Dust Evolution in the Dwarf Galaxy Holmberg II
  A detailed photometric study of star-forming regions (SFRs) in the galaxy
Holmberg II has been carried out using archival observational data from the far
infrared to ultraviolet obtained with the GALEX, Spitzer, and Herschel
telescopes. Spectroscopic observations with the 6-m telescope of Special
Astrophysical Observatory of the Russian Academy of Sciences are used to
estimate ages and metallicities of SFRs. For the first time, the ages of SFRs
have been related to their emission parameters in a wide spectral range and
with the physical parameters determined by fitting the observed spectra. It is
shown that fluxes at 8 and 24 micron characterizing the emission of polycyclic
aromatic hydrocarbons (PAHs) and hot dust grains decrease with age, but their
ratio increases. This implies that the relative PAH contribution to the total
infrared flux increases with age. It is suggested that the detected increase in
the ratio of the fluxes at 8 and 24 micron is related to the growth in the PAH
mass due to destruction of larger grains.
