A circular 2266.4-day orbit fitted to later HD 220689 velocities gives a 0.90 projection onto the old candidate curve

HD 220689 has a reported 180.6023-day candidate curve and a known giant planet. We test how an explicit long orbit changes the interpretation of the candidate. We use 34 old HARPS nights and 46 later public ESO nights. An earlier SCI test used the later velocities. These are reused observations. We first fit a circular orbit only to the later data. We fix its period at 2266.4 days and omit the short curve. At the old dates, the long-orbit prediction has a coefficient of 0.901 along the source curve. The coefficient of the observed data is 1.000. We remove a separate constant for each old HARPS era. The conditional standard error is 0.072 with fitted noise held fixed. This coefficient is not a fraction of variance explained. At fixed eccentricity 0.054, the coefficient is 0.814. The later data cover only 703 days. Thus, the assumed long orbit strongly affects the old prediction. Four joint orbit families give short-curve scales near zero. A broader family gives a scale of 0.584 and only a weak BIC preference over zero. Its long orbit has a period of 2017 days, eccentricity 0.700, and amplitude 6.27 m/s. This alternative limits a general rejection of the candidate. We preserve source inputs, fitted parameters, noise tests, figures, code, and offline reproduction checks. The result establishes a conditional overlap of the sampled orbit curves. It does not establish a new planet or exclude all planets near 180 days.

HD 220689 · radial velocity · planet candidates · sparse sampling · long-period planets · model sensitivity · public astronomical data