12,124 research outputs found
Brane-world stars from minimal geometric deformation, and black holes
We build analytical models of spherically symmetric stars in the brane-world,
in which the external space-time contains both an ADM mass and a tidal charge.
In order to determine the interior geometry, we apply the principle of minimal
geometric deformation, which allows one to map General Relativistic solutions
to solutions of the effective four-dimensional brane-world equations. We
further restrict our analysis to stars with a radius linearly related to the
total General Relativistic mass, and obtain a general relation between the
latter, the brane-world ADM mass and the tidal charge. In these models, the
value of the star's radius can then be taken to zero smoothly, thus obtaining
brane-world black hole metrics with a tidal charge solely determined by the
mass of the source and the brane tension. General conclusions regarding the
minimum mass for semiclassical black holes will also be drawn.Comment: 23 pages, 2 figures, references added and update
AGB populations in post-starburst galaxies
In a previous paper we compared the SEDs of a sample of 808 K+A galaxies from
the FUV to the MIR to the predictions of the spectrum synthesis models
explicitly using AGB components. Here we use the new AGB-light models from C.
Maraston (including less fuel for the later stages of stellar evolution and
improved calibrations) to address the discrepancies between our observations
and the AGB-heavy models used in our previous paper, which over-predict the
infrared fluxes of post-starburst galaxies by an order of magnitude. The new
models yield a much better fit to the data, especially in the near-IR, compared
to previous realizations where AGB stars caused a large excess in the H and K
bands. We { also compare the predictions of the M2013 models to those with BC03
and find that both reproduce the observations equally well. } We still find a
significant discrepancy with { both sets of models} in the Y and J bands, which
however is probably due to the spectral features of AGB stars. We also find
that { both the M2013 and the BC03 models} still over-predict the observed
fluxes in the UV bands, even invoking extinction laws that are stronger in
these bands. While there may be some simple explanations for this discrepancy,
we find that further progress requires new observations and better modelling.
Excess mid-infrared emission longward of 5m is well modelled by a
Black-Body, which may arise from dust emission from the
circumstellar envelopes of Oxygen rich M stars (expected for a metal-rich
population of AGB stars).Comment: A&A accepte
Advances in Ductile Iron Research: new metallurgical understanding and its technological significance
The present work gives an updated view about important metallurgical concepts, concerning the influence that solidification structure, microsegregation, piece size and austenite characteristics, exert on final microstructure, properties and processing control. The discussions are based on original results obtained by using special experimental techniques developed by the authors. New evidences about the solidification macrostructure, microsegregation patterns and austenite type (recrystallized and non recrystallized), allow a better understanding of the solidification and the solid state transformations taking place in conventional and thin wall ductile iron castings.Fil: Sikora, Jorge Antonio. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y TecnologĂa de Materiales. Universidad Nacional de Mar del Plata. Facultad de IngenierĂa. Instituto de Investigaciones en Ciencia y TecnologĂa de Materiales; ArgentinaFil: Boeri, Roberto Enrique. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y TecnologĂa de Materiales. Universidad Nacional de Mar del Plata. Facultad de IngenierĂa. Instituto de Investigaciones en Ciencia y TecnologĂa de Materiales; Argentin
HII Galaxies as deep cosmological probes
We re-investigated the use of the Hubble diagram to measure the cosmological
constant () and the mass density of the Universe (). We find
an important focusing effect in for redshifts about 3. This effect
implies that the apparent magnitude of a standard candle at redshifts z=2-3 has
almost no dependence on for . This means that
can be measured independently of by targeting the
redshift range according to an estimate of the value of .
We explore the evidence in support of the suggestion that extreme starburst
galaxies also known as HII galaxies can be used as distance estimators over a
wide range of redshifts and reaching very high values. We have compiled
literature data of HII galaxies up to and found a good correlation
between their luminosity and velocity dispersion measured from their strong
emission lines, thus confirming the correlation already known to exist for HII
galaxies in the nearby Universe. Several systematic effects such as age,
extinction, kinematics, and metallicity are discussed as well as the effects of
different cosmologies.Comment: To appear in MNRAS, 7 pages, 6 figure
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