Data Set Overview ================= This data set contains raw images of Comet 9P/Tempel 1 obtained with MIRSI (the Mid-InfraRed Spectrometer and Imager) at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. Included are dark images used in processing the comet observations. Nightly images of HR5340 (Alpha Boo) were obtained as the primary flux standard. Calibration images were also obtained of HR5315 (on July 13 and 18 only), HR5056 (Spica, one observation on July 6), and of the asteroid 68 Leto. Nightly logs giving details of the observations, including sky conditions, are provided in the documents directory. The MIRSI camera is described in a paper by Deutsch et al. 2003. It utilizes a 320 x 240 Si:As Impurity Band Conduction (IBC) array developed by Raytheon/SBRC. On the IRTF, MIRSI has a 85 x 64 arcsec field of view with a pixel scale of 0.27 arcsec. The nominal point source sensitivity for a 1-sigma detection in a 60 second integration is 20 mJy at 10 microns, and 100 mJy at 20 microns. The MIRSI observations of Comet Tempel 1 were taken through a series of discrete filters with the following parameters: Band Central wavelength Band pass (microns) M 4.9 21% 7.7 9.0% 8.7 8.9% 9.8 9.4% N 10.4 46% 11.6 9.9% 12.5 9.6% 18.4 8.0% Details for the standard stars are listed below. In the case of HR5340 (Alpha Boo) published magnitudes are provided for bandpasses close to those provided with MIRSI. HR 5056 Alpha Vir (Spica) Spectral type = B1V V = 1.04 N (est.) ~ 1.6 HR 5315 Kappa Vir Spectral type = K3III V = 4.19 N = 0.88 HR 5340 Alpha Boo (Arcturus) Spectral type = K2III V = -0.04 N = -3.16 4.8 microns = -2.93 Cohen et al. 1995 7.8 microns = -3.08 Gezari et al. 1993 8.7 microns = -3.12 Cohen et al. 1995 9.8 microns = -3.13 Gezari et al. 1993 10.3 microns = -3.15 Gezari et al. 1993 11.7 microns = -3.16 Cohen et al. 1995 12.5 microns = -3.23 Gezari et al. 1993 18.4 microns = -3.20 Gezari et al. 1993 The observations were made in chop-nod mode, resulting in 3-D image cubes with four image planes of 320 by 240 pixels each: two chop pairs that are offset by a small nod in the telescope position. The dark frames were recorded as 2-D 'grab frame' images. The MIRSI array is read out through 16 parallel readout lines, each controlling the output from 20 array columns. There is common-mode (common to each of the 16 outputs) pattern noise that repeats every 20 columns, but which is temporally variable from frame to frame. There are also column bleed and level shifts which occur adjacent to very bright pixels, as well as row-wise repetition of bright pixels in all outputs. Except for bleeding and level shifts, various median filtering techniques can be used to minimize the pattern noise in each output region as part of the data reduction. Some HINTS for Data Reduction: At mid-infrared wavelengths, the atmosphere and telescope are both significant sources of thermal radiation. As a result, sky images taken in the mid-IR have very high background counts, to the level where bright point sources are difficult to see in a single, non-sky-subtracted image. For this reason, all of the data presented here are taken as series of chop-nod image sets, which allow for proper sky subtraction. Each data file contains four image planes stacked along the third dimension. These image planes, referred to here as A, B, C, and D, are the first chop pair (A and B), where the telescope secondary is chopped back and forth usually in the N-S direction at a frequency of a few Hz, followed by the second chop pair (C and D) taken after the telescope position was nodded slightly, usually in the E-W direction. To reduce these data, one of the first steps involves subtracting the background sky in each of the corresponding pairs: A - B, B - A, C - D, and D - C. If the telescope chop and nod distances were relatively small (smaller than the field of view on the array), then a positive - negative pair of images should appear in each of these subtractions. Because the chopping of the secondary offsets the light path in the camera, a residual signature of the telescope radiation may remain in the subtracted image. This can be removed by subtracting the results from the two nod positions - ie: (A - B) - (C - D). Again, if the chop and nod distances are relatively small, the result from this subtraction should contain four images, two positive and two negative, often in a square pattern (if the N-S secondary mirror chop distance was the same as the E-W telescope nod distance). Depending on the stretch of the image, pattern noise may be visible in the background of the chop-nod subtracted image. This repetitive common-mode noise pattern (described above) can be mostly removed by: 1) subdividing the image into 16 sub-images, each corresponding to 1 readout channel, 20 columns wide, 2) subtracting any residual mean sky level from each sub-image (to zero out small shifts in the background between the different readout channels), and 3) taking the pixel-by-pixel median of the sub-images. This produces a noise pattern image (with mean count level of zero) that can be subtracted from each readout channel. When observing bright sources, level shifts in the background are usually seen in those channels containing the brightest pixels (shifts in the background level in that 20-column wide channel, in those rows either above or below the bright source on the array). These level shifts can be modeled and removed in the final stages of data processing. Summary: These data were obtained through a coordinated effort by the following observers: Diane Wooden Carey Lisse Neil Dello Russo David Harker Michael S. Kelley Chick Woodward MIRSI is a PI instrument, made available at the IRTF through an agreement with Boston University. As part of that agreement, the MIRSI instrument team should be included in the authorship of any publications resulting from this data set. Confidence Level Overview ========================= The quality of the MIRSI data is limited by various sources of electronic noise, including the temporally-variable pattern noise that repeats across each output section (the effects of which can be minimized using median filtering techniques), and bleeding and level shifts associated with bright sources, such as standard stars. The start times recorded in the MIRSI image headers are derived from the instrument computer clock. Because the IC clock is not automatically synchronized to a time standard, slow drifts in this clock lead to uncertainties of several seconds in the exposure start times. The observation end times are estimated by the MIRSI software, based on the total exposure times, readout and chop frequency parameters.