[vsnet-chat 657] Re: the AAVSO V Magnitude Experiment

["STAN WALKER" <astroman@voyager.co.nz>]

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> From: Fraser Farrell <fraserf@dove.net.au>
> To: jmattei@aavso.org
> Cc: vsnet-chat@kusastro.kyoto-u.ac.jp

Greetings, Fraser,

I was also interested in the V magnitude experiment which seems to have
arisen from Berto Monard's comments some months ago. But I was puzzled both
by the colour range in the stars chosen and the low altitude of the
selected field - even from the Northern Hemisphere. Since they're doing a
critical evaluation of the eye as compared to the Johnson V filter one
should remove extraneous problems like extinction and possible colour
terms.

The eye also receives a reasonable signal in both the B and R filters. Thus
it has a large second order extinction term. At the rather low altitude of
this field in September the eye response would probably peak well redward
of the Johnson V peak - introducing a spurious effect of at least 10-15%.
The
range in star colours would also make the results confusing - without your
three variable stars!

A better comparison would be achieved by using yellow or orange stars more
or less at the observer's zenith - and certainly much brighter ones!
Bearing in mind the 15% or so inherent inaccuracy of visual estimates would
it be possible to make the hundreds of measures necessary to detect
anything without a field becoming so well known that the results suffered
from preconceptions? I'm intrigued by the concept but maybe the experiment
needs to be more rigorous.

Regards,
Stan Walker

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