from aperture photometry is highly correlated with $x$ and $y$ sub-pixel positions. We correct for this by fitting a cubic function. Top panels show the correlation between the raw flux and pixel position. Bottom panels shows the corrected flux plotted against pixel position. Spearman’s $\rho$ coefficient is a measure of the significance of correlation between two values – in all cases Spearman’s $\rho$ coefficient decreases after pixel phase correction. []{data-label="fig:2M0045_pixelphase"}](correlationch2-eps-converted-to.pdf "fig:")

Photometry was obtained from the Basic Calibrated Data (BCD) images produced by the Spitzer Science Center using pipeline version S19.2. The routine was used to find the centroids of the target and reference stars of similar brightness in the field of view. Aperture photometry was performed on the target and reference stars using apertures with radii of $2.0-4.0$ pixels, in steps of $0.2$. We choose the final aperture size that produces the lowest rms target light curve. Outliers were identified and rejected from the raw light curves using a $6\sigma$ clip.

*Spitzer*/IRAC photometry is known to exhibit a systematic effect due to intra-pixel sensitivity variations, known as the pixel phase effect. The top panels Figure \[fig:2M0045\_pixelphase\] show that the raw photometery is highly correlated with the $x$ and $y$ 