KITT PEAK FLAMINGOS INFORMATION
Contents
*** Spectroscopic Cautions ***
FLAMINGOS Manuals:
- 4-meter Observer's Guide [.pdf file] – REVISED January 2007
- 2.1-m Observer’s Guide [.pdf file] -- REVISED January 2007
- 2.1-meter Guider usage [.pdf file]
- MOSplate Design, etc. [.pdf file]
One may also download manuals from the FLAMINGOS web site at http://flamingos.astro.ufl.edu/Manuals
Introduction
FLAMINGOS, the Florida Multi-object Imaging
Near-IR Grism Observational Spectrometer,
has been in use at
The information on this web page is intended primarily for scheduled users and those interested in proposing to use the instrument. The information will be updated as needed to reflect the most recent status of the instrument. This information is current as of March 2007.
Availability
In the past, FLAMINGOS has been shared between
IMPORTANT NOTE FOR PROPOSERS! In order to make it easier to schedule and
support the MOS mode, any programs that will use multislit
mode should identify the instrument as FLMNM in the proposal. Requests for
imaging or long-slit mode (or both) should identify the
instrument as FLMN.
FLAMINGOS is a wide-field IR imager and multi-slit spectrometer designed and built by Richard Elston at the University of Florida, with some collaboration and support from NOAO. The imaging mode is provided by a fairly conventional optical train, consisting of a refractive collimator, filters, cold stop and a camera, which images the focal plane onto a 2K x 2K HgCdTe detector. The instrument can be used on both the 2.1-m and 4-m telescopes; pixel scale and field of view values for each telescope are summarized below:
FLAMINGOS Imaging Parameters
|
Telescope |
4-m |
2.1-m |
|
arcsec/pixel |
0.316 |
0.606 |
|
Field of View (arcmin) |
10 x 10 |
20 x 20 |
The filters available for imaging are J, H, K and Ks. The filters are located in a fast beam, so that narrowband filters will not work very well over the full field, and there are no current plans to provide any.
The cold stops are on a wheel, so that an optimized cold stop is available for each telescope.
The image quality of the optics (as designed and toleranced) is well-matched to typical image quality on the 4-m, and is about 2 pixels FHWM over most of the field (a little worse at the corners and at the very left-hand side of the array). This does mean that imaging on the 2.1-m will mostly not be seeing-limited, particularly at the corners, where field curvature becomes significant.
The spectroscopic mode is provided by a cold slit mask placed at the telescope focal plane, which is in front of the camera dewar, and by a grism placed after the cold stop. The slit masks are mounted in a wheel in a separate MOS dewar in front of the camera section at the telescope focal plane. The MOS dewar can be warmed up and cooled down quickly, allowing the masks to be changed during the day. The wheel can accommodate 11 slit masks (enough for a reasonable night’s program), in addition to permanently-mounted long slits. The width of the slit masks is roughly 1/3 of the imaging field (i.e., about 3 x 9.5 arcmin on the 4-m). A second wheel contains deckers, which restrict the field of view as appropriate for imaging, long-slit spectra, and multi-slit spectra.
At present, there are two grisms covering the JH and HK atmospheric windows which provide two-pixel R ~ 1000 – 1800, depending on the wavelength and filter/grism combination. At this resolution, one obtains full spectral coverage even for off-center slit locations at the edges of the slit masks for HK spectroscopy, but there will be some spectral vignetting for JH spectroscopy for slit locations at the edges of the masks.
2-m Declination
Limit
The instrument will run into the fork of the 2-m telescope at declinations north of +80. There is no hour angle limit, (although the instrument doesn't clear the control room roof by much). Anyone who needs to observe fields north of +78 must propose to use the 4-m telescope.
Further
Information
Additional information on FLAMINGOS can be found through the FLAMINGOS home page.
FLAMINGOS Imaging Performance
Measured values for imaging performance are given in the tables below. Prospective users need to remember that near-infrared background can vary by a factor of three or more; for the K and Ks filters, where the background is mainly thermal emission, it is correlated with temperature and therefore quite seasonal. At J and H the background is primarily OH airglow and levels are unpredictable. A detailed discussion of background variation provided in the SQIID manual is equally applicable to FLAMINGOS.
The performance values for the 2.1-m and 4-m telescopes are based on actual data, although from a limited number of nights and at different times of the year, so they are not exactly self-consistent. The 4-m performance numbers are nominally the same as those for ISPI at the CTIO Blanco 4-m. The observed performance from the extensive GOODS survey at J and Ks agree to within 0.1 – 0.2 mag.
NOTE: The upper right quadrant of the array has a higher read noise than the other three quadrants. This can also be seen on dark images as an apparent periodic pattern. Extensive work during the summer of 2003 on the MCE-4 controller did result in improved performance, except in this quadrant, and the cause remains unknown. This should not seriously affect imaging applications, since the limiting noise is determined by the sky background, but it could have some effect on lower-background spectroscopy. For single-object longslit spectroscopy, one may wish to keep the spectra on the lower two quadrants.
One should estimate the imaging performance on the KPNO 4-m telescope using the ISPI Exposure Time Calculator, since the performance of the two instruments is virtually identical. The IRAF Exposure Time Calculator, which uses the IRAF task ccdtime, may be used to estimate the performance of FLAMINGOS on the 2.1-m telescope; this will also work for the 4-m, but for consistency, we recommend that the ISPI performance be used. The ccdtime task assumes that the effective aperture is 1.4 times the seeing, so to duplicate the performance given in the 2.1-m table below, a seeing of 2.1 arcsec must be used. Different values for the assumed seeing will, of course, result in different results for the predicted performance.
Predicted FLAMINGOS Performance on
KPNO 4-m
FWHM=3 pixels 0.95 arcsec
Aperture 2.2 arcsec diameter
|
Filter |
Mag=15 e- sec-1 |
Sky mag arcsec-2 |
Sky e- sec-1 pix-1 |
60 sec 10 sigma |
600 sec 10 sigma |
3600 sec 10 sigma |
|
J |
3450 |
15.7 |
180 |
18.8 |
20.0 |
21.0 |
|
H |
4480 |
13.9 |
1250 |
18.0 |
19.2 |
20.2 |
|
K |
4360 |
12.9 |
3050 |
17.5 |
18.7 |
19.7 |
|
Ks |
3800 |
13.1 |
2210 |
17.6 |
18.8 |
19.8 |
Predicted FLAMINGOS Performance on
KPNO 2.1-m
FWHM=2 pixels 1.2 arcsec
Aperture 2.8 arcsec diameter
|
Filter |
Mag=15 e- sec-1 |
Sky mag arcsec-2 |
Sky e- sec-1 pix-1 |
60 sec 10 sigma |
600 sec 10 sigma |
3600 sec 10 sigma |
|
J |
1050 |
15.1 |
335 |
17.6 |
18.8 |
19.8 |
|
H |
1320 |
13.1 |
2815 |
16.7 |
17.9 |
18.9 |
|
K |
1300 |
12.7 |
4028 |
16.5 |
17.7 |
18.7 |
|
Ks |
1140 |
12.9 |
3925 |
16.3 |
17.6 |
18.6 |
The instrument gain is approximately 4.9 electrons/ADU for imaging (bias = 1.0 v)
The sensitivity values are based on aperture photometry for the diameters listed above the tables. Sensitivity will scale with aperture size, since most of the photons in an aperture will be due to sky.
Note that the exposure times do not include overheads associated with writing data to disk, moving the telescope between dithers, acquiring the field, etc. For short exposures, overhead will significantly reduce efficiency. The instrument overhead is quite short (less than 10 seconds) to read out the array and write the data to disk, so for most observing programs the time between images is determined by telescope overheads involved in dithering or rastering. For short offsets, the offset and settling times combined should be around 10 seconds.
The detector full well is sufficiently large that maximum exposure times at K are around 30 seconds (at least in the winter), 45 seconds at Ks and a minute or more at J and H. As noted above, the overhead in writing to disk is modest.
Although the minimum legal exposure time is under 2 seconds, in practice the instrument cannot keep up with exposure sequences for times that short, and a minimum practical time is around 5 seconds. Users should also be aware that even at longer exposure times, a small fraction of the images in any sequence may be lost, and should plan so that loss of a single frame does not seriously compromise their program. (This is a good rule for IR imaging in general.)
Imaging Linearity
The linearity correction (courtesy of Anthony Gonzalez at UF) for the imaging mode can be expressed as a third-order polynomial:
y = 1.00425 * x – 1.01413 * 10-6
* x2 + 4.18096 * 10-11 * x3
where x is the raw signal and y is the linearity corrected signal in ADU. For the IRAF ‘irlincor’ task, the coefficients are:
a = 1.00425, b = -0.03323, c = 0.04489
FLAMINGOS Spectroscopy
FLAMINGOS presently contains two grisms, one optimized for the JH bands and the other for HK, with a resolution (2 pixels) of approximately 1300 for both at the middle of the wavelength band. Blocking filters for JH (0.9 – 1.8 microns) and HK (1.25 – 2.5 microns) provide coverage of the combined bands with the appropriate grism. As shown in the table below, the JH spectrum covers almost all of the array, so there will be some vignetting of the spectrum for MOS slitlets which are offset near the edges of the masks. This is not the case for the HK spectra, which cover significantly less than the full width of the array.
Approximate Spectroscopic Format
|
Band |
Pixel 1 (A) |
Pixel 2048 (A) |
Δλ/pixel (A) |
|
JH |
8910 |
18514 |
4.680 |
|
HK |
10347 |
27588 |
8.551 |
For spectroscopy, one uses a different bias (0.75 v) than is used for imaging, and the conversion gain is slightly different (4.1 e/ADU).
At the 4-m, the instrument rotator may be used to rotate the position angle of the slit between 0 and 180 degrees. At the 2.1-m, the slit orientation is fixed N-S.
Performance is more difficult to characterize for spectroscopy than for imaging, since both the signal and sky background have spectral structure, so that "sensitivity" is a strong function of the particular wavelength of interest, especially at resolutions around 1000. An illustration of the sky background in the JH spectroscopy mode is shown below in Figures 1 and 2.
Figure 1. A selected subregion of the FLAMINGOS array (2048 x 190) showing the night sky spectrum in JH spectroscopy mode with a 4-pixel slit. The integration time is 600 s. Wavelength increases from left to right.
Figure 2. Plot of the JH sky spectrum from Fig. 1, showing the atmospheric OH emission lines. Signal is ADUs (NREADS=1) in 600 s. Ordinate is in pixels.
Spectroscopic Signal Levels
The FLAMINGOS signals for JH and HK spectroscopy are illustrated in Figure
3. These were obtained on the
Figure 3. Raw FLAMINGOS signal levels in ADU/s for a 0.0 mag star through a wide slit for the JH region (top panel) and HK region (bottom panel). The signal in the HK spectrum redward of 2.5 microns is second order H band signal.
Spectroscopic Background
Ideally, the performance of a spectrograph is limited by the sky background, which consists primarily of emission lines from OH in the upper atmosphere in the J, H, and short K bands (Figure 1) and thermal continuum which increases sharply beginning at approximately 2.2 microns. The division of FLAMINGOS into separate MOS and camera dewars requires a vacuum-tight transparent interface between the two to permit bringing the MOS dewar up to atmospheric pressure for mask changes; this is the BaF2 field lens which also serves as the camera dewar window. The presence of a warm optical element behind the slit plane results in significant additional thermal background which is dispersed by the grism onto the detector and limits the performance of the instrument for spectroscopy. This is particularly significant for HK spectroscopy, where the dispersed thermal background completely dominates the spectral image (Figure 4).
Figure 4. Raw image of a MOS spectrum in HK mode, showing the substantial dispersed thermal background superposed on the spectra of the MOS slitlets. The higher background spectra at the top and bottom are from the four square acquisition boxes on the MOS mask.
The background near the lower center of the array [1200:1225,605:630] was measured for various combinations of grism and blocking filter; the results are displayed below. As expected, the background with the HK grism correlates with the long wavelength cutoff of the blocking filter. In addition, the imaging filters (J, H, K, Ks) are of excellent quality and have higher throughput than the spectroscopic JH and HK blocking filters. Therefore, observers who have scientific interest only in the K band (or a portion thereof), should consider using either the K or Ks filter as a blocker with the HK grism to take advantage of both higher signals and lower background. A somewhat surprising result is that the background through the JH blocker is significantly higher than with the H filter when used with the JH grism, even though the long wavelength cutoff is nominally the same for both filters. This could result from the true JH cutoff being somewhat longer than the nominal 1.80 microns or from a small long wavelength leak in that filter. This background (~ 4 e/s) is sufficient to degrade the predicted performance between OH lines by almost one magnitude.
Background
(ADU/s; 1 LNR; 0.75v bias) in Different Spectroscopic Modes
|
Grism |
Filter |
Background (ADU/s) |
|
JH |
H |
0.18 |
|
JH |
JH |
0.95 |
|
HK |
H |
0.17 |
|
HK |
Ks |
12.7 |
|
HK |
K |
19.6 |
|
HK |
HK |
47.3 |
Approximate spectroscopic sensitivities based on the observed signal and background levels are summarized below. These were estimated using a slit throughput of 0.5, which is typical for a 2 or 3 pixel slit at the 4-m under nominal seeing conditions. The JH background is fairly uniform across the array and, as noted above, limits the performance between the OH lines, but not at the OH line wavelengths.
Approximate Spectroscopic
Sensitivities
|
Band |
Magnitude in 1 hour, 10-sigma |
|
|
4-m |
2.1-m |
|
|
JH, between OH lines |
15.5 |
14.5 |
|
JH, on OH line peak |
14.5 |
13.8 |
|
HK, mid-array |
13.4 |
12.7 |
Single Slit
Spectroscopy
The FLAMINGOS MOS wheel contains single slits of widths 2, 3, 6, 9, 12, and 20 pixels. The 3 and 6-pixel slits cover almost the entire array length, but the others cover approximately 65% of the array. In addition, there is a 3-pixel long slit installed in one of the 11 MOS positions.
Additional 2, 3, and 4-pixel wide custom slit masks useable for observations of compact objects also can be installed in the MOS wheel. These masks have two 60 arcsec long slits (at the 4-m) offset by 60 arcsec on either side of the center. At the center is a 10-arcsec square hole which can be used for target acquisition. This permits one to acquire and center a target in the hole prior to offsetting to the slit without the need to move the MOS and decker wheels between imaging and spectroscopic positions. For easily-identified targets, this can save some acquisition overhead at the telescope.
Important Note: In June 2006, the MOS wheel was found to have shifted axially from the actual input focal plane defined by the camera dewar optics by approximately 2 mm. This produced a significant defocus of the MOS slitlets and long slits in the MOS wheel. The cause of this is unknown, but might have been within the camera dewar. This problem was addressed by shimming the MOS masks in the wheel so they (and any long slits mounted in mask frames) are now in focus, but the long slits permanently mounted in the MOS wheel cannot be shimmed in this manner, so they are, for now, unusable.
MOS Mask
Information
NOAO presently supports multi-object spectroscopy from the community only
at the
Masks will be made from user-supplied celestial coordinates (a , d). These will need to be provided to NOAO
several weeks in advance of the observing run. Details will be provided to
successful proposers.
In addition, it is possible to use the .pos output files from the
The coordinates will need to be accurate enough to ensure that objects are centered on the slit (a 2-pixel slit is ~0.6 arcsec at the 4-m). Each mask must contain at least three well-distributed setup star apertures typically 8 arcsec square. These stars are required to acquire the field and center the target objects on their respective slits, since it is seldom practical to check mask alignment using program objects directly. Note that these stars will produce their own spectra during the observations, so the real estate in the dispersion axis occupied by the setup stars is not available for program objects. The acquisition and centering procedures involve the use of the IRAF ucsclris.xbox task and are fully described in the 4-m FLAMINGOS Observers Guide. A more simplified IDL script, which is available at the telescope, has also been used successfully to align the MOS masks with the field.
The mask wheel holds 11 masks; cycling the MOS dewar containing the mask wheel takes a good part of the day, so one is limited to 11 MOS fields per night.
The full suite of spectroscopic capabilities is being offered, but prospective users should read the caveats on spectroscopy below.
· Setup of spectroscopic observations can be time-consuming, and observers will need to do significant pre-observation planning.
· For long slit spectroscopy, unless the program objects are bright enough to be easily centered (H<17 or so on the 4-m), a nearby offset star is strongly recommended. This should be close enough to permit guider-controlled offsets on the 4-m. Long-slit observations on objects fainter than H~16 are probably best done on the 4-m rather than at the 2.1-m.
· Long-slit spectroscopy at the 2.1-m is possible, but more complicated than at the 4-m. The 2.1-m does not have a movable guide probe, but instead utilizes a fixed off-axis mirror feeding the guider ICCD camera. The guide field is approximately 5.5 x 4.2 arcmin and is roughly 200 arcsec E and 1500 arcsec S of the FLAMINGOS field center. Although one can position a cursor to guide on a star anywhere in this field, it is not possible to reposition the mirror to cover a wider patrol field. Note that one must allow sufficient clearance from the N-S edges of the field to beam switch along the slit while keeping the guide star in the field of view. We strongly recommend that investigators check for potential guide stars prior to submitting a proposal for 2.1-m spectroscopy, particularly for fields out of the galactic plane. Alternatively, one should be prepared to observe alternate program objects in the event that some of the primary targets may not be observable due to the lack of a suitable guide star.
· Note, too, that large offsets along the slit (as opposed to typical 10 arcsec or so of "dither") on either telescope will require careful setup to ensure that the object is centered on the slit at both beam positions.
· For multi-object spectroscopy, observers will need accurate coordinates of their program objects, and of three setup stars in the program field. Details of the coordinate requirements will be provided to successful proposers. Anyone planning such observations should also plan to obtain the required coordinates and provide them to KPNO support at least 3 weeks in advance of scheduled time to permit vendor fabrication of the masks.
·
In writing proposals, observers should allow
approximately 20 minutes for acquisition and set-up for standard (point source)
long slit observations. They should allow at least 45 minutes for MOS
observations, probably more for the first field of the run. Anyone considering observations different from
the standard types described above should consult with NOAO (or
Spectroscopic Calibration
Flatfielding
Because the sky background has spectral structure (see Figure 1 above), there is no spectroscopic equivalent to flatfielding on the sky, as is commonly done for imaging. It is therefore necessary to obtain dedicated flatfields using the telescope flatfield lights to illuminate the interior of the dome. As with imaging dome flats, one should take a number (> 10) of images of the illuminated dome, followed by an equal number with the lights off for bias subtraction. Because there is a thermal continuum component (particularly in the HK mode), one should not use darks as the bias reference for the flats.
· Since there is some flexure within the instrument, we recommend that dome flats be taken with the telescope in approximately the same orientation as used during an observation. This is particularly important for MOS observations, since the slit lengths are generally short, and any flexure will result in a relative displacement of the observation and flatfield slit illumination functions. For MOS observations, it is important to obtain separate flatfields for each MOS mask to ensure that the same portions of the array are illuminated by both the observations and flatfields. The easiest way to accomplish this is to rotate the dome in front of the telescope after an observation (or one may want to move the telescope back to its position at the observation midpoint) and illuminate the interior of the dome with the flatfield lights.
· For longslit observations, the effects of flexure will be evident only at the ends of the slit, so it may be acceptable to obtain a single set of flatfield observations at the beginning or end of the night using the standard White Spot.
· The comparison source built into the 4-m rotator/guider has a limited projection field (since it was designed for the RC spectrograph) which will not fill the 3 x 9.5 arcmin field of the MOS or longslit input, so its use for flatfielding is not recommended. If one is using one of the KPNO custom slits with the acquisition box in the center and two 1 arcmin long slits on either side, it is possible to use the 4-m comparison source.
Wavelength Calibration
The atmospheric OH emission lines which appear in the raw observations provide a natural template for wavelength calibration. These lines are well-distributed throughout the J, H, and most of the K bands, out to about 2.32 microns. When doing MOS observations, each spectrum will have a unique wavelength zero point, which is a function of the location of the slit in the dispersion coordinate, so the OH lines are generally the most useful calibrator. It is possible, on the 4-m telescope, to use the HeNeAr emission line calibration source in the guider/rotator (there is no guider or calibration source at the 2.1-m telescope). However, because this source (like the continuum source) does not fully illuminate the MOS input field, it may not be useful for MOS calibrations.
At the spectral resolution of FLAMINGOS, many of the OH lines (and some of the HeNeAr lines) will be blended. Therefore, it is important to select isolated lines which can be confidently identified when wavelength calibrating the spectra. Figures 5 and 6 show calibrated spectra of the HeNeAr source taken through a 4-pixel slit.
Files of both the OH lines and HeNeAr lines may be downloaded for use in calibrating spectra. The files have multiple columns corresponding to vacuum wavenumbers, vacuum wavelengths, and “air” wavelengths. One may select the desired column to create the calibration of your choice by using the IRAF fields task. For example, to pick column 4 in the file ‘OH_lines.txt’ (air wavelengths), execute in IRAF:
fields OH_lines.txt 4 > OH_lines.ang.dat
The latter file can then be used as the line reference source for the identify task (you may need to ‘sort’ the file so that the numbers are monotonically increasing for the automatic identification to work properly).
· There is some small distortion of the FLAMINGOS field from the wide field camera. In addition, a grism (unlike a reflection grating) will not in general have a linear relation between pixel and sin(b), since the prism itself has some dispersion. As a result, it may be necessary to use a relatively high order function (i.e., Legendre order 4 or 5) to get a fit over the entire JH or HK region. One can experiment with breaking the spectrum into separate bands and fitting the wavelengths within each band separately.
· The HK spectrum covers significantly less than the full 2048 pixels. We recommend truncating the spectral image at the end of the K band (2.45 microns) before carrying out the wavelength identification to keep the fitting function well-behaved.
Figure 5. Wavelength fit for the JH spectroscopy mode to a HeNeAr spectrum. The fit used 50 lines, a Legendre order 5 polynomial, with an rms of 1.4 A.
Figure 6. Wavelength fit for the HK spectroscopy mode to a HeNeAr spectrum. The fit used 15 lines, a Legendre order 4 polynomial, with an rms of 1.7 A. The spectrum was truncated to ~ 1400 pixels prior to the fitting.
Temperature Readout
The temperatures of both the detector mount and the work surface of the MOS dewar are logged every 10 minutes and stored on flmn-2m-1a and flmn-4m-1a in the subdirectories /home/2mguest/Temperature_Data and /home/4mguest/Temperature_Data when FLAMINGOS is in use at the 2.1-m and 4-m telescopes, respectively. Every time the temperature daemon is restarted, a new logfile is created with the general form ‘Temperature.4mguest.2005.Mar.29.0001.dat’. The current open file is also plotted on the terminal. It is important to keep an eye on the temperatures by periodically referring to either the temperature plots or the Status GUI, to ensure that neither the camera nor the MOS dewars have exhausted their supply of LN2. Ideally, the camera dewar holds ~ 30 hr and thus needs refilling only once/day. The MOS dewar holds > 14 hr and thus should be filled twice/day, at the beginning and end of the night. There are some circumstances which can result in shorter hold times, with the risk of running out of cryogen during the night:
· A poor vacuum will result in accelerated boiloff and a shorter hold time. This is primarily an issue with the MOS dewar, which is brought up to atmospheric pressure and re-pumped every time the masks are changed.
· It is possible to misinterpret splashing of LN2 from the vent port as a full dewar and thus end up only partially filling the tank. When filling, ensure that there is a steady stream of LN2 from the vent port.
· If the telescope is moved to an unusual position during the daytime (e.g., to the SE annex at the 4-m), the instrument may end up in an orientation which results in spilling significant amounts of LN2 from the dewar.
It is also important to recognize what can be considered “normal” behavior, in contrast to a clear sign of cryogen exhaustion.
Detector Temperature
The detector temperature is read by a sensor on the detector mount, which is strapped to the LN2 flask of the camera dewar. It will generally vary slowly with time, in response to the dome temperature, but usually by no more than 0.5 K over a day. A significant monotonic increase in temperature should be a warning sign of cryogen exhaustion.
MOS Temperature
The MOS temperature is measured by a sensor on the top of the MOS work surface, which is the top surface of the LN2 tank in the MOS dewar. Copper rods extending down into the LN2 provide the thermal path to the cryogen. As the LN2 level drops, the thermal path between the work surface and the liquid becomes longer, so the temperature (under a constant thermal load) will slowly increase. In addition, the orientation of the instrument may increase or decrease the thermal conductance between the liquid and the work surface. As a result, one can see fluctuations of several degrees on top of a monotonic increase during the course of a night. Figures 7 – 9 illustrate the temperature profiles one can expect during normal operation, exhaustion of LN2, and the forced warmup using the MOS dewar heaters.
The FLAMINGOS manual notes that the MOS temperature should be nominally in the 75 – 85 K range, but under some conditions and orientations, values above 90 K may be seen. The critical factor which identifies cryogen exhaustion is a rapid monotonic temperature increase which continues even if the instrument is returned to an upright orientation. Temperatures as high as 120 K will not introduce noticeable thermal radiation into either spectroscopic or imaging observations, but one should not attempt to move the MOS or decker wheels under such conditions, since the drive train will not be isothermal, and the mechanisms may operate poorly or not at all.
Figure 7. Temperature profile of the detector (red) and MOS work surface (black) over a 16 hour time period. The MOS dewar was filled (F) at about 0100, but the LN2 ran out at about 1100. Note that the temperature rises approximately linearly at about 12 K/hr. The dewar was refilled at 1300 and required about 30 minutes to return to a normal operating temperature.
Figure 8. Temperature profile of the detector (red) and MOS work surface (black) over a 24 hour time period. The instrument was used for normal observing until 1140, when the MOS heaters were turned on to permit access to the MOS wheel. This results in an initial rise as the work surface heats up, then a more gradual rise as the residual LN2 is boiled off. At about 1240, the LN2 was gone and the warmup accelerated to about 50 K/hr until the target temperature of 300 K was reached. The dewar was refilled (F) at 1900 and reached a normal operating temperature in about 4 hours.
Figure 9. Exploded view of Fig.8, showing the MOS temperature profile during a normal observing period. The MOS dewar was filled (F) at about 0100 and used for observing until 1140, when the heater was turned on. The fluctuations of up to 10 K during this period are due to a combination of a monotonic increase as the LN2 slowly boils off and changes in the thermal conductance path between the LN2 and the MOS temperature sensor as the orientation of the instrument changes during the night. Occasional jumps in both the detector and MOS temperature (which occasionally give unphysical temperature readouts) are due to noise during the sampling and are not a cause for concern.
Performance Reports
Over the operational lifetime of FLAMINGOS on
In late 2004, a user noted significant errors in point-source photometry in the upper right quadrant of the detector from observations of star-forming regions with a large number of 2MASS-calibrated sources over the field. These data had been reduced in the normal fashion using flatfielding and observations of photometric standards. A careful analysis by Steve Eikenberry and Nick Raines (UF) showed that stellar images in a portion of this quadrant had PSFs with a significant amount of flux in low-level extended wings, flux which would have been missed with conventional photometric apertures. This was tentatively ascribed to the evident deterioration of the anti-reflection coating on the BaF2 field lens, which was apparently scattering light from stars falling in that region of the field. Although this was never conclusively proved, the removal of the anti-reflection coating and re-installation of the lens with no coating has apparently eliminated the problem. Report No. 5 (see below) is an analysis of the current (2007) imaging quality of FLAMINGOS prepared by Lucas Macri.
More detailed analysis of these and other issues are covered in the following reports, which may be downloaded for off-line consumption. Problems or issues which occur in the future may be addressed in additional reports.
FLAMINGOS Report No. 1 (17 August 2006)
FLAMINGOS Report No. 2 (08 September 2006)
FLAMINGOS Report No. 3 (17 October 2006)
FLAMINGOS Report No. 4 (22 February 2007)
FLAMINGOS Report No. 5 (13 March 2007)