by Laisha Shaneysha Castillo
I wanted to share a progress update on the analysis for an exoplanet transit of WASP-194 b that was observed recently by Ryan McDaniel on May 26, 2026 at RFO. I contacted AAVSO to obtain a comparison star sequence for the host star, WASP-194, and they followed up and let me know the sequence was ready.
I used the comparison star sequence to calculate a light curve of the observations from that night using AAVSO’s VPhot software and have been improving the quality of the light curve since then with by trial and error adjustments to the photometry settings. After receiving the star chart with comparison sequence, I started by reviewing the image quality metrics and noticed that the SNR dropped off significantly toward the end of the observations. I identified and removed two low-SNR images that were likely adding noise to the final result.
This is the initial Magnitude vs Time photometry plot for Wasp 194 making use of all comparison stars. This gave me the photometry for each of the comparison stars so I could check for stability and trends of any comparison star that isn’t really non-variable and that may be affecting the photometry for Wasp 194.
I plotted the magnitudes of the comparison stars side by side:
Based on those plots, I selected Star 117 as the check star and narrowed the comparison star set to 113, 114, and 128. Reprocessing the data with those selections immediately improved the light curve and reduced a noticeable amount of scatter.
Here’s the updated plot with the selected check/comparison stars. I immediatly saw a flatter baseline and less noise in the data:
From there, I spent some time investigating a nearby companion star of Wasp 194 that may be contaminating the target measurements.To reduce the contamination, I looked into changing the aperture. I extracted the FWHM values into Python and calculated the mean, median, and mode to get a better idea of what aperture sizes might be appropriate. I tested several approaches, including different fixed FWHM values and different aperture scaling factors. While some settings produced small changes, the standard variable aperture using 1.5 FWHM still appears to give the most reliable result for now.
Knowing the mean FWHM, I adjusted the initial FWHM value in the analysis setting for smoother processing, but it suprisingly improved the reduction slightly:
Overall, each round of adjustments improved the light curve. The latest version has a much cleaner baseline, noticeably less noise, and a more clearly visible transit signal compared to the initial reduction. There may still be some residual effects from changing observing conditions and possible contamination from the nearby star, but the data quality is significantly better than where we started.
Next, I’ll continue looking into ways to objectively optimize the aperture size and further reduce any contamination effects from the nearby companion star. I’ll also start generating a light curve with the best reduction in AstroimageJ.
Here’s a link to my analysis notes (Wasp 194 Analysis Notes) where I go into way more detail in my thought process. There are a couple more things I want to verify, such as if the location of what I believe is the transit in that curve matches the expected Tc from TESS. Still a work in progress.