Radiation-hydrodynamics simulations of surface convection in low-mass stars: connections to stellar structure and asteroseismology

Radiation-hydrodynamical simulations of surface convection in low-mass stars can be exploited to derive estimates of i) the efficiency of the convective energy transport in the stellar surface layers; ii) the convection-related photometric micro-variability. We comment on the universality of the mixing-length parameter, and point out potential pitfalls in the process of its calibration which may be in part responsible for the contradictory findings about its variability across the Hertzsprung-Russell digramme. We further comment on the modelling of the photometric micro-variability in HD49933 - one of the first main COROT targets.Comment: 6 pages, 5 figures, Proceedings paper of IAU Symposium 25

International Fragmentation of Production and the Labour Input into Germany’s Exports – An Input-Output-Analysis

The import penetration of exports has become a topic of public debate, particularly in the context of Germany’s position as one of the world’s leading exporters. The growth in the volume of intermediate products purchased from abroad for subsequent processing into export goods in Germany seems to be undermining the importance of exports as a driver of domestic production and employment. The gains that arise from an increase in exports seem to have been offset by the losses caused by the crowding out of local production by imports. Empirical evidence on the impact of this international integration of the goods market on the German labour market is ambiguous. Short-term negative effects on employment are claimed to be offset by the long-term benefit that the jobs lost in the short run will eventually be replaced by higher-skilled jobs with better perspectives. Against this background, the following hypothesis is tested empirically: Germany is poor in natural resources, but rich in skilled labour. In line with the Heckscher- Ohlin theory, Germany should therefore specialize in the production of export goods and services that are relatively intensive in these factors and should import those goods and services that are relatively intensive in unskilled labour. The empirical part of the paper deals with the extent of the German export penetration by imports. At first, it analyses by what ways imports are affecting the exports directly and indirectly and shows the consequences of import penetration of exports for the national output and employment. Secondly, consequences for employment are split in different skill types of labour. These issues are discussed with the standard open static inputoutput- model. The data base is a time series of official input-output tables. The employment effects for Germany divided by skill types of labour are investigated using skill matrices generated by the authors.international trade, labour and skills market interactions, input-output models

Prospects of using simulations to study the photospheres of brown dwarfs

We discuss prospects of using multi-dimensional time-dependent simulations to study the atmospheres of brown dwarfs and extrasolar giant planets, including the processes of convection, radiation, dust formation, and rotation. We argue that reasonably realistic simulations are feasible, however, separated into two classes of local and global models. Numerical challenges are related to potentially large dynamic ranges, and the treatment of scattering of radiation in multi-D geometries.Comment: 6 pages, 3 figures, to appear in the Proceedings of the IAU Symposium 239 "Convection in Astrophysics", eds. F. Kupka, I.W. Roxburgh, and K.L. Cha

Cu I resonance lines in turn-off stars of NGC 6752 and NGC 6397. Effects of granulation from CO5BOLD models

Context. Copper is an element whose interesting evolution with metallicity is not fully understood. Observations of copper abundances rely on a very limited number of lines, the strongest are the Cu I lines of Mult. 1 at 324.7 nm and 327.3 nm which can be measured even at extremely low metallicities. Aims. We investigate the quality of these lines as abundance indicators. Method. We measure these lines in two turn-off (TO) stars in the Globular Cluster NGC 6752 and two TO stars in the Globular Cluster NGC 6397 and derive abundances with 3D hydrodynamical model atmospheres computed with the CO5BOLD code. These abundances are compared to the Cu abundances measured in giant stars of the same clusters, using the lines of Mult. 2 at 510.5 nm and 578.2 nm. Results. The abundances derived from the lines of Mult. 1 in TO stars differ from the abundances of giants of the same clusters. This is true both using CO5BOLD models and using traditional 1D model atmospheres. The LTE 3D corrections for TO stars are large, while they are small for giant stars. Conclusions. The Cu I resonance lines of Mult. 1 are not reliable abundance indicators. It is likely that departures from LTE should be taken into account to properly describe these lines, although it is not clear if these alone can account for the observations. An investigation of these departures is indeed encouraged for both dwarfs and giants. Our recommendation to those interested in the study of the evolution of copper abundances is to rely on the measurements in giants, based on the lines of Mult. 2. We caution, however, that NLTE studies may imply a revision in all the Cu abundances, both in dwarfs and giants.Comment: to be published on A\&

Overtures to the pulsational instability of ZZ Ceti variables

Results of nonradial, nonadiabatic pulsation calculations on hydrogen-rich white dwarf models are presented. In contrast to earlier attempts, the modeling builds on hydrodynamically simulated convective surface layers supplemented with standard interior models. Based on our stellar models and despite of various simple attempts to couple convection and pulsation we could not reproduce theoretically the presently adopted location of the observed blue edge of the ZZ Ceti variables. When the convective efficiency is high enough we found a sensitive dependence of the stability properties of the g-modes on the pulsational treatment of shear within the convection zone.Comment: 13 pages, postscript figures included in text, uuencoded gzipped ps-file. Submitted for publication in Astron.&Astrophy