2001/04/06 by M. Bellazzini, F. R. Ferraro, E. Pancino · 8 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/321613
15 pages including 4 figures. Needs the aastex.cls macro. Accepted by ApJ
arxiv created 2001/04/06 · openalex publication_date 2001/08/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
The absolute I magnitude of the tip of the red giant branch ( M ) is one of the most promising standard candles actually used in astrophysics as a fundamental pillar for the cosmological distance scale. With the aim of improving the observational basis of its calibration, we have obtained an accurate estimate of the M for the globular cluster ω Centauri, based (1) on the largest photometric database ever assembled for a globular cluster, by Pancino and colleagues, and (2) on a direct distance estimate for ω Cen, recently obtained by Thompson and colleagues from a detached eclipsing binary. The derived value M = -4.04 ± 0.12 provides, at present, the most accurate empirical zero point for the calibration of the M - relation at ~ -1.7. We also derive a new empirical M -[Fe/H] relation based on the large IR data set of red giants in Galactic globular clusters recently presented by Ferraro and colleagues. This database (extending up to [Fe/H] = -0.2) covers a more appropriate metallicity range for extragalactic applications than previous empirical calibrations (which were limited to [Fe/H] ≤ -0.7). The proposed relation is in excellent agreement with the newly determined zero point.