Printer Friendly

CanariCam

CanariCam is a mid-infrared (7.5 - 25 micron) imager with spectroscopic, coronagraphic, and polarimetric capabilities, which will be mounted at one of the Nasmyth foci of the GTC. It is designed to work as a diffraction-limited imager at 8 microns. The instrument uses a Raytheon 320x240 Si:As detector which covers a field of view of ~26"x19" on the sky. Most mechanism motors and optics are inside a cryostat which is cooled down to 28K using a He cryo-cooler system. Temperature control of the detector ensures that its optimum operating temperature (~9K) is stable in the mK range.

CanariCam is designed to reach the diffraction limit of the telescope at mid-IR wavelengths. However, to do this routinely the telescope will have to be equipped with a fast-guiding mode that will allow for fast tip-tilt correction. Currently fast guiding is not yet available and hence initially the very best image quality cannot be guaranteed.

The following table summarizes all observing modes available for CanariCam. Only those modes that have been fully commissioned are offered in the current semester.

Imaging	Spectroscopy*
Coronography**	Polarimetry***
* Only low resolution spectroscopy at 10 micron is offered. Low resolution spectroscopy at 20 micron and high resolution spectroscopy are not offered. ** Not offered ***Not offered

General Information:

• Mid-IR Observing
• Instrument Features
• Instrument Detector
• Observing Modes
• Imaging
• Filters
• Spectroscopy
• Gratings
• Slits
• Wavelength calibration
• Coronography
• Polarimetry
• Entrance Windows
• Observing Strategy
• Overheads
• Calibrations
• Data Structure
• Data Reduction
• Tips for filling in the Phase-2
• Observing Tools
• Exposure Time Calculator (external link)
• Commissioning Data (new window)
• Guaranteed Time - Reserved Targets (new window)
• Support Astronomers at GTC
• Useful Documents
• More Information (external links)
• Acknowledgements

Instrument Features

The following table summarizes some basic parameters of the instrument.

Spectral Range	8-25 µm
Field of View	25.6" X 19.2"
Plate Scale	0.08", Nyquist sampled at 8 µm
Detector	See table below
Image Quality	EER80 < 2 pix (0.16") in imaging mode Diffraction limited at λ > 8 µm
Observing modes
Imaging Spectroscopy Coronography Polarimetry	Filters: (N,Q) and Narrow Band (18) Slit lenght: 19.2", width:0.17-1.04" R= 175,1313 (8-14 µm); 120,891 (16-26 µm) 10 micron window (8-14 µm) 10 micron window (8-14 µm)

Optical Layout

CanariCam’s optical train consists of three powered mirrors and six flat mirrors, two of which are inserted into the beam when needed. The relationship of the powered mirrors and the various image planes is indicated in the figure below. The first powered mirror (transfer mirror M1) forms an image of the telescope entrance pupil and reimages the telescope focal plane. The second powered mirror (collimator M2) collimates the beam and forms a second image of the pupil. The third powered mirror (camera M3) images the telescope focal plane onto the detector. A flat mirror or one of several diffraction gratings is inserted near the final pupil image (p2) for imaging or spectroscopy. To improve operational efficiency, an additional flat mirror can be inserted just up-stream from the diffraction grating during spectroscopic observations to permit monitoring of the source location on the slit without the need of moving the grating turret from the grating to the mirror position. These and the remaining flat mirrors have been added to the system to fold the beam and permit packaging the system into a fairly compact layout. Aperture stops and coronagraphic masks are located at the telescope focal plane, rotating and fixed Lyot (pupil) stops and a selection of up to 26 discrete filters on a double filter wheel are located at or very near the first pupil image (p1), and a selection of spectroscopic slits are located at the first re-image of the telescope focal plane (i1). For polarimetry, rotatable half-wave plates can be inserted into the beam just up-stream from the telescope focal plane, and a Wollaston prism can be inserted into the collimated beam near p2. Finally, a lens doublet can be inserted between the first pupil and the first re-image of the telescope focal plane in order to view the pupil, and a lens doublet can be inserted near the telescope focal plane in order to view the outside (external) surface of the entrance window.

Top: Unfolded optical layout of CanariCam indicating relationship of powered components to image and pupil planes. Bottom: 3D-view of the optical layout

Back to index

Instrument Detector

The following table summarizes some basic parameters of the detector.

Detector	Raytheon CRC-774 320 x 240 Si:As IBC
Fiel of View	25.6"x19.2"
Physical Pixel Size	50 x 50 μm (0.08arcsec)
Full-well Capacity	1.0e7 or 3.0e7 electrons (high or low gain)
Array Readnoise	Deep well: 3.6 ADU or 2060 e- Shallow well: 4.6 ADU or 828 e-
Dark Current	≤ 100 electrons/sec @ T = 6 K
Dwell depth	14106 - 41106 e-
Quantum Yield	>40% at peak Number of Output Channels : 16

Note: At the time of factory acceptance, only two dead pixels were identified in the detector, with coordinates (207,82) and (208,82).

A plot of the quantum efficiency and an image of the detector can be found below.

Quantum Efficiency of CanariCam detector

Readout Modes

To date, the Raytheon device remains the largest format mid-IR array in astronomical use. However, this device displays several unwanted effects when exposed to a very bright source. Below we discuss these effects as well as readout methods used to reduce them.

Each contiguous group of 20 vertical columns is read out through one of the 16 output channels (i.e., columns 1-20 are readout through channel 1, columns 21-40 are readout through channel 2, etc.). In addition, the first pixel read out in each channel is the lower-left one and the last is the upper right one.

1. Single-Point Sampling (S1) Advantages: Minimum frame time - 5 ms Disadvantages: Vertical "level-drop" patterns appear for brigth sources. Horizontal "level-drop" patterns appear for bright sources.
2. Correlated Quadruple Sampling (S1R3) Advantages: Vertical level-drop patterns are removed. Disadvantages: Minimum frame time is increased to 20 ms -> Broad-band imaging may be difficult or impossible with this mode. Increased readout noise -> May reduce sensitivity in high-resolution spectroscopy. NOTE: Artifacts are only < 1% the source peak and only appear in very bright objects.
3. Double correlated sampling with column clump read (S1R1_CR) Advantages: It eliminates the vertical "level drop" pattern. Minimum frametime is 9 ms, which is acceptable for imaging in high background conditions. Disadvantages: The horizontal "level-drop" patterns still appear for bright sources.

Note: The most approprate readout mode for each observing condition is to be determined during the on-sky commissioning of the instrument.

In the following figure we show an example of the cross talk features seen in the CanariCam detector in the S1R3 readout mode. The image was taken in the lab with a 3-spot mask in the ArIII filter. The depth of the cross-talk (dark horizontal strips crossing the 2 brightest spots) has a dependency on frame time, but does not depend on the separation from the source. In any case these features are always < 1% of the source peak.

Cross talk features seen in the CanariCam detector in the S1R3 readout mode

Back to index

Observing Modes

Imaging Observing Mode

Imaging with CanariCam is diffraction-limited at 8 micron over the full 26"x19" field of view. The detector plate scale (0.08 arcsec/pixel) ensures the diffraction-limited Point Spread Function is Nyquist sampled at 8 micron. During factory acceptance testing, image distortion accross the FOV has been proved to be less than 2 pixels center-to-corner.

Back to index

CanariCam Filters

CanariCam mounts 6 medium-band Silicate filters and 12 narrow, medium and broad band filters that were specified by the VISIR filter consortium. Filters were provided by the University of Reading.

A very slight, but noticeable, difference among some of the filters in the optical beam direction after passage through the filters. This results in a slight shift in the location of an astronomical image as one changes filters.

ID #	Name	λcentral (µm)	Δλ (µm)	Transmission (plot)	Transmission (ASCII file)
1	Si-1	7.8	1.1	>60% Si-1	Si-1.txt
2	PAH1(+ArIII)	8.60	0.43	>70% PAH1+ArIII_ref1	PAH1+ArIII_ref1.txt
3	Si-2	8.7	1.1	>60% Si-2	Si-2.txt
4	ArIII(+PAH1)	8.99	0.13	>70% ArIII+PAH1_ref2	ArIII+PAH1_ref2.txt
5	Si-3	9.8	1.0	>60% Si-3	Si-3.txt
6	Si-4	10.3	0.9	>60% Si-4	Si-4.txt
7	N	10.36	5.2	>80% N_band	N_band.txt
8	SIV	10.52	0.16	>70% SIV	SIV.txt
9	PAH2	11.30	0.60	>70% PAH2	PAH2.txt
10	Si-5	11.6	0.9	>60% Si-5	Si-5.txt
11	SiC	11.75	2.5	>80% SiC	SiC.txt
12	Si-6	12.5	0.7	>60% Si-6	Si-6.txt
13	NeII	12.81	0.2	>70% NeII	NeII.txt
14	NeII_ref2	13.10	0.2	>70% NeII_ref2	NeII_ref2.txt
15	QH2	17.0	0.4	>60% QH2	QH2.txt
16	Q1	17.65	0.9	>70% Q1	Q1.txt
17	Q4	20.5	1.0	>70% Q4	Q4.txt
18	Q-W	20.9	8.8	>60% Q_wide	Q_wide.txt
19	Q8	24.5	0.8	>60% Q8	Q8.txt

Back to index

Spectroscopic Observing Mode

Two low resolution gratings are provided, one spanning 7.4-13.5 µm and the other spanning 15.7-25.3 µm in a single setting. A high resolution grating is provided in each of these atmospheric windows, with the gratings being adjustable to center on the detector any wavelength within that window. Long Slits (19" length) of 9 different widths located in the slit wheel can be selected depending on the wavelength, resolution and conditions of the observation.

Back to index

Gratings

The gratings are optimized for use in first order, although use in other orders is permitted. When using the high-resolution gratings, the grating may be positioned to center any wavelength within the operating range on the detector array. Multiple settings of the high-resolution gratings are needed to span the entire 10 or 20 μm atmospheric window. When using either of the low-resolution gratings, a single setting places the entire operational wavelength range for that grating on the detector array.

Values shown in table are predicted, not measured.

Characterístics	10 µm LR	20 µm LR	10 µm HR	20 µm HR
Central λc (µm)	10.5	20.5	10.5	20.5
Blaze λ (µm)	9.87	19.96	10.08	20.18
Blaze Angle (°)	2.6	4.0	16.4	20.8
Lines/mm	9.1	6.1	56.0	35.2
ΔλDet (µ,m)	6	9	0.98	1.54
Angle of incidence (°)	14.8	15.7	29.5	33.7
Angle diffraction (°) at λcenter	9.2	8.3	5.5	9.7
R=λ/Δλ	175	175	1300	890
Smallest Resolvable Δλ (µm)	0.06	0.17	0.008	0.023

Back to index

Slits

Slits with different widths will be available to match the wavelength, conditions and resolution. Typically for each grating there will be 2 slits available corresponding to the resolution and two times the resolution at the maximum wavelength (1 and 2 λ/D)

Slit Width [arcsec]	Slit Width [pixels]	GTC Diffraction Limited λcentral [micron]
0.17	2.08	7.0
0.20	2.45	8.3
0.23	2.85	9.5
0.26	3.25	10.7
0.36	4.31	14.9
0.41	5.01	16.9
0.45	5.70	18.6
0.52	6.50	21.5
1.04	13.0	seeing limited

Back to index

Wavelength calibration

There are two possible ways of wavelength calibrating CanariCam spectra. One can use a polystyrene film located in one fo the filter wheels, which has very well defined absorption features. Most users, though would prefer to use sky lines to do their wavelength calibration.

The figures below illustrate an example of a low-res spectrum taken with CanariCam at 10 micron with the polystyrene film.

Spectrum of the polystyrene film taken with CanariCam 10 micron low-res grating in the lab and the same film. The wavelength range is 7.3 micron to 13.3 micron, left to right.

Back to index

Coronographic Observing Mode

The coronograph is designed to suppress the emission in the PSF wings of a bright source so that very faint companions or extended emission (e.g. from a disk) can be detected. It consists of a hard-edged, low-reflectivity mask of 0.83 arcsec in radius and a rotating Lyot stop resembling the pupil of the telescope. Coronography plate scale is the same as that for the imaging mode.

Although the field of view is the full imaging field of view (except for that portion of the field covered by the occulting mask), superior results will be obtained for the central ~10arcsec centered on the occulted point source.

Based on simulations, it is expected that at 1 arcsec from the primary, the intensity of a bright point source in the coronagraphic mode will be at least a factor of 10 lower than it is in normal imaging mode.

The figure below shows one of the Lyot masks used for coronography. The image was taken in the lab as part of the factory acceptance testing of CanariCam The Lyot stop wheel can be rotated to ensure the Lyot mask follows the pupil as the telescope follows a star on the sky.

Lyot masks used for coronography.

Back to index

Polarimetric Observing Mode

CanariCam permits dual-beam polarimetry in the 10 micron window by insertion of half-wave plates, a field mask and a Wollaston prism.

The half-wave plate can be rotated to four position angles (0°,22.5°, 45° and 67.5°), which results in the rotation (relative to the Wollaston prism and detector) of the plane of polarization. The Wollaston prism separates the two planes of polarization (the ordinary and extraordinary rays), which are subsequently imaged on the detector. The focal-plane mask prevents overlap of the orthogonally polarized images for extended sources. The retardance/efficiency versus wavelength, and the laboratory transmission of the combined HWP and Wollaston was measured to be 83% at 10.5 micron.

The field of view is reduced by a factor of ~2 through the inclusion of a polarimetry mask in the aperture wheel. This is required so that the orthogonally polarised light (o and e rays) from the source (sky) do not overlap onto each other.

As there is some chromatic birefringence, the 'slots' of the polarimetry mask in CanariCam are slightly oversized. The useful exposed field of view is 320x25 pixels per slot per polarised beam, corresponding to 25.6"x2". A total of >2.5 slots can be cleanly used, hence providing a field of view of 25.6"x5" in imaging polarimetry mode.

Sckech of how dual-beam imaging polarimetry works. The light any object of the sky, which can or cannot be polarized, passes through the HWP. The HWP polarizes the beam linearly in one direction. Then the polarization mask selects only half of the FOV. Finally the beam is split in ordinary and extraordinary rays (O and E rays).

Image polarimetry of a black body (laboratory ambient temperature) taken with CanariCam. The light has passed through the HWP, polarimetric mask and Wollaston prism. Narrow and very dark stips are due to the mask slots being oversized.

Back to index

Entrance Windows

Several types of window material, such as KBr, are highly transmissive at mid-infrared wavelengths and strong enough to serve as a pressure bulkhead, but they have moderate drawbacks when used as windows; e.g., they are easy to scratch and/or hygroscopic, or only transmissive over limited wavelength regions.

To permit the observer to select the appropriate window for a given combination of scientific requirements and observing conditions, three science entrance windows are installed.

The available window materials are:

• ZnSe, which has exceptionally high transmission at 10 microns, but is opaque at 20 microns. It's the best choice for 10 microns' observations.
• KBr, which has excellent transmission at 10 and 20 microns, but degrades under high humidity conditions.
• KRS-5, which is insensitive to moisture and transmits at both 10 and 20 microns, though it is less transparent than both the KBr and ZnSe.

At 10 micron the ZnSe transmission is 94%, and for KRS-5 the throughput is >66% for all wavelengths >6 micron.

Window tranmissions measured using an infrared FTS spectrograph. KBr and KRS-5 factory transmission curves at 20 microns can be seen in the CanariCam User Manual.

Back to index

Observing Strategy

In-depth information of the observing strategy is given in the CanariCam User Manual and also in the Gemini mid-IR resources web page. A summary of the main features is given in this page.

Mid-IR sources normally are over 4 orders of magnitude fainter than the background emission. Time variations in the noise associated with the detector electronics, and telescope and sky background make imperative the use of a quasi-real time subtraction of the background contribution. The technique used to achieve an accurate background subtraction is the combination of chopping the telescope secondary mirror and nodding the telescope (chop-nod). The chop-nod technique ensures the removal of the radiative offset, a background emission that remains after subtraction of chopping on- and off-source images, due to the fact that the background seen by CanariCam detector is not the same in both orientations of the telescope's secondary mirror.

The chopping profile is defined by the chop angle and and chop throw. The chop angle is the orientation of the chop direction on the sky. The chop throw is the angular separation between the on-source and off-source positions on the sky.

General case for the chop profile.

It is possible to chop off the detector or to chop on the detector. In the former case the source will not be present in the off-source image, while in the later case the source will appear in the off-source images. There is not advantage on using one or the other method regarding the final signal-to-noise ration achieved on the target (see details in the CanariCam User Manual. However, chopping on the detector is more recommended for compact targets, because with this technique only 1/4 of the array FOV can be used. Chopping off the detector is normally recommended in the case of extended sources.

Figure below shows the case of chopping off the detector. Different background contributions are represented by different background colors in the detector. The radiative offse is represented by a triangular section on the detector. The radiative offset in the second step (second row of detectors) is approximately the same but with oposite sign. By adding up On(A)-Off(A)+On(B)-Off(B) exposures the radiative offset contribution is removed.

Case of Chopping off the detector.

Figure below shows the case of chopping on the detector with nodding perpendicular to the chopping direction. In the represented case chopping is along the vertical dimension of the detector and nodding along the horizontal one. Only 1/4 of the array FOV can be used.

Case of chopping on the detector with nodding perpendicular to the chopping direction.

Overheads

Based on the experience acquired during CanariCam on-sky commissioning, the following overheads should be taken into account during proposal preparation.

• Imaging: There is an overhead of 10 minutes for acquisition, start guiding and instrument set-up. Besides, the elapsed time (total time to perform the observation) is typically 2.7 times the on-source time. Therefore, to estimate the total time required to perform an observation in imaging mode, the following formula should be used:
  Total Time [min] = 10 + 2.7 * (On-source time [min])
• Spectroscopy: There is an overhead of 20 minutes for acquisition, start guiding and instrument set-up. The elapsed time is 3.1 times the on-source time. Therefore, to estimate the total time required to perform an observation in spectroscopic mode, the following formula should be used:
  Total Time [min] = 20 + 3.1 * (On-source time [min])
• Polarimetry: There is an overhead of 15 minutes for acquisition, start guiding and instrument set-up. The elapsed time is 2.7 times the on-source time. Therefore, to estimate the total time required to perform an observation in spectroscopic mode, the following formula should be used:
  Total Time [min] = 15 + 2.7 * (On-source time [min]).

In all cases, the difference between the on-source and elapsed time is due to:

• The dead time while the telescope is switching between nod positions,
• The fact that half of the time is spent on the sky, due to chopping,
• The dead time while M2 is switching between chop beams.

Note: The on-source integration time is the one used in the Integration Time Calculator.

Besides the overheads associated to each observing mode, the following overheads should be taken into account for every required standard (see Section Calibrations below), assuming an on-source time of 0.5 mininutes:

• Flux, PSF, polarised and unpolarised standards: 15 min
• Telluric standards: 20 min

In the case of spectroscopic observations, wavelength calibration by means of the Polystyrene plate has an extra overhead of 5 minutes.

Back to index

Calibrations

Due to the spatial and time variability of the background in the mid-IR and the wide range of observational setups available with CanariCam, all calibrations required for a science program shall be defined by the PI at the Phase-1 and Phase-2 stages and will be charged to the program. Hence, the PI must ensure that adequate calibrations are defined in line with the scientific objectives of the program. Nevertheless, the observatory will normally take a flux standard, in imaging mode, in the Si5 and Q1 filters, once or twice per night, to asses the quality of the mid-IR sky. Such data will be provided.

We recommend the following link to the Gemini web site to search for standards close to a given Right Ascension and Declination:Mid-IR standard star selection tool.

In the following lines, we give some recommendations on the type of calibrations that may be required for each type of program (please refer to Section Overheads for information on the overheads to be taken into account for calibration standards).

• Bad pixel mask. No bad pixel mask is provided, since only two bad pixels are know to CanariCam detector (see Section Instrument Detector). These should be taken into account during data reduction.
• Darks and Bias. They are not needed, since these are removed automatically with the chopping and nodding technique.
• Flat fields. Falt fielding has not been thoroughly explored with CanariCam. However, based on T-ReCS experience at Gemini, flat fields can be more damaging to data quality (increased noise) than an improvement. Hence, flat fields are not taken with CanariCam.
• Flux standards for imaging. In observations with an elapsed time shorter or equal than 1.5 hours, one flux standard at a similar airmass to the science target should be defined. In observations longer than 1.5 hours, two telluric standards, one at approximately the initial airmass and one at the final airmass of the science observations should be defined. Photometric accuracy is limited to ~10% by the uncertainty in the airmass correction and in the fluxes of the standards themselves.
• PSF standards for imaging. Normally used to characterise the PSF if deconvolution of the science data is going to be performed during post-processing. In general, the flux standard should provide a approximate measurement of the PSF. However, if dedicated PSF stars are required, the time required to observe them should be taken into account in the time request.
• Flux standards for spectroscopy. Absolute flux calibration through narrow slits is very unreliable and many stars commonly used as mid-IR telluric standards do not have well-known fluxes. It is recommended to include imaging observations at a similar wavelength if absolute flux calibration is important for the science outcome.
• Telluric standards for spectroscopy. These are used to remove the telluric lines from the science spectra. In observations with an elapsed time shorter or equal than 1.5 hours, one telluric standard at a similar airmass to the science target should be defined. In observations longer than 1.5 hours, two telluric standards, one at approximately the initial airmass and one at the final airmass of the science observations should be defined.
• Wavelength calibration for spectroscopy. Wavelength calibration is normally performed by identification of sky lines in the science spectrum. Therefore, extra observations of arc lamps are not required. CanariCam also has a Polystyrene plate that can be used for wavelength calibration. The Polystyrene plate has to be introduced in the optical path of the science spectrum, once the science observation has been concluded. Hence, this option has an extra overhead of 5 min (Overheads).
• Unpolarised and polarised standards for imaging polarimetry. Unpolarised standards are used to determine the instrumental polarisation, while polarised standards are used to calibrate the degree and angle of polarisation of the observations. The same rule as for the rest of the standards apply, i.e. one of each should be defined if the science observation is shorter than 1.5 hours and two of each for longer observations.
• Atmospheric extinction. Atmospheric extinction in the mid-IR is very hard to determine due to the string variability of the background emission. The best way to minimise the uncertainty in the airmass is to observe a flux standard as close as possible to science target.

Back to index

Data Structure

CanariCam data is delivered in standard multi-extension FITS (MEF) file format. Each extension contains the 320x240 pixel image, as well as specific headers relevant to those extensions. The zeroth header is a general header, containing greater information about the full data file.

In chop and chop-nod modes, there are 2 chop positions per saveset, and M savesets, meaning that each image is therefore [320,240,2,M]. Almost all science data are taken in chop-nod mode, and each extension contains the savesets for a single nod position. CanariCam can be used in the nod sequences ABAB or ABBA, with the difference being only an insignificant change in overheads. However, it is essential for a minimum number of AB pairs to be observed to permit adequate correction for radiative offset.

The exposure time can be a confusing term when applied to mid-IR observations, there are four exposure time commonly expressed:

• Frame time. This is the time between readouts of the array and is controlled through the optimized software settings. Typical times are ~25 ms.
• Saveset time. This is the time between each co-added dataset that is saved to disc. This is the smallest quantum of data saved by CanariCam. This is controlled through the optimized software settings. Typical times are ~10 s.
• Exposure time. This is the user-selected time interval over which the source will be observed. The time can vary greatly depending on source flux, but typically it is in the range ~60-600s.
• Clock (or total) time. This is the total time need for the observation to be completed, and includes the necessary overheard of chopping and nodding. The multiplicative factor to convert exposure time to clock time is dependant on the observing mode, chop and other parameters used, but is estimated to be ~3 for imaging, ~4 for spectroscopy and ~3.75 for imaging polarimetry (telescope and instrument setup excluded).

It is important to note that only the exposure time is input by the user (either in the ETC or in the Phase-2 form). All other parameters are set automatically.

Back to index

Data Reduction

The minimum software requirements for reduction and analysis of the CanariCam data are:

1. The latest working version of IRAF, which can be obtained from: http://iraf.noao.edu
2. The Gemini package of IRAF (version 1.9.1 or newer). The package can be downloaded from: http://www.gemini.edu/sciops/data-and-results/processing-software
3. To make the Gemini package compatible with CanariCam data, the following patch should be downloaded and the original midir package should be replaced with the patch. You can find the replacement instructions in the following link.
4. For polarimetric data reduction, the Starlink software, version Hawaiki or newer. The package can be downloaded from: http://starlink.jach.hawaii.edu/

Detailed information on how to use the software to reduce data for the different CanariCam observing modes can be found in the CanariCam User Manual.

Back to index

Tips for filling in the Phase-2

As indicated in the Phase-2 help manual, CanariCam users have the option of relaxing Phase-1 constraints as approved by the Time Allocation Committee (TAC) in terms of requested Full Width Half Maximun (FWHM) of the Point Spread Function (PSF) and Precipitable Water Vapor (PWV). This may be useful when combining N-band and Q-band observations in a single proposal, but which may have very different requirements due to the very different wavelength. Such relaxation of observing conditions can be done independently for each Observing Block (OB) of the same proposal. This provides enough flexibility to relax, for instance, the PWV conditions for observations in the 10 micron window, which is not as sensitive to the atmospheric water vapor content as the 20 micron window. Similarly, some users may want to relax the requirement on the FWHM of the PSF in the 20 micron window, where the diffraction limit is less restrictive than in the 10 micron window. Since OBs are treated as indivisible atoms within an observing program, only one set of observing constraints can be defined for the whole of the OB, even if the OB contains different types of observations. If, for any reason, it is not possible to use the same observing constraints for 10 and 20 micron observations, then separated OBs should be defined for each wavelength range.

Back to index

Observing Tools

Gemini Observatory staff has made an excellent work by providing observers with thorough information and useful tools to prepare their mid-IR observations. We encourage prospective CanariCam observers to consult the Mid-IR resources page at the Gemini Observatory web site. Two of these tools are:

• Mid-IR standard star selection tool
• Mid-IR in-band fluxes

Such tools can be used during proposal preparation to search for standard stars close to your favourite science target and to have a rough estimate of their fluxes. Note that some of the T-ReCS filters (e.g. Si filter) coincide with CanariCam filters.

Back to index

Support Astronomers in charge of CanariCam in GTC

• (Contact person)

Useful Documents

• CanariCam Astronomers User Manual
• http://adsabs.harvard.edu/abs/2001hsa..conf..395P
• http://adsabs.harvard.edu/abs/2008SPIE.7014E..83L
• http://adsabs.harvard.edu/abs/2008SPIE.7014E..79M
• http://adsabs.harvard.edu/abs/2008SPIE.7014E..25T
• http://adsabs.harvard.edu/abs/2007RMxAC..29....9P
• http://adsabs.harvard.edu/abs/2005RMxAC..24....7P
• http://adsabs.harvard.edu/abs/2005ASPC..343...38P
• http://adsabs.harvard.edu/abs/2003SPIE.4841..913T

More information:

• URL: CanariCam (University of Florida)

Acknowledgements

This web page and the CanariCam User Manual makes extensive use of the detailed information provided by the Gemini mid-IR team. We are deeply grateful to the Gemini Observatory staff for sharing with us their work and for allowing us to publish part of their mid-IR resources in our web site. The key people associated with those activities are Drs. Rachel Mason, Kevin Volk, and Scott Fisher. We also use sections of the Starlink POLPACK software, written and documented by Berry & Gledhill. Much of the IRAF script work for the software was written by, or under the direction of, Kathleen Labrie, also at Gemini.

We have made use of the atmospheric transmission models generated using the ATRAN modelling software (Lord, S.D. 1992, NASA Technical Memor. 103957) and published in the Gemini Observatory web site.

Back to index