The XSL DR3 spectra are combined-arm spectra, with log10 sampled wavelengths in rest-frame. The spectra are provided as FITS binary tables, each containing four or three columns:

1. WAVE: Wavelength [in nm]. As the spectra are rest-framed, the wavelength ranges are spectrum-dependent.
2. FLUX: Flux spectrum [in erg/s/cm²/Å]
3. DEREDDENED FLUX: Flux spectrum [in erg/s/cm²/Å], corrected for Galactic extinction.
4. ERR: Error spectrum: [same units as Flux]


Naming examples of DR3 spectra:
1. xsl_spectrum_X0000_merged.fits - four column binary tables [WAVE, FLUX, FLUX_DR, ERR]
2. xsl_spectrum_MD000_merged.fits - new M dwarf spectrum; four column binary tables [WAVE, FLUX, FLUX_DR, ERR]
3. xsl_spectrum_X0000_merged_scl.fits - spectrum is corrected for galactic dust extinction and flux losses with a spline function; a four column binary tables [WAVE, FLUX, FLUX_SC, ERR]
4. xsl_spectrum_X0000_merged_ncl.fits - spectrum IS NOT corrected for slit flux losses (but IS for galactic extinction, use with caution!); a four column binary tables [WAVE, FLUX, FLUX_DR, ERR]
5. xsl_spectrum_X0000_merged_ncge.fits - spectrum IS NOT corrected for galactic dust extinction (but IS for slit flux losses); a three column binary tables [WAVE, FLUX, ERR].
6. xsl_spectrum_X0000_merged_ncl_ncge.fits - spectrum IS NOT corrected for slit flux losses NOR corrected for galactic dust extinction; a three column binary tables [WAVE, FLUX, ERR].


A Python3 script is enclosed to help our users to read the DR3 spectra: plot_xsl_dr3.py. Please read the comments below running the program.
1. Modules to be installed: Numpy, astropy.io.fits
2. Variables to be defined:
   1. path_data: Path for the input XSL DR3 data


Please see the XSL keywords dictionary (primary header) Table B.1 of Verro et al. (2022a). The primary header also includes the relevant keywords describing the values and origin of UVB-VIS and VIS-NIR arm merging parameters and the total galactic dust extinction in V.