Composition of an Emission Line System in Black Hole Host Globular
  Cluster RZ2109
  We present an analysis of optical spectra from the globular cluster RZ2109 in
NGC4472, which hosts the first unambiguous globular cluster black hole. We use
these spectra to determine the elemental composition of the emission line
system associated with this source, and to constrain the age and metallicity of
the host globular cluster. For the emission line system of RZ2109, our analysis
indicates the [O III]5007 equivalent width is 33.82 +- 0.39 Ang and the H beta
equivalent width is 0.32 +- 0.32 Ang , producing a formal [O III]5007/H beta
emission line ratio of 106 for a 3200 km/s measurement aperture covering the
full velocity width of the [O~III]5007 line. Within a narrower 600 \kms
aperture covering the highest luminosity velocity structure in the line
complex, we find O III]5007/H beta = 62. The measured O III]5007/H beta ratios
are significantly higher than can be produced in radiative models of the
emission line region with solar composition, and the confidence interval limits
exclude all but models which have gas masses much larger than those for a
single star. Therefore, we conclude that the region from which the [O~III]5007
emission originates is hydrogen-depleted relative to solar composition gas.
This finding is consistent with emission from an accretion-powered outflow
driven by a hydrogen-depleted donor star, such as a white dwarf, being accreted
onto a black hole.
