The Project 1640 instrument on the 200-inch Hale telescope at Palomar Observatory is a coronagraphic instru- ment with an integral eld spectrograph at the back end, designed to nd young, self-luminous planets around nearby stars. To reach the necessary contrast for this, the PALM-3000 adaptive optics system corrects for fast atmospheric speckles, while CAL, a phase-shifting interferometer in a Mach-Zehnder con guration, measures the quasistatic components of the complex electric eld in the pupil plane following the coronagraphic stop. Two additional sensors measure and control low-order modes. These eld measurements may then be combined with a system model and data taken separately using a white-light source internal to the AO system to correct for both phase and amplitude aberrations. Here, we discuss and demonstrate the procedure to maintain a half-plane dark hole in the image plane while the spectrograph is taking data, including initial on-sky performance.
P1640 calibrator is a wavefront sensor working with the P1640 coronagraph and the Palomar 3000 actuator
adaptive optics system (P3K) at the Palomar 200 inch Hale telescope. It measures the wavefront by interfering
post-coronagraph light with a reference beam formed by low-pass filtering the blocked light from the coronagraph
focal plane mask. The P1640 instrument has a similar architecture to the Gemini Planet Imager (GPI) and its
performance is currently limited by the quasi-static speckles due to non-common path wavefront errors, which
comes from the non-common path for the light to arrive at the AO wavefront sensor and the coronagraph mask.
By measuring the wavefront after the coronagraph mask, the non-common path wavefront error can be estimated
and corrected by feeding back the error signal to the deformable mirror (DM) of the P3K AO system. Here, we
present a first order wavefront estimation algorithm and an instrument calibration scheme used in experiments
done recently at Palomar observatory. We calibrate the P1640 calibrator by measuring its responses to poking
DM actuators with a sparse checkerboard pattern at different amplitudes. The calibration yields a complex
normalization factor for wavefront estimation and establishes the registration of the DM actuators at the pupil
camera of the P1640 calibrator, necessary for wavefront correction. Improvement of imaging quality after feeding
back the wavefront correction to the AO system demonstrated the efficacy of the algorithm.
Project 1640, a high-contrast spectral-imaging effort involving a coordinated set of instrumentation and software, built at
AMNH, JPL, Cambridge and Caltech, has been commissioned and is fully operational. This novel suite of
instrumentation includes a 3388+241-actuator adaptive optics system, an optimized apodized pupil Lyot coronagraph, an
integral field spectrograph, and an interferometric calibration wave front sensor. Project 1640 is the first of its kind of
instrumentation, designed to image and characterize planetary systems around nearby stars, employing a variety of
techniques to break the speckle-noise barrier. It is operational roughly one year before any similar project, with the goal
of reaching a contrast of 10-7 at 1 arcsecond separation. We describe the instrument, highlight recent results, and
document on-sky performance at the start of a 3-year, 99-night survey at the Palomar 5-m Hale telescope.
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.
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
The Keck Interferometer Nuller (KIN) is now largely in place at the Keck Observatory, and functionalities and
performance are increasing with time. The main goal of the KIN is to examine nearby stars for the presence of exozodiacal
emission, but other sources of circumstellar emission, such as disks around young stars, and hot exoplanets are
also potential targets. To observe with the KIN in nulling mode, knowledge of the intrinsic source spectrum is essential,
because of the wide variety of wavelengths involved in the various control loops - the AO system operates at visible
wavelengths, the pointing loops use the J-band, the high-speed fringe tracker operates in the K-band, and the nulling
observations take place in the N-band. Thus, brightness constraints apply at all of these wavelengths. In addition, source
structure plays a role at both K-band and N-band, through the visibility. In this talk, the operation of the KIN is first
briefly described, and then the sensitivity and performance of the KIN is summarized, with the aim of presenting an
overview of the parameter space accessible to the nuller. Finally, some of the initial observations obtained with the KIN
We describe the results of laboratory experiments, using a mock-up stellar interferometer equipped with specialized hardware, undertaken to measure differential-phase to considerable precision (0.1 mrad) over an octave of bandwidth in the infrared. Differential-phase is a precision technique that can detect subtle temporal changes in the relative (color-dependent) photocenter of an astronomical target - making it useful for direct detection of some hot-Jupiter planets from the ground. The set up described herein was built as part of the Keck Interferometer project.
The Keck Interferometer Nuller (KIN) will be used to examine nearby stellar systems for the presence of circumstellar exozodiacal emission. A successful pre-ship review was held for the KIN in June 2004, after which the KIN was shipped to the Keck Observatory. The integration of the KIN's many sub-systems on the summit of Mauna Kea, and initial on-sky testing of the system, has occupied the better part of the past year. This paper describes the KIN system-level configuration, from both the hardware and control points of view, as well as the current state of integration of the system and the measurement approach to be used. During the most recent on-sky engineering runs in May and July 2005, all of the sub-systems necessary to measure a narrowband null were installed and operational, and the full nulling measurement cycle was carried out on a star for the first time.
Mid-infrared (8-13μm) nulling is a key observing mode planned for the NASA-funded Keck Interferometer at the Keck Observatory on the summit of Mauna Kea in Hawaii. By destructively interfering and thereby canceling the on-axis light from nearby stars, this observing mode will enable the characterization of the faint emission from exo-zodiacal dust surrounding these stellar systems. We report here the null leakage error budget and pre-ship results obtained in the laboratory after integration of the nulling beam combiner with its mid-infrared camera and key components of the Keck Interferometer. The mid-infrared nuller utilizes a dual-polarization, modified Mach-Zehnder (MMZ) beam combiner in conjunction with an atmospheric dispersion corrector to achieve broadband achromatic nulling.
The first high-dynamic-range interferometric mode planned to come on line at the Keck Observatory is mid-infrared nulling. This observational mode, which is based on the cancellation of the on-axis starlight arriving at the twin Keck telescopes, will be used to examine nearby stellar systems for the presence of circumstellar exozodiacal emission. This paper describes the system level layout of the Keck Interferometer Nuller (KIN), as well as the final performance levels demonstrated in the laboratory integration and test phase at the Jet Propulsion Laboratory prior to shipment of the nuller hardware to the Keck Observatory in mid-June 2004. On-sky testing and observation with the mid-infrared nuller are slated to begin in August 2004.
One of the science goals of NASA's Navigator program is ground-based narrow-angle astrometry for extra-solar planet detection, which could be done as part of the proposed Outrigger Telescopes Project. The narrow-angle measurement process, which would use the outrigger telescopes, starts with the determination of the conventional interferometer astrometric baseline, determined from wide-angle astrometry of Hipparcos stars. A baseline monitor system would be employed at each outrigger telescope. This system monitors the pivot point of each telescope - the end point of the astrometric baseline - to measure telescope imperfections that would cause the baseline to vary with telescope rotation. The baseline monitor includes azimuth and elevation cameras that monitor runout along the azimuth and elevation axes of the telescopes. In conjunction with the baseline monitor system, a pivot monitor camera in the dual-star module is used to register the laser metrology corner-cube reflector to the telescope pivot, tying the narrow-angle baseline, which applies to the narrow-angle astrometric measurement, to the wide-angle baseline. In this paper we present the proposed designs for the baseline monitor and pivot-point camera.
The fringe detection and tracking system of the Keck Interferometer, Fatcat, has been operational ever since first fringes at Keck, albeit not in full capacity. At present it supports single baseline (Keck-Keck) operations only. We briefly discuss the instrument design from a hardware and controls standpoint. We also show some recent data from the instrument and summarize some performance limits.
A key thrust of NASA's Origins program is the development of
astronomical interferometers. Pursuing this goal in a cost-effective and expedient manner from the ground has led NASA to develop the Keck Interferometer, which saw first fringes between the twin 10m Keck telescopes in March of 2001. In order to enhance the imaging potential of this facility, and to add astrometric capabilities for the detection of giant planets about nearby stars, four 1.8 m 'outrigger' telescopes may be added to the interferometer. Robust performance of the multi-aperture instrument will require precise alignment of the large number of optical elements found in the six optical beamtrains spread about the observatory site. The requirement for timely and reliable alignments dictated the development of an automatic alignment system for the Keck Interferometer. The autoaligner consists of swing-arm actuators that insert light-emitting diodes on the optical axis at the location of each optical element, which are viewed by a simple fixed-focus CCD camera at the end of the beamtrain. Sub-pixel centroiding is performed upon the slightly out-of-focus target spots using images provided by a frame grabber, providing steering information to the two-axis actuated optical elements. Resulting mirror-to-mirror alignments are good to within 2 arcseconds, and trimming the alignment of a full beamtrain is designed to take place between observations, within a telescope repointing time. The interactions of the autoaligner with the interferometer delay lines and coude trains are discussed in detail. The overall design of the interferometer's autoaligner system is presented, examining the design philosophy, system sequencing, optical element actuation, and subsystem co-alignment, within the context of satisfying performance requirements and cost constraints.