RESULTS OF THE CANARICAM COMMISSIONING

• Imaging
• Sensitivity
• Image Quality
• On-chip vs Off-chip Chopping and Nodding
• Chop Tails
• Chop Frequency
• Radiative Offset and Nod Dwell Time
• Symmetric vs Asymmetric Chopping
• Frame Times
• Readout Mode
• Detector Features
• Plate Scale
• Verification Images
• Spectroscopy
• Data Quality and PWV
• Slow Guiding Accuracy
• LATEST NEWS

Since September 2010, an important effort has been put into getting GTC ready for commissioning and scientific operation of CanariCam. Pre-commissioning tests to gauge the operability of the telescope with CanariCam have been taking place almost every month. Finally, CanariCam commissioning was performed between June 19^th and 24^th. This run was followed by two more runs, one in July (29^th and 30^th) and one in August (4^th and 5^th). Commissioning observations and analysis have been performed in a combined effort of UF and GTC teams.

During these three periods it was possible to commission the imaging mode as well as the 10-micron low resolution spectroscopic mode. Useful data were also taken in the polarimetric and 20-micron low resolution spectroscopic modes. No data have been taken yet in coronograpic or high resolution spectroscopic mode.

In all, commissioning data analysis shows that GTC is ready for the operation with CanariCam in imaging mode (10 and 20 microns) and in low resolution spectroscopy at 10 micron, although there are some limitations that will be described below. Preliminary results from low resolution spectroscopy at 20 micron and polarimetry at 10 micron (note that polarimetry at 20 micron is not available in CanariCam) show that these modes are in good health, but more work needs to be done before they can be offered widely for common use by the GTC community.

Further commissioning tests have been performed on December 6th to 11th and 17th to 19th, 2011 and on January 5th to 8th, 2012. During these commissioning periods more data were taken in the polarimetry mode and low resolution spectroscopy at 20 micron. Also the first high resolution spectra at 10 micron were obtained. Data analysis for the polarimetry and low resolution spectroscopy is currently being performed. Given the amount of data gathered and initial analysis results, we are in the position of offering low resolution spectroscopy at 20 micron for semester 2012B.

In what follows, we show some of the commissioning results in imaging mode, which can be useful for proposal preparation and observation planning. Commissioning results regarding low resolution spectroscopy will be posted soon.

Imaging

Sensitivity

The following table shows the sensitivity in some key filters, since they are also used in T-ReCS at Gemini and therefore they can be used for comparison. Measured sensitivities are also compared with the values estimated with the CanariCam ITC.

Filter	FWHM	Ropt	Rfull	Flux	Sensitivity	T-ReCS	CC ITC
	(")	(")	(")	(Jy)	(mJy)(*)	(mJy)	(mJy)
Si1-7.8	0.28	0.24	2.32	130.17	6.39	6.7	5.0
Si2-8.7	0.29	0.20	2.28	92.79	0.80	1.4	1.2
Si3-9.8	0.30	0.24	2.40	77.23	2.10	3.4	2.7
Si4-10.3	0.30	0.20	2.00	69.98	1.15	2.2	2.0
Si5-11.6	0.31	0.20	2.08	58.62	1.42	1.6	2.5
Si6-12.5	0.34	0.24	2.16	51.00	3.02	2.7	5.4
SiC-11.75	0.37	0.28	2.28	58.29	2.68	---	1.8
Q1-17.65	0.49	0.32	2.20	13.13	14.32	---	15.5

(*) Data taken under poor PWV conditions (8-11 mm)

The column Sensitivity shows the sensitivities measured using the star HD186791, on June, 25^th. The method to calculate the sensitivity was the following. Aperture photometry was performed on each image with increasing aperture radius. Two aperture radii were taken, one containing the full flux of the star (Rfull) and the other one giving the maximum SNR (Ropt). A template spectrum of the star and the transmission curve of each filter was used to estimate the theoretical flux of the star in each band in Jy (column Flux). For each filter, the theoretical flux in Jy was divided by the number of ADU in the Rfull aperture and by the on-source integration time to obtain the conversion factor Jy/ADU/s. The measured SNR in each filter within the Ropt aperture was scaled to an on-source time of 30 min. Finally, the conversion factor (Jy/ADU/s) was used to estimate the flux of a source yielding a SNR of 5 in 30 min in the Ropt aperture, which is our nominal definition of sensitivity (column Sensitivity). This definition is the same as the one used in Gemini, which allows us straight comparison of our values with the ones published in their T-ReCS web site (see the original T-ReCS values here).

The last column of the table shows the sensitivity as calculated with the CanariCam ITC. The ITC seems to yield higher values of sensitivity than the real data. Nevertheless, when estimating the time required to perform an observation during proposal preparation, the ITC should be used.

Image Quality

Currently, GTC can only do slow guiding, i.e. guiding corrections are sent to the telescope axes, which occurs at a typical frequency of ~0.2 Hz. However, to be able to reach the diffraction limit of the telescope with CanariCam, it is necessary to implement the functionality of fast guiding. This consists of commanding the telescope secondary mirror at high frequency (>50Hz), to correct for tip/tilt motions on the image. Until fast guiding is implemented, it will be difficult to reach the GTC diffraction limit with CanariCam, particularly at short wavelengths. Hence, CanariCam images are currently seeing-limited. Still, it is possible to see diffraction rings in cases where the seeing is good (≤1" in the optical).

The following figure shows the measured EER curves in several filters, compared with the corresponding diffraction limit EER80 at each filter's wavelength. These data were taken on June 25^th, in good seeing conditions (optical seeing of 0.9").

It is clear that the measured EER80 (red vertical line) is worse than the diffraction-limited EER80 (blue vertical line – based on the optical model of CanariCam+GTC). In contrast, the following figure shows the same analysis during a night with bad seeing conditions (1.3" in the optical):

In this case the measeured EER80 is always >1", being more than twice the theoretical EER80.

The following figure illustrates the diffraction rings in the filters Si5 (11.6 microns) and Q1 (17.65 micron).

Observations were done on June 22^nd, corresponding to the mid-IR standard HD140573, which has a flux of 30.7Jy and 13.1Jy in the Si5 and Q1 filters respectively (45.3Jy in the N filter). The FOV shown in the images is 7x7 arcsec. The FWHM of the PSF in each image is 0.36" (Si5) and 0.46" (Q1), which corresponds to 1.29 and 1.07 times the diffraction FWHM, respectively. Two diffraction rings can be seen in the Si5 image and only one weak ring can be seen in the Q1 image.

Previous images were reduced using the IRAF/GEMINI package, where individual savesets (see CanariCam User Manual for a description of the reduction tools and CanariCam data structure) were stacked to produce the shown images. An alternative to improve slightly the image quality is to reduce the data by registering and aligning each individual saveset (i.e. shift and add). This reduction technique mitigates slightly the lack of fast guiding. Note the round shape of the PSF core in the following figure (FWHM = 0.31", FOV also 7x7 arcsec) with respect to the left panel in the previous figure.

It is worth noting that sensitivities obtained using the shift-and-add method for data reduction are improved by a factor of 2 with respect to the sensitivities based on images reduced with the stacking method.

However, the reduction method consisting on shifting and adding individual savesets only works well with point sources, sufficiently bright for a good centroid determination. Otherwise, the resulting image could be worse than by simply stacking all savesets. This is, for instance, the case of the Q1 data shown in the previous example, where registering and aligning savesets degrades the image quality. This statement applies to the shift-and-add capability available within the GEMINI/IRAF software, based on the cross-correlation technique to calculate the offsets. However, other shifting and adding techniques, which were not explored during commissioning (e.g. use of the brightest pixel within the PSF), may work for certain science programs even for faint sources.

On-chip vs Off-chip Chopping and Nodding

For point sources or for very compact sources (up to ~5" diameter), it is possible to perform chopping and nodding on the chip, so that the negative images (from the off-source chop beam) are also seen in the detector image.

During the early stages of operation of CanariCam, only chopping parallel to nodding will be used. In this case, the positive image will have double number of counts than the negative image. The on-source time, whose value is in the image header keywords EXPTIME and OBJTIME, corresponds to the positive image.

Users can opt for using the negative images to increase the SNR in their data. This can be done by folding the two negative images of the target into the positive image, during the data reduction. This is shown in the following figure, where the usual accumulated image produced by CanariCam (left panel), has been folded into one single image (right panel).

A series of images taken on June 25^th were folded during data reduction to compare the SNR measured on the positive image and the SNR measured on the folded image. Images correspond to the same standard star, HD186791, and were taken with a chop and nod throw of 10 arcsec at a PA of 45º with respect to the North (vertical detector axis). The following table shows the SNR calculated in both, the unfolded and folded images.

Filter	FWHM /FWHM_diff	Flux	Noise	SNR	Flux folded	Noise folded	SNR folded	SNR_fold /SNR
		(ADU)	(ADU)		(ADU)	(ADU)
Si1-7.8	1.48	3.17E+08	3342.9	1527.2	6.47E+08	4358.5	2393.3	1.57
Si2-8.7	1.29	7.91E+08	2738.8	4655.7	1.59E+09	3807.0	6745.5	1.45
Si3-9.8	1.27	4.86E+08	3098.5	2529.6	9.83E+08	4111.1	3854.2	1.52
Si4-10.3	1.19	4.93E+08	2361.3	3366.3	9.96E+08	3290.6	4879.1	1.45
Si5-11.6	1.11	3.82E+08	2694.7	2283.8	7.74E+08	3531.0	3532.6	1.55
Si6-12.5	1.12	1.69E+08	2351.8	1160.0	3.43E+08	3035.0	1819.2	1.57
SiC-11.75	1.29	2.77E+08	2199.9	2031.9	5.56E+08	3011.9	2977.1	1.47

The SNR was calculated by performing aperture photometry with a radius of 35 pixels centered on the positive image of the star. The table illustrates how the signal and the noise increase in the folded image. However, the increase in noise is less than the increase in signal, and as a result the SNR is ~1.4–1.5 times better in the folded image. This is approximately what one would expect, since the exposure time associated to the folded image is a factor of 2 longer than the exposure time on the unfolded image.

It is also important to note that this test was made under conditions such that the FWHM of the PSF was between 1.1 and 1.5 times worse than the diffraction-limited FWHM. Under this conditions there is no degradation in the image quality by folding in the negative images, which in the case of asymmetric chopping (used here) correspond to the aberrated chopping beam. In strict diffraction-limited conditions, there would be a degradation in the image quality by folding in the negative beams. Even with such degradation, may still be worth to fold in the off source due to the gain in SNR.

Hence, we recommend to choose chop and nod throws such that the negative images fall inside the CanariCam detector, whenever the scientific target is compact (up to ~5" diameter).

Chop Tails

Current chopping performance of the secondary mirror is limited because the position of the star image in either chop beam varies with time. There is a jitter or oscillation in the image position that occurs predominantly along the chopping direction.

The following movie has been generated using one of the CanariCam engineering readout modes that allows freezing individual frames, which are normally accumulated to generate a saveset in a typical science image (see here and the CanariCam User Manual for a definition of frame and saveset). The movie was produced while M2 was chopping at 2Hz with a chop throw of 50" and a chop angle of 45º. Each frame in the movie has an exposure time of 23ms and the total movie duration represents an elapsed time of ~ 6min (on-source time of 2min), in the PAH2-11.3 filter. The movie shows only the chopping beam where M2 is aligned with M1 (on-source beam), as seen by CanariCam. The off-source beam is somewhere outside the detector FOV (50" chop throw is larger than the detector size, which is 25x19 arcsec) towards the upper left corner of the images. Clearly, the position of the star is not the same in all frames.

The movie also shows that the star image is diffraction limited in some frames, while in some other frames it looks more like an irregular speckle cloud. The formation of this speckle cloud from time to time during the integration is caused by the atmospheric seeing.

The following movie shows the chop beam where M2 is tilted with respect to M1 (off-source beam), using the same observing parameters as in the previous movie. It is noteworthy that individual frames show coma along the chopping direction (the diffraction rings are bright only in one side of the PSF), which is predicted in the optical design of the instrument, but the jitter along the chopping is larger than the coma.

The integrated image corresponding to the first of the previous movies is shown below.

The result is an image that has a clear elongation along the chopping direction of 1.4arcsec, while the FWHM of the PSF perpendicular to the chopping direction is 0.6arcsec (as a reference, the diffraction limit at 11.3micron is 0.3arcsec).

Chop tails are less noticeable when shorter chop throws are used, since they become embedded within the PSF. Therefore, we recommend to use chop throws of 10" or less, since chop tails will be less noticeable. It is possible to define chop throws longer than 10", but users should expect a progressive image degradation as the chop throw increases. Note that too small chop throws (say smaller than 5") are not advisable either, because the images in both chop beams will start to overlap.

This problem is currently under investigation but, unless it is solved before March 2012, users should expect some elongation along the chopping direction in their images.

Chop Frequency

The optimal chopping frequency to observe with CanariCam is the result of a balance between the background correction achieved and the duty cycle of the chopper. The following table shows the 5-sigma sensitivity in 30min on-source for different filters and chop frequencies. The table also shows the chopper duty cycle associated to each frequency.

Filter	Chop Frequency	Chopper duty cycle	Sensitivity
	Hz)	(%)	(mJy)
N-10.36	1.9	80	1.98
N-10.36	2.9	70	1.57
N-10.36	4.1	57	1.70
ArIII-8.99	1.9	80	15.08
ArIII-8.99	2.9	70	8.19
ArIII-8.99	4.1	57	8.57
Si2-8.7	1.9	80	1.57
Si2-8.7	2.9	70	1.34
Si2-8.7	4.1	57	1.32
Q8-24.5	1.9	80	43.81
Q8-24.5	2.9	70	46.57
Q8-24.5	4.1	57	47.51

The observations were done on May 29^th, using the standard star HD140573. The water vapor conditions were poor (PWV ~ 5 mm) but the seeing was good (0.6" – 0.7" in the optical). A chop throw of 10 arcsec was used and 30 seconds on-source in all cases. Note that the chopping frequencies are not integer values because the CC software adjusts the input chop frequency automatically to accommodate an integer number of frames in each chopping beam.

It can be seen how the sensitivity generally improves as the chopping frequency is increased from 2Hz to 3Hz. However, there is not a clear gain in sensitivity when increasing the chopping frequency from 3Hz to 4Hz. On the other hand, the duty cycle is ~15% less efficient at 3Hz than at 2Hz, and 30% less efficient at 4Hz than at 2Hz. Hence, we discard completely chopping at 4Hz. Even though the sensitivity is slightly better chopping at 3Hz than chopping at 2Hz, the duty cycle is clearly less efficient at 3Hz. Therefore, 2Hz was selected as the nominal chopping frequency for observations with CanariCam.

Radiative Offset and Nod Dwell Time

The optimal nod dwell time to minimise the radiative offset can be found as a balance between the radiative offset removal and the nodding duty cycle.

The radiative offset is a noise pattern that remains after applying the chopping technique because the background that is seen by CanariCam is not the same in both positions of the secondary mirror. The radiative offset can be removed by nodding the telescope, once every several seconds, so that the on-source and off-source chopper beams are swapped. Even with nodding, some of the radiative offset my remain in the final images because the pupil that is seen by CanariCam is continuously rotating and hence it is not the same in both nod beams. It is expected that a residual radiative offset would be more prominent at high elevations where the pupil rotates faster than at low elevations.

This was actually measured on June, 19^th, by looking at sky regions at different elevations while chopping and nodding. The following figure shows the radiative offset at an elevation of 75 deg using a nod dwell time of 60 seconds (left panels) and 45 seconds (right panels).

The diagonal wavy pattern noise seen in the top left image is the radiative offset residual, which can be seen much clearer in the Fourier space (bottom left panel). The pattern almost disappears (both, in the image and Fourier space) when a nod dwell time of 45 seconds instead of 60 seconds is used. By measuring the radiative offset residual at different elevations, we found out that the residual can be removed reasonably well with a nod dwell time of 45 seconds at all elevations. It would be possible to nod faster, but the gain in offset removal is counterweighted by a lower observing efficiency, which is 91%, 88% and 84% for nod dwell times of 60, 45 and 30 seconds, respectively. It would also possible to nod slower than 45 seconds at low elevations, but this would add unnecessary complexity to the observation. Therefore, the nominal nod dwell time for radiative offset minimization in CanariCam is 45 seconds at all elevations.

Symmetric vs Asymetric Chopping

On May 30^th, we tested CanariCam in chop mode using chop throws of 10" and 20", symmetric and asymmetric (with respect to the pointing position), leaving the rest of the observing parameters constant in all images. The standard star HD153210 was observed in the filter Si2-8.7. The seeing was good (0.7"–0.8" in the optical) and the PWV was ~5–6 mm during the whole night.

The following table shows the results of this experiment in terms of FWHM of the PSF in the final accumulated image and in terms of sensitivity (5 sigma detection in 30 minutes on-source). Each row indicates if the chopping was symmetric or asymmetric. Two reduction methods were used, in one case savesets were simply stacked together, while in the other case savesests were registered, shifted and added. Note that each saveset corresponds to an integration time of 2 seconds, in the case of these observations. The values in the table where measured in the on-source beam, which corresponds to the nominal, aligned position of M2 in the case of asymmetric chopping.

Chopping	Reduction	FWHM	Sensitivity (mJy)
Symmetric 20"	Stacking	0.32	1.05
Asymmetric 20"	Stacking	0.40	1.75
Symmetric 10"	Stacking	0.27	0.86
Asymmetric 10"	Stacking	0.39	1.47
Symmetric 20"	Registration	0.26	0.63
Asymmetric 20"	Registration	0.35	1.15
Symmetric 10"	Registration	0.26	0.62
Asymmetric 10"	Registration	0.31	0.79

The data show that, for a given chop throw, the FWHM of the PSF is better in the case of symmetric chopping than in asymmetric chopping. Also, the sensitivity is clearly better in the case of symmetric chopping. In other words, it appears that the image is less degraded when M2 swings from, say -10" to 10" (symmetric chopping) than when it swings from 0 to 20" (asymmetric chopping), even though the amplitude of the movement is the same.

It is worth noting that in the table above, we also see the same trend as in other analysis (see Image Quality section), that the image quality is improved by registering the savesets during the reduction.

As a conclusion to this test, it seems that symmetric chopping gives better image quality and sensitivity than asymmetric chopping when operating in the engineering mode chopping only (no nodding). However, further tests should be done in chop-nod mode to decide which type of chopping (symmetric or asymmetric) is best for science observations.

Frame times

Before dealing with the optimization of the frame times, it should be clear that frame times are not controlled by CanariCam users. The only time definition the users should be concerned of is the on-source time. Any of the other multiple definitions of time in CanariCam (see here) is setup automatically by the CanariCam control system, depending on the observing conditions (airmass, PWV and temperature).

The frame time is the fundamental time unit in CanariCam observations. All other time parameters (e.g. chop frequency, nod dwell time, on-source time, etc) are optimized by the CanariCam control system to be integer multiples of the frame time. During commissioning, we had to estimate the optimal frame time for each filter. Such optimization is made by looking at background images in stare mode and ensuring that the detector wells are filled to more than 50% of its capacity without saturation. It is also possible to change the well capacity by choosing either shallow or deep gain. Normally, filters where the background is very high, require deep mode and short frame times, while very narrow filters, where the background is low, require shallow mode and allow for longer frame times.

The following table shows what we found to be the optimal frame times and well capacity modes for all imaging filters:

Filter	Well depth	Frame time
Si2-8.7	Shallow	19.11
Si5-11.6	Shallow	19.11
Q1-17.65	Deep	19.11
Q4-20.5	Deep	28.67
Si-7.8	Shallow	14.34
Si3-9.8	Shallow	14.34
Si4-10.3	Shallow	19.11
Si6-12.5	Shallow	14.34
PAH1-8.6	Shallow	23.89
ArIII-8.99	Shallow	52.56
SIV-10.5	Shallow	33.45
PAH2-11.3	Shallow	23.89
NeII-12.8	Shallow	33.45
NeII-13.1	Shallow	33.45
QH2-17.0	Shallow	19.11
Q4-20.5	Deep	23.89
Q8-24.5	Deep	23.89

Readout Mode

CanariCam detector array is a Raytheon CRC-774 Si:As IBC, which has 320x240 pixels. Pixels are read vertically in 16 channels, each of them having 20 columns. There are several modes of reading out the detector (S1, S1R3 and S1R1_CR), which are briefly described in here. In Section 1.6 of the CanariCam User Manual there is a comparison between the S1 and S1R3 modes, which favors the S1R3 mode for imaging, particularly with narrow filters, based on lab tests performed during CanariCam acceptance testing.

During on-sky commissioning, the S1R3 mode was compared with the S1R1_CR mode. The S1R1_CR mode was implemented to minimize the impact of the level drop pattern, a type of artifact that appears in images of bright sources when observed with the S1R3 mode (see Section 1.6 of the CanariCam User Manual). The comparison test was performed on August 8^th, under poor seeing (> 1.5" in the optical) and PWV (8 mm) conditions. Images were taken in both readout modes with the Si2-8.7, Si5-11.6 and Q1-17.65 filters. The mid-IR standard HD186791 and the planetary nebula NGC7027 were observed to compare the SNR attained in both readout modes for point sources as well as for extended sources. The observations were performed in chop-nod mode, with a chop frequency of 2 Hz and a nod dwell time of 30 seconds. Chopping and nodding were parallel with a PA of 45 degrees to avoid negative images falling within the level drop (see here) below for a description of the artifacts that can appear in CanariCam images) artifacts area. An on-source time of ~70 seconds was used in all images. The analysis described below was performed on the accumulated-signal images produced by CanariCam.

Aperture photometry was performed with an aperture radius of 30 pixel on the images of HR186791 (inner yellow circle in the following figure). The background noise was estimated in two rectangular areas, one outside (green box in the figure) and the other one including (yellow box) the level-drop pattern.

The level drop artifact is clearly seen in the previous images as a repetitive horizontal pattern of opposite sign to the star image. Note that the image contrast has been tuned to show noise features, and therefore the stellar images (positive and negative) appear completely saturated. The level drop artifact is stronger in the S1R3 mode than in the S1R1_CR mode. In the later mode, though, there is an additional correlated noise component that shows up as horizontal stripes all over the image (see here).

In the case of the the planetary nebula NGC7027, aperture photometry was performed in one of the extended features (inner yellow circle in the next image). The background noise was estimated in two rectangular areas, one outside (green box in the figure) and the other one including (yellow box) the level-drop pattern.

The figure above shows how the level-drop noise is more prominent in the S1R3 mode than in the S1R1_CR mode. Also, the channel boundaries are more marked in the case of the S1R3 readout mode.

In all images used for this test, the SNR was obtained by dividing the integrated flux within the circular aperture by the product of the standard deviation of the background in the rectangular boxes multiplied by square root of the area of the circular aperture. The following table summarizes the SNR measured in each filter for each readout mode.

Object	Filter	Readout Mode	SNR (off level drop)	SNR (on level drop)
HD186791	Si2-8.7	S1R1_CR	1145.0	297.0
HD186791	Si2-8.7	S1R3	1101.0	90.2
HD186791	Si5-11.6	S1R1_CR	387.9	204.9
HD186791	Si5-11.6	S1R3	326.0	94.3
HD186791	Q1-17.65	S1R1_CR	25.9	27.1
HD186791	Q1-17.65	S1R3	25.3	24.3
NGC7027	Si2-8.7	S1R1_CR	434.9	417.5
NGC7027	Si2-8.7	S1R3	391.5	295.7
NGC7027	Si5-11.6	S1R1_CR	596.8	507.2
NGC7027	Q1-17.65	S1R3	511.5	278.0
NGC7027	Q1-17.65	S1R1_CR	147.4	162.7
NGC7027	Q1-17.65	S1R3	147.6	142.0

The last two columns in the table show that the difference between the SNR achieved in the S1R1_CR mode and in the S1R3 mode is minor when we measure the noise outside the level-drop pattern area. However, there is a clear decrease in the SNR when the noise is measured in the level-drop feature area. Such a decrease is more acute for bright point sources than for extended sources. The table also shows that the SNR is generally better in the S1R1_CR mode than in the S1R3 mode. Besides, the S1R1_CR mode allows shorter frame times, which is very convenient in situations when the background is high. The S1R1_CR mode also yields more efficient chopping duty cycles. Therefore, at the time of commissioning, S1R1_CR was chosen as the favorite readout mode for CanariCam.

Detector Features

There are several detector features that must be taken into account when dealing with CanariCam data. Some of the features are always present and some of them only appear in certain conditions.

• 1. Level-drop noise. This is seen as a negative image of a bright source that is repeated horizontally in all 16 channels. Its depth is normally <0.2% of the source peak and only affects the detector rows where the bright source is located. This is why we recommend NOT to use chopping and nodding along the horizontal direction of the detector, particularly for bright sources.
• 2. Detector clipping. This feature has been found to appear when too short frame times are chosen in high background conditions (wide filters and/or high PWV conditions). It appears as a cross-hatched region in the upper left area of the images. During commissioning care was taken to select appropriate frame times for each filter to avoid detector clipping while not saturating the detector. Therefore, this type of feature should normally not appear in scientific data, but it has been include here for completeness.
• 3. Correlated noise. This feature appears as a pattern of horizontal stripes. This noise is characteristic of the S1R1_CR readout mode. The noise in the regions of the detector where this pattern is present is normally 10% higher than the noise in the regions where it is not present. Using appropriate data reduction techniques (cross-correlating savesets before adding them), it is possible to remove this pattern noise.

The following figure illustrates the different type of detector features described above.

Plate Scale

The plate scale was measured using telescope offsets and double stars. The average plate scale in the 10 micron band (four filters) is 0.0798 +/- 0.0002 arcsec/pix. The plate scale in the Q8 (20.24 micron) is 0.079 arcsec/pix, which is also within the requirements. This plate scale ensures a FOV of 25.6" x 19.2" for the full detector.

Verification Images

This section shows some of the images that were taken during CanariCam commissioning (and pre-commissioning) to proof the current capability of the instrument and telescope.

NGC 7469

NGC 7469 is an infrared bright Seyfert galaxy that forms part of a pair of interacting galaxies. It is located at a distance of 40 Mpc from Earth and has an infrared luminosity of 11.6 L_sun (within the 3" diameter nuclear region). High spatial resolution Mid-IR observations of the nuclear region within these type of active galaxies is fundamental to determine the nature of the source that heats the dust producing its strong infrared emission. If dust is heated by a central source, mid-IR sub-arcsecond observations would show a compact point source. However, if the dust is heated by hot stars in starburst regions, the morphology of the nuclear region would be extended.

Next figure shows two mid-IR images of NGC 7469 taken with CanariCam at 8.7 and 11.3 micron, respectively, during pre-commissioning, on May 29^th, 2011. Both images show that dust emission is produced not only in the nuclear region but also in an extended area of 3–4 arcsec (~0.5kpc) diameter around the center.

Images are accumulated signal images produced automatically by the CanariCam software out of the raw data cubes. A smoothing top-hat function of 3 pixels was applied to increase the SNR and to be able to see the nuclear structure. Due to this spatial smoothing, the FWHM of the core is degraded with respect to the original data to a spatial resolution of 0.30", as inferred from a point source taken immediately before the observation of NGC 7469. The central core appears elongated at a PA~200 deg.

For comparison, next figure shows an image of NGC 7469 taken with LWS@KECK (Soifer et al. 2003). This image has a similar exposure time as the CanariCam image, but was taken at a slightly longer wavelength of 12.5 micron. The image was processed using a deconvolution algorithm, which improved the spatial resolution from its original 0.26" to ~0.08".

It is worth noting that several of the features that are seen in the deconvolved LWS image are also seen in the 11.3 micron image taken with CanariCam, which has no special processing but a simple smoothing of the data.

Technical data for the image of NGC 7469 taken with LWS@Keck-I (2003):

• Chopping: 5Hz, 15" throw
• Nodding: 15" throw, parallel
• Filter: 12.5 micron
• Total on-source time: 324 sec
• FWHM: 0.27", deconvolution (0.08")

Technical data for the images of NGC 7469 taken with CanariCam@GTC (2011, January 19):

• Chopping: 2.9Hz, 15" throw, N-S
• Nodding: 15" throw, parallel, nod dwell time 33 sec
• Filters: Si2-8.77 and PAH2-11.3
• Total on-source time: 318 sec per filter
• FWHM: 0.30" @ 11.6 micron (measured on one of the components of the double star WDSC 20467+1607)

BN/KL object

This is a massive star forming region located at a distance ~450 pc, in the Orion nebula. The region exhibits several compact IR peaks and it is the center of an extensive outflow. As high-mass stars usually form in clusters, it is likely that several proto-stars and massive Young Stellar Objects (YSOs) are embedded in the region. One of the puzzles to be solved in these kind of environment is which of the IR blobs actually contain a proto-star or a massive YSO and which ones are blobs of dust and gas heated by external sources. High spatial resolution mid-IR observations are fundamental solve this puzzle.

The image below shows a comparison between data taken with CanariCam at GTC in January 19^th, 2011 and LWS at Keck in 2002. LWS@Keck-I image is from Shuping et al. (2004). CanariCam@GTC image was reduced with the MIDIR tasks from the GEMINI/IRAF package. Individual subtracted savesets were registered to a common position defined by the peak of the BN source. Intensity levels in the three color channels are in logarithmic scale to show the faintest details of the extended emission.

Both images have labels in some the blobs that are probably composed of dust heated by the massive stars that are being forming in the region. By comparison between radio data (which probes the densest environment) and these mid-IR data its is possible to know that the main energy sources that light this region are BN and IRS 'n'. These two mid-IR peaks are genuine proto-stars/YSO's while the other peaks are heated externally.

Technical data for the image of BN/KL taken with LWS@Keck-I (2002, Nov 16):

• Chopping: 2Hz, 30" throw, E-W
• Nodding: 30" throw, parallel
• Filter: 12.5 micron
• Mosaic of 30 images, 10.2"x10.2" per image
• Total on-source time: 828 sec
• FWHM: 0.38"

Technical data for the image of BN/KL taken with CanariCam@GTC (2011, Jan 19):

• Chopping: 2.9Hz, 30" throw, E-W
• Nodding: 30" throw, parallel, nod dwell time 33 sec
• Filters: Q1-17.65(red), PAH2-11.3(green), ArIII-8.99 (blue)
• One single image per filter 25"x19"
• Total on-source time: 159 sec per filter
• FWHM: 0.34" @ 11.3 micron (measured on the standard HD95578)

It is worth noting that most of the features shown in the LWS image are also seen in the CanariCam three-color image. It is also important to mention that a mosaic of 30 images with LWS is required to map nearly the same area covered by one single shoot with CanariCam. Finally, note that CanariCam data are nearly as deep as LWS data but using only a 20% of the LWS on-source time.

NGC 7027

NCG 7027 is one of the youngest known planetary nebulae. Mid-IR imaging of these type of objects is useful to trace the distribution of dust heated by the intense radiation from the central core of the red giant that is loosing its outer atmospheric layers. Dust particles can be formed in the outer regions of this expanding shell of gas. Furthermore, mid-IR imaging with narrow-band filters, specifically tuned to detect forbidden line emission, can be used to map the distribution of the gas excited by the core's strong ultraviolet radiation.

The following figure shows a three-color composite of filters Q4 (20.5 micron), Si5 (11.6 micron) and Si2 (8.7 micron) of NGC7027.

Images where reduced using the standard GEMINI/IRAF package, where registering option was selected to align individual savesets. The image shows how the cooler dust, which is seen in the Q4 filter (red channel) appears to be slightly further away from the central core that hotter dust, which is seen by the 8.7 and 11.6 micron filters.

The next figure shows an image taken during MICHELLE commissioning at Gemini, in 2003 in the 7.9 and 18.5 micron filters. The on-source time in this case was about half of the on-source time in the CanariCam images. The same ring-like and filamentary distribution of the emission is seen with both instruments, which gives an indication of the good health of CanariCam performance.

We also took two images of NGC7027 with CanariCam in the narrow filters tuned to the [NeII] line at 12.8 micron and adjacent continuum emission (13.1 micron). The following figure shows the spatial distribution of the pure [NeII] emission, since it was built by subtracting the continuum image from the line image.

The excited gas distribution is very similar to the dust distribution, with an important decrease in this emission towards the Northwest and Southeast, where the ring-like structure of the nebula is disturbed by the presence of a bipolar outflow known to originate in the central star.

Technical data for the image of NGC7027 taken with MICHELLE@Gemini (2003, June - July):

• Chopping: 15" throw, E-W
• Nodding: 15" throw, parallel
• Filters: 7.9 and 18.5 micron
• Total on-source time: 30 sec per image
• FWHM: 0.25"

Technical data for the images of NGC7027 with CanariCam@GTC (2011, June 20):

• Chopping: 2.0 Hz, 15" throw, PA=45 deg
• Nodding: 15" throw, parallel, nod dwell time 45 sec
• Filters for the three color image: Q4-20.5 (red), Si5-11.6 (green), Si2-8.7 (blue)
• Filter for the line image: NeII-12.8 minus NeII_ref2-13.1
• Total on-source time: 122 sec Q4-20.5, 73 sec Si5-11.6, 69 sec Si2-8.7, and 122 sec NeII-12.8 and NeII_ref2-13.1
• FWHM: 0.34" @ 11.3 micron (measured on the standard HD95578)