Exoplanets and Stellar Physics

Abstract:

Hydrothermal plumes may be responsible for transmitting radiogenic or tidally generated heat from Europa's rocky interior through a liquid ocean to the base of its ice shell. This process has been implicated in the formation of chaos regions and lenticulae by melting or exciting convection in the ice layer. In contrast to earlier work, we argue that Europa's ocean should be treated as an unstratified fluid. We have adapted and expanded upon existing work describing buoyant plumes in a rotating, unstratified environment. We discuss the scaling laws governing the flow and geometry of plumes on Europa and perform a laboratory experiment to obtain scaling constants and to visualize plume behavior in a Europa‐like parameter regime. We predict that hydrothermal plumes on Europa are of a lateral scale (at least 25–50 km) comparable to large chaos regions; they are too broad to be responsible for the formation of individual lenticulae. Plume heat fluxes (0.1–10 W/m2) are too weak to allow complete melt‐through of the ice layer. Current speeds in the plume (3–8 mm/s) are much slower than indicated by previous studies. The observed movement of ice blocks in the Conamara Chaos region is unlikely to be driven by such weak flow.

Abstract:

A method for simulating light curves containing stellar micro-variability for a range of spectral types and ages is presented. It is based on parameter-by-parameter scaling of a multi-component fit to the solar irradiance power spectrum (based on VIRGO/PMO6 data), and scaling laws derived from ground based observations of various stellar samples. A correlation is observed in the Sun between the amplitude of the power spectrum on long (weeks) timescales and the BBSO Ca II K-line index of chromospheric activity. On the basis of this evidence, the chromospheric activity level, predicted from rotation period and B - V colour estimates according to the relationship first introduced by Noyes (1983) and Noyes et al. (1984), is used to predict the variability power on weeks time scales. The rotation period is estimated on the basis of a fit to the distribution of rotation period versus B - V observed in the Hyades and the Skumanich (1972) spin-down law. The characteristic timescale of the variability is also scaled according to the rotation period. This model is used to estimate the impact of the target star spectral type and age on the detection capability of space based transit searches such as Eddington and Kepler. K stars are found to be the most promising targets, while the performance drops significantly for stars earlier than G and younger than 2.0 Gyr. Simulations also show that Eddington should detect terrestrial planets orbiting solar-age stars in most of the habitable zone for G2 types and all of it for K0 and K5 types.

Abstract:

A data reduction software package is developed to reduce data of the near-IR integral field spectrometer SPIFFI built at MPE. The basic data reduction routines are coded in ANSI C. The high level scripting language Python is used to connect the C-routines allowing fast prototyping. Several Python scripts are written to produce the needed calibration data and to generate the final result, a wavelength calibrated data cube with the instrumental signatures removed.