IRTF

The IRTF is a 3.0 m telescope optimized for infrared observations, located on the summit of Mauna Kea, Hawaii. Because it is owned by NASA observing is available to the entire astronomical community. At the IRTF I will be using the MIRAC2 camera in collaboration with William Hoffmann (U. Arizona), Giovanni Fazio (CfA), Joseph Hora (Inst. for Astronomy), and Lynne Deutsch (U. Mass). MIRAC2 is a Mid-InfraRed Array Camera which utilizes a Rockwell HF16 128x128 Si:As hybrid BIB array. Reflective optics in the camera liquid-helium cryostat yield achromatic diffraction-limited imaging at a nominal scale on IRTF of 0.34 arcsec/pixel with zoom capability from 0.25 to 0.50 arcsec/pixel. There are two cold filter wheels with 15% bandwidth filters at 2.2 and 4.9 , a 5% bandwidth filter at 7.8 , 10% bandwidth filters at 8.8, 9.8, 10.3, 11.7, and 12.5 , 4% bandwidth filters at 17.2 and 17.9 , 9% bandwidth filter at 20.8 , 2% bandwidth filter at 24.5 m , an N-band filter (8.2 - 13.3 ), a Q-short filter (16.85 - 19 ), and a CVF with 1.8% resolution from 7.7 to 14.5 . A PC with a Digital Signal Processor (DSP) card controls the telescope secondary chopper and data acquisition, storage, processing and display, and initiates telescope nod and offset motions via ethernet, or RS232. A C program is available for processing the files stored in MIRAC format, combining the chop and nod images, applying flat fielding corrections, and producing image files in FITS format. Typical sensitivities expected at IRTF are 30 mJy/arcsec at 11.7 and 110 mJy/arcsec at 20.9 , all chop-nod, one minute total total observing time (Hoffmann et al. 1993, Hoffmann et al. 1994).

The IRTF is chosen for this aspect of the observations for three main reasons.

1. An imaging mid-IR camera on a telescope with the capability of secondary chopping is required. The 3.5 m telescope at APO does not have this capability.

2. The wavelengths involved are on the Wien end of the Planck spectrum, requiring a large aperture to accomplish the project in a reasonable amount of integration time.

3. In both atmospheric windows, water vapor plays an important part in determining atmospheric transmission. The high elevation of Mauna Kea allows us to observe above much of the water vapor in the Earth's atmosphere.