Valentino Gonzalez(1), Ivo Labbe(2), Rychard Bouwens(1,3),  Garth Illingworth(1) 
1.-UCO/Lick, University of California Santa Cruz  2.-Carnegie Observatories 
3.-Leiden Observatory, Leiden University, Leiden, Netherlands 

The recent advent of the WFC3 camera onboard the HST has recently
expanded our window of observation well beyond z~7. Due to the
faintness of the sources, however, access to their rest frame optical
properties through mid- IR observations remains limited to z<8. In our
presentation we take advantage of an early selection of 11 bright z~7
candidates found by Bouwens et al. (2009, in prep.) over a large area
of ~80 arcmin^2 of NICMOS data in and around the two GOODS fields.  We
complement these observations with the very deep 3.6 and 4.5 mu
Spitzer IRAC imaging available through the GOODS program which grants
us access to the rest frame optical properties of these bright sources
in an individual basis. We study the stellar populations of these
sources by fitting synthetic spectra from the Bruzual and Charlot 2003
stellar population models.  We compare our results to similar studies
at 4<z<6 and surprisingly find that, contrary to what is observed at
much lower redshifts, z<2, the mean specific SFR of the sources seems
to remain constant at ~2 Gyr^-1, suggesting that star formation
proceeds in a different manner in these early times. We also show how
more recent selections based on the latest WFC3/IR observations
confirm and extend these findings to much fainter limits.  Taking
advantage of this large area and two separate pointings, we also make
a robust measurement of the Stellar Mass density of the universe when
it was only 750 Myr old and use this quantity to constrain the SFR
density of the universe at even earlier times.