8 research outputs found
Light Propagation in inhomogeneous Universes
Using a multi-plane lensing method that we have developed, we follow the
evolution of light beams as they propagate through inhomogeneous universes. We
use a P3M code to simulate the formation and evolution of large-scale
structure. The resolution of the simulations is increased to sub-Megaparsec
scales by using a Monte Carlo method to locate galaxies inside the
computational volume according to the underlying particle distribution. The
galaxies are approximated by isothermal spheres, with each morphological type
having its own distribution of masses and core radii. The morphological types
are chosen in order to reproduce the observed morphology-density relation. This
algorithm has an effective resolution of 9 orders of magnitudes in length, from
the size of superclusters down to the core radii of the smallest galaxies.
We consider cold dark matter models normalized to COBE, and perform a large
parameter survey by varying the cosmological parameters Omega_0, lambda_0, H_0,
and n (the tilt of the primordial power spectrum). The values of n are chosen
by imposing particular values or sigma_8, the rms mass fluctuation at a scale
of 8/h Mpc. We use the power spectrum given by Bunn & White. This is the
largest parameter survey ever done is this field.Comment: 3 pages, gzip'ed tar file, including TeX source (not Latex). To be
published in a periodical of the Yukawa Institute for Theoretical Physics
(1998
Analysis of ``Gauge Modes'' in Linearized Relativity
By writing the complete set of (ADM) equations for linearized waves,
we are able to demonstrate the properties of the initial data and of the
evolution of a wave problem set by Alcubierre and Schutz. We show that the
gauge modes and constraint error modes arise in a straightforward way in the
analysis, and are of a form which will be controlled in any well specified
convergent computational discretization of the differential equations.Comment: 11pages LaTe
Laju Pengembangan Alam Semesta Berdasarkan Data Supernova Tipe Ia
Analisa data yang diperoleh dari supernova tipe Ia (SN Ia) dapat memberikan informasi mengenai pengembangan alam semesta. Laju pengembangan alam semesta didefiniskan dengan konstanta Hubble (H0). Dalam tugas akhir ini digunakan 151 data SN Ia dengan z †0,05 yang diunduh dari Supernova Cosmology Project. Metode yang digunakan untuk mendapatkan nilai H0 yaitu dengan mendapatkan nilai gradien dari diagram Hubble memberikan hasil H0 = 66,67 ± 1,20 km s-1 Mpc-1 dan menggunakan persamaan Friedmann yang dilambangkan dengan H0â dengan masukkan beberapa nilai konstanta perlambatan (q0). Residu (H0â-H0) terkecil memberikan H0â = 66,73 km s-1 Mpc-1 (q0 = -0,55) dengan residu 0,059087403, H0â= 66,69 km s-1 Mpc-1 (q0 = 0,5) dengan residu 0,023110894, H0 = 67,94 km s-1 Mpc-1 (q0 = -1) dengan residu 0,069846939 dan H0 = 67,91 km s-1 Mpc-1 (q0 = 0,15) dengan residu 0,036582237. Hasil ini menunjukkan bahwa menggunakan data dengan z rendah akan memberikan nilai H0 yang berbeda dengan z tinggi. Berdasarkan keempat nilai residu di atas yang memiliki perbedaan sangat kecil namun memberikan bentuk geometri yang berbeda sehingga geometri alam semesta tidak dapat ditentukan dari hanya menggunakan data supernova tipe Ia dengan redshift rendah.Kata Kunci : Supernova tipe Ia, konstanta Hubble, gradien, persamaan Friedman
Constraints on Dark Energy Models in Cosmology from Double-Source Plane Strong Lensing System
Measuring the impact of Indonesian antennas on global geodetic VLBI network
International audienceIn the near future, two radio telescopes will be installed in the Indonesian region. These telescopes are proposed to be integrated into the existing Very Long Baseline Interferometry (VLBI) network both for astronomical and geodetical purposes. Here we simulate the impact of the inclusion of the future Indonesian antennas to the estimates of Earth Orientation Parameters and the station position. The simulation was performed in two types of VLBI sessions. First, we analyse the contribution of Indonesian antennas to the existing intensive session INT3 (IN320-314), which focuses on the estimation of dUT1. We found that the addition of Indonesian antennas has reduced the estimated dUT1 repeatability value by about 25%. Next, we simulate the 24-hour session by considering two existing network configurations, which are R4 (R4934) and AOV (AOV049). Overall we found that the addition of Indonesian antennas to each network configuration decreases the repeatability value of the Earth Orientation Parameter by about 20%. Meanwhile, the repeatability value of station position is reduced up to 12%. This reduction is already achieved even when we include only one Indonesian antenna