گردهمایی پژوهی نجوم ایران
سال:1393 | دوره:18 |تعداد مقالات:22

USING THE NON-CONONICAL MODEL OF SCALAR FIELD, THE COSMOLOGICAL CONSEQUENCES OF A PERVASIVE, SELF-INTERACTING, HOMOGENEOUS AND ROLLING SCALAR FIELD ARE STUDIED. IN THIS MODEL, THE SCALAR-FIELD POTENTIAL IS "NONLINEAR" AND DECREASES IN MAGNITUDE BY INCREASING THE VALUE OF THE SCALAR FIELD. A SPECIAL SOLUTION OF THE NONLINEAR FIELD EQUATIONS OF F THAT IS A TIME DEPENDENT, FIXED POINT IS OBTAINED. THE FIXED POINT RELIES ON THE NON-CONONICAL TERM OF ACTION AND Q- PARAMETER WHICH IS APPEARED IN ENERGY DENSITY OF SCALAR FIELD RED-SHIFT. THE BEHAVIOR OF BARYONIC PERTURBATIONS IN LINEAR PERTURBATION SCENARIO A CONSIDERABLE AMOUNT OF ENERGY DENSITY OF SCALAR-FIELD AT LOW RED-SHIFTS PREVENTS THE GROWTH OF PERTURBATIONS IN THE ORDINARY MATTER FLUID. THE ENERGY DENSITY IN THE SCALAR FIELD IS NOT APPRECIABLY PERTURBED BY NONRELATIVISTIC GRAVITATIONAL FIELDS, EITHER IN THE RADIATION-DOMINATED, MATTER-DOMINATED, OR SCALAR-FIELD-DOMINATED EPOCHS.

WE PRESENT THE RESULTS OF WIDE FIELD INFRARED AND NEAR-INFRARED SURVEY OF 5.8 DEG AROUND THE PLEIADES CLUSTER CENTRE. WE REMOVE NON-CLUSTER CONTAMINATION ON THE BASIS OF PROPER MOTIONS AND J AND K PHOTOMETRY OF PPMXL CATALOGUE AND W1 AND W2 PHOTOMETRY FROM THE WISE SURVEY AND PRESENT 1157 CANDIDATES CLUSTER MEMBERS DOWN TO 0.04Mʘ. WE HAVE USED THIS LIST OF MEMBERS TO INVESTIGATE THE CLUSTER BINARITY, MASS FUNCTION AND MASS SEGREGATION. WE FIND A BINARY FRACTION OF 41 ± 10 PERCENT. THE CANDIDATE’S RADIAL DISTRIBUTION PRESENTS EVIDENCE THAT MASS SEGREGATION HAS ALREADY OCCURRED IN THE CLUSTER. THE PLEIADES MASS FUNCTION IS THEN DERIVED ACROSS THE STELLAR-SUBSTELLAR BOUNDARY AND WE FIND THAT, BETWEEN 0.04Mʘ AND 4Mʘ, IT IS WELL REPRESENTED BY A POWER-LAW, DN/DM µ M-A, WITH INDEX OF ALOW = 0.69 ± 0.06 FOR LOW MASS AND AHIGH = 2.83 ± 0.18 FOR HIGH MASS STARS. FINALLY, THE CANDIDATE’S RADIAL DISTRIBUTION AND MASS FUNCTION PRESENTS EVIDENCE THAT MASS SEGREGATION HAS ALREADY OCCURRED IN THE CLUSTER.

WE FIRST GIVE A VERY SHORT REVIEW OF VARIOUS MECHANISMS FOR THE FORMATION OF STRUCTURES IN PROTOPLANETARY DISCS. THEN WE INVESTIGATE DRAG FORCE DRIVEN INSTABILITY IN DUSTY PROTOPLANETARY DISCS IN THE LINEAR REGIME. …

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NGC 147 AND NGC 185 ARE LOW METALLICITY DWARF ELLIPTICAL GALAXIES. THEY ARE KNOWN TO BE THE SATELLITES FOR ANDROMEDA GALAXY AND FORM A PAIR WITH A ROUGHLY EQUAL MASS. IN SPITE OF SIMILARITIES MENTIONED, NGC 147 AND NGC 185 HAVE BEEN THROUGH DIFFERENT STAR FORMATION HISTORY AND AT THE PRESENT TIME THEY HAVE DIFFERENT AMOUNT OF INTERSTELLAR GAS AND DUST. WE PRESENT THE FIRST RECONSTRUCTION OF STAR FORMATION HISTORY AND EXPLORE THE FEEDBACK FROM DUSTY STELLAR WIND.OUR METHOD IS BASED ON PULSATING ASYMPTOTIC GIANT BRANCH STARS (AGBS). STARS IN THIS LATE STAGES OF EVOLUTION DERIVE THEIR MAXIMUM LUMINOSITY WHICH IS DIRECTLY RELATED TO BIRTH MASS. BY USING LONG PERIOD VARIABLE STARS WE OBTAIN THE AMOUNT OF GASEOUS MASS CONVERTED TO STELLAR MASS, LOOKING BACK IN TIME. AS A RESULT WE FIND ONE PEAK OF STAR FORMATION AS OLD AS 7 GYR AND 10 GYR IN NGC 147 AND NGC 185 RESPECTIVELY. HOWEVER, THE STAR FORMATION RATE IN NGC 185 SWIFTLY DROPS DOWN TO AN APPROXIMATELY CONSTANT AMOUNT.FURTHERMORE, AGBS LOSE MOST OF THEIR MASS DURING THE STELLAR WINDS. WE HAVE MODELED THE SPECTRAL ENERGY DISTRIBUTION OF INDIVIDUAL STARS WITH DUSTY CODE AND THE STELLAR MASS LOSS RATE HAVE BEEN OBTAINED IN ORDER OF 10-6M⊙YR-1. ESTIMATION THE TOTAL MASS LOSS RATE IS IN PROGRESS. THIS WILL HELP US TO JUDGE THE FUTURE STAR FORMATION.

HERE, WE INVESTIGATE THE GROWTH OF MATTER DENSITY PERTURBATIONS AS WELL AS THE GENERALIZED SECOND LAW (GSL) OF THERMODYNAMICS IN THE FRAMEWORK OF F(R)-GRAVITY. WE CONSIDER A SPATIALLY FLAT FRW UNIVERSE FILLED WITH THE PRESSURE LESS MATTER AND RADIATION WHICH IS ENCLOSED BY THE DYNAMICAL APPARENT HORIZON WITH THE HAWKING TEMPERATURE. FOR SOME VIABLE F(R) MODELS CONTAINING THE STAROBINSKY, HU-SAWICKI, EXPONENTIAL, TSUJIKAWA, AND AB MODELS, WE FIRST EXPLORE NUMERICALLY THE EVOLUTION OF SOME COSMOLOGICAL PARAMETERS LIKE THE HUBBLE PARAMETER, THE RICCI SCALAR, THE DECELERATION PARAMETER, THE DENSITY PARAMETERS AND THE DECELECTIVE EQUATION OF STATE PARAMETER. THEN, WE EXAMINE THE VALIDITY OF GSL AND OBTAIN THE GROWTH FACTOR OF STRUCTURE FORMATION. WE FIND THAT FOR THE AFOREMENTIONED MODELS, THE GSL IS SATISFIED FROM THE EARLY TIMES TO THE PRESENT EPOCH. BUT IN THE FUTURE, THE GSL FOR THE ALL MODELS BUT THE HU-SAWICKI AND AB MODELS, IS VIOLATED IN SOME RANGES OF REDSHIFT. OUR NUMERICAL RESULTS ALSO SHOW THAT FOR THE ALL MODELS THE GROWTH FACTOR FOR LARGER STRUCTURES LIKE THE ACDM MODEL FIT THE DATA VERY WELL.

WE PRESENT ANALYSIS OF PERIOD AND LIGHT CURVE (LC) VARIATIONS IN RY AQR SYSTEM, THE FOURIER FREQUENCY ANALYSIS INDICATES THAT PRIMARY IS A PULSATING, D-SCUTI VARIABLE STAR, MOREOVER O-C CURVE ANALYSIS SHOWS THAT THE PERIOD OF THE SYSTEM IS SECULARLY DECREASING WITH A RATE OF DP/DT=0.074 SEC/YR. THIS DECREASE IN THE ORBITAL PERIOD VARIATIONS WAS ATTRIBUTED TO A MASS AND ANGULAR MOMENTUM LOSS FROM THE SYSTEM WITH RATE 2.57´10−10M⊙/YR. APART FROM THE SECULAR PERIOD DECREASES THE ORBITAL PERIOD OF THE SYSTEM IS MODULATED BY A CYCLIC PERIOD OF 72.69 YR, THIS PERIOD WAS ATTRIBUTED TO A THIRD BODY ORBITING AROUND THE BARYCENTER OF THE SYSTEM.

IN THIS PAPER, I REVIEW THE CURRENT STATUS OF THE MODIFIED GRAVITY (THE SO-CALLED MOG). THEN I WILL CONSIDER THE LOCAL/ GLOBAL GRAVITATIONAL STABILITY OF SELF-GRAVITATING DISKS IN MOG. …

WE PRESENT HERE LIGHT CURVES (LC) ANALYSIS AND PERIOD VARIATIONS OF TWO ULTRA-SHORT PERIOD BINARY SYSTEMS. PERIOD ANALYSIS OF THE SYSTEM KIC 7375612 INDICATES A SECULAR DECREASE IN THE PERIOD WITH RATE 0.001SECYR-1, WHICH WAS ATTRIBUTED TO THE MASS AND ANGULAR MOMENTUM LOSS (AML) WITH RATES M = -6.37 ´ 10-13M⊙, DJ = -7.63 ´ 1035KG.MYR-1 , RESPECTIVELY, ESTIMATED IN THIS WORK. APART FROM THE MASS & AML DETECTED. IT WAS FOUND THAT THE ORBITAL PERIOD OF THIS SYSTEM IS MODULATED WITH AN ALTERNATING VARIATION OF PERIOD 898 ± 14 D, WHICH WAS ATTRIBUTED TO A THIRD BODY CIRCLING AROUND THE SYSTEM. MOREOVER LCS ANALYSIS OF THESE SYSTEMS WERE PERFORMED BY PHOEBE CODE, IN BOTH DETACHED & OVER CONTACT UMA MODES, THE RESULTS FAVORS THE DETACHED SOLUTION RATHER THAN OVER CONTACT. THERE BY SUPPORTING THE STEPEINS STATEMENT THAT, LOW MASS SHORT PERIOD BINARY SYSTEMS MIGHT HAVE NOT HAD ENOUGH TIME TO FILL THEIR ROCHE LOBE AND OVER FLOW ITS MASS VIA AML.

IN THIS PAPER WE CONSIDER THE MOTION OF TEST PARTICLES IN THE BLACK HOLE SPACE-TIME GIVEN BY P. D. MENNHEIM AND D. KAZANAS. WE DERIVE THE ANALYTICAL SOLUTIONS FOR THE EQUATION OF MOTION OF NEUTRAL TEST PARTICLES. THE GEODESIC EQUATIONS CAN BE SOLVED IN TERMS OF WEIERSTRASS ELLIPTIC FUNCTIONS AND DERIVATIVES OF KLEINIAN SIGMA FUNCTIONS. THE DIFFERENT TYPES OF THE RESULTING ORBITS ARE CHARACTERIZED IN TERMS OF THE CONSERVED ENERGY AND ANGULAR MOMENTUM.

WE INVESTIGATE ORBITAL MOTION OF BROAD-LINE REGION (BLR) CLOUDS IN AGNS BY CONSIDERING CENTRAL GRAVITATIONAL FORCE AND NON-ISOTROPIC RADIATION FORCE. IT IS ASSUMED THAT THE INTERCLOUD GAS CAN BE DESCRIBED USING ADVECTION-DOMINATED ACCRETION FLOWS (ADAFS) WHERE ITS PRESSURE DISTRIBUTION DEPENDS ON BOTH THE RADIAL DISTANCE AND THE LATITUDINAL ANGLE. …

DUE TO MANY REASONS, FLUCTUATIONS IN COSMOLOGICAL FIELDS BECOME STOCHASTIC. THEREFORE, WE HAVE TO RELY ON ROBUST METHODS TO EXTRACT RELIABLE RESULTS. SOME OF STOCHASTIC FIELDS IN COSMOLOGY AND ASTROPHYSICS IN VARIOUS DIMENSIONS ARE INITIAL CONDITIONS, CMB, LARGE SCALE FLUCTUATIONS AND LYMAN-ALPHA FOREST AND ETC. IN THIS TALK, I WILL GIVE SOME MOTIVATIONS ABOUT STOCHASTICITY IN COSMOLOGICAL FIELDS AND THEN SOME TOPOLOGICAL AND GEOMETRICAL MEASURES WILL BE ASSESSED AND DISCUSSED.

WITHIN THE FRAMEWORK OF FRW COSMOLOGY, WE STUDY THE STRUCTURE FORMATION IN THE PRESENCE OF INTERACTION BETWEEN VISCOUS MODIFIED GHOST DARK ENERGY (MGDE) AND DARK MATTER (DM). FOR A SPATIALLY NON-FLAT FRW UNIVERSE CONTAINING MGDE AND DM, WE SOLVE NUMERICALLY THE DIFFERENTIAL EQUATION GOVERNING THE MGDE DENSITY PARAMETER. CONSEQUENTLY, WE OBTAIN THE GROWTH RATE OF MATTER FOR OUR MODEL IN A LINEAR PERTURBATION REGIME. WE CONCLUDE THAT THE EVOLUTION OF DM DENSITY PERTURBATION IN THE PRESENCE OF INTERACTION WITH VISCOUS MGDE SHOWS A SUPPRESSION OF GROWTH OF STRUCTURE.

BASED ON OBSERVATIONAL DATA IT IS CLEARED THAT THE SPICULES AXIS HAVE TRANSVERSAL OSCILLATIONS. THESE OSCILLATIONS MAY BE MODELED VIA EITHER KINK WAVES OR ALFVEN WAVES. IN THE PRESENT WORK WE MODEL THESE WAVES AS TORSIONAL ALFVEN WAVES. THE SUMER/SOHO SPECTROSCOPIC DATA ARE USED TO CALCULATE THE PERIOD RATIO OF FUNDAMENTAL MODE AND ITS FIRST HARMONIC. IT IS SHOWED THAT THIS VALUE HAS DEPARTURES FROM ITS CANONICAL VALUE OF 2 BECAUSE OF STEADY FLOWS AND DENSITY STRATIFICATION.

IN THIS PAPER, WE WILL DESCRIBE THE MOTION OF THREE BODY MOTION, ALSO WITH SPECIAL CASE OF CIRCULAR RESTRICTED THREE BODY MOTION (CRTB). BY SOLVING EQUATIONS OF MOTION FOR SEVERAL SITUATIONS, WE OBTAIN THE VELOCITIES FOR WHICH, THE PLANET KEEPS IN STABLE ORBITS. LAGRANGIAN POINTS ARE ALSO IMPORTANT SUGGESTIONS FOR STABLE ORBITS. IN THIS INVESTIGATION, WE FOUND THAT A VAST MAJORITY OF PLANETS FOUND IN BINARY SYSTEMS ARE IN BINARIES WITH ECCENTRICITIES NEAR TO 0. SO WE CHOSE TO FOCUS ON CRTBS. EVEN ROCHE LIMIT IS CONSIDERED IN THE LOWER LIMITS OF THE ORBITS.

HERE, WE INVESTIGATE THE GSL OF GRAVITATIONAL THERMODYNAMICS IN THE FRAMEWORK OF MODIFIED GAUSS-BONNET GRAVITY OR F(G)-GRAVITY. WE CONSIDER A SPATIALLY FRW UNIVERSE FILLED WITH THE MATTER AND RADIATION ENCLOSED BY THE DYNAMICAL APPARENT HORIZON WITH THE HAWKING TEMPERATURE. FOR TWO VIABLE F(G) MODELS, WE FIRST NUMERICALLY SOLVE THE SET OF DIFFERENTIAL EQUATIONS GOVERNING THE DYNAMICS OF F(G)-GRAVITY. THEN, WE OBTAIN THE EVOLUTIONS OF THE HUBBLE PARAMETER, THE GAUSS-BONNET CURVATURE INVARIANT TERM, THE DENSITY AND EQUATION OF STATE PARAMETERS AS WELL AS THE DECELERATION PARAMETER. FINALLY, WE EXAMINE THE VALIDITY OF THE GSL. FOR THE SELECTED F(G) MODELS, WE CONCLUDE THAT BOTH MODELS HAVE A STABLE DE SITTER ATTRACTOR. THE EQUATION OF STATE PARAMETERS BEHAVE QUITE SIMILAR TO THOSE OF THE LCDM MODEL IN THE RADIATION/MATTER DOMINATED EPOCHS, THEN THEY ENTER THE PHANTOM REGION BEFORE REACHING THE DE SITTER ATTRACTOR WITH W = -1. THE DECELERATION PARAMETER STARTS FROM THE RADIATION/MATTER DOMINATED ERAS, THEN TRANSITS FROM A COSMIC DECELERATION TO ACCELERATION AND FINALLY APPROACHES A DE SITTER REGIME AT LATE TIMES, AS EXPECTED. FURTHERMORE, THE GSL IS RESPECTED FOR BOTH MODELS DURING THE STANDARD RADIATION/MATTER DOMINATED EPOCHS. THEREAFTER WHEN THE UNIVERSE BECOMES ACCELERATING, THE GSL IS VIOLATED IN SOME RANGES OF SCALE FACTOR. AT LATE TIMES, THE EVOLUTION OF THE GSL PREDICTS AN ADIABATIC BEHAVIOR FOR THE ACCELERATED EXPANSION OF THE UNIVERSE.

LIGHT AND PERIOD ANALYSES FOR TWO ULTRA-SHORT BINARY SYSTEMS, FOUND BY KEPLER SPACE TELESCOPE WERE CARRIED OUT FOR THE FIRST TIME, USING PHOEBE CODE. ANALYSIS OF PERIOD VARIATIONS FOR KIC 8758716 SYSTEM, SHOWS MASS AND ANGULAR MOMENTUM LOSS WITH RATES M= 1.087×10−12, DJ = −3.99×1036KG.M YR−1, RESPECTIVELY. HOWEVER PERIOD ANALYSIS OF THE KIC 10855535 INDICATES A SINUSOIDAL VARIATION INDICATIVE OF PRESENCE OF A THIRD BODY ORBITING THE SYSTEM WITH PERIOD 412 D. IN ADDITION ANALYSIS OF PHOTOMETRIC LIGHT CURVES (LC) WERE PERFORMED IN BOTH DETACHED AND OVER CONTACT MODES. THE RESULTS OF ANALYSIS INDICATE THAT THESE SYSTEMS ARE IN DETACHED CONFIGURATION RATHER THAN CONTACT, CONSISTENT WITH THE STEPIEN’S THEORY OF ANGULAR MOMENTUM LOSS (AML).

THE AIM OF THIS PAPER IS TO INVESTIGAT THE ROLE OF MAGNETIC DIFFUSIVITY PARAMETER ON THE STRUCTURE OF ADAFS. WE USE THE SELF-SIMILAR ASSUMPTION IN RADIAL DIRECTION TO SOLVE THE MHD EQUATIONS FOR HOT ACCRETION DISKS. THE TOROIDAL COMPONENT OF MAGNETIC FIELD AND ALL THREE COMPONENTS OF THE VELOCITY FIELD N º (N𝑟, NQ, NJ) ARE CONSIDERED IN OUR WORK. OUR RESULTS INDICATE THAT THE OUTFLOW REGION, WHERE THE REDIAL VELOCITY BECOMES POSITIVE IN A CERTAIN INCLINATION ANGLE Q0, ALWAYS EXISTS. WE SEE THAT THE STRONGER MAGNETIC DIFFUSIVITY PARAMETER DOES NOT HAVE ANY SENSIBLE EFFECT ON THE INCLINATION ANGLE, Q0. NUMERICAL CALCULATIONS OF OUR MODEL HAVE REVEALED THAT THE MAGNETIC DIFFUSIVITY PARAMETER HAS A SIGNIFICANT EFFECT ON THE VERTICAL STRUCTURE OF ACCRETION DISKS.

OVER THE LAST DECADE, WE HAVE WITNESSED ENORMOUS PROGRESS IN THE ABILITY TO UNDERSTAND THE FORMATION AND EVOLUTION OF GALAXIES. HOWEVER, THERE ARE MANY OPEN QUESTIONS STILL REMAINING ON ALL ASPECTS OF THE GALAXY FORMATION AND EVOLUTION. …

WE STUDY THE INTERMEDIATE INFLATION IN A NON-CANONICAL SCALAR FIELD FRAMEWORK WITH A POWER-LIKE LAGRANGIAN. WE OBTAIN AN INVERSE POWER LAW INFLATIONARY POTENTIAL AND APPROXIMATE THE TOTAL E-FOLD NUMBER OF INFLATION IN OUR MODEL. THEN, WE ESTIMATE THE INFLATIONARY OBSERVABLES AND SHOW THAT IN CONTRAST WITH THE STANDARD CANONICAL INTERMEDIATE INFLATION, OUR NON-CANONICAL MODEL IS COMPATIBLE WITH THE OBSERVATIONAL RESULTS OF PLANCK 2015. SUBSEQUENTLY, WE OBTAIN AN APPROXIMATION FOR THE ENERGY SCALE AT THE INITIAL TIME OF INFLATION AND SHOW THAT IT CAN BE OF ORDER OF THE PLANCK ENERGY SCALE. THEREFORE, WE CAN RESOLVE ONE OF THE MYSTERIES OF THE INFLATION THEORY.

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INTERMEDIATE INFLATION IS CONSIDERED IN A NON-CANONICAL SCALAR FIELD MODEL, IN WHICH THE KINETIC TERM OF SCALAR FIELD IS TAKEN AS A POWER-LAW FUNCTION. THE FREE PARAMETERS OF THE MODEL ARE CONSTRAINED BY USING THE MOST RECENT OBSERVATIONAL DATA RELATED TO SCALAR SPECTRA INDEX, TENSOR-TO-SCALAR RATIO, AND SCALAR PERTURBATION AMPLITUDE. THE RESULTS ARE USED TO DEPICT THE POTENTIAL BEHAVIOR OF THE MODEL AND ESTIMATE THE INITIAL AND FINAL TIME OF INFLATION.