From: Don Groom (deg@panisse.lbl.gov)
Date: Thu May 29 2003 - 09:38:51 PDT
I find this flurry of notes about biases in our low-extinction method
vaguely disturbing. While I certainly can't make the learned comments
about the details of the data that others can, I note:
1. ANYTHING we say is a Bayesian prior! E.g.:
a. B-V = 0 after we remove outliers.
b. We confuse measurements with True Values but assume the negative
ones have no weight (the Reiss method)
c. Maybe the non-outliers have some average reddening, e.g. 0.05, and
we should take a simple Gaussian around this central value (I don't
see this supported by Fig 3, but Serena knows best).
2. I used AN OLD VERSION (Mar 21) of Rob's all_intrinsic.dat to check the
veracity of the error bars: Attached is an ideogram of eb_v assuming the
given deb_v for all 79 objects in the table (I know, scrambling all the
cases in Fig 3); file is attached. In a well-ordered world it would be
sort of Gaussian, maybe a little peakier. It could be argued that the peak
at 0.1 is produced by objects with genuine reddening, but the peaks at
negative eb_v indicate that we can conclude no such thing. What we CAN
conclude is that (a) the errors are certainly underestimated for some of
the cases where the measured quantity is negative, and (b) there's no
convincing evidence for a non-zero <b-v>.
It would be interesting to do this over with all 4 cuts in Fig 3 and
current values.
Don
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Don Groom (Particle Data Group, Supernova Cosmology Project)
DEGroom(at)lbl.gov www-ccd.lbl.gov Voice: 510/486-6788 FAX: 510/486-4799
Analog: 50-308//Berkeley Lab//Berkeley, CA 94720
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