Sharif Digital Repository

e H-R diagram for stars within 100 parsecs from the sun were simulated using Padova isorones, Besanc¸on Galaxy disc model and various star formation rates. using Chi-square test the different star formation rates were compared. the results favours an increasing star formation rate  

One of the beautiful branches of Astrophysics is studing of binary systems and specially eclipsing binary sytems which is included transiting eclipsing extrasolar planets. Detecting of extrasolar planets with transit method is based on which a planet orbits around a star and when its orbit alignment is such that planet along our line of sight across disk of star, it causes eclipse of star and a drop in star’s brightness and from this we can find the existence of a planet. In analysis of observational light curve (obtained from data acquisition with photometry method) a synthetic light curve, constructed from a theoretical model which is based on transit, planet and star geometry, is... 

The cosmological observations, like the luminosity distance of type Ia Supernovas, Cosmic Microwave Background radiation (CMB), Baryon Acoustic Oscillations (BAO) and Large Scale Structure (LSS) observations indicate that the Universe is nearly flat and also it is in a phase of acceleration. In the context of standard cosmological models, it means that the Universe is made of an unknown component (Dark Energy), which approximately has 70% of total energy-momentum of the Universe. The Cosmological Constant(CC) in the paradigm of ΛCDM model is the easiest model to describe the acceleration of the Universe. On the other hand the fine tuning (CC problem) and coincidence problems open new... 

In this thesis first we will review gravitational lensing and microlensing, then we will introduce all direct and indirect methods for detecting exo-planets. gravitational microlensing is one of these methods in detecting exo-planets. In the second part first we will explain a powerful numerical method for calculating magnification, position and the shape of images by combining of tree code and inverse rays hooting algorithm. Then we simulated the caustic crossing of Hot Jupiters using that algorithm. Finally with performing Monte-Carlo simulation we will obtain the detection efficiency for detecting this class of exo-planets during caustic crossing and we will estimate the number of these... 

Gravitational Microlensing is one of the most powerful methods of detecting very low mass objects like Exoplanets and Brown dwarfs. The most important parameter that we can extract from a microlensing event is Einstein radius crossing time t_E. In this thesis, with performing Monte-Carlo simulation, we will obtain t_E distribution for brown dwarf population. Then we will show that this population can be a good candidate for very short microlensing events with t_E<2 days. The data set used in this analysis was taken in 2006 and 2007 seasons by the MOA-II survey, with the 1.8-m MOA-II telescope located at the Mt. John University Observatory, New Zealand  

Star Formation History (SFH) is one of the important quantities to constrain galaxy formation and evolution scenarios and star formation models. In this thesis we aim to derive SFH for solar neighbourhood stars. We can use absolute magnitude-color diagram of a stellar system to derive the SFH. The method is to consider different functions for SFH and compare the resulting colormagnitude diagram with observational data. We used HIPPARCOS satellite data in this thesis. Hipparcos has measured astrometric parameters for about 120000 stars very accurately, which enables us to compare the color-magnitude of those stars with theoretical color-magnitudes. In this thesis, using Monte Carlo method, we... 

In my Thesis we are going to explain Large Scale Weak Lensing observations by weak field approximation of non-local modified gravity. We try to explain the weak lensing of galaxy clusters after collision without any need to dark matter, which could be an important test of the modified gravity model.One of the important questions of modern cosmology is the nature of dark matter,the concept which was created to explain what ordinary baryonic matter can’t explain.However, one alternative way is to modify Einstein’s General Relativity. One of the main pillars of General Relativity is the locality assumption. Non-local gravity puts aside this assumption. The Newtonian limit of this theory is... 

One of the important concepts in cosmology is that all of the observations is done on the past light-cone. In general, cosmological linear perturbation theory is done in a particular gauge and often on spacelike hyperplanes. Then in order to link quantities calculated in perturbation theory with observables, we have to take into account effects coming from projecting these quantities onto past light-cone. We aim in this thesis to study these effects and to calculate corrections over observable quantities such as, two point correlation function and power spectrum of matter perturbations in cosmos. For a particular observational example, in the end we study clustering of structures in... 

Einstein's theory of General Relativity is the cornerstone in many modern physics areas in which the strong gravitational field is engaged, i.e. modern cosmology, neutron star and black hole physics, generation of gravitational waves, and several other cosmic phenomena. Despite its simple appearance, the theory of general relativity is practically rigorous. Einstein's field equations are consist of 10 coupled, non-linear, partial differential equations in 4 space-time dimensions. Except for some highly symmetric space-times, general relativity does not provide exact analytical solutions to real problems with a low level of symmetry, since the field equations would be strongly complex for... 

In this thesis, we first review MOdified Gravity (MOG) theory as an alternative to dark matter models and then investigate some of the phenomena related to galaxy dynamics and gravitational lensing within the framework of this theory. In the last step, we present a model for the interaction of the fifth force field and the electromagnetic field. This model is based on the definition of a current density of matter using the energy momentum tensor in which the Lorentz symmetry is broken. This is due to the existence of a constant coefficient in the interaction, which can be considered as a fixed background field or observer 4-velocity that couples to energy momentum tensor. After introducing... 

Gravitational Microlensing has been used as a powerful tool for astrophysical studies and exoplanet detections. In the gravitational microlensing, we have two images with negative and positive parities. The negative-parity image is a fainter image and is produced at a closer angular separation with respect to the lens star. In the case of a red-giant lens star and large impact parameter of lensing, this image can be eclipsed by the lens star. The result would be dimming the flux receiving from the combination of the source and the lens stars and the light curve resembles to an eclipsing binary system. In this work, we introduce this phenomenon and propose an observational procedure for... 

After Supernovae and gamma-ray bursts, Quasars are the brightest in the Universe. They are powered by supermassive black holes which lie at the center of the galaxies. Perturbations in space-time metrics by massive galaxies near the line of sight of the quasar can lead to strong lensing and create multiple pictures. Gravitationally lensed quasar systems yield abundant data sets for astrophysical and cosmological experimentation. In this thesis survey results of the multiply lensed SDSS J1206+4332 is studied. Candidate phenomenons are microlensing and gravitational grating. Gravitational grating studies the interaction of electromagnetic wave and gavitational wave in both geometric and wave... 

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... 

We investigate the possibility of exoplanet detection orbiting source stars in microlensing events through the Spitzer and WFIRST follow-up observations.We perform a Monto Carlo simulation on the detection rate of exoplanets via microlensing, assuming that each source star has at least one exoplanet. The exoplanet can reflect part of the light from the parent star or emit internal thermal radiation. In this new detection channel, we use microlensing as an amplifier to magnify the reflection light from the planet.In the literature, this mode of detecting exoplanets has been investigated much less than the usual mode in which the exoplanets are considered as one companion in binary lens... 

At the beginning of the 20th century, Albert Einstein introduced the equations of general relativity, opening a new avenue for investigating various phenomena. One of the predictions of these equations, gravitational lensing, was observed by Eddington during his lifetime, confirming the theory's ability to describe nature. Gravitational lensing can be categorized into three types: strong lensing, weak lensing, and microlensing. The current focus of research is on observing the separation phenomenon in gravitational microlensing. The observation of gravitational microlensing provides valuable insights into the composition of celestial bodies in the universe. Calculating the mass of different... 

The purpose of this research is theoretical and numerical investigations on centrifugal compressor. A computer code has been developed to simulate single-zone and two-zone model, based on the revised formulation for real gas, using Peng-Robinson equations. Single-zone modeling, also known as meanline method, established based on 1-D equations of fluid dynamics considering ideal gas relations, empirical loss correlations, slip factors, impeller efficiency and no wake or separation regions. Considering usual significant separated regions in the gas path of impellers, two-zone (jet and wake zone) model has been developed to achieve a more reliable simulation by using fewer correlations based on... 

The Sudoku puzzle is played on a 9 × 9 grid which is divided into nine boxes each with 3 × 3 cells. Initially, some digits between 1 and 9 are given on the grid as the clues. Generalized Sudoku (a table of n2 by n2 that includes n2 blocks with n cells and in each of its rows, columns and blocks has all numbers from 1 to n2 appeared once and only once) can be considered too. Millions of people around the world are tackling one of the hardest problems in computer science without even knowing it. The first such puzzle appeared in the May 1979 edition of Dell P encil P uzzles and W ord Games and, according to research done by W ill Shortz, the crossword editor of the N ew Y ork T imes, was...