General description: The spPlate files contain the combined spectra for all exposures of a given plate. There are typically four 900s exposures which may have been taken in a single night, or over multiple nights. This page is an updated summary of the SDSS2 spPlate data model.
Naming convention: spPlate-pppp-mmmmm.fits, where pppp is a 4-digit plate number, and mmmmm is a 5-digit MJD.
Approximate size: 110 Mbytes.
File type: FITS
Read by products: spreduce1d.pro, sspp
Written by products: spcombine.pro
| HDU0 | NPIX x NFIBER float image | Flux in units of 10^-17^ erg/s/cm^2^/Ang |
| HDU1 | NPIX x NFIBER float image | Inverse variance (1/sigma^2^) for HDU 0 |
| HDU2 | NPIX x NFIBER 32-bit int image | AND mask |
| HDU3 | NPIX x NFIBER 32-bit int image | OR mask |
| HDU4 | NPIX x NFIBER float image | Wavelength dispersion in pixels |
| HDU5 fields | binary table | Plug-map structure from plPlugMapM file |
| HDU6 | NPIX x NFIBER float image | Average sky flux in units of 10^-17^ erg/s/cm^2^/Ang |
Additional HDUs may be present for engineering purposes, but are not supported and are subject to change. Users should refrain from using HDUs not listed here.
There are two masks, an "AND" mask and an "OR" mask. The spectra are constructed from 3 or more 15-minute observations, and the "AND" mask bits are set if that bit is set for each and every input observation. The "OR" mask bits are set if that bit is set for any of the observations. Usually, I only look at the "AND" mask.
The mask bits are set as follows:
0 NOPLUG Fiber not listed in plugmap file
1 BADTRACE Bad trace from routine TRACE320CRUDE
2 BADFLAT Low counts in fiberflat
3 BADARC Bad arc solution
4 MANYBADCOLUMNS >10% pixels are bad columns
5 MANYREJECTED >10% pixels are rejected in extraction
6 LARGESHIFT Large spatial shift between flat and object pos'n
7 BADSKYFIBER Sky Fiber shows extreme residuals
8 NEARWHOPPER Within 2 fibers of a whopping fiber (deprecated)
10 SMEARIMAGE Smear available for red and blue cameras (deprecated)
11 SMEARHIGHSN S/N sufficient for full smear fit (deprecated)
12 SMEARMEDSN S/N only sufficient for scaled median fit (deprecated)
16 NEARBADPIXEL Bad pixel within 3 pixels of trace
17 LOWFLAT Flat field less than 0.5
18 FULLREJECT Pixel fully rejected in extraction (INVVAR=0)
19 PARTIALREJECT Some pixels rejected in extraction
20 SCATTEREDLIGHT Scattered light significant
21 CROSSTALK Cross-talk significant
22 NOSKY Sky level unknown at this wavelength (INVVAR=0)
23 BRIGHTSKY Sky level > flux + 10*(flux error)
AND sky > 2.0 * median(sky,99 pixels)
24 NODATA No data available in combine B-spline (deprecated; INVVAR=0)
25 COMBINEREJ Rejected in combine B-spline
26 BADFLUXFACTOR Low flux-calibration or flux-correction factor
27 BADSKYCHI Relative chi^2 > 3 in sky residuals at this wavelength
28 REDMONSTER Contiguous region of bad chi^2 in sky residuals
(with threshhold of relative chi^2 > 3)
When low numbered bits (<16) are set, those will be set for half of the spectra — either the blue or red spectrograph. The higher-numbered bits (>=16) are set for individual pixels.
Which mask bits are important? The conditions that are considered very bad are already used to set the errors to infinity for the effected pixels (specifically, the inverse variance is set to zero). The most useful mask bit to look at is BRIGHTSKY, which indicates when the sky is so bright relative to the object that perhaps one shouldn't trust any of the object flux there. Our reported errors are meant to include sky-subtraction errors, but there are instances (particularly around 5577) where these errors may be untrustworthy.
Dispersion and sky: The dispersion per pixel and the sky flux are computed at each pixel by re-weighting the individual spectra at each pixel according to their formal errors. This re-weighting is only approximate.
Sky wavelengths: Note that the sky lines are slightly shifted in the reductions because we transform the velocities to the barycenter of the solar system. Each exposure that contributes to the co-added spectra will have slightly different barycenter correction, so the "average sky" contains a superposition of these slightly-offset sky lines. These shifts keep the object spectra as-measured at the barycenter, regardless of the time of year or the Earth's rotation relative to the spectroscopic targets.
SIMPLE FIT STANDARD BITPIX PIXEL NAXIS NUMBER OF ARRAY DIMENSIONS NAXIS1 WIDTH (NPIX) NAXIS2 HEIGHT (NFIBER) BSCALE BZERO EXTEND TELESCOP Sloan 2.5-M FILENAME NGUIDE Number of guider frames during exposure SEEING20 20% seeing during exposure (arcsec) SEEING50 50% seeing during exposure (arcsec) SEEING80 80% seeing during exposure (arcsec) RMSOFF20 20% RMS offset of guide fibers (arcsec) RMSOFF50 50% RMS offset of guide fibers (arcsec) RMSOFF80 80% RMS offset of guide fibers (arcsec) DATASEC DAQVER Data acquisition version CAMDAQ Camera Data acquisition version ERRCNT Error current SYNCERR SLINES PIXERR Pixel Error PLINES Pixel Lines FLAVOR Type of frame RA Right ascension of telescope boresight (deg) DEC Declination of telescope boresight (deg) EQUINOX RA,Dec equinox RADECSYS RA,Dec coordination system FOCUS Focus piston (microns) NAME Name of the currently loaded plugging pppp-mmmmm-dd format PLATEID The number of the currently loaded plate CARTID The cartridged used in this plugging. MAPID The mapping version of the currently loaded plate POINTING The currently specified pointing MJD APO MJD day at the start of the exposure MJDLIS TAI-BEG TAI seconds at start of exposure DATE-OBS TAI date at start of exposure (YYYY-MM-DDTHH:MM:SS) COLLA The position of the A collimator motor COLLB The position of the B collimator motor COLLC The position of the C collimator motor HARTMANN Left,Right,Out,Both,Invalid,Unknown NEXP Number of exposures in this file BESTEXP The best exposure (determined by (S/N)^2?) EXPID01 ID string for exposure 1 EXPID02 ID string for exposure 2 EXPID03 ID string for exposure 3 EXPID04 ID string for exposure 4 EXPID05 ID string for exposure 5 EXPID06 ID string for exposure 6 EXPID07 ID string for exposure 7 EXPID08 ID string for exposure 8 EXPID09 ID string for exposure 9 EXPID10 ID string for exposure 10 EXPID11 ID string for exposure 11 EXPID12 ID string for exposure 12 NEXP_B1 b1 camera number of exposures NEXP_B2 b2 camera number of exposures NEXP_R1 r1 camera number of exposures NEXP_R2 r2 camera number of exposures EXPT_B1 b1 camera exposure time (seconds) EXPT_B2 b2 camera exposure time (seconds) EXPT_R1 r1 camera exposure time (seconds) EXPT_R2 r2 camera exposure time (seconds) EXPTIME Minimum of exposure times for all cameras SPCOADD Time when SPCOADD finished DATASUM Unsigned integer value of the checksum COMMENT General comments AUTHOR File authors VERSIDL Version of IDL VERSUTIL Version of idlutils VERSREAD Version of idlspec2d for pre-processing raw dat VERS2D Version of idlspec2d for 2D reduction VERSCOMB Version of idlspec2d for combining multiple spe VERSLOG Version of SPECLOG product VERSFLAT Version of SPECFLAT product TWOPHASE (propoagated from spCFrame for one b1 exposure -- see that file) RDNOISE (propoagated from spCFrame for one b1 exposure -- see that file) BADPIXEL (propoagated from spCFrame for one b1 exposure -- see that file) RUN2D Spectro-2D reduction name QUALITY image quality TAI-END TAI seconds at start of exposure XSIGMA XSIGMIN XSIGMAX WSIGMA WSIGMIN WSIGMAX PLUGFILE PlugPlate file name, (plPlugMapM-pppp-ddddd-nn.par) LAMPLIST List of lamp lines SKYLIST List of sky lines HELIO_RV Heliocentric correction (added to velocities) VACUUM Wavelengths are in vacuum SFLATTEN Superflat has been applied PSFSKY Order of PSF skysubtraction SKYCHI2 Mean chi^2 of sky-subtraction SCHI2MIN Minimun chi^2 of sky-subtraction SCHI2MAX Maximun chi^2 of sky-subtraction PREJECT Profile area rejection threshold SPEC1_G (S/N)^2 for spec 1 at mag 22.00 SPEC1_R (S/N)^2 for spec 1 at mag 21.00 SPEC1_I (S/N)^2 for spec 1 at mag 21.00 SPEC2_G (S/N)^2 for spec 2 at mag 22.00 SPEC2_R (S/N)^2 for spec 2 at mag 21.00 SPEC2_I (S/N)^2 for spec 2 at mag 21.00 SN2EXT1G Extinction corrected (S/N)^2 SN2EXT1R Extinction corrected (S/N)^2 SN2EXT1I Extinction corrected (S/N)^2 SN2EXT2G Extinction corrected (S/N)^2 SN2EXT2R Extinction corrected (S/N)^2 SN2EXT2I Extinction corrected (S/N)^2 NSTD Number of (good) std stars GOFFSTD Spectrophoto offset for std stars in G-band GRMSSTD Spectrophoto RMS for std stars in G-band ROFFSTD Spectrophoto offset for std stars in R-band RRMSSTD Spectrophoto RMS for std stars in R-band IOFFSTD Spectrophoto offset for std stars in I-band IRMSSTD Spectrophoto RMS for std stars in I-band GROFFSTD Spectrophoto offset for std stars in (GR) GRRMSSTD Spectrophoto RMS for std stars in (GR) RIOFFSTD Spectrophoto offset for std stars in (RI) RIRMSSTD Spectrophoto RMS for std stars in (RI) LOWREJ Extraction: low rejection HIGHREJ Extraction: high rejection SCATPOLY Extraction: Order of scattered light polynomial PROFTYPE Extraction profile: 1=Gaussian NFITPOLY Extraction: Number of parameters in each profil XCHI2 Extraction: Mean chi^2 XCHI2MIN Extraction: Minimum chi^2 XCHI2MAX Extraction: Maximum chi^2 AIRMASS Given airmaa NWORDER Linear-log10 coefficients WFITTYPE Linear-log10 dispersion COEFF0 Central wavelength (log10) of first pixel COEFF1 Log10 dispersion per pixel UNAME FBADPIX Fraction of bad pixels FBADPIX1 Fraction of bad pixels on spectro-1 FBADPIX2 Fraction of bad pixels on spectro-2 WAT0_001 System scale WAT1_001 Wtype, Label, Units CRVAL1 Central wavelength (log10) of first pixel CD1_1 Log10 dispersion per pixel CRPIX1 Starting pixel (1-indexed) CTYPE1 DC-FLAG Log-linear flag BUNIT 1E-17 erg/cm^2/s/Ang END
XTENSION IMAGE extension BITPIX Number of bits per data pixel NAXIS Number of data axes NAXIS1 Width (NPIX) NAXIS2 Height (NFIBER) PCOUNT No Group Parameters GCOUNT One Data Group WAT0_001 System scale WAT1_001 Wtype, Label, Units label CRVAL1 Central wavelength (log10) of first pixel CD1_1 Log10 dispersion per pixel CRPIX1 Starting pixel (1-indexed) CTYPE1 DC-FLAG Log-linear flag BUNIT 1E-17 erg/cm^2/s/Ang END
XTENSION IMAGE extension BITPIX Number of bits per data pixel NAXIS Number of data axes NAXIS1 Width (NPIX) NAXIS2 Height (NFIBER) PCOUNT No Group Parameters GCOUNT One Data Group WAT0_001 WAT1_001 CRVAL1 Central wavelength (log10) of first pixel CD1_1 Log10 dispersion per pixel CRPIX1 Starting pixel (1-indexed) CTYPE1 DC-FLAG Log-linear flag END
XTENSION IMAGE extension BITPIX Number of bits per data pixel NAXIS Number of data axes NAXIS1 Width (NPIX) NAXIS2 Height (NFIBER) PCOUNT No Group Parameters GCOUNT One Data Group WAT0_001 System scale WAT1_001 Wtype, Label, Units label CRVAL1 Central wavelength (log10) of first pixel CD1_1 Log10 dispersion per pixel CRPIX1 Starting pixel (1-indexed) CTYPE1 DC-FLAG Log-linear flag END
XTENSION IMAGE extension BITPIX Number of bits per data pixel NAXIS Number of data axes NAXIS1 Width (NPIX) NAXIS2 Height (NFIBER) PCOUNT No Group Parameters GCOUNT One Data Group WAT0_001 System scale WAT1_001 Wtype, Label, Units labe CRVAL1 Central wavelength (log10) of first pixel CD1_1 Log10 dispersion per pixel CRPIX1 Starting pixel (1-indexed) CTYPE1 DC-FLAG Log-linear flag END
XTENSION Binary table written by MWRFITS v1.4a BITPIX Required value NAXIS Required value NAXIS1 Number of bytes per row NAXIS2 Number of rows PCOUNT Normally 0 (no varying arrays) GCOUNT Required value TFIELDS Number of columns in table END
OBJID LONG Array(5) HOLETYPE STRING SS RA DOUBLE D.DD in decimal degrees DEC DOUBLE D.DD in decimal degrees MAG FLOAT Array(5) STARL FLOAT F.FF EXPL FLOAT F.FF DEVAUCL FLOAT F.FF OBJTYPE STRING SS XFOCAL DOUBLE D.DD YFOCAL DOUBLE D.DD SPECTROGRAPHID LONG LL FIBERID LONG LL THROUGHPUT LONG LL PRIMTARGET LONG LL SECTARGET LONG LL OFFSETID LONG LL SCI_EXPTIME FLOAT F.FF SOURCETYPE STRING SS LAMBDA_EFF FLOAT F.FF ZOFFSET FLOAT F.FF BLUEFIBER FLOAT F.FF BOSS_TARGET1 LONG LL(?) BOSS_TARGET2 LONG LL(?) ANCILLARY_TARGET1 LONG LL(?) ANCILLARY_TARGET2 LONG LL(?) RUN LONG LL RERUN STRING SS CAMCOL LONG LL FIELD LONG LL ID LONG LL PSFFLUX FLOAT Array(5) PSFFLUX_IVAR FLOAT Array(5) FIBERFLUX FLOAT Array(5) FIBERFLUX_IVAR FLOAT Array(5) FIBER2FLUX FLOAT Array(5) FIBER2FLUX_IVAR FLOAT Array(5) CALIBFLUX FLOAT Array(5) CALIBFLUX_IVAR FLOAT Array(5) SFD_EBV FLOAT F.FF
XTENSION Image Extension created by MWRFITS v1.4a BITPIX Number of bits per data pixel NAXIS Number of data axes NAXIS1 Width (NPIX) NAXIS2 Height (NFIBER) PCOUNT No Group Parameters GCOUNT One Data Group END