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Abstract We assess the impact of Caiiλλ3934, 3969 and Naiλλ5891, 5897 absorption arising in the interstellar medium (ISM) on the Sloan Digital Sky Survey-IV MaNGA Stellar Library (MaStar) and produce corrected spectroscopy for 80% of the 24,162-star catalog. We model the absorption strength of these transitions as a function of the stellar distance, Galactic latitude, and dust reddening based on high-spectral resolution studies. With this model, we identify 6342 MaStar stars that have negligible ISM absorption (W^ISM(CaiiK) < 0.07 Å andW^ISM(Nai5891) < 0.05 Å). For 12,110 of the remaining stars, we replace their NaiD profile (and their Caiiprofile for effective temperaturesT_eff> 9000 K) with a coadded spectrum of low-ISM stars with similarT_eff, surface gravity, and metallicity. For 738 additional stars withT_eff> 9000 K, we replace these spectral regions with a matching ATLAS9-based BOSZ model. This results in a mean reduction inW(CaiiK) (W(NaiD)) of 0.4–0.7 Å (0.6–1.1 Å) for hot stars (T_eff> 7610 K), and a mean reduction inW(NaiD) of 0.1–0.2 Å for cooler stars. We show that interstellar absorption in the simple stellar population (SSP) model spectra constructed from the original library artificially enhancesW(CaiiK) by ≳20% at young ages (<400 Myr); dramatically enhances the strength of stellar NaiD in starbursting systems (by ≳50%); and enhances stellar NaiD in older stellar populations (≳10 Gyr) by ≳10%. We provide SSP spectra constructed from the cleaned library and discuss the implications of these effects for stellar population synthesis analyses constraining the stellar age, [Na/Fe] abundance, and initial mass function. 

{"Abstract":["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.\n\nThe 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.    \n\nMANGAID - The XX-XXXXXX format MaNGA IDWAVE - 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 3REPLACEMENT_NAID_FLG - Flag indicating treatment of the NaID spectral region.  Described in Table 3NSIG_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)"],"Other":["Preferred Citation\n\nIf you use these library spectra in your research, we ask that you please cite our article, "Sloan Digital Sky Survey IV MaStar: Quantification and Abatement of Interstellar Absorption in the Largest Empirical Stellar Spectral Library," Rubin et al. (2025), ApJ, 981 31, doi:10.3847/1538-4357/ad8eb6.  Please also cite this Zenodo deposit."]}