Hidrodinámica y magnetismo estelares

la convección estelary las erupciones solares gigantes

Hidrodinámica y magnetismo estelares

la convección estelary las erupciones solares gigantes

Fernando Moreno InsertisInstituto de Astrofisica de Canarias

Photosphere

Ca-K chromospheric emissionSOHO-EIT 284 Å coronal emission

Sch

arm

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ans

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G-b

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425,

200

3Au

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TRACE (17.1 nm): emergence of an active region and flaring

1. 2.

3.

I. To understand the fundamental features of the eruption processes in the Sun

II.

To model the emergence of magnetized plasma through the convection cells into the atmosphere

III.

Global, long-term objective: to disclose via numerical experiments the complicated structure of the atmosphere of the Sun and cool stars.

Objective of our numerical modeling efforts:

Niels-Bohr Inst. , Copenhagen

• Klaus Galsgaard

University of St Andrews

• Alan Hood

• Vasilis Archontis (1. 2006 → )

• Michelle Murray

Instituto de Astrofisica de Canarias

• Fernando Moreno-Insertis

• Abel Tortosa

• Vasilis Archontis ( → 1. 2006)

Collaboration (since 2004)

Naval Research Lab., Washington

• Ignacio Ugarte

• Hydrodynamics + magnetic fields

• No radiation transfer

• Simplified thermodynamics.

Part 1: high-temperature jets in the corona

A. Tortosa, F. Moreno-InsertisF. Moreno-Insertis, K. Galsgaard, I. Ugarte Urra

Method used: • solve the equations of hydrodynamics for a magnetized plasma

• thermodynamics: ideal gas, no heat conduction

Mass, momentum andenergy conservation eqs

Faraday, Ohm, Ampere

+ equation of state

Numerical code (Galsgaard + Nordlund)

• Explicit finite-difference scheme• Staggered, non-uniform (but non-adaptive) grid

• 6th order derivation + 5th order interpolation in space• 3d order Hyman update in time

• Shocks, current sheets, sharp transitions are resolved using hyperdiffusivity algorithms

The background stratification

integration domain isothermal corona

steep temperature rise (T.R.)

isothermal photosphere

upper convection zone

Pressure contrast: 10

9

Density contrast: 2 10

10

Typical computational requirements

Standard run: • Numerical grid of 512x512x512 points • RAM memory requirements: typically around 10 GB

Storage requirements: • Experiment with 100 snapshots: 400 GBs

Parallelization: • Excellent up to 512 CPUs• Method used: MPI

Yohkoh’s high-velocity jets in soft X-Rays (SXT)

Shimojo et al, PASJ 48, 1996

• Hinode XRT: observation of X-Ray jets in coronal holes

Inverted-Y jet shapes

Heyvaerts, Priest

& Rust 1977

Reconnection and jet emission following flux

emergence:

Our results:

• We studied a jet that appeared right after a magnetic bipole emerged at the photosphere.

• Observations: → X-Rays and Extreme UV (Hinode satellite)

→ full disk magnetograms (SOHO MDI)

• Computer modeling:

→ study the emergence of magnetized plasma into a coronal hole

3D numerical simulation

carried out

in the Marenostrum and LaPalma

supercomputing installations

of the Red Española de Supercomputación

Background coronal field

• For this experiment, physical values adequate to a coronal hole were used:

→ ρ ≈ 2 108 atoms cm-3

→ open ambient field lines→ coronal field strength: 10 G→ T ≈ 1.1 106 K

• Domain size:

(x,y,z) 34 000 km x 38 000 km x 33 000 km (5 000 km below, 29 000 km above the solar surface)

Current distribution

(t=15 min)

Velocity map

(t=22 min)

3D view: current and temperature

Temperature map

(t=22 min)

Horizontal drift of the 2-chamber + jet structure

Agreement between the numerical results and the observations

• Maximum jet velocity at 160 km /s

• Jet duration between 10 and 20 min

• Transverse (=drift?) velocities between 0 and 20 km / s

=> the overall agreement is excellent

• Observations: Savcheva etal 2007

• Statistics from 7197 polar jets using Hinode/Soho

• Hydrodynamics + radiation transfer + + magnetic fields => realistic models of convective cells.

Part 2: Experiments with convection

A. Tortosa, F. Moreno-Insertis

• The equation of radiation transfer is solved for I(ν, n, x)

→ along 24 rays at each grid point

→ for a number of frequency bins

• The radiative heating / cooling is calculated through:

Radiation transfer / heating of the plasma

Simulation of emergence of magnetic flux across solar convection including

chromospheric layers

• Size of simulation domain: 16,000 km (x); 12,000 km (y); 3,800 km (z)

• Computational grid: 320 points x 240 points x 190 points

• Optical depth unity located ~ 2600 km above bottom boundary

• Open bottom boundary + periodic side boundaries

Observation of emergence of an active region

in the solar photosphere

80-min 80-min GG-band movie of AR 8737 (Dutch Open Telescope) -band movie of AR 8737 (Dutch Open Telescope)

Area: 51 Area: 51 × 35 arcsec× 35 arcsec22

Anomalous granulation during flux emergence episodes

Temperature structure at the visible surface and at the chromosphere (t=12.6 min and t=14.5 min)Temperature structure at the visible surfaceand in the chromosphere (t=12.6, 14.5 min)

Temperature structure at the visible surfaceand in the chromosphere (t=12.6 min; 14.5 min)

Topology of field lines issuing from photospheric concentrations

Plasma dynamics and heating resulting from impact

by upcoming shock wave

Some final points

• With 3D massively parallel numerical experiments important

aspects of the giant stellar eruptions can be explained.

• There is still a long way to go to understand some basic aspects and many details of those phenomena.

• The amazing pace of improvement of computing equipment and visualization tools promises fast progress in the coming years.