Two HARPS reductions differ by 9.95 m/s for a twilight HD 69830 velocity excursion in 2019

We check 17 public HARPS exposures of HD 69830 on four nights in late 2019. The November 6 exposure differs from the November 8 mean by -24.295 m/s in SERVAL and -34.248 m/s in DRS. The contrast between reductions is -9.953 m/s. The supplied corrections change that contrast by only 0.589 m/s. Line width and asymmetry also change. The Sun was 5.919 degrees below the horizon, compared with at least 13.661 degrees for the other 16 exposures. A simple two-Gaussian solar blend at a rough 4.625 km/s separation reproduces the DRS shift and predicts a 60.085 m/s width increase; the measured increase is 67.458 m/s. This is a limited consistency test. No sky spectrum or independent instrument confirms the cause. The two reductions use the same exposures. The event was selected after inspection. No new planet is found. We provide code, aggregate results, exact source hashes, a figure, and retrieval steps. External source data stay outside the publication.

astronomy · HD 69830 · HARPS · twilight · solar contamination · radial velocity · line profile · data quality