High-resolution survey for planetary companions to young stars in the Taurus molecular cloud

Direct imaging in the infrared at the diffraction limit of large telescopes is a unique probe of the properties of young planetary systems. We survey 55 single class I and class II stars in Taurus in the L’ filter using natural and laser guide star adaptive optics and the near-infrared camera (NIRC2) of the Keck II telescope, in order to search for planetary-mass companions. We use both reference star differential imaging and kernel phase techniques, achieving typical 5σ contrasts of ∼6 mag at separations of 0.2 arcsec and ∼8 mag beyond 0.5 arcsec. Although, we do not detect any new faint companions, we constrain the frequency of wide separation massive planets, such as HR 8799 analogues. We find that, assuming hot-start models and a planet distribution with power-law mass and semimajor axis indices of −0.5 and −1, respectively, less than 20 per cent of our target stars host planets with masses >2 MJ at separations >10 au.The observatory was made possible by the generous financial support of the W. M. Keck Foundation. ALW would like to thank the Australian Government for their support through the Australian Postgraduate Award Scholarship and the Research School of Astronomy and Astrophysics at the Australian National University for the ANU Supplementary PhD Scholarship

Tiny grains shining bright in the gaps of Herbig Ae transitional discs

This work presents a study of two Herbig Ae transitional discs, Oph IRS 48 and HD 169142; which both have reported rings in their dust density distributions. We use Keck-II/NIRC2 adaptive optics imaging observations in the L′ filter (3.8 μm) to probe the regions of these discs inwards of ∼20au from the star. We introduce our method for investigating these transitional discs, which takes a forward modelling approach: making a model of the disc (using the Monte Carlo radiative transfer code RADMC3D), convolving it with point spread functions of calibrator stars, and comparing the convolved models with the observational data. The disc surface density parameters are explored with a Monte Carlo Markov Chain technique. Our analysis recovers emission from both of the discs interior to the well-known optically thick walls, modelled as a ring of emission at ∼15au in Oph IRS 48, and ∼7au for HD 169142, and identifies asymmetries in both discs. Given the brightness of the near-symmetric rings compared to the reported companion candidates, we suggest that the reported companion candidates can be interpreted as slightly asymmetric disc emission or illumination.EKB would like to thank the Australian Government for their support through the Australian Government Research Training Program Stipend Scholarship and the Research School of Astronomy and Astrophysics at the Australian National University for the Masters of Astronomy and Astrophysics (Advanced) Scholarship. MJI gratefully acknowledges funding provided by the Australian Research Council’s Future Fellowship (FT130100235). CF gratefully acknowledges funding provided by the Australian Research Council’s Discovery Projects (grants DP150104329 and DP170100603) and Future Fellowship Scheme (grant FT180100495), as well as the Australia-Germany Joint Research Cooperation Scheme (UA-DAAD

Orbital Motion of the Wide Planetary-mass Companion GSC 6214-210 b: No Evidence for Dynamical Scattering

Direct-imaging exoplanet surveys have discovered a class of 5–20 MJup substellar companions at separations >100 au from their host stars, which present a challenge to planet and star formation models. Detailed analysis of the orbital architecture of these systems can provide constraints on possible formation mechanisms, including the possibility that they were dynamically ejected onto a wide orbit. We present astrometry for the wide planetary-mass companion GSC 6214-210 b (240 au; ≈14 MJup) obtained using NIRC2 with adaptive optics at the Keck telescope over 10 years. Our measurements achieved astrometric uncertainties of ≈1 mas per epoch. We determined a relative motion of 1.12 ± 0.15 mas yr−1 (0.61 ± 0.09 km s−1), the first detection of orbital motion for this companion. We compute the minimum periastron for the companion due to our measured velocity vector and derive constraints on the orbital parameters through our modified implementation of the Orbits for the Impatient rejection sampling algorithm. We find that close periastron orbits, which could indicate that the companion was dynamically scattered, are present in our posterior but have low likelihoods. For all orbits in our posterior, we assess the detectability of close-in companions that could have scattered GSC 6214-210 b from a closer orbit, and find that most potential scatterers would have been detected in previous imaging. We conclude that formation at small orbital separation and subsequent dynamical scattering through interaction with another potential close-in object is an unlikely formation pathway for this companion. We also update stellar and substellar properties for the system using the new parallax from Gaia DR2.L.A.P. was supported by a NASA/Keck Data Analysis Grant and by the McDonald Observatory Board of Visitors, the Cox Endowment Fund of the UT-Austin Department of Astronomy, the Barry Goldwater Scholarship and Excellence in Education Foundation, and the Astronaut Scholarship Foundation. T.J.D. acknowledges research support from Gemini Observatory. M.J.I. was supported by the Australian Research Council Future Fellowship (FT130100235). E.K.B. gratefully acknowledges the support of the Australian Government Research Training Program Stipend Scholarship

A potent series targeting the malarial cGMP-dependent protein kinase clears infection and blocks transmission

Protein kinases are promising drug targets for treatment of malaria. Here, starting with a medicinal chemistry approach, Baker et al. generate an imidazopyridine that selectively targets Plasmodium falciparum PKG, inhibits blood stage parasite growth in vitro and in mice and blocks transmission to mosquitoes