Uncertainties in The Interstellar Extinction Curve and the Cepheid
  Distance to M101
  I revisit the Cepheid-distance determination to the nearby spiral galaxy M101
(Pinwheel Galaxy) of Shappee & Stanek (2011), in light of several recent
investigations questioning the shape of the interstellar extinction curve at
$\lambda \approx 8,000$ \AA (i.e. I-band). I find that the relatively steep
extinction ratio $A_{I}/E(V-I)=1.1450$ (Fitzpatrick & Massa 2007) is slightly
favoured relative to $A_{I}/E(V-I)=1.2899$ (Fitzpatrick 1999) and significantly
favoured relative the historically canonical value of $A_{I}/E(V-I)=1.4695$
(Cardelli et al. 1989). The steeper extinction curves, with lower values of
$A_{I}/E(V-I)$, yield fits with reduced scatter, metallicity-dependences to the
dereddened Cepheid luminosities that are closer to values inferred in the local
group, and that are less sensitive to the choice of reddening cut imposed in
the sample selection. The increase in distance modulus to M101 when using the
preferred extinction curve is ${\Delta}{\mu} \sim 0.06$ mag, resulting in an
estimate of the distance modulus to M101 relative to the LMC of $
{\Delta}\mu_{\rm{LMC}} \approx 10.72 \pm 0.03$ (stat). The best-fit
metallicity-dependence is $dM_{I}/d\rm{[O/H]} \approx (-0.38 \pm 0.14$ (stat))
mag dex$^{-1}$.
