We present a new distance estimation for the Milky Way dwarf spheroidal satellite Sculptor obtained from multi-epoch mid-infrared observations of RR Lyrae stars .
The 3.6 \mu m observations have been acquired with the Infrared Array Camera on board the Spitzer Space Telescope as part of the SMHASH Program .
Mid-infrared light curves for 42 RRL were obtained , from which we measured Sculptor ’ s distance modulus to be \mu = 19.60 \pm 0.02 ( statistical ) \pm 0.04 ( photometric ) mag ( with \sigma _ { sys } = 0.09 mag ) , using the 3.6 \mu m empirical period-luminosity relations derived from the Galactic globular cluster M4 , or \mu = 19.57 \pm 0.02 ( statistical ) \pm 0.04 ( photometric ) mag ( with \sigma _ { sys } = 0.11 mag ) using empirical relations in the same passband recently derived from the Large Magellanic Cloud globular cluster Reticulum .
Both these measurements are in good agreement with values presented in previous works with Sculptor RR Lyrae stars in optical bands , and are also consistent with recent near-infrared RR Lyrae results .
Best agreement with the literature is found for the latter modulus which is equivalent to a distance of d = 82 \pm 1 ( statistical ) \pm 2 ( photometric ) kpc ( with \sigma _ { sys } = 4 kpc ) .
Finally , using a subsample of RR Lyrae stars with spectroscopic metallicities , we demonstrate that these distance estimates are not affected by metallicity effects .