Detecting circumstellar disks around gravitational microlenses

Institute for Astrophysics, University of Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany e-mail: mhunder@astro.physik.uni-goettingen.de

Received: 2 December 2008
Accepted: 23 March 2009

Abstract

Aims. We investigate the chance of detecting proto-planetary or debris disks in stars that induce microlensing event (lenses), and consider the modification of the light curve shapes due to occultation and extinction by the disks, as well as the gravitational deflection caused by the additional mass.

Methods. The magnification of gravitational microlensing events is calculated using the ray shooting method. The occultation is taken into account by neglecting or weighting the images on the lens plane according to a transmission map of the corresponding disk for a point source point lens (PSPL) model. The estimated frequency of events is obtained by considering the possible inclinations and optical depths of the disk.

Results. We conclude that gravitational microlensing can be used, in principle, as a tool for detecting debris disks beyond 1 kpc, but estimate that each year around 1 debris disk is expected for lens stars of F, G, or K spectral type and about 10 debris disks might have shown signatures in existing datasets.