V. Jatenco-Pereira

University of São Paulo, San Paulo, São Paulo, Brazil

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Publications (96)206.47 Total impact

  • A. A. Vidotto, M. Opher, V. Jatenco-Pereira, T. I. Gombosi
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    ABSTRACT: The topology of the magnetic field of young stars is important not only for the investigation of magnetospheric accretion, but also responsible in shaping the large-scale structure of stellar winds, which are crucial for regulating the rotation evolution of stars. Because winds of young stars are believed to have enhanced mass-loss rates compared to those of cool, main-sequence stars, the interaction of winds with newborn exoplanets might affect the early evolution of planetary systems. This interaction can also give rise to observational signatures which could be used as a way to detect young planets, while simultaneously probing for the presence of their still elusive magnetic fields. Here, we investigate the interaction between winds of young stars and hypothetical planets. For that, we model the stellar winds by means of 3D numerical magnetohydrodynamic simulations. Although these models adopt simplified topologies of the stellar magnetic field (dipolar fields that are misaligned with the rotation axis of the star), we show that asymmetric field topologies can lead to an enhancement of the stellar wind power, resulting not only in an enhancement of angular momentum losses, but also intensifying and rotationally modulating the wind interactions with exoplanets.
    12/2013;
  • V. Jatenco-Pereira
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    ABSTRACT: The need of a minimum amount of ionization in protostellar accretion discs is necessary for the magnetorotational instability to take place. This instability is believed to be the mechanism responsible for a magnetohydrodynamic (MHD) turbulence that could lead to the accretion observed. In this work, we study the role of MHD waves as a source of heating in discs. We analyse if Alfvén waves, when damped during their propagation through the disc, can transfer enough energy in order to raise its temperature. As the discs are composed of dust, we suggest here that the Alfvén waves are damped by the dust-cyclotron mechanism of damping. In this mechanism when charged dust particles acquire the same (cyclotron) frequency as the waves, a resonance occurs that leads to the damping of the waves. Here, we present a disc model with two heating mechanisms: the `anomalous' viscosity considered in terms of the α parametrization and the damping of Alfvén waves. We vary the space parameters in order to study the second mechanism's behaviour. We show that the waves can increase the temperature of the disc and flatten the traditional r3/4 effective temperature profile of the disc.
    Monthly Notices of the Royal Astronomical Society 06/2013; 431(4):3150-3158. · 5.52 Impact Factor
  • V. Jatenco-Pereira
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    ABSTRACT: A minimum amount of ionization in proto-stellar accretion disks is necessary for the magneto-rotational instability (MRI) to take place, leading to accretion of material towards the central star. As proto-stellar disks are composed of dust, in this work we consider the damping of Alfvén waves due to dust-cyclotron resonances as an additional heating mechanism to viscous accretion disks. When charged grains become coupled to the waves, they introduce a cutoff (resonance) in the Alfvén wave spectrum, providing an important damping mechanism for the waves. Here, we show that the damping of the waves can increase the temperature of the disk, resulting in an increase on the ionization fraction, thus reducing the extension of quiescent zones in the disk.
    12/2012;
  • R. M. Evans, M. Opher, V. Jatenco-Pereira, T. I. Gombosi
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    ABSTRACT: Surfave Alfvén wave damping has been used by many authors in order to provide an heating and acceleration mechanism for driving winds in many regions of HR diagram. Based on the 1D solar wind model of Jatenco-Pereíra et al. (1994) we investigate the effect of surface Alfvén wave damping, for solar minima conditions, using a three-dimensional (3D) magnetohydrodynamics (MHD) model. The surface Alfvén wave damping length LSW depends on the superradial expansion factor S of magnetic field lines. We quantify S for Carrington Rotation 1912 with a steady state solar background generated with the Space Weather Modeling Framework, and compare with estimates by Dobrzycka et al. (1999) using SOHO observations. We estimate the surface Alfvén wave damping for active regions, quiet sun, and the border between open and closed magnetic field lines (Evans et al. 2009).
    12/2011;
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    A. A. Vidotto, M. Opher, V. Jatenco-Pereira, T. I. Gombosi
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    ABSTRACT: We perform 3D time-dependent numerical MHD simulations of the wind and magnetospheric structures of weak-lined T Tauri stars, in the case there is a misalignment between the axis of rotation of the star and its magnetic dipole moment vector. The model allow us to study the interaction of a magnetized wind with a magnetized exoplanet. Such interaction gives rise to reconnection, generating electrons that propagate along the planet's magnetic field lines and produce electron cyclotron radiation at radio wavelengths. This radio emission could be detectable by LOFAR in the near future.
    10/2011;
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    A. Vidotto, M. Opher, V. Jatenco-Pereira, T. I. Gombosi
    09/2010;
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    A. A. Vidotto, M. Opher, V. Jatenco-Pereira, T. I. Gombosi
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    ABSTRACT: Based on our previous work (Vidotto et al. 2009a), we investigate the effects on the wind and magnetospheric structures of weak-lined T Tauri stars due to a misalignment between the axis of rotation of the star and its magnetic dipole moment vector. In such configuration, the system loses the axisymmetry presented in the aligned case, requiring a fully 3D approach. We perform 3D numerical MHD simulations of stellar winds and study the effects caused by different model parameters. The system reaches a periodic behavior with the same rotational period of the star. We show that the magnetic field lines present an oscillatory pattern and that by increasing the misalignment angle, the wind velocity increases. Our wind models allow us to study the interaction of a magnetized wind with a magnetized extra-solar planet. Such interaction gives rise to reconnection, generating electrons that propagate along the planet's magnetic field lines and produce electron cyclotron radiation at radio wavelengths. We find that a close-in Jupiter-like planet orbiting at 0.05AU presents a radio power that is ~5 orders of magnitude larger than the one observed in Jupiter, which suggests that the stellar wind from a young star has the potential to generate strong planetary radio emission that could be detected in the near future with LOFAR. This radio power varies according to the phase of rotation of the star. We also analyze whether winds from misaligned stellar magnetospheres could cause a significant effect on planetary migration. Compared to the aligned case, we show that the time-scale tau_w for an appreciable radial motion of the planet is shorter for larger misalignment angles. While for the aligned case tau_w~100Myr, for a stellar magnetosphere tilted by 30deg, tau_w ranges from ~40 to 70Myr for a planet located at a radius of 0.05AU. (Abridged) Comment: 21 pages, 16 figures, 2 tables (emulateapj.cls). Accepted for publication in the ApJ
    The Astrophysical Journal 07/2010; · 6.73 Impact Factor
  • G.R. Keller, V. Jatenco-Pereira
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    ABSTRACT: The Wolf–Rayet (WR) stars are hot luminous objects which are suffering an extreme mass loss via a continuous stellar wind. The high values of mass loss rates and high terminal velocities of the WR stellar winds constitute a challenge to the theories of radiation driven winds. Several authors incorporated magnetic forces to the line driven mechanism in order to explain these characteristics of the wind. Observations indicate that the WR stellar winds may reach, at the photosphere, velocities of the order of the terminal values, which means that an important part of the wind acceleration occurs at the optically thick region. The aim of this study is to analyze a model in which the wind in a WR star begins to be accelerated in the optically thick part of the wind. We used as initial conditions stellar parameters taken from the literature and solved the energy, mass and momentum equations. We demonstrate that the acceleration only by radiative forces is prevented by the general behavior of the opacities. Combining radiative forces plus a flux of Alfvén waves, we found in the simulations a fast drop in the wind density profile which strongly reduces the extension of the optically thick region and the wind becomes optically thin too close its base. The understanding how the WR wind initiate is still an open issue.
    Advances in Space Research 01/2010; · 1.18 Impact Factor
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    R. M. Evans, M. Opher, V. Jatenco-Pereira, T. I. Gombosi
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    ABSTRACT: Here we investigate the contribution of surface Alfven wave damping to the heating of the solar wind in minima conditions. These waves are present in regions of strong inhomogeneities in density or magnetic field (e. g., the border between open and closed magnetic field lines). Using a 3-dimensional Magnetohydrodynamics (MHD) model, we calculate the surface Alfven wave damping contribution between 1-4 solar radii, the region of interest for both acceleration and coronal heating. We consider waves with frequencies lower than those that are damped in the chromosphere and on the order of those dominating the heliosphere. In the region between open and closed field lines, within a few solar radii of the surface, no other major source of damping has been suggested for the low frequency waves we consider here. This work is the first to study surface Alfven waves in a 3D environment without assuming a priori a geometry of field lines or magnetic and density profiles. We determine that waves with frequencies >2.8x10^-4 Hz are damped between 1-4 solar radii. In quiet sun regions, surface Alfven waves are damped at further distances compared to active regions, thus carrying additional wave energy into the corona. We compare the surface Alfven wave contribution to the heating by a variable polytropic index and find that it an order of magnitude larger than needed for quiet sun regions. For active regions the contribution to the heating is twenty percent. As it has been argued that a variable gamma acts as turbulence, our results indicate that surface Alfven wave damping is comparable to turbulence in the lower corona. This damping mechanism should be included self consistently as an energy driver for the wind in global MHD models. Comment: Accepted to ApJ (scheduled September '09), 22 pages, 8 figures
    08/2009;
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    A. A. Vidotto, M. Opher, V. Jatenco-Pereira, T. I. Gombosi
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    ABSTRACT: By means of numerical simulations, we investigate magnetized stellar winds of pre-main-sequence stars. In particular we analyze under which circumstances these stars will present elongated magnetic features (e.g., helmet streamers, slingshot prominences, etc). We focus on weak-lined T Tauri stars, as the presence of the tenuous accretion disk is not expected to have strong influence on the structure of the stellar wind. We show that the plasma-beta parameter (the ratio of thermal to magnetic energy densities) is a decisive factor in defining the magnetic configuration of the stellar wind. Using initial parameters within the observed range for these stars, we show that the coronal magnetic field configuration can vary between a dipole-like configuration and a configuration with strong collimated polar lines and closed streamers at the equator (multi-component configuration for the magnetic field). We show that elongated magnetic features will only be present if the plasma-beta parameter at the coronal base is beta<<1. Using our self-consistent 3D MHD model, we estimate for these stellar winds the time-scale of planet migration due to drag forces exerted by the stellar wind on a hot-Jupiter. In contrast to the findings of Lovelace et al. (2008), who estimated such time-scales using the Weber & Davis model, our model suggests that the stellar wind of these multi-component coronae are not expected to have significant influence on hot-Jupiters migration. Further simulations are necessary to investigate this result under more intense surface magnetic field strengths (~2-3 kG) and higher coronal base densities, as well as in a tilted stellar magnetosphere. Comment: Accepted for publication in the Astrophysical Journal, 10 pages, 5 figures, emulateapj
    The Astrophysical Journal 08/2009; · 6.73 Impact Factor
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    A. A. Vidotto, M. Opher, V. Jatenco-Pereira, T. I. Gombosi
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    ABSTRACT: By means of self-consistent 3D MHD numerical simulations, we analyze magnetized solar-like stellar winds and their dependence on the plasma-beta parameter. We adopt in our simulations a heating parameter described by gamma, which is responsible for the thermal acceleration of the wind. We analyze winds with polar magnetic field intensities ranging from 1 to 20G. We show that the wind structure presents characteristics that are similar to the solar coronal wind. The steady-state magnetic field topology for all cases is similar, presenting a configuration of helmet streamer-type, with zones of closed field lines and open field lines coexisting. Higher magnetic field intensities lead to faster and hotter winds. The increase of the field intensity generates a larger dead zone in the wind, i. e., the closed loops that inhibit matter to escape from latitudes lower than ~45 degrees extend farther away from the star. The Lorentz force leads naturally to a latitude-dependent wind. We show that by increasing the density and maintaining B0=20G, the system recover back to slower and cooler winds. For a fixed gamma, we show that the key parameter in determining the wind velocity profile is the beta-parameter at the coronal base. Therefore, there is a group of magnetized flows that would present the same terminal velocity despite of its thermal and magnetic energy densities, as long as the plasma-beta parameter is the same. This degeneracy, however, can be removed if we compare other physical parameters of the wind, such as the mass-loss rate. We analyze the influence of gamma in our results and we show that it is also important in determining the wind structure. (Abridged)
    The Astrophysical Journal 04/2009; 699(1). · 6.73 Impact Factor
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    A.A. Vidotto, V. Jatenco-Pereira
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    ABSTRACT: Alfvén waves have been invoked as an important mechanism of particle acceleration in stellar winds of cool stars. After their identification in the solar wind they started to be studied in winds of stars located in different regions of the HR diagram. We discuss here some characteristics of these waves and we present a direct application in the acceleration of late-type stellar winds.
    Advances in Space Research 01/2009; · 1.18 Impact Factor
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    A. A. Vidotto, M. Opher, V. Jatenco-Pereira, T. I. Gombosi
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    ABSTRACT: We investigate magnetized solar-like stellar winds by means of self-consistent three-dimensional (3D) magnetohydrodynamics (MHD) numerical simulations. We analyze winds with different magnetic field intensities and densities as to explore the dependence on the plasma-beta parameter. By solving the fully ideal 3D MHD equations, we show that the plasma-beta parameter is the crucial parameter in the configuration of the steady-state wind. Therefore, there is a group of magnetized flows that would present the same terminal velocity despite of its thermal and magnetic energy densities, as long as the plasma-beta parameter is the same. Comment: 2 pages, 4 figures, Proceedings of the IAU Symposium 259, "Cosmic Magnetic Fields: From Planets, to Stars and Galaxies", November 2008
    Proceedings of the International Astronomical Union 01/2009;
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    R. M. Evans, M. Opher, V. Jatenco-Pereira, T. I. Gombosi
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    ABSTRACT: Here we investigate the contribution of surface Alfvén wave damping to the heating of the solar wind in minima conditions. These waves are present in the regions of strong inhomogeneities in density or magnetic field (e.g., the border between open and closed magnetic field lines). Using a three-dimensional (3D) magnetohydrodynamics (MHD) model, we calculate the surface Alfvén wave damping contribution between 1 and 4 R sun (solar radii), the region of interest for both acceleration and coronal heating. We consider waves with frequencies lower than those that are damped in the chromosphere and on the order of those dominating the heliosphere: 3 × 10-6 to 10-1 Hz. In the region between open and closed field lines, within a few R sun of the surface, no other major source of damping has been suggested for the low frequency waves we consider here. This work is the first to study surface Alfvén waves in a D environment without assuming a priori a geometry of field lines or magnetic and density profiles. We demonstrate that projection effects from the plane of the sky to 3D are significant in the calculation of field line expansion. We determine that waves with frequencies >2.8 ×10-4 Hz are damped between 1 and 4 R sun. In quiet-Sun regions, surface Alfvén waves are damped at further distances compared to active regions, thus carrying additional wave energy into the corona. We compare the surface Alfvén wave contribution to the heating by a variable polytropic index and find it as an order of magnitude larger than needed for quiet-Sun regions. For active regions, the contribution to the heating is 20%. As it has been argued that a variable gamma acts as turbulence, our results indicate that surface Alfvén wave damping is comparable to turbulence in the lower corona. This damping mechanism should be included self-consistently as an energy driver for the wind in global MHD models.
    The Astrophysical Journal 01/2009; 703(1):179-186. · 6.73 Impact Factor
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    ABSTRACT: Excitation of a global Alfvén wave (GAW) is proposed as a viable mechanism to explain plasma heating in the magnetosphere of young stars. The wave and basic plasma parameters are compatible with the requirement that the dissipation length of GAWs be comparable to the distance between the shocked region at the star's surface and the truncation region in the accretion disk. A two-fluid magnetohydrodynamic plasma model is used in the analysis. A current-carrying filament along magnetic field lines acts as a waveguide for the GAWs. The current in the filament is driven by plasma waves along the magnetic field lines and/or by plasma crossing magnetic field lines in the truncated region of the disk of the accreting plasma. The conversion of a small fraction of the kinetic energy into GAW energy is sufficient to heat the plasma filament to observed temperatures.
    The Astrophysical Journal 12/2008; 600(1):292. · 6.73 Impact Factor
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    D. Falceta-Gonçalves, Z. Abraham, V. Jatenco-Pereira
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    ABSTRACT: The study of Wolf–Rayet stars plays an important role in evolutionary theories of massive stars. Among these objects, ∼20 per cent are known to be in binary systems and can therefore be used for the mass determination of these stars. Most of these systems are not spatially resolved and spectral lines can be used to constrain the orbital parameters. However, part of the emission may originate in the interaction zone between the stellar winds, modifying the line profiles and thus challenging us to use different models to interpret them. In this work, we analysed the He iiλ4686 Å+ C ivλ4658 Å blended lines of WR 30a (WO4+O5) assuming that part of the emission originate in the wind–wind interaction zone. In fact, this line presents a quiescent base profile, attributed to the WO wind, and a superposed excess, which varies with the orbital phase along the 4.6-d period. Under these assumptions, we were able to fit the excess spectral line profile and central velocity for all phases, except for the longest wavelengths, where a spectral line with constant velocity seems to be present. The fit parameters provide the eccentricity and inclination of the binary orbit, from which it is possible to constrain the stellar masses.
    Monthly Notices of the Royal Astronomical Society 12/2007; 383(1):258 - 262. · 5.52 Impact Factor
  • V Jatenco-Pereira
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    ABSTRACT: We discuss some of the astrophysical problems in which Alfvén waves can play an important role. The problems that we focus in are: (i) Alfvén waves in stellar winds; (ii) formation of extragalactic jets by Alfvén waves, and (iii) formation of quasar clouds by a thermal instability and Alfvén waves.
    Physica Scripta 01/2007; 1995(T60):113. · 1.03 Impact Factor
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    A. A. Vidotto, V. Jatenco-Pereira
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    ABSTRACT: In order for the magneto-rotational instability to take place, we need a sufficiently ionized disk. Here, we study, besides viscous dissipation, another heating mechanism for the disk that involves the damping of Alfvén waves due to its interaction with dust grains.
    Proceedings of the International Astronomical Union 07/2006; 2:491 - 491.
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    D. Falceta-Goncalves, Z. Abraham, V. Jatenco-Pereira
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    ABSTRACT: One of the most intriguing spectral features of WR binary stars is the presence of time-dependent line profiles. Long term observations of several systems revealed the periodicity of this variability, synchronized with the orbital movement. Several partially successful models have been proposed to reproduce the observed data. The most promising assume that the origin of the emission is the wind-wind interaction zone. In this scenario, two high velocity and dense winds produce a strong shock layer, responsible for most of the X-rays observed from these systems. As the secondary star moves along its orbital path, the shock region of conical shape, changes its position with relation to the line of sight. As a consequence, the stream measured Doppler shift presents time variations resulting in position changes of the spectral line. In our work, we present an alternative model, introducing turbulence in the shock layer to account for the line broadening and opacity effects for the asymmetry in the line profiles. We showed that the gas turbulence avoids the need of an unnaturally large contact layer thickness to reproduce line broadening. Also, we demonstrated that if the emission from the opposing cone surface is absorbed, the result is a single peaked profile. This result fully satisfies the recent data obtained from massive binary systems, and can help on the determination of both winds and orbital parameters. We successfully applied this model to the Br22 system and determined its orbital parameters. Comment: To appear in the MNRAS
    Monthly Notices of the Royal Astronomical Society 07/2006; · 5.52 Impact Factor
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    A. A. Vidotto, D. Falceta-Goncalves, V. Jatenco-Pereira
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    ABSTRACT: Cool giant and supergiant stars generally present low velocity winds with high mass loss rates. Several models have been proposed to explain the acceleration process of these winds. Although dust is known to be present in these objects, the radiation pressure on these particles is uneffective in reproducing the observed physical parameters of the wind. The most promising acceleration mechanism cited in the literature is the transference of momentum and energy from Alfven waves to the gas. Usually, these models consider the wind to be isothermal. We present a stellar wind model in which the Alfven waves are used as the main acceleration mechanism, and determine the temperature profile by solving the energy equation taking into account both the radiative losses and the wave heating. We also determine self-consistently the magnetic field geometry as the result of the competition between the magnetic field and the thermal pressures gradient. As main result, we show that the magnetic geometry present a super-radial index in the region where the gas pressure is increasing. However, this super-radial index is greater than that observed for the solar corona. Comment: Accepted for publication in Space Science Reviews. Presented at the World Space Environment Forum 2005, Austria. 8 pages, 2 figures
    Space Science Reviews 03/2006; · 5.52 Impact Factor