Detection of Dark Companions via The Combination of Eclipse Timing Variation, Hipparcos, and/or Gaia Astrometry: The Cases of V Puppis and CY Ari

Abstract The third body is expected to shape the formation and evolution of close binary systems. In this work, we develop a method to detect and characterize the tertiary companion around eclipsing binaries through the combined analysis of eclipse timing variation, Hipparcos, and/or Gaia astrometry. This method allows us to determine both the true mass and the inclination of the tertiary body that inferred from light-travel time effect. For the massive B-type binary V Pup, we do not confirm the previously reported 5.47 yr signal; instead, we identify a longer period of 14 yr. The orbital semimajor axis and mass of the outer body are revised to a C = 17.88 − 0.15 + 0.15 au and M C = 7.73 − 0.14 + 0.14 M ⊙ , confirming it as a promising stellar-mass black-hole candidate for further follow-up study. For the tertiary of the contact binary CY Ari, we obtain P C = 5.40 6 − 0.016 + 0.017 yr, e C = 0.52 6 − 0.027 + 0.032 , I C = 85.6 − 6.5 + 7.8 °, and a true mass of M C = 0.64 0 − 0.029 + 0.029 M ⊙ , supporting the white dwarf hypothesis proposed in previous study. The orbits of both systems are nearly edge-on ( I = 90°), implying that they may form in a coplanar environment. We highlight the advantages of our method for detecting dark companions in binary and triple systems.