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Reporting data for time series photometry

DJOD · 33

Hors ligne DJOD

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le: mai 06, 2019, 05:28:20 05
Hi all

Is there any way to report SNR for the variable and comp stars when doing time series analysis?

Also, when I graph the lightcurve using GNUplot, there are error bars included, but it is unclear to me how the error bars are calculated.  Can you advise how they are derived?

Many thanks
David

Clear skies
David
Brisbane, Australia


Hors ligne lock042

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Réponse #1 le: mai 06, 2019, 07:39:43 07
I'm not sure to understand your first question.
About the mag errors, if it can help you, here the code to compute the errors:

static double getMagErr(double intensity, double area, int nsky, double skysig) {
double skyvar, sigsq;
double err1, err2, err3;
double phpadu;

skyvar = skysig * skysig; /* variance of the sky brightness */
sigsq = skyvar / nsky; /* square of the standard error of the mean sky brightness */
phpadu = getCameraGain();
err1 = area * skyvar;
err2 = intensity / phpadu;
err3 = sigsq * area * area;

return fmin(9.999, 1.0857 * sqrt(err1 + err2 + err3) / intensity);



Hors ligne lock042

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Réponse #2 le: mai 06, 2019, 01:54:18 13
Also, you can export data shown in the graph.



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Réponse #3 le: mai 12, 2019, 04:23:40 04
Hi Lock

Sorry if I have been unclear.  To help, I have included some screen shots of VPHOT, which is used by AAVSO to do time-series photometry.

For each image, there is a SNR value - I think they calculate this based on the numbers in the sky aperture versus the measuring circle. And they calculate the error for each mag references as 2.5 * Math.Log10(1 + 1 / SNR).

I have been using the export function, which is very helpful, but it only exports the (truncated) JD and the mags for the the variable and the comp stars.  It would be really great if the export could include:
  • Julian Date (full, not truncated)
  • Mag, SNR, FWHM and Err for each star in the sequence

This type of data is really important when preparing submissions to AAVSO or preparing papers.

Let me know if this makes more sense or if there is anything else that would help.

Regards & Thanks
David

Clear skies
David
Brisbane, Australia


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Réponse #4 le: mai 13, 2019, 10:17:39 22
Hi, thanks for the information, we'll try to improve that.
I don't know more than what lock posted on the error computation.
Best regards



Hors ligne lock042

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Réponse #5 le: mai 22, 2019, 04:50:29 16
Julian date is no more truncated.