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Last name: CHAUVINEAU
First name: Bertrand
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Brans–Dicke gravity admits spherical solutions describing naked singularities rather than black holes. Depending on some parameters entering such a solution, stable circular orbits exist for all radii. One shows that, despite the fact a naked singularity is an infinite redshift location, the far observed orbital motion frequency is unbounded...
A new method is proposed, that establishes a one to one correspondance between the whole set of static axially symmetric vacuum general relativity solutions and a specific class of stationary axially symmetric scalar-Einstein (Rab=∂aφ∂bφ) solutions for any mass and angular momentum. The method explicitly takes advantage of the Kerr metric Ricci...
International audience
International audience
International audience
One points out that a metric used as a General Relativity filled by a massless scalar φ solution in several studies, and that would have been a generalization of the Janis-Newman-Winicour spherical solution to the rotating case, does not solve the corresponding Einstein equation Rab=∂aφ∂bφ. As a consequence, the (conformally related)...
One reconsiders strong lensing by the naked singularity that enters the Fisher/Janis-Newman-Winicour (F/JNW) scalar-tensor spacetime, characterized by a mass m and a scalar parameter b. One mainly focuses on the strongly scalarized case where the bending of light experiments a maximum value, resulting in the formation of a b dependent caustic...
One provides the exact expressions of the (β,γ,δ) post-Newtonian (PN) parameters in terms of the total energy and pressure integrals of a static spherical star, acting as the source of the gravitational field in Bergmann-Wagoner-Nordtvedt scalar-tensor gravity. This fixes the 2PN behavior of remote light rays in terms of the source's internal...
International audience
We present an exact static spherisymmetric solution for the Brans-Dicke action sourced by a self-gravitating massless Klein-Gordon helicity-0 field. In contrast to the Maxwell electromagnetic field, a Klein-Gordon field possesses an energy-momentum tensor with $\textit{non-vanishing trace}$. Upon a Weyl mapping into the Einstein frame, the...
The Brans Class I solution in Brans-Dicke gravity is a staple in the study of gravitational theories beyond General Relativity. Discovered in 1961, it describes the exterior vacuum of a spherical Brans-Dicke star and is characterized by two adjustable parameters. Surprisingly, the relationship between these parameters and the properties of the...
International audience
International audience
Scalar–tensor (ST) gravity is considered in the case where the scalar is an external field. We show that general relativity (GR) and usual ST gravity are particular cases of the external scalar–tensor (EST) gravity. It is shown with a particular cosmological example that it is possible to join a part of a GR solution to a part of a ST one such...
The joint ESA/NASA LISA mission consists in three spacecraft on heliocentric orbits, flying in a triangular formation of 5 Mkm each side, linked by infrared optical beams. The aim of the mission is to detect gravitational waves in a low frequency band. For properly processing the science data, the propagation delays between spacecraft must be...
In the context of star capture by a black hole, a new noticeable difference between Brans-Dicke theory and general relativity gravitational radiation is pointed out. This feature stems from the non-stationarity of the black hole state, barring Hawking's theorem.
The series of measurements of the Solar radius at CALERN site of the observatoire de la Côte d'Azur (OCA) spans about 30 years. Measurements of the Sun were first achieved visually by the same single observer, then gradually grew more man-independent with the use of CCD acquisitions. The DORAYSOL instrument was designed and built up to keep...
Context. In 2015, the International Astronomical Union (IAU) passed Resolution B3, which defined a set of nominal conversion constants for stellar and planetary astronomy. Resolution B3 defined a new value of the nominal solar radius (R N = 695 700 km) that is different from the canonical value used until now (695 990 km). The nominal solar...
Based on a fully passive space segment, the lunar laser ranging experiment is the last of the Apollo Lunar Surface Experiments Package to operate. Observations from the Grasse lunar laser ranging station have been made on a daily basis since the first echoes obtained in 1981. In this paper, first, we review the principle and the technical...
Based on a fully passive space segment, the Lunar Laser Ranging experiment is the last of the Apollo Lunar Surface Experiments Package to operate. Observations from Grasse Lunar Laser Ranging station have been realized on a daily basis since the first echoes obtained in 1981. We will give a brief summary of the progress made at Grasse Laser...
Based on a fully passive space segment, the lunar laser ranging experiment is the last of the Apollo Lunar Surface Experiments Package to operate. Observations from the Grasse lunar laser ranging station have been made on a daily basis since the first echoes obtained in 1981. In this paper, first, we review the principle and the technical...
Ground based solar observations are strongly affected by optical turbulence. The concept of a new instrument which allows to measure both spatial and temporal parameters of atmospheric turbulence has been proposed in the late 90s. The instrument MISOLFA (Moniteur d'Images Solaire Franco-Algérien) is based on this concept and has been developped...