Assessing Magnitude‐Dependent Selection in the Cataclysmic Variable Orbital‐Period Gap

Since cataclysmic variable (CV) catalogues are compiled via magnitude‐limited surveys, we investigate whether the bias due to brightness and distance‐dependence of detectability can explain the well‐known ∼2–3 h orbital period gap. We apply the selection criteria to 1214 CVs obtained from Gaia DR3 with orbital periods from the literature, reducing the final sample to 563 CVs with reliable astrometry and extinction‐corrected magnitudes at . Using the gap range of 2.45–3.18 h determined independently by SDSS I–IV, we examine two possible biases due to observations: weighting of the uncorrected histogram and comparing extinction‐corrected absolute magnitude, , inside and outside the gap. The reweighted histogram demonstrates an even larger deficit in comparison with the unweighted histogram and is detected in of bootstrap samples ( CIs). The 32 gap systems have a brighter median than outside‐gap systems ( vs. ), disproving the hypothesis of a faint gap population. While these results favour an astrophysical origin over magnitude‐ and distance‐dependent incompleteness as the main cause of the period deficit, they neither confirm it nor rule out other selection effects.