CLASSY. II. A Technical Overview of the COS Legacy Archive Spectroscopic Survey*

Abstract The COS Legacy Archive Spectroscopic SurveY (CLASSY) is designed to provide the community with a spectral atlas of 45 nearby star-forming galaxies that were chosen cover similar properties those seen at high z ( > 6). prime high-level science product CLASSY accurately coadded UV spectra, ranging from ∼1000 2000 Å, derived combination archival and new data obtained HST’s Cosmic Origins Spectrograph (COS). This paper details multistage technical processes creating this methodologies involved in extracting, reducing, aligning, coadding far-ultraviolet near-ultraviolet (NUV) spectra. We guidelines on how successfully utilize observations extended sources, despite being optimized for point best-practice recommendations coaddition spectra general. Moreover, we discuss effects our reduction techniques scientific application data. In particular, find accounting flux calibration offsets can affect stellar populations, while customized extractions NUV sources are essential correctly diagnosing metallicity via C iii ] nebular emission. Despite changes resolution up ∼25% between individual sets (due line-spread function), no adverse affects observed difference velocity width outflow velocities isolated absorption lines when measured final combined products, owing part signal-to-noise regime S/N < 20.