2,552 research outputs found
Macroscopic Screening of Coulomb Potentials From UV/IR-Mixing
We compute the static potential in a non-commutative theory including a term
due to UV/IR-mixing. As a result, the potential decays exponentially fast with
distance rather than like a power law Coulomb type potential due to the
exchange of massless particles. This shows that when quantum effects are taken
into account the introduction of non-commutativity not only modifies physics at
short distances but has dramatic macroscopic consequences as well. As a result,
we give a lower bound on the scale of non-commutativity (if present at all) to
be compatible with observations.Comment: 10 pages, V2 minor wording and reference
The impact of M-dwarf atmosphere modelling on planet detection
Being able to accurately estimate stellar parameters based on spectral
observations is important not only for understanding the stars themselves but
it is also vital for the determination of exoplanet parameters. M dwarfs are
discussed as targets for planet detection as these stars are less massive, less
luminous and have smaller radii making it possible to detect smaller and
lighter planets. Therefore M-dwarfs could prove to be a valuable source for
examining the lower mass end of planet distribution, but in order to do that,
one must first take care to understand the characteristics of the host stars
well enough. Up to date, there are several families of stellar model
atmospheres. We focus on the ATLAS9, MARCS and Drift-Phoenix families in the
M-dwarf parameter space. We examine the differences in the (Tgas, pgas)
structures, synthetic photometric fluxes and related colour indices.We find
discrepancies in the hotter regions of the stellar atmosphere between the ATLAS
and MARCS models. The MARCS and Drift-Phoenix models appear to agree to a
better extend with variances of less than 300K. We have compiled the broad-band
synthetic photometric fluxes of all models for the Johnson UBVRI and 2MASS
JHKs. The fluxes of MARCS differ from both ATLAS and Drift-Phoenix models in
the optical range.Comment: submitted to the proceedings of the conference 'Brown dwarfs come of
age', May 20-24 2013, Memorie della Societa Astronomica Italian
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