ABSTRACT. The Keck Observatory began science observations with a laser guide star adaptive optics system, the first such system on an 8-10 m class telescope, in late 2004. This new capability greatly extends the scientific potential of the Keck II Telescope, allowing near-diffraction-limited observations in the near-infrared using natural guide stars as faint as 19th magnitude. This paper describes the conceptual approach and technical implementation followed for this system, including lessons learned, and provides an overview of the early science capabilities.

We report the first detection of a credible progenitor system for a Type Ic supernova (SN Ic), SN 2017ein. We present spectra and photometry of the SN, finding it to be similar to carbon-rich, low-luminosity SNe Ic. Using a post-explosion Keck adaptive optics image, we precisely determine the position of SN 2017ein in pre-explosion HST images, finding a single source coincident with the SN position. This source is marginally extended, and is consistent with being a stellar cluster. However, under the assumption that the emission of this source is dominated by a single point source, we perform point-spread function photometry, and correcting for line-of-sight reddening, we find it to have M F555W = −7.5 ± 0.2 mag and m F555W − m F814W =−0.67 ± 0.14 mag. This source is bluer than the main sequence and brighter than almost all Wolf-Rayet stars, however it is similar to some WC+O-and B-star binary systems. Under the assumption that the source is dominated by a single star, we find that it had an initial mass of 55 +20 −15 M ⊙ . We also examined binary star models to look for systems that match the overall photometry of the pre-explosion source and found that the best-fitting model is a 80+48 M ⊙ close binary system in which the 80 M ⊙ star is stripped and explodes as a lower mass star. Late-time photometry after the SN has faded will be necessary to cleanly separate the progenitor star emission from the additional coincident emission.

Near-infrared observations of the z = 2.286 IRAS source FSC 10214+4724, made with the near-infrared camera on t~e W. M. Keck Telescope, are reported. Deep broad-band images at 2.15 and 1.27 µm, and narrow-band images at 2.165 and 2.125 µm with 0':6 to 0''.9 seeing show that FSC 10214+4724 consists of at least t~ree distinct ~ompon~nts in a compact group of galaxies. The source of the infrared luminosity appears ~o be t~ a strongly mteractmg galaxy that has a luminosity ~ 100 times that of a present-day L * galaxy. The mteractton suggests an "age" of this galaxy of ~ 10 9 yr. The Hex emission is resolved as a source of diameter ~ 5 kpc, suggesting that a starburst contributes to the observed Hex emission. There is an excess of objects in the FSC 10214 + 4724 field that could represent galaxies in an associated cluster.

We present the first science results from the Keck Interferometer, a direct-detection infrared interferometer utilizing the two 10 m Keck telescopes. The instrument and system components are briefly described. We then present observations of the T Tauri object DG Tau, which is resolved by the interferometer. The resolved component has a radius of 0.12-0.24 AU, depending on the assumed stellar and extended component fluxes and the model geometry used. Possible origins and implications of the resolved emission are discussed.

The Keck Interferometer (KI) combined the two 10 m W. M. Keck Observatory telescopes on Mauna Kea, Hawaii, as a long-baseline near-and mid-infrared interferometer. Funded by NASA, it operated from 2001 until 2012. KI used adaptive optics on the two Keck telescopes to correct the individual wavefronts, as well as active fringe tracking in all modes for path-length control, including the implementation of cophasing to provide long coherent integration times. KI implemented high sensitivity fringe-visibility measurements at H (1:6 μm), K (2:2 μm), and L (3:8 μm) bands, and nulling measurements at N band (10 μm), which were used to address a broad range of science topics. Supporting these capabilities was an extensive interferometer infrastructure and unique instrumentation, including some additional functionality added as part of the NSF-funded ASTRA program. This paper provides an overview of the instrument architecture and some of the key design and implementation decisions, as well as a description of all of the key elements and their configuration at the end of the project. The objective is to provide a view of KI as an integrated system, and to provide adequate technical detail to assess the implementation. Included is a discussion of the operational aspects of the system, as well as of the achieved system performance. Finally, details on V 2 calibration in the presence of detector nonlinearities as applied in the data pipeline are provided.