MIRAC3: A Mid-Infrared Array Camera


NOTE: This page describes the MIRAC3 instrument which has been decommissioned. If you are looking for documentation on the current MIRAC instrument, see the MIRAC4 and BLINC documentation page.

General Description

Mid-Infrared image of the Galactic Center
MIRAC3 was a Mid-InfraRed Array Camera built for ground based astronomy at Steward Observatory, University of Arizona and Harvard- Smithsonian Center for Astrophysics. (The instrument has been decommissioned, the current instrument being operated is "MIRAC4"). It utilized a Rockwell HF16 128x128 arsenic-doped silicon blocked-impurity-band hybrid array operating in a liquid helium-cooled cryostat at 5 K. It had an operating wavelength range of 2 to 26 microns. Using 16 parallel readout lines giving a frame rate up to .92 kHz, the array provided both low noise and good linearity at high background flux, which are essential for 10 and 20 micron ground-based observing conditions. The array has a peak quantum efficiency of approximately 0.42 at 22 microns, and a linear well size of 3x10^7 electrons. The quantum efficiencies at 2.2, 5, and 10 um are approximately .05, .25, and .30, respectively. The system has been used at Steward Observatory 2.3 meter telescope at Kitt Peak, the MMT on Mount Hopkins, the Magellan telescope on Las Campanas, and at the IRTF and UKIRT telescopes on Mauna Kea.

Optics and filters

Reflective optics in the camera cryostat provide achromatic diffraction-limited imaging at a nominal scale on IRTF of .34 arcsec/pixel (lambda/2D at 10 microns) and a maximum field size of 44x44 arcsec. The camera cryostat contains two cold filter wheels with a 16% bandwidth filters at 2.2, 3.8. and 4.8 microns, a 4% bandwidth filter at 7.9 microns, 10% bandwidth filters at 8.8, 9.8, 10.3, 11.7, and 12.5 microns, 2.6% bandwidth filters at 17.4 and 17.8 microns, 10% bandwidth filter at 18.0 microns, 7% bandwidth filter at 20.6 microns, and an N-band filter (8.1 - 13.1 microns). A pupil slide provides for focal ratios of f/15, f/16, f/32, f/36, and f/45 for the MMT, SOFIA, CTIO 4-meter, IRTF/UKIRT, and Steward Observatory 2.3-meter telescopes.

The filter transmission and calibration was published in Mamajek et al. (2004; ApJ, 612, 496). See Eric's web page for the transmission curves and other info.

Electronics and computer

Digital and analog electronics mounted at the cryostat provide for single and double read with a minimum pixel sample time of 1.07 usec and a minimum full array read time of 1.09 msec. The array can be read out in continuous or burst mode, with frame time (on-chip integration time) up to 256 read times. Hard-wired arithmetic units provide for fast coadding of up to 4095 frames before sending the images via an optical fiber to a digital array processor (DSP) in a Pentium PC. A sub-portion of the array in units of 32x32 pixels can be chosen for coadding and transmitting to the PC. Full array coimages can be sent to the DSP at a rate of 56 Hz and 1/16 of the array at a rate of 800 Hz. The camera controller generates the telescope secondary chopper motion and wait times synchronously with the read and frame times. The PC and array processor control the data acquisition, storage, processing and display, and initiate telescope motions via ethernet or RS232. The data can be stored both on the PC hard disk and on a facility computer disk via the ethernet. A c program is available for processing the files stored in MIRAC format, combining the chop and nod images, applying a mask and flat fielding corrections, and producing image files in FITS format.

Typical sensitivities expected at IRTF are 26 mJy/arcsec at 11.7 microns (10% bandwidth filter) and 100 mJy/arcsec at 20.6 microns (6.8% bandwidth filter), all chop-nod, one minute total observing time, with the source in one of four beams. Use the MIRAC3 Sensitivity Estimator to estimate the required observing time under various conditions.

The MIRAC camera was built as a collaborative effort among the University of Arizona Steward Observatory (William F. Hoffmann and Joseph L. Hora), the Smithsonian Astrophysical Observatory (Giovanni G. Fazio, Lynne K. Deutsch), and the Naval Research Laboratory (K. Shivanandan). The BLINC (Bracewell Infrared Nulling Cryostat) was built by Steward Observatory (Hinz, R. Angel, N. Woolf, Hoffmann, & D. McCarthy). The MIRAC camera has undergone several upgrades (see the History link below). The camera system is currently operated by Phil Hinz and William Hoffmann at Steward Observatory.

History of MIRAC


Examples of MIRAC Results



Availability

The MIRAC3 camera has been decommissioned. A new camera is currently in use at the MMT, "MIRAC4". Contact Phil Hinz at Steward Observatory, University of Arizona, for the most current information.

The MIRAC Sensitivity Estimator will assist in calculating the required total time to obtain a certain signal/noise for objects of a given flux.


MIRAC manual

This is the complete manual for the MIRAC3 camera, dated May 22, 1999. Read the README file about this distribution.


Obtaining and Reducing MIRAC Data



References

Technical publications:

Astronomical papers


Links to other sites:
CfA Home Page

Questions about this page to: jhora@cfa.harvard.edu

Last modified: 2011 August 26