I downloaded spectra from Sloan Digital Sky Survey (SDSS), which has the following column headers flux, loglam, ivar, and_mask, or_mask, wdisp, sky and model (determined by tdump and tprint in pyraf.stsdas).
I know about flux, loglam, sky and model but I wanted to know what are the other headings are and where are they used. ['loglam' is the log10(wavelength)]
Also, is there any way from which I can determine redshift using the SDSS spectra, by not looking on the quasar page.
The answers can be found on the Documentation page:
HDU 1 (extname COADD): Coadded Spectrum from spPlate
Binary table with columns:
Required 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
AND and OR masks denotes rows where data is flagged in all or one columns, respectively.
As for redshift determination from SDSS spectra; you can identify emission line features like e.g. the H$\alpha$ - [N II] triplet around 6700 Å restframe, of the O II 3727+3729 doublet, or the H$\beta$ + [O III] 4959+5007 complex, and dividing their observed wavelengths by their restframe wavelengths.
