I Light fluctuations and finding exoplanets

[Paul Colby]

All light sources fluctuate and I've wondered if auto correlation of the natural fluctuation of a star's output might be used to range it's planets? The concept is to stare at a star (like Kepler does) and record high frequency intensity fluctuations say at a sample rate of 10 times per second. Fluctuations at this rate which are not due to intervening dust would have to arise from very small features on the photosphere of the star. An exoplanet in the correct phase would be illuminated by some of the same star light and would reflect light with the same time fluctuations. One then computes the time auto correlation function. In principle there would be a peak in correlation at a time delay equal to the path difference (8ish minutes for an Earth like planet) with a correlation magnitude proportional to the phase and albedo of the planet.

Okay, the off the cuff answer is "what are you on crack?" stars are really really big. Everything averages to zero in that frequency band so no, can't work.

 

[Drakkith]

I'd expect any such signal to be buried deep in the noise of the starlight, so you'd need a HUGE telescope to get a SNR high enough to see any correlation.

 

[Paul Colby]

I'd expect any such signal to be buried deep in the noise of the starlight, so you'd need a HUGE telescope to get a SNR high enough to see any correlation.

Yes, I expect this is the case for most stars like the sun for example. The photon counting noise is easy to estimate but the spectrum of fluctuations of a star much less so. Not all stars are the same. What Kepler light curves I've seen don't seem dominated by photon statistics but this is just a guess on my part.

 

[Drakkith]

Yes, I expect this is the case for most stars like the sun for example. The photon counting noise is easy to estimate but the spectrum of fluctuations of a star much less so. Not all stars are the same. What Kepler light curves I've seen don't seem dominated by photon statistics but this is just a guess on my part.

That's the thing about noise. You can estimate it all you want. But you cannot remove it. Hence the need for large telescopes to get that SNR high enough to see those small fluctuations!