Affiliation
American Association of Variable Star Observers (AAVSO)
Sat, 06/21/2014 - 20:18
I am requesting trials of my new AAVSO Extended format Plotting workbooks
by CBA and AAVSO observers. The web site is:
http://lewcook.com/LewAAVSOFmtPlt.htm
You may download it there. The purchase price of this software is ZERO,
NADA, NIL, FREE, GRATIS and NOTHING.
Please take a look and let me know of any difficulties you have if you use
the workbook(s). They are available in Excel 97 and 2010 formats.
Lew
Publications: lewcook.com/publist.htm
I removed the comment because it was no longer needed.
Lew, in your plots on the web page, I noticed that there were variations in the magnitude of the comp star plot. Isn't that going to be a constant plot, or do you want the raw instrumental magnitudes (-2.5*LOG(gain*netcounts/EXPTIME) entered in your program rather than the instrumental magnitudes that you get from Maxim and a number of other programs (rawt - rawc + C and rawk - rawc + C)?
If you are using the "Maxim" style instrumental magnitudes and are "reverse calculating" the comp instrumental magnitude from the check star magnitude, then won't inherent valiability in the check star or comp star (i.e. you accidentally picked a variable star as one or both of these) be reflected equally in the magnitude of the comp and check stars making it seem that the variability is atmospheric when actually due to variability inherent to the stars? I know that isn't very likely if you are using AAVSO sequence stars as the comp and check, but stranger things have happened and you might not be using AAVSO sequence stars if there are none in your FOV, which can happen with a long focal length telescope and a small CCD chip (e.g. a 4500 mm FL telescope and a 512 x 512 x 13 micon active area E2V chip).
Brad Walter, WBY
Thanks for the question. The (raw) instrumental magnitudes for C and K stars come from the output of the photometry program's AAVSO Extended Format report, and I think all are calculated using some version of the equation (-2.5*LOG(gain*netcounts/EXPTIME) you cited. I see LesvePhotometry gives some number much larger than the numbers I have get from VPhot (VPhot is smaller by many magnitudes -10 compared to +17 ). I calculate the Variable inst magnitude by subtracting the known value of the Comp star from the reported Variable mag and adding back the MEASURED Comp mag. If the comp star is variable, then, yes, that variation will show up in the Variable measurement.
What I have done with the input data input in the spreadsheet is this:
For the LIGHT CURVE, I Plot the data in the column C (var mag) against JD (column B).
For the Instrumental Magnitudes, I plot the data in cols. I and K (Comp and checK mags) and the calculated variable measurement. To get the Variable instrumental (raw) magnitude, I reverse the way it was calculated in the first place: I add back the Comp star measured value (the data in Col. I) to the mag reported for the variable (col C) and subtract the (standard, known) C star magnitude.
To get the K-C value, I simply subtract the measurement reported in the C star column (I) from that reported in the K star column (K).
For Ensemble Photometry, there is NO Comp value reported (and no trustworthy way to determine what it may have been). I do not calculate the Comp value from the checK reported value.
IF one or the other of the stars used in the measurement as standards turns out to be variable, there is no way of determining WHICH ONE it is, other than to use the data for the instrumental mags, reduce those measurements to outside the atmosphere and examine that data (not included in this Workbook).
Did that answer your question?