4,242 research outputs found
Sub-Microarcsecond Astrometry and New Horizons in Relativistic Gravitational Physics
Attaining the limit of sub-microarcsecond optical resolution will completely
revolutionize fundamental astrometry by merging it with relativistic
gravitational physics. Beyond the sub-microarcsecond threshold, one will meet
in the sky a new population of physical phenomena caused by primordial
gravitational waves from early universe and/or different localized astronomical
sources, space-time topological defects, moving gravitational lenses, time
variability of gravitational fields of the solar system and binary stars, and
many others. Adequate physical interpretation of these yet undetectable
sub-microarcsecond phenomena can not be achieved on the ground of the
"standard" post-Newtonian approach (PNA), which is valid only in the near-zone
of astronomical objects having a time-dependent gravitational field. We
describe a new, post-Minkowskian relativistic approach for modeling astrometric
observations having sub-microarcsecond precision and briefly discuss the
light-propagation effects caused by gravitational waves and other phenomena
related to time-dependent gravitational fields. The domain of applicability of
the PNA in relativistic space astrometry is explicitly outlined.Comment: 5 pages, the talk given at the IAU Colloquium 180 "Towards Models and
Constants for Sub-Microarcsecond Astrometry", Washington DC, March 26 - April
2, 200
PEXO : a global modeling framework for nanosecond timing, microsecond astrometry, and μm/s radial velocities
54 pages, 2 tables, 19 figures, accepted for publication in ApJS, PEXO is available at https://github.com/phillippro/pexoThe ability to make independent detections of the signatures of exoplanets with complementary telescopes and instruments brings a new potential for robust identification of exoplanets and precision characterization. We introduce PEXO, a package for Precise EXOplanetology to facilitate the efficient modeling of timing, astrometry, and radial velocity data, which will benefit not only exoplanet science but also various astrophysical studies in general. PEXO is general enough to account for binary motion and stellar reflex motions induced by planetary companions and is precise enough to treat various relativistic effects both in the solar system and in the target system. We also model the post-Newtonian barycentric motion for future tests of general relativity in extrasolar systems. We benchmark PEXO with the pulsar timing package TEMPO2 and find that PEXO produces numerically similar results with timing precision of about 1 ns, space-based astrometry to a precision of 1{\mu}as, and radial velocity of 1 {\mu}m/s and improves on TEMPO2 for decade-long timing data of nearby targets, due to its consideration of third-order terms of Roemer delay. PEXO is able to avoid the bias introduced by decoupling the target system and the solar system and to account for the atmospheric effects which set a practical limit for ground-based radial velocities close to 1 cm/s. Considering the various caveats in barycentric correction and ancillary data required to realize cm/s modeling, we recommend the preservation of original observational data. The PEXO modeling package is available at GitHub (https://github.com/phillippro/pexo).Peer reviewe
Relativistic gravitational deflection of light and its impact on the modeling accuracy for the Space Interferometry Mission
We study the impact of relativistic gravitational deflection of light on the
accuracy of future Space Interferometry Mission (SIM). We estimate the
deflection angles caused by the monopole, quadrupole and octupole components of
gravitational fields for a number of celestial bodies in the solar system. We
observe that, in many cases, the magnitude of the corresponding effects is
significantly larger than the 1 uas accuracy expected from SIM. This fact
argues for the development of a relativistic observational model for the
mission that would account for the influence of both static and time-varying
effects of gravity on light propagation. Results presented here are different
from the ones obtained elsewhere by the fact that we specifically account for
the differential nature of the future SIM astrometric measurements. We also
obtain an estimate for the accuracy of possible determination of the
Eddington's parameter \gamma via SIM global astrometric campaign; we conclude
that accuracy of ~7 x 10^{-6} is achievable via measurements of deflection of
light by solar gravity.Comment: revtex4, 20 pages, 9 figures, 13 table
The Ray Tracing Analytical Solution within the RAMOD framework. The case of a Gaia-like observer
This paper presents the analytical solution of the inverse ray tracing
problem for photons emitted by a star and collected by an observer located in
the gravitational field of the Solar System. This solution has been conceived
to suit the accuracy achievable by the ESA Gaia satellite (launched on December
19, 2013) consistently with the measurement protocol in General relativity
adopted within the RAMOD framework. Aim of this study is to provide a general
relativistic tool for the science exploitation of such a revolutionary mission,
whose main goal is to trace back star directions from within our local curved
space-time, therefore providing a three-dimensional map of our Galaxy. The
results are useful for a thorough comparison and cross-checking validation of
what already exists in the field of Relativistic Astrometry. Moreover, the
analytical solutions presented here can be extended to model other measurements
that require the same order of accuracy expected for Gaia.Comment: 29 pages, 1 figur
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