Astr110 Photography Projects, Fall 2004

M97, Betsy DeHaan

The Owl Nebula M97 is one of the fainter objects in Messier's catalog, discovered by Perre Mechain on February 16, 1781.The mass of the nebula has been estimated to amount 0.15 solar masses. Its distance is uncertain; the Sky Catalog 2000 has 1,300 light years, I.S. Shklovsky 1,430, O'Dell and Kohoutek independently found 1,600 in the early 1960s. Its dynamical age is about 6,000 years.The expanding gas shell is excited to shine by the high-energy radiation emitted from the central star; the material in the shell is moreover accelerated so that the expansion gets faster by the time. The shining gas shell is then visible as a planetary nebula.

M97 is one of the more complex planetary nebulae. Its appearance has been interpreted as that of a cylindrical torus shell (or globe without poles), viewed oblique, so that the projected matter-poor ends of the cylinder correspond to the owl's eyes. As often for planetary nebulae, the Owl is significantly brighter visually than photographically, as most light is emitted in one green spectral line. In the background of this nebula, there are several small nebulous objects, most probably very distant galaxies, the brightest of these objects being superimposed by the brighter star. This brightest background object can be found on many larger-field exposures of the Owl Nebula.

References:
http://www.seds.org/messier/m/m097.html, http://www.seds.org/messier/planetar.html