simpix

Summary:

simpix files contain the noiseless CCD pixel image. The corresponding pix-*.fits files contain the noisy realization of this image like the real data would see. It optionally contains the x and y trace locations vs. wavelength.

Naming Convention:

simpix-{CAMERA}-{EXPID}.fits, where {CAMERA} is the spectrograph camera, e.g. b0, r1, z9; and {EXPID} is the 8-digit exposure ID.

Regex:

simpix-[brz][0-9]-[0-9]{8}\.fits

File Type:

FITS, 128 MB

Contents

Number	EXTNAME	Type	Contents
HDU0	ELECTRONS	IMAGE	Noiseless simulated image
HDU1	XCOEFF	IMAGE	Optional: Legendre coefficients for x vs. wavelength
HDU2	YCOEFF	IMAGE	Optional: Legendre coefficients for y vs. wavelength

FITS Header Units

HDU0

EXTNAME = ELECTRONS

Noiseless simulated image in electrons

Required Header Keywords

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	4096	int	Number of pixels in y (wavelength direction)
NAXIS2	4096	int	Number of pixels in x (fiber direction)
VSPECTER	0.0.0	str	Specter version used to simulate this image

Data: FITS image [float64]

HDU1

EXTNAME = XCOEFF

Legendre coefficients to describe the spectral trace x vs. wavelength.

To evaluate, convert the wavelength in Angstroms to the domain [-1,1] using WAVEMIN and WAVEMAX, and then evaluate the Legendre polynomial:

w = 2*(wavelength - WAVEMIN) / (WAVEMAX - WAVEMIN) - 1.0
x = numpy.polynomial.legval(w, xcoeff[i])

Required Header Keywords

Most keywords are inherited from the input PSF, which inherited them from the input Zemax spot files.

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	8	int	Number of Legendre coefficients
NAXIS2	500	int	Number of spectra
EXTNAME	XCOEFF	str
DATAMIN	1.17549435082e-38	float	minimum allowed data value
DATAMAX	3.40282346638e+38	float	maximum allowed data value
DATATYPE	Normalized Image	str	Type of image
SPECTRO	DESI-0224-v1.ZMX(95% are better)	str
ARM	Blue	str	Spectrograph Arm
ARMINT	1	int	Spectrograph Arm
WAVECENT	476.5	float	Center Wavelength (nm)
XCENT	5.379251126	float	Detector X Centroid (mm)
YCENT	-29.956071488	float	Detector Y Centroid (mm)
XDIRCOS	-0.0353851399911	float	x direction cosine
YDIRCOS	-0.976475545755	float	y direction cosine
ZDIRCOS	4.77449053078e-312	float	z direction cosine
PIXSIZE	0.001	float	size of pixel (mm)
DIFFRACT	T	bool	diffraction added?
DETEFF	T	bool	detector effects added?
PUPIL	126.5	float	Camera Pupil (mm)
FOCALLEN	215.0	float	Camera focal length (mm)
E2VFLAG	T	bool	e2v detector
TEMP	175.0	float	Detector T (K)
DETSIG	5.0	float	sigma for detector (um)
DETTHICK	0.0	float	thickness of detector (um)
DATE	2013-09-12	str	Date
CTYPE1	X	str	X coordinate (mm)
CTYPE2	Y	str	Y coordinate (mm)
CRPIX1	113.0	float	Reference X pixel
CRPIX2	113.0	float	Reference Y pixel
CRVAL1	5.380413942	float	Reference X value
CRVAL2	-29.95920258	float	Reference Y value
CDELT1	0.001	float	X pixel size (mm)
CDELT2	0.001	float	Y pixel size (mm)
PSFTYPE	SPOTGRID	str	Grid of simulated PSF spots
NPIX_X	4096	int	Number of CCD pixels in X direction
NPIX_Y	4096	int	Number of CCD pixels in Y direction
NSPEC	500	int	Number of spectra
NWAVE	11	int	Number of wavelength samples
CCDPIXSZ	0.015	float	CCD pixel size [mm]
DFIBER	0.23	float	Center-to-center pitch of fibers on slit [mm]
DGROUP	0.556	float	Spacing between fiber groups on slit [mm]
NGROUPS	20	int	Number of fiber groups per slit
NFIBGRP	25	int	Number of fibers per group
WAVEMIN	3533	int	Min wavelength for Legendre domain [-1,1]
WAVEMAX	5998	int	Max wavelength for Legendre domain [-1,1]
WMIN_ALL	3569	int	Min wavelength seen by all spectra [Ang]
WMAX_ALL	5949	int	Max wavelength seen by all spectra [Ang]

Data: FITS image [float64]

HDU2

EXTNAME = YCOEFF

Legendre coefficients to describe the spectral trace y vs. wavelength. See the description in HDU1 for how to evaluate these.

Required Header Keywords

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	8	int
NAXIS2	500	int
EXTNAME	YCOEFF	str
WAVEMIN	3533	int	Min wavelength on the CCD [Ang]
WAVEMAX	5998	int	Max wavelength on the CCD [Ang]
WMIN_ALL	3569	int	Min wavelength seen by all spectra [Ang]
WMAX_ALL	5949	int	Max wavelength seen by all spectra [Ang]

Data: FITS image [float64]