A Spitzer IRAC Imaging Survey for T Dwarf Companions Around M, L, and T Dwarfs: Observations, Results, and Monte Carlo Population Analyses

We report observational techniques, results, and Monte Carlo population analyses from a Spitzer Infrared Array Camera imaging survey for substellar companions to 117 nearby M, L, and T dwarf systems (median distance of 10 pc, mass range of 0.6 to \sim0.05 M\odot). The two-epoch survey achieves typical detection sensitivities to substellar companions of [4.5 {\mu}m] \leq 17.2 mag for angular separations between about 7" and 165". Based on common proper motion analysis, we find no evidence for new substellar companions. Using Monte Carlo orbital simulations (assuming random inclination, random eccentricity, and random longitude of pericenter), we conclude that the observational sensitivities translate to an ability to detect 600-1100K brown dwarf companions at semimajor axes greater than ~35 AU, and to detect 500-600K companions at semimajor axes greater than ~60 AU. The simulations also estimate a 600-1100K T dwarf companion fraction of < 3.4% for 35-1200 AU separations, and < 12.4% for the 500-600K companions, for 60-1000 AU separations.Comment: 35 pages, 6 figure

Binarity at the L/T brown dwarf transition

Current atmospheric models cannot reproduce some of the characteristics of the transition between the L dwarfs with cloudy atmospheres and the T dwarfs with dust-depleted photospheres. It has been proposed that a majority of the L/T transition brown dwarfs could actually be a combinaison of a cloudy L dwarf and a clear T dwarf. Indeed binarity seems to occur more frequently among L/T transition brown dwarfs. We aim to refine the statistical significance of the seemingly higher frequency of binaries. Co-eval binaries would also be interesting test-beds for evolutionary models. We obtained high-resolution imaging for six mid-L to late-T dwarfs, with photometric distances between 8 and 33pc, using the adaptive optics systems NACO at the VLT, and the Lick system, both with the laser guide star. We resolve none of our targets. Combining our data with published results, we obtain a frequency of resolved L/T transition brown dwarfs of (31+21-15)%, compared to (21+10-7)% and (14+14-7)% for mid-L and T dwarfs (90% of confidence level). These fractions do not significantly support, nor contradict, the hypothesis of a larger binary fraction in the L/T transition. None of our targets has companions with effective temperatures as low as 360-1000K at separations larger than 0.5".Comment: 6 pages, 4 figures, accepted by A&

Cooperation of the Dam1 and Ndc80 kinetochore complexes enhances microtubule coupling and is regulated by aurora B

The Dam1 complex, regulated by aurora B phosphorylation, confers a more stable microtubule association for the Ndc80 complex at kinetochores (see also related paper by Lampert et al. in this issue)

Multiplicity of very low-mass objects in the Upper Scorpius OB association: a possible wide binary population

We report the initial results of a VLT/NACO high spatial resolution imaging survey for multiple systems among 58 M-type members of the nearby Upper Scorpius OB association. Nine pairs with separations below 100 have been resolved. Their small angular separations and the similarity in the brightness of the components (DMagK <1 for all of them), indicate there is a reasonable likelihood several of them are true binaries rather than chance projections. Follow-up imaging observations with WHT/LIRIS of the two widest binaries confirm that their near-infrared colours are consistent with physical very low mass binaries. For one of these two binaries, WHT/LIRIS spectra of each component were obtained. We find that the two components have similar M6-M7 spectral types and signatures of low-gravity, as expected for a young brown dwarf binary in this association. Our preliminary results indicate a possible population of very low-mass binaries with semimajor axis in the range 100 AU 150 AU, which has not been seen in the Pleiades open cluster. If these candidates are confirmed (one is confirmed by this work), these results would indicate that the binary properties of very low-mass stars and brown dwarfs may depend on the environment where they form.Comment: 11 pages, 1 table, 7 figures, request high resolution copies to [email protected]

Resolved Hubble Space spectroscopy of ultracool binary systems

Using the low-resolution mode of the Space Telescope Imaging Spectrograph (STIS) aboard the \emph{Hubble Space Telescope} (HST), we have obtained spatially resolved spectra of 20 ultracool dwarfs. 18 of them belong to 9 known very low-mass binary systems with angular separations in the range 0.37-0.098 arcseconds. We have derived spectral types in the range dM7.5 to dL6 from the PC3 index, and by comparing our STIS spectra with ground-based spectra of similar spectral resolution from Mart{\'\i}n et al. (1999). We have searched for H$_\alpha$ emission in each object but it was clearly detected in only 2 of them. We find that the distribution of H$_\alpha$ emission in our sample is statistically different from that of single field dwarfs, suggesting an intriguing anticorrelation between chromospheric activity and binarity for M7--M9.5 dwarfs. We provide measuments of the strength of the main photospheric features and the PC3 index, and we derive calibrations of spectral subclasses versus F814W and K-band absolute magnitudes for a subset of 10 dwarfs in 5 binaries that have known trigonometric parallaxes.Comment: accepted for publication in A&

Victim-offender mediation and social work: focus groups with mediators in Flanders

The role of social work in the restorative justice field remains largely unexplored. This article reports on the findings of focus groups conducted with mediators of juvenile and adult mediation practices in Flanders (Belgium) to gain more insight into how mediators perceive their professional role and to what extent they refer to individual and structural dimensions of social work practice. Implications for future social work involvement and research are made

Exploring recent developments in restorative policing in England and Wales

The evolution of the policing role over the last decade has led to 33 police forces in England and Wales integrating restorative justice practices, in one form or another, into their responses to minor crime committed for the first time by both youths and adults. Most recently, this reform dynamic has been used in response to more serious offences committed by persistent offenders and expanded to include all stages of the criminal justice process. Despite the significant positive rhetoric that surrounds the adoption and use of restorative justice, there are a number of procedural and cultural challenges that pose a threat to the extent to which restorative justice may become embedded within the policing response. This article explores these developments and highlights where potential problems for implementation may arise as well as some strategies to overcome them

Structural plasticity of the living kinetochore

The kinetochore is a large, evolutionarily conserved protein structure that connects chromosomes with microtubules. During chromosome segregation, outer kinetochore components track depolymerizing ends of microtubules to facilitate the separation of chromosomes into two cells. In budding yeast, each chromosome has a point centromere upon which a single kinetochore is built, which attaches to a single microtubule. This defined architecture facilitates quantitative examination of kinetochores during the cell cycle. Using three independent measures-calibrated imaging, FRAP, and photoconversion-we find that the Dam1 submodule is unchanged during anaphase, whereas MIND and Ndc80 submodules add copies to form an "anaphase configuration" kinetochore. Microtubule depolymerization and kinesin-related motors contribute to copy addition. Mathematical simulations indicate that the addition of microtubule attachments could facilitate tracking during rapid microtubule depolymerization. We speculate that the minimal kinetochore configuration, which exists from G1 through metaphase, allows for correction of misattachments. Our study provides insight into dynamics and plasticity of the kinetochore structure during chromosome segregation in living cells