Degeneracies

Models of microlensing events often have a large number of inter-related parameters, and finding the correct solution to understand a given event can be challenging. The parameter space is complex and suffers a number of degeneracies. Here we explore the circumstances where these arise.

This page is a work in progress and more detailed descriptions are being developed.

Degeneracies affecting all events

• Impact parameter sign degeneracy
• Positive/negative \(u_{0}\) with the same \(\pi_{E}\) Dominik et al.(2018)
• Blended light
• Rho degeneracy Chung et al. (2017), Han et al.(2020)
• Extreme finite source Johnson et al.(2021)
• PSPL with different \(t_{E}\) Mróz et al.(2017)
• Finite/point source degeneracy Poleski et al.(2017), Han et al.(2019)

Binary lens degeneracies

• Wide-close degeneracy
• Wide degeneracy Bennett et al.(2012), Sumi et al.(2016)
• Jerk parallax Gould (2004), Park et al.(2004)
• Parallax vs. orbital motion Gaudi et al.(2008), Batista et al.(2011), Skowron et al.(2011)
• Binary with orbial motion vs. triple lens Bennett et al.(1999), Jung et al.(2013), Han et al.(2016)
• Binary caustic and source size Hwang et al.(2018)
• Parallax vs. xallerap
• Inside/outside degeneracy for minor image perturbation Han et al.(2018)
• Binary lens vs. binary source Calchi Novati et al.(2018), Suzuki et al.(2018), Dominik et al.(2019)
• Families of binary lens models for double-peaked high-mag events Dominik et al.(2018)
• \(t_{*}\) for binary lenses Bennett et al.(2014)
• Caustic-chiral degeneracy Skowron et al.(2018), Han et al.(2018)
• Ubiquitous unifying degeneracy for two-body systems Zhang, Gaudi & Bloom (2022)

Planetary binary degeneracies

• Inner/outer degeneracy Gaudi & Gould (1997), Calchi Novati et al (2018)
• Planet vs. equal-mass binary Choi et al.(2012)
• Binary source vs. planetary lens Gaudi (1998), Jung et al.(2017)
• s vs. 1/s for planetary caustics Bhattacharya et al.(2016), Poleski et al.(2018), Song, Mao & An (2014), Lee (2017)

Triple lens degeneracies

• Binary with orbial motion vs. triple lens Bennett et al.(1999), Jung et al.(2013), Han et al.(2016)
• Planet in binary vs. multi-planet systems Han et al.(2019)

Space-based observations

• Satellite parallax Refsdal (1966), Gould (1994)
• Circular degeneracy in parallax Gould (2019)