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| Paper: |
Discovering Extrasolar Planets with Microlensing Surveys |
| Volume: |
505, Astronomical Surveys and Big Data |
| Page: |
35 |
| Authors: |
Wambsganss, J. |
| Abstract: |
An astronomical survey is commonly understood as a mapping of a large region of the sky, either photometrically (possibly in various filters/wavelength ranges) or spectroscopically. Often, catalogs of objects are produced/provided as the main product or a by-product. However, with the advent of large CCD cameras and dedicated telescopes with wide-field imaging capabilities, it became possible in the early 1990s, to map the same region of the sky over and over again. In principle, such data sets could be combined to get very deep stacked images of the regions of interest. However, I will report on a completely different use of such repeated maps: Exploring the time domain for particular kinds of stellar variability, namely microlens-induced magnifications in search of exoplanets. Such a time-domain microlensing survey was originally proposed by Bohdan Paczynski in 1986 in order to search for dark matter
objects in the Galactic halo. Only a few years later three teams started this endeavour.
I will report on the history and current state of gravitational microlensing surveys. By now, routinely 100 million stars in the Galactic Bulge are monitored a few times per week by so-called survey teams. All stars with constant apparent brightness and those following known variability patterns are filtered out in order to detect the roughly 2000 microlensing events per year which are produced by stellar lenses. These microlensing events are identified “online” while still in their early phases and then monitored with much higher cadence by so-called follow-up teams. The most interesting of such events are those produced by a star-plus-planet lens. By now of order 30 exoplanets have been discovered by these combined microlensing surveys. Microlensing searches for extrasolar planets are complementary to other exoplanet search techniques. There are two particular advantages: The microlensing method is sensitive down to Earth-mass planets even with ground-based telecopes, and it can be easily used to determine the global abundance of planets in the Milky Way. Recent results of these microlensing surveys are presented and discussed, e. g. the discovery that on average every Milky Way star has at least one planet of Neptune mass or higher. |
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