$\mu_{\star}$ Masses: Weak Lensing Calibration of the Dark Energy Survey
  Year 1 redMaPPer Clusters using Stellar Masses
  We present the weak lensing mass calibration of the stellar mass based
$\mu_{\star}$ mass proxy for redMaPPer galaxy clusters in the Dark Energy
Survey Year 1. For the first time we are able to perform a calibration of
$\mu_{\star}$ at high redshifts, $z>0.33$. In a blinded analysis, we use $\sim
6,000$ clusters split into 12 subsets spanning the ranges $0.1 \leqslant
z<0.65$ and $\mu_{\star}$ up to $\sim 5.5 \times 10^{13} M_{\odot}$, and infer
the average masses of these subsets through modelling of their stacked weak
lensing signal. In our model we account for the following sources of systematic
uncertainty: shear measurement and photometric redshift errors, miscentring,
cluster-member contamination of the source sample, deviations from the NFW halo
profile, halo triaxiality and projection effects. We use the inferred masses to
estimate the joint mass--$\mu_{\star}$--$z$ scaling relation given by $\langle
M_{200c} | \mu_{\star},z \rangle = M_0 (\mu_{\star}/5.16\times 10^{12}
\mathrm{M_{\odot}})^{F_{\mu_{\star}}} ((1+z)/1.35)^{G_z}$. We find $M_0= (1.14
\pm 0.07) \times 10^{14} \mathrm{M_{\odot}}$ with $F_{\mu_{\star}}= 0.76 \pm
0.06$ and $G_z= -1.14 \pm 0.37$. We discuss the use of $\mu_{\star}$ as a
complementary mass proxy to the well-studied richness $\lambda$ for: $i)$
exploring the regimes of low $z$, $\lambda<20$ and high $\lambda$, $z \sim 1$;
$ii)$ testing systematics such as projection effects for applications in
cluster cosmology.
