[Aavso-photometry] Transform coefficients andtwo-filtermeasurements

[Wolfgang Renz]

Hello

The passband shape issue can get even much worse if stars show
no flat continuum but more than very significant emission or absorb-
tion lines (e.g. with novae having very strong Halpha emissions, many
WR stars, or the TiO absorbtion bands of carbon or mira stars).

For some (theoretical) details on this issue see e.g. (including their
references and citations):

1994A&AS..104..121H - Reliable photometric reductions to the
standard UBV (or uvby) system and accurate UBV magnitudes of
bright standard stars from the northern part of the international Be
program - Harmanec, P.; Horn, J.; Juza, K.
http://adsabs.harvard.edu/abs/1994A%26AS..104..121H

2001A&A...369.1140H - Useful transformations between photometric
systems - Harmanec, P.; Bozic, H.
http://adsabs.harvard.edu/abs/2001A%26A...369.1140H

1989PASP..101..849B - The design and testing of filter-detector
systems using synthetic photometry - Beckert, Donald C.; Newberry,
Michael V.
http://adsabs.harvard.edu/abs/1989PASP..101..849B

1996A&AS..119..569R - A method to optimize intermediate-pass-
band photometric systems - Royer, P.; Manfroid, J.
http://adsabs.harvard.edu/abs/1996A%26AS..119..569R

1995IAUS..167..145Y - Choosing Filters to Make CCD Photometry
Transformable to Other Detectors - Young, Andrew T.
http://adsabs.harvard.edu/abs/1995IAUS..167..145Y

1994A&A...288..683Y - Improvements to photometry VI. Passbands
and transformations - Young, A. T.
http://adsabs.harvard.edu/abs/1994A%26A...288..683Y

1992A&A...257..366Y - Improvements in photometry. V. High-order
moments in transformation theory - Young, Andrew T.
http://adsabs.harvard.edu/abs/1992A%26A...257..366Y
(Read especially 7. Conclusions.)

They also gives an argument why the  pretty symetrical SDSS pass-
bands should be supperior to the JC  bands with their red tails for
transformation and color conversion. But such filter with steep profiles
also require to match them as good as possible.

So if one wants to do it as exact a possible (which is usually not
required for most photometric applications), one might even have
to introduce third and fourth order terms.

Clear skies
 Wolfgang

-- 
Wolfgang Renz, Karlsruhe, Germany