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You will find on this web page several fits files containing the Theoretical (or "perfect") PSFs of the Keck telescope generated for the near IR cameras of the Keck AO systems in broadband filters only.
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Details about the calculation
The calculation is based on a previous work done for the estimation of image quality of segmented, multi-mirror and monolithic primary telescope (see Marchis & Cuevas, RMxAA, 35, p 31-44). I used a simple version of this program with a 36-hexagonal segment pupil and without applying any optical aberrations. I also introduce on the pupil the baffle of the secondary mirror and the separation of a 1 cm separation between each segment (see Fig. 1). The calculation of the PSF is based on the classical Fourier Optics. It was made over a 1024*1024 array. Each pixel represents 3 cm in the real telescope pupil. Since I am estimated the broadband filter PSFs, I have to also considere that in fact the PSF is the mean of several PSFs for which the relative intensity depends on the the combination of the filter profile and the atmospheric transmission.
Fig. 1: 36-segment Pupilaof the Keck telescope
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PSFs for the NIRC-2 camera
These PSFs have been generated with a pixel scale of 9.94 mas (+/- 0.5%) and 39.69 mas (+/- 0.5%). The plate measurement was performed using an internal focal plane array pinholes on the center of the chip. Sky images of a part of M92 gave some consistent results (information provided by Dave Thompson). I have used the profiles of the J, H, Kp NIRSPEC broad bands filters and the Lp and Ms bands filters profiles provided by H. Roe (see his web page for details). Atmospheric transmission profile based on Atran program (elevation of 9600 ft, 3.00mm precipitable H20, 0 deg Zenith Angle and a resolution of 0.007 micron) was included to get a realistic total transmission profile.
Fig. 2: Atmospheric and filter profiles between 3-5 microns
Three PSFs are available in fits 512*512 pixel double precision format.
| PSF |
File |
FWHM (diffraction limite) |
| PSF in J band | psfNIRC2J.fits (2053 Kb) | FWHM_x=26.47 mas & FWHM_y=26.45 mas |
| PSF in H band | psfNIRC2H.fits (2053 Kb) | FWHM_x=32.89 mas & FWHM_y=32.86 mas |
| PSF in Kp band | psfNIRC2Kp.fits (2053 Kb) | FWHM_x=43.44 mas & FWHM_y=43.39 mas |
PSF in Lp band | psfNIRC2Lp.fits (2053 Kb) | FWHM_x=75.20 mas & FWHM_y=75.13 mas |
PSF in Ms band | psfNIRC2Ms.fits (2053 Kb) | FWHM_x=93.91 mas & FWHM_y=93.83 mas |
PSF in Kp band | psfNIRC2Kp_WF.fits (2053 Kb) | FWHM_x=42.92 mas & FWHM_y=42.88 mas |
PSF in Lp band | psfNIRC2Lp_WF.fits (2053 Kb) | FWHM_x=79.33 mas & FWHM_y=79.26 mas |
PSF in Ms band | psfNIRC2Ms_WF.fits (2053 Kb) | FWHM_x=95.53 mas & FWHM_y=95.44 mas |
Fig. 3: NIRC-2/Keck Perfect PSF in J, H, Kp bands (from the left to the right at the bottom) and Lp, Ms (from the left to the right at the top).
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PSFs for the NIRSPEC camera
These PSFs have been generated with a pixel scale of 16.82 mas (+/- 0.5%) (calibration done on the fiber and check afterwhile on the sky with Hipparcos stars by D. Le Mignant) corresponding to the pixel scale we measured on our February 2001 data (see our plate scale calibration method on the following link). The profile of the J (NISPEC-3), H (NIRSPEC-5), Kp broad bands filters and the atmospheric absorption have been taken into account in the calculation of the each PSF.
Three PSFs are available in fits 256*256 pixel double precision format.
| PSF |
File |
FWHM (diffraction limite) |
| PSF in J band | psfNIRSPECJ.fits (517 Kb) | FWHM_x=25.13 mas & FWHM_y=25.10 mas |
| PSF in H band | psfNIRSPECH.fits (517 Kb) | FWHM_x=34.13 mas & FWHM_y=34.10 mas |
| PSF in Kp band | psfNIRSPECKp.fits (517 Kb) | FWHM_x=45.14 mas & FWHM_y=45.10 mas |
Fig. 2: Perfect PSFs of NIRSPEC/Keck in J, H, K bands (from left to right). Nice isn't it?
These PSF have been calculated with a pixel scale of 17.3 mas in the central wavelength of each filters, i.e. 1.260 microns in J band, 1.648 microns in H band and 2.127 microns in Kp band. It should be a good approximation of the real profile of the theoretical broadband PSF. The filter profiles were not available at the time I was running this calculation. The KCAM camera is not used anymore for scientific work, so there is no purpose to run a precise calculation (contact me if you need it anyway).
| PSF |
File |
FWHM |
| PSF in J band | psfKcamJ.fits (261 Kb) | FWHM_x=31.54 mas & FWHM_y=31.54 mas |
| PSF in H band | psfKcamH.fits (261 Kb) | FWHM_x=34.19 mas & FWHM_y=34.16 mas |
| PSF in Kp band | psfKcamKp.fits (261 Kb) | FWHM_x=43.68 mas & FWHM_y=43.63 mas |
These perfect PSFs should be useful for several purposes:
Quality of the observations A common way to estimate the quality of your AO observations is to calculate the Strehl Ratio on your data (on a star or any unresolved object). You have to normalize the intensity of you observed PSF to the unity and the SR will be the ratio between the maximum of the observed PSF on the maximum of the theoretical PSF (which should be also normalized).
Profile of the PSF for some specific tasks, like the detection of companions, circumstellar disks, jets or enveloppes around stars, the theoretical PSF may be useful. Especially if you are observing at more than 2 microns, for which the stability of the PSF is quite high..
and so on....
Feel free to use these PSFs for your work. I will appreciate if you just mention in your article or presentation where these theoretical PSFs come from. If you need a specific PSF for any special instruments and/or filters, I may also generate it. Contact me by email.
Acknowledgements: Thanks to David Le Mignant for providing me the data needed for this calculation and for sharing all his good idea with me. I am also grateful to Henry Roe for providing the filter profiles and I wish him a good luck in Caltech for his postdoc.
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