Sergi R. Hildebrandt

FastCam: a new lucky imaging instrument for medium-sized telescopes

FastCam is an instrument jointly developed by the Spanish Instituto de Astrofísica de Canarias and the Universidad Politécnica de Cartagena designed to obtain high spatial resolution images in the optical wavelength range from ground-based telescopes. The instrument consists of a very low noise and very fast readout speed EMCCD camera capable of reaching the diffraction limit of medium-sized telescopes from 500 to 850 nm. FastCam incorporates a FPGAs-based device to save and evaluate those images minimally disturbed by atmospheric turbulence in real time. The undisturbed images represent a small fraction of the observations. Therefore, a special software package has been developed to extract, from cubes of tens of thousands of images, those with better quality than a given level. This is done in parallel with the data acquisition at the telescope. After the first tests in the laboratory, FastCam has been successfully tested in three telescopes: the 1.52-meter TCS (Teide Observatory), the 2.5-meter NOT, and the 4.2-meter WHT (Roque de los Muchachos Observatory). The theoretical diffraction limit of each telescope has been reached in the I band (850 nm) -0.15, 0.08 and 0.05 arcsec, respectively-, and similar resolutions have been also obtained in the V and R bands. Future work will include the development of a new instrument for the 10.4-meter GTC telescope on La Palma.

Regular Sources of the Kerr-Schild class for Rotating and Nonrotating Black Hole Solutions

A unified approach to regular interiors of black holes with smooth matter distributions in the core region is given. The approach is based on a class of Kerr-Schild metrics representing minimal deformations of the Kerr-Newman solution, and allows us to give a common treatment for (charged and uncharged) rotating and nonrotating black holes. It is shown that the requirement of smoothness of the source constraints the structure of the core region in many respects: in particular, for Schwarzschild holes a de Sitter core can be selected, which is surrounded by a smooth shell giving a leading contribution to the total mass of the source. In the rotating, noncharged case the source has a similar structure, taking the form of a (anisotropic and rotating) de Sitter-like core surrounded by a rotating elliptic shell. The Kerr singular ring is regularized by anisotropic matter rotating in the equatorial plane, so that the negative sheet of the Kerr geometry is absent. In the charged case the sources take the form of “bags”, which can have de Sitter or anti de Sitter interiors and a smooth domain wall boundary, with a tangential stress providing charge confinement. The ADM and Tolman relations are used to calculate the total mass of the sources.

The Family of regular interiors for nonrotating black holes with T0(0)=T1(1)

We find the general solution for the spacetimes describing the interior of static black holes with an equation of state of the type

Kerr–Schild Symmetries

{T}_{0}^{0}{=T}_{1}^{1}

Aligned electromagnetic excitations of a black hole and their impact on its quantum horizon

(T

Rotating “black holes” with holes in the horizon

being the stress-energy tensor). This form is the one expected from taking into account different quantum effects associated with strong gravitational fields. We recover all the particular examples found in the literature. We remark that all the solutions found follow the natural scheme of an interior core linked smoothly with the exterior solution by a transient region. We also discuss their local energy properties and give the main ideas involved in a possible generalization of the scheme in order to include other realistic types of sources.

High spatial resolution and high contrast optical speckle imaging with FASTCAM at the ORM

We study continuous groups of generalized Kerr–Schild transformations and the vector fields that generate them in any n-dimensional manifold with a Lorentzian metric. We prove that all these vector fields can be intrinsically characterized and that they constitute a Lie algebra if the null deformation direction is fixed. The properties of these Lie algebras are briefly analyzed and we show that they are generically finite-dimensional but that they may have infinite dimension in some relevant situations. The most general vector fields of the above type are explicitly constructed for the following cases: any two-dimensional metric, the general spherically symmetric metric and deformation direction, and the flat metric with parallel or cylindrical deformation directions.

Review: Kerr-Schild and Generalized Metric Motions

The potential of combining Adaptive Optics (AO) and Lucky Imaging (LI) to achieve high precision astrometry and differential photometry in the optical is investigated by condu cting observations of the close 0: 1 brown dwarf binary GJ569Bab. We took 50000 I-band images with our LI instrument FastCam attached to NAOMI, the 4.2-m William Herschel Telescope (WHT) AO facility. In order to extract the most of the astrometry and photometry of the GJ569Bab system we have resorted to a PSF fitting technique us ing the primary star GJ569A as a suitable PSF reference which exhibits an I-band magnitude of 7: 78�0: 03. The AO+LI observations at WHT were able to resolve the binary system GJ569Bab located at 4: 00 92� 0: 05 from GJ569A. We measure a separation of 98: 4�1: 1 mas and I-band magnitudes of 13: 86�0: 03 and 14: 48�0: 03 and I− J colors of 2.72� 0.08 and 2.83� 0.08 for the Ba and Bb components, respectively. Our study rules out the presence of any other companion to GJ569A down to magnitude I�17 at distances larger than 1 00 . The I− J colors measured are consistent with M8.5-M9 spectral types for the Ba and Bb components. The available dynamical, photometric and spectroscopic data are consistent with a binary system with Ba being slightly (10-20%) more massive than Bb. We obtain new orbital parameters which are in good agreement with those in the literature.

A Physical Application of Kerr-Schild Groups

Abstract We show that elementary aligned electromagnetic excitations of black holes, as coming from exact Kerr–Schild solutions, represent light-like beams pulses which have a very strong back reaction on the metric and change the topology of the horizon. Based on Yorks proposal, that elementary deformations of the BH horizon are related with elementary vacuum fluctuations, we analyze deformations of the horizon caused by the beam-like vacuum fluctuations and obtain a very specific feature of the topological deformations of the horizon. In particular, we show how the beams pierce the horizon, forming a multitude of micro-holes in it. A conjecture is taken into consideration, that these specific excitations are connected with the conformal-analytic properties of the Kerr geometry and are at the base of the emission mechanism.