*Sky & Telescope Illustration by Casey Reed
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International Year of Astronomy | American Association of Variable Star Observers (AAVSO)
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International Year of Astronomy | American Association of Variable Star Observers (AAVSO)
Brian,Your new spreadsheet is very impressive and it certainly reduces the amount of data manipulation required by the user. However, I am concerned that in achieving a higher degree of efficiency, your method moves away from demonstrating basic concepts that are beneficial in a “tutorial”. Maybe an application of Ockham’s Razor is appropriate here. In his words, “Pluralitas non est ponenda sine neccesitate'', or to paraphrase, “if two different procedures produce the same result, the simplest is best.” Of course the question becomes how should we define simplest? Should it be “simplest in execution” or “simplest to understand”? Again, I would propose that for a tutorial, “simplest to understand” is how we should proceed, in which case, I believe the original spreadsheet is the way to go.If you do decide to use the new spreadsheet, I would suggest following changes:- Delete the “Spectral Type” column. The information is not used.- Also, delete the “Cat Mag” column. It is the same as “Cat V”.- Use a standardized nomenclature for the various magnitudes. For example:- I. Mag to I Mag- Cat B to B Cat- Cat V to V Cat- Color Index to (B-V)- I.-Cat to D Cat- Magnitude to V Mag (in the last table)- Add and define the equation form y=mx+b.- Add definitions for Cat B, Cat V, se slope, r squared, se b, se y and V Mag.I hope you find this useful,Tom
I extended Brians new spreadsheet a bit, also using Tom's ideas,. If I understand this correctly, Brians new spread sheet allows the user to enter only one instrument magnitude per exposure , that of Eps Aur. It doesn't cover the popular approach to use a TC that is measured once (or at least only once per night) and then take measurements of eps Aur plus one or two comparison stars per exposure. The table of comparison stars lacks So I made the attached version of the sheet, maybe someone can check it out. Main additions: * Iadded the two most popular comp stars, eta Aur and zeta Aur (ok, zeta Aur has to be used with some care for obvious reasons). * You can enter more than one instr mag for comparison stars * You have three methods to choose from to calculate TC and zero points. (a fourth method is not yet implemented) * There's a graph that visualizes the final Vmag estimates for all your measurements (to help spot outliers) * Inclusion of mean value and SD over several measurements, as a quality measure * The sheet includes more instructions what to do next with it (Step 1, Step2 , Step 3, Step 4) Some notes * I'm not sure that the catalog values (mag and B-V) for eta Aur and zeta Aur are the best available, maybe Brian can supply the corresponding values from the same source that was used for the other stars * The cells that are highlighted in grey should IMHOeventually be hidden, but I left them visible for now to allow better understanding of the sheet * The sheet was done with a German version of StarOffice, I hope there is no compatibility issue with English/US Excel. EDIT: I've uploaded my Excel sheet also to the Excel reduction wiki page, I guess that's theplace it should have gone in the first place.... CS HBE
Tom and Heinz, I agree that the sheet I made does lack some features, but I think will serve well as a low-level introduction (read: beginner) sheet. Just about 10 seconds before I received a notification email about Heinz's post, I finished writing the beginner how-to for my sheet. I have the impression that participation in the site is down, so I think it's important that we get something out there as soon as possible. I think it is more important that the beginner-level tutorials show people that they can do DSLRphotometry, rather than present them with a lot of technical aspects right away (that could scare them off). I think the intermediate ones should include more theory and corrections. Air mass must be corrected for in the intermediate level tutorial as for anything >34 degrees from the zenith, the differential air mass across the image really starts to add up quickly. I followed Tom's advice with changing things in the spreadsheet to match the traditional nomenclature. The tutorial also walks the user though calculating the average and stanard deviation for the calibrated mags. Heinz, I agree that eta and zeta should be included. I'll modify my sheet to use the traditional set of compairsion stars (eta, zeta, lambda) plus three from the set Tom included with the lowest uncertainties. I pulled the numbers from VizieR and am building a table of comparision stars, their source will be mentioned as well as breif instructions on the catalog I used in VizieR. I think a hybrid of our sheets is the correct answer. I don't know if the TC coefficient changes much in a DSLR camera over a single observing session (10-20 minutes?), but I suspect the zero-point offset changes dramatically. I'll read and reply again here in a little bit. Brian P.S. Forgot to attach the file. Slighly improved, but still lacking in some areas. It's a quick method to introduce DSLR photometry. Can the three of us get an intermediate version worked up in the next few days?
Hi Brian, I agree, the Beginner Sheet should be a nice thing to have fast. The only real issue I have with this new sheet is that you seem to have to specify an instrument maginitude for every single of the comp stars, and some beginners might have problems identifying all of them and ensuring they are all in a single frame when using longer focus length. At least I found no obvious way to leave out any of the values. I think this is because in your sheet, the matrix version of linear regression functions are used and they don't tolerate empty fields AFAIK. But you can also use der "vector" fucntions (SLOPE and INTERCEPT ) which DOtolerate empty cells in the data series. I've demonstrated this in the attached edited version (here I left out the instr. mag for rho Aur, a bit of an outlier anyway in your sample :-) ). CS HBE
Very good idea! I forgot about those two functions. I've updated the sheet to use those instead. Since our last exchange, I also created a calibration standards page. I'll add in a plot of the stars circled and labeled to assist beginners in identifying stars. Full tutorial announcement to be made soon. Brian
Hi Brian & Heinz, Wow! You guys were really busy over the weekend. My EXCEL skills are pretty rudimentary so I'm still trying to catch up with all your work. I, too, agree with your point, Brian, about getting things published ASAP. I'm looking forward to seeingthe finished product. Tom p.s. Oops! I'm signed in under my granddaughter's name. She is observing eps Aur visually for a science fair project and was putting in data over the weekend. I forgot to log her out - oh boy! 8-)