Results from high resolution solar images and spectra obtained at the Pic du Midi Observatory (1986–1990)

Roudier, Th.; Müller, R.; Vigneau, J.; Auffret, H.; Espagnet, O.; Simon, G.; Title, A. M.; Frank, Z.; Shine, R. A.; Tarbell, T. D.; Mein, P.; Malherbe, J.-M.

doi:10.1016/0273-1177(91)90380-3

Cited by 8 publications

(9 citation statements)

References 5 publications

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“…These data have already been studied with Fourier techniques (Straus et al, 1999). As can be seen from the image, many spatial scales are present and the spectrum appears to be very broad with no characteristic lengths (Roudier et al, 1991). The POD of the velocity field u(x, y, t) (x, y being the coordinates on the surface of the Sun) yields a set of eigenfunctions [Ψ j (x, y)] and corresponding coefficients [a j (t)], as well as the sequence of eigenvalues λ j (j = 0, 1, .…”

Section: The Data Setmentioning

confidence: 97%

Spatio-Temporal Analysis of Photospheric Turbulent Velocity Fields Using the Proper Orthogonal Decomposition

et al. 2008

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The spatio-temporal dynamics of the solar photosphere are studied by performing a proper orthogonal decomposition (POD) of line-of-sight velocity fields computed from high-resolution data coming from the SOHO/MDI instrument. Using this technique, we are able to identify and characterize the different dynamical regimes acting in the system. All of the POD modes are characterized by two well-separated peaks in the frequency spectra. In particular, low-frequency oscillations, with frequencies in the range 20 -130 µHz, dominate the most energetic POD modes (excluding solar rotation) and are characterized by spatial patterns with typical scales of about 3 Mm. Patterns with larger typical scales, of about 10 Mm, are dominated by p-mode oscillations at frequencies of about 3000 µHz. The p-mode properties found by POD are in agreement with those obtained with the classical Fourier analysis. The spatial properties of high-energy POD modes suggest the presence of a strong coupling between low-frequency modes and turbulent convection.

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Section: The Data Setmentioning

confidence: 97%

Spatio-Temporal Analysis of Photospheric Turbulent Velocity Fields Using the Proper Orthogonal Decomposition

et al. 2008

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“…2D spectrograms have been obtained using a Multichannel Subtractive Double Pass (MSDP) spectrograph (Roudier et al 1991;Espagnet et al 1993Espagnet et al , 1995 or Fabry-Perot interferometers (Salucci et al 1994;Bendlin & Volkmer 1993;Krieg et al 2000;Hirzberger et al 2001). …”

Section: Introductionmentioning

confidence: 99%

Time series of high resolution photospheric spectra in a quiet region of the Sun

Puschmann¹,

Cobo²,

Vázquez³

et al. 2005

A&A

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From the inversion of a time series of high resolution slit spectrograms obtained from the quiet sun, the spatial and temporal distribution of the thermodynamical quantities and the vertical flow velocity is derived as a function of optical depth (log τ) and geometrical height (z). Spatial coherence and phase shift analyses between temperature and vertical velocity depict the height variation of these physical quantities for structures of different size. An average granular cell model is presented, showing the granule-intergranular lane stratification of temperature, vertical velocity, gas pressure and density as a function of log τ and z. Studies of a specific small and a specific large granular cell complement these results. A strong decay of the temperature fluctuations with increasing height together with a less efficient penetration of smaller cells is revealed. The T − T coherence at all granular scales is broken already at log τ = −1 or z ∼ 170 km. At the layers beyond, an inversion of the temperature contrast at granular scales >1. 5 is revealed, both in log τ and z. At deeper layers the temperature sensitivity of the H − opacity leeds to much smaller temperature fluctuations at equal log τ than at equal z, in concordance with Stein & Nordlund (1998, ApJ, 499, 914). Vertical velocities are in phase throughout the photosphere and penetrate into the highest layers under study. Velocities at the largest granular scales (∼ 4 ) are still found even at log τ ∼ −2.8 or z ∼ 370 km. Again a less efficient height penetration of smaller cells concerning convective velocities is revealed, although still at log τ ∼ −2 or z ∼ 280 km structures >1. 4 are detected. A similar size distribution of velocity and temperature structures with height provides observational evidence for substantial overshoot into the photosphere. At deep photospheric layers, the behaviour of the vertical velocities reflected in simulations is for the first time qualitatively reproduced by observations: intergranular velocities are larger than the granular ones and, both reach extrema, where the granular one is shifted towards higher layers.

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“…However, the granules observed on the solar surface have a typical size of about 2 Mm (see e.g. Muller 1989;Roudier et al 1991). Furthermore, the observations reported by Espagnet et al (1993) and Hirzberger et al (1997) suggest that k c /k 0 ≈ 2.…”

Section: Lorentzian Versus Exponential χ Kmentioning

confidence: 94%

“…However, in the case of the Sun, for instance, the granules have a size of about 2 Mm (see e.g. Muller 1989;Roudier et al 1991) while the pressurescale height, H p , is of the order of few hundred kilometers at the photosphere. Because near the photosphere the density scaleheight H ρ is of the same order as H p and even lower, our assumption does not hold near the photosphere.…”

Section: Appendix A: Theoretical Developments Appendix B: Approximatimentioning

confidence: 99%

Stellar granulation as seen in disk-integrated intensity

Samadi

Belkacem

Ludwig

2013

A&A

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Context. Solar granulation has been known for a long time to be a surface manifestation of convection. The space-borne missions CoRoT and Kepler enable us to observe the signature of this phenomena in disk-integrated intensity on a large number of stars. Aims. The space-based photometric measurements show that the global brightness fluctuations and the lifetime associated with granulation obeys characteristic scaling relations. We thus aimed at providing simple theoretical modeling to reproduce these scaling relations, and subsequently at inferring the physical properties of granulation across the Hertzsprung-Russell diagram. Methods. We developed a simple 1D theoretical model. The input parameters were extracted from 3D hydrodynamical models of the surface layers of stars, and the free parameters involved in the model were calibrated with solar observations. Two different prescriptions for representing the Fourier transform of the time-correlation of the eddy velocity were compared: a Lorentzian and an exponential form. Finally, we compared our theoretical prediction with 3D radiative hydrodynamical (RHD) numerical modeling of stellar granulation (hereafter ab initio approach). Results. Provided that the free parameters are appropriately adjusted, our theoretical model reproduces the observed solar granulation spectrum quite satisfactorily; the best agreement is obtained for an exponential form. Furthermore, our model results in granulation spectra that agree well with the ab initio approach using two 3D RHD models that are representative of the surface layers of an F-dwarf and a red-giant star. Conclusions. We have developed a theoretical model that satisfactory reproduces the solar granulation spectrum and gives results consistent with the ab initio approach. The model is used in a companion paper as theoretical framework for interpretating the observed scaling relations.

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Results from high resolution solar images and spectra obtained at the Pic du Midi Observatory (1986–1990)

Cited by 8 publications

References 5 publications

Spatio-Temporal Analysis of Photospheric Turbulent Velocity Fields Using the Proper Orthogonal Decomposition

Spatio-Temporal Analysis of Photospheric Turbulent Velocity Fields Using the Proper Orthogonal Decomposition

Time series of high resolution photospheric spectra in a quiet region of the Sun

Stellar granulation as seen in disk-integrated intensity

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