1,829 research outputs found
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
The Influence of Dust Formation Modelling on Na I and K I Line Profiles in Substellar Atmospheres
We aim to understand the correlation between cloud formation and alkali line
formation in substellar atmospheres.We perform line profile calculations for Na
I and K I based on the coupling of our kinetic model for the formation and
composition of dust grains with 1D radiative transfer calculations in
atmosphere models for brown dwarfs and giant gas planets. The Na I and K I line
profiles sensibly depend on the way clouds are treated in substellar atmosphere
simulations. The kinetic dust formation model results in the highest
pseudo-continuum compared to the limiting cases.Comment: 5 pages, Accepted for publication in MNRA
The Influence of Galactic Cosmic Rays on Ion-Neutral Hydrocarbon Chemistry in the Upper Atmospheres of Free-Floating Exoplanets
Cosmic rays may be linked to the formation of volatiles necessary for
prebiotic chemistry. We explore the effect of cosmic rays in a
hydrogen-dominated atmosphere, as a proof-of-concept that ion-neutral chemistry
may be important for modelling hydrogen-dominated atmospheres. In order to
accomplish this, we utilize Monte Carlo cosmic ray transport models with
particle energies of eV eV in order to investigate the
cosmic ray enhancement of free electrons in substellar atmospheres. Ion-neutral
chemistry is then applied to a Drift-Phoenix model of a free-floating giant gas
planet. Our results suggest that the activation of ion-neutral chemistry in the
upper atmosphere significantly enhances formation rates for various species,
and we find that CH, CH, NH, CH and possibly
CH are enhanced in the upper atmospheres because of cosmic rays. Our
results suggest a potential connection between cosmic ray chemistry and the
hazes observed in the upper atmospheres of various extrasolar planets.
Chemi-ionization reactions are briefly discussed, as they may enhance the
degree of ionization in the cloud layer.Comment: 22 pages, 4 figures. Accepted to the International Journal of
Astrobiolog
- …