spectra-SURVEY-PROGRAM-PIXNUM.fits¶

Summary:: DESI spectra grouped by nested healpix number
Naming Convention:: spectra-SURVEY-PROGRAM-PIXNUM.fits, where SURVEY is e.g. main or sv1, PROGRAM is e.g. bright or dark and PIXNUM is the HEALPixel number.
Regex:: spectra-(cmx|main|special|sv1|sv2|sv3)-(backup|bright|dark|other)-[0-9]+\.fits
File Type:: FITS, 408 MB

Spectra files contain non-coadded spectra for multiple targets observed on multiple individual exposures and cameras. The format can contain any arbitrary set of targets, though the standard DESI spectroscopic pipeline outputs are grouped either by a single petal of a given tile, or all targets on a single healpix.

Tile-based spectra can be grouped in multiple ways across exposures and nights; see the top-level SPECPROD/tiles/ description for an overview of the per-tile GROUPTYPE and GROUPID options. Healpix-based spectra are grouped by SURVEY and PROGRAM. Science analyses may release spectra in other groups, e.g. all the spectra selected for a particular analysis.

Please see coadd files for a coadded version of the same spectra in a very similar format.

The FIBERMAP table contains metadata about each target, with one row per target per exposure. The corresponding SCORES table contains quantities measured from the spectra, also with one row per target per exposure.

The spectra themselves are in a set of image HDUs for the FLUX, IVAR (inverse variance), MASK, and spectral RESOLUTION, each prefixed with a spectrograph camera name, e.g. B, R, or Z for DESI, though the format in general could support other numbers and names of cameras for other instruments. A row of each image HDU correponds to the target from the same row index of the FIBERMAP and SCORES HDUs.

See the end of tile-based spectra for examples of reading this file format.

Note: the table below is the order in which these HDUs appear in DESI spectroscopic pipeline output, but the order is arbitrary and they should be read by name not by number.

Contents¶

Number	EXTNAME	Type	Contents
HDU00		IMAGE	Empty
HDU01	FIBERMAP	BINTABLE	fibermap table
HDU02	SCORES	BINTABLE	scores table
HDU03	B_WAVELENGTH	IMAGE	Wavelength array of b-channel spectra
HDU04	B_FLUX	IMAGE	Flux of b-channel spectra
HDU05	B_IVAR	IMAGE	Inverse variance of b-channel spectra
HDU06	B_MASK	BINTABLE	Mask of b-channel spectra
HDU07	B_RESOLUTION	IMAGE	Resolution matrices of b-channel spectra
HDU08	R_WAVELENGTH	IMAGE	Wavelength array of r-channel spectra
HDU09	R_FLUX	IMAGE	Flux of r-channel spectra
HDU10	R_IVAR	IMAGE	Inverse variance of r-channel spectra
HDU11	R_MASK	BINTABLE	Mask of r-channel spectra
HDU12	R_RESOLUTION	IMAGE	Resolution matrices of r-channel spectra
HDU13	Z_WAVELENGTH	IMAGE	Wavelength array of z-channel spectra
HDU14	Z_FLUX	IMAGE	Flux of z-channel spectra
HDU15	Z_IVAR	IMAGE	Inverse variance of z-channel spectra
HDU16	Z_MASK	BINTABLE	Mask of z-channel spectra
HDU17	Z_RESOLUTION	IMAGE	Resolution matrices of z-channel spectra

FITS Header Units¶

HDU00¶

HEALPixel keywords.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
SPGRP	healpix	str	Spectral grouping method
SPGRPVAL	26371	int	Grouping value = healpixel number
HPXPIXEL	26371	int	Nested nside=64 healpixel number
HPXNSIDE	64	int	Healpix nside
HPXNEST	True	str	Healpix nested? (vs. ring)
SURVEY	main	str	DESI Survey (sv1, sv3, main…)
PROGRAM	bright	str	DESI Program (dark, bright, …)
CHECKSUM	8DPU9BMR8BMR8BMR	str	HDU checksum updated 2021-07-19T17:59:29
DATASUM	0	str	data unit checksum updated 2021-07-19T17:59:29

Empty HDU.

HDU01¶

EXTNAME = FIBERMAP

Fibermap table with per-target metdata.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	413	int	Width of table in bytes
NAXIS2	1031	int	Number of rows in table
CHECKSUM	U9Fia89iV8Cia89i	str	HDU checksum
DATASUM	3589169610	str	data unit checksum

Required Data Table Columns¶

Propagated from the FIBERMAP HDU of the input cframe files.

Name	Type	Units	Description
TARGETID	int64		Unique DESI target ID
PETAL_LOC	int16		Petal location [0-9]
DEVICE_LOC	int32		Device location on focal plane [0-523]
LOCATION	int64		Location on the focal plane PETAL_LOC*1000 + DEVICE_LOC
FIBER	int32		Fiber ID on the CCDs [0-4999]
FIBERSTATUS	int32		Fiber status mask. 0=good
TARGET_RA	float64	deg	Barycentric right ascension in ICRS
TARGET_DEC	float64	deg	Barycentric declination in ICRS
PMRA	float32	mas yr^-1	proper motion in the +RA direction (already including cos(dec))
PMDEC	float32	mas yr^-1	Proper motion in the +Dec direction
REF_EPOCH	float32	yr	Reference epoch for Gaia/Tycho astrometry. Typically 2015.5 for Gaia
LAMBDA_REF	float32	Angstrom	Requested wavelength at which targets should be centered on fibers
FA_TARGET	int64		Targeting bit internally used by fiberassign (linked with FA_TYPE)
FA_TYPE	binary		Fiberassign internal target type (science, standard, sky, safe, suppsky)
OBJTYPE	char[3]		Object type: TGT, SKY, NON, BAD
FIBERASSIGN_X	float32	mm	Fiberassign expected CS5 X location on focal plane
FIBERASSIGN_Y	float32	mm	Fiberassign expected CS5 Y location on focal plane
PRIORITY	int32		Target current priority
SUBPRIORITY	float64		Random subpriority [0-1) to break assignment ties
OBSCONDITIONS	int32		Bitmask of allowed observing conditions
RELEASE	int16		Imaging surveys release ID
BRICKID	int32		Brick ID from tractor input
BRICK_OBJID	int32		Imaging Surveys OBJID on that brick
MORPHTYPE	char[4]		Imaging Surveys morphological type from Tractor
FLUX_G	float32	nanomaggy	Flux in the Legacy Survey g-band (AB)
FLUX_R	float32	nanomaggy	Flux in the Legacy Survey r-band (AB)
FLUX_Z	float32	nanomaggy	Flux in the Legacy Survey z-band (AB)
FLUX_IVAR_G	float32	nanomaggy^-2	Inverse variance of FLUX_G (AB)
FLUX_IVAR_R	float32	nanomaggy^-2	Inverse variance of FLUX_R (AB)
FLUX_IVAR_Z	float32	nanomaggy^-2	Inverse variance of FLUX_Z (AB)
MASKBITS	int16		Bitwise mask from the imaging indicating potential issue or blending
REF_ID	int64		Tyc11,000,000+Tyc210+Tyc3 for Tycho-2; “sourceid” for Gaia DR2
REF_CAT	char[2]		Reference catalog source for star: “T2” for Tycho-2, “G2” for Gaia DR2, “L2” for the SGA, empty otherwise
GAIA_PHOT_G_MEAN_MAG	float32	mag	Gaia G band magnitude
GAIA_PHOT_BP_MEAN_MAG	float32	mag	Gaia BP band magnitude
GAIA_PHOT_RP_MEAN_MAG	float32	mag	Gaia RP band magnitude
PARALLAX	float32	mas	Reference catalog parallax
BRICKNAME	char[8]		Brick name from tractor input
EBV	float32	mag	Galactic extinction E(B-V) reddening from SFD98
FLUX_W1	float32	nanomaggy	WISE flux in W1 (AB)
FLUX_W2	float32	nanomaggy	WISE flux in W2 (AB)
FLUX_IVAR_W1	float32	nanomaggy^-2	Inverse variance of FLUX_W1 (AB)
FLUX_IVAR_W2	float32	nanomaggy^-2	Inverse variance of FLUX_W2 (AB)
FIBERFLUX_G	float32	nanomaggy	Predicted g-band flux within a fiber of diameter 1.5 arcsec from this object in 1 arcsec Gaussian seeing
FIBERFLUX_R	float32	nanomaggy	Predicted r-band flux within a fiber of diameter 1.5 arcsec from this object in 1 arcsec Gaussian seeing
FIBERFLUX_Z	float32	nanomaggy	Predicted z-band flux within a fiber of diameter 1.5 arcsec from this object in 1 arcsec Gaussian seeing
FIBERTOTFLUX_G	float32	nanomaggy	Predicted g-band flux within a fiber of diameter 1.5 arcsec from all sources at this location in 1 arcsec Gaussian seeing
FIBERTOTFLUX_R	float32	nanomaggy	Predicted r-band flux within a fiber of diameter 1.5 arcsec from all sources at this location in 1 arcsec Gaussian seeing
FIBERTOTFLUX_Z	float32	nanomaggy	Predicted z-band flux within a fiber of diameter 1.5 arcsec from all sources at this location in 1 arcsec Gaussian seeing
SERSIC	float32		Power-law index for the Sersic profile model (MORPHTYPE=”SER”)
SHAPE_R	float32	arcsec	Half-light radius of galaxy model (>0)
SHAPE_E1	float32		Ellipticity component 1 of galaxy model for galaxy type MORPHTYPE
SHAPE_E2	float32		Ellipticity component 2 of galaxy model for galaxy type MORPHTYPE
PHOTSYS	char[1]		‘N’ for the MzLS/BASS photometric system, ‘S’ for DECaLS
PRIORITY_INIT	int64		Target initial priority from target selection bitmasks and OBSCONDITIONS
NUMOBS_INIT	int64		Initial number of observations for target calculated across target selection bitmasks and OBSCONDITIONS
SV1_DESI_TARGET [1]	int64		DESI (dark time program) target selection bitmask for SV1
SV1_BGS_TARGET [1]	int64		BGS (bright time program) target selection bitmask for SV1
SV1_MWS_TARGET [1]	int64		MWS (bright time program) target selection bitmask for SV1
SV1_SCND_TARGET [1]	int64		Secondary target selection bitmask for SV1
DESI_TARGET	int64		DESI (dark time program) target selection bitmask
BGS_TARGET	int64		BGS (Bright Galaxy Survey) target selection bitmask
MWS_TARGET	int64		Milky Way Survey targeting bits
SCND_TARGET	int64		Target selection bitmask for secondary programs
PLATE_RA	float64	deg	Barycentric Right Ascension in ICRS to be used by PlateMaker
PLATE_DEC	float64	deg	Barycentric Declination in ICRS to be used by PlateMaker
NUM_ITER	int64		Number of positioner iterations
FIBER_X	float64	mm	CS5 X location requested by PlateMaker
FIBER_Y	float64	mm	CS5 Y location requested by PlateMaker
DELTA_X	float64	mm	CS5 X requested minus actual position
DELTA_Y	float64	mm	CS5 Y requested minus actual position
FIBER_RA	float64	deg	RA of actual fiber position
FIBER_DEC	float64	deg	DEC of actual fiber position
EXPTIME	float64	s	Length of time shutter was open
PSF_TO_FIBER_SPECFLUX	float64		fraction of light from point-like source captured by 1.5 arcsec diameter fiber given atmospheric seeing
NIGHT	int32
EXPID	int32		DESI Exposure ID number
MJD	float64		Modified Julian Date when shutter was opened for this exposure
TILEID	int32		Unique DESI tile ID

HDU02¶

EXTNAME = SCORES

Scores / metrics measured from the spectra for use in QA and systematics studies. These are propagated from the input cframe SCORES HDU.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	488	int	width of table in bytes
NAXIS2	1031	int	number of rows in table

Required Data Table Columns¶

Name	Type	Description
TARGETID	int64	Unique DESI target ID
SUM_RAW_COUNT_B	float64	Sum of raw counts in B camera
MEDIAN_RAW_COUNT_B	float64	Median of raw counts in B camera
MEDIAN_RAW_SNR_B	float64	Median(raw signal/noise) in B camera
SUM_FFLAT_COUNT_B	float64	Sum of fiber-flatfielded counts B camera
MEDIAN_FFLAT_COUNT_B	float64	Median of fiber-flatfielded counts in B camera
MEDIAN_FFLAT_SNR_B	float64	Median(S/N) of fiberflatfielded counts in B camera
SUM_SKYSUB_COUNT_B	float64	Sum of sky-subtracted counts in B camera
MEDIAN_SKYSUB_COUNT_B	float64	Median of sky-subtracted counts in B camera
MEDIAN_SKYSUB_SNR_B	float64	Median(S/N) of sky-subtracted counts in B camera
SUM_CALIB_COUNT_B	float64	Sum of calibrated flux in B camera
MEDIAN_CALIB_COUNT_B	float64	Median of calibrated flux in B camera
MEDIAN_CALIB_SNR_B	float64	Median(S/N) of calibrated flux in B camera
TSNR2_GPBDARK_B	float64	template (S/N)^2 for dark targets in guider pass band on B
TSNR2_ELG_B	float64	ELG B template (S/N)^2
TSNR2_GPBBRIGHT_B	float64	template (S/N)^2 for bright targets in guider pass band on B
TSNR2_LYA_B	float64	LYA B template (S/N)^2
TSNR2_BGS_B	float64	BGS B template (S/N)^2
TSNR2_GPBBACKUP_B	float64
TSNR2_QSO_B	float64	QSO B template (S/N)^2
TSNR2_LRG_B	float64	LRG B template (S/N)^2
SUM_RAW_COUNT_R	float64	Sum of raw counts in R camera
MEDIAN_RAW_COUNT_R	float64	Median of raw counts in R camera
MEDIAN_RAW_SNR_R	float64	Median(raw signal/noise) in R camera
SUM_FFLAT_COUNT_R	float64	Sum of fiber-flatfielded counts R camera
MEDIAN_FFLAT_COUNT_R	float64	Median of fiber-flatfielded counts in R camera
MEDIAN_FFLAT_SNR_R	float64	Median(S/N) of fiberflatfielded counts in R camera
SUM_SKYSUB_COUNT_R	float64	Sum of sky-subtracted counts in R camera
MEDIAN_SKYSUB_COUNT_R	float64	Median of sky-subtracted counts in R camera
MEDIAN_SKYSUB_SNR_R	float64	Median(S/N) of sky-subtracted counts in R camera
SUM_CALIB_COUNT_R	float64	Sum of calibrated flux in R camera
MEDIAN_CALIB_COUNT_R	float64	Median of calibrated flux in R camera
MEDIAN_CALIB_SNR_R	float64	Median(S/N) of calibrated flux in R camera
TSNR2_GPBDARK_R	float64	template (S/N)^2 for dark targets in guider pass band on R
TSNR2_ELG_R	float64	ELG R template (S/N)^2
TSNR2_GPBBRIGHT_R	float64	template (S/N)^2 for bright targets in guider pass band on R
TSNR2_LYA_R	float64	LYA R template (S/N)^2
TSNR2_BGS_R	float64	BGS R template (S/N)^2
TSNR2_GPBBACKUP_R	float64
TSNR2_QSO_R	float64	QSO R template (S/N)^2
TSNR2_LRG_R	float64	LRG R template (S/N)^2
SUM_RAW_COUNT_Z	float64	Sum of raw counts in Z camera
MEDIAN_RAW_COUNT_Z	float64	Median of raw counts in Z camera
MEDIAN_RAW_SNR_Z	float64	Median(raw signal/noise) in Z camera
SUM_FFLAT_COUNT_Z	float64	Sum of fiber-flatfielded counts Z camera
MEDIAN_FFLAT_COUNT_Z	float64	Median of fiber-flatfielded counts in Z camera
MEDIAN_FFLAT_SNR_Z	float64	Median(S/N) of fiberflatfielded counts in Z camera
SUM_SKYSUB_COUNT_Z	float64	Sum of sky-subtracted counts in Z camera
MEDIAN_SKYSUB_COUNT_Z	float64	Median of sky-subtracted counts in Z camera
MEDIAN_SKYSUB_SNR_Z	float64	Median(S/N) of sky-subtracted counts in Z camera
SUM_CALIB_COUNT_Z	float64	Sum of calibrated flux in Z camera
MEDIAN_CALIB_COUNT_Z	float64	Median of calibrated flux in Z camera
MEDIAN_CALIB_SNR_Z	float64	Median(S/N) of calibrated flux in Z camera
TSNR2_GPBDARK_Z	float64	template (S/N)^2 for dark targets in guider pass band on Z
TSNR2_ELG_Z	float64	ELG Z template (S/N)^2
TSNR2_GPBBRIGHT_Z	float64	template (S/N)^2 for bright targets in guider pass band on Z
TSNR2_LYA_Z	float64	LYA Z template (S/N)^2
TSNR2_BGS_Z	float64	BGS Z template (S/N)^2
TSNR2_GPBBACKUP_Z	float64
TSNR2_QSO_Z	float64	QSO Z template (S/N)^2
TSNR2_LRG_Z	float64	LRG Z template (S/N)^2

HDU03¶

EXTNAME = B_WAVELENGTH

1D array of B-camera wavelengths in Angstrom, in vacuum (not in air), in the rest frame of the solar system barycenter.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	2751	int	Number of wavelengths
BUNIT	Angstrom	str

Data: FITS image [float64, 2751]

HDU04¶

EXTNAME = B_FLUX

2D array of calibrated spectral flux of dimension [nspec, nwave] in units of 1e-17 erg / (s cm2 Angstrom). nspec is the number of fibers per camera. nwave in the length of the wavelength array. The spectra of all fibers share the same wavelength grid, given in HDU B_WAVELENGTH.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	2751	int	`nwave` number of wavelengths
NAXIS2	1031	int	`nspec` number of spectra
BUNIT	10**-17 erg/(s cm2 Angstrom)	str

Data: FITS image [float32, 2751x1031]

HDU05¶

EXTNAME = B_IVAR

Inverse variance of flux (1/sigma^2) in units of (10^{-17} erg/s/cm2/A)^-2. Uncertainties comprise statistical uncertainties from the error propagation of the initial CCD pixel variance, the calibration uncertainties, plus an additional term on bright sky lines to account for the imperfect sky subtraction.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	2751	int	`nwave` number of wavelengths
NAXIS2	1031	int	`nspec` number of spectra
BUNIT	10**+34 (s2 cm4 Angstrom2) / erg2	str

Data: FITS image [float32, 2751x1031]

HDU06¶

EXTNAME = B_MASK

Mask of spectral data; 0=good. See the bitmask documentation page for the definition of the bits.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	2751	int	`nwave` number of wavelengths
NAXIS2	1031	int	`nspec` number of spectra
BZERO	2147483648	int	offset data range to that of unsigned long
BSCALE	1	int	default scaling factor

Data: FITS image [int32 (compressed), 2751x1031]

HDU07¶

EXTNAME = B_RESOLUTION

Resolution matrix stored as a 3D sparse matrix, modeling the per-fiber non-Gaussian effective line-spread-function resolution. See the frame RESOLUTION HDU documentation for details about using this HDU.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	2751	int	`nwave` number of wavelengths
NAXIS2	11	int	`ndiag` number of diagonals
NAXIS3	1031	int	`nspec` number of spectra

Data: FITS image [float32, 2751x11x1031]

A sparse resolution matrix may be created for spectrum i with:

from desispec.resolution import Resolution
R = Resolution(data[i])

Or using lower-level scipy.sparse matrices:

import scipy.sparse
import numpy as np
nspec, ndiag, nwave = data.shape
offsets = ndiag//2 - np.arange(ndiag, dtype=int)
R = scipy.sparse.dia_matrix((data[i], offsets), shape=(nwave, nwave))

HDU08¶

EXTNAME = R_WAVELENGTH

1D array of R-camera wavelengths in Angstrom, in vacuum (not in air), in the rest frame of the solar system barycenter.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	2326	int	number of wavelengths
BUNIT	Angstrom	str

Data: FITS image [float64, 2326]

HDU09¶

EXTNAME = R_FLUX

2D array of calibrated spectral flux of dimension [nspec, nwave] in units of 1e-17 erg / (s cm2 Angstrom). nspec is the number of fibers per camera. nwave in the length of the wavelength array. The spectra of all fibers share the same wavelength grid, given in HDU R_WAVELENGTH.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	2326	int	`nwave` number of wavelengths
NAXIS2	1031	int	`nspec` number of spectra
BUNIT	10**-17 erg/(s cm2 Angstrom)	str

Data: FITS image [float32, 2326x1031]

HDU10¶

EXTNAME = R_IVAR

Inverse variance of flux (1/sigma^2) in units of (10^{-17} erg/s/cm2/A)^-2. Uncertainties comprise statistical uncertainties from the error propagation of the initial CCD pixel variance, the calibration uncertainties, plus an additional term on bright sky lines to account for the imperfect sky subtraction.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	2326	int	`nwave` number of wavelengths
NAXIS2	1031	int	`nspec` number of spectra
BUNIT	10**+34 (s2 cm4 Angstrom2) / erg2	str

Data: FITS image [float32, 2326x1031]

HDU11¶

EXTNAME = R_MASK

Mask of spectral data; 0=good. See the bitmask documentation page for the definition of the bits.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	2326	int	`nwave` number of wavelengths
NAXIS2	1031	int	`nspec` number of spectra
BZERO	2147483648	int	offset data range to that of unsigned long
BSCALE	1	int	default scaling factor

Data: FITS image [int32 (compressed), 2326x1031]

HDU12¶

EXTNAME = R_RESOLUTION

Resolution matrix stored as a 3D sparse matrix, modeling the per-fiber non-Gaussian effective line-spread-function resolution. See the frame RESOLUTION HDU documentation for details about using this HDU.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	2326	int	length of data axis 1
NAXIS2	11	int	length of data axis 2
NAXIS3	1031	int	length of data axis 3

Data: FITS image [float32, 2326x11x1031]

HDU13¶

EXTNAME = Z_WAVELENGTH

1D array of Z-camera wavelengths in Angstrom, in vacuum (not in air), in the rest frame of the solar system barycenter.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	2881	int	`nwave` number of wavelengths
BUNIT	Angstrom	str

Data: FITS image [float64, 2881]

HDU14¶

EXTNAME = Z_FLUX

2D array of calibrated spectral flux of dimension [nspec, nwave] in units of 1e-17 erg / (s cm2 Angstrom). nspec is the number of fibers per camera. nwave in the length of the wavelength array. The spectra of all fibers share the same wavelength grid, given in HDU Z_WAVELENGTH.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	2881	int	`nwave` number of wavelengths
NAXIS2	1031	int	`nspec` number of spectra
BUNIT	10**-17 erg/(s cm2 Angstrom)	str

Data: FITS image [float32, 2881x1031]

HDU15¶

EXTNAME = Z_IVAR

Inverse variance of flux (1/sigma^2) in units of (10^{-17} erg/s/cm2/A)^-2. Uncertainties comprise statistical uncertainties from the error propagation of the initial CCD pixel variance, the calibration uncertainties, plus an additional term on bright sky lines to account for the imperfect sky subtraction.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	2881	int	`nwave` number of wavelengths
NAXIS2	1031	int	`nspec` number of spectra
BUNIT	10**+34 (s2 cm4 Angstrom2) / erg2	str

Data: FITS image [float32, 2881x1031]

HDU16¶

EXTNAME = Z_MASK

Mask of spectral data; 0=good. See the bitmask documentation page for the definition of the bits.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	2881	int	`nwave` number of wavelengths
NAXIS2	1031	int	`nspec` number of spectra
BZERO	2147483648	int	offset data range to that of unsigned long
BSCALE	1	int	default scaling factor

Data: FITS image [int32 (compressed), 2881x1031]

HDU17¶

EXTNAME = Z_RESOLUTION

Diagonals of z-channel resolution matrix.

Resolution matrix stored as a 3D sparse matrix, modeling the per-fiber non-Gaussian effective line-spread-function resolution. See the frame RESOLUTION HDU documentation for details about using this HDU.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	2881	int	`nwave` number of wavelengths
NAXIS2	11	int	`ndiag` number of diagonals
NAXIS3	1031	int	`nspec` number of spectra

Data: FITS image [float32, 2881x11x1031]

Notes and Examples¶

The format supports arbitrary channel names as long as for each channel {X} there is a set of HDUs named {X}_WAVELENGTH, {X}_FLUX, {X}_IVAR, {X}_MASK, {X}_RESOLUTION.

For the SURVEY=cmx m33 tile (TILEID=80615) tile and all the SURVEY=sv1 tiles (except TILEID=80971-80976, the dc3r2 ones), proper-motion correction was applied at the fiberassign design step; thus the following columns can have different values than in the desitarget products: TARGET_RA, TARGET_DEC, REF_EPOCH, PLATE_RA, PLATE_DEC, and PLATE_REF_EPOCH.

For targets with a non-zero proper motion, FIBER_RA and FIBER_DEC refer to the position at the reference epoch (but note that the proper-motion correction has been applied at the time of the observation, it is just not recorded in FIBER_RA and FIBER_DEC).