Observational calibration of the projection factor of Cepheids: III. The long-period Galactic Cepheid RS Puppis

Pierre Kervella, Boris Trahin, Howard E. Bond, Alexandre Gallenne, Laszlo Szabados, Antoine Mérand, Joanne Breitfelder, Julien Dailloux, Richard I. Anderson, Pascal Fouqué, Wolfgang Gieren, Nicolas Nardetto, Grzegorz Pietrzyński

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

The projection factor (p-factor) is an essential component of the classical Baade-Wesselink (BW) technique, which is commonly used to determine the distances to pulsating stars. It is a multiplicative parameter used to convert radial velocities into pulsational velocities. As the BW distances are linearly proportional to the p-factor, its accurate calibration for Cepheids is of critical importance for the reliability of their distance scale. We focus on the observational determination of the p-factor of the long-period Cepheid RS Pup (P = 41.5 days). This star is particularly important as this is one of the brightest Cepheids in the Galaxy and an analog of the Cepheids used to determine extragalactic distances. An accurate distance of 1910 ± 80 pc (± 4.2%) has recently been determined for RS Pup using the light echoes propagating in its circumstellar nebula. We combine this distance with new VLTI/PIONIER interferometric angular diameters, photometry, and radial velocities to derive the p-factor of RS Pup using the code Spectro-Photo-Interferometry of Pulsating Stars (SPIPS). We obtain p = 1.250 ± 0.064 (± 5.1%), defined for cross-correlation radial velocities. Together with measurements from the literature, the p-factor of RS Pup confirms the good agreement of a constant p = 1.293 ± 0.039 (±3.0%) model with the observations. We conclude that the p-factor of Cepheids is constant or mildly variable over a broad range of periods (3.7 to 41.5 days).

Original languageEnglish
Article numberA127
JournalAstronomy and Astrophysics
Volume600
DOIs
Publication statusPublished - Apr 1 2017

Keywords

  • Distance scale
  • Stars: distances
  • Stars: individual: RS Pup
  • Stars: variables: Cepheids
  • Techniques: interferometric
  • Techniques: photometric

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Kervella, P., Trahin, B., Bond, H. E., Gallenne, A., Szabados, L., Mérand, A., Breitfelder, J., Dailloux, J., Anderson, R. I., Fouqué, P., Gieren, W., Nardetto, N., & Pietrzyński, G. (2017). Observational calibration of the projection factor of Cepheids: III. The long-period Galactic Cepheid RS Puppis. Astronomy and Astrophysics, 600, [A127]. https://doi.org/10.1051/0004-6361/201630202