On the abundances of GRO J1655-40

Context: The detection of overabundances of $\alpha$-elements and lithium in the secondary star of a black-hole binary provides important insights about the formation of a stellar-mass black-hole. $\alpha$-enhancement might theoretically also be the result of pollution by the nucleosynthesis occurring during an outburst, or through spallation by the jet. Aims: We study the abundances, and their possible variations with time, in the secondary star of the runaway black-hole binary GRO J1655--40, in order to understand their origin. Methods: We present a detailed comparison between a Keck spectrum obtained in 1998 found in the literature, archival VLT-UVES data taken in 2004 and new VLT-UVES spectra obtained early 2006. We carefully determine the equivalent widths of different $\alpha$-elements (Mg, O, Ti, S and Si) with their associated uncertainty. We use the well-studied comparison star HD 156098 as well as synthetic spectra to match the spectrum of GRO J1655--40 in order to determine the abundances of these elements. Results: We see no significant variations of equivalent widths with time. Our fit using HD 156098 reveals that there is significant overabundance of oxygen in all our spectra, but no overabundances of any of the other $\alpha$-elements. Finally, we do not detect the lithium line at 6707 \AA. Conclusions: We show that there is no detected pollution in GRO J1655--40 after the burst in 2005. Moreover, we argue that uncertainties in the equivalent widths were previously underestimated by a factor of $\sim$3. Consequently, our results challenge the existence of general overabundances of $\alpha$-elements observed in this galactic black-hole binary, and thus the accepted interpretation that they are of supernova origin. The physical cause of the overabundance of oxygen remains unclear

Solar-like oscillations and magnetic activity of the slow rotator EK Eri

We aim to understand the interplay between non-radial oscillations and stellar magnetic activity and test the feasibility of doing asteroseismology of magnetically active stars. We analyze 30 years of photometric time-series data, 3 years of HARPS radial velocity monitoring, and 3 nights of high-cadence HARPS asteroseismic data. We construct a high-S/N HARPS spectrum that we use to determine atmospheric parameters and chemical composition. Spectra observed at different rotation phases are analyzed to search for signs of temperature or abundance variations. An upper limit on the projected rotational velocity is derived from very high-resolution CES spectra. We detect oscillations in EK Eri with a frequency of the maximum power of nu_max = 320+/-32 muHz, and we derive a peak amplitude per radial mode of ~0.15 m/s, which is a factor of ~3 lower than expected. We suggest that the magnetic field may act to suppress low-degree modes. Individual frequencies can not be extracted from the available data. We derive accurate atmospheric parameters, refining our previous analysis. We confirm that the main light variation is due to cool spots, but that other contributions may need to be taken into account. We suggest that the rotation period is twice the photometric period, i.e., P_rot = 2 P_phot = 617.6 d. We conclude from our derived parameters that v sin i < 0.40 km/s. We also link the time series of direct magnetic field measurements available in the literature to our newly derived photometric ephemeris.Comment: 11 pages, 10 figures. Accepted by A&

Paired atom laser beams created via four-wave mixing

A method to create paired atom laser beams from a metastable helium atom laser via four-wave mixing is demonstrated. Radio frequency outcoupling is used to extract atoms from a Bose Einstein condensate near the center of the condensate and initiate scattering between trapped and untrapped atoms. The unequal strengths of the interactions for different internal states allows an energy-momentum resonance which leads to the creation of pairs of atoms scattered from the zero-velocity condensate. The resulting scattered beams are well separated from the main atom laser in the 2-dimensional transverse atom laser profile. Numerical simulations of the system are in good agreement with the observed atom laser spatial profiles, and indicate that the scattered beams are generated by a four-wave mixing process, suggesting that the beams are correlated.Comment: 5 pages, 3 figure

Putting evolutionary biology back in the ecological theatre: a demographic framework mapping genes to communities

Question: How can we link genotypic, phenotypic, individual, population, and community levels of organization so as to illuminate general ecological and evolutionary processes and provide a framework for a quantitative, integrative evolutionary biology? Framework: We introduce an evolutionary framework that maps different levels of biological diversity onto one another. We provide (1) an overview of maps linking levels of biological organization and (2) a guideline of how to analyse the complexity of relationships from genes to population growth. Method: We specify the appropriate levels of biological organization for responses to selection, for opportunities for selection, and for selection itself. We map between them and embed these maps into an ecological setting