qsonic 0.2.0

Quasar continuum fitter for DESI

Lightining-fast continuum fitting

QSOnic is an MPI-parallelized, highly optimized quasar continuum fitting package for DESI built on the same algorithm as picca, but faster. It also provides an efficient API to read DESI quasar spectra.

The key differences

• Coadding of spectrograph arms is optional and performed after continuum fitting.

• Continuum is multiplied by a fiducial mean flux when provided.

• You can pass fiducial var_lss (column VAR) and mean flux (column MEANFLUX) for observed wavelength LAMBDA in STATS extention of a FITS file. Wavelength should be linearly and equally spaced. This is the same format as rawio output from picca.

• If no fiducial is passed, we fit only for var_lss (no eta fitting currently).

• Internal weights for continuum fitting and coadding are based on smoothed IVAR, but output WEIGHT is not smoothed.

• Chi2 information as well as best fits are saved in continuum_chi2_catalog.fits. Chi2 is calculated using smooth ivar and var_lss, and does not subtract sum of ln(weights).

Similarities

• Delta files are the same. CONT column is mean flux times continuum even when fiducial mean flux is passed.

• MEANSNR in header file and chi2 catalog is average of flux times square root of positive ivar values. Header values are per arm, but catalog values are the average over all arms.