Sedighe Sajadian
A5076561882- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Gamma-ray bursts and supernovae
- Adaptive optics and wavefront sensing
- Astronomical Observations and Instrumentation
- Planetary Science and Exploration
- Geophysics and Gravity Measurements
- Statistical and numerical algorithms
- Galaxies: Formation, Evolution, Phenomena
- History and Developments in Astronomy
- Nuclear Physics and Applications
- Dark Matter and Cosmic Phenomena
- Spacecraft Dynamics and Control
- Astrophysical Phenomena and Observations
- Space Satellite Systems and Control
- Astronomical and nuclear sciences
- Solar and Space Plasma Dynamics
- Technology Assessment and Management
- Semiconductor Lasers and Optical Devices
- Spaceflight effects on biology
- Advanced Optical Sensing Technologies
- High-pressure geophysics and materials
- Geomagnetism and Paleomagnetism Studies
Perimeter Institute
2025
Isfahan University of Technology
2017-2024
Chungbuk National University
2020
Sharif University of Technology
2010-2016
Damghan University
2015
Institute for Research in Fundamental Sciences
2014
Abstract We report the first unambiguous detection and mass measurement of an isolated stellar-mass black hole (BH). used Hubble Space Telescope (HST) to carry out precise astrometry source star long-duration ( t E ≃ 270 days), high-magnification microlensing event MOA-2011-BLG-191/OGLE-2011-BLG-0462 (hereafter designated as MOA-11-191/OGLE-11-462), in direction Galactic bulge. HST imaging, conducted at eight epochs over interval 6 yr, reveals a clear relativistic astrometric deflection...
Abstract The Double Asteroid Redirection Test (DART) spacecraft successfully performed the first test of a kinetic impactor for asteroid deflection by impacting Dimorphos, secondary near-Earth binary (65803) Didymos, and changing orbital period Dimorphos. A change in approximately 7 min was expected if incident momentum from DART directly transferred to target perfectly inelastic collision 1 , but studies probable impact conditions properties indicated that considerable enhancement ( β )...
The discovery rate of near-Earth asteroids (NEAs) has steadily increased over the past three decades, yet physical characterization these objects not kept pace. In an effort to help address this gap, we combined targeted photometric observations, archival data, and sparse data from Asteroid Terrestrial-impact Last Alert System (ATLAS) survey extract as much information possible about NEAs' rotation rates, spin-axis orientations, shapes. We selected 17 NEAs with a potential for shape...
Abstract Stellar light curves from edge-on double white dwarf (DWD) systems have periodic lensing/eclipsing signals at times of alignment between the two components as seen by observer. Here, we study characterization and detection these signals. In common DWDs, Einstein radii similar orders magnitude to dwarfs (WDs), projected source lens normalized radius ( ρ ⋆ l ) are ∼1. Both them reduced with orbital period mass. If ≃ 1 lensing-induced minor image is always blocked lens, which results...
Abstract Contact binaries are found throughout the solar system. The recent discovery of Selam, satellite MBA (152830) Dinkinesh, by NASA LUCY mission has made it clear that term ‘contact binary’ covers a variety different types bi-modal mass distributions and formation mechanisms. Only modelling more contact can this population be properly understood. We determined spin state shape model for Apollo group binary asteroid (388188) 2006 DP14using ground-based optical radar observations...
We investigate lens orbital motion in astrometric microlensing and its detectability. In events, the light centroid shift source trajectory (the trajectory) falls off much more slowly than amplification as distance from position increases. As a result, perturbations developed with time such can make considerable deviations trajectories. The rotation of due to produces detectable deviation because cross-section is larger photometric one. Among binary events trajectories, those stellar-mass...
Transits in the planetary system WASP-4 were recently found to occur 80s earlier than expected observations from TESS satellite. We present 22 new times of mid-transit that confirm existence transit timing variations, and are well fitted by a quadratic ephemeris with period decay dP/dt = -9.2 +/- 1.1 ms/yr. rule out instrumental issues, stellar activity Applegate mechanism as possible causes. The light-time effect is also not favoured due non-detection changes systemic velocity. Orbital...
Abstract The impact of the Double Asteroid Redirection Test spacecraft into Dimorphos, moon asteroid Didymos, changed Dimorphos’s orbit substantially, largely from ejection material. We present results 12 Earth-based facilities involved in a world-wide campaign to monitor brightness and morphology ejecta first 35 days after impact. After an initial brightening ∼1.4 mag, we find consistent dimming rates 0.11–0.12 mag day −1 week, 0.08–0.09 over entire study period. system returned its...
Abstract The NASA’s Double-Asteroid Redirection Test (DART) was a unique planetary defence and technology test mission, the first of its kind. main spacecraft DART mission impacted target asteroid Dimorphos, small moon orbiting Didymos (65803), on 2022 September 26. impact brought up mass ejecta which, together with direct momentum transfer from collision, caused an orbital period change 33 ± 1 minutes, as measured by ground-based observations. We report here outcome optical monitoring...
EROS has searched for microlensing toward four directions in the Galactic plane away from center. The interpretation of catalog optical depth is complicated by spread source distance distribution. We compare observations with models, tuned to fit catalogs, and take into account all observational data such as depth, Einstein crossing durations, color magnitude distributions catalogued stars. simulated EROS-like catalogs using Hipparcos database, mass distribution, an interstellar extinction...
In this work, we study the advantages of using a Lucky Imaging camera for observations potential planetary microlensing events. Our aim is to reduce blending effect and enhance exoplanet signals in binary lensing systems composed an corresponding parent star. We simulate light curves based on present surveys follow-up telescopes where one them equipped with camera. This used at Danish 1.54-m telescope. Using specific observational strategy, Earth-mass planet resonance regime, detection...
We study the benefits of polarimetry observations microlensing events to detect and characterize circumstellar discs around microlensed stars located at Galactic bulge. These which are unresolvable from their host make a net polarization effect due projected elliptical shapes. Gravitational can magnify these signals them be resolved. The main aim this work is determine what extra information about extracted in addition those given by photometry ones. Hot closer more likely detected...
A close-in giant planetary (CGP) system has a net polarization signal whose value varies depending on the orbital phase of planet. This is either caused by stellar occultation or reflected starlight from surface orbiting When CGP located in Galactic bulge, its becomes too weak to be measured directly. One method for detecting and characterizing these signatures due distant systems gravitational microlensing. In this work, we focus potential polarimetric observations highly magnified...
Abstract The upcoming Large Synoptic Survey Telescope (LSST) survey will provide an unprecedented opportunity for studying populations of intrinsically faint objects using microlensing. LSST’s large field view and aperture allow effective time-series observations many stars in the Galactic disk bulge. Here, we combine models (for <?CDATA $| b| \lt {10}^{^\circ }$?> ) simulations LSST to study how observing strategies affect number properties microlensing events detected by LSST. Generally,...
We report the discovery and analysis of planetary microlensing event OGLE-2017-BLG-0406, which was observed both from ground by ${\it Spitzer}$ satellite in a solar orbit. At high magnification, anomaly light curve densely ground-based-survey follow-up groups, it found to be explained lens with planet/host mass ratio $q=7.0 \times 10^{-4}$ light-curve modeling. The ground-only Spitzer}$-"only" data each provide very strong one-dimensional (1-D) constraints on 2-D microlens parallax vector...
The formation and dynamical history of hot Jupiters is currently debated, with wide stellar binaries having been suggested as a potential pathway. Additionally, contaminating light from both binary companions unassociated stars can significantly bias the results planet characterisation studies, but be corrected for if properties star are known. We search to known transiting exoplanet host stars, in order determine multiplicity Jupiter stars. also characterise along line sight, allowing...
We investigate the possibility of exoplanet detection orbiting source stars in microlensing events through WFIRST observations. perform a Monto Carlo simulation on rate exoplanets via microlensing, assuming that each star has at least one exoplanet. The can reflect part light from parent or emit internal thermal radiation. In this new channel, we use as an amplifier to magnify reflection planet. literature, mode detecting been investigated much less than usual which are considered companion...
We present the discovery and validation of two TESS exoplanets orbiting nearby M dwarfs: TOI-2084 b, TOI-4184b. characterized host stars by combining spectra from Shane /Kast Magellan /FIRE, spectral energy distribution analysis, stellar evolutionary models. In addition, we used Gemini-South/Zorro & -North/Alopeke high-resolution imaging, archival science images, statistical packages to support planetary interpretation. performed a global analysis multi-colour photometric data...
We report the mass and distance measurements of two single-lens events from 2017 Spitzer microlensing campaign. The ground-based observations yield detection finite-source effects, microlens parallaxes are derived joint analysis observations. find that lens OGLE-2017-BLG-1254 is a $0.60 \pm 0.03 M_{\odot}$ star with $D_{\rm LS} = 0.53 0.11~\text{kpc}$, where LS}$ between source. second event, OGLE-2017-BLG-1161, subject to known satellite parallax degeneracy, thus either...
We report the analysis of planetary microlensing event OGLE-2018-BLG-1185, which was observed by a large number ground-based telescopes and $Spitzer$ Space Telescope. The light curve indicates low planet-host star mass ratio $q = (6.9 \pm 0.2) \times 10^{-5}$, is near peak wide-orbit exoplanet mass-ratio distribution. estimate host planet masses with Bayesian using measured angular Einstein radius under assumption that stars all have an equal probability to this planet. flux variation...
We present the analysis of event OGLE-2017-BLG-1186 from 2017 Spitzer microlensing campaign. This is a remarkable because its source photometrically bright and variable, which makes it possible to perform an asteroseismic using ground-based data. find that star oscillating red giant with average timescale $\sim 9$ d. The also provides us properties including angular size ($\sim 27~\mu{\rm as}$) distance 11.5$ kpc), are essential for inferring lens. When fitting light curve, we test...
The kinematics of isolated brown dwarfs in the Galaxy, beyond solar neighborhood, is virtually unknown. Microlensing has potential to probe this hidden population, as it can measure both mass and five six phase-space coordinates (all except radial velocity) even a dark lens. However, measurements microlens parallax finite-source effects are needed order recover full information. Here, we combine $Spitzer$ satellite measurement with ground-based light curve, which exhibits strong effects,...
Abstract Wavelets are waveform functions that describe transient and unstable variations, such as noise. In this work, we study the advantages of discrete continuous wavelet transforms (DWTs CWTs) microlensing data to denoise them extract their planetary signals intrinsic pulsations hidden by We first generate synthetic apply denoising them. For these simulated with ideally Gaussian noise based on Optical Gravitational Lensing Experiment (OGLE) photometric accuracy, DWTs reduces standard...
Aims. Our aim in this paper is to refine the orbital and physical parameters of HATS-2 planetary system study transit timing variations atmospheric composition thanks observations that span more than 10 yr were collected using different instruments pass-band filters. We also investigate alignment by studying anomalies light curves induced starspots on photosphere parent star. Methods. analysed new events from both ground-based telescopes NASA’s TESS mission. Anomalies detected most modelled...