Infrared Instrumentation for Small Telescopes Klaus W. Hodapp University of Hawaii, Institute for Astronomy Hilo, Hawaii

Why Infrared Astronomy ? C Credit: Keck Observatory

Infrared Astronomy: The Good IR penetrates interstellar dust (Galactic Center, Star Forming Regions) Even very high redshift objects are visible. Cool objects (brown dwarfs and young gas planets) are observable. Surface mineralogy Seeing is a little better in the NIR Adaptive Optics does work in the NIR

Example: Dynamics of stars around the central black hole Sagitarius A in our Milky Way Work by: Andrea Ghetz et al. and Reinhardt Genzel et al.

High-Redshift Objects Remain Visible at Infrared Wavelengths “drop out” at short Wavelengths when Lyman absorption gets red-shifted to that wavelength.

Adaptive optics at 8m-class telescopes works very well at near-infrared wavelenghts. NGC1333 SVS13 with Keck/OSIRIS Integral Field Spectroscopy Credit: SEEDS project

The chemical composition of rocky surfaces of planetary objects can be studied with broad, multi-spectral imaging, including infrared wavelengths. Multi-spectral image of the Moon, obtained by the Galileo mission shortly after its launch towards Jupiter.

Infrared Astronomy (from the Ground): The Bad Thermal background above 1.8µm OH Airglow worst in H band Atmospheric Transmission is dependent on water vapor and therefore is variable Diffraction is of same size as seeing for small telescopes

OH Airglow is intense in the near-infrared, before thermal emission rises for λ ≥ 2 µm. Credit: Gemini Observatory

At mid-infrared wavelengths, ground-based observations are severely limited by thermal background radiation. Ground-based 10 µm observations are as bad as optical observations during the day, with your telescope on fire ! Credit: Absil et al. (2006)

Infrared detector arrays in a CCD-like configuration are only suitable for observations λ ≤ 1.8µm. A Teledyne H2RG detector array installed in a GL Scientific test cryostat. Used for a solar instrument.

University of Hawaii, IfA For longer wavelengths, the detector must be shielded from ambient temperature radiation. Cold Lyot-stop optics reduce the exposure to thermal radiation to exactly the radiation coming through the telescope optics. The IRIS camera optics: the field lens is CaF2, the main lens group is BaF2, Schott SF6 and BaF2 the field flattener lens is CaF2 9/22/2013 University of Hawaii, IfA

University of Hawaii, IfA Mechanical Design of the IRIS Camera Cryostat. The IRIS camera uses most components of the old QUIRC camera, but has new optics, requiring some level of redesign of the cryostat components. 9/22/2013 University of Hawaii, IfA

Atmospheric transmission depends on elevation and weather.

Infrared Astronomy: The Ugly Instruments must be cryogenic above 1.8µm λ > 1.8µm Instruments require cold pupil stop. Detectors are an order of magnitude more expensive. Infrared Photometry requires high, dry and stable sites. In Summary: The cost of building and operating an infrared instrument is one order of magnitude higher than for similar optical instruments.

Experience from Major Observatories: After ISO, Spitzer, and Herschel, with SOFIA operational and JWST getting ready, ground-based Observatories are reducing their 10 - 20µm capabilities. Instruments in the 3.0 – 5.5µm range were expensive to build, but get relatively little use. Best scientific return is in the 1.0 – 2.5µm (NIR) range. Carefully evaluate the need for K band. Time-Domain studies are in their infancy. Adaptive optics is very important.

The Present Generation of Infrared Detector Arrays Teledyne: HAWAII-2RG + ASIC Readout Signal offsets of each of the 32 amplifiers can be corrected using reference pixels (R).

The NEWFIRM Focal Plane 2×2 Raytheon Orion InSb Arrays, Richard Joyce (NOAO) Raytheon Orion 2Kx2K InSb arrays NEWFIRM 4K x 4K array; Mike Merrill NOAO Gemini Data Workshop

The ESO VISTA focal plane is populated with 4×4 mosaic of Raytheon VIRGO detectors (2Kx2K, 2.5µm, HgCdTe). Credit: ESO

SELEX ES of the U.K. Is primarily a defense company, but is developing some interesting new detector arrays for astronomy at reasonable prices.

1.75 e/pixel sensitivity with APD gain of 33 APD sensor ROIC ME788 Cutoff wavelength - 2.45 µm Temperature - 40K Integration time – 5.06ms Bandwidth – 5MHz APD gain – 33x Optics Filter K short Pattern contrast – 1.75 e/pixel Signal processing Double correlated clamp 16 frames averaged Data courtesy of ESO