Distance to M31 With the HST and Hipparcos Red Clump Stars

K. Z. Stanek; P. M. Garnavich

doi:10.1086/311539

paper

Distance to M31 With the HST and Hipparcos Red Clump Stars

arXiv:astro-ph/9802121 · doi:10.1086/311539

Abstract

Following an approach by Paczyński & Stanek we compare red clump stars with parallaxes known to better than 10% in the Hipparcos catalog with the red clump stars observed in three fields in M31 using the HST. There are $\sim 600$ and $\sim 6, 300$ such stars in the two data sets, respectively. The local red clump luminosity function is well represented by a Gaussian with the peak at $M_{I, m} = - 0.23$ , and the dispersion $σ_{R C} \approx 0.2$ mag. This allows a single step determination of the distance modulus to M31 $μ_{0, M 31} = 24.471 \pm 0.035 \pm 0.045$ mag (statistical plus systematic error) and the corresponding distance $R_{M 31} = 784 \pm 13 \pm 17 k p c$ . The number of red clump stars is large enough that the formal statistical error in the distance is only $≲ 2$ %. We also correct the treatment of the local interstellar extinction by Paczyński & Stanek and we obtain the Galactocentric distance modulus $μ_{0, GC} = 14.57 \pm 0.04 \pm 0.04$ mag (statistical plus systematic error), and the corresponding Galactocentric distance $R_{0} = 8.2 \pm 0.15 \pm 0.15 k p c$ .

accepted by the ApJ Letters, 11 pages, 4 figures

Distance to M31 With the HST and Hipparcos Red Clump Stars

Abstract

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