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 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)

本文件包含经校正的斯隆数字巡天四号（SDSS-IV）MaNGA恒星库（MaStar）版本，该版本针对银河系星际介质（ISM）中产生的CaII 3934、3969与NaI D 5891、5897谱线吸收效应完成了校正。相关校正方法的完整细节详见Rubin等人（2025）的研究成果。

简言之，我们首先基于高分辨率光谱研究，构建了上述谱线吸收强度随恒星距离、银纬及尘埃红移变化的物理模型。依托该模型，我们筛选出6342颗星际介质吸收效应可忽略的MaStar恒星。对于剩余的12110颗恒星，我们将其NaI D谱轮廓（有效温度高于9000K的恒星同时替换其CaII谱轮廓）替换为具有相似有效温度、表面重力与金属丰度的低星际介质吸收恒星的叠加光谱。另有738颗有效温度高于9000K的恒星，我们采用基于ATLAS9的BOSZ模型替换其对应光谱区域。该处理流程为24162颗恒星的星表中的80%提供了校正后的光谱数据。

本文件中的光谱与已统一至MaStar光谱分辨率99.5百分位曲线的版本完全一致，相关数据已发布于https://www.sdss4.org/dr17/mastar/mastar-spectra（上述已校正的光谱区域除外）。本数据集的数据模型说明如下：
MANGAID：格式为XX-XXXXXX的MaNGA星系编号
WAVE：真空波长网格，波长采样为对数分度，单位为埃（Angstroms）
FLUX：观测通量，已校正银河系星际介质污染。已完成地球大气上方的消光校正，但未校正银河系固有消光，单位为10^-17 erg/s/cm²/Å
IVAR：通量的逆方差，单位为10^34 s²cm⁴Ų/erg²
PREDISP：仪器展宽σ，未包含像素积分效应，单位为埃
SRES：光谱分辨率计算公式为：SRES = WAVE/(√(8×ln2) × PREDISP)
REPLACEMENT_CAII_FLG：CaII光谱区域处理标记，详见表3
REPLACEMENT_NAID_FLG：NaI D光谱区域处理标记，详见表3
NSIG_THRESH：若构建了经验替换样本堆，则为恒星参数空间中与经验替换样本的最大三维距离，详见3.1与3.2节（记为Ψ_thresh）
ewCaIIK_pred：由2.2节所述模型预测的星际CaII K线等效宽度，单位为埃
ewNaI5891_pred：由2.2节所述模型预测的星际NaI D 5891线等效宽度，单位为埃
ewNaI5897_pred：由2.2节所述模型预测的星际NaI D 5897线等效宽度，单位为埃