82,087 research outputs found
On the White Dwarf distances to Galactic Globular Clusters
We analyze in detail various possible sources of systematic errors on the
distances of globular clusters derived by fitting a local template DA white
dwarf sequence to the cluster counterpart (the so-called WD-fitting technique).
We find that the unknown thickness of the hydrogen layer of white dwarfs in
clusters plays a non negligible role. For reasonable assumptions - supported by
the few sparse available observational constraints - about the unknown mass and
thickness of the hydrogen layer for the cluster white dwarfs, a realistic
estimate of the systematic error on the distance is within +-0.10 mag. However,
particular combinations of white dwarf masses and envelope thicknesses - which
at present cannot be excluded a priori - could produce larger errors.
Contamination of the cluster DA sequence by non-DA white dwarfs introduces a
very small systematic error of about -0.03 mag in the Mv/(V-I) plane, but in
the Mv/(B-V) plane the systematic error amounts to ~ +0.20 mag. Contamination
by white dwarfs with helium cores should not influence appreciably the
WD-fitting distances. Finally, we obtain a derivative D((m-M)v)/D(E(B-V))~ -5.5
for the WD-fitting distances, which is very similar to the dependence found
when using the Main Sequence fitting technique.Comment: 12 pages, 11 figures A&A, accepted for publicatio
Axions and White Dwarfs
White dwarfs are almost completely degenerate objects that cannot obtain
energy from the thermonuclear sources and their evolution is just a
gravothermal process of cooling. The simplicity of these objects, the fact that
the physical inputs necessary to understand them are well identified, although
not always well understood, and the impressive observational background about
white dwarfs make them the most well studied Galactic population. These
characteristics allow to use them as laboratories to test new ideas of physics.
In this contribution we discuss the robustness of the method and its
application to the axion case.Comment: 4 pages, 1 figure, to appear in the Proceedings for the 6th Patras
meeting on Axions, WIMPs and WISP
Preface "Nonlinear processes in oceanic and atmospheric flows"
Nonlinear phenomena are essential ingredients in many oceanic and atmospheric
processes, and successful understanding of them benefits from multidisciplinary
collaboration between oceanographers, meteorologists, physicists and
mathematicians. The present Special Issue on ``Nonlinear Processes in Oceanic
and Atmospheric Flows'' contains selected contributions from attendants to the
workshop which, in the above spirit, was held in Castro Urdiales, Spain, in
July 2008. Here we summarize the Special Issue contributions, which include
papers on the characterization of ocean transport in the Lagrangian and in the
Eulerian frameworks, generation and variability of jets and waves, interactions
of fluid flow with plankton dynamics or heavy drops, scaling in meteorological
fields, and statistical properties of El Ni\~no Southern Oscillation.Comment: This is the introductory article to a Special Issue on "Nonlinear
Processes in Oceanic and Atmospheric Flows'', published in the journal
Nonlinear Processes in Geophysics, where the different contributions are
summarized. The Special Issue itself is freely available from
http://www.nonlin-processes-geophys.net/special_issue103.htm
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