Teams / DSLR Documentation and Reduction / New spreadsheet with automatic calculation of Tc and k'

New spreadsheet with automatic calculation of Tc and k'

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I haven't noticed the Teams before and have now joined the DSLR team. I have uploaded my spreadsheet for reduction under "Final Reduction". This is the sheet I have used all along the campaign and it has worked very well. It has an automatic calculation of Tc, k' and Zp using the least-square method between the compairsion stars. After the coefficients is calculated they are applied to the variable star (epsilon in this case). There is also an error calculation done between the compairsion stars so you could see how well your instrumental magnitudes fit. By this you can estimate how good your images is and be confident on how good your end result is. For example I usually got an avereage error of less than +/-0.02 magnitudes with a maximum of +/-0.05 betwen the compairson stars if the sky is good and epsilon has haigh altitude. During the brightest period during may/june it dropped to average +/-0.05 and maximum of +/-0.10. I judge then that the result for epsilon is in the same region.As a calcultate the Tc every time I hade seen how it has changed by altitude. This is what should be expected as all stars go redder as they are near the horizon (think of the sun goes red at sunset). I have got a good correlation between Tc and air mass. At airass 1 (zenith) it was -0.12, at airmass 2 (30ยบ altitude) it dropped to -0.10 and with the huge airmasses up to 7 that was during june the Tc dropped to -0.02.The k' can also vary a great deal. This is mostly due to how clear the sky is. A hazy or moisty sky generally gives a higher k'.If there is any questions of the functions in my spreadsheet just ask!

Improved reduction sheet.

Hi there! Here is a new version of my Excel sheet for data reduction. It is built on Photometry4.xls but has now automatic calculation of altitude and airmass from the stars RA/Dec, observation time and the observes location. This is the same calculations that I included in Reduction-Intermediate_2.xls. You still have to remove the rows for the compairsion stars you do not plan to use. But this is an one-time effort. If you remove these stars and fill in your observatory location you can then save the document as a new personal template. Then you only need to fill in date, time and instrumental magnitude for each observation session. In the attached file I have enteredexample data that also has to be removedbefore you saveyour personal template.

Photometry5.xls 98 KB
Tested the tutorial package

I downloaded Tom Pearson's DSLR example images to see what I got. I stacked the darks to a master dark, stacked the flats and subtracted the masterdark, stacked the images subtracted masterdark and divided the flat. The pictures was taken 2010-01-26 01:15UT, I presume from Virginia Beach. I found 18 of my 20 compairsion stars on the image. The altitude varried by 76-86º, so there shouldn't be any air mass correction to talk about. I then meassured thefinal imagein 5 different ways. 1) By TeleAuto, Ellipsoidal gaussian method, 9 pixels half width model window (this is the default and my normal setting), pointing on the brightes pixel. 2) By TeleAuto, Ellipsoidal gaussian method, 9 pixels half width model window, pointingat the center of the star. 3) By TeleAuto, Ellipsoidal gaussian method,11 pixels half width model window, pointin at the center of the star. 4) By Iris, Aperture photometry, using rings of 9-16-24 pixels, pointing at the center of the star. 5) By Iris, Aperture photometry, using rings of 6-12-20 pixels, pointing at the center of the star. I find pointing a bit difficult. The stars in the tutorial was a bit more defocused than I ussualy does. In the tutorial they had a FWHM (Full Width, Half Maximum) of about 4.5, I try to seek for a FWHM of 2.5. A greater FWHM spread the light on more pixels, but the stars also tend to be dounaugt shaped instead of bullets and a bigger target to point att when you do the meassurment. Both in TeleAuto and Iris I got different values when I point to neighboring pixels at the center of a star. So it isn't easy to know what pixel or what value to use. At my own pictures I point at the brightest pixel and that pixel is usually in the center of the star. The 5 meassurments gave the follwing result. 4 of them seems ok, only test 4 gave a lot of scatter between the compairsion stars and a different Tc (but an ok value for epsilon) 1) epsilon: 3.685, Tc: -0.110, s.d between comp. stars: 0.025 2) epsilon: 3.690, Tc: -0.110, s.d between comp. stars: 0.024 3) epsilon: 3.696, Tc: -0.108, s.d between comp. stars: 0.021 4) epsilon: 3.718, Tc: -0.089, s.d between comp. stars: 0.058 5) epsilon: 3.720, Tc: -0.110, s.d between comp. stars: 0.032 The k' got funny values from +0.2 to -1.8, but this is what to expect with practically no air mass effect. My own meassurment from 2010-01-25was3.702.

Quite Good

This is somthing we've been needing to do for quite some time:show that the different reduction packages give similar results. It's good to see that all of the measurements of the same data yield magnitudes that overlap within their standard deviations. Good work!

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