SDSS-IV MaStar: An Empirical Stellar Spectral Library Corrected for the Effects of Milky Way Interstellar Absorption

This file contains a version of the SDSS-IV MaNGA Stellar Library (MaStar) which has been corrected for the effects of absorption in the CaII 3934, 3969 and NaI D 5891, 5897 transitions arising in the Milky Way's interstellar medium (ISM). These corrections are described in full in Rubin et al. (2025). In brief, we first develop a model of the absorption strengths of these transitions as a function of stellar distance, Galactic latitude, and dust reddening based upon high-spectral resolution studies. We use this model to identify 6342 MaStar stars with negligible ISM absorption. For 12110 of the remaining stars, we replace their NaI D profile (and their CaII profile for effective temperatures > 9000 K) with a coadded spectrum of low-ISM stars with similar effective temperature, surface gravity, and metallicity. For 738 additional stars with effective temperatures > 9000 K, we replace these spectral regions with a matching ATLAS9-based BOSZ model. This procedure yields corrected spectroscopy for 80% of the 24162-star catalog. The spectra in this file are identical to those which have been unified to the 99.5th-percentile spectral resolution curve for MaStar and made available at https://www.sdss4.org/dr17/mastar/mastar-spectra (with the exception of the corrected spectral regions described above). The datamodel is described below. MANGAID - The XX-XXXXXX format MaNGA ID WAVE - Vacuum wavelength grid. The wavelength sampling is logarithmic (Angstroms) FLUX - Observed flux, corrected for Milky Way ISM contamination. Extinction-corrected to above the Earth's atmosphere but not corrected for Galactic extinction (10^-17 erg/s/cm^2/Ang) IVAR - Inverse variance of the flux (10^34 s^2cm^4Ang^2/erg^2) PREDISP - Instrumental broadening sigma. Does not include the effect of pixel integration (Angstroms) SRES - Spectral resolution = WAVE/(sqrt(8*ln(2)) * PREDISP) REPLACEMENT_CAII_FLG - Flag indicating treatment of the CaII spectral region. Described in Table 3 REPLACEMENT_NAID_FLG - Flag indicating treatment of the NaID spectral region. Described in Table 3 NSIG_THRESH - Maximum 3D distance in stellar parameter space from stars included in empirical replacement stack, if one was constructed. Described in Sec. 3.1 and 3.2 (Psi_thresh) ewCaIIK_pred - Interstellar CaII K EW predicted by model described in Sec. 2.2 (Angstroms) ewNaI5891_pred - Interstellar NaI D 5891 EW predicted by model described in Sec. 2.2 (Angstroms) ewNaI5897_pred - Interstellar NaI D 5897 EW predicted by model described in Sec. 2.2 (Angstroms)