Sharif Digital Repository

Within less than 15 years, the count of known planets orbiting stars other than the Sun has risen from none to more than 400 with detections arising from four successfully applied techniques: Doppler-wobbles, planetary transits, gravitational microlensing, and direct imaging. While the hunt for twin Earths is on, a statistically well-defined sample of the population of planets in all their variety is required for probing models of planet formation and orbital evolution so that the origin of planets that harbour life, like and including ours, can be understood. Given the different characteristics of the detection techniques, a complete picture can only arise from a combination of their... 

With several detections, the technique of gravitational microlensing has proven useful for studying planets that orbit stars at Galactic distances, and it can even be applied to detect planets in neighbouring galaxies. So far, planet detections by microlensing have been considered to result from a change in the bending of light and the resulting magnification caused by a planet around the foreground lens star. However, in complete analogy to the annual parallax effect caused by the revolution of the Earth around the Sun, the motion of the source star around the common barycentre with an orbiting planet can also lead to observable deviations in microlensing light curves that can provide... 

We analyze the planetary microlensing event MOA-2010-BLG-328. The best fit yields host and planetary masses of Mh = 0.11 ± 0.01 M Ȯ and Mp = 9.2 ± 2.2 M ⊕, corresponding to a very late M dwarf and sub-Neptune-mass planet, respectively. The system lies at D L = 0.81 ± 0.10 kpc with projected separation r ⊥ = 0.92 ± 0.16 AU. Because of the host's a priori unlikely close distance, as well as the unusual nature of the system, we consider the possibility that the microlens parallax signal, which determines the host mass and distance, is actually due to xallarap (source orbital motion) that is being misinterpreted as parallax. We show a result that favors the parallax solution, even given its... 

The microlensing event OGLE-2008-BLG-510 is characterized by an evident asymmetric shape of the peak, promptly detected by the Automated Robotic Terrestrial Exoplanet Microlensing Search (ARTEMiS) system in real time. The skewness of the light curve appears to be compatible both with binary-lens and binary-source models, including the possibility that the lens system consists of an M dwarf orbited by a brown dwarf. The detection of this microlensing anomaly and our analysis demonstrate that: (1) automated real-time detection of weak microlensing anomalies with immediate feedback is feasible, efficient and sensitive, (2) rather common weak features intrinsically come with ambiguities that are... 

Microlensing detections of cool planets are important for the construction of an unbiased sample to estimate the frequency of planets beyond the snow line, which is where giant planets are thought to form according to the core accretion theory of planet formation. In this paper, we report the discovery of a giant planet detected from the analysis of the light curve of a high-magnification microlensing event MOA 2010-BLG-477. The measured planet-star mass ratio is q = (2.181 ± 0.004) × 10-3 and the projected separation is s = 1.1228 ± 0.0006 in units of the Einstein radius. The angular Einstein radius is unusually large θE = 1.38 ± 0.11 mas. Combining this measurement with constraints on the... 

We report the gravitational microlensing discovery of a sub-Saturn mass planet, MOA-2009-BLG-319Lb, orbiting a K-or M-dwarf star in the inner Galactic disk or Galactic bulge. The high-cadence observations of the MOA-II survey discovered this microlensing event and enabled its identification as a high-magnification event approximately 24 hr prior to peak magnification. As a result, the planetary signal at the peak of this light curve was observed by 20 different telescopes, which is the largest number of telescopes to contribute to a planetary discovery to date. The microlensing model for this event indicates a planet-star mass ratio of q = (3.95 ± 0.02) × 10-4 and a separation of d = 0.97537... 

We report the discovery of a Jupiter-mass planet orbiting an M-dwarf star that gave rise to the microlensing event OGLE-2011-BLG-0265. Such a system is very rare among known planetary systems and thus the discovery is important for theoretical studies of planetary formation and evolution. High-cadence temporal coverage of the planetary signal, combined with extended observations throughout the event, allows us to accurately model the observed light curve. However, the final microlensing solution remains degenerate, yielding two possible configurations of the planet and the host star. In the case of the preferred solution, the mass of the planet is Mp = 0.9 ± 0.3 MJ, and the planet is... 

We present the first measurement of the planet frequency beyond the "snow line," for the planet-to-star mass-ratio interval-4.5 < logq <-2, corresponding to the range of ice giants to gas giants. We find d 2Np1/dlog q d log s= (0.36 ± 0.15) dex dlog q d logs at the mean mass ratio q = 5 × 10-4 with no discernible deviation from a flat (öpik's law) distribution in logprojected separation s. The determination is based on a sample of six planets detected from intensive follow-up observations of high-magnification (A > 200) microlensing events during 2005-2008. The sampled host stars have a typical mass Mhost ∼ 0.5 M⊙, and detection is sensitive to planets over a range of planet-star-projected... 

In recent years a large number of hot Jupiters orbiting in a very close orbit around the parent stars have been explored with the transit and Doppler effect methods. Here in this paper we study the gravitational microlensing effect of a binary lens on a parent star with a hot Jupiter revolving around it. Caustic crossing of the planet makes enhancements on the light curve of the parent star in which the signature of the planet can be detected by high-precision photometric observations. We use the inverse ray shooting method with tree code algorithm to generate the combined light curve of the parent star and the planet. In order to investigate the probability of observing the planet signal,... 

We report the discovery of a cold Super-Earth planet (mp = 4.4 ± 0.5 M) orbiting a lowmass (M = 0.23 ± 0.03 M) M dwarf at projected separation a = 1.18 ± 0.10 a.u., i.e., about 1.9 times the distance the snow line. The system is quite nearby for a microlensing planet, DL = 0.86 ± 0.09 kpc. Indeed, it was the large lens-source relative parallax πrel = 1.0 mas (combined with the low mass M) that gave rise to the large, and thus well-measured, "microlens parallax πE ∞ (πrel/M)1/2 that enabled these precise measurements. OGLE-2017-BLG-1434Lb is the eighth microlensing planet with planet-host mass ratio q < 1×10-4. We apply a new planet-detection sensitivity method, which is a variant of "V/Vmax,... 

For all exoplanet candidates, the reliability of a claimed detection needs to be assessed through a careful study of systematic errors in the data to minimize the false positives rate. We present a method to investigate such systematics in microlensing data sets using the microlensing event OGLE-2013-BLG-0446 as a case study. The event was observed from multiple sites around the world and its high magnification (Amax ∼ 3000) allowed us to investigate the effects of terrestrial and annual parallax. Real-time modeling of the event while it was still ongoing suggested the presence of an extremely low-mass companion (∼3M) to the lensing star, leading to substantial follow-up coverage of the... 

We present high-precision photometry of five consecutive transits of WASP-18, an extrasolar planetary system with one of the shortest orbital periods known. Through the use of telescope defocusing we achieve a photometric precision of 0.47-0.83 mmag per observation over complete transit events. The data are analyzed using the JKTEBOP code and three different sets of stellar evolutionary models. We find the mass and radius of the planet to be M b = 10.43 ± 0.30 ±0.24 M Jup and R b = 1.165± 0.055 ±0.014 R Jup (statistical and systematic errors), respectively. The systematic errors in the orbital separation and the stellar and planetary masses, arising from the use of theoretical predictions,... 

The Galactic bulge source MOA-2010-BLG-523S exhibited short-term deviations from a standard microlensing light curve near the peak of an A max ∼ 265 high-magnification microlensing event. The deviations originally seemed consistent with expectations for a planetary companion to the principal lens. We combine long-term photometric monitoring with a previously published high-resolution spectrum taken near peak to demonstrate that this is an RS CVn variable, so that planetary microlensing is not required to explain the light-curve deviations. This is the first spectroscopically confirmed RS CVn star discovered in the Galactic bulge  

We present photometric observations of four transits in the WASP-17 planetary system, obtained using telescope defocusing techniques and with scatters reaching 0.5mmag per point. Our revised orbital period is 4.0 ± 0.6s longer than previous measurements, a difference of 6.6σ, and does not support the published detections of orbital eccentricity in this system. We model the light curves using the jktebop code and calculate the physical properties of the system by recourse to five sets of theoretical stellar model predictions. The resulting planetary radius, R b = 1.932 ± 0.052 ± 0.010R Jup (statistical and systematic errors, respectively), provides confirmation that WASP-17b is the largest... 

We present microlens parallax measurements for 21 (apparently) isolated lenses observed toward the Galactic bulge that were imaged simultaneously from Earth and Spitzer, which was ∼1 AU west of Earth in projection. We combine these measurements with a kinematic model of the Galaxy to derive distance estimates for each lens, with error bars that are small compared to the Sun's galactocentric distance. The ensemble therefore yields a well-defined cumulative distribution of lens distances. In principle, it is possible to compare this distribution against a set of planets detected in the same experiment in order to measure the Galactic distribution of planets. Since these Spitzer observations... 

We present high-precision photometry of three transits of the extrasolar planetary system WASP-2, obtained by defocusing the telescopes, and achieving scatters of between 0.42 and 0.73 mmag versus the best-fitting model. These data are modelled using the jktebop code, and taking into account the light from the recently discovered faint star close to the system. The physical properties of the WASP-2 system are derived using tabulated predictions from five different sets of stellar evolutionary models, allowing both statistical and systematic error bars to be specified. We find the mass and radius of the planet to be Mb= 0.846 ± 0.055 ± 0.023 MJup and Rb= 1.043 ± 0.029 ± 0.015RJup. It has a... 

We present and analyse light curves of four transits of the Southern hemisphere extrasolar planetary system WASP-4, obtained with a telescope defocused so the radius of each point spread function was 17 arcsec (44 pixels). This approach minimizes both random and systematic errors, allowing us to achieve scatters of between 0.60 and 0.88 mmag per observation over complete transit events. The light curves are augmented by published observations and analysed using the jktebop code. The results of this process are combined with theoretical stellar model predictions to derive the physical properties of the WASP-4 system. We find that the mass and radius of the planet are M b = 1.289 +0.090 -0.090... 

Context. The extrasolar planet WASP-67 b is the first hot Jupiter definitively known to undergo only partial eclipses. The lack of the second and third contact points in this planetary system makes it difficult to obtain accurate measurements of its physical parameters  

Aims. We present 11 high-precision photometric transitobservations of the transiting super-Earth planet GJ≠1214≠b. Combining these data with observations from other authors, we investigate the ephemeris for possible signs of transit timing variations (TTVs) using a Bayesian approach. Methods. The observations were obtained using telescope-defocusing techniques, and achieve a high precision with random errors in the photometry as low as 1 mmag per point. To investigate the possibility of TTVs in the light curve, we calculate the overall probability of a TTV signal using Bayesian methods. Results. The observations are used to determine the photometric parameters and the physical properties... 

WASP-80 is one of only two systems known to contain a hot Jupiter which transits its M-dwarf host star. We present eight light curves of one transit event, obtained simultaneously using two defocussed telescopes. These data were taken through the Bessell I, Sloan g and near-infrared JHK passbands. We use our data to search for opacity-induced changes in the planetary radius, but find that all values agree with each other. Our data are therefore consistent with a flat transmission spectrum to within the observational uncertainties. We also measure an activity index of the host star of log R 'HK =-4.495 log R HK ′ =-4.495, meaning that WASP-80 A shows strong chromospheric activity. The...