From: Peter Nugent (nugent@panisse.lbl.gov)
Date: Thu Mar 20 2003 - 09:15:39 PST
> (3) We can move forward and say that we know the K-corrections have
> changed and that we think we underestimtaed the size of that
> systematic in the previous paper.
This is the only option that is valid since it is both scientifically
honest and in fact probably the main reason things have changed. The
k-corrections that we did in P99 were not only based on the spline fits
but assumed that since both B and V 'stretched' the difference did and
thus we could get away with 'stretching' the k-corrections. This is ok as
it captures the shape of the k-crrections very well, but one of the things
it fails to capture is that there is also an offset, ie. B-V at max is a
function of stretch as well. So not only do the k-corrections stretch but
they shift up and down as well. We completely ignored this.
Now at the time it was thought that it wasn't that big a deal. And I think
that was fair. This hack gets you to within 0.02 magnitudes for normal SNe
with normal colors when B and V are the main focus of what we are doing.
However, when we look at the effect of the U-band with it's large
variations at a given stretch and as a function of stretch, this effect
becomes quite significant and will yield just the problems in the analysis
that Greg has pointed out in his e-mail and Rob pointed out in his about
the U-B colors of the k-corrections used in P99. In addition, you will
find that this effect is even more significant when you realize that the
k-corrections Rob used, which are good and have adjustments for (B-V) as a
function of stretch, change things more compared to P99 for the higher
stretch SNe, oh and btw there are more SNe w/ s > 1.0 at z > 0.5.
I guess what I'd like to see to confirm this Rob is if you could make that
table you just did for for (U-B) at s=1.0 for the old k-corrs for (B-V)
at s = 0.9, 1.0 and 1.1 at max. I think this will be more revealing. My
guess is that they will all be the same since no offset was included and
yours will be quite different.
Cheers,
Peter
-- Peter E. Nugent Staff Computational Scientist - Scientific Computing Group - NERSC Lawrence Berkeley National Laboratory M.S. 50F-1650 - 1 Cyclotron Road - Berkeley, CA, 94720-8139 Phone:(510) 486-6942 - Fax:(510) 486-5812 E-mail: penugent@LBL.gov - Web: http://supernova.LBL.gov/~nugent
This archive was generated by hypermail 2.1.4 : Thu Mar 20 2003 - 09:15:53 PST