G. Scarpetta

Generalized Uncertainty Principle from Quantum Geometry

The generalized uncertainty principle of string theory is derived in the frameworkof quantum geometry by taking into account the existence of an upper limit onthe acceleration of massive particles.

Strong Field Limit of Black Hole Gravitational Lensing

We give the formulation of the gravitational lensing theory in the strong field limit for a Schwarzschild black hole as a counterpart to the weak field approach. It is possible to expand the full black hole lens equation to work a simple analytical theory that describes the physics in the strong field limit at a high accuracy degree. In this way, we derive compact and reliable mathematical formulae for the position of additional critical curves, relativistic images and their magnification, arising in this limit.

High-precision photometry by telescope defocussing - II. The transiting planetary system WASP-4

We present high-precision photometry of two transit events of the extrasolar planetary system WASP-5, obtained with the Danish 1.54 m telescope at ESO La Silla. In order to minimise both random and flat-fielding errors, we defocussed the telescope so its point spread function approximated an annulus of diameter 40 pixels (16 00 ). Data reduction was undertaken using standard aperture photometry plus an algorithm for optimally combining the ensemble of comparison stars. The resulting light curves have point-to-point scatters of 0.50 mmag for the first transit and 0.59 mmag for the second. We construct detailed signal to noise calculations for defocussed photometry, and apply them to our observations. We model the light curves with the JKTEBOP code and combine the results with tabulated predictions from theoretical stellar evolutionary models to derive the physical properties of the WASP-5 system. We find that the planet has a mass of Mb = 1.637± 0.075± 0.033 MJup, a radius of Rb = 1.171± 0.056± 0.012 RJup, a large surface gravity of gb = 29.6± 2.8 m s i2 and a density of rb = 1.02±0.14±0.01 rJup (statistical and systematic uncertainties). The planet’s high equilibrium temperature of Teq = 1732± 80 K, makes it a good candidate for detecting secondary eclipses.

Analytic Kerr black hole lensing for equatorial observers in the strong deflection limit

In this paper we present an analytical treatment of gravitational lensing by Kerr black holes in the limit of very large deflection angles, restricting to observers in the equatorial plane. We accomplish our objective starting from the Schwarzschild black hole and adding corrections up to second order in the black hole spin. This is sufficient to provide a full description of all caustics and the inversion of lens mapping for sources near them. On the basis of these formulae we argue that relativistic images of low mass x-ray binaries around Sgr

Dynamics of relativistic particles with Lagrangians dependent on acceleration

{\mathrm{A}}^{*}

Kerr black hole lensing for generic observers in the strong deflection limit

are very likely to be seen by future x-ray interferometry missions.

High-precision photometry by telescope defocusing - III. The transiting planetary system WASP-2★: High-precision defocused photometry of WASP-2

Models of relativistic particles with Lagrangians L(k1), depending on the curvature of the worldline k1, are considered. By making use of the Frenet basis, the equations of motion are reformulated in terms of the principal curvatures of the worldline. It is shown that for arbitrary Lagrangian function L(k1) these equations are completely integrable, i.e., the principal curvatures are defined by integrals. The constants of integration are the particle mass and its spin. The developed method is applied to the study of a model of a relativistic particle with maximal proper acceleration, whose Lagrangian is uniquely determined by a modified form of the invariant relativistic interval. This model gives us an example of a consistent relativistic dynamics obeying the principle of a superiorly limited value of the acceleration, advanced recently.

High-precision photometry by telescope defocusing – IV. Confirmation of the huge radius of WASP-17 b†

We generalize our previous work on gravitational lensing by a Kerr black hole in the strong deflection limit, removing the restriction to observers on the equatorial plane. Starting from the Schwarzschild solution and adding corrections up to the second order in the black hole spin, we perform a complete analytical study of the lens equation for relativistic images created by photons passing very close to a Kerr black hole. We find out that, to the lowest order, all observables (including shape and shift of the black hole shadow, caustic drift and size, images position and magnification) depend on the projection of the spin on a plane orthogonal to the line of sight. In order to break the degeneracy between the black hole spin and its inclination relative to the observer, it is necessary to push the expansion to higher orders. In terms of future very-long base line interferometry observations, this implies that very accurate measures are needed to determine these two parameters separately.

Neutrino optics and oscillations in gravitational fields

We present high-precision photometry of three transits of t he extrasolar planetary system WASP-2, obtained by defocussing the telescope, and achievi ng point-to-point scatters of between 0.42 and 0.73 mmag. These data are modelled using the JKTEBOP code, and taking into account the light from the recently-discovered faint s tar close to the system. The physical properties of the WASP-2 system are derived using tabulated pr ictions from five different sets of stellar evolutionary models, allowing both statist ical and systematic errorbars to be specified. We find the mass and radius of the planet to be M = 0.847± 0.038± 0.024MJup andRb = 1.044± 0.029± 0.015RJup. It has a low equilibrium temperature of 1280± 21K, in agreement with a recent finding that it does not have an atmo spheric temperature inversion. The first of our transit datasets has a scatter of only 0.42 mma g with respect to the best-fitting light curve model, which to our knowledge is a record for grou nd-based observations of a transiting extrasolar planet.

Microlensing search towards M31

We present photometric observations of four transits in the WASP-17 planetary system, obtained using telescope defocusing techniques and with scatters reaching 0.5?mmag per point. Our revised orbital period is 4.0 +/- 0.6?s longer than previous measurements, a difference of 6.6s, and does not support the published detections of orbital eccentricity in this system. We model the light curves using the jktebop code and calculate the physical properties of the system by recourse to five sets of theoretical stellar model predictions. The resulting planetary radius, Rb = 1.932 +/- 0.052 +/- 0.010?RJup (statistical and systematic errors, respectively), provides confirmation that WASP-17?b is the largest planet currently known. All 14 planets with radii measured to be greater than 1.6?RJup are found around comparatively hot (Teff > 5900?K) and massive (MA > 1.15?M?) stars. Chromospheric activity indicators are available for eight of these stars, and all imply a low activity level. The planets have small or zero orbital eccentricities, so tidal effects struggle to explain their large radii. The observed dearth of large planets around small stars may be natural but could also be due to observational biases against deep transits, if these are mistakenly labelled as false positives and so not followed up.