The stellar and sub-stellar IMF of simple and composite populations

The current knowledge on the stellar IMF is documented. It appears to become top-heavy when the star-formation rate density surpasses about 0.1Msun/(yr pc^3) on a pc scale and it may become increasingly bottom-heavy with increasing metallicity and in increasingly massive early-type galaxies. It declines quite steeply below about 0.07Msun with brown dwarfs (BDs) and very low mass stars having their own IMF. The most massive star of mass mmax formed in an embedded cluster with stellar mass Mecl correlates strongly with Mecl being a result of gravitation-driven but resource-limited growth and fragmentation induced starvation. There is no convincing evidence whatsoever that massive stars do form in isolation. Various methods of discretising a stellar population are introduced: optimal sampling leads to a mass distribution that perfectly represents the exact form of the desired IMF and the mmax-to-Mecl relation, while random sampling results in statistical variations of the shape of the IMF. The observed mmax-to-Mecl correlation and the small spread of IMF power-law indices together suggest that optimally sampling the IMF may be the more realistic description of star formation than random sampling from a universal IMF with a constant upper mass limit. Composite populations on galaxy scales, which are formed from many pc scale star formation events, need to be described by the integrated galactic IMF. This IGIMF varies systematically from top-light to top-heavy in dependence of galaxy type and star formation rate, with dramatic implications for theories of galaxy formation and evolution.Comment: 167 pages, 37 figures, 3 tables, published in Stellar Systems and Galactic Structure, Vol.5, Springer. This revised version is consistent with the published version and includes additional references and minor additions to the text as well as a recomputed Table 1. ISBN 978-90-481-8817-

What’s in a “research passport”? A collaborative autoethnography of institutional approvals in public involvement in research

© 2016 Laterza et al. Background In the growing literature on public involvement in research (PIR), very few works analyse PIR organizational and institutional dimensions in depth. We explore the complex interactions of PIR with institutions and bureaucratic procedures, with a focus on the process of securing institutional permissions for members of the public (we refer to them as “research partners”) and academics involved in health research. Methods We employ a collaborative autoethnographic approach to describe the process of validating “research passports” required by UK NHS trusts, and the individual experiences of the authors who went through this journey– research partners and academics involved in a qualitative study of PIR across eight health sciences projects in England and Wales. Results Our findings show that research partners encountered many challenges, as the overall bureaucratic procedures and the emotional work required to deal with them proved burdensome. The effects were felt by the academics too who had to manage the whole process at an early stage of team building in the project. Our thematic discussion focuses on two additional themes: the emerging tensions around professionalisation of research partners, and the reflexive effects on PIR processes. Conclusions In the concluding section, we make a number of practical recommendations. Project teams should allow enough time to go through all the hurdles and steps required for institutional permissions, and should plan in advance for the right amount of time and capacity needed from project leaders and administrators. Our findings are a reminder that the bureaucratic and organisational structures involved in PIR can sometimes produce unanticipated and unwanted negative effects on research partners, hence affecting the overall quality and effectiveness of PIR. Our final recommendation to policy makers is to focus their efforts on making PIR bureaucracy more inclusive and ultimately more democratic

PSR J1740-3052: a pulsar with a massive companion

We report on the discovery of a binary pulsar, PSR J1740-3052, during the Parkes multibeam survey. Timing observations of the 570-ms pulsar at Jodrell Bank and Parkes show that it is young, with a characteristic age of 350 kyr, and is in a 23 1-d, highly eccentric orbit with a companion whose mass exceeds 11 M.. An accurate position for the pulsar was obtained using the Australia Telescope Compact Array. Near-infrared 2.2-mum observations made with the telescopes at the Siding Spring observatory reveal a late-type star coincident with the pulsar position. However, we do not believe that this star is the companion of the pulsar, because a typical star of this spectral type and required mass would extend beyond the orbit of the pulsar. Furthermore, the measured advance of periastron of the pulsar suggests a more compact companion, for example, a main-sequence star with radius only a few times that of the Sun. Such a companion is also more consistent with the small dispersion measure variations seen near periastron. Although we cannot conclusively rule out a black hole companion, we believe that the companion is probably an early B star, making the system similar to the binary PSR J0045-7319