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

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

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 (T$_{\rm eff}=2500$K$\,...\,$4000K, log(g)=3.0$\,...\,$5.0, [M/H]=$-2.5\,...\,0.5$). We examine the differences in the (T$_{\rm gas}$, p$_{\rm gas}$)-structures, in synthetic photometric fluxes and in colour indices. Model atmospheres results for higher log(g) deviate considerably less between different models families than those for lower log(g) for all T$_{\rm eff}=2500$K$\,...\,$4000K examined. We compiled the broad-band synthetic photometric fluxes for all available model atmospheres (incl. M-dwarfs and brown dwarfs) for the UKIRT WFCAM ZYJHK, 2MASS JHKs and Johnson UBVRI filters, and calculated related colour indices. Synthetic colours in the IR wavelengths diverge by no more than 0.15 dex amongst all model families. For all spectral bands considered, model discrepancies in colour diminish for higher T$_{\rm eff}$ 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 $10^6$ eV $< E < 10^{12}$ 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 C$_2$H$_2$, C$_2$H$_4$, NH$_3$, C$_6$H$_6$ and possibly C$_{10}$H 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