Type IIP Supernovae as Cosmological Probes: A SEAM Distance to SN 1999em

Due to their intrinsic brightness, supernovae make excellent cosmological probes. We describe the SEAM method for obtaining distances to Type IIP supernovae (SNe IIP) and present a distance to SN 1999em for which a Cepheid distance exists. Our models give results consistent with the Cepheid distance, even though we have not attempted to tune the underlying hydrodynamical model, we have simply chosen the best fits. This is in contradistinction to the expanding photosphere method (EPM) which yields a distance to SN 1999em that is 50% smaller than the Cepheid distance. We emphasize the differences between SEAM and EPM. We show that the dilution factors used in the EPM analysis were systematically too small at later epochs. We also show that the EPM blackbody assumption is suspect. Since SNe IIP are visible to redshifts as high as z ∼< 6, with the JWST, SEAM may be a valuable probe of the early universe. Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks, Rm. 131, Norman, OK 73019, USA Computational Research Division, Lawrence Berkeley National Laboratory, MS 50F-1650, 1 Cyclotron Rd, Berkeley, CA 94720-8139 USA Laboratoire de Physique Nucléaire et de Haute Energies, CNRS-IN2P3, University of Paris VII, Paris, France Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany