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6.1. Observing strategies

Recent results suggest the following observational strategies might be useful.

  1. Observe two bandpasses (e.g. V and I) so that possible systematic effects with color (metallicity and age) can be identified and removed (see Ashman, Conti, & Zepf 1995, and Elson & Santiago 1996b).
  2. Observe farther toward the infrared (e.g. I band) to minimize possible correlations of M0V with metallicity (see Ashman, Conti, & Zepf 1995).
  3. For HST observations, use dithered exposures to help remove hot pixels and improve spatial resolution.

6.2. Future Work

What are the key observations likely to be over the next five years?

  1. The determination of whether the GCLF is different for spiral and elliptical galaxies. The most straightforward approach would be to use HST to observe spirals and ellipticals in tight groups, or possibly in pairs.
  2. A better determination of the zeropoint for the GCLF in bright elliptical galaxies using Cepheid variables in the Virgo, Fornax, and other nearby groups and clusters. This will remove the dependence on spiral galaxies where the GCLF is less well defined.
  3. A better determination of the appropriate expansion velocity to use for the estimate of the Hubble constant. While the Jerjen & Tammann (1993) approach is promising, it can be improved using the more extensive data currently available. In addition, the same method should be used for the Fornax cluster and other key groups where Cepheid measurements are available (e.g. the Leo group).
  4. Observations of the GCLF in a sample of bright elliptical galaxies with good sky coverage in the range 2,000 - 10,000 km s-1 (with HST) to minimize the dependence on peculiar velocities.

6.3. Conclusions

  1. The GCLF for bright ellipticals turns out to be an excellent distance indicator, much better than might be expected based on current theoretical ideas about the formation and destruction of clusters. The intrinsic dispersion in M0V is approx 0.12 mag.
  2. The value of M0V appears to be nearly universal. The current database can begin to support the search for possible (small) second-order correlations of M0V with various properties (e.g. Hubble type, color, environment).
  3. Cepheid variables can be used to determine the GCLF zeropoint for bright ellipticals rather than relying on the Milky Way, M31, and an assumption of universality.
  4. HST provides an excellent tool for measuring the GCLF, providing limiting magnitudes roughly two to three magnitudes deeper than ground-based observations.
  5. The number of high quality GCLFs will increase dramatically in the next decade, making this one of the most important methods of measuring distances.

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