TILEID-sky.fits

Summary:

This file contains the sky targets covered by the tile disk-footprint.

Naming Convention:

{TILEID}-sky.fits, where {TILEID} is the zero-padded, 6-digit TILED.

Regex:

[0-9]{6}-sky\.fits

File Type:

FITS, 23 MB

Contents

Number	EXTNAME	Type	Contents
HDU0		IMAGE	Empty HDU
HDU1	SKY_TARGETS	BINTABLE	Sky targets covered by the tile disk-footprint.

FITS Header Units

HDU0

This HDU has no non-standard required keywords.

Empty HDU.

HDU1

EXTNAME = SKY_TARGETS

Sky targets 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	152	int	width of table in bytes
NAXIS2	163775	int	number of rows in table
SUPP	F	bool
DR	9	int

Required Data Table Columns

Name	Type	Units	Description
RELEASE	int32		Imaging surveys release ID
BRICKID	int32		Brick ID from tractor input
BRICKNAME	char[8]		Brick name 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
BLOBDIST	float32	pix	Maximum distance from a detected Legacy Surveys source
FIBERFLUX_G	float32	nanomaggy	g-band flux measured in aperture of radius 0.75 arcsec, extracted from the Legacy Surveys coadd stacks
FIBERFLUX_R	float32	nanomaggy	r-band flux measured in aperture of radius 0.75 arcsec, extracted from the Legacy Surveys coadd stacks
FIBERFLUX_Z	float32	nanomaggy	z-band flux measured in aperture of radius 0.75 arcsec, extracted from the Legacy Surveys coadd stacks
FIBERFLUX_IVAR_G	float32	nanomaggy^-2	Inverse variance of FIBERFLUX_G
FIBERFLUX_IVAR_R	float32	nanomaggy^-2	Inverse variance of FIBERFLUX_R
FIBERFLUX_IVAR_Z	float32	nanomaggy^-2	Inverse variance of FIBERFLUX_Z
TARGETID	int64		Unique DESI target ID
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
SUBPRIORITY	float64		Random subpriority [0-1) to break assignment ties
OBSCONDITIONS	int64		Bitmask of allowed observing conditions
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
HPXPIXEL	int64		HEALPixel containing this location at NSIDE=64 in the NESTED scheme
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

Notes and Examples

The FIBERFLUX quantities use a different definition FIBERFLUX as measured in other files. See also the skies files files produced by desitarget.

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

• nanomaggy^-2 is incorrectly recorded as 1/nanomaggy^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["FIBERFLUX_IVAR_G"].unit))