HST FOS Integrated Spectra of Four M31 Globular Clusters

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Session 104 -- Globilar Clusters
Display presentation, Thursday, 12, 1995, 9:20am - 6:30pm

[104.15] HST FOS Integrated Spectra of Four M31 Globular Clusters

J. Ponder, D. Burstein (ASU), C.-C. Wu (CSC), R.W. O'Connell (UVa), J.A. Rose (UNC), J.A. Frogel (OSU), M. Rieke (UofA)

HST FOS spectra at $\rm 8\AA$ spectral resolution have been obtained of the M~31 globular clusters M~IV, M~II, K~280 and K~58, using the 1$''$ circular aperture. The spectra cover the range $\rm 2200\AA$ to $\rm 4800\AA$ (gratings G270H and G400H) with S/N $>$ 20 at the quoted spectral resolution. Far-UV G130H spectra did not have high enough S/N to be useful. Agreement in flux level is good to $<5\%$ in the wavelength overlap region between the G270H and G400H spectra for each cluster.

The estimated [Fe/H] values for the four clusters are -2.0, -0.8, -0.3 and 0.0, respectively. The average line strengths in the four spectra parallel the respective [Fe/H] values, with M~IV being very weak-lined and K~58 being exeptionally strong-lined. From these data, UV and optical lines strengths have been measured on the systems of Fanelli et al. (1992); Davidge \& Clark (1994); Brodie \& Huchra (1990), as well as on the Lick system (Gonzalez 1993; Worthey 1992; both UCSC Ph.D. theses). UV line strengths measured from these spectra are compared quantitatively to those of galactic stars as measured by several authors. We find that the $\rm 3380 \AA$ NH feature is exceptionally strong in the spectra of the M31 globular clusters, implying a large nitrogen abundance for the brightest main sequence stars in these clusters, whose flux dominates at $\rm 3380 \AA$. Even the most metal-poor cluster, M~IV is seen to have NH in absorption.

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