Informing the Cataclysmic Variable Sequence from Gaia Data: The Orbital-period-Color-Absolute-magnitude Relationship


The orbital-period (P $_orb$) gap in the population of cataclysmic variables (CVs) informs the theoretical narrative of CV evolution, yet a complete understanding of the driving angular momentum loss mechanisms above and below this gap remains elusive. Here we identify, for standard CVs, a new, apparently monotonic relationship between quiescent color (G $_BP$-G $_RP$), absolute magnitude (M $_ G $), and P $_orb$ (between 70 minutes and 8 hr) revealed in Gaia DR2 and EDR3. We show that P $_orb$ increases in the color-absolute-magnitude diagram roughly orthogonally to the white dwarf and main sequences. We find the orbital-period-color-absolute-magnitude relationship to be stable across different CV subtypes: dwarf novae, intermediate polars, polars, and novalike systems. We place our findings in context with the known semiempirical donor sequence for CVs and find a dependence between color and M $_ G $ for a given P $_orb$ specifically for dwarf novae and intermediate polars above the period gap. These relations have the potential to inform a more complete picture of CV evolution.

Astrophysical Journal