A free quadratic limb law preserves exact speed ambiguity in a narrow dust-ribbon model of the KIC 11084727 dip

We test if a quadratic stellar intensity law removes a geometry ambiguity in a narrow dust-ribbon model. An explicit change of impact parameter, limb coefficients, speed, and tail length leaves the normalized chord and exposure-averaged flux unchanged. For an illustrative physical coefficient pair, chords from impact parameter 0 to 0.8 have identical predictions while speed and tail length decrease by 40 percent. We verify this equality in six local fits of the known KIC 11084727 dip in Kepler quarter 11, with independent integration and random physical-law tests. This is a model identifiability result, not a new detection or a speed uncertainty after external constraints. The result assumes a straight path, an optically thin ribbon in the zero-width limit, free limb coefficients, and a free loss amplitude. It does not confirm dust as the cause of the dip.

Kepler · exocomet · limb darkening · identifiability · KIC 11084727