Journal Article

The Cepheid distance to the Large Magellanic Cloud and NGC 4258 by the surface brightness technique and improved calibration of the cosmic distance scale

G. P. Di Benedetto

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 390, issue 4, pages 1762-1776
Published in print November 2008 | ISSN: 0035-8711
Published online October 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13884.x
The Cepheid distance to the Large Magellanic Cloud and NGC 4258 by the surface brightness technique and improved calibration of the cosmic distance scale

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I report on the implementation of the surface brightness (SB) technique aimed at deriving reliable Cepheid angular diameters at optical wavelengths and then Baade–Wesselink (BW) distances using spectroscopic linear radii. The technique is applied to calibrate the Galactic distance scale and the distance to the Large Magellanic Cloud (LMC) based on this Galactic calibration. The LMC distance benefits from the large number of Cepheids with high-precision photometry and reddening data available by the Optical Gravitational Lensing Experiment of Udalski et al. and from improvements and refinements, including (i) a least-squares (LS) fitting approach to the individual distances to recover the distance modulus unbiased by the period distribution of target Cepheids and (ii) a better understanding of the metallicity effects on the period–luminosity relations and SB scales. The resulting true distance modulus of the LMC is μO(LMC) =[18.559 ± 0.003 (random) ± 0.026 (systematic)] mag.

The SB technique is also applied to confidently determine the Cepheid distance to the maser host galaxy NGC 4258. Cepheids in the inner region with near solar metallicity yield a true distance modulus of μO(NGC 4258) =[29.28 ± 0.03 (random) ± 0.03 (systematic)] mag, in excellent agreement, at the 0.01 mag level, with the high-weight geometric water maser distance modulus. It is shown that the current data-reduction approach of averaging individual Cepheid distances can introduce significant systematic errors in the distance scale calibration. From a small sample of Hubble Space Telescope (HST) based galaxies, I derive an overall error of (12 ± 5) per cent, which would suggest a downward revision of the Freedman et al. Hubble constant to the value H0= (63 ± 7) km s−1Mpc−1, other things being equal.

Keywords: Cepheids; Magellanic Clouds; distance scale

Journal Article.  12172 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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