TILEID-gfa.fits

Summary:: This file contains the stars for the ETC / GUIDE / FOCUS covered by the tile disk-footprint.
Naming Convention:: {TILEID}-gfa.fits, where {TILEID} is the zero-padded, 6-digit TILED.
Regex:: [0-9]{6}-gfa\.fits
File Type:: FITS, 6 MB

Contents

Number	EXTNAME	Type	Contents
HDU0		IMAGE	Empty HDU
HDU1	TARGETS	BINTABLE	Stars for the ETC / GUIDE / FOCUS covered by the tile disk-footprint.

FITS Header Units

HDU0

This HDU has no non-standard required keywords.

Empty HDU.

HDU1

EXTNAME = TARGETS

Stars for the ETC / GUIDE / FOCUS covered by the tile disk-footprint: those are read from the desitarget catalogs and provided as input to fiberassign.

Required Header Keywords

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	164	int	width of table in bytes
NAXIS2	43904	int	number of rows in table
SURVEY	main	str
RESOLVE	T	bool
MASKBITS	T	bool
BACKUP	F	bool
NOSEC	F	bool
DR	9	int

Required Data Table Columns

Name	Type	Units	Description
RELEASE	int32		Imaging surveys release ID
TARGETID	int64		Unique DESI target ID
BRICKID	int32		Brick ID from tractor input
BRICK_OBJID	int32		Imaging Surveys OBJID on that brick
RA	float64	deg	Barycentric Right Ascension in ICRS
DEC	float64	deg	Barycentric declination in ICRS
RA_IVAR	float32	deg^-2	Inverse variance of RA (no cosine term!), excluding astrometric calibration errors
DEC_IVAR	float32	deg^-2	Inverse variance of DEC, excluding astrometric calibration errors
MORPHTYPE	char[4]		Imaging Surveys morphological type from Tractor
MASKBITS	int16		Bitwise mask from the imaging indicating potential issue or blending
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)
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
REF_EPOCH	float32	yr	Reference epoch for Gaia/Tycho astrometry. Typically 2015.5 for Gaia
PARALLAX	float32	mas	Reference catalog parallax
PARALLAX_IVAR	float32	mas^-2	Inverse variance of PARALLAX
PMRA	float32	mas / yr	proper motion in the +RA direction (already including cos(dec))
PMDEC	float32	mas / yr	Proper motion in the +Dec direction
PMRA_IVAR	float32	yr^2 / mas^2	Inverse variance of PMRA
PMDEC_IVAR	float32	yr^2 / mas^2	Inverse variance of PMDEC
GAIA_PHOT_G_MEAN_MAG	float32	mag	Gaia G band magnitude
GAIA_PHOT_G_MEAN_FLUX_OVER_ERROR	float32		Gaia G band signal-to-noise
GAIA_PHOT_BP_MEAN_MAG	float32	mag	Gaia BP band magnitude
GAIA_PHOT_BP_MEAN_FLUX_OVER_ERROR	float32		Gaia BP band signal-to-noise
GAIA_PHOT_RP_MEAN_MAG	float32	mag	Gaia RP band magnitude
GAIA_PHOT_RP_MEAN_FLUX_OVER_ERROR	float32		Gaia RP band signal-to-noise
GAIA_ASTROMETRIC_EXCESS_NOISE	float32		Gaia astrometric excess noise
URAT_ID	int64		ID in the URAT catalog for sources where URAT supplemented missing Gaia astrometric information
URAT_SEP	float32	arcsec	Separation between URAT and Gaia sources where URAT supplemented missing Gaia astrometric information
GAIA_PHOT_G_N_OBS	int32		Gaia G band number of observations
HPXPIXEL	int64		HEALPixel containing this location at NSIDE=64 in the NESTED scheme

Notes and Examples

Some units in this file do not conform to the FITS standard:

deg^-2 is incorrectly recorded as 1/deg^2
nanomaggy^-2 is incorrectly recorded as 1/nanomaggy^2
mas^-2 is incorrectly recorded as 1/mas^2

Such issues can typically be fixed by parsing the unit through astropy after reading in a Table, e.g.:

import astropy.units as u
from astropy.table import Table
objs = Table.read(filename, 1)
u.Unit(str(objs["RA_IVAR"].unit))