Moderate-Resolution Near-Infrared Spectroscopy of Cool Stars: A New [ITAL]K[/ITAL]-Band Library

I present an atlas of near-infrared K-band spectra of 31 late-type giants andsupergiants, and two carbon stars. The spectra were obtained at resolvingpowers of 830 and 2000, and have a signal-to-noise ratio of 100 or higher.These data are complemented with results from similar existing libraries inboth K- and H-band, and are used to identify various tools useful for stellarpopulation studies at moderate resolution. I focus on several of the mostprominent absorption features and (1) investigate the effects of spectralresolution on measurements of their equivalent width (EW), (2) examine thevariations with stellar parameters of the EWs, and (3) construct compositeindices as indicators of stellar parameters and of the contribution from excesscontinuum sources commonly found in star-forming and AGN galaxies. Among thefeatures considered, the CO (2,0) and CO (6,3) bandheads together with the SiI1.59 micron feature, first proposed by Oliva, Origlia, and coworkers,constitute the best diagnostic set for stellar spectral classification and forconstraining the excess continuum emission. The CaI 2.26 micron and MgI 2.28micron features offer alternatives in the K-band to the CO (6,3) bandhead andSiI feature.Comment: 31 pages, incl. 8 postscript figures, 4 tables; accepted for publication in the Astronomical Journa