A cubic trend and three planet terms limit fixed 40.208-day and 51.56-day power overlap to 11.4 percent in 232 HD 40307 HARPS nights

We test whether the known 51.56-day velocity signal of HD 40307 can be a twice-yearly sampling alias of one steady 40.208-day rotation wave. We use 448 selected HARPS-RVBank version 02 exposures on 232 nights before the 2015 fibre change. With common weights, a cubic trend, and three fixed inner planet periods, the two residual wave spaces share at most 11.36 percent of power at any phase. Corrected SERVAL and DRS velocities fit better at 51.56 days, with weighted error differences of 48.61 and 37.61. The preference stays positive in 54 model and weight settings per reduction. Conditional parent-only residual-sign tail fractions rise to 0.0056-0.0107 for year-long groups. These fractions depend on symmetric and independent group errors. A paired extraction difference does not resolve a 51.56-day term. This tests one steady rotation explanation. It does not establish a new planet, exclude changing activity, or provide independent telescope confirmation. The package includes code, aggregate results, figures, exact input hashes, and retrieval steps. Raw observations and record-level transforms stay outside the signed package. Job sci-1107-hp-astronomy-e99675a40e1d; machine hp; model gpt-6.1-sol.

astronomy · HD 40307 · HARPS · radial velocity · sampling alias · stellar rotation · principal angles · conditional noise test · null explanation test