Determining the photometric capabilities of the CTIO 0.9-m telescope

Abstract

Exoplanet detections are becoming more and more frequent as our ability to detect transits and Doppler shifted stellar spectra improves. Here, we report on eight observing nights at the SMARTS 0.9m telescope in Chile at the Cerro Tololo Inter-American Observatory (CTIO), covering 13 nearby stars in the range of 11th to 14th visual magnitude. We used the defocus method to spread the point spread function (PSF) of the star across a larger portion of the CCD to achieve longer exposure times yielding a higher signal to noise ratio and a higher amount of data every night as less time was spent on CCD read-out and data storage over time. Spreading the PSF and increasing exposure time has drawbacks, as it inevitably increases the sky background in each image and makes it difficult to extricate the target star's PSF from a crowded background of neighboring stars. We explore the short term, high time-resolution ability of the 0.9m CTIO telescope to produce stable photometry of M-dwarfs. The results show that the 0.9m telescope can be used to produce stable photometry to near 2 to 3 milli-magnitudes if user error does not introduce artificial noise. We can use this telescope to compare the noise of stars to the predictions of starspot models. There is also value in searching for a correlation between photometric and radial velocity noise in stars that could mask or produce false positive exoplanet detections.