THE TEMPERATURE OF NONSPHERICAL CIRCUMSTELLAR DUST GRAINS

                    N.V.Voshchinnikov and D.A.Semenov
          Astronomy Department and Sobolev Astronomical Institute,
           St.Petersburg University, St.Petersburg, 198504 Russia


                                ABSTRACT

   The temperature of prolate and oblate spheroidal dust grains in
the envelopes of stars of various spectral types are calculated.
Homogeneous particles with axial ratios a/b<=10 composed of amorphous
carbon, iron, dirty ice, various silicates, and other materials
are considered. The temperature of spherical and spheroidal particles
were found to vary similarly with particle size, distance to the
star, and stellar temperature. The temperature ratio T_d (spheroid)/
T_d (sphere) depends most strongly on the grain chemical composition
and shape. Spheroidal grains are generally colder than spherical
particles of the same volume; only iron spheroids can be slightly
hotter than iron spheres. For a/b about 2, the temperature
deviations do not exceed 10%. If a/b>4, the temperatures can differ
by 30-40%. For a fixed dust mass in the medium, the fluxes at
wavelengths lambda>100 micron are higher if the grains are
nonspherical, which gives overestimated dust masses from millimeter
observations. The effect of grain shape should also be taken into
account when modeling the Galactic dust emission properties
calculated when searching for fluctuations of the cosmic microwave
background radiation in its Wien wing.