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استخراج نمایه ی تاریکی لبه ی ستاره های دوردست از پدیده های ریزهمگرایی گرانشی با استفاده از روش اجزای محدود
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استخراج نمایه ی تاریکی لبه ی ستاره های دوردست از پدیده های ریزهمگرایی گرانشی با استفاده از روش اجزای محدود

گلچین، لعیا Golchin, Laya

Measuring Limb Darkening of Distant Stars Using Microlensing Events by Finite Element Method

Golchin, Laya | 2020

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 53844 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Rahvar, Sohrab
  7. Abstract:
  8. The finite-size effect in gravitational microlensing provides a possibility to measure the variation of surface brightness of stars from centre to limb which is called limb darkening profile. Measuring limb darkening profile provides information about star atmosphere. It is also useful in other fields of astrophysics. In this thesis we develop a numerical method to recover limb darkening of source stars from single lens microlensing light curves with finite source effect in which the lens transits the source disk. We use the Finite Element Method (FEM) as an inversion tool for discretization and inversion of the finite source effect integral equation. This method makes no explicit assumption about the shape of the brightness profile more than the flatness of the profile near the centre of the stellar disc and its smoothness. From the simulation, we investigate the accuracy and stability of this method and we use regularization techniques to stabilize it. This method can be used as an standard method to study stellar atmosphere using light curves of future microlensing observations. Finally, we apply this method to seven single lens, finite source events in which light curves have been observed with a high cadence near the peak. The recovered intensity profile of stars from our analysis are more consistent with square-root limb darkening law and two events are just consistent with the square-root law, one of the profiles is inconsistent with both linear and square root profiles but this inconsistency is less severe for square-root profile
  9. Keywords:
  10. Gravitational Microlensing ; Finite Element Method ; Numerical Method ; Atomosphere ; Limb Darkening ; Microlensing

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