Starting point / motivation
The long-term evolution of a planetary atmosphere is predominantly controlled by escape, a process leading atmospheric gas to leave the planet's gravitational well and disperse into space. The ultraviolet (UV) transit observations of extra-solar planets conducted so far led to the detection of a large variety of phenomena, but, at present, the theories explaining them exceed the number of relevant transit observations.
There is a whole wealth of phenomena, also variable in time, that requires a large observational effort to understand, effort that cannot be undertaken by the Hubble Space Telescope, which is our almost only UV "eye" and has now a very limited life-time. Owing to the large size of the transiting atmospheres and to the short orbital periods of close-in planets, the physics of atmospheric mass-loss can be studied with a dedicated small instrument operating at near-UV wavelengths (250 – 320 nm).
Contents and goals
In 2016, we proposed to NASA to build, launch, and operate the Colorado Ultraviolet Transit Experiment (CUTE), which is a 6U CubeSat specifically designed to provide exactly the kind of spectroscopic observations that are urgently needed to further understand atmospheric escape.
CUTE has been graded as the best UV/visible CubeSat submitted to NASA in 2016 with final funding decision expected to come in January - February 2017.
We propose here to develop CUTE's data simulator, generate an exposure time and signal-to-noise calculator, perform tests to foresee the effects of possible deviations from the nominal instrument alignment, and produce a stable and flexible data reduction pipeline.
We will simulate CUTE's optical system and perform ray tracing from the light source onto the CCD detector using point-like light sources with different spectral distributions and fluxes to simulate data obtained by observing different stellar types and magnitudes.
We will first concentrate on the nominal case and produce a wide range of simulated CUTE stellar spectra that will be used to start planning/preparing the data reduction pipeline and to develop an exposure time and signal-to-noise ratio calculator. We will use the data simulator also to construct synthetic CUTE transit datasets that will be used to train the science team in the data analysis.
Despite all efforts taken to avoid this, small deviations of the optical system from the initial conditions may occur during/after launch. We will therefore use the data simulator to identify the effects that these deviations will have on the data. We will finally develop the on-board data reduction pipeline that will carry out dark and bias subtraction, cosmic-ray correction, removal of the flat-field, and spectral extraction.
The final reduction steps (wavelength and flux calibrations) will be carried out on the ground. Thanks to the development of the data simulator, we will be able to produce a flexible pipeline capable of dealing with a number of possible in-flight complications.
The project is timed in such a way that its end will be a few months after launch in order to perform fine tuning of the pipeline during commissioning and to provide initial data reduction support to the science team.
Austrian Academy of Sciences
Austrian Academy of Sciences
Dr. luca Fossati