OA@INAFhttps://openaccess.inaf.itThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Wed, 17 Apr 2024 12:27:07 GMT2024-04-17T12:27:07Z50211A Bayesian estimation of the helioseismic solar agehttp://hdl.handle.net/20.500.12386/24161Title: A Bayesian estimation of the helioseismic solar age
Authors: BONANNO, Alfio Maurizio; Fröhlich, H. -E.
Abstract: Context. The helioseismic determination of the solar age has been a subject of several studies because it provides us with an independent estimation of the age of the solar system. <BR /> Aims: We present the Bayesian estimates of the helioseismic age of the Sun, which are determined by means of calibrated solar models that employ different equations of state and nuclear reaction rates. <BR /> Methods: We use 17 frequency separation ratios r<SUB>02</SUB>(n) = (ν<SUB>n,l = 0</SUB>-ν<SUB>n-1,l = 2</SUB>)/(ν<SUB>n,l = 1</SUB>-ν<SUB>n-1,l = 1</SUB>) from 8640 days of low-ℓBiSON frequencies and consider three likelihood functions that depend on the handling of the errors of these r<SUB>02</SUB>(n) ratios. Moreover, we employ the 2010 CODATA recommended values for Newton's constant, solar mass, and radius to calibrate a large grid of solar models spanning a conceivable range of solar ages. <BR /> Results: It is shown that the most constrained posterior distribution of the solar age for models employing Irwin EOS with NACRE reaction rates leads to t<SUB>☉</SUB> = 4.587 ± 0.007 Gyr, while models employing the Irwin EOS and Adelberger, et al. (2011, Rev. Mod. Phys., 83, 195) reaction rate have t<SUB>☉</SUB> = 4.569 ± 0.006 Gyr. Implementing OPAL EOS in the solar models results in reduced evidence ratios (Bayes factors) and leads to an age that is not consistent with the meteoritic dating of the solar system. <BR /> Conclusions: An estimate of the solar age that relies on an helioseismic age indicator such as r<SUB>02</SUB>(n) turns out to be essentially independent of the type of likelihood function. However, with respect to model selection, abandoning any information concerning the errors of the r<SUB>02</SUB>(n) ratios leads to inconclusive results, and this stresses the importance of evaluating the trustworthiness of error estimates.
Acknowledgments: A.B. would like to thank Gianni Strazzulla and Brandon Johnson for enlightening discussions about calcium-aluminum-rich inclusions and the meteoritic age of the solar system.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/20.500.12386/241612015-01-01T00:00:00ZA Hot Saturn Orbiting an Oscillating Late Subgiant Discovered by TESShttp://hdl.handle.net/20.500.12386/30434Title: A Hot Saturn Orbiting an Oscillating Late Subgiant Discovered by TESS
Authors: Huber, Daniel; Chaplin, William J.; Chontos, Ashley; Kjeldsen, Hans; Christensen-Dalsgaard, Jørgen; Bedding, Timothy R.; Ball, Warrick; Brahm, Rafael; Espinoza, Nestor; Henning, Thomas; Jordán, Andrés; Sarkis, Paula; Knudstrup, Emil; Albrecht, Simon; Grundahl, Frank; Fredslund Andersen, Mads; Pallé, Pere L.; Crossfield, Ian; Fulton, Benjamin; Howard, Andrew W.; Isaacson, Howard T.; Weiss, Lauren M.; Handberg, Rasmus; Lund, Mikkel N.; Serenelli, Aldo M.; Rørsted Mosumgaard, Jakob; Stokholm, Amalie; Bieryla, Allyson; Buchhave, Lars A.; Latham, David W.; Quinn, Samuel N.; Gaidos, Eric; Hirano, Teruyuki; Ricker, George R.; Vanderspek, Roland K.; Seager, Sara; Jenkins, Jon M.; Winn, Joshua N.; Antia, H. M.; Appourchaux, Thierry; Basu, Sarbani; Bell, Keaton J.; Benomar, Othman; BONANNO, Alfio Maurizio; Buzasi, Derek L.; Campante, Tiago L.; Çelik Orhan, Z.; CORSARO, ENRICO MARIA NICOLA; Cunha, Margarida S.; Davies, Guy R.; Deheuvels, Sebastien; Grunblatt, Samuel K.; Hasanzadeh, Amir; DI MAURO, Maria Giuseppina; García, Rafael A.; Gaulme, Patrick; GIRARDI, Leo Alberto; Guzik, Joyce A.; Hon, Marc; Jiang, Chen; Kallinger, Thomas; Kawaler, Steven D.; Kuszlewicz, James S.; Lebreton, Yveline; Li, Tanda; Lucas, Miles; Lundkvist, Mia S.; Mann, Andrew W.; Mathis, Stéphane; Mathur, Savita; Mazumdar, Anwesh; Metcalfe, Travis S.; MIGLIO, ANDREA; Monteiro, Mário J. P. F. G.; Mosser, Benoit; Noll, Anthony; Nsamba, Benard; Ong, Jia Mian Joel; Örtel, S.; Pereira, Filipe; Ranadive, Pritesh; Régulo, Clara; Da Silva Rodrigues, Thaise; Roxburgh, Ian W.; Silva Aguirre, Victor; Smalley, Barry; Schofield, Mathew; Sousa, Sérgio G.; Stassun, Keivan G.; Stello, Dennis; Tayar, Jamie; White, Timothy R.; Verma, Kuldeep; Vrard, Mathieu; Yıldız, M.; Baker, David; Bazot, Michaël; Beichmann, Charles; Bergmann, Christoph; Bugnet, Lisa; Cale, Bryson; Carlino, Roberto; Cartwright, Scott M.; Christiansen, Jessie L.; Ciardi, David R.; Creevey, Orlagh; Dittmann, Jason A.; Do Nascimento, Jose-Dias, Jr.; Van Eylen, Vincent; Fürész, Gabor; Gagné, Jonathan; Gao, Peter; Gazeas, Kosmas; Giddens, Frank; Hall, Oliver J.; Hekker, Saskia; Ireland, Michael J.; Latouf, Natasha; LeBrun, Danny; Levine, Alan M.; Matzko, William; Natinsky, Eva; Page, Emma; Plavchan, Peter; Mansouri-Samani, Masoud; McCauliff, Sean; Mullally, Susan E.; Orenstein, Brendan; Garcia Soto, Aylin; Paegert, Martin; van Saders, Jennifer L.; Schnaible, Chloe; Soderblom, David R.; Szabó, Róbert; Tanner, Angelle; Tinney, C. G.; Teske, Johanna; Thomas, Alexandra; Trampedach, Regner; Wright, Duncan; Yuan, Thomas T.; Zohrabi, Farzaneh
Abstract: We present the discovery of HD 221416 b, the first transiting planet identified by the Transiting Exoplanet Survey Satellite (TESS) for which asteroseismology of the host star is possible. HD 221416 b (HIP 116158, TOI-197) is a bright (V = 8.2 mag), spectroscopically classified subgiant that oscillates with an average frequency of about 430 μHz and displays a clear signature of mixed modes. The oscillation amplitude confirms that the redder TESS bandpass compared to Kepler has a small effect on the oscillations, supporting the expected yield of thousands of solar-like oscillators with TESS 2 minute cadence observations. Asteroseismic modeling yields a robust determination of the host star radius (R <SUB>⋆</SUB> = 2.943 ± 0.064 R <SUB>☉</SUB>), mass (M <SUB>⋆</SUB> = 1.212 ± 0.074 M <SUB>☉</SUB>), and age (4.9 ± 1.1 Gyr), and demonstrates that it has just started ascending the red-giant branch. Combining asteroseismology with transit modeling and radial-velocity observations, we show that the planet is a “hot Saturn” (R <SUB>p</SUB> = 9.17 ± 0.33 R <SUB>⊕</SUB>) with an orbital period of ∼14.3 days, irradiance of F = 343 ± 24 F <SUB>⊕</SUB>, and moderate mass (M <SUB>p</SUB> = 60.5 ± 5.7 M <SUB>⊕</SUB>) and density (ρ <SUB>p</SUB> = 0.431 ± 0.062 g cm<SUP>-3</SUP>). The properties of HD 221416 b show that the host-star metallicity-planet mass correlation found in sub-Saturns (4-8 R <SUB>⊕</SUB>) does not extend to larger radii, indicating that planets in the transition between sub-Saturns and Jupiters follow a relatively narrow range of densities. With a density measured to ∼15%, HD 221416 b is one of the best characterized Saturn-size planets to date, augmenting the small number of known transiting planets around evolved stars and demonstrating the power of TESS to characterize exoplanets and their host stars using asteroseismology.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/20.500.12386/304342019-01-01T00:00:00ZA Novel Approach to β-Decay: PANDORA, a New Experimental Setup for Future in-Plasma Measurementshttp://hdl.handle.net/20.500.12386/32959Title: A Novel Approach to β-Decay: PANDORA, a New Experimental Setup for Future in-Plasma Measurements
Authors: Mascali, David; Santonocito, Domenico; Amaducci, Simone; Andò, Lucio; ANTONUCCIO, Vincenzo; Biri, Sándor; BONANNO, Alfio Maurizio; Bonanno, Vincenza; Briefi, Stefan; Busso, Maurizio; Celona, Luigi; Cosentino, Luigi; CRISTALLO, Sergio; Cuffiani, Marco; De Angelis, Costantino; De Angelis, Giacomo; De Salvador, Davide; Di Donato, Loreto; Ducret, Jean Eric; Vakili, Aref Eshkevar; Fantz, Ursel; Galatà, Alessio; Gallo, Carmelo Sebastiano; Gammino, Santo; Isernia, Tommaso; Koivisto, Hannu; Kratz, Karl Ludwig; Kronholm, Risto; La Cognata, Marco; Leoni, Silvia; Locatelli, Andrea; Maggiore, Mario; Maimone, Fabio; Malferrari, Luciana; Mancini, Giorgio; Maunoury, Laurent; Mauro, Giorgio Sebastiano; Mazzaglia, Maria; Mengoni, Alberto; Miraglia, Andrea; Mishra, Bharat; Musumeci, Mario; Napoli, Daniel Ricardo; Naselli, Eugenia; Odorici, Fabrizio; Palladino, Libero; Palmisano, Giuseppe; Pavone, Santi; Pennisi, Salvatore; Perego, Albino; Pidatella, Angelo; Rácz, Richard; Reitano, Riccardo; Rifuggiato, Danilo; Rinaldi, Matteo; Russo, Antonio Domenico; Russo, Filippo; Schillaci, Gaetano; Selleri, Stefano; Simonucci, Stefano; Sorbello, Gino; Spartà, Roberta; Taioli, Simone; Tinschert, Klaus; Torrisi, Giuseppe; Trifirò, Antonio; Tsikata, Sedina; Tumino, Aurora; VESCOVI, DIEGO; Vincetti, Luca
Abstract: Theoretical predictions as well as experiments performed at storage rings have shown that the lifetimes of β-radionuclides can change significantly as a function of the ionization state. In this paper we describe an innovative approach, based on the use of a compact plasma trap to emulate selected stellar-like conditions. It has been proposed within the PANDORA project (Plasmas for Astrophysics, Nuclear Decay Observation and Radiation for Archaeometry) with the aim to measure, for the first time in plasma, nuclear β-decay rates of radionuclides involved in nuclear-astrophysics processes. To achieve this task, a compact magnetic plasma trap has been designed to reach the needed plasma densities, temperatures, and charge-states distributions. A multi-diagnostic setup will monitor, on-line, the plasma parameters, which will be correlated with the decay rate of the radionuclides. The latter will be measured through the detection of the γ-rays emitted by the excited daughter nuclei following the β-decay. An array of 14 HPGe detectors placed around the trap will be used to detect the emitted γ-rays. For the first experimental campaign three isotopes,176Lu,134Cs, and94Nb, were selected as possible physics cases. The newly designed plasma trap will also represent a tool of choice to measure the plasma opacities in a broad spectrum of plasma conditions, experimentally poorly known but that have a great impact on the energy transport and spectroscopic observations of many astrophysical objects. Status and perspectives of the project will be highlighted in the paper.
Sat, 01 Jan 2022 00:00:00 GMThttp://hdl.handle.net/20.500.12386/329592022-01-01T00:00:00ZAcoustic oscillations and dynamo action in the G8 sub-giant EK Eridanihttp://hdl.handle.net/20.500.12386/29799Title: Acoustic oscillations and dynamo action in the G8 sub-giant EK Eridani
Authors: BONANNO, Alfio Maurizio; CORSARO, ENRICO MARIA NICOLA; Del Sordo, F.; Pallé, P. L.; Stello, D.; Hon, M.
Abstract: We present further evidence of acoustic oscillations in the slowly rotating overactive G8 sub-giant EK Eri. This star was observed with the 1m Hertzsprung SONG telescope at the Observatorio del Teide for two different runs of 8 and 13 nights, respectively, that were separated by about a year. We determined a significant excess of power around ν<SUB>max</SUB> = 253 ± 3 μHz in the first observing run and were able to determine a large separation, ∆ν = 16.43 ± 0.22 μHz. No significant excess of power was instead detected in a subsequent SONG observing season, as also supported by our analysis of the simultaneous TESS photometric observations. We propose a new amplitude-luminosity relation in order to account for the missing power in the power spectrum. Based on the evolutionary stage of this object, we argue that a standard α<SUP>2</SUP>Ω dynamo cannot be excluded as the possible origin for the observed magnetic field. <P />A table of the radial velocities is only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A106">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A106</A> Based on observations made with the Hertzsprung SONG telescope operated on the Spanish Observatorio del Teide on the island of Tenerife by the Aarhus and Copenhagen Universities and by the Instituto de Astrofísica de Canarias.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/20.500.12386/297992019-01-01T00:00:00ZAnalytic mean-field α^2-dynamo with a force-free coronahttp://hdl.handle.net/20.500.12386/28389Title: Analytic mean-field α^2-dynamo with a force-free corona
Authors: BONANNO, Alfio Maurizio; DEL SORDO, FABIO
Abstract: Context. Stellar dynamos are affected by boundary conditions imposed by stellar coronae. Under some approximations, it is possible to find analytical solutions. Interior dynamo models often consider a current-free corona without taking into account the constraints imposed by the presence of currents in the corona. <BR /> Aims: We aim to analytically evaluate the effect of coronal currents and of an outer boundary condition on the efficiency of an α<SUP>2</SUP> dynamo. We intend to estimate the change in geometry and dynamo excitation numbers with respect to the current-free case. <BR /> Methods: We analytically solved the turbulent dynamo induction equation for a homogeneous, non-mirror symmetric turbulence in a spherical domain surrounded by a linear force-free corona with the mean magnetic field B satisfying ∇ × B = βB. <BR /> Results: The dynamo number is a decreasing function of β. Moreover, if the current is parallel to the field (β > 0), the dynamo number is smaller than in the force-free case. In contrast, for (β < 0), the dynamo number is greater than in the force-free case. Conclusions: Currents in the corona need to be taken into account because they affect the condition for excitation of a dynamo.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/20.500.12386/283892017-01-01T00:00:00ZASTRI Mini-Array core science at the Observatorio del Teidehttp://hdl.handle.net/20.500.12386/34538Title: ASTRI Mini-Array core science at the Observatorio del Teide
Authors: VERCELLONE, STEFANO; BIGONGIARI, Ciro; Burtovoi, A.; CARDILLO , MARTINA; CATALANO, Osvaldo; Franceschini, A.; LOMBARDI, Saverio; NAVA, Lara; Pintore, Fabio; STAMERRA, Antonio; TAVECCHIO, Fabrizio; ZAMPIERI, Luca; Alves Batista, R.; AMATO, Elena; ANTONELLI, Lucio Angelo; Arcaro, C.; Becerra González, J.; Bonnoli, G.; Böttcher, M.; BRUNETTI, Gianfranco; COMPAGNINO, Antonio Alessio; Crestan, S.; D'AI', Antonino; Fiori, M.; GALANTI, Giorgio; GIULIANI, ANDREA; de Gouveia Dal Pino, E. M.; GREEN, JARRED GERSHON; LAMASTRA, Alessandra; LANDONI, Marco; LUCARELLI, Fabrizio; MORLINO, Giovanni; OLMI, Barbara; Peretti, E.; PIANO, Giovanni; PONTI, Gabriele; PORETTI, Ennio; Romano, P.; SATURNI, Francesco Gabriele; SCUDERI, Salvatore; Tutone, A.; UMANA, Grazia Maria Gloria; Acosta-Pulido, J. A.; Barai, P.; BONANNO, Alfio Maurizio; BONANNO, Giovanni; BRUNO, Pietro Giuseppe; BULGARELLI, ANDREA; CONFORTI, Vito; COSTA, Alessandro; CUSUMANO, GIANCARLO; DEL SANTO, MELANIA; del Valle, M. V.; DELLA CECA, Roberto; Falceta-Gonçalves, D. A.; FIORETTI, Valentina; Germani, S.; García-López, R. J.; Ghedina, A.; GIANOTTI, Fulvio; Giordano, V.; Kreter, M.; Incardona, F.; Iovenitti, S.; LA BARBERA, ANTONINO; LA PALOMBARA, NICOLA; LA PAROLA, VALENTINA; LETO, Giuseppe; Longo, F.; López-Oramas, A.; MACCARONE, MARIA CONCETTA; MEREGHETTI, Sandro; MILLUL, Rachele; Naletto, G.; PAGLIARO, ANTONIO; PARMIGGIANI, Nicolo'; RIGHI, Chiara; Rodríguez-Ramírez, J. C.; ROMEO, Giuseppe; SANGIORGI, Pierluca; Santos de Lima, R.; TAGLIAFERRI, Gianpiero; TESTA, Vincenzo; Tosti, G.; Vázquez Acosta, M.; Żywucka, N.; Caraveo, P. A.; PARESCHI, Giovanni
Abstract: The ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) Project led by the Italian National Institute for Astrophysics (INAF) is developing and will deploy at the Observatorio del Teide a mini-array (ASTRI Mini-Array) composed of nine telescopes similar to the small-size dual-mirror Schwarzschild-Couder telescope (ASTRI-Horn) currently operating on the slopes of Mt. Etna in Sicily. The ASTRI Mini-Array will surpass the current Cherenkov telescope array differential sensitivity above a few tera-electronvolt (TeV), extending the energy band well above hundreds of TeV. This will allow us to explore a new window of the electromagnetic spectrum, by convolving the sensitivity performance with excellent angular and energy resolution figures. In this paper we describe the Core Science that we will address during the first four years of operation, providing examples of the breakthrough results that we will obtain when dealing with current open questions, such as the acceleration of cosmic rays, cosmology and fundamental physics and the new window, for the TeV energy band, of the time-domain astrophysics.
Sat, 01 Jan 2022 00:00:00 GMThttp://hdl.handle.net/20.500.12386/345382022-01-01T00:00:00ZAsymptotically safe cosmology - A status reporthttp://hdl.handle.net/20.500.12386/28387Title: Asymptotically safe cosmology - A status report
Authors: BONANNO, Alfio Maurizio; Saueressig, Frank
Abstract: Asymptotic safety, based on a non-Gaussian fixed point of the gravitational renormalization group flow, provides an elegant mechanism for completing the gravitational force at sub-Planckian scales. At high energies, the fixed point controls the scaling of couplings such that unphysical divergences are absent, while the emergence of classical low-energy physics is linked to a crossover between two renormalization group fixed points. These features make asymptotic safety an attractive framework for the building of a cosmological model. The resulting scenarios may naturally give rise to a quantum-gravity-driven inflationary phase in the very early universe and an almost scale-free fluctuation spectrum. Moreover, effective descriptions arising from an improvement of the renormalization group permit a direct comparison to cosmological observations as, e.g., Planck data.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/20.500.12386/283872017-01-01T00:00:00ZAsymptotically safe inflation from quadratic gravityhttp://hdl.handle.net/20.500.12386/24045Title: Asymptotically safe inflation from quadratic gravity
Authors: BONANNO, Alfio Maurizio; Platania, Alessia
Abstract: Asymptotically Safe theories of gravity have recently received much attention. In this work we discuss a class of inflationary models derived from quantum-gravity modification of quadratic gravity according to the induced scaling around the non-Gaussian fixed point at very high energies. It is argued that the presence of a three dimensional ultraviolet critical surface generates operators of non-integer power of the type <SUP>R 2 - θ / 2</SUP> in the effective Lagrangian, where θ > 0 is a critical exponent. The requirement of a successful inflationary model in agreement with the recent Planck 2015 data puts important constraints on the strength of this new type of couplings.
Acknowledgments: Acknowledgements The authors would like to thank Gian Paolo Vacca and Sergey Vernov for important suggestions and comments.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/20.500.12386/240452015-01-01T00:00:00ZBouncing and emergent cosmologies from Arnowitt-Deser-Misner RG flowshttp://hdl.handle.net/20.500.12386/28390Title: Bouncing and emergent cosmologies from Arnowitt-Deser-Misner RG flows
Authors: BONANNO, Alfio Maurizio; Gionti, S. J. Gabriele; Platania, Alessia
Abstract: Asymptotically safe gravity provides a framework for the description of gravity from the trans-Planckian regime to cosmological scales. According to this scenario, the cosmological constant and Newton’s coupling are functions of the energy scale whose evolution is dictated by the renormalization group (RG) equations. The formulation of the RG equations on foliated spacetimes, based on the Arnowitt-Deser-Misner (ADM) formalism, furnishes a natural way to construct the RG energy scale from the spectrum of the Laplacian operator on the spatial slices. Combining this idea with an RG improvement procedure, in this work we study quantum gravitational corrections to the Einstein-Hilbert action on Friedmann-Lemaître-Robertson-Walker backgrounds. The resulting quantum-corrected Friedmann equations can give rise to both bouncing cosmologies and emergent Universe solutions. Our bouncing models do not require the presence of exotic matter and emergent Universe solutions can be constructed for any allowed topology of the spatial slices.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/20.500.12386/283902018-01-01T00:00:00ZCharacterizing black hole metrics in quadratic gravityhttp://hdl.handle.net/20.500.12386/30433Title: Characterizing black hole metrics in quadratic gravity
Authors: BONANNO, Alfio Maurizio; Silveravalle, S.
Abstract: The recent discovery of non-Schwarzschild black hole spacetimes has opened new directions of research in higher-derivative gravitational theories. However, despite intense analytical and numerical efforts, the link with the linearized theory is still poorly understood. In this work we address this point for the Einstein-Weyl Lagrangian, whose weak field limit is characterized by the standard massless graviton and a spin-2 ghost. We show that the strength of the Yukawa term at infinity determines the thermal properties of the black hole and the structure of the singularity near r =0 . Moreover, inspired by recent results in the asymptotic safety scenario we investigate the consequences of an imaginary ghost mass. In this case we find a countable set of solutions all characterized by spatial oscillations of typical wavelength determined by the mass of the spin-2 field.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/20.500.12386/304332019-01-01T00:00:00ZChromospheric Emission of Planet Candidate Host Stars: A Way to Identify False Positiveshttp://hdl.handle.net/20.500.12386/25001Title: Chromospheric Emission of Planet Candidate Host Stars: A Way to Identify False Positives
Authors: Karoff, Christoffer; Albrecht, Simon; BONANNO, Alfio Maurizio; Faurschou Knudsen, Mads
Abstract: It has been hypothesized that the presence of closely orbiting giant planets is associated with enhanced chromospheric emission of their host stars. The main cause for such a relation would likely be enhanced dynamo action induced by the planet. We present measurements of chromospheric emission in 234 planet candidate systems from the Kepler mission. This ensemble includes 37 systems with giant-planet candidates, which show a clear emission enhancement. The enhancement, however, disappears when systems that are also identified as eclipsing binary candidates are removed from the ensemble. This suggests that a large fraction of the giant-planet candidate systems with chromospheric emission stronger than the Sun are not giant-planet systems, but false positives. Such false-positive systems could be tidally interacting binaries with strong chromospheric emission. This hypothesis is supported by an analysis of 188 eclipsing binary candidates that show increasing chromospheric emission as function of decreasing orbital period.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/20.500.12386/250012016-01-01T00:00:00ZCosmic censorship in quantum Einstein gravityhttp://hdl.handle.net/20.500.12386/28388Title: Cosmic censorship in quantum Einstein gravity
Authors: BONANNO, Alfio Maurizio; Koch, B.; Platania, A.
Abstract: We study the quantum gravity modification of the Kuroda-Papapetrou model induced by the running of the Newton’s constant at high energy in quantum Einstein gravity. We argue that although the antiscreening character of the gravitational interaction favours the formation of a naked singularity, quantum gravity effects turn the classical singularity into a ‘whimper’ singularity which remains naked for a finite amount of advanced time.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/20.500.12386/283882017-01-01T00:00:00ZCosmological bounds on the field content of asymptotically safe gravity-matter modelshttp://hdl.handle.net/20.500.12386/28391Title: Cosmological bounds on the field content of asymptotically safe gravity-matter models
Authors: BONANNO, Alfio Maurizio; Platania, Alessia; Saueressig, Frank
Abstract: We use the non-Gaussian fixed points (NGFPs) appearing in the renormalization group flow of gravity and gravity-matter systems to construct models of NGFP-driven inflation via a renormalization group improvement scheme. The cosmological predictions of these models depend sensitively on the characteristic properties of the NGFPs, including their position and stability coefficients, which in turn are determined by the field content of the underlying matter sector. We demonstrate that the NGFPs appearing in gravity-matter systems where the matter content is close to the one of the standard model of particle physics are the ones compatible with cosmological data. Somewhat counterintuitively, the negative fixed point value of the dimensionless cosmological constant is essential for these findings.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/20.500.12386/283912018-01-01T00:00:00ZGlobal simulations of Tayler instability in stellar interiors: the stabilizing effect of gravityhttp://hdl.handle.net/20.500.12386/29801Title: Global simulations of Tayler instability in stellar interiors: the stabilizing effect of gravity
Authors: Guerrero, G.; Del Sordo, F.; BONANNO, Alfio Maurizio; Smolarkiewicz, P. K.
Abstract: Unveiling the evolution of toroidal field instability, known as Tayler instability, is essential to understand the strength and topology of the magnetic fields observed in early-type stars, in the core of the red giants, or in any stellar radiative zone. We want to study the non-linear evolution of the instability of a toroidal field stored in a stably stratified layer, in spherical symmetry and in the absence of rotation. In particular, we intend to quantify the suppression of the instability as a function of the Brunt-Väisäla (ω<SUB>BV</SUB>) and the Alfvén (ω<SUB>A</SUB>) frequencies. We use the magnetohydrodynamic (MHD) equations as implemented in the anelastic approximation in the EULAG-MHD code and perform a large series of numerical simulations of the instability exploring the parameter space for the ω<SUB>BV</SUB> and ω<SUB>A</SUB>. We show that beyond a critical value gravity strongly suppress the instability, in agreement with the linear analysis. The intensity of the initial field also plays an important role: weaker fields show much slower growth rates. Moreover, in the case of very low gravity, the fastest growing modes have a large characteristic radial scale, at variance with the case of strong gravity, where the instability is characterized by horizontal displacements. Our results illustrate that the anelastic approximation can efficiently describe the evolution of toroidal field instability in stellar interiors. The suppression of the instability as a consequence of increasing values of ω<SUB>BV</SUB> might play a role to explain the magnetic desert in Ap/Bp stars, since weak fields are only marginally unstable in the case of strong gravity.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/20.500.12386/298012019-01-01T00:00:00ZIGR J17480-2446: a new class of accreting binaries?http://hdl.handle.net/20.500.12386/24162Title: IGR J17480-2446: a new class of accreting binaries?
Authors: BONANNO, Alfio Maurizio; Urpin, V.
Abstract: Context. The recent discovery of long-period, low magnetic field pulsars in low-mass X-ray binaries (LMXBs) represents a challenge for the standard evolutionary scenario. These pulsars have a magnetic field strength comparable to that of millisecond pulsars (~10<SUP>8</SUP>-10<SUP>9</SUP> G), but their period is at least an order of magnitude longer. <BR /> Aims: We discuss the origin of this new class of pulsars within the standard picture of LMXBs formation and apply our results to the case of IGR J17480-2446. <BR /> Methods: The magnetothermal evolution of the binary system is studied numerically by taking into account the effect of different accretion rates during the Roche-lobe overflow in the framework of the minimal cooling scenario. <BR /> Results: We show that, in addition to standard millisecond pulsars, long-period low magnetic field pulsars should also be expected as a possible outcome of the binary evolution, depending on the strength of the accretion rate during the Roche-lobe overflow. In particular, we argue that IGR J17480-2446 belongs to this new class of objects.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/20.500.12386/241622015-01-01T00:00:00ZInternal rotation of 13 low-mass low-luminosity red giants in the Kepler fieldhttp://hdl.handle.net/20.500.12386/27145Title: Internal rotation of 13 low-mass low-luminosity red giants in the Kepler field
Authors: Triana, S. A.; CORSARO, ENRICO MARIA NICOLA; De Ridder, J.; BONANNO, Alfio Maurizio; Pérez Hernández, F.; García, R. A.
Abstract: Context. The Kepler space telescope has provided time series of red giants of such unprecedented quality that a detailed asteroseismic analysis becomes possible. For a limited set of about a dozen red giants, the observed oscillation frequencies obtained by peak-bagging together with the most recent pulsation codes allowed us to reliably determine the core/envelope rotation ratio. The results so far show that the current models are unable to reproduce the rotation ratios, predicting higher values than what is observed and thus indicating that an efficient angular momentum transport mechanism should be at work. Here we provide an asteroseismic analysis of a sample of 13 low-luminosity low-mass red giant stars observed by Kepler during its first nominal mission. These targets form a subsample of the 19 red giants studied previously, which not only have a large number of extracted oscillation frequencies, but also unambiguous mode identifications. <BR /> Aims: We aim to extend the sample of red giants for which internal rotation ratios obtained by theoretical modeling of peak-bagged frequencies are available. We also derive the rotation ratios using different methods, and compare the results of these methods with each other. <BR /> Methods: We built seismic models using a grid search combined with a Nelder-Mead simplex algorithm and obtained rotation averages employing Bayesian inference and inversion methods. We compared these averages with those obtained using a previously developed model-independent method. <BR /> Results: We find that the cores of the red giants in this sample are rotating 5 to 10 times faster than their envelopes, which is consistent with earlier results. The rotation rates computed from the different methods show good agreement for some targets, while some discrepancies exist for others.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/20.500.12386/271452017-01-01T00:00:00ZIsotropic Lifshitz critical behavior from the functional renormalization grouphttp://hdl.handle.net/20.500.12386/24209Title: Isotropic Lifshitz critical behavior from the functional renormalization group
Authors: BONANNO, Alfio Maurizio; Zappalà, D.
Abstract: The Lifshitz critical behavior for a single component field theory is studied for the specific isotropic case in the framework of the Functional Renormalization Group. Lifshitz fixed point solutions of the flow equation, derived by using a Proper Time regulator, are searched at lowest and higher order in the derivative expansion. Solutions are found when the number of spatial dimensions d is contained within the interval 5.5 < d < 8. <P />
Acknowledgments: Acknowledgements The authors thank A. Codello and H. Diehl for e-mail correspondence.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/20.500.12386/242092015-01-01T00:00:00ZObservational evidence for enhanced magnetic activity of superflare starshttp://hdl.handle.net/20.500.12386/24998Title: Observational evidence for enhanced magnetic activity of superflare stars
Authors: Karoff, Christoffer; Knudsen, Mads Faurschou; De Cat, Peter; BONANNO, Alfio Maurizio; Fogtmann-Schulz, Alexandra; Fu, Jianning; FRASCA, Antonio; Inceoglu, Fadil; Olsen, Jesper; Zhang, Yong; Hou, Yonghui; Wang, Yuefei; Shi, Jianrong; Zhang, Wei
Abstract: Superflares are large explosive events on stellar surfaces one to six orders-of-magnitude larger than the largest flares observed on the Sun throughout the space age. Due to the huge amount of energy released in these superflares, it has been speculated if the underlying mechanism is the same as for solar flares, which are caused by magnetic reconnection in the solar corona. Here, we analyse observations made with the LAMOST telescope of 5,648 solar-like stars, including 48 superflare stars. These observations show that superflare stars are generally characterized by larger chromospheric emissions than other stars, including the Sun. However, superflare stars with activity levels lower than, or comparable to, the Sun do exist, suggesting that solar flares and superflares most likely share the same origin. The very large ensemble of solar-like stars included in this study enables detailed and robust estimates of the relation between chromospheric activity and the occurrence of superflares.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/20.500.12386/249982016-01-01T00:00:00ZStellar Dynamo Models with Prominent Surface Toroidal Fieldshttp://hdl.handle.net/20.500.12386/24999Title: Stellar Dynamo Models with Prominent Surface Toroidal Fields
Authors: BONANNO, Alfio Maurizio
Abstract: Recent spectro-polarimetric observations of solar-type stars have shown the presence of photospheric magnetic fields with a predominant toroidal component. If the external field is assumed to be current-free it is impossible to explain these observations within the framework of standard mean-field dynamo theory. In this work, it will be shown that if the coronal field of these stars is assumed to be harmonic, the underlying stellar dynamo mechanism can support photospheric magnetic fields with a prominent toroidal component even in the presence of axisymmetric magnetic topologies. In particular, it is argued that the observed increase in the toroidal energy in low-mass fast-rotating stars can be naturally explained with an underlying αΩ mechanism.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/20.500.12386/249992016-01-01T00:00:00ZThe accretion rate and minimum spin period of accreting pulsarshttp://hdl.handle.net/20.500.12386/24046Title: The accretion rate and minimum spin period of accreting pulsars
Authors: BONANNO, Alfio Maurizio; Urpin, V.
Abstract: We consider combined rotational, magnetic, and thermal evolution of the neutron star during the accretion phase in a binary system. A rapid accretion-driven decay of the magnetic field decreases substantially the efficiency of angular momentum transfer. As a result, the neutron star cannot spin-up to periods shorter than some limiting value even if accretion is very long and accretion rate is high. The proposed mechanism can explain a discrepancy between the shortest detected period and minimal possible spin period of neutron stars.
Acknowledgments: We would like to thank Dany Page for kindly providing us with the mean-field EOS used in the calculation.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/20.500.12386/240462015-01-01T00:00:00ZThe EXOTIME project: signals in the O-C diagrams of the rapidly pulsating subdwarfs DW Lyn, V1636 Ori, QQ Vir, and V541 Hyahttp://hdl.handle.net/20.500.12386/31643Title: The EXOTIME project: signals in the O-C diagrams of the rapidly pulsating subdwarfs DW Lyn, V1636 Ori, QQ Vir, and V541 Hya
Authors: Mackebrandt, F.; Schuh, S.; SILVOTTI, Roberto; Kim, S. -L.; Kilkenny, D.; Green, E. M.; Lutz, R.; Nagel, T.; Provencal, J. L.; Otani, T.; Oswalt, T. D.; BENATTI, SERENA; LANTERI, Luciano; BONANNO, Alfio Maurizio; FRASCA, Antonio; Janulis, R.; Paparó, M.; Molnár, L.; CLAUDI, Riccardo; Østensen, R. H.
Abstract: Aims: We aim to investigate variations in the arrival time of coherent stellar pulsations due to the light-travel time effect to test for the presence of sub-stellar companions. Those companions are the key to one possible formation scenario of apparently single sub-dwarf B stars. <BR /> Methods: We made use of an extensive set of ground-based observations of the four large amplitude p-mode pulsators DW Lyn, V1636 Ori, QQ Vir, and V541 Hya. Observations of the TESS space telescope are available on two of the targets. The timing method compares the phase of sinusoidal fits to the full multi-epoch light curves with phases from the fit of a number of subsets of the original time series. <BR /> Results: Observations of the TESS mission do not sample the pulsations well enough to be useful due to the (currently) fixed two-minute cadence. From the ground-based observations, we infer evolutionary parameters from the arrival times. The residual signals show many statistically significant periodic signals, but no clear evidence for changes in arrival time induced by sub-stellar companions. The signals can be explained partly by mode beating effects. We derive upper limits on companion masses set by the observational campaign. <P />Photometric data of Fig. 1, results in Figs. 8, 10, 12, and 14, and figures in the appendix are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/638/A108">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/638/A108</A> <P />Based on observations obtained at the 0.9 m SARA-KP telescope, which is operated by the Southeastern Association for Research in Astronomy (<A href="https://www.saraobservatory.org/">http://saraobservatory.org</A>).
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/20.500.12386/316432020-01-01T00:00:00Z