Finitesource and finitelens effects in astrometric microlensing
Abstract
The aim of this paper is to study the astrometric trajectory of microlensing events with an extended lens and/or source. We consider not only a dark lens but also a luminous lens as well. We find that the discontinuous finitelens trajectories given by Takahashi will become continuous in the finitesource regime. The point lens (source) approximation alone gives an under (over)estimation of the astrometric signal when the size of the lens and source are not negligible. While the finiteness of the source is revealed when the lens transits the surface of the source, the finitelens signal is most prominent when the lens is very close to the source. Astrometric microlensing towards the Galactic bulge, Small Magellanic Cloud and M31 are discussed, which indicate that the finitelens effect is beyond the detection limit of current instruments. Nevertheless, it is possible to distinguish between selflensing and halo lensing through a (non)detection of the astrometric ellipse. We also consider the case where the lens is luminous itself, as has been observed where a lensing event was followed up with the Hubble Space Telescope. We show that the astrometric signal will be reduced in a luminouslens scenario. The physical properties of the event, such as the lenssource flux ratio, the size of the lens and source nevertheless can be derived by fitting the astrometric trajectory.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 September 2010
 DOI:
 10.1111/j.13652966.2010.17049.x
 arXiv:
 arXiv:1005.3021
 Bibcode:
 2010MNRAS.407.1597L
 Keywords:

 gravitational lensing: micro;
 astrometry;
 dark matter;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 12 pages, 12 figures, 1 table, published in MNRAS