Hubble Space Telescope Fine Guidance Sensor Parallaxes of Galactic Cepheid Variable Stars: Period-Luminosity Relations and Applications

Details Hubble Space Telescope Fine Guidance Sensor Parallaxes of Galactic Cepheid Variable Stars: Period-Luminosity Relations and Applications Hubble Space Telescope Fine Guidance Sensor Parallaxes of Galactic Cepheid Variable Stars: Period-Luminosity Relations and Applications

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20910201b&link_type=abstract

2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #102.01; Bulletin of the American Astronomical Society,

Astronomy and Astrophysics

Astronomy

1

Scientific paper

We present new absolute trigonometric parallaxes and relative proper motions for nine Galactic Cepheid variable stars: l Car, zeta Gem, beta Dor, W Sgr, X Sgr, Y Sgr, FF Aql, T Vul, and RT Aur, with an average parallax error of 8%. Two stars (FF Aql and W Sgr) required the inclusion of binary astrometric perturbations, providing Cepheid mass estimates. With these parallaxes we compute absolute magnitudes in V, I, K, and Wesenheit WVI bandpasses, corrected for interstellar extinction and Lutz-Kelker bias. Adding our previous absolute magnitude determination for δ Cep, we construct Period-Luminosity relations (PLR) for ten Galactic Cepheids.
We compare our new PLR with those adopted by several recent investigations, including the Freedman and Sandage H0 projects. Adopting our PLR would tend to increase the Sandage H0 value, but leave the Freedman H0 unchanged. Comparing our Galactic Cepheid PLR with those derived from LMC Cepheids, we find the slopes for K and WVI identical in the two galaxies within their respective errors. Our data lead to a WVI distance modulus for the Large Magellanic Cloud, m-M=18.50±0.03. Recently derived metallicity corrections yield a corrected LMC distance modulus of m-M=18.40±0.05. Applying our PLR directly to Cepheids in NGC 4258 provides a distance modulus, m-M=29.21±0.02, in good agreement with the maser distance modulus, m-M=29.29±0.15. From our metallicity-corrected LMC distance modulus and the Macri et al. (2006) difference in distance moduli we obtain m-M=29.28±0.08.
To further improve extragalactic distance determinations, parallaxes of additional long-period Cepheids would be extremely valuable, but will require the microarcsecond precision of, for example, the Space Interferometry Mission (SIM).
Support for this work was provided by NASA through grants GO-09879 and GO-10106 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

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