Intermediate Reduction Spreadsheet Modification

Affiliation
American Association of Variable Star Observers (AAVSO)
Thu, 07/30/2015 - 22:12

Hi,

I've been using this spreadsheet and wanted to know if someone could help me modify it, if it is easy enough to do. I took pictures of SZ Aql last night but only got the target, check and three comps instead of 6. Didn't think it would be a problem, thought I could just enter the three comps into the spreadsheet and get my result. Turns out you can't, it has an Excel array which I haven't figured out how to modify, yet.

Anyway, thanks!

Oh, are there more stars on chart 15143BBY whose magnitude we know?

Gary

Affiliation
American Association of Variable Star Observers (AAVSO)
You can!

Hi Gary,
you can slightly modify the spreadsheet in this way.
In the spreadsheet, data for the six comparison stars are in rows between 19-24, one for each row.
Suppose, for example, that you have only 3 comparison stars instead of 6.
You have to insert the data for the your comparison stars in rows 19-21. You can delete the content of the row 22-24.
Then, select with the mouse the cells from B42 to D43. In the line input you will see the following matrix formula:
=REGR.LIN(I19:I24;F19:G24;1;1)
You have to modify this formula replacing the number 24 to 21.
=REGR.LIN(I19:I21;F19:G21;1;1)
After you've changed the formula, hold simultaneously the keys <Shift> + <Ctrl> and then press <Enter>. Be carefully because pressing only <Enter> without <Shift> + <Ctrl>, you get an error message.
Repeat the same procedure for the cells from G42 to H43.
Selecting those cells, in the line input you see the following matrix formula:
=REGR.LIN(I19:I24;F19:F24;1;1)
Like before, you have to modify this formula replacing the number 24 to 21.
=REGR.LIN(I19:I21;F19:F21;1;1)
Confirm the formula with the  <Shift> <Ctrl> + <Enter>.
Finally, delete the cells from C56 to D57 in "Data Quality Check".
That's all.

Regards,

Luigi

 

You can but you shouldn't

Hi Gary and Luigi,

you "could" use just three comp stars with the Intermediate Reduction spreadsheet, but I strongly recommend against doing so. Essentially the spreadsheet is fitting a plane to the measured comp star magnitudes. With just three comps you'll get a perfect fit even if one of the comps is not suitable (incorrect catalog magnitude or B-V, contamination from nearby star, etc).

At the very least you should use 4 comps in the ensemble, 5 or more would be better. Cheers,

Mark

Affiliation
American Association of Variable Star Observers (AAVSO)
Intermediate spreadsheet

Hi all,

I fully agree with Mark, the use of that spreadsheet is not that simple: as I recently explained it to Luigi there are many issues in that technique. It would properly work ONLY with a large number of comp stars AND if they have a neutral color distribution in the sky. 

There are other issues if used high in the sky, here the various errors, like catalog errors, dominate the extinction differences and the result could be very wrong correction coefficients.

That "intermediate spread sheet" is a true problem, I would prefer it to be withdrawn from CS and replaced with something more classical: separate determination of the color correction coefficient and separate extinction coefficient determination when observations are done at low enough elevation.

Clear Skies !

Roger

Affiliation
American Association of Variable Star Observers (AAVSO)
Hi Mark and Roger

Hi Mark and Roger,
you are right, I only wanted to explain how modify the spreadsheet for use it with a different number of comparison stars instead of 6 fixed in the spreadsheet.

Regards,

Luigi