LUMINOSITY AND TEMPERATURE FROM NEAR-INFRARED SPECTRA OF LATE-TYPE GIANT STARS

We present moderate resolution (lambda/Delta-lambda approximate to 138 0 and lambda/Delta lambda approximate to 4830) spectra of 43 KO to M6 III stars covering 2.19-2.34 mu m and measure equivalent widths of the strongest absorption features-Na I, Ca I, and (CO)-C-12(2,0) -present on the spectra. The high-resolution Wallace & Hinkle [ApJS, 107, 312 (1996)] spectral atlas shows that our moderate-resolution measurements of the atomic features have significant contributions from other spec ies, such as Sc, S, Fe, Ti, Si, and V. We also find that our measured equivalent widths are affected by CN absorption present in the continu um bands. In spite of this, the equivalent widths of Na I and Ca I fea tures at moderate resolution still show a strong dependence on effecti ve temperature. The CO equivalent width at moderate resolution is less affected by other lines and continuum placement than the atomic featu res, because of its relatively greater strength. We compare our data t o similar data taken for late-type dwarf stars [Ali et al., AJ, 110, 2 415 (1995)] and find that a two-dimensional spectral classification ca n be constructed based on the near-IR spectra. The quantity log[EW(CO) /(EW(Na)+EW(Ca))] is a strong luminosity indicator independent of effe ctive temperature, while the equivalent width of (CO)-C-12(2,0) has a well-defined dependence on effective temperature for a given luminosit y. This two-dimensional spectral classification is ideal for cool star s obscured by dust in, for example, the central part of the Galactic b ulge and regions of star formation. (C) 1997 American Astronomical Soc iety.