From: Chris Lidman (clidman@eso.org)
Date: Fri Feb 20 2004 - 09:34:53 PST
Hi Serena,
I computed the means and standard deviations for the colour-selected
A0 catalog. I.e. the one in which |B-V| < 0.05.
Catalogue mean(B-V)_J mean(V_J-J_2MASS) mean(V_J-J_2MASS)
=========================================================================
A0V |B-V| < 0.05 0.004 (0.025) 0.044 (0.056) -0.003 (0.029)
=========================================================================
The values in brackets are the standard deviations. If the distribution
is Gaussian then the error in the mean is stddev/sqrt(n) where n is
the number of samples. Since n=57, the error in the mean for the three
colours are 0.003, 0.007 and 0.004 magnitudes respectrively.
Hence a reasonable error in the mean (V-J-J_2MASS) colours of
unreddened A0 stars in the Hipparcos input catalogue is
0.007 magnitudes.
The other method produced a larger correction, but had a larger
uncertainty 0.012 magnitudes.
Hence one could argue that the two estimates are marinally
compatible within the statistical errors and hence there is no
need for a systematic uncertainty.
Cheers, Chris.
On Wed, 2004-02-18 at 07:16, Serena Nobili wrote:
> Dear Chris,
>
> I had a look at your document about Optical-IR colors. I think that
> perhaps the numbers in Table 2 could have an uncertainty, that you could
> estimate from the dispersion in the same sample you have used for
> estimating those numbers. If I assume (but it would be good if you could
> compute it) an uncertainty of 0.01 on the offset between the 2MASS J-band system
> and the Johnson V-band system, i.e. 0.043 +- 0.01, then the 2 estimates in
> Section 2 and 3 of your document, would agree within the statistical
> uncertainty. Thus, we can assume no systematic uncertainty on the
> correction, i.e. J(BB)=J(LCO) + 0.036 (+- 0.012) without systematic
> uncertainty. What do you think?
> Cheers
>
> Serena
>
>
>
>
> On 14 Feb 2004, Chris Lidman wrote:
>
> >
> >Dear Colleagues,
> > I've written a short research note on Optical-IR colours which you
> >might find interesting. It is available at:
> >
> >http://www.sc.eso.org/~clidman/
> >
> > Usual username and password apply.
> >
> >Cheers, Chris
> >
> >
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