110 research outputs found
Winds driven by super-star clusters: The self-consistent radiative solution
Here we present a self-consistent stationary solution for spherically
symmetric winds driven by massive star clusters under the impact of radiative
cooling. We demonstrate that cooling may modify drastically the distribution of
temperature if the rate of injected energy approaches a critical value. We also
prove 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. Finally we thoroughly discuss the expected appearance of super-star
cluster winds in the X-ray and visible line regimes. The three solutions here
found: the quasi-adiabatic, the strongly radiative wind and the inhibited
stationary solution, are then compared to the winds from Arches cluster, NGC
4303 central cluster and to the supernebula in NGC 5253.Comment: 9 pages, 5 figures, accepted for publication by The Astrophysical
Journa
Supernovae and their expanding blast waves during the early evolution of Galactic globular clusters
Our arguments deal with the early evolution of Galactic globular clusters and
show why only a few of the supernovae products were retained within globular
clusters and only in the most massive cases ( Msol), while less
massive clusters were not contaminated at all by supernovae. Here we show that
supernova blast waves evolving in a steep density gradient undergo blowout and
end up discharging their energy and metals into the medium surrounding the
clusters. This inhibits the dispersal and the contamination of the gas left
over from a first stellar generation. Only the ejecta from well centered
supernovae, that evolve into a high density medium available for a second
stellar generation in the most massive clusters would be retained. These are
likely to mix their products with the remaining gas, leading in these cases
eventually to an Fe contaminated second stellar generation.Comment: Accepted for publication in the Astrophysical Journal Letters,
10pages, 1 figur
The realm of the Galactic globular clusters and the mass of their primordial clouds
By adopting the empirical constraints related to the estimates of Helium
enhancement (), present mass ratio between first and second stellar
generations () and the actual mass of Galactic globular clusters
(), we envisage a possible scenario for the formation of these stellar
systems. Our approach allows for the possible loss of stars through evaporation
or tidal interactions and different star formation efficiencies. In our
approach the star formation efficiency of the first generation
() is the central factor that links the stellar generations as
it not only defines both the mass in stars of the first generation and the
remaining mass available for further star formation, but it also fixes the
amount of matter required to contaminate the second stellar generation. In this
way, is fully defined by the He enhancement between successive
generations in a GC. We also show that globular clusters fit well within a
{\it vs} diagram which indicates three different
evolutionary paths. The central one is for clusters that have not loss stars,
through tidal interactions, from either of their stellar generations, and thus
their present value is identical to the amount of low mass stars ( 1 M) that resulted from both stellar generations. Other possible
evolutions imply either the loss of first generation stars or the combination
of a low star formation efficiency in the second stellar generation and/or a
loss of stars from the second generation. From these considerations we derive a
lower limit to the mass () of the individual primordial clouds that
gave origin to globular clusters.Comment: 17 pages, 2 figures, accepted for publication in the Astrophysical
Journa
Supersonic turbulence in Giant HII Regions: clues from 30 Doradus
The tight correlation between turbulence and luminosity in Giant HII Regions
is not well understood. While the luminosity is due to the UV radiation from
the massive stars in the ionizing clusters, it is not clear what powers the
turbulence. Observations of the two prototypical Giant HII Regions in the local
Universe, 30 Doradus and NGC604, show that part of the kinetic energy of the
nebular gas comes from the combined stellar winds of the most massive stars -
the cluster winds, but not all. We present a study of the kinematics of 30
Doradus based on archival VLT FLAMES/GIRAFFE data and new high resolution
observations with HARPS. We find that the nebular structure and kinematics are
shaped by a hot cluster wind and not by the stellar winds of individual stars.
The cluster wind powers most of the turbulence of the nebular gas, with a small
but significant contribution from the combined gravitational potential of stars
and gas. We estimate the total mass of 30 Doradus and we argue that the region
does not contain significant amounts of neutral (HI) gas, and that the giant
molecular cloud 30Dor-10 that is close to the center of the nebula in
projection is in fact an inflating cloud tens of parsecs away from R136, the
core of the ionizing cluster. We rule out a Kolmogorov-like turbulent kinetic
energy cascade as the source of supersonic turbulence in Giant HII Regions.Comment: 15 pages, 18 figures, submitted for publication in A&A. Major
revision has been fully implemented in this version, including a more
comprehensive analysis and discussion of present result
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