Constraining dust and color variations of high-z SNe using NICMOS on Hubble Space Telescope

We present data from the Supernova Cosmology Project for five high redshift
Type Ia supernovae (SNe Ia) that were obtained using the NICMOS infrared camera
on the Hubble Space Telescope. We add two SNe from this sample to a rest-frame
I-band Hubble diagram, doubling the number of high redshift supernovae on this
diagram. This I-band Hubble diagram is consistent with a flat universe
(Omega_Matter, Omega_Lambda= 0.29, 0.71). A homogeneous distribution of large
grain dust in the intergalactic medium (replenishing dust) is incompatible with
the data and is excluded at the 5 sigma confidence level, if the SN host galaxy
reddening is corrected assuming R_V=1.75. We use both optical and infrared
observations to compare photometric properties of distant SNe Ia with those of
nearby objects. We find generally good agreement with the expected color
evolution for all SNe except the highest redshift SN in our sample (SN 1997ek
at z=0.863) which shows a peculiar color behavior. We also present spectra
obtained from ground based telescopes for type identification and determination
of redshift.