==== gfas ==== :Summary: DESI guide/focus/alignment (GFA) files contain a single binary table covering the entire footprint. They contain objects derived from matches between Gaia and the Legacy Surveys and the associated quantities used by fiber assignment to select sources for guiding and focus. :Naming Convention: ``gfas-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: ``gfas-hp-?[0-9]+\.fits`` :File Type: FITS, 20 MB - 8.5 GB Contents ======== ====== =========== ======== ============ Number EXTNAME Type Contents ====== =========== ======== ============ HDU0_ IMAGE Empty HDU1_ GFA_TARGETS BINTABLE Target table ====== =========== ======== ============ FITS Header Units ================= HDU0 ---- This HDU has no non-standard required keywords. Empty HDU. HDU1 ---- EXTNAME = GFA_TARGETS Target selection table Required Header Keywords ~~~~~~~~~~~~~~~~~~~~~~~~ .. collapse:: Required Header Keywords Table .. rst-class:: keywords ======== ============= ===== ================================== KEY Example Value Type Comment ======== ============= ===== ================================== NAXIS1 164 int width of table in bytes NAXIS2 142824 int number of rows in table DR 9 int Legacy Surveys Data Release used to find targets MAGLIM 21.0 float magnitude limit on GFA targets in Gaia G-band 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 NOURAT F bool ``True`` if the URAT catalog was not used to supplement missing proper motions GAIADR "edr3" str Gaia Data Release used to select GFAs HPXNSIDE 64 int HEALPix nside for column `HPXPIXEL` HPXNEST T bool HEALPix nested (not ring) ordering FILENSID 2 int HEALPix nside covered by file FILENEST T bool HEALPix nested (not ring) ordering FILEHPX 11 int HEALPix pixel(s) covered by file ======== ============= ===== ================================== Required Data Table Columns ~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. rst-class:: columns ================================= =========== ================== =================== Name Type Units Description ================================= =========== ================== =================== RELEASE int32 Legacy Surveys (`LS`_) `Release`_ TARGETID int64 Unique targeting ID BRICKID int32 Brick ID from tractor input BRICK_OBJID int32 OBJID (unique to brick, but not to file) RA float64 deg Right ascension DEC float64 deg Declination RA_IVAR float32 deg**-2 Right ascension inverse variance DEC_IVAR float32 deg**-2 Declination inverse variance MORPHTYPE char[4] `Morphological Model`_ type MASKBITS int16 Bitmask for ``coadd/*/*/*maskbits*`` maps, as on the `LS DR9 bitmasks page`_ FLUX_G float32 nanomaggy `LS`_ flux from tractor input (g) FLUX_R float32 nanomaggy `LS`_ flux from tractor input (r) FLUX_Z float32 nanomaggy `LS`_ flux from tractor input (z) FLUX_IVAR_G float32 nanomaggy**-2 Inverse Variance of FLUX_G FLUX_IVAR_R float32 nanomaggy**-2 Inverse Variance of FLUX_R FLUX_IVAR_Z float32 nanomaggy**-2 Inverse Variance of FLUX_Z REF_ID int64 Tyc1*1,000,000+Tyc2*10+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 Reference catalog proper motion in the RA direction PMDEC float32 mas / yr Reference catalog 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 Number of observations in Gaia G band HPXPIXEL int64 HEALPixel containing target at HPXNSIDE ================================= =========== ================== =================== .. _`LS`: https://www.legacysurvey.org/dr9/catalogs/ .. _`ellipticity component`: https://www.legacysurvey.org/dr9/catalogs/ .. _`Release`: https://www.legacysurvey.org/release/ .. _`Morphological Model`: https://www.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 .. _`SFD98`: http://ui.adsabs.harvard.edu/abs/1998ApJ...500..525S .. _`LS DR9 bitmasks page`: https://www.legacysurvey.org/dr9/bitmasks/ .. _`SGA`: https://github.com/moustakas/SGA Notes ===== 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.: .. code-block:: python import astropy.units as u from astropy.table import Table objs = Table.read(filename, 1) u.Unit(str(objs["RA_IVAR"].unit)) See https://www.legacysurvey.org for more details about columns in the data model.