104 research outputs found
'Bonn' Optimized Stellar Tracks (BoOST). Simulated Populations of Massive and Very Massive Stars as Input for Astrophysical Applications
Massive and very massive stars can play important roles in stellar
populations by ejecting strong stellar winds and exploding in energetic
phenomena. It is therefore of high importance that their behaviour is properly
accounted for in synthetic model populations. Here we present nine grids of
stellar evolutionary model sequences, together with finely resolved
interpolated sequences and synthetic populations, of stars with 9-500 Msun and
with metallicities ranging from Solar down to 1/250 Solar. The stellar models
were computed with the 'Bonn' evolutionary code (covering core-hydrogen- and
core-helium-burning phases, both complete). Post-processing for publication has
been done using optimized methods, developed by our team, for massive and very
massive stars. Interpolation and population synthesis were also performed on
the models by our newly developed routine synStars. Eight of the grids
represent slowly rotating massive stars with normal/classical evolution, while
one grid represents fast rotating, chemically-homogeneously evolving models.
Apart from the common stellar parameters such as mass, radius, surface
temperature, luminosity and mass loss rate, we present stellar wind properties
such as estimated wind velocity and kinetic energy of the wind. Additionally,
we provide complete chemical yields of 34 isotopes, and estimates for the
masses of the compact object remnants. The 'Bonn' Optimized Stellar Tracks
(BoOST) project is published as simple tables - including stellar models,
interpolated tracks and synthetic populations - thus ideal for further
scientific applications. For example, star-formation studies could be done with
BoOST to cover broad metallicity ranges, and so could be simulations of
high-redshift galaxies. Additionally, gravitational-wave event rate predictions
could be refined using BoOST by accounting for very massive stars at
low-metallicity.Comment: Submitted to ApJ. We welcome feedback and requests from the communit
Supersonic Line Broadening within Young and Massive Super Star Clusters
The origin of supersonic infrared and radio recombination nebular lines often
detected in young and massive superstar clusters are discussed. We suggest that
these arise from a collection of repressurizing shocks (RSs), acting
effectively to re-establish pressure balance within the cluster volume and from
the cluster wind which leads to an even broader although much weaker component.
The supersonic lines are here shown to occur in clusters that undergo a bimodal
hydrodynamic solution (Tenorio-Tagle et al. 2007), that is within clusters that
are above the threshold line in the mechanical luminosity or cluster mass vs
the size of the cluster (Silich et al. 2004). The plethora of repressurizing
shocks is due to frequent and recurrent thermal instabilities that take place
within the matter reinserted by stellar winds and supernovae. We show that the
maximum speed of the RSs and of the cluster wind, are both functions of the
temperature reached at the stagnation radius. This temperature depends only on
the cluster heating efficiency (). Based on our two dimensional
simulations (Wunsch et al. 2008) we calculate the line profiles that result
from several models and confirm our analytical predictions. From a comparison
between the predicted and observed values of the half-width zero intensity of
the two line components we conclude that the thermalization efficiency in SSC's
above the threshold line must be lower than 20%.Comment: 17 pages, 3 figures, accepted by Ap
SILCC VII -- Gas kinematics and multiphase outflows of the simulated ISM at high gas surface densities
We present magnetohydrodynamic (MHD) simulations of the star-forming
multiphase interstellar medium (ISM) in stratified galactic patches with gas
surface densities 10, 30, 50, and 100
. The SILCC project simulation framework accounts
for non-equilibrium thermal and chemical processes in the warm and cold ISM.
The sink-based star formation and feedback model includes stellar winds,
hydrogen-ionising UV radiation, core-collapse supernovae, and cosmic ray (CR)
injection and diffusion. The simulations follow the observed relation between
and the star formation rate surface density
. CRs qualitatively change the outflow phase structure.
Without CRs, the outflows transition from a two-phase (warm and hot at 1 kpc)
to a single-phase (hot at 2 kpc) structure. With CRs, the outflow always has
three phases (cold, warm, and hot), dominated in mass by the warm phase. The
impact of CRs on mass loading decreases for higher and
the mass loading factors of the CR-supported outflows are of order unity
independent of . Similar to observations, vertical
velocity dispersions of the warm ionised medium (WIM) and the cold neutral
medium (CNM) correlate with the star formation rate as , with . In the absence of stellar
feedback, we find no correlation. The velocity dispersion of the WIM is a
factor higher than that of the CNM, in agreement with local
observations. For the WIM motions
become supersonic.Comment: 19 pages, 9 figures, submitted to MNRA
On the Hydrodynamic Interplay Between a Young Nuclear Starburst and a Central Super Massive Black Hole
We present 1D numerical simulations, which consider the effects of radiative
cooling and gravity on the hydrodynamics of the matter reinserted by stellar
winds and supernovae within young nuclear starbursts with a central
supermassive black hole (SMBH). The simulations confirm our previous
semi-analytic results for low energetic starbursts, evolving in a
quasi-adiabatic regime, and extend them to more powerful starbursts evolving in
the catastrophic cooling regime. The simulations show a bimodal hydrodynamic
solution in all cases. They present a quasi-stationary accretion flow onto the
black hole, defined by the matter reinserted by massive stars within the
stagnation volume and a stationary starburst wind, driven by the high thermal
pressure acquired in the region between the stagnation and the starburst radii.
In the catastrophic cooling regime, the stagnation radius rapidly approaches
the surface of the starburst region, as one considers more massive starbursts.
This leads to larger accretion rates onto the SMBH and concurrently to powerful
winds able to inhibit interstellar matter from approaching the nuclear
starburst.
Our self-consistent model thus establishes a direct physical link between the
SMBH accretion rate and the nuclear star formation activity of the host galaxy
and provides a good upper limit to the accretion rate onto the central black
hole.Comment: 20 pages, 6 figures, accepted for publication in The Astrophysical
Journal
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