Re: Aperture size to optimise SNR

Posted by karenacollins on May 08, 2023; 7:54am
URL: http://astroimagej.170.s1.nabble.com/Aperture-size-to-optimise-SNR-tp2228p2234.html

Also, RMS should be used to select the best aperture, but you need to define the model to measure RMS against first (i.e. the transit model for exoplanet observing). BIC is used to decide if a transit model is preferred over a flat lightcurve model, and to determine if additional detrend parameters are justified statistically. The BIC should drop by at least 14 (2 x 7 transit model parameters) to justify a transit detection, and should drop by an addition 2 to justify a new detrend parameter. Even if BIC supports adding more than one detrend parameter, I generally recommend only one detrend parameter for ground-based light curves, unless you have at least as much baseline coverage as you have in-transit coverage, and even then I'd strongly lean toward airmass detrending over other detrending. If there is a nearby star, often FWHM or tot_C_cnts detrending may work better or in addition to airmass. The bottom line is that you want detrending to "clean up" a trend (curve or tilt) and/or wiggles in the data, but not completely build a transit in data when there is no transit obvious in the undetrended data, or otherwise completely reshape a light curve.