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Daytona Beach


Physical Sciences

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We present deep VI photometry of stars in the globular cluster M5 (NGC 5904) based on images taken with the Hubble Space Telescope. The resulting color-magnitude diagram reaches below V ≈27 mag, revealing the upper 2–3 mag of the white dwarf cooling sequence and main-sequence stars 8 mag and more below the turnoff. We fit the main sequence to subdwarfs of known parallax to obtain a true distance modulus of (m ̶ M )0 = 14:45 ± 0:11 mag. A second distance estimate based on fitting the cluster white dwarf sequence to field white dwarfs with known parallax yielded (m _ M)0 = 14:67 ± 0:18 mag. We discuss the nature of the difference between the two distance estimates and suggest approaches for reducing the uncertainty in white dwarf fitting estimates for future studies. We couple our distance estimates with extensive photometry of the cluster’s RR Lyrae variables to provide a calibration of the RR Lyrae absolute magnitude yielding MV (RR) = 0:42 ± 0:10 mag at [Fe/H] = ̶ 1:11 dex. We provide another luminosity calibration in the form of reddening-free Wasenheit functions. Comparison of our calibrations with predictions based on recent models combining stellar evolution and pulsation theories shows encouraging agreement, and the existing differences may provide useful feedback to the models.

Publication Title

The Astrophysical Journal


Institute of Physics Publishing, Inc.

Grant or Award Name

NASA/STScI grant HST-GO-08310-97A. T. v. H. and NASA LTSA grant 02-0045-0082

Additional Information

Dr. von Hippel was not affiliated with Embry-Riddle Aeronautical University at the time this paper was published.