A new calibration of Galactic Cepheid period-luminosity relations from B to K bands, and a comparison to LMC relations

Abstract

Context. The universality of the Cepheid period-luminosity (PL) relations has been under discussion since metallicity effects were assumed to play a role in the value of the intercept and, more recently, of the slope of these relations. Aims. The goal of the present study is to calibrate the Galactic PL relations in various photometric bands (from B to K) and to compare the results to the well-established PL relations in the LMC. Methods. We use a set of 59 calibrating stars, the distances of which are measured using five different distance indicators: Hubble Space Telescope and revised Hipparcos parallaxes, infrared surface brightness and interferometric Baade-Wesselink parallaxes, and classical Zero-Age-Main-Sequence-fitting parallaxes for Cepheids belonging to open clusters or OB stars associations. A detailed discussion of absorption corrections and projection factor to be used is given. Results. We find no significant difference in the slopes of the PL relations between LMC and our Galaxy. Conclusions. We conclude that the Cepheid PL relations have universal slopes in all photometric bands, not depending on the galaxy under study (at least for LMC and Milky Way). The possible zero-point variation with metal content is not discussed in the present work, but an upper limit of 18.50 for the LMC distance modulus can be deduced from our data.

The long-period Galactic Cepheid RS Puppis

“…Considering the intensity-mean magnitudes m B = 8.446 and m V = 7.009 from Berdnikov (private communication), an extinction of E(B − V) = 0.457 ± 0.009 (Fouqué et al 2007), and the reddening laws from Laney & Stobie (1993), the absolute magnitudes of RS Pup in B and V are M B = −5.11 ± 0.05 and M V = −6.09 ± 0.05. Our distance is in good agreement with several other estimates, including the value derived by Havlen (1972a) of 1780 ± 200 pc using the same method.…”

“…Gieren et al (1993), namely p = 1.39−0.03 log P, which amounts to 1.341 in the case of RS Pup (log P = 1.6174). Fouqué et al (2007) derived a distance of 1830 pc based on the same data, but using a lower projection factor based on a mean relation derived by Nardetto et al (2007), p = 1.366−0.075 log P (cross-correlation method), which leads to 1.245 in the case of RS Pup. This revision is based on recent hydrodynamical models of RS Pup itself, combined with high-resolution spectroscopic measurements.…”

Anchors for the cosmic distance scale: the Cepheid QZ Normae in the open cluster NGC 6067

“…Furthermore, spectra and U BV photometry are needed for bright B-stars in close proximity to QZ Nor, in order to determine that Cepheid's reddening. Mean reddening estimates compiled for V340 Nor and QZ Nor by Fouqué et al (2007) imply that there is a ∆E(B − V ) ∼ 0.07 differential offset between the Cepheids, a result that would benefit from independent confirmation. Assessing the period evolution of the Cepheids will likewise be beneficial (Turner et al 2006;Neilson et al 2012b), as the analysis can independently confirm that V340 Nor and QZ Nor lie in separate crossing modes (Fig.…”

Pulsating variable stars in the Magellanic Clouds

“…Is the CCs P L relation universal, as suggested, for instance, by Fouqué et al (2007), so that we are allowed to apply the LMC P L to CCs in other galaxies? Does it depend on metal abundance, as also suggested by nonlinear pulsation models (see, e.g., Bono et al 2008, and references therein)?…”