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- Type of Document: Ph.D. Dissertation
- Language: Farsi
- Document No: 44721 (04)
- University: Sharif University of Technology
- Department: Physics
- Advisor(s): Rahvar, Sohrab
- Abstract:
- In this thesis, we investigate two subjects in gravitational microlensing. In first part we study wave optics effect in light curve of a binary system. Gravitational lensing occurs when light deflects in a gravitational field. This deflection produces multi-images from real one. In microlensing regime, images can not be detected separately and gravitational lensing appears as magnifying source’s flux . Microlensing has been studied mostly in geometric optics regime. At larger wavelengths, mostly at radio wavelengths, we expect to see the effects of wave optics in microlensing. Stars at radio wave are faint and to detect them we need a powerful radio telescope. In the near future, SKA (Square Kilometer Array), very large array with one square kilometer effective area to collect photon, will be launched. Giants stars are brighter than main sequence stars in radio frequency and SKA can see them at this wavelengths. We use giant stars as source for a microlensing event. In this thesis, we study effect of wave optics in the light curve of a binary system. Our results show that for a binary system including a planet, the wave optics signal is stronger than binary system with equal masses. We find those parts of caustic that generate strong wave optics signal.After studying wave optics effect, the observability of these effects will be studied and benefit of this method will be argued.In the second part, we study detectability of spots over source in microlensing events. Strong magnetic field at surface of stars generate spots and study of them can help improving evolutionary model for stars. Using microlensing, we can detect and study a spot on the surface of star at bulge. When a source crosses the caustic, there is a large magnification contrast between those parts over caustic and other parts. This contrast can be as large as a few hundred and help detection of spots.We simulate some data around caustic and try to retrieve initial parameter of spot.Our results show that location of spot at caustic crossing play an important rule to detect spot’ signal. Finally we study detection of spots statistically
- Keywords:
- Gravitational Microlensing ; Binary Lenses ; Wave Optics ; Radio Astronomy ; Starspots
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