Radio Emission from Ultra-Cool Dwarfs

The 2001 discovery of radio emission from ultra-cool dwarfs (UCDs), the very low-mass stars and brown dwarfs with spectral types of ~M7 and later, revealed that these objects can generate and dissipate powerful magnetic fields. Radio observations provide unparalleled insight into UCD magnetism: detections extend to brown dwarfs with temperatures <1000 K, where no other observational probes are effective. The data reveal that UCDs can generate strong (kG) fields, sometimes with a stable dipolar structure; that they can produce and retain nonthermal plasmas with electron acceleration extending to MeV energies; and that they can drive auroral current systems resulting in significant atmospheric energy deposition and powerful, coherent radio bursts. Still to be understood are the underlying dynamo processes, the precise means by which particles are accelerated around these objects, the observed diversity of magnetic phenomenologies, and how all of these factors change as the mass of the central object approaches that of Jupiter. The answers to these questions are doubly important because UCDs are both potential exoplanet hosts, as in the TRAPPIST-1 system, and analogues of extrasolar giant planets themselves.Comment: 19 pages; submitted chapter to the Handbook of Exoplanets, eds. Hans J. Deeg and Juan Antonio Belmonte (Springer-Verlag

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

How tracking structures attitudes towards ethnic out-groups and interethnic interactions in the classroom: an ethnographic study in Belgium

The influence of the ethnic composition of schools on interethnic relations and attitudes has been studied extensively and has received ample interest from policy makers. However, less attention has been paid to the structures and processes inside schools that organize interethnic relations and attitudes. In Flanders (Belgium), secondary education is organized by grouping students in different tracks, which are hierarchically ordered and prepare students for different futures. Tracking in Flanders is intended to group students according to their abilities but together with this, students are grouped according to their ethnic and socioeconomic background. In the present study, the interethnic relations and attitudes in each track will be explored, based on ethnographic observations and semi-structured interviews in three multi-ethnic secondary schools in one city. Our findings suggest that different patterns occur across three groups of tracks: the most appreciated fields of study in academic, the intermediary (less appreciated fields of study in academic and technical tracks) and vocational tracks. According to the relative sizes of ethnic groups and track specific characteristics, interethnic relations were characterized respectively by ethnic segregation, positive experiences of interethnic contact or ethnic conflict/tensions. The ethnic composition of classrooms seemed to matter for students' ethnic in-group identifications and evaluations and perceived out-group threats

Productive entrepreneurship and the effectiveness of insolvency legislation: a cross-country study

This paper studies the association between the effectiveness of insolvency regulations and entrepreneurship using multilevel modeling of about 300,000 individuals in 27 countries over the 2005-2010 period. We investigate the relationship between three different measures of "resolving insolvency" (time, cost, and recovery rate) from the World Bank and four different measures of entrepreneurship from the Global Entrepreneurship Monitor, controlling for relevant individual- and country-level facets. We find that opportunity-driven and innovation-oriented entrepreneurs are more severely affected by onerous insolvency regulations than necessity-motivated entrepreneurs. However, entrepreneurs envisioning rapid employment growth are not affected by onerous insolvency regulations. We discuss contributions to comparative entrepreneurship research and public policy.Funding Agencies|Swedish Research CouncilSwedish Research Council [DNR 340-2013-5460]</p