arXiv subjects

P. Bruno

Publications and source records attributed to P. Bruno.

At least 37 records · Page 2Linked to original sources

arXiv2017

New spectro-photometric characterization of the substellar object HR 2562 B using SPHERE

HR2562 is an F5V star located at ~33 pc from the Sun hosting a substellar companion that was discovered using the GPI instrument. The main objective of the present paper is to provide an extensive characterisation of the substellar companion, by deriving its fundamental properties. We observed HR 2562 with the near-infrared branch (IFS and IRDIS) of SPHERE at the VLT. During our observations IFS was operating in the YJ band, while IRDIS was observing with the $H$ broad-band filter. The data were reduced with the dedicated SPHERE GTO pipeline, which is custom-designed for this instrument. On the reduced images, we then applied the post-processing procedures that are specifically prepared to subtract the speckle noise. The companion is clearly detected in both IRDIS and IFS datasets. We obtained photometry in three different spectral bands. The comparison with template spectra allowed us to derive a spectral type of T2-T3 for the companion. Using both evolutionary and atmospheric models we inferred the main physical parameters of the companion obtaining a mass of 32+/-14$~MJup, T_{eff}=1100+/-200 K and log(g)=4.75+/-0.41.

astro-ph.EP↗

arXiv2017

Dynamical models to explain observations with SPHERE in planetary systems with double debris belts

A large number of systems harboring a debris disk show evidence for a double belt architecture. One hypothesis for explaining the gap between the belts is the presence of one or more planets dynamically carving it. This work aims to investigate this scenario in systems harboring two components debris disks. All the targets in the sample were observed with the SPHERE instrument which performs high-contrast direct imaging. Positions of the inner and outer belts were estimated by SED fitting of the infrared excesses or, when available, from resolved images of the disk. Very few planets have been observed so far in debris disks gaps and we intended to test if such non-detections depend on the observational limits of the present instruments. This aim is achieved by deriving theoretical predictions of masses, eccentricities and semi-major axes of planets able to open the observed gaps and comparing such parameters with detection limits obtained with SPHERE. The relation between the gap and the planet is due to the chaotic zone around the orbit of the planet. The radial extent of this zone depends on the mass ratio between the planet and the star, on the semi-major axis and on the eccentricity of the planet and it can be estimated analytically. We apply the formalism to the case of one planet on a circular or eccentric orbit. We then consider multi-planetary systems: 2 and 3 equal-mass planets on circular orbits and 2 equal-mass planets on eccentric orbits in a packed configuration. We then compare each couple of values (M,a), derived from the dynamical analysis of single and multiple planetary models, with the detection limits obtained with SPHERE. Our results show that the apparent lack of planets in gaps between double belts could be explained by the presence of a system of two or more planets possibly of low mass and on an eccentric orbits whose sizes are below the present detection limits.

astro-ph.EP↗

arXiv2017

Orbiting a binary: SPHERE characterisation of the HD 284149 system

In this paper we present the results of the SPHERE observation of the HD 284149 system, aimed at a more detailed characterisation of both the primary and its brown dwarf companion. We observed HD 284149 in the near-infrared with SPHERE, using the imaging mode (IRDIS+IFS) and the long-slit spectroscopy mode (IRDIS-LSS). The data were reduced using the dedicated SPHERE pipeline, and algorithms such as PCA and TLOCI were applied to reduce the speckle pattern. The IFS images revealed a previously unknown low-mass (~0.16$M_{\odot}$) stellar companion (HD 294149 B) at ~0.1$^{\prime\prime}$, compatible with previously observed radial velocity differences, as well as proper motion differences between Gaia and Tycho-2 measurements. The known brown dwarf companion (HD 284149 b) is clearly visible in the IRDIS images. This allowed us to refine both its photometry and astrometry. The analysis of the medium resolution IRDIS long slit spectra also allowed a refinement of temperature and spectral type estimates. A full reassessment of the age and distance of the system was also performed, leading to more precise values of both mass and semi-major axis. As a result of this study, HD 284149 ABb therefore becomes the latest addition to the (short) list of brown dwarfs on wide circumbinary orbits, providing new evidence to support recent claims that object in such configuration occur with a similar frequency to wide companions to single stars.

astro-ph.EP↗

arXiv2016

Upper limits for Mass and Radius of objects around Proxima Cen from SPHERE/VLT

The recent discovery of an earth-like planet around Proxima Centauri has drawn much attention to this star and its environment. We performed a series of observations of Proxima Centauri using SPHERE, the planet finder instrument installed at the ESO Very Large Telescope UT3, using its near infrared modules, IRDIS and IFS. No planet was directly detected but we set upper limits on the mass up to 7 au exploiting the AMES-COND models. Our IFS observations reveal that no planet more massive than ~6-7 M Jup can be present within 1 au. The dual band imaging camera IRDIS also enables us to probe larger separations than the other techniques like the radial velocity or astrometry. We obtained mass limits of the order of 4 M Jup at separations of 2 au or larger representing the most stringent mass limits at separations larger than 5 au available at the moment. We also did an attempt to estimate the radius of possible planets around Proxima using the reflected light. Since the residual noise for this observations are dominated by photon noise and thermal background, longer exposures in good observing conditions could further improve the achievable contrast limit.

astro-ph.EP↗

arXiv2014

AtmoHEAD 2013 workshop / Atmospheric Monitoring for High-Energy Astroparticle Detectors

A 3-day international workshop on atmospheric monitoring and calibration for high-energy astroparticle detectors, with a view towards next-generation facilities. The atmosphere is an integral component of many high-energy astroparticle detectors. Imaging atmospheric Cherenkov telescopes and cosmic-ray extensive air shower detectors are the two instruments driving the rapidly evolving fields of very-high- and ultra-high-energy astrophysics. In these instruments, the atmosphere is used as a giant calorimeter where cosmic rays and gamma rays deposit their energy and initiate EASs; it is also the medium through which the resulting Cherenkov light propagates. Uncertainties in real-time atmospheric conditions and in the fixed atmospheric models typically dominate all other systematic errors. With the improved sensitivity of upgraded IACTs such as H.E.S.S.-II and MAGIC-II and future facilities like the Cherenkov Telescope Array (CTA) and JEM-EUSO, statistical uncertainties are expected to be significantly reduced, leaving the atmosphere as the limiting factor in the determination of astroparticle spectra. Varying weather conditions necessitate the development of suitable atmospheric monitoring to be integrated in the overall instrument calibration, including Monte Carlo simulations. With expertise distributed across multiple collaborations and scientific domains, an interdisciplinary workshop is being convened to advance progress on this critical and timely topic.

astro-ph.IM↗

arXiv2014

The Site of the ASTRI SST-2M Telescope Prototype: Atmospheric Monitoring and Auxiliary Instrumentation

ASTRI is a Flagship Project led by the Italian National Institute of Astrophysics, INAF. The main objective of the ASTRI project is to develop a prototype of the Small Size class Telescope for the Cherenkov Telescope Array (CTA) in a dual-mirror configuration (SST-2M). The ASTRI SST-2M is an end-to-end prototype that will be fully developed by the ASTRI Collaboration from the optics design and manufacturing to the focal plane camera, from the structure of the mount to all the needed software. The ASTRI SST-2M prototype will be placed at the INAF "M.G. Fracastoro" observing station in Serra La Nave on the Etna Mountain near Catania, Italy. The technological solutions adopted will be tested on field: observations of the Crab Nebula and of other sources will be essential part of the science verification phase, with the aim to assess the achievement of the scientific requirements. In the following we present the Serra La Nave site together with all the auxiliary instruments needed for atmospheric monitoring and characterization, calibration and science verification of the ASTRI SST-2M prototype.

astro-ph.IM↗

arXiv2013

GIANO-TNG spectroscopy of red supergiants in the young star cluster RSGC2

The inner disk of the Galaxy has a number of young star clusters dominated by red supergiants that are heavily obscured by dust extinction and observable only at infrared wavelengths. These clusters are important tracers of the recent star formation and chemical enrichment history in the inner Galaxy. During the technical commissioning and as a first science verification of the GIANO spectrograph at the Telescopio Nazionale Galileo, we secured high-resolution (R~50,000) near-infrared spectra of three red supergiants in the young Scutum cluster RSGC2. Taking advantage of the full YJHK spectral coverage of GIANO in a single exposure, we were able to identify several tens of atomic and molecular lines suitable for chemical abundance determinations. By means of spectral synthesis and line equivalent width measurements, we obtained abundances of Fe and other iron-peak elements such as V, Cr, Ni, of alpha (O, Mg, Si, Ca and Ti) and other light elements (C, N, Na, Al, K, Sc), and of some s-process elements (Y, Sr). We found iron abundances between half and one third solar and solar-scaled [X/Fe] abundance patterns of iron-peak, alpha and most of the light elements, consistent with a thin-disk chemistry. We found a depletion of [C/Fe] and enhancement of [N/Fe], consistent with CN burning, and low 12C/13C abundance ratios (between 9 and 11), requiring extra-mixing processes in the stellar interiors during the post-main sequence evolution. Finally, we found a slight [Sr/Fe] enhancement and a slight [Y/Fe] depletion (by a factor of <=2), with respect to solar.

astro-ph.GA↗

arXiv2013

PAOLO: a Polarimeter Add-On for the LRS Optics at a Nasmyth focus of the TNG

We describe a new polarimetric facility available at the Istituto Nazionale di AstroFisica / Telescopio Nazionale Galileo at La Palma, Canary islands. This facility, PAOLO (Polarimetric Add-On for the LRS Optics), is located at a Nasmyth focus of an alt-az telescope and requires a specific modeling in order to remove the time- and pointing position-dependent instrumental polarization. We also describe the opto-mechanical structure of the instrument and its calibration and present early examples of applications.

astro-ph.IM↗

arXiv2013

The ASTRI Mini-Array Science Case

ASTRI is a Flagship Project financed by the Italian Ministry of Education, University and Research, and led by INAF, the Italian National Institute of Astrophysics. Within this framework, INAF is currently developing an end-to-end prototype of a Small Size Telescope in a dual-mirror configuration (SST-2M) for the Cherenkov Telescope Array (CTA), scheduled to start data acquisition in 2014. Although the ASTRI SST-2M prototype is mainly a technological demonstrator, it will perform scientific observations of the Crab Nebula, Mrk 421 and Mrk 501 at E>1 TeV. A remarkable improvement in terms of performance could come from the operation, in 2016, of a SST-2M mini-array, composed of a few SST-2M telescopes to be placed at final CTA Southern Site. The SST mini-array will be able to study in great detail relatively bright sources (a few x 10E-12 erg/cm2/s at 10 TeV) with angular resolution of a few arcmin and energy resolution of about 10-15%. Thanks to the stereo approach, it will be possible to verify the wide field of view (FoV) performance through the detections of very high-energy showers with core located at a distance up to 500 m, to compare the mini-array performance with the Monte Carlo expectations by means of deep observations of selected targets, and to perform the first CTA science at the beginning of the mini-array operations. Prominent sources such as extreme blazars, nearby well-known BL Lac objects and radio-galaxies, galactic pulsar wind nebulae, supernovae remnants, micro-quasars, and the Galactic Center can be observed in a previously unexplored energy range, in order to investigate the electron acceleration and cooling, relativistic and non relativistic shocks, the search for cosmic-ray (CR) Pevatrons, the study of the CR propagation, and the impact of the extragalactic background light on the spectra of the sources.

astro-ph.HE↗

arXiv2013

The dual-mirror Small Size Telescope for the Cherenkov Telescope Array

In this paper, the development of the dual mirror Small Size Telescopes (SST) for the Cherenkov Telescope Array (CTA) is reviewed. Up to 70 SST, with a primary mirror diameter of 4 m, will be produced and installed at the CTA southern site. These will allow investigation of the gamma-ray sky at the highest energies accessible to CTA, in the range from about 1 TeV to 300 TeV. The telescope presented in this contribution is characterized by two major innovations: the use of a dual mirror Schwarzschild-Couder configuration and of an innovative camera using as sensors either multi-anode photomultipliers (MAPM) or silicon photomultipliers (SiPM). The reduced plate-scale of the telescope, achieved with the dual-mirror optics, allows the camera to be compact (40 cm in diameter), and low-cost. The camera, which has about 2000 pixels of size 6x6 mm^2, covers a field of view of 10°. The dual mirror telescopes and their cameras are being developed by three consortia, ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana, Italy/INAF), GATE (Gamma-ray Telescope Elements, France/Paris Observ.) and CHEC (Compact High Energy Camera, universities in UK, US and Japan) which are merging their efforts in order to finalize an end-to-end design that will be constructed for CTA. A number of prototype structures and cameras are being developed in order to investigate various alternative designs. In this contribution, these designs are presented, along with the technological solutions under study.

astro-ph.IM↗

arXiv2013

Expected performance of the ASTRI-SST-2M telescope prototype

ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) is an Italian flagship project pursued by INAF (Istituto Nazionale di Astrofisica) strictly linked to the development of the Cherenkov Telescope Array, CTA. Primary goal of the ASTRI program is the design and production of an end-to-end prototype of a Small Size Telescope for the CTA sub-array devoted to the highest gamma-ray energy region. The prototype, named ASTRI SST-2M, will be tested on field in Italy during 2014. This telescope will be the first Cherenkov telescope adopting the double reflection layout in a Schwarzschild-Couder configuration with a tessellated primary mirror and a monolithic secondary mirror. The collected light will be focused on a compact and light-weight camera based on silicon photo-multipliers covering a 9.6 deg full field of view. Detailed Monte Carlo simulations have been performed to estimate the performance of the planned telescope. The results regarding its energy threshold, sensitivity and angular resolution are shown and discussed.

astro-ph.IM↗

arXiv2013

Towards the ASTRI mini-array

The Cherenkov Telescope Array (CTA) will consist of an array of three types of telescopes covering a wide energy range, from tens of GeV up to more than 100 TeV. The high energy section (> 3 TeV) will be covered by the Small Size Telescopes (SST). ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) is a flagship project of the Italian Ministry of Research and Education led by INAF, aiming at the design and construction of a prototype of the Dual Mirror SST. In a second phase the ASTRI project foresees the installation of the first elements of the SST array at the CTA southern site, a mini-array of 5-7 telescopes. The optimization of the layout of this mini-array embedded in the SST array of the CTA Observatory has been the object of an intense simulation effort. In this work we present the expected mini-array performance in terms of energy threshold, angular and energy resolution and sensitivity.

astro-ph.IM↗

arXiv2013

The ASTRI Project: a mini-array of dual-mirror small Cherenkov telescopes for CTA

ASTRI is a flagship project of the Italian Ministry of Education, University and Research, which aims to develop an end-to-end prototype of the CTA small-size telescope. The proposed design is characterized by a dual-mirror Schwarzschild-Couder configuration and a camera based on Silicon photo-multipliers, two challenging but innovative technological solutions which will be adopted for the first time on a Cherenkov telescope. Here we describe the current status of the project, the expected performance and the possibility to realize a mini-array composed by a few small-size telescopes, which shall be placed at the final CTA Southern Site.

astro-ph.IM↗

arXiv2013

A GIANO-TNG high resolution IR spectrum of the airglow emission

A flux-calibrated high resolution spectrum of the airglow emission is a practical lambda-calibration reference for astronomical spectral observations. It is also useful for constraining the molecular parameters of the OH molecule and the physical conditions in the upper mesosphere. methods: We use the data collected during the first technical commissioning of the GIANO spectrograph at the Telescopio Nazionale Galileo (TNG). The high resolution (R~50,000) spectrum simultaneously covers the 0.95-2.4 micron wavelength range. Relative flux calibration is achieved by the simultaneous observation of spectrophotometric standard star. results: We derive a list of improved positions and intensities of OH infrared lines. The list includes Lambda-split doublets many of which are spectrally resolved. Compared to previous works, the new results correct errors in the wavelengths of the Q-branch transitions. The relative fluxes of OH lines from different vibrational bands show remarkable deviations from theoretical predictions: the Deltav=3,4 lines are a factor of 2 and 4 brighter than expected. We also find evidence of a significant fraction (1-4%) of OH molecules with ``non-thermal'' population of high-J levels. Finally we list wavelengths and fluxes of 153 lines not attributable to OH. Most of these can be associated to O2, while 37 lines in the H band are not identified. The O2 and unidentified lines in the H band account for ~5% of the total airglow flux in this band.

astro-ph.IM↗

arXiv2012

Non-collinear magnetic ordering in compressed FePd$_3$ ordered alloy: a first principles study

By means of ab initio calculations based on the density functional theory we investigated magnetic phase diagram of ordered FePd$_3$ alloy as a function of external pressure. Considering several magnetic configurations we concluded that the system under pressure has a tendency to non-collinear spin alignment. Analysis of the Heisenberg exchange parameters $J_{ij}$ revealed strong dependence of iron-iron magnetic couplings on polarization of Pd atoms. To take into account the latter effect we built an extended Heisenberg model with higher order (biquadratic) terms. Minimizing the energy of this Hamiltonian, fully parameterized using the results of ab initio calculations, we found a candidate for a ground state of compressed FePd$_3$, which can be seen as two interpenetrating "triple-Q" phases.

cond-mat.mtrl-sci↗

arXiv2011

Graphene in periodically alternating magnetic field: unusual quantization of the anomalous Hall effect

We study the energy spectrum and electronic properties of graphene in a periodic magnetic field of zero average with a symmetry of triangular lattice. The periodic field leads to formation of a set of minibands separated by gaps, which can be manipulated by external field. The Berry phase, related to the motion of electrons in $k$ space, and the corresponding Chern numbers characterizing topology of the energy bands are calculated analytically and numerically. In this connection, we discuss the anomalous Hall effect in the insulating state, when the Fermi level is located in the minigap. The results of calculations show that in the model of gapless Dirac spectrum of graphene the anomalous Hall effect can be treated as a sum of fractional quantum numbers, related to the nonequivalent Dirac points.

cond-mat.mtrl-sci↗

arXiv2009

Magnetic Anistropy due to the Casimir Effect

We consider the Casimir interaction between a ferromagnetic and a non-magnetic mirror, and show how the Casimir effect gives rise to a magnetic anisotropy in the ferromagnetic layer. The anisotropy is out-of-plane if the non-magnetic plate is optically isotropic. If the non-magnetic plate shows a uniaxial optical anisotropy (with optical axis in the plate plane), we find an in-plane magnetic anisotropy. In both cases, the energetically most favorable magnetization orientation is given by the competition between polar, longitudinal and transverse contributions to the magneto-optical Kerr effect, and will therefore depend on the interplate distance. Numerical results will be presented for a magnetic plate made out of iron, and non-magnetic plates of gold (optically isotropic), quartz, calcite and barium titanate (all uniaxially birefringent).

quant-ph↗

arXiv2009

Structural phase transitions and fundamental band gaps of Mg(x)Zn(1-x)O alloys from first principles

The structural phase transitions and the fundamental band gaps of Mg(x)Zn(1-x)O alloys are investigated by detailed first-principles calculations in the entire range of Mg concentrations x, applying a multiple-scattering theoretical approach (Korringa-Kohn-Rostoker method). Disordered alloys are treated within the coherent potential approximation (CPA). The calculations for various crystal phases have given rise to a phase diagram in good agreement with experiments and other theoretical approaches. The phase transition from the wurtzite to the rock-salt structure is predicted at the Mg concentration of x = 0.33, which is close to the experimental value of 0.33 - 0.40. The size of the fundamental band gap, typically underestimated by the local density approximation, is considerably improved by the self-interaction correction. The increase of the gap upon alloying ZnO with Mg corroborates experimental trends. Our findings are relevant for applications in optical, electrical, and in particular in magnetoelectric devices.

cond-mat.mtrl-sci↗