We present the discovery and follow-up observations of the afterglow of the Gamma-Ray Burst (GRB) 011121 and its associated supernova SN 2001ke. Images were obtained with the OGLE 1.3m telescope in BV RI passbands, starting 10.3 hours after the burst. The temporal analysis of our early data indicates a steep decay, independent of wavelength with F ν ∝ t −1.72±0.05 . There is no evidence for a break in the light curve earlier than 2.5 days after the burst. The spectral energy distribution determined from the early broad-band photometry is a power-law with F ν ∝ ν −0.66±0.13 after correcting for a large reddening. Spectra, obtained with the Magellan 6.5m Baade telescope, reveal narrow emission lines from the host galaxy which provide a redshift of z = 0.362 ± 0.001 to the GRB. We also present late R and J-band observations of the afterglow ∼ 7 − 17 days after the burst. The late-time photometry shows a large deviation from the initial decline and our data combined with Hubble Space Telescope photometry provide strong evidence for a supernova peaking about 12 rest-frame days after the GRB. The first spectrum ever obtained of a GRB supernova at cosmological distance revealed a blue continuum. SN 2001ke was more blue near maximum than SN 1998bw and faded more quickly which demonstrates that a range of properties are possible in supernovae which generate GRBs. The blue color is consistent with a supernova interacting with circumstellar gas and this progenitor wind is also evident in the optical afterglow. This is the best evidence to date that classical, long gamma-ray bursts are generated by core-collapse supernovae.Subject headings: gamma-rays: bursts -supernovae: general -supernovae: individual (SN 2001ke) 1 Based on data from the OGLE 1.3m and the Magellan 6.5m Baade telescopes and the Hubble Space Telescope.

We describe the design, development, and performance of HAWK-I, the new High-Acuity Wide-field K-band Imager for ESO's Very Large Telescope, which is equipped with a mosaic of four 2 k × 2 k arrays and operates from 0.9−2.4 μm over 7.5 × 7.5 with 0.1 pixels. A novel feature is the use of all reflective optics that, together with filters of excellent throughput and detectors of high quantum efficiency, has yielded an extremely high throughput. Commissioning and science verification observations have already delivered a variety of excellent and deep images that demonstrate its high scientific potential for addressing important astrophysical questions of current interest.

Astrometric detection and mass determination of Earth-mass exoplanets requires sub-µas accuracy, which is theoretically possible with an imaging space telescope using field stars as an astrometric reference. The measurement must however overcome astrometric distortions which are much larger than the photon noise limit. To address this issue, we propose to generate faint stellar diffraction spikes using a teo-dimensional grid of regularly spaced small dark spots added to the surface of the primary mirror (PM). Accurate astrometric motion of the host star is obtained by comparing the position of the spikes to the background field stars. The spikes do not contribute to scattered light in the central part of the field and therefore allow unperturbed coronagraphic observation of the star's immediate surrounding. Because the diffraction spikes are created on the PM and imaged on the same focal plane detector as the background stars, astrometric distortions affect equally the diffraction spikes and the background stars, and are therefore calibrated. We describe the technique, detail how the data collected by the wide-field camera are used to derive astrometric motion, and identify the main sources of astrometric error using numerical simulations and analytical derivations. We find that the 1.4 m diameter telescope, 0.3 deg 2 field we adopt as a baseline design achieves 0.2 µas single measurement astrometric accuracy. The diffractive pupil concept thus enables sub-µas astrometry without relying on the accurate pointing, external metrology or high stability hardware required with previously proposed high precision astrometry concepts. Subject headings: astrometry -telescopes -techniques: high angular resolution -planets and satellites: detection 1.2. Brief overview of the technique Astrometric measurement from wide-field images is fundamentally limited, in a perfect system, by photon noise and sampling effects, which are quantified in the Appendix and taken into account in this paper for numerical performance estimates. These fundamental limits are however not the focus of this paper, which is aimed at providing a solution to the three main practical challenges to performing precision absolute astrometry of a bright star from a wide-field image when using numerous faint field stars as the astrometric reference.

Extra-solar planets direct imaging is now a reality with the deployment and commissioning of the first generation of specialized ground-based instruments (GPI, SPHERE, P1640 and SCExAO). These systems allow of planets 10 7 times fainter than their host star. For space-based missions (EXCEDE, EXO-C, EXO-S, WFIRST), various teams have demonstrated laboratory contrasts reaching 10 −10 within a few diffraction limits from the star. However, all of these current and future systems are designed to detect faint planets around a single host star or unresolved multiples, while most non M-dwarf stars such as Alpha Centauri belong to multi-star systems. Direct imaging around binaries/multiple systems at a level of contrast allowing Earth-like planet detection is challenging because the region of interest is contaminated by the hosts star companion as well as the host Generally, the light leakage is caused by both diffraction and aberrations in the system. Moreover, the region of interest usually falls outside the correcting zone of the deformable mirror (DM) for the companion. Until now, it has been thought that removing the light of a companion star is too challenging, leading to the exclusion of binary systems from target lists of direct imaging coronographic missions.In this paper, we will show different new techniques for high-contrast imaging of planets around multi-star systems and detail the Super-Nyquist Wavefront Control (SNWC) method, which allows to control wavefront errors beyond nominal control region of the DM. Using the SNWC we reached contrasts around 5 × 10 −9 in a 10% bandwidth.