arXiv subjects

Antonio Pérez-Garrido

Publications and source records attributed to Antonio Pérez-Garrido.

14 recordsLinked to original sources

arXiv2026

Scattering matrix elements and energy spectrum of one-dimensional hybrid PT-symmetric finite systems

In this work, we provide a complete description of the scattering matrix elements and electron energy spectrum in one dimensional PT-symmetric hybrid finite systems, using the characteristic determinant approach. We present an analytical formulation of the problem and obtain a closed-form expression for the energy spectrum of the system, consisting of a region of real potential (passive region) surrounded by regions of gain and loss on the left and right, respectively. It has been shown that under certain conditions and a specific ratio between the real and imaginary parts of the complex potentials, it is possible to find analytical expressions for the spectral singularities at which the scattering matrix elements of the hybrid structure tend to infinity at a specific real energy. Within the framework of the same approach, we present a compact analytical expression for the quantization condition that determines the energy spectrum of a model corresponding to the placement of a rigid lattice within a finite-sized box.

cond-mat.mes-hall↗

arXiv2024

Tunneling time in coupled-channel systems

In present work, we present a couple-channel formalism for the description of tunneling time of a quantum particle through a composite compound with multiple energy levels or a complex structure that can be reduced to a quasi-one-dimensional multiple-channel system.

cond-mat.other↗

arXiv2023

Tunneling time and Faraday/Kerr effects in $\mathcal{PT}$-symmetric systems

We review the generalization of tunneling time and anomalous behaviour of Faraday and Kerr rotation angles in parity and time ($\mathcal{P}\mathcal{T}$)-symmetric systems. Similarities of two phenomena are discussed, both exhibit a phase transition-like anomalous behaviour in certain range of model parameters. Anomalous behaviour of tunneling time and Faraday/Kerr angles in $\mathcal{P}\mathcal{T}$-symmetric systems is caused by the motion of poles of scattering amplitudes in energy/frequency complex plane.

cond-mat.other↗

arXiv2018

The TP3-WFS: a new guy in town

The TP3-WFS (Two Pupil Plane Positions Wavefront Sensor) is, to the best of the authors' knowledge, the first physical implementation of the geometrical wavefront reconstruction algorithm that has been tested in a telescope as part of an actual AO-enabled instrument. The main advantage of this algorithm is that it theoretically provides a fairly good reconstruction accuracy even under very low levels of light, in the order of a few hundreds of photons. This paper presents the first control-related results obtained at the William Herschel Telescope (WHT). Such results demonstrate the feasibility of this novel WFS as part of a real-time AO control loop.

astro-ph.IM↗

arXiv2017

Completing the puzzle: AOLI full-commissioning fresh results and AIV innovations

The Adaptive Optics Lucky Imager (AOLI) is a new instrument designed to combine adaptive optics (AO) and lucky imaging (LI) techniques to deliver high spatial resolution in the visible, 20 mas, from ground-based telescopes. Here we present details of the integration and verification phases explaining the defiance that we have faced and the innovative and versatile solution of modular integration for each of its subsystems that we have developed. Modularity seems a clue key for opto-mechanical integration success in the extremely-big telescopes era. We present here the very fresh preliminary results after its first fully-working observing run on the WHT.

astro-ph.IM↗

arXiv2017

A new L5 brown dwarf member of the Hyades cluster with chromospheric activity

Our aim is to identify brown dwarf members of the nearby Hyades open star cluster to determine the photometric and spectroscopic properties of brown dwarfs at moderately old ages and extend the knowledge of the substellar mass function of the cluster. We cross-matched the 2MASS and AllWISE public catalogues and measured proper motions to identify low-mass stars and brown dwarf candidates in an area of radius eight degrees around the central region of the Hyades cluster. We identified objects with photometry and proper motions consistent with cluster membership. For the faintest ($J$\,=\,17.2 mag) most promising astrometric and photometric low-mass candidate 2MASS\,J04183483$+$2131275\@, with a membership probability of 94.5\%, we obtained low-resolution (R\,=\,300--1000) and intermediate-resolution (R\,=\,2500) spectroscopy with the 10.4m Gran Telescopio Canarias. From the low-resolution spectra we determined a L5.0$\pm$0.5 spectral type, consistent with the available photometry. In the intermediate dispersion spectrum we detected H$α$ in emission (marginally resolved with a full width half maximum of $\sim$2.8 Å) and determined a $\log ($L$_{\rm{H}α}$/L$_{\rm bol})=-6.0$ dex. From H$α$ we obtained a radial velocity of 38.0$\pm$2.9 km$\cdot$s$^{-1}$, which combined with the proper motion leads to space velocities which are fully consistent with membership in the Hyades cluster.

astro-ph.SR↗

arXiv2016

An instrumental puzzle: the modular integration of AOLI

The Adaptive Optics Lucky Imager, AOLI, is an instrument developed to deliver the highest spatial resolution ever obtained in the visible, 20 mas, from ground-based telescopes. In AOLI a new philosophy of instrumental prototyping has been applied, based on the modularization of the subsystems. This modular concept offers maximum flexibility regarding the instrument, telescope or the addition of future developments.

astro-ph.IM↗

arXiv2016

Commissioning and First Observations with Wide FastCam at the Telescopio Carlos Sánchez

The FastCam instrument platform, jointly developed by the IAC and the UPCT, allows, in real-time, acquisition, selection and storage of images with a resolution that reaches the diffraction limit of medium-sized telescopes. FastCam incorporates a specially designed software package to analyse series of tens of thousands of images in parallel with the data acquisition at the telescope. Wide FastCam is a new instrument that, using the same software for data acquisition, does not look for lucky imaging but fast observations in a much larger field of view. Here we describe the commissioning process and first observations with Wide FastCam at the Telescopio Carlos Sánchez (TCS) in the Observatorio del Teide.

astro-ph.IM↗

arXiv2015

Discovery of a young planetary mass companion to the nearby M dwarf VHS J125601.92-125723.9

In a search for common proper motion companions using the VISTA Hemisphere Survey and 2MASS catalogs we have identified a very red (J-Ks=2.47 mag) late-L dwarf companion of a previously unrecognized M dwarf VHS J125601.92-125723.9, located at a projected angular separation of 8.06"+/-0.03". From low-resolution optical and near-IR spectroscopy we classified the primary and the companion as an M7.5+/-0.5 and L7+/-1.5, respectively. The primary shows weaker alkali lines than field dwarfs of similar spectral type, but still consistent with either a high-gravity dwarf or a younger object of hundreds of millions of years. The secondary shows spectral features characteristic for low surface gravity objects at ages below several hundred Myr, like the triangular shape of the H-band continuum and alkali lines weaker than in field dwarfs of the same spectral type. The absence of lithium in the atmosphere of the primary and the likely membership to the Local Association allowed us to constrain the age of the system to the range of 150-300 Myr. We report a measurement of the trigonometric parallax pi=78.8+/-6.4 mas, which translates into a distance of 12.7+/-1.0 pc; the pair thus has a projected physical separation of 102+/-9 AU. We derived the Lbol of the components and compared them with theoretical evolutionary models to estimate the masses and effective temperatures. For the primary, we determined log(Lbol/LSun)=-3.14+/-0.10, and a mass of 73 (+20,-15} MJup at the boundary between stars and brown dwarfs and Teff of 2620+/-140 K. For the companion we obtained log(Lbol/LSun)=-5.05+/-0.22 and a mass of 11.2 (+9.7,-1.8) MJup placing it near the deuterium-burning mass limit. The effective temperature derived from evolutionary models is 880 (+140,-110) K, about 400-700 K cooler than expected for field late-L dwarfs.

astro-ph.EP↗

arXiv2014

High-Resolution Imaging in the Visible on Large Ground-Based Telescopes

Lucky Imaging combined with a low order adaptive optics system has given the highest resolution images ever taken in the visible or near infrared of faint astronomical objects. This paper describes a new instrument that has already been deployed on the WHT 4.2m telescope on La Palma, with particular emphasis on the optical design and the predicted system performance. A new design of low order wavefront sensor using photon counting CCD detectors and multi-plane curvature wavefront sensor will allow virtually full sky coverage with faint natural guide stars. With a 2 x 2 array of 1024 x 1024 photon counting EMCCDs, AOLI is the first of the new class of high sensitivity, near diffraction limited imaging systems giving higher resolution in the visible from the ground than hitherto been possible from space.

astro-ph.IM↗

arXiv2013

Delimiting Maximal Kissing Configurations in Four Dimensions

How many unit $n-$dimensional spheres can simultaneously touch or kiss a central $n-$dimensional unit sphere? Beyond mathematics this question has implications for fields such as cryptography and the structure of biologic and chemical macromolecules. The kissing number is only known for dimensions 1-4, 8 and 24 (2, 6, 12, 24, 240, 19650, respectively) and only particularly obvious for dimensions one and two. Indeed, in four dimensions it is not even known if Platonic polytope unique to that dimension known as the 24-cell is the unique kissing configuration. We have not been able to prove that the 24-cell is unique, but, using a physical approach utilizing the hopf map from four to three dimensions, we for the first time delimit the possible other configurations which could be kissing in four dimensions.

math.MG↗

arXiv2012

High-resolution optical imaging of the core of the globular cluster M15 with FastCam

We present high-resolution I-band imaging of the core of the globular cluster M15 obtained at the 2.5 m Nordic Optical Telescope with FastCam, a low readout noise L3CCD based instrument. Short exposure times (30 ms) were used to record 200000 images (512 x 512 pixels each) over a period of 2 hours 43 min. The lucky imaging technique was then applied to generate a final image of the cluster centre with FWHM ~ 0".1 and 13" x 13" FoV. We obtained a catalogue of objects in this region with a limiting magnitude of I=19.5. I-band photometry and astrometry are reported for 1181 stars. This is the deepest I-band observation of the M15 core at this spatial resolution. Simulations show that crowding is limiting the completeness of the catalogue. At shorter wavelengths, a similar number of objects has been reported using HST/WFPC observations of the same field. The cross-match with the available HST catalogues allowed us to produce colour-magnitude diagrams where we identify new Blue Straggler star candidates and previously known stars of this class.

astro-ph.GA↗

arXiv2007

A low mass cluster of extremely red galaxies at z=1.10 in the GOODS Southern Field

We have studied the spatial clustering of high redshift (z > 1) extremely red objects (EROs) as a function of photometric redshift in the GOODS Southern Field using public data. A remarkable overdensity of extremely red galaxies (I-Ks > 4) is found at an average photometric redshift z=1.10. Nine objects (six are EROs) within 50 arcsec of the brightest infrared galaxy in this overdensity present spectroscopic redshifts in the range 1.094 < z < 1.101 with a line-of-sight velocity dispersion of 433 km/s typical of an Abell richness class R=0 cluster. Other potential members of this cluster, designated as GCL J0332.2-2752, have been identified using photometric redshifts and the galaxy density profile studied as a function of radius. The mass of the cluster is preliminary estimated at M ~ 5-7 x 10^{13} M_{\sun}. Using available Chandra data, we limit the rest-frame X-ray luminosity of the cluster to less than L_X = 7.3 x 10^{42} erg/s (0.5-2.0 keV). This low-mass, low L_X cluster at z > 1 shows the potential of EROs to trace clusters of galaxies at high redshift.

astro-ph↗

arXiv1998

Simulations of Two-Dimensional Melting on the Surface of a Sphere

We have simulated a system of classical particles confined on the surface of a sphere interacting with a repulsive $r^{-12}$ potential. The same system simulated on a plane with periodic boundary conditions has van der Waals loops in pressure-density plots which are usually interpreted as evidence for a first order melting transition, but on the sphere such loops are absent. We also investigated the structure factor and from the width of the first peak as a function of density we can show that the growth of the correlation length is consistent with KTHNY theory. This suggests that simulations of two dimensional melting phenomena are best performed on the surface of a sphere.

cond-mat.stat-mech↗