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skies-supp-hp-HP.rst

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supplemental skies

Summary:DESI supplemental sky locations contain a single binary table covering the entire Gaia footprint. They are generated to help find sky locations in regions that are not covered by Legacy Surveys imaging. Supplemental sky locations are produced at random positions across the sky and are subsequently removed if they either lie close to a Gaia source or share an nside = 4096 HEALPixel with an existing pixel-based sky location from the Legacy Surveys.
Naming Convention:skies-supp-hp-HP.fits, where HP is the HEALPixel covered at the (nested) HEALPixel nside included in the file header as FILENSID (e.g. 11).
Regex:skies-supp-hp-?[0-9]+\.fits
File Type:FITS, 186 KB - 9.4 MB

Contents

Number EXTNAME Type Contents
HDU0   IMAGE Empty
HDU1 SKY_TARGETS BINTABLE Table of sky locations

FITS Header Units

HDU0

This HDU has no non-standard required keywords.

Empty HDU.

HDU1

EXTNAME = SKY_TARGETS

Table of sky locations

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ======== ============= ===== ==================================
    KEY      Example Value Type  Comment
    ======== ============= ===== ==================================
    NAXIS1   136           int   width of table in bytes
    NAXIS2   2342          int   number of rows in table
    SUPP     T             bool  ``True`` if sky locations are supplemental (i.e. are `not` derived from the `Legacy Surveys`_)
    GAIADR   2             int   Gaia Data Release used to select supplemental skies
    NPERSDEG 18000.0       float density of sky locations generated per sq. deg.
    HPXNSIDE 64            int   HEALPix nside for column `HPXPIXEL`
    HPXNEST  T             bool  HEALPix nested (not ring) ordering
    SUBPSEED 12583926      int   random seed used to generate `SUBPRIORITY` values
    RADIUS   2.0           float separation (arcsec) at which to avoid Gaia sources
    MINDEC   -90.0         float minimum declination for GFAs that are not selected from the Legacy Surveys
    MINGALB  0.0           float closest latitude to Galactic Plane for GFAs that are not selected from the Legacy Surveys
    MASKED   T             bool  ``True`` if targets were masked to avoid bright sources
    MASKDIR  "masks/"      str   location of directory of masks used to avoid bright sources
    CMDLINE  "/global/"    str   command-line call used to generate target file
    FILENSID 2             int   HEALPix nside covered by file
    FILENEST T             bool  HEALPix nested (not ring) ordering
    FILEHPX  "11"          str   HEALPix pixel(s) covered by file
    ======== ============= ===== ==================================

Required Data Table Columns

.. rst-class:: columns
Name Type Units Description
RELEASE int32   Legacy Surveys (LS) Release
BRICKID int32   Brick ID from tractor input
BRICKNAME char[8]   Brick name from tractor input
BRICK_OBJID int32   OBJID (unique to brick, but not to file)
RA float64 deg Right ascension
DEC float64 deg Declination
BLOBDIST float32 pix Maximum distance from a detected Legacy Surveys source
FIBERFLUX_G float32   g-band object model flux
FIBERFLUX_R float32   r-band object model flux
FIBERFLUX_Z float32   z-band object model flux
FIBERFLUX_IVAR_G float32   Inverse Variance of FIBERFLUX_G
FIBERFLUX_IVAR_R float32   Inverse Variance of FIBERFLUX_R
FIBERFLUX_IVAR_Z float32   Inverse Variance of FIBERFLUX_Z
TARGETID int64   Unique targeting ID
DESI_TARGET int64   DESI (dark time program) target selection bitmask
BGS_TARGET int64   BGS (bright time program) target selection bitmask
MWS_TARGET int64   MWS (bright time program) target selection bitmask
SUBPRIORITY float64   Random subpriority [0-1] to break assignment ties
OBSCONDITIONS int64   Flag target to be observed in combinations of dark/bright observing layer
PRIORITY_INIT int64   Initial priority for target calculated across 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 sky location

Notes

As quantities in the supplemental skies files are derived from Gaia, quantities from the Legacy Surveys that aren't also in Gaia (i.e. fluxes) are populated with meaningless values.