2001/10/24 by F. Caputo, M. Marconi, I. Musella · 4 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Cepheid variable #Cosmic distance ladder #Distance modulus #Galaxies: Formation, Evolution, Phenomena #Galaxy #Local Group #Maser #Metallicity #Spiral galaxy #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/338137
24 pages, 1 postscript figure accepted for publication on the Astrophysical Journal
arxiv created 2001/10/24 · openalex publication_date 2002/02/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
In a recent paper describing Hubble Space Telescope observations of Cepheids in the spiral galaxy NGC 4258, Newman et al. report that the revised calibrations and methods for the Key Project on the Extragalactic Distance Scale yield that the true distance modulus of this galaxy is μ 0, 4258 = 29.40 ± 0.09 mag, corresponding to a metric distance of 7.6 ± 0.3 Mpc. This Cepheid distance, which holds for 18.50 mag as the true distance modulus of the Large Magellanic Cloud (LMC), is not significantly larger than 7.2 ± 0.5 Mpc, the value determined by Herrnstein et al. from purely geometric considerations on the orbital motions of water maser sources. However, if the metallicity difference Δ[O/H] ~ 0.35 between NGC 4258 and the LMC is taken into account, then the Key Project methods lead to a metallicity-corrected value of μ 0, 4258 = 29.47 ± 0.09 mag, with μ 0, LMC = 18.50 mag, namely, to a Cepheid distance of 7.8 ± 0.3 Mpc, which is 1.2 σ from the maser determination. One might argue that these results are suggesting that a smaller distance to the LMC, μ 0, LMC ~ 18.3 mag, should be used to calibrate the Cepheid brightness. However, even though the well-known controversy between short and long distance scale is far from being settled and current determinations of the LMC distance modulus span ~0.4 mag, it seems that the various empirical methods converge on the value adopted by the Key Project (see Carretta et al.). In this paper we show that the metallicity correction on Cepheid distance determinations, as suggested by pulsation models with three different chemical abundances ( Y = 0.25, Z = 0.004; Y = 0.25, Z = 0.008; Y = 0.28, Z = 0.02), might provide a natural way of reaching a close agreement between Cepheid and maser distances to NGC 4258 for a wide variety of LMC distance determinations. In fact, by adopting μ 0, LMC = 18.50 ± 0.10 mag we derive a Cepheid distance of 7.3 ± 0.6 Mpc, which is only 0.2 σ from the maser determination, while using μ 0, LMC = 18.60 ± 0.10 or 18.40 ± 0.10 mag, the Cepheid and maser distances are 0.8 σ and 0.4 σ apart, respectively.