DR19 includes a single LVM tile, that provides a first look at the data format that will be used in future LVM data releases. Due to ongoing developments and testing of the LVM data reduction pipeline, there are a number of known issues and caveats in the released DRP version, and resulting data products. We include a summary of the key known issues below.
Data Reduction Issues
- Flux calibration issues remain at the spectral channel boundaries and overlap regions (e.g., dips at ~5800A and ~7570A)
- Flat fielding applied fiber to fiber has issues detected at a 5% level
- No telluric corrections are applied
- SCI method of flux calibration (used for the DR19 tile) is systematically offset from the more accurate STAN method by ~1.3
- The errors are overestimated by a factor of 2.5 (as provided in IVAR)
- Small systematic differences in fluxes are seen between spectrographs
- The sky subtraction module uses a simple approach, with several known limitations. Caution is advised when searching for faint lines that may be blended with sky lines. The sky spectrum that has been subtracted for each fiber is contained in the `SKY’ extension
- The pixel mask tends to overflag pixels
Known Header Issues (Including Incorrect Header Values)
- Barycentric and heliocentric corrections are contained in the header, but are not applied to the spectra
- The sky subtraction related headers, labelled with `SKYMODEL’ and `GEOCORONAL’, are mostly incorrect
- The astrometric solution for the RA and Dec coordinates are not in the fits file header, but are correct in the `SLITMAP’ extension. In the header, the PO{telescope}RA and PO{telescope}DE should be more accurate than the TE{telescope}RA and TE{telescope}DE, with {telescope} being SCI, SKYE, or SKYW for the science, sky east, and sky west telescopes, respectively.