By analyzing global covariance matrices from the imaka GLAO system at the UH 2.2m telescope, it is possible to reconstruct ground layer strength, the integrated turbulence strength as well as the vertical turbulence profile. These are compared to simultaneous profiles obtained by the Maunakea facility MASS/DIMM. A method has been developed to directly compute the phase structure function from the covariances of the slopes, obtained from the telemetry data. The phase structure function allows to test the validity of the Kolmogorov (or van Karman) model and the spatial frequency content of the turbulence: Dome and telescope tube seeing are expected to have an excess of high spatial frequencies, which is detrimental to the PSF by amplifying the halo, and which the AO system cannot correct. The telescope, the dome and their interaction with the ground layer produce a complex environment for the turbulence. We are therefore developing a small, portable optical turbulence sensor which we will be able to use to scan the dome and telescope tube to quantify the local presence of turbulence. This is the AIR-FLOW (Airborne Interferometric Recombiner - Fluctuations of Light at Optical Wavelengths) project. With imaka and AIR-FLOW we hope to generate a coherent and quantitative account of the turbulence type and strength present in the telescope beam and to accurately match this detailed phase information to the focal plane images. Such a level of detail is required to understand and eventually be able to control the local environment for optimized image quality. We foresee this expertise will be especially valuable for ELTs, where the halo around the PSF will act like an extra source of background.
We present on-sky results from the wide field ground-layer adaptive optics (GLAO) system on the University of Hawaii 2.2-meter telescope on Maunakea. We demonstrate improvements in image quality at visible wavelengths under a variety of seeing conditions. We discuss the gains for a variety of figures of merit including the full-width at half-maximum, the equivalent noise area, and the encircled energy diameter. These gains and figures of merit are discussed in the context of our GLAO science cases. In addition, we present the system image quality error budget, measurements of the dominant error terms, and their impact on the delivered focal plane images.
We present the integration status for 'imaka, the ground-layer adaptive optics (GLAO) system on the University of Hawaii 2.2-meter telescope on Maunakea, Hawaii. This wide-field GLAO pathfinder system exploits Maunakea's highly confined ground layer and weak free-atmosphere to push the corrected field of view to ∼1/3 of a degree, an areal field approaching an order of magnitude larger than any existing or planned GLAO system, with a FWHM ∼ 0.33" in the visible and near infrared. We discuss the unique design aspects of the instrument, the driving science cases and how they impact the system, and how we will demonstrate these cases on the sky.
We present high resolution optical turbulence profiles of the dome and ground-layers measured using a set of Shack-
Hartmann wavefront sensors deployed over a field of view of between 0.5 and 1.0 degrees at the focal planes of the
University of Hawaii 2.2-m telescope and the Canada-France-Hawaii Telescope on Maunakea, Hawaii. Observations with the experiment were made over the course of several nights on each telescope. We obtain estimates of the strength, distribution, and velocities of optical turbulence from the covariance matrices and maps of the measured wavefront gradients and a decomposition of the measured wavefronts into Zernike polynomials. We find agreement with previous measurements on Maunakea that the ground layer is largely confined within the first tens of meters above the ground and moves at the ground wind velocity. In addition, we spatially resolve the optical turbulence that arises from within the dome. For both facilities we find that the dome seeing is a major component of the overall turbulence strength accounting for more than half of the turbulence within the ground layer and that the dome seeing changes very slowly with a characteristic frequency of less than 1 Hz. While the variety of observing conditions sampled is low, we find that the characteristics of the dome seeing with observation elevation angle and the azimuth angle with respect to the ground wind are quite different on the two telescopes suggesting a different origin to the seeing within the two enclosures.
Astronomy with ground-layer adaptive optics systems will push observations with AO to much larger fields of view than previously achieved. Observations such as astrometry of stars in crowded stellar fields and deep searches for very distant star-forming galaxies pushes the systems to the widest possible fields of view. Optical turbulence profiles on Maunakea, Hawaii suggest that such a system could deliver corrected fields of view several tens of arcminutes in size at resolutions close to the free-atmosphere seeing. We present the status of a pathfinder wide field of view ground-layer adaptive optics system on the UH2.2m telescope that will demonstrate key cases and serve as a test bed for systems on larger telescopes and for systems with even larger fields of view.
From 2008 December to 2012 September, the NICI (Near-Infrared Coronagraphic Imager at the Gemini-South 8.1-m) Planet-Finding Campaign (Liu et al. 2010) obtained deep, high-contrast AO imaging of a carefully selected sample of over 200 young, nearby stars. In the course of the campaign, we discovered four co-moving brown dwarf companions: PZ Tel B (36±6 MJup, 16.4±1.0 AU), CD-35 2722B (31±8 MJup, 67±4 AU), HD 1160B (33+12 -9 MJup, 81± AU), and HIP 79797Bb (55+20-19MJup, 3 AU from the previously known brown dwarf companion HIP 79797Ba), as well as numerous stellar binaries. Three survey papers have been published to date, covering: 1) high mass stars (Nielsen et al. 2013), 2) debris disk stars (Wahhaj et al. 2013), and 3) stars which are members of nearby young moving groups (Biller et al. 2013). In addition, the Campaign has yielded new orbital constraints for the ~8-10 MJup planet Pic β (Nielsen et al. 2014) and a high precision measurement of the star-disk offset for the well-known disk around HR 4796A (Wahhaj et al. 2014). Here we discuss constraints placed on the distribution of wide giant exoplanets from the NICI Campaign, new substellar companion discoveries, and characterization both of exoplanets and circumstellar disks.
Ground-layer adaptive optics (GLAO) has the potential to dramatically increase the efficiency and capabilities of
existing ground-based telescopes over a broad range of astronomical science. Recent studies of the optical turbulence
above several astronomical sites (e.g. Mauna Kea, Paranal, and Antarctica) show that GLAO can be extended to fields of
view of several tens of arcminutes in diameter, larger than previously thought, with angular resolutions close to the freeatmosphere
seeing. This is a pivotal result since GLAO science cases benefit from the largest possible corrected fields
of view. The corrected areal field of a GLAO system is potentially 2-3 orders of magnitude larger than has been
demonstrated to date. The 'Imaka team is working toward an instrument that takes advantage of the one-degree field
afforded by Mauna Kea. In this paper we summarize the design/simulation work to date along with our plan to develop
an instrument that reaches for this wide field of view.
Our team is carrying out a multi-year observing program to directly image and characterize young extrasolar
planets using the Near-Infrared Coronagraphic Imager (NICI) on the Gemini-South 8.1-meter telescope. NICI
is the first instrument on a large telescope designed from the outset for high-contrast imaging, comprising a
high-performance curvature adaptive optics (AO) system with a simultaneous dual-channel coronagraphic imager.
Combined with state-of-the-art AO observing methods and data processing, NICI typically achieves ≈2
magnitudes better contrast compared to previous ground-based or
space-based planet-finding efforts, at separations
inside of ≈2". In preparation for the Campaign, we carried out efforts to identify previously unrecognized
young stars as targets, to develop a rigorous quantitative method for constructing our observing strategy, and to
optimize the combination of angular differential imaging and spectral differential imaging. The Planet-Finding
Campaign is in its second year, with first-epoch imaging of 174 stars already obtained out of a total sample of
300 stars. We describe the Campaign's goals, design, target selection, implementation, on-sky performance, and
preliminary results. The NICI Planet-Finding Campaign represents the largest and most sensitive imaging survey
to date for massive
(>~ 1 MJup) planets around other stars. Upon completion, the Campaign will establish the best
measurements to date on the properties of young gas-giant planets at
-> 5-10 AU separations. Finally, Campaign
discoveries will be well-suited to long-term orbital monitoring and detailed spectrophotometric followup with
next-generation planet-finding instruments.
We discuss observing strategy for the Near Infrared Coronagraphic Imager (NICI) on the 8-m Gemini South
telescope. NICI combines a number of techniques to attenuate starlight and suppress superspeckles: 1) coronagraphic
imaging, 2) dual channel imaging for Spectral Differential Imaging (SDI) and 3) operation in a fixed
Cassegrain rotator mode for Angular Differential Imaging (ADI). NICI will be used both in service mode and
for a dedicated 50 night planet search campaign. While all of these techniques have been used individually in
large planet-finding surveys, this is the first time ADI and SDI will be used with a coronagraph in a large survey.
Thus, novel observing strategies are necessary to conduct a viable planet search campaign.
We present the coronagraphic and adaptive optics performance of the Gemini-South Near-Infrared Coronagraphic Imager (NICI). NICI includes a dual-channel imager for simultaneous spectral difference imaging, a dedicated 85-element curvature adaptive optics system, and a built-in Lyot coronagraph. It is specifically designed to survey for and image large extra-solar gaseous planets on the Gemini Observatory 8-meter telescope in Chile. We present the on-sky performance of the individual subsystems along with the end-to-end contrast curve. These are compared to our model predictions for the adaptive optics system, the coronagraph, and the spectral difference imaging.
The Near-Infrared Coronagraphic Imager (NICI) is a high-contrast AO imager at the
Gemini South telescope. The camera includes a coronagraphic mask and dual channel imaging
for Spectral Differential Imaging (SDI). The instrument can also be used in a fixed Cassegrain
Rotator mode for Angular Differential Imaging (ADI). While coronagraphy, SDI, and ADI have
been applied before in direct imaging searches for exoplanets. NICI represents the first time that
these 3 techniques can be combined. We present preliminary NICI commissioning data using
these techniques and show that combining SDI and ADI results in significant gains.
The design of the Redstar3 array control system including operational requirements and performance is presented. The architecture is intended to support next generation large format infrared/optical arrays and mosaics by using a new scalable approach that takes advantage of commercially available electronics. Specifically, an approach of using a combination of high speed fiber links, networked PCs and Linux to replace the previous generation of VME based DSPs will be discussed in detail. The design will be used to control HAWAII-2RG (1-4.9μm 2Kx2K HgCdTe), Aladdin II and III (1-5 μm 1Kx1K InSb) arrays in facility class instruments for Gemini, NSO and IRTF. It is also intended to be the platform for high count curvature correction, waveform sense and control for adaptive optics.
The Near Infrared Coronagraphic Imager for Gemini South (NICI) is a dual beam coronagraphic camera operating over the 1.0 to 5.5 micrometer wavelength range with a dedicated adaptive optics system. NICI target science, design and capabilities will be described as an introduction to this instrument slated for deployment in mid 2005.
In order to extend the US Naval Observatory (USNO) small-angle astrometric capabilities to near infrared wavelengths we have designed and manufactured a 1024 x 1024 InSb re-imaging infrared camera equipped with an array selected from the InSb ALADDIN (Advanced Large Area Detector Development in InSb) development
program and broadband and narrowband 0.8 - 3.8 μm filters. Since the USNO 1.55-m telescope is optimized for observations at visible wavelengths with an oversized secondary mirror and sky baffles, the straylight rejection capabilities of the ASTROCAM Lyot stop and baffles are of critical importance for its sensitivity and flat-
fielding capabilities. An Offner relay was chosen for the heart of the system and was manufactured from the same melt of aluminum alloy to ensure homologous contraction from room temperature to 77 K. A blackened cone was installed behind the undersized hole (the Lyot stop) in the Offner secondary. With low distortion, a well-sampled point spread function, and a large field of view, the system is well suited for astrometry. It is telecentric, so any defocus will not result in a change of image scale. The DSP-based electronics allow readout of the entire array with double-correlated sampling in 0.19 seconds, but shorter readout is possible with single sampling or by reading out only small numbers of subarrays. In this paper we report on the optical, mechanical, and electronic design of the system and present images and results on the sensitivity and astrometric stability obtained with the system, now operating routinely at the 1.55-m telescope with a science-grade ALADDIN array.
The IRTF is a 3.0 meter, f/38, infrared optimized, cassegrain telescope operated under contract from NASA with the primary mission of providing ground-based support for NASA's planetary missions. We are currently in the design and construction phase of a 36 element, curvature-based, natural guide star, adaptive optics facility installation for the IRTF. System architecture will be modeled on the highly successful AO systems developed at the University of Hawaii. The system should achieve an AO efficiency, q >= 0.4. The Strehl ratio is expected to exceed 0.8 in the K band. We estimate a limiting guide star magnitude for full correction of mR equals 14.4.
SpeX is a medium-resolution 0.8-5.5 micrometers cryogenic spectrograph being built at the Institute for Astronomy, University of Hawaii, for the NASA IR Telescope Facility on Mauna Kea. SpeX was funded by the National Science Foundation in July 1994. First-light is expected in 1999. The primary scientific driver of the instrument is to provide maximum simultaneous wavelength coverage at a spectral resolving power which is well-matched to many planetary, stellar and galactic features, and which adequately separates sky emission lines and disperses sky spectral resolutions of R approximately 1000-2000 simultaneously across 0.9-2.5 micrometers , 2.0-4.2 micrometers , or 2.4- 5.5 micrometers . SpeX will use an Aladdin II 1024 X 1024 InSb array in its spectrograph and an Aladdin II 512 X 512 InSb array in its IR slit-viewer.
Imaging planets, brown dwarfs and disks around nearby stars is a challenging endeavor due to the required scene contrast. Success requires imaging down to m equals 20-25 within arcseconds of stars that are 4th-6th magnitude. Light scattered and diffracted from a variety of sources increases the background flux in the area of interest by orders of magnitude masking the target objects. As first shown by M. B. Lyot in 1939 masks can be placed in the focal pane and pupil planes of a camera to occult the bright central source making it possible to image the faint extensions around it. CoCo is an experiment in using a coronagraphic camera, for IR observations, on a large telescope in an effort to understand how a coronagraph can help and how to properly design one of the new generation of large telescopes. Recent result with CoCo show a factor of 5-10 reduction in background levels in the area from 2-7 arcseconds from the central object. This paper will describe those result and summarize what has been learned towards building coronagraphic cameras for today's large telescopes.
The NASA IRTF is building a multiple digital signal processor (DSP) based array electronics control system for SpeX, an NSF funded 1 to 5 micron medium resolution spectrograph. SpeX will use a 1024 X 1024 InSb array for spectroscopy and one 512 X 512 quadrant of another 1024 X 1024 InSb array for slit field viewing and IR guiding. An additional system is also being produce at the Institute for Astronomy for the SUBARU IR camera and spectrograph (IRCS). Plans for IRCS include the use of a 1024 X 1024 InSb array for spectroscopy and one 1024 X 1024 InSb array for IR imaging. This document will provide the instrument derived requirements, an overall system description, and some of the tradeoffs and technical choices made. The design for both system is an evolutionary upgrade of the current IRTF array control electronics system used in a 256 X 256 InSb based imager, a 256 X 256 InSb and 512 X 512 CCD in an echelle spectrograph, an 800 X 800 CCD based tiptilt correction system and a non-IRTF 128 X 128 Si:As BIB array based imager.
Over the past 6 years the instrumentation team at the NASA IR Telescope Facility (IRTF) has designed and built 3 major facility instruments, two cameras and a spectrometer, for use by the IR astronomical community. We will report on many new techniques for cryostat construction that have been developed that deviate from traditional practices. These include aluminum electron beam welded vacuum and cryogenic enclosures, rectangular cryostat formats, use of closed cycle coolers and their performance, use of all aluminum structures, optimization of cryogenic performance without super insulation, activated charcoal getters, and optomechanical mounting. Cryostat performance data and methods for estimating cryostat performance will also be included.
This paper describes the design of an IR cold coronagraph (CoCo) built by SETS Technology, Inc., for use at the NASA 3 m IR Telescope Facility (IRTF) at Mauna Kea Observatory, for the imaging of faint IR sources in proximity to bright sources. The coronagraph is designed to obtain high contrast photometric images by use of an occulting mask and a pupil mask. The coronagraph is to be used in combination with the IRTF NSFCAM, which covers 1-5 micrometers and uses a 256x256 InSb array. The platescale can be varied from 0.06'/pixel to 0.15'/pixel, covering a field of view of 14' and 38', respectively. Selectable apodized and hard occulting masks are mounted on a wheel as the first element in the system to reduce scattered light. Selectable pupil masks are cooled to 77K within the CoCo cryostat. The cryostat consists of a liquid nitrogen can for cooling the optics, masks, and baffles. The CoCo dewar is mounted on a slide in a housing to allow it to move out of the beam path so that the NSFCAM may be used with or without the coronagraph during the same observing period.
The NASA Infrared Telescope Facility is a 3 meter infrared optimized telescope available to the astronomical community based on a peer reviewed applications. Efforts underway for two years to reduce the telescope emission in the infrared have reduced the telescope emissivity by more than a factor of two. This paper will report on the present telescope emissivity, the method used to measure the telescope emissivity, and cleaning procedures.
We have just recently commissioned a new 1.0-5.5 micrometers IR array camera for the NASA IR Telescope Facility based upon the Santa Barbara Research Center 256x256 InSb array. The primary features of this new instrument are three user-selected platescales, a variety fo fixed bandpass filters, 1 to 2% spectral resolution circular variable filters, coronagraph masks, polarization imaging capability, an optical guider/imager, and a grism. In this paper we briefly outline the design and performance of the camera system, describe some unique operating modes, and show some recent images.
The design of a multichannel occultation photometer built under NASA contract to SETS Technology, Inc., for the NASA 3-m IR telescope facility (IRTF) and the JPL Table Mountain telescope is described. This instrument acquires data in four selectable passbands (two 1 to 5 micrometers channels and two 10 to 20 micrometers channels), with very high sensitivity and approximately 100% duty cycle on-source during chopping. The optics are optimized for uniform response across an aperture of up to 20 arcseconds on the IRTF. The cryogenic system is a two-can cryostat with one liquid nitrogen can for cooling the radiation shields, optics, filters, and baffles, and a liquid helium can for cooling the IR detectors. The instrument operates two types of IR detector technologies. The 1 to 5 micrometers detectors are low-capacitance, single-element InSb detectors. The 10 micrometers detectors are blocked impurity band detectors. The instrument also has a 64 by 64 visible CCD array as an additional channel for guiding and visible photometry. A global positioning system unit is incorporated into the system for time and location stamping of occultation events. The instrument design and construction are discussed.
The design of a multipurpose 1 - 5.5 micrometers infrared camera (NSFCAM) for the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, is described. The camera is built around the new 256 X 256 InSb array manufactured by Santa Barbara Research Center (SBRC) and incorporates a variety of observing modes to fulfill its role as a major facility instrument. These include three remotely-selectable image scales, a selection of fixed bandpass filters, R equals 50 - 100 spectral resolution circularly variable filters, a grism, coronographic masks, and a polarization imaging capability. Through the use of flexible array clocking schemes, driven by programmable digital signal processors (DSPs), we plan to implement several new operating modes, including real-time shift and add for image stabilization, and fast subarray readouts for occultations. Simultaneous optical and infrared imaging of the same field will be possible through the use of a cold dichroic beamsplitter. This feature is primarily intended for use with the IRTF tip-tilt image stabilization system currently being built. Given a suitable guide star, the camera should achieve near-diffraction limited imaging at 2 - 5 micrometers . In this paper we discuss the design of the optics, cryogenic, electronics and software needed to provide the camera with these capabilities.
A 1 - 5.4 micrometers Cryogenic Echelle Spectrograph (CSHELL) for the NASA Infrared Telescope Facility is described. It achieves a resolving power of 5,000 to 40,000 using slits ranging from 4.0' to 0.5' in width and 30' long. It operates in a single-order long-slit mode, and a circular variable filter is used as an order sorter. Two infrared arrays are employed to achieve spectral coverage from 1 - 5.4 micrometers : a 256 X 256 HgCdTe NICMOS-3 array for 1 - 2.5 micrometers and a SBRC 58 X 62 InSb array for 2.8 - 5.4 micrometers . A closed- cycle cooler is employed to keep the optics and supporting structure at 73 K and to maintain the detectors at their proper operating temperatures. The entire spectrograph fits within an envelope of 64 cm X 35 cm X 27 cm. The instrument is controlled by a microcomputer mounted on the telescope, but the observer commands the instrument from a UNIX X Windows workstation on the Internet. This use of the Internet for communication between instrument control and user interface computers facilitates remote observing. A limiting magnitude of 12.3 mag is achieved for S/N equals 10 in 1 hour integration time, at resolving power of 20,000 at 2.2 micrometers wavelength.
As part of the Canada-France-Hawaii Telescope's (CFHT) New Imaging Program we recently fabricated a pair of 1.0 - 2.5 micrometers facility cameras, known as 'Redeye'. Each camera uses a Rockwell NICMOS3 Hg:CdTe array with 256 X 256 pixels. The two cameras are virtually identical in all respects except one houses 1.7:1.0 reimaging optics, while the other houses 0.7:1.0 reimaging optics. The cameras were commissioned in January 1993 and we anticipate developing several new observing modes in the near future.
The design of an infrared cryogenic echelle spectrograph for use on the NASA Infrared Telescope Facility is described. The resolving power achieved over the range 1-5.4 microns is 1-40,000 with slit widths of 2.0-0.5 arcsec. The spectrograph is used in a single order with a 30-arcsec-long slit. No cross dispersion is provided because of the small number of orders that can be observed at once and the need to keep the instrument as small as possible. A closed-cycle cooler is used in lieu of cryogens in order to achieve greater reliability and ease of use at the telescope. The optical layout, the design philosophy, the modes of operation, and the construction details are provided.
ProtoCAM, a new infrared array camera, has been built for the NASA 3-m Infrared Telescope Facility (IRTF). The camera is built around a 62 x 58 InSb hybrid array and is sensitive throughout the 1-5-micron atmospheric windows. The camera is equipped with standard astronomical filters as well as a full complement of continuously variable filters providing a spectral resolution down to 1 percent. On the IRTF, the platescale is variable real-time from 0.14 to 0.35 arcsec. The camera, the electronics, the software, and the performances are discussed, and some preliminary astronomical results are presented.