Daniel Patrick Pappalardo

The Multi-Object Double Spectrographs for the Large Binocular Telescope

The Multi-Object Double Spectrographs (MODS) are two identical high-throughput optical low- to medium-resolution CCD spectrometers being deployed at the Large Binocular Telescope (LBT). Operating in the 340-1000nm range, they use a large dichroic to split light into separately-optimized red and blue channels that feature reflective collimators and decentered Maksutov-Schmidt cameras with monolithic 8×3K CCD detectors. A parallel infrared laser closed-loop image motion compensation system nulls spectrograph flexure giving it high calibration stability. The two MODS instruments may be operated together with digital data combination as a single instrument giving the LBT an effective aperture of 11.8-meter, or separately configured to flexibly use the twin 8.4-meter apertures. This paper describes the properties and performance of the completed MODS1 instrument. MODS1 was delivered to LBT in May 2010 and is being prepared for first-light in September 2010.

A Novel Double Imaging Camera (ANDICAM)

We describe an instrument that is capable of taking simultaneous images at one optical (UBVRI) and one near-infrared (JHK) wavelength. The instrument uses relatively simple optics and a dichroic to image the same field on to an optical CCD and an HgCdTe array. The mechanical and thermal design is similar to previous instruments built by our group and the array controllers are based on the same architecture. The instrument has been in use for the past four years on the CTIO/Yale 1m telescope in Chile and has an excellent operational/reliability record. A number of notable science results have been obtained with the instrument; especially interesting are several photometric monitoring projects that have been possible, since the instrument is available every night on the telescope.

Mechanisms and instrument electronics for the Ohio State Multi-Object Spectrograph (OSMOS)

The Ohio State Multi-Object Spectrograph (OSMOS) is a new facility imager and spectrograph for the 2.4m Hiltner telescope at the MDM Observatory. We present a detailed description of the mechanical and electronic solutions employed in OSMOS, many of which have been developed and extensively tested in a large number of instruments built at Ohio State over the past ten years. These solutions include robust aperture wheel and linear stage designs, mechanism control with MicroLYNX programmable logic controllers, and WAGO fieldbus I/O modules.

A multi-object double spectrograph for the Large Binocular Telescope

We are building a Multi-Object Double Spectrograph for the Large Binocular Telescope. The instrument is designed to have high throughput from 320 to 1000 nm, spectral resolutions of 1,000-10,000, and multi-object capability over a 6 arcminute field. The design incorporates a dichroic and splits the science beam into a blue and a red channel, each of which can illuminate an 8,192 pixel long detector (with 15 micron pixels) with good image quality. The highly modular design can hold up to three gratings and an imaging flat and a selection of filters in each channel, all of which are quickly accessible; this allows for substantial observing flexibility. Progress on the construction of the instrument and future plans will be described.

On-sky performance of the Multi-Object Double Spectrograph for the Large Binocular Telescope

The Multi-Object Double Spectrographs (MODS) are two identical high-throughput optical dichroic-split double-beam low- to medium-dispersion CCD spectrometers being deployed at the Large Binocular Telescope (LBT). They operate in the 3200-10500Å range at a nominal resolution of λ/δλ≈2000. MODS1 saw first-light at the LBT in September 2010, finished primary commissioning in May 2011, and began regular partner science operations in September 2011. MODS2 is being readied for delivery and installation at the end of 2012. This paper describes the on-sky performance of MODS1 and presents highlights from the first year of science operations.

KOSMOS and COSMOS: new facility instruments for the NOAO 4-meter telescopes

We describe the design, construction and measured performance of the Kitt Peak Ohio State Multi-Object Spectrograph (KOSMOS) for the 4-m Mayall telescope and the Cerro Tololo Ohio State Multi-Object Spectrograph (COSMOS) for the 4-m Blanco telescope. These nearly identical imaging spectrographs are modified versions of the OSMOS instrument; they provide a pair of new, high-efficiency instruments to the NOAO user community. KOSMOS and COSMOS may be used for imaging, long-slit, and multi-slit spectroscopy over a 100 square arcminute field of view with a pixel scale of 0.29 arcseconds. Each contains two VPH grisms that provide R~2500 with a one arcsecond slit and their wavelengths of peak diffraction efficiency are approximately 510nm and 750nm. Both may also be used with either a thin, blue-optimized CCD from e2v or a thick, fully depleted, red-optimized CCD from LBNL. These instruments were developed in response to the ReSTAR process. KOSMOS was commissioned in 2013B and COSMOS was commissioned in 2014A.

The commissioning instrument for the dark energy spectroscopic instrument

We describe the design of the Commissioning Instrument for the Dark Energy Spectroscopic Instrument (DESI). DESI will obtain spectra over a 3 degree field of view using the 4-meter Mayall Telescope at Kitt Peak, AZ. In order to achieve the required image quality over this field of view, a new optical corrector is being installed at the Mayall Telescope. The Commissioning Instrument is designed to characterize the image quality of the new optical system. The Commissioning Instrument has five commercial cameras; one at the center of the focal surface and four near the periphery of the field and at the cardinal directions. There are also 22 illuminated fiducials, distributed throughout the focal surface, that will be used to test the system that will map between the DESI fiber positioners and celestial coordinates. We describe how the commissioning instrument will perform commissioning tasks for the DESI project and thereby eliminate risks.

The aluminizing system for the 8.4 meter diameter LBT primary mirrors

The recently commissioned system for aluminizing the 8.408 meter diameter Large Binocular Telescope mirrors has a variety of unusual features. Among them are aluminizing the mirror in the telescope, the mirror is horizon pointing when aluminized, boron nitride crucibles are used for the sources, only 28 sources are used, the sources are powered with 280 Volts at 20 kHz, high vacuum is produced with a LN2 cooled charcoal cryo-panel, an inflatable edge seal is used to isolate the rough vacuum behind the mirror from the high vacuum space, and a burst disk is mounted in the center hole to protect the mirror from overpressure. We present a description of these features. Results from aluminizing both primary mirrors are presented.

Ohio State University Imaging Sciences Laboratory (ISL)

The ISL is a successful astronomical instrumentation program that has completed three major instruments and many smaller projects since 1987. We have developed the capabilities to perform all aspects of instrument design and construction and a range of unique skills and methods. We maintain a permanent staff that currently consists of two scientists specializing in optical design and detector systems, a seniors mechanical engineer, a programmer, an electronic engineer, a mechanical designer, two machinists, and a lab assistant. Instrumentation projects also draw upon faculty and graduate student effort.

The DESI shutter with integrated fiber illumination system

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 40 million galaxies over 14,000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We describe the unique shutter design that incorporates a fiber illumination system into the shutter blade. When activated, the fiber illumination system directs intense 430-480nm wavelength light at the instrument’s fiber slit in order to back-illuminate the telescope’s focal plane and verify the location of the robotic fiber positioners. The back-illumination is typically active during science exposure read-outs and therefore requires the shutter to attenuate light by a factor of at least 107. This paper describes how we have integrated the fiber illumination system into the shutter blade, as well as incorporated an inflatable seal around the shutter aperture to achieve the light attenuation requirement. We also present lab results that characterize the fiber illumination and shutter attenuation. Finally, we discuss the control scheme that executes exposure and fiber illumination modes, and meets the shutter timing requirements.