Hello all,
this month I am performing transformation coefficinets computing for my optical system+filters+camera, using M67 field.
Thanks to several articles, specially the one by Gordon Sarty, I learned on how to compute coefficients from instrumental magnitudes and standard values provided by Henden. I think I have all clear about the procedure.
But now, even Sarty's paper makes an introduction about trasformations, I cannot get a complete comprehension of transformation principles: why there are a certain number of band coefficients, and one another of color coefficients? Is transformation taking into account the difference in response between real filter and the Kron-Bessell-Cousins specification altogether with optical system transmision and ccd's quantum efficiency? and more questions.....
Is there a theoretical source about transformations available?
Thanks.
Miguel
I am answering myself :-D
The article on CCD transformation equations by Bruce Gary seems to look into essential principles on transformations.
http://reductionism.net.seanic.net/CCD_TE/cte.html
Bruce is a retired radio scientist from JPL and has done a spledid job on explainning the details of transformation equations pertainning to photometry, especially with the photometric functions from software like MaximDL . I'm working on adapting his techniques for zero-point and star color sensitivity from M67 and NGC 1342 and the fields of the variables I observe. He has a nice high air mass cluster (NGC 1342) with photometry information to calibrate against; see http://brucegary.net/NGC1342/
James
p.s. Note: Per B.G...."that my secondary calibrations do not have the benefit of peer review, and they are therefore uncorroborated by any other observer. "
Hi James, thanks for the NGC1342 reference.
They are very appreciated Bruce Gary's contributions.
Best regards
I didn't see anyone mention what I consider the "standard" text for photometry, Astronomical Photometry, A text and Handbook for the Advanced Amateur and Professional Astronomer, by Henden and Katichuck. Even though the book was written in the pre CCD era when photometry was done with photoelectric photometers and about 1/3 of the book deals specifically with that technology, It has very complete and clear explanations of photometry that are equally applicable to CCD observations. If I only owned one book on photometry, there is no question this would be the book, at least until Arne completes the new one it is rumored he is working on. Since the book is pre CCD, it does not cover image calibration. It also doesn't cover variations over a properly calibrated image that affect photometric precision and accuracy. Usually those variables aren't significant until you get down to millimag level photometry as long as you don't try to measure stars very close to the edge of the chip.
Chapter 1 sections 1.6 through 1.10 - describe the basic principles and 1.9 introduces the concept of transforming to standard systems.
Chapter 2 on photometric systems gives theoretical background of photometric systems and relates them to the M-K classification system and the HR diagram.
Chapter 4 on data reduction deals with the nitty-gritty of calculating instrumental magnitudes, correcting for extinction and transforming to a standard system.
Chapter 9 deals with Practical observing techniques
Several appendices are very relevant
G Extinction calculation example
H Transformation coefficients Example
J Light radiation from stars dealing with the very precise mathematical definitions of intensity, flux and luminosity plus theoretical background for atmospheric extinction and further theoretical explanation of transformation based on equivalent wavelength of observation.
There is also a chapter and an appendix on statistical concepts you need to understand for error quantification.
Brad Walter, WBY
Thanks for your comment, I'd like to get Henden and Kaitchuck book but it won't be easy.
Regards
Miguel
Actually it shouldn't be very hard. It is available on line directly from the publishers, Willmann-Bell, or you can order it through Amazon. Better yet, order it though the AAVSO link to Amazon so AAVSO gets a sales commission at no additional cost to you.
Brad Walter, WBY.