C. Felizardo

Observations of DG Tauri with the Keck Interferometer

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.

Keck Interferometer Nuller Data Reduction and On-Sky Performance

We describe the Keck Interferometer nuller theory of operation, data reduction, and on-sky performance, particularly as it applies to the nuller exozodiacal dust key science program that was carried out between 2008 February and 2009 January. We review the nuller implementation, including the detailed phasor processing involved in implementing the null-peak mode used for science data and the sequencing used for science observing. We then describe the Level 1 reduction to convert the instrument telemetry streams to raw null leakages, and the Level 2 reduction to provide calibrated null leakages. The Level 1 reduction uses conservative, primarily linear processing, implemented consistently for science and calibrator stars. The Level 2 processing is more flexible, and uses diameters for the calibrator stars measured contemporaneously with the interferometer’s K-band cophasing system in order to provide the requisite accuracy. Using the key science data set of 462 total scans, we assess the instrument performance for sensitivity and systematic error. At 2.0 Jy we achieve a photometrically-limited null leakage uncertainty of 0.25% rms per 10 minutes of integration time in our broadband channel. From analysis of the Level 2 reductions, we estimate a systematic noise floor for bright stars of ~0.2% rms null leakage uncertainty per observing cluster in the broadband channel. A similar analysis is performed for the narrowband channels. We also provide additional information needed for science reduction, including details on the instrument beam pattern and the basic astrophysical response of the system, and references to the data reduction and modeling tools.

The Keck Interferometer

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.

Finite-Fault Rupture Detector (FinDer): Going Real-Time in Californian ShakeAlert Warning System

Rapid detection of local and regional earthquakes and issuance of fast alerts for impending shaking is considered beneficial to save lives, reduce losses, and shorten recovery times after destructive events (Allen et al., 2009). Over the last two decades, several countries have built operational earthquake early warning (EEW) systems, including Japan (Hoshiba et al., 2008), Mexico (Espinosa-Aranda et al., 1995), Romania (Mărmureanu et al., 2011), Turkey (Erdik et al., 2003), Taiwan (Hsiao et al., 2011), and China (Peng et al., 2011). Other countries, such as the United States (Bose, Allen, et al., 2013), Italy (Satriano et al., 2011), and Switzerland (Behr et al., 2015), are currently developing systems or evaluating algorithms in their seismic real-time networks.

Keck Interferometer nuller update

The Keck Interferometer combines the two 10 m Keck telescopes as a long baseline interferometer, funded by NASA, as a joint development among the Jet Propulsion Laboratory, the W. M. Keck Observatory, and the Michelson Science Center. Since 2004, it has offered an H- and K-band fringe visibility mode through the Keck TAC process. Recently this mode has been upgraded with the addition of a grism for higher spectral resolution. The 10 um nulling mode, for which first nulling data were collected in 2005, completed the bulk of its engineering development in 2007. At the end of 2007, three teams were chosen in response to a nuller key science call to perform a survey of nearby stars for exozodiacal dust. This key science observation program began in Feb. 2008. Under NSF funding, Keck Observatory is leading development of ASTRA, a project to add dual-star capability for high sensitivity observations and dual-star astrometry. We review recent activity at the Keck Interferometer, with an emphasis on the nuller development.

Self-phase-referenced spectro-interferometry on the Keck interferometer

As part of the astrometric and phase-referenced astronomy (ASTRA) project, three new science modes are being developed for the Keck Interferometer that extend the science capabilities of this instrument to include higher spectral resolution, fainter magnitudes, and astrometry. We report on the successful implementation of the first of these science modes, the self-phase-referencing mode, which provides a K-band (λ = 2.2 μm) spectral resolution of R ∼ 1000 on targets as faint as 7.8 mag with spatial resolution as fine as λ/B = 5 mas in the K band, with the 85 m interferometer baseline. This level of spectral resolution would not have been possible without a phase-referencing implementation extending the integration time limit imposed by atmospheric turbulence. For narrow spectral features, we demonstrate a precision of ± 0.01 on the differential V^2(λ), and ± 1.7 mrad on the differential phase Φ(λ), equivalent to a differential astrometry precision of ± 1.45 μas. This new Keck Interferometer instrument is typically used to study the geometry and location of narrow spectral features at high angular resolution, referenced to a continuum. By simultaneously providing spectral and spatial information, the geometry of velocity fields (e.g., rotating disks, inflows, outflows, etc.) larger than 150 km s^(-1) can also be explored.

Recent progress at the Keck Interferometer: operations and V2 science

The Keck Interferometer combines the two 10m diameter Keck telescopes for near-infrared fringe visibility, and mid-infrared nulling observations. We report on recent progress with an emphasis on new visibility observing capabilities, operations improvements for visibility and nulling, and on recent visibility science. New visibility observing capabilities include a grism spectrometer for higher spectral resolution. Recent improvements include a new AO output dichroic for increased infrared light throughput, and the installation of new wave-front controllers on both Keck telescopes. We also report on recent visibility results in several areas including (1) young stars and their circumstellar disks, (2) pre-main sequence star masses, and (3) Circumstellar environment of evolved stars. Details on nuller instrument and nuller science results, and the ASTRA phase referencing and astrometry upgrade, are presented in more detail elsewhere in this conference.

Earthquake Early Warning ShakeAlert System: West Coast Wide Production Prototype

Earthquake early warning (EEW) is an application of seismological science that can give people, as well as mechanical and electrical systems, up to tens of seconds to take protective actions before peak earthquake shaking arrives at a location. Since 2006, the U.S. Geological Survey has been working in collaboration with several partners to develop EEW for the United States. The goal is to create and operate an EEW system, called ShakeAlert, for the highest risk areas of the United States, starting with the West Coast states of California, Oregon, and Washington. In early 2016, the Production Prototype v.1.0 was established for California; then, in early 2017, v.1.2 was established for the West Coast, with earthquake notifications being distributed to a group of beta users in California, Oregon, and Washington. The new ShakeAlert Production Prototype was an outgrowth from an earlier demonstration EEW system that began sending test notifications to selected users in California in January 2012. ShakeAlert leverages the considerable physical, technical, and organizational earthquake monitoring infrastructure of the Advanced National Seismic System, a nationwide federation of cooperating seismic networks. When fully implemented, the ShakeAlert system may reduce damage and injury caused by large earthquakes, improve the nation’s resilience, and speed recovery.

First Keck Interferometer measurements in self-phase referencing mode: spatially resolving circum-stellar line emission of 48 Lib

Recently, the Keck interferometer was upgraded to do self-phase-referencing (SPR) assisted K-band spectroscopy at R ~ 2000. This means, combining a spectral resolution of 150 km/s with an angular resolution of 2.7 mas, while maintaining high sensitiviy. This SPR mode operates two fringe trackers in parallel, and explores several infrastructural requirements for off-axis phase-referencing, as currently being implemented as the KI-ASTRA project. The technology of self-phasereferencing opens the way to reach very high spectral resolution in near-infrared interferometry. We present the scientific capabilities of the KI-SPR mode in detail, at the example of observations of the Be-star 48 Lib. Several spectral lines of the cirumstellar disk are resolved. We describe the first detection of Pfund-lines in an interferometric spectrum of a Be star, in addition to Br γ. The differential phase signal can be used to (i) distinguish circum-stellar line emission from the star, (ii) to directly measure line asymmetries tracing an asymetric gas density distribution, (iii) to reach a differential, astrometric precision beyond single-telescope limits sufficient for studying the radial disk structure. Our data support the existence of a radius-dependent disk density perturbation, typically used to explain slow variations of Be-disk hydrogen line profiles.

First faint dual-field phase-referenced observations on the Keck interferometer

Ground-baseed long baselinne interferomeeters have lonng been limiteed in sensitiviity by the shoort integration periods imposed by atmospheric tuurbulence. Thee first observaation fainter thhan this limit wwas performedd on January 222, 2011 when the Keck Interferommeter observedd a K=11.5 taarget, about onne magnitude fainter than iits K=10.3 limmit. This observation wwas made posssible by the Duual Field Phase Referencing instrument of the ASTRA pproject: simultaaneously measuring thhe real-time efffects of the atmmosphere on a nearby bright guide star, andd correcting foor it on the fainnt target, integration tiime longer thaan the turbulennce time scale are made possible. As a preelude to this ddemonstration, we first present the implementatioon of Dual FField Phase RReferencing onn the interferoometer. We tthen detail itss on-sky performance focusing on tthe accuracy oof the turbulennce correction, and on the reesulting fringe contrast stabiility. We conclude witth a presentatioon of early resuults obtained wwith Laser Guidde Star AO andd the interferommeter.