In Astronomical Data Group Meeting at Flatiron today, Rodrigo Luger (Flatiron) spoke about what he calls the “null space” for reconstruction of stellar surface features (or exoplanet surface features) from light curves. If you just have a rotating ball, glowing but with a surface pattern of emissivity, and you just get to see an integrated light curve, you can only reconstruct certain parts of any representation of its surface. For example, all the odd-ell modes (after ell of 1) contribute exactly zero signal! And there are other degeneracies, depending on orientation. These degeneracies are exact!
What Luger showed today is that some of these degeneracies are broken just by limb darkening! And others are broken if you have transiting planets. And if you are reconstructing a planet, others are broken by the terminator of any reflected light. All of these results and considerations will feed into an information theory of stellar and exoplanet light curves.
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