Calibration of the distance scale from galactic Cepheids: I Calibration based on the GFG sample

摘要

New estimates of the distances of 36 nearby galaxies are presented based onaccurate distances of galactic Cepheids obtained by Gieren, Fouque and Gomez(1998) from the geometrical Barnes-Evans method. The concept of 'sosie' is applied to extend the distance determination toextragalactic Cepheids without assuming the linearity of the PL relation. Doingso, the distance moduli are obtained in a straightforward way. The correction for extinction is made using two photometric bands (V and I)according to the principles introduced by Freedman and Madore (1990). Finally,the statistical bias due to the incompleteness of the sample is correctedaccording to the precepts introduced by Teerikorpi (1987) without introducingany free parameters (except the distance modulus itself in an iterativescheme). The final distance moduli depend on the adopted extinction ratio {R_V}/{R_I}and on the limiting apparent magnitude of the sample. A comparison with thedistance moduli recently published by the Hubble Space Telescope Key Project(HSTKP) team reveals a fair agreement when the same ratio {R_V}/{R_I} is usedbut shows a small discrepancy at large distance. In order to bypass the uncertainty due to the metallicity effect it issuggested to consider only galaxies having nearly the same metallicity as thecalibrating Cepheids (i.e. Solar metallicity). The internal uncertainty of thedistances is about 0.1 magnitude but the total uncertainty may reach 0.3magnitude.