Calibrating the P‐Factor in the IR Baade‐Wesselink Method for Classical and Dwarf Cepheids

The Baade‐Wesselink method using VJK photometry was shown by Laney and Stobie (1995) to yield apparently precise results, free of obvious systematics with phase, surface gravity and microturbulence. Here we extend the empirical calibration of the p‐factor [1] to a maximal sample of galactic classical Cepheids. HADS or ‘dwarf Cepheids’ have been shown to follow the same PL relation (at least for high‐metallicity objects), and a HADS sample is therefore added in order to extend the period range and examine the variation of the p‐factor with period. The derived pulsation parallaxes give a slope of $0.07±0.02,$ in good agreement with the calculations of Nardetto et al. [2]. Applying this period vs. p‐factor relation to 68 galactic pulsation parallaxes gives a slope for the galactic PL relation in good agreement with the LMC PL relation.