Spitzer 24 μm Time Series Observations of the Eclipsing M Dwarf Binary GU Boötis

We present a set of Spitzer 24 μm MIPS time series observations of the M dwarf eclipsing binary star GU Boötis. Our data cover three secondary eclipses of the system: two consecutive events and an additional eclipse 6 weeks later. The study's main purpose is the long-wavelength (and thus limb-darkening-independent) characterization of GU Boo's light curve, allowing for independent verification of the results of previous optical studies. Our results confirm previously obtained system parameters. We further compare GU Boo's measured 24 μm flux density to the value predicted by spectral fitting and find no evidence for circumstellar dust. In addition to GU Boo, we characterize (and show examples of) light curves of other objects in the field of view. Analysis of these light curves serves to characterize the photometric stability and repeatability of Spitzer's MIPS 24 μm array over short (days) and long (weeks) timescales at flux densities between approximately 300 and 2000 μJy. We find that the light-curve rms about the median level falls into the 1%-4% range for flux densities higher than 1 mJy. Finally, we comment on the fluctuations of the 24 μm background on short and long timescales.