This package is primarily intended for working with data from the SDSS-III BOSS survey, but can also be used to access older data from SDSS-I/II and newer data from the SEQUELS ancillary program and the SDSS-IV eBOSS survey (see /envvar for details).
BOSS data consists of spectroscopic observations of astrophysical targets. An observation is identified by a triplet of numbers (PLATE,MJD,FIBER). Most BOSS targets only have a single observation. Each observation consists of several 15-minute exposures using red and blue cameras with overlapping wavelength coverage that are combined to give a single co-added spectrum.
The table below summarizes the different files produced by the spectroscopic pipeline containing the individual and combined exposures contributing to each observation. Files contain from 1 to 1000 spectra, with some duplication between files. Each file provides wavelength, flux, inverse variance, mask bits and subtracted sky for each of its spectra.
| Type | Size | #Tgts | #Exp | Coadd? | Calib? | Datamodel Bossdata Class | |
|---|---|---|---|---|---|---|---|
| lite | 0.2Mb |
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lite <spectra/lite/PLATE4/spec> |
bossdata.spec.SpecFile |
| spec | 1.7Mb |
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spec <spectra/PLATE4/spec> |
bossdata.spec.SpecFile |
| plate | 110Mb |
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plate <PLATE4/spPlate> |
bossdata.plate.PlateFile |
| cframe | 70Mb |
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cframe <PLATE4/spCFrame> |
bossdata.plate.FrameFile |
| frame | 30Mb |
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frame <PLATE4/spFrame> |
bossdata.plate.FrameFile |
| raw | 37Mb |
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sdR | bossdata.raw.RawImageFile |
The following examples show how the same combined spectrum can be plotted <bossplot> from lite files and plate files:
bossplot --plate 6641 --mjd 56383 --fiber 30
bossplot --plate 6641 --mjd 56383 --fiber 30 --platefileIndividual exposures can also be plotted using either spec files, cframe files or frame files:
bossplot --plate 6641 --mjd 56383 --fiber 30 --exposure 0
bossplot --plate 6641 --mjd 56383 --fiber 30 --exposure 2 --cframe
bossplot --plate 6641 --mjd 56383 --fiber 30 --exposure 2 --frameNote that the indexing of exposures is different for spec files, which only index exposures used in the final coadd, and (c)frame files which index all available exposures. The indices used in the example all refer to exposure number 00158842, which can be verified by adding the --verbose option to these commands. The difference between the cframe and frame files is that the frame gives fluxes in units of flat-fielded detected electrons, before the step of calibrating fluxes using standard stars.
The following per-exposure calibration data products can also be accessed using the ftype parameter to bossdata.plate.Plan.get_exposure_name and bossdata.spec.Exposures.get_exposure_name. These files are in 1-1 correspondence with the sp(C)Frame files.
| Size | Type | Datamodel | Description |
|---|---|---|---|
| 5Mb | science | spFluxcalib <PLATE4/spFluxcalib> |
Flux calibration vectors derived from standard stars |
| 1Mb | science | spFluxcorr <PLATE4/spFluxcorr> |
Flux correction vectors for a science exposure |
| 6Mb | arc | spFlat <PLATE4/spArc> |
Results derived from an arc calibration exposure |
| 4Mb | flat | spFlat <PLATE4/spFlat> |
Results derived from an flat calibration exposure |
The definitive reference for how these calibration data are created and used is the IDL pipeline code.