424 research outputs found
Insight into atmospheres of extrasolar planets through plasma processes
Extrasolar planets appear in a chemical diversity unseen in our own solar
system. Despite their atmospheres being cold, continuous and transient plasma
processes do affect these atmosphere where clouds form with great efficiency.
Clouds can be very dynamic due to winds for example in highly irradiated
planets like HD 189733b, and lightning may emerge. Lightning, and discharge
events in general, leave spectral fingerprints, for example due to the
formation of HCN. During the interaction, lightning or other flash--ionisation
events also change the electromagnetic field of a coherent, high energy
emission which results a characteristic damping of the initial, unperturbed
(e.g. cyclotron emission) radiation beam. We summarise this as 'recipe for
observers'. External ionisation by X-ray or UV e.g. from within the
interstellar medium or from a white dwarf companion will introduce additional
ionisation leading to the formation of a chromosphere. Signatures of plasma
processes therefore allow for an alternative way to study atmospheres of
extrasolar planets and brown dwarfs.Comment: refereed proceeding (3 referees) for 'Planetary Radio Emissions
VIII', Austrian Academy of Sciences Pres
Career situation of female astronomers in Germany
We survey the job situation of women in astronomy in Germany and of German
women abroad and review indicators for their career development. Our sample
includes women astronomers from all academic levels from doctoral students to
professors, as well as female astronomers who have left the field. We find that
networking and human support are among the most important factors for success.
Experience shows that students should carefully choose their supervisor and
collect practical knowledge abroad. We reflect the private situation of female
German astronomers and find that prejudices are abundant, and are perceived as
discriminating.We identify reasons why women are more likely than men to quit
astronomy after they obtain their PhD degree. We give recommendations to young
students on what to pay attention to in order to be on the successful path in
astronomy.Comment: published in Astronomical Note
Careers in astronomy in Germany and the UK
We discuss the outcomes of surveys addressing the career situation of
astronomers in Germany and the UK, finding social and cultural differences
between communities as well as gender bias in both.Comment: Astronomy and Geophysics. 13 page pdf with colour image
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 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
Planetary host stars: Evaluating uncertainties in ultra-cool model atmospheres
M-dwarfs are emerging in the literature as promising targets for detecting
low-mass, Earth-like planets. An important step in this process is to determine
the stellar parameters of the M-dwarf host star as accurately as possible.
Different well-tested stellar model atmosphere simulations from different
groups are widely applied to undertake this task. This paper provides a
comparison of different model atmosphere families to allow a better estimate of
systematic errors on host-star stellar parameter introduced by the use of one
specific model atmosphere family only. We present a comparison of the ATLAS9,
MARCS, Phoenix and Drift-Phoenix model atmosphere families including the
M-dwarf parameter space (TK4000K,
log(g)=3.05.0, [M/H]=). We examine the differences in
the (T, p)-structures, in synthetic photometric fluxes
and in colour indices. Model atmospheres results for higher log(g) deviate
considerably less between different models families than those for lower log(g)
for all TK4000K examined. We compiled the broad-band
synthetic photometric fluxes for all available model atmospheres (incl.
M-dwarfs and brown dwarfs) for the UKIRT WFCAM ZYJHK, 2MASS JHKs and Johnson
UBVRI filters, and calculated related colour indices. Synthetic colours in the
IR wavelengths diverge by no more than 0.15 dex amongst all model families. For
all spectral bands considered, model discrepancies in colour diminish for
higher T atmosphere simulations. We notice differences in synthetic
colours between all model families and observed example data (incl. Kepler 42
and GJ1214).Comment: accepted for publication in MNRA
Modelling the local and global cloud formation on HD 189733b
Context. Observations suggest that exoplanets such as HD 189733b form clouds
in their atmospheres which have a strong feedback onto their thermodynamical
and chemical structure, and overall appearance. Aims. Inspired by mineral cloud
modelling efforts for Brown Dwarf atmospheres, we present the first spatially
varying kinetic cloud model structures for HD 189733b. Methods. We apply a
2-model approach using results from a 3D global radiation-hydrodynamic
simulation of the atmosphere as input for a detailed, kinetic cloud formation
model. Sampling the 3D global atmosphere structure with 1D trajectories allows
us to model the spatially varying cloud structure on HD 189733b. The resulting
cloud properties enable the calculation of the scattering and absorption
properties of the clouds. Results. We present local and global cloud structure
and property maps for HD 189733b. The calculated cloud properties show
variations in composition, size and number density of cloud particles which are
strongest between the dayside and nightside. Cloud particles are mainly
composed of a mix of materials with silicates being the main component. Cloud
properties, and hence the local gas composition, change dramatically where
temperature inversions occur locally. The cloud opacity is dominated by
absorption in the upper atmosphere and scattering at higher pressures in the
model. The calculated 8{\mu}m single scattering Albedo of the cloud particles
are consistent with Spitzer bright regions. The cloud particles scattering
properties suggest that they would sparkle/reflect a midnight blue colour at
optical wavelengths.Comment: Accepted for publication (A&A) - 21/05/2015 (Low Resolution Maps
Rain and clouds in brown dwarf atmospheres: A coupled problem from small to large
The large scale structure of a brown dwarf atmosphere is determined by an
interplay of convection, radiation, dust formation, and gravitational settling,
which possibly provides an explanation for the observed variability. The result
is an element depletion of the dust forming regions and an element enrichment
of the dust evaporating sites. The formation of dust cloud structures in
substellar atmospheres is demonstrated based on a consistent theoretical
description of dust formation and destruction, gravitational settling, and
element depletion including the effect of convective overshoot.
Since the viscosity is small in brown dwarf atmospheres, the convection
creates a turbulent environment with fluctuations of all thermodynamic state
variables on a wide range of spatial scales. Hence, the classical turbulent
closure problem needs to be tackled in connection with dust formation in
substellar objects, because a complete three-dimensional and time-dependent
solution of the model equations is simply not possible. Structure formation may
be seeded on the smallest scales, when chemical processes are involved. In
order to understand the interaction of turbulence and dust formation, we have
performed investigations of the smallest scale regimes in 1D and in 2D in order
to identify the governing processes of the unresolved scale regime.Comment: 8 pages, 5 figures, conference contribution to the Cool stars,
Stellar Systems and the Sun 13, AG Summer meeting 2004, submitte
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
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