Physical and Chemical Conditions of the Protostellar Envelope and the
  Protoplanetary Disk in HL Tau
  We report our SMA observations of the Class \RN{1}-\RN{2} protostar HL Tau in
the $^{13}$CO (2--1), C$^{18}$O (2--1), SO(5$_6$--4$_5$), and the 1.3 mm
dust-continuum emission and our analyses of the ALMA long baseline data of the
HCO$^{+}$ (1--0) emission. The 1.3 mm continuum emission observed with the SMA
shows compact ($\sim$0$\farcs$8 $\times$ 0$\farcs$5) and extended
($\sim$6$\farcs$5 $\times$ 4$\farcs$3) components, tracing the protoplanetary
disk and the protostellar envelope, respectively. The $^{13}$CO, C$^{18}$O, and
HCO$^+$ show a compact ($\sim$ 200 AU) component at velocities higher than 3 km
s$^{-1}$ from the systemic velocity and an extended ($\sim$ 1000 AU) component
at the lower velocities. The high-velocity component traces the Keplerian
rotating disk, and the low-velocity component traces the infalling envelope.
The HCO$^+$ high-velocity component is fitted with a Keplerian disk model with
a central stellar mass of 1.4 $M_{\odot}$. The radial intensity profiles of the
$^{13}$CO and C$^{18}$O along the disk major axis are fitted with a
disk+envelope model, and the gas masses of the disk and envelope are estimated
to be $2\mbox{--}40\times10^{-4}$ $M_{\odot}$ and $2.9\times10^{-3}$
$M_{\odot}$, respectively. The disk dust mass has been estimated to be
$1\mbox{--}3 \times 10^{-3}$ $M_{\odot}$ in the literature. Thus, our estimated
disk gas mass suggests that the gas-to-dust mass ratio in the disk is $<$10, a
factor of ten lower than the estimated ratio in the envelope. We discuss the
possible gas depletion or CO depletion in the planet-forming candidate HL Tau
in the context of disk and envelope evolution.
