The young open cluster Trumpler 3
  We present a photometric and spectroscopic study of the poorly investigated
open cluster Trumpler~3. Basic parameters such as the age of $70\pm10$ Myr, the
color excess $E(B-V)=0.30\pm0.02$ mag, the distance of $0.69\pm0.03$ kpc and
the limiting radius of 12' were redetermined and compared with previous
preliminary studies. The distance of $0.65\pm0.09$ kpc was determined
independently by spectral parallaxes. Simultaneously, our analysis allowed us
to estimate a total number of members to be $N_{\rm{tot}}=570\pm90$ and a total
mass of the cluster to be $M_{\rm{tot}}=270\pm40$ $\rm{M}_{\odot}$. We also
determined a state of cluster's dynamical evolution. We conclude that
Trumpler~3 is a young low-massive stellar ensemble with a typical mass function
slope, located near to the outer edge of the Galaxy's Orion Spur. As a result
of a wide-field search for short period variable stars, 24 variables were
discovered in the cluster's area. Only one of them -- a variable of the
$\gamma$-Dor type -- was found to be a likely cluster member.
