exposures-SPECPROD.fits

Summary:

File containing metadata about individual DESI exposures. There are two tables. The first is per-exposure and the second is per-camera per-exposure. The per-exposure table includes observational information as well as derived quantities estimating the observational depth for each target class, quoted in seconds of effective, idealized observing time. The second provides similar information on a per-camera basis.

Naming Convention:

exposures-{SPECPROD}.fits, where {SPECPROD} is the official name of the full reduction, e.g. everest.

Regex:

exposures-[a-z0-9_-]+\.fits

File Type:

FITS, 19 MB

Contents

Number	EXTNAME	Type	Contents
HDU0		IMAGE	Empty
HDU1	EXPOSURES	BINTABLE	Per-exposure metadata
HDU2	FRAMES	BINTABLE	Per-camera per-exposure metadata

FITS Header Units

HDU0

This HDU has no non-standard required keywords.

Empty HDU.

HDU1

EXTNAME = EXPOSURES

Binary table containing metadata about individual DESI exposures. This includes observational information as well as derived quantities estimating the observational depth for each target class, quoted in seconds of effective, idealized observing time.

Required Header Keywords

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	337	int	Number of columns
NAXIS2	3912	int	Number of exposure rows

Required Data Table Columns

Name	Type	Units	Description
NIGHT	int32		Observing night
EXPID	int32		DESI Exposure number
TILEID	int32		DESI Tile ID
TILERA	float64	deg	RA of tile given in fiberassign file
TILEDEC	float64	deg	DEC of tile given in fiberassign fileDEC of tile given in fiberassign file
MJD	float64		Modified Julian Date when shutter was opened for this exposure.
SURVEY	char[7]		Survey name
PROGRAM	char[6]		Program name
FAPRGRM	char[*]		Fiberassign program name
FAFLAVOR	char[*]		Fiberassign flavor name
EXPTIME	float64	s	Length of time shutter was open.
EFFTIME_SPEC	float64	s	Effective exposure time for nominal conditions derived from the TSNR2 fits to the spectroscopy
GOALTIME	float64	s	Goal for total effective exposure time for the tile
GOALTYPE	char[6]		The intended observing conditions for the tile
MINTFRAC	float64		Minimum fraction of GOALTIME acceptable for considering a tile complete
AIRMASS	float32		Average airmass during this exposure.
EBV	float64		Galactic extinction E(B-V) reddening from SFD98
SEEING_ETC	float64	arcsec	Average FWHM atmospheric seeing during this exposure as measured by ETC.
EFFTIME_ETC	float32	s	Effective exposure time for nominal conditions inferred from ETC data
TSNR2_ELG	float32		ELG template (S/N)^2 summed over B,R,Z
TSNR2_QSO	float32		QSO template (S/N)^2 summed over B,R,Z
TSNR2_LRG	float32		LRG template (S/N)^2 summed over B,R,Z
TSNR2_LYA	float64		LYA template (S/N)^2 summed over B,R,Z
TSNR2_BGS	float32		BGS template (S/N)^2 summed over B,R,Z
TSNR2_GPBDARK	float32		GPBDARK template (S/N)^2 summed over B,R,Z
TSNR2_GPBBRIGHT	float32		GPBBRIGHT template (S/N)^2 summed over B,R,Z
TSNR2_GPBBACKUP	float32		GPBBACKUP template (S/N)^2 summed over B,R,Z
LRG_EFFTIME_DARK	float32	s	Effective exposure time for nominal dark conditions inferred for LRG targets
ELG_EFFTIME_DARK	float32	s	Effective exposure time for nominal dark conditions inferred for ELG targets
BGS_EFFTIME_BRIGHT	float32	s	Effective exposure time for nominal bright conditions inferred for BGS targets
LYA_EFFTIME_DARK	float64	s	Effective exposure time for nominal dark conditions inferred for LYA targets
GPB_EFFTIME_DARK	float32	s	Effective exposure time for nominal dark conditions inferred for GPB targets
GPB_EFFTIME_BRIGHT	float32	s	Effective exposure time for nominal bright conditions inferred for GPB targets
GPB_EFFTIME_BACKUP	float32	s	Effective exposure time for nominal backup conditions inferred for GPB targets
TRANSPARENCY_GFA	float64		Average airmass during this exposure as measured by GFA.
SEEING_GFA	float64	arcsec	Average FWHM atmospheric seeing during this exposure as measured by GFA.
FIBER_FRACFLUX_GFA	float64		Fraction of the flux entering the fiber relative to nominal 1.1” seeing using the PSF inferred from the GFAs
FIBER_FRACFLUX_ELG_GFA	float64		Fraction of the flux entering the fiber relative to nominal 1.1” seeing using the PSF inferred from the GFAs for a source with an ELG profile (0.45” exponential galaxy profile)
FIBER_FRACFLUX_BGS_GFA	float64		Fraction of the flux entering the fiber relative to nominal 1.1” seeing using the PSF inferred from the GFAs for a source with a BGS profile (deV profile, half light radius of 1.5”)
FIBERFAC_GFA	float64		Fraction of light entering a fiber relative to expectations for 1.1” seeing, transparency 1, for an object with a PSF profile, measured by comparing the flux integrated over a 107 micron diameter circle on the GFA images centered at the PlateMaker expectations for where stars should land.
FIBERFAC_ELG_GFA	float64		Same as FIBERFAC_GFA except for an ELG profile
FIBERFAC_BGS_GFA	float64		Same as FIBERFAC_GFA except for a BGS profile
AIRMASS_GFA	float64		Average airmass during this exposure as measured by GFA.
SKY_MAG_AB_GFA	float64		Sky background in the GFA passband, measured from the GFA backgrounds.
SKY_MAG_G_SPEC	float64		Sky background measured in the spectroscopy integrated over the DECam g passband, AB mags.
SKY_MAG_R_SPEC	float64		Sky background measured in the spectroscopy integrated over the DECam r passband, AB mags.
SKY_MAG_Z_SPEC	float64		Sky background measured in the spectroscopy integrated over the DECam z passband, AB mags.
EFFTIME_GFA	float64	s	Effective exposure time for nominal conditions inferred from GFA data
EFFTIME_DARK_GFA	float64	s	Effective exposure time for nominal dark conditions inferred from GFA data
EFFTIME_BRIGHT_GFA	float64	s	Effective exposure time for nominal bright conditions inferred from GFA data
EFFTIME_BACKUP_GFA	float64	s	Effective exposure time for nominal backup conditions inferred from GFA data

HDU2

EXTNAME = FRAMES

Binary table containing metadata about individual DESI exposures per camera. This includes observational information as well as derived quantities estimating the observational depth for each target class, quoted as TSNR2_*. TSNR2_* can be converted to EFFTIME using the desispec function desispec.tsnr.tsnr2_to_efftime(tsnr2,target_type).

Required Header Keywords

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	167	int	Number of columns
NAXIS2	111720	int	Number of per-camera per-exposure rows

Required Data Table Columns

Name	Type	Units	Description
NIGHT	int32		Observing night
EXPID	int32		DESI Exposure number
TILEID	int32		DESI Tile ID
TILERA	float64	deg	RA of tile given in fiberassign file
TILEDEC	float64	deg	DEC of tile given in fiberassign file
MJD	float64		Modified Julian Date when shutter was opened for this exposure.
EXPTIME	float32	s	Length of time shutter was open.
AIRMASS	float32		Average airmass during this exposure.
EBV	float64		Galactic extinction E(B-V) reddening from SFD98
SEEING_ETC	float64	arcsec	Average FWHM atmospheric seeing during this exposure as measured by ETC.
EFFTIME_ETC	float32	s	Effective exposure time for nominal conditions derived from exposure ETC data
CAMERA	char[2]		Camera identifier. Passband and SPECGRPH ([brz][0-9]).
TSNR2_GPBDARK	float32		GPBDARK template (S/N)^2 summed over B,R,Z
TSNR2_ELG	float32		ELG template (S/N)^2 summed over B,R,Z
TSNR2_GPBBRIGHT	float32		GPBBRIGHT template (S/N)^2 summed over B,R,Z
TSNR2_LYA	float64		LYA template (S/N)^2 summed over B,R,Z
TSNR2_BGS	float32		BGS template (S/N)^2 summed over B,R,Z
TSNR2_GPBBACKUP	float32		GPBBACKUP template (S/N)^2 summed over B,R,Z
TSNR2_QSO	float32		QSO template (S/N)^2 summed over B,R,Z
TSNR2_LRG	float32		LRG template (S/N)^2 summed over B,R,Z
SURVEY	char[7]		Survey name
GOALTYPE	char[6]		The intended observing conditions for the tile
FAPRGRM	char[*]		PROGRAM in fiberassign file
FAFLAVOR	char[*]		FLAVOR in fiberassign file
MINTFRAC	float64		Minimum fraction of GOALTIME acceptable for considering a tile complete
GOALTIME	float64	s	Goal for total effective exposure time for the tile

Notes and Examples

This file is based on the guadalupe production. There are minor type differences for these columns in both HDU1 and HDU2: FAPRGRM, FAFLAVOR, EBV, EFFTIME_ETC. Type warnings about these columns should be ignored.