================== 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 ================================= ========== ======= =================== .. _`Legacy Surveys`: http://legacysurvey.org .. _`LS`: http://legacysurvey.org/dr9/catalogs/ .. _`ellipticity component`: http://legacysurvey.org/dr9/catalogs/ .. _`Release`: http://legacysurvey.org/release/ .. _`Morphological Model`: http://legacysurvey.org/dr9/catalogs/ .. _`Tycho-2`: https://heasarc.nasa.gov/W3Browse/all/tycho2.html .. _`Gaia`: https://gea.esac.esa.int/archive/documentation//GDR2/Gaia_archive/chap_datamodel/sec_dm_main_tables/ssec_dm_gaia_source.html 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.