22 research outputs found
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
Star Formation in Tadpole Galaxies
Tadpole Galaxies look like a star forming head with a tail structure to the
side. They are also named cometaries. In a series of recent works we have
discovered a number of issues that lead us to consider them extremely
interesting targets. First, from images, they are disks with a lopsided
starburst. This result is firmly established with long slit spectroscopy in a
nearby representative sample. They rotate with the head following the rotation
pattern but displaced from the rotation center. Moreover, in a search for
extremely metal poor (XMP) galaxies, we identified tadpoles as the dominant
shapes in the sample- nearly 80% of the local XMP galaxies have a tadpole
morphology. In addition, the spatially resolved analysis of the metallicity
shows the remarkable result that there is a metallicity drop right at the
position of the head. This is contrary to what intuition would say and
difficult to explain if star formation has happened from gas processed in the
disk. The result could however be understood if the star formation is driven by
pristine gas falling into the galaxy disk. If confirmed, we could be unveiling,
for the first time, cool flows in action in our nearby world. The tadpole class
is relatively frequent at high redshift - 10% of resolvable galaxies in the
Hubble UDF but less than 1% in the local Universe. They are systems that could
track cool flows and test models of galaxy formation.Comment: arXiv admin note: text overlap with arXiv:1302.435
The pressure confined wind of the massive and compact superstar cluster M82-A1
The observed parameters of the young superstar cluster M82-A1 and its
associated compact HII region are here shown to indicate a low heating
efficiency or immediate loss, through radiative cooling, of a large fraction of
the energy inserted by stellar winds and supernovae during the early evolution
of the cluster. This implies a bimodal hydrodynamic solution which leads to a
reduced mass deposition rate into the ISM, with a much reduced outflow
velocity. Furthermore, to match the observed parameters of the HII region
associated to M82-A1, the resultant star cluster wind is here shown to ought to
be confined by a high pressure interstellar medium. The cluster wind
parameters, as well as the location of the reverse shock, its cooling length
and the radius of the standing outer HII region are derived analytically. All
of these properties are then confirmed with a semi-analytical integration of
the flow equations, which provides us also with the run of the hydrodynamic
variables as a function of radius. The impact of the results is discussed and
extended to other massive and young superstar clusters surrounded by a compact
HII region.Comment: 19 pages, 4 figures, accepted for publication in Ap
The circumstellar medium of the peculiar supernova SN1997ab
We report the detection of the slow moving wind into which the compact
supernova remnant SN 1997ab is expanding. Echelle spectroscopy provides clear
evidence for a well resolved narrow (Full Width at Zero Intensity, FWZI ~ 180
km/s) P-Cygni profile, both in Ha and Hb, superimposed on the broad emission
lines of this compact supernova remnant. From theoretical arguments we know
that the broad and strong emission lines imply a circumstellar density (n ~
10^7 cm^-3). This, together with our detection, implies a massive and slow
stellar wind experienced by the progenitor star shortly prior to the explosion.Comment: 10 pages, 2 figures, acepted for publication in MNRAS. Uses
referee.sty, psfig.sty and mn.sty. A postscript file can also be retrieved at
http://www.strw.LeidenUniv.nl/~salamanc/latest.htm
On the formation of massive stellar clusters
Here we model a star forming factory in which the continuous creation of
stars results in a highly concentrated, massive (globular cluster-like) stellar
system. We show that under very general conditions a large-scale gravitational
instability in the ISM, which triggers the collapse of a massive cloud, leads
with the aid of a spontaneous first generation of massive stars, to a standing,
small-radius, cold and dense shell. Eventually, as more of the collapsing
matter is processed and incorporated, the shell becomes gravitationally
unstable and begins to fragment, allowing the formation of new stars, while
keeping its location. This is due to a detailed balance established between the
ram pressure from the collapsing cloud which, together with the gravitational
force exerted on the shell by the forming cluster, acts against the mechanical
energy deposited by the collection of new stars. We analyze the mass spectrum
of fragments that result from the continuous fragmentation of the standing
shell and show that its shape is well approximated at the high mass end by a
power law with slope -2.25, very close to the value that fits the universal
IMF. The self-contamination resultant from the continuous generation of stars
is shown to lead to a large metal spread in massive ( 10 M)
clusters, while clusters with a mass similar to 10 M or smaller,
simply reflect the initial metalicity of the collapsing cloud. This is in good
agreement with the data available for globular clusters in the Galaxy.Comment: 9 pages, 8 postscript figures - change of the address #3; - Sect.
2.2. paragraph 2: second sentence removed, third sentence change