Milky Way Mapper Caveats

The meta-caveat is that caveats will continue to be added as we identify them.

Current caveats

  • While most ASTRA files are typically separated between BOSS and APOGEE, the mwmTargets file is built on the target level rather than on a spectra basis. Therefore, the DR20 mwmTargets-0.8.1.fits.gz file (and its associated DR20 CAS table) only contains targets observed with BOSS. If you need the APOGEE targets, look in the mwmTargets-0.6.0.fits.gz file (and its associated DR19 CAS table). However, keep in mind that it will contain both BOSS and APOGEE targets.
  • The DR20 0.8.1 ASTRA files (https://dr20.sdss.org/sas/dr20/spectro/astra/0.8.1/) only contain BOSS Spectra. If you want to look at parameters from APOGEE spectra, use the 0.6.0 ASTRA files (https://dr20.sdss.org/sas/dr20/spectro/astra/0.6.0/). One should note that 0.6.0 contains both APOGEE and BOSS spectra, where the BOSS spectra results are superseded by the 0.8.1 results.
  • If a result seems suspicious, look at the BOSS or APOGEE spectrum
  • FieldIDs between 16000 and 100000 are designed as FPS commissioning and engineering fields. While valid science can be done with these fields, caution is advised.
    • Field 016181 is a commission field where the telescope position was moved each exposure, so this field should not be used for science
  • The line labels for the Ca II H & K lines in the DR19 BOSS Spectra PNG images are reversed.
  • In the plate era DR19 data from the BOSS drp (FieldIDs < 16000), the gaia_g mags are gaia_bp magnitudes. These values have been corrected in the data visualizations tools associated with Zora.
  • BOSS DRP (IDLspec2d) object classifications are primarily focused on the identification of galaxy vs. quasar vs. star. Although sub-classifications are provided, they are not optimized for accuracy. In particular, the CV star templates have more degrees of freedom than other stellar templates, which can result in unphysical solutions where negative PCA components of the CV templates can fit the absorption features of White Dwarfs. Fixing this has not been a high priority since the primary classification of “star” vs. “galaxy” or “qso” is still correct.
  • The Stellar parameters produced by PyXCSAO in the BOSS DRP (IDLspec2d) are typically inconsistent with the sub-classifications provided, as different analysis codes produce them. The PyXCSAO parameters should be trusted over the subclasses.
  • Due to the noise characteristics of individual BOSS visits, the parameters and classifications might vary between visits. Typically, the highest S/N visit provides the most trustworthy results, but it is up to the end user to confirm their choice of spectral parameters.
  • The corrected temperatures for M giants in DR19 ASPCAP are cooler than in previous post-processed ASPCAP products, because the temperature correction was extrapolated rather than being set a constant value
  • The corrected ASPCAP metallicities of M dwarfs should be adjusted again using the equation in Qiu et al. (2026)
  • Visual vetting shows DR20 SnowWhite classifications may be unreliable up to 20% of the time.
  • Spectroscopic parameters from SnowWhite do not include 3D-corrections from Tremblay et al. (2013).
  • Some targets processed by Astra had erroneous data removed from their mwmStar files. For these targets, the first HDU extension, BOSS/APO, has no data but contains an invalid DATASUM header value. The files themselves, as well as data from other extensions, are still readable and accessible.
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