Aarhus University Seal / Aarhus Universitets segl

Frank Grundahl

A New Type of Ambiguity in the Planet and Binary Interpretations of Central Perturbations of High-magnification Gravitational Microlensing Events

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaperJournal articleResearchpeer-review

  • The OGLE Collaboration
  • ,
  • The MOA Collaboration
  • ,
  • The RoboNet Collaboration
  • ,
  • The MiNDSTEp Consortium
  • ,
  • The μFUN Collaboration
  • ,
  • The PLANET Collaboration
High-magnification microlensing events provide an important channel to detect planets. Perturbations near the peak of a high-magnification event can be produced either by a planet or a binary companion. It is known that central perturbations induced by both types of companions can be generally distinguished due to the essentially different magnification pattern around caustics. In this paper, we present a case of central perturbations for which it is difficult to distinguish the planetary and binary interpretations. The peak of a lensing light curve affected by this perturbation appears to be blunt and flat. For a planetary case, this perturbation occurs when the source trajectory passes the negative perturbation region behind the back end of an arrowhead-shaped central caustic. For a binary case, a similar perturbation occurs for a source trajectory passing through the negative perturbation region between two cusps of an astroid-shaped caustic. We demonstrate the degeneracy for two high-magnification events of OGLE-2011-BLG-0526 and OGLE-2011-BLG-0950/MOA-2011-BLG-336. For OGLE-2011-BLG-0526, the χ2 difference between the planetary and binary model is ~3, implying that the degeneracy is very severe. For OGLE-2011-BLG-0950/MOA-2011-BLG-336, the stellar binary model is formally excluded with Δχ2 ~ 105 and the planetary model is preferred. However, it is difficult to claim a planet discovery because systematic residuals of data from the planetary model are larger than the difference between the planetary and binary models. Considering that two events observed during a single season suffer from such a degeneracy, it is expected that central perturbations experiencing this type of degeneracy is common.
Original languageEnglish
JournalAstrophysical Journal
Volume756
Issue1
Pages (from-to)48
Number of pages9
ISSN0004-637X
DOIs
Publication statusPublished - 1 Sep 2012

See relations at Aarhus University Citationformats

ID: 51158433