H$_2$S observations in young stellar disks in Taurus
  Context. Studying gas chemistry in protoplanetary disks is key to
understanding the process of planet formation. Sulfur chemistry in particular
is poorly understood in interstellar environments, and the location of the main
reservoirs remains unknown. Protoplanetary disks in Taurus are ideal targets
for studying the evolution of the composition of planet forming systems.
  Aims. We aim to elucidate the chemical origin of sulfur-bearing molecular
emission in protoplanetary disks, with a special focus on H$_2$S emission, and
to identify candidate species that could become the main molecular sulfur
reservoirs in protoplanetary systems.
  Methods. We used IRAM 30m observations of nine gas-rich young stellar objects
(YSOs) in Taurus to perform a survey of sulfur-bearing and oxygen-bearing
molecular species. In this paper we present our results for the CS 3-2 ($\nu_0$
= 146.969 GHz), H$_2$CO 2$_{11}$-1$_{10}$ ($\nu_0$ = 150.498 GHz), and H$_2$S
1$_{10}$-1$_{01}$ ($\nu_0$ = 168,763 GHz) emission lines.
  Results. We detected H$_2$S emission in four sources out of the nine
observed, significantly increasing the number of detections toward YSOs. We
also detected H$_2$CO and CS in six out of the nine. We identify a tentative
correlation between H$_2$S 1$_{10}$-1$_{01}$ and H$_2$CO 2$_{11}$-1$_{10}$ as
well as a tentative correlation between H$_2$S 1$_{10}$-1$_{01}$ and H$_2$O
8$_{18}$-7$_{07}$. By assuming local thermodynamical equilibrium, we computed
column densities for the sources in the sample, with N(o-H$_2$S) values ranging
between $2.6\times10^{12}$ cm$^{-2}$ and $1.5\times10^{13}$ cm$^{-2}$.
