structured environment into which the SN energy is released allows even weaker coupling to the remaining dense material and practically all of the SN energy reaches the wider environment. The molecular material is almost completely dispersed and destroyed after 6 Myr. The escape fraction of ionizing radiation is estimated to be about 50 per cent during the first 4 Myr of the clusters life. A similar model with a larger and more massive GMC clump reveals the same general picture, though more time is needed for it to be destroyed.
The X-ray emission from a simulated massive stellar cluster is investigated. The emission is calculated from a 3D hydrodynamical model which incorporates the mechanical feedback from the stellar winds of 3 O-stars embedded in a giant molecular cloud
clump containing 3240 M$_{odot}$ of molecular material within a 4 pc radius. A simple prescription for the evolution of the stars is used, with the first supernova explosion at t=4.4 Myrs. We find that the presence of the GMC clump causes short-lived attenuation effects on the X-ray emission of the cluster. However, once most of the material has been ablated away by the winds the remaining dense clumps do not have a noticable effect on the attenuation compared with the assumed interstellar medium column. We determine the evolution of the cluster X-ray luminosity, L$_X$, and spectra, and generate synthetic images. The intrinsic X-ray luminosity drops from nearly 10$^{34}$ ergs s$^{-1}$ while the winds are `bottled up, to a near constant value of 1.7$times 10^{32}rm ergs s^{-1}$ between t=1-4 Myrs. L$_X$ reduces slightly during each stars red supergiant stage due to the depressurization of the hot gas. However, L$_X$ increases to $approx 10^{34}rm,ergs s^{-1}$ during each stars Wolf-Rayet stage. The X-ray luminosity is enhanced by 2-3 orders of magnitude to $sim 10^{37}rm ergs s^{-1}$ for at least 4600 yrs after each supernova, at which time the blast wave leaves the grid and the X-ray luminosity drops. The X-ray luminosity of our simulation is generally considerably fainter than predicted from spherically-symmetric bubble models, due to the leakage of hot gas material through gaps in the outer shell. This process reduces the pressure within our simulation and thus the X-ray emission. However, the X-ray luminosities and temperatures which we obtain are comparable to similarly powerful massive young clusters.
Stellar winds and supernova (SN) explosions of massive stars (stellar feedback) create bubbles in the interstellar medium (ISM) and insert newly produced heavy elements and kinetic energy into their surroundings, possibly driving turbulence. Most of
this energy is thermalized and immediately removed from the ISM by radiative cooling. The rest is available for driving ISM dynamics. In this work we estimate the amount of feedback energy retained as kinetic energy when the bubble walls have decelerated to the sound speed of the ambient medium. We show that the feedback of the most massive star outweighs the feedback from less massive stars. For a giant molecular cloud (GMC) mass of 1e5 solar masses (as e.g. found in the Orion GMCs) and a star formation efficiency of 8% the initial mass function predicts a most massive star of approximately 60 solar masses. For this stellar evolution model we test the dependence of the retained kinetic energy of the cold GMC gas on the inclusion of stellar winds. In our model winds insert 2.34 times the energy of a SN and create stellar wind bubbles serving as pressure reservoirs. We find that during the pressure driven phases of the bubble evolution radiative losses peak near the contact discontinuity (CD), and thus, the retained energy depends critically on the scales of the mixing processes across the CD. Taking into account the winds of massive stars increases the amount of kinetic energy deposited in the cold ISM from 0.1% to a few percent of the feedback energy.
The supersonic stellar and disk winds possessed by massive young stellar objects will produce shocks when they collide against the interior of a pre-existing bipolar cavity (resulting from an earlier phase of jet activity). The shock heated gas emits
thermal X-rays which may be observable by spaceborne observa- tories such as the Chandra X-ray Observatory. Hydrodynamical models are used to explore the wind-cavity interaction. Radiative transfer calculations are performed on the simulation output to produce synthetic X-ray observations, allowing constraints to be placed on model parameters through comparisons with observations. The model reveals an intricate interplay between the inflowing and outflowing material and is successful in reproducing the observed X-ray count rates from massive young stellar objects.
We study the populations of massive stars in the Carina region and their energetic feedback and ejection of $^{26}$Al. We did a census of the stellar populations in young stellar clusters within a few degrees of the Carina Nebula. For each star we es
timated the mass, based on the spectral type and the host cluster age. We used population synthesis to calculate the energetic feedback and ejection of $^{26}$Al from the winds of the massive stars and their supernova explosions. We used 7 years of INTEGRAL observations to measure the $^{26}$Al signal from the region. The INTEGRAL $^{26}$Al signal is not significant with a best-fit value of about 1.5e-5 ph/cm^2/s, approximately half of the published Compton Gamma Ray Observatory (CGRO) result, but in agreement with the latest CGRO estimates. Our analysis of the stellar populations in the young clusters leads to an expected signal of half the observed value, but the results are consistent within 2 sigma. We find that the fraction of $^{26}$Al ejected in Wolf-Rayet winds is high, and the observed signal is unlikely to be caused by $^{26}$Al ejected in supernovae alone, indicating a strong wind ejection of $^{26}$Al. Due to the lack of prominent O stars, regions with ages $gtrsim$10 Myr are often neglected in studies of OB associations. We find that in the Carina region such clusters contribute significantly to the stellar mass and the energetics of the region.
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