21,210 research outputs found
Linear Solar Models
We present a new approach to study the properties of the sun. We consider
small variations of the physical and chemical properties of the sun with
respect to Standard Solar Model predictions and we linearize the structure
equations to relate them to the properties of the solar plasma. By assuming
that the (variation of) the present solar composition can be estimated from the
(variation of) the nuclear reaction rates and elemental diffusion efficiency in
the present sun, we obtain a linear system of ordinary differential equations
which can be used to calculate the response of the sun to an arbitrary
modification of the input parameters (opacity, cross sections, etc.). This new
approach is intended to be a complement to the traditional methods for solar
model calculation and allows to investigate in a more efficient and transparent
way the role of parameters and assumptions in solar model construction. We
verify that these Linear Solar Models recover the predictions of the
traditional solar models with an high level of accuracy.Comment: 29 pages, 10 figure
CARMA interferometric observations of 2MASS J044427+2512: the first spatially resolved observations of thermal emission of a brown dwarf disk
We present CARMA 1.3 mm continuum data of the disk surrounding the young
brown dwarf 2MASS J044427+2512 in the Taurus molecular cloud. The high angular
resolution of the CARMA observations (0.16 arcsec) allows us to spatially
resolve for the first time the thermal emission from dust around a brown dwarf.
We analyze the interferometric visibilities and constrain the disk outer radius
adopting disk models with power-law radial profiles of the dust surface
density. In the case of a power-law index equal to or lower than 1, we obtain a
disk radius in the range of about 15 - 30 AU, while larger disks are inferred
for steeper radial profiles. By combining this information on the disk spatial
extent with the sub-mm spectral index of this source we find conclusive
evidence for mm-sized grains, or larger, in this brown dwarf disk. We discuss
the implications of our results on the models of dust evolution in
proto-planetary disks and brown dwarf formation.Comment: 14 pages, 3 figures, Accepted for publication in ApJ Letter
Helioseismology and Beryllium neutrino
We derive a lower limit on the Beryllium neutrino flux on earth,
, in the absence of oscillations,
by using helioseismic data, the B-neutrino flux measured by Superkamiokande and
the hydrogen abundance at the solar center predicted by Standard Solar Model
(SSM) calculations. We emphasize that this abundance is the only result of SSMs
needed for getting . We also derive lower bounds for the
Gallium signal, SNU, and for the Chlorine signal,
SNU, which are about above their
corresponding experimental values, SNU and SNU.Comment: 10 pages plus 1 ps figure, RevTeX styl
A hot bubble at the centre of M81
Context. Messier 81 has the nearest active nucleus with broad H
emission. A detailed study of this galaxy's centre is important for
understanding the innermost structure of the AGN phenomenon.
Aims. Our goal is to seek previously undetected structures using additional
techniques to reanalyse a data cube obtained with the GMOS-IFU installed on the
Gemini North telescope (Schnorr M\"uller et al. 2011).
Method. We analysed the data cube using techniques of noise reduction,
spatial deconvolution, starlight subtraction, PCA tomography, and comparison
with HST images.
Results. We identified a hot bubble with T 43500 K that is associated
with strong emission of [N II]5755\AA\ and a high [O
I]6300/H ratio; the bubble displays a bluish continuum,
surrounded by a thin shell of H + [N II] emission. We also reinterpret
the outflow found by Schnorr M\"uller et al. (2011) showing that the
blueshifted cone nearly coincides with the radio jet, as expected.
Conclusions. We interpret the hot bubble as having been caused by post
starburst events that left one or more clusters of young stars, similar to the
ones found at the centre of the Milky Way, such as the Arches and the IRS 16
clusters. Shocked structures from combined young stellar winds or supernova
remnants are probably the cause of this hot gas and the low ionization
emission.Comment: 5 pages, 4 figures, accepted for publication in A&
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