The spec-PLATE-MJD-FIBER.fits files contain a repackaging of all spectral data for a given plugging (plate, mjd, fiber), including both the coadded spectrum and optionally the individual exposure frames. This groups the information from spFrame, spCFrame, spFlat, spPlate, spZbest, spZline, and spAll so that for each object one only needs to read a single file.
HDU 0 : Header info from spPlate HDU 1 : Coadded spectrum from spPlate HDU 2 : Summary metadata copied from spAll HDU 3 : Line fitting metadata from spZline HDU 4+ : [Optional] Individual spCFrame spectra [B, R for each exposure]
A "lite" version of these files also exists in the "lite" subdirectory tree. These contain HDUS 0-3, but do not have the individual frame data and thus are much smaller.
spec-[0-9]{4}-[0-9]{5}-[0-9]{4}\.fits
, where
[0-9]{4}
is a zero-padded, four-digit number containing the plate
number, [0-9]{5}
is a five-digit number containing the MJD
number and [0-9]{4}
is a four-digit number containing the fiber id.Copied from spPlate with the following additions/modifications:
Binary table with columns:
Name | Type | Comment |
---|---|---|
flux | float32 | coadded calibrated flux [10-17 ergs/s/cm2/Å] |
loglam | float32 | log10(wavelength [Å]) |
ivar | float32 | inverse variance of flux |
and_mask | int32 | AND mask |
or_mask | int32 | OR mask |
wdisp | float32 | wavelength dispersion in pixel=dloglam units |
sky | float32 | subtracted sky flux [10-17 ergs/s/cm2/Å] |
model | float32 | pipeline best model fit used for classification and redshift |
BOSS spectra: copy of row from spAll for this (plate, mjd, fiber)
SDSS-I/-II spectra: copy of row from specObj for this (plate, mjd, fiber)
copy of row from spZLine for this (plate, mjd, fiber)
For each exposure there is one HDU for the red camera and one for the blue. These are in the order of the EXPIDnn keywords in the HDU 0 header, and their EXTNAME keywords match the EXPIDnn keywords from HDU 0.
Required Header Keywords: Taken from spCFrame files. BOSS spectra have the addition of YPIX0 defining the y-pixel location of the first flux bin.
Binary table with columns:
Name | Type | Comment |
---|---|---|
flux | float32 | coadded calibrated flux [10-17 ergs/s/cm2/Å] |
loglam | float32 | log10(wavelength [Å]) |
ivar | float32 | inverse variance of flux |
mask | int32 | mask |
wdisp | float32 | wavelength dispersion in dloglam units |
sky | float32 | subtracted sky flux [10-17 ergs/s/cm2/Å] |
calib | float32 | conversion between flux and electrons: flux = electrons*calib |
x | float32 | x-pixel location of trace on CCD (BOSS spectra only) |
How to convert flux, sky, and ivar back to extracted photons (electrons):
obj_photons = flux / calib sky_photons = sky / calib ivar_photons = ivar * calib^2