From: Chris Lidman (clidman@eso.org)
Date: Sun Feb 08 2004 - 05:14:18 PST
Hi Serena,
I did some other cuts. For example I restricted the selection to
targets that were more than 30 degrees from the Galactic plane. This
did not change the results. It is interesting to note that B-V is also
non-zero. This could mean several things. It could mean, for example,
that the sample is slightly reddened
If it were extinction, then
If E(B-V)=0.015 = A(V)=0.046, A(J)=0.013, A(K)=0.005
and one would measure
V-J = 0.033
J-K = 0.008
This leaves us with an offset of V-J = 0.037 magnitudes
So extinction might explain part of it.
The remaining 0.037 magnitudes could be the IR system on which
we have based our IR photometry. Our IR photometry is based on the
LCO system. For an A0V star one can show J_LCO = J_BB - 0.036, ie
J_LCO magnitudes are typically 0.036 magnitudes brighter than
BB (Bessell and Brett) magnitudes. Bessell and Brett have defined
their system so that V-J = 0 for a A0V star.
Thus the stars that are common to Hipparcos and 2MASS mighht have V-J =
0.07 because of extinction and the standard star system on
which the 2MASS system is based.
This means that the Beethoven magnitude becomes 0.037 magnitudes
fainter in J and the colours become bluer. I do not know how it would
affect the magnitude of the other SNe because I do not know on which
photometric system the J band measurements are based.
I leave it to you to decide if you want to adjust the Beethoven
magnitude. If you correct it then the uncertainty quoted at the end of
section 4.1 becomes smaller - of the order of 0.02 magnitudes. However,
a systematic uncertainty of 0.05 magnitudes certainly applies to the IR
photometry of 99ff and 99Q and this should be stressed.
I've read the paper and I have some minor comments which I will send you
in a later e-mail.
Cheers, Chris.
attached mail follows:
Hi Serena,
I did a quick test on the compatibility of the fundamental ZPs of
visual and near-IR standard star systems by examining the median V-J
colour of A0V stars that are in the Hipparcos catalogue. I did
this by cross correlating Hipparcos stars with the 2MASS catalogue. I
first pruned the Hipparcos catalogue of obviously reddened stars by
choosing stars with B-V < 0.05.
The resulting median colours of stars in the matched catalogue (557
stars) are
B-V = 0.015
V-J = 0.070
J-K = 0.002
I find this interesting. I must say, that I am not too surprised
by the discrepancy. I might refine these numbers over the next few days
as I restrict the matching by other criteria.
Cheers, Chris.
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