PPMXL photometric study of four open cluster candidates (Ivanov 2,
  Ivanov 7, Ivanov 9 and Harvard 9)
  The astrophysical parameters of four unstudied open star cluster candidates -
Harvard 9, Ivanov 2, Ivanov 7, and Ivanov 9 - have been estimated for the first
time using the PPMXL database. The stellar density distributions and
color-magnitude diagrams for each cluster are used to determine the geometrical
structure (cluster center, limited radius, core and tidal radii, the distances
from the Sun, from the Galactic center and from the Galactic plane). Also, the
main photometric parameters (age, distance modulus, color excesses, membership,
total mass, relaxation time, luminosity and mass functions) are estimated.
