Lowell Observatory's Discovery Channel Telescope is a 4.3m telescope designed and constructed for optical and near infrared astronomical observation. It is equipped with a cube capable of carrying five instruments and the wave front sensing and guider systems at the f/6.1 RC focus. We report on the overall operations methods for the facility, including coordination of day and night activities, and then cover pointing, and unguided and guided tracking performance of the mount. We also discuss the implementation and performance of the open loop model for, and manual wavefront sensing and correction with the active optics system. We conclude with a report on the early integrated image quality and science performance of the facility using the first science instrument, the Large Monolithic Imager.
The 4.3m Discovery Channel Telescope (DCT) has been conducting part-time science operations since January 2013.
The f/6.1, 0.5° field-of-view at the RC focus is accessible through the Cassegrain instrument cube assembly, which can
support 5 co-mounted instruments with rapid feed selection via deployable fold mirrors. Lowell Observatory has
developed the Large Monolithic Imager (LMI), a 12.3' FOV 6K x 6K single CCD camera with a dual filter wheel, and
installed at the straight-through, field-corrected RC focal station, which has served as the primary early science DCT
instrument. Two low-resolution facility spectrographs are currently under development with first light for each
anticipated by early 2015: the upgraded DeVeny Spectrograph, to be utilized for single object optical spectroscopy, and
the unique Near-Infrared High-Throughput Spectrograph (NIHTS), optimized for single-shot JHK spectroscopy of faint
solar system objects. These spectrographs will be mounted at folded RC ports, and the NIHTS installation will feature
simultaneous optical imaging with LMI through use of a dichroic fold mirror. We report on the design, construction,
commissioning, and progress of these 3 instruments in detail. We also discuss plans for installation of additional facility
instrumentation on the DCT.
The High-speed Imaging Photometer for Occultations (HIPO) is a special purpose science instrument for SOFIA. HIPO
can be co-mounted with FLITECAM in the so-called FLIPO configuration for stellar occultation or extrasolar planet
transit observations. We gained some flight experience with HIPO and FLITECAM in 2011 as described in a previous
publication (Dunham, et al., Proc SPIE, 8446-42, 2012). Since that time a number of improvements to HIPO have been
made and a deeper understanding of the airborne environment's impact on photometric precision at optical wavelengths
has been obtained. The improvements to HIPO include an improved beamsplitter for the FLIPO configuration, adding
deep depletion CCDs as a detector option, expanding the filter set to include a Sloan Digital Sky Survey filter set as well
as two custom filters for transit work, and an ability to guide the SOFIA telescope using HIPO data being acquired for
science purposes. We now understand that variations in PSF size due to varying static air density has a noticeable
impact on photometric stability while the related effect of Mach number is unimportant. The seriousness of ozone
absorption in the Chappuis band is now understood and an approach to avoid this has been found. Finally we present
demonstration transit data to illustrate our current transit photometry capability.
The Stratospheric Observatory for Infrared Astronomy (SOFIA) has recently concluded a set of engineering flights for Observatory performance evaluation. These in-flight opportunities have been viewed as a first comprehensive assessment of the Observatory's performance and will be used to address the development activity that
is planned for 2012, as well as to identify additional Observatory upgrades. A series of 8 SOFIA Characterization
flights have been conducted from June to December 2011. The HIPO science instrument in
conjunction with the DSI Super Fast Diagnostic Camera (SFDC) have been used to evaluate pointing stability,
including the image motion due to rigid-body and
flexible-body telescope modes as well as possible aero-optical
image motion. We report on recent improvements in pointing stability by using an Active Mass Damper system
installed on Telescope Assembly. Measurements and characterization of the shear layer and cavity seeing, as
well as image quality evaluation as a function of wavelength have been performed using the HIPO+FLITECAM
Science Instrument conguration (FLIPO). A number of additional tests and measurements have targeted basic
Observatory capabilities and requirements including, but not limited to, pointing accuracy, chopper evaluation
and imager sensitivity. This paper reports on the data collected during these
flights and presents current SOFIA
Observatory performance and characterization.
HIPO is a special purpose science instrument for SOFIA that was also designed to be used for Observatory test work. It
was used in a series of flights from June to December 2011 as part of the SOFIA Characterization and Integration
(SCAI) flight test program. Partial commissioning of HIPO and the co-mounted HIPO-FLITECAM (FLIPO)
configuration were included within the scope of the SCAI work. The commissioning measurements included such
things as optical throughput, image size and shape as a function of wavelength and exposure time, image motion
assessment over a wide frequency range, scintillation noise, photometric stability assessment, twilight sky brightness,
cosmic ray rate as a function of altitude, telescope pointing control, secondary mirror control, and GPS time and position
performance. As part of this work we successfully observed a stellar occultation by Pluto, our first SOFIA science data.
We report here on the observed in-flight performance of HIPO both when mounted alone and when used in the FLIPO
Lowell Observatory's Discovery Channel Telescope is a 4.3m telescope designed for optical and near infrared astronomical observation. At first light, the telescope will have a cube capable of carrying five instruments and the wave front sensing and guider system at the f/6.1 RC focus. The corrected RC focus field of view is 30’ in diameter. Nasmyth and prime focus can be instrumented subsequently. Early commissioning work with the installed primary mirror and its support system started out using one of the wave front sensing probes mounted at prime focus, and has continued at RC with the recent installation of the secondary mirror. We will report on the on-sky pointing and tracking performance of the telescope, initial assessment of the functionality of the active optics support system, and tests of the early image quality of the telescope and optics. We will also describe the suite of first light instruments, and early science operations.
The 4.3m Discovery Channel Telescope delivers an f/6.1 unvignetted 0.5° field to its RC focal plane. In order to support
guiding, wavefront sensing, and instrument installations, a Cassegrain instrument support assembly has been developed
which includes a facility guider and wavefront sensor package (GWAVES) and multiple interfaces for instrumentation.
A 2-element, all-spherical, fused-silica corrector compensates for field curvature and astigmatism over the 0.5° FOV,
while reducing ghost pupil reflections to minimal levels. Dual roving GWAVES camera probes pick off stars in the
outer annulus of the corrected field, providing simultaneous guiding and wavefront sensing for telescope operations. The
instrument cube supports 5 co-mounted instruments with rapid feed selection via deployable fold mirrors. The corrected
beam passes through a dual filter wheel before imaging with the 6K x 6K single CCD of the Large Monolithic Imager
(LMI). We describe key development strategies for the DCT Cassegrain instrument assembly and GWAVES, including
construction of a prime focus test assembly with wavefront sensor utilized in fall 2011 to begin characterization of the
DCT primary mirror support. We also report on 2012 on-sky test results of wavefront sensing, guiding, and imaging
with the integrated Cassegrain cube.
The Discovery Channel Telescope (DCT) is a 4.3-meter telescope with a thin meniscus primary mirror (M1) and a
honeycomb secondary mirror (M2). The optical design is an f/6.1 Ritchey-Chrétien (RC) with an unvignetted 0.5°
Field of View (FoV) at the Cassegrain focus. We describe the design, implementation and performance of the DCT
active optics system (AOS). The DCT AOS maintains collimation and controls the figure of the mirror to provide
seeing-limited images across the focal plane. To minimize observing overhead, rapid settling times are achieved
using a combination of feed-forward and low-bandwidth feedback control using a wavefront sensing system.
In 2011, we mounted a Shack-Hartmann wavefront sensor at the prime focus of M1, the Prime Focus Test Assembly
(PFTA), to test the AOS with the wavefront sensor, and the feedback loop. The incoming wavefront is decomposed
using Zernike polynomials, and the mirror figure is corrected with a set of bending modes. Components of the
system that we tested and tuned included the Zernike to Bending Mode transformations. We also started open-loop
feed-forward coefficients determination.
In early 2012, the PFTA was replaced by M2, and the wavefront sensor moved to its normal location on the
Cassegrain instrument assembly. We present early open loop wavefront test results with the full optical system and
instrument cube, along with refinements to the overall control loop operating at RC Cassegrain focus.
HIPO is a special purpose instrument for SOFIA, the Stratospheric Observatory For Infrared Astronomy. It is a high-speed,
imaging photometer that will be used for a variety of time-resolved precise photometry observations, including
stellar occultations by solar system objects and transits by extrasolar planets. HIPO will also be used during the test
program for the SOFIA telescope, a process that began with a series of ground-based tests in 2004. The HIPO
requirements, optical design, overall description, and an early look at performance and planned data acquisition modes
have appeared in earlier papers (e.g. Dunham, et al., Proc. SPIE 5492, 592-603 (2004)). This paper provides an update
to the instrument description, final lab measurements of instrument performance, and a discussion of the data produced
by the various observing modes.
The Discovery Channel Telescope (DCT) is a 4.2-m telescope being built at a new site near Happy Jack, in northern Arizona. The DCT features a 2-degree-diameter field of view at prime focus and a Ritchey-Chretien (RC) configuration with Cassegrain and Nasmyth focus capability for optical/IR imaging and spectroscopy. Formal groundbreaking at the Happy Jack site for the DCT occurred on 12 July 2005, with construction of major facility elements underway.
HIPO is a special purpose instrument for SOFIA, the Stratospheric Observatory For Infrared Astronomy. It is a high-speed, imaging photometer that will be used for a variety of time-resolved precise photometry observations, including stellar occultations by solar system objects and transits by extrasolar planets. HIPO has two independent CCD detectors and can also co-mount with FLITECAM, an
InSb imager and spectrometer, making simultaneous photometry at three wavelengths possible. HIPO's flexible design and high-speed imaging capability make it well suited to carry out initial test observations on the completed SOFIA system, and to this end a number of additional
features have been incorporated. Earlier papers have discussed the design requirements and optical design of HIPO. This paper provides an overview of the instrument, describes the instrument's features, and reviews the actual performance, in most areas, of the completed instrument.
We present results of an extended campaign to test astronomical and environmental qualities of the intended site for the Discovery Channel Telescope, located at 2361m elevation near Happy Jack, AZ. A semi-permanent test station has been in operation since January 2003, consisting of a Differential Image Motion Measurement (DIMM) system and a weather station. Median seeing derived from DIMM measurements for January 2003 - May 2004 on 117 separate nights was 0.84 arcsec, with a first-quartile average of 0.62 arcsec. A wind sensor array deployed on a 12.2m tower is used to characterize air flow over the site. We find that ground induced turbulence becomes more prevalent below the 7.3m level. The Lowell DIMM system has also been run adjacent to the WIYN telescope for simultaneous comparative
seeing measurements. Absolute correlations of DIMM seeing with WIYN image quality were good over two nights' observing under a range of environmental conditions.