Pre-main Sequence stars in LH91
  We study the accretion properties of pre-main sequence low-mass stars in the
LH 91 association within the Large Magellanic Clouds. Using optical multiband
photometry obtained with the Hubble Space Telescope, we identify 75 candidates
showing H$\alpha$ excess emission above the 3$\sigma$ level with equivalent
width $EW_{H\alpha}$ $\ge$ 10 \AA. We estimate the physical parameters
(effective temperature, luminosity, age, mass, accretion luminosity and mass
accretion rate) of the pre-main sequence stellar candidates. The age
distribution suggests a star formation ranging from few Myr up to $\sim$ 60 Myr
with a gap between $\sim$ 5 Myr and 10 Myr. The masses of the PMS candidates
span from 0.2 $M_{\odot}$ for the cooler objects to 1.0 $M_{\odot}$ with a
median of $\sim$ 0.80 $M_{\odot}$. The median value of the accretion luminosity
of our 75 PMS stars is about 0.12 $L_{\odot}$, the median value of the mass
accretion rate is about 4.8 $\times$ $10^{-9}$ $M_{\odot} yr^{-1}$ with higher
values for the younger population ($\sim$ 1.2 $\times$ $10^{-8}$ $M_{\odot}
yr^{-1}$), and lower values for the older candidates ($\sim$ 4.7 $\times$
$10^{-9}$ $M_{\odot} yr^{-1}$). We compare our results with the findings on LH
95, the closer region to LH 91 for which accretion properties of PMS candidates
were derived. An interesting qualitative outcome is that LH 91 seems to be in a
more evolved stage. Moreover, we find that the PMS candidates are distributed
homogeneously, without any evidence of clumps around more massive stars.
