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An introduction to the MULTI radiative transfer code

An introduction to the MULTI radiative transfer code. Lars Heggland Institute of Theoretical Astrophysics, University of Oslo Kwasan Observatory, Kyoto University. Radiative transfer. The study of generation and transport of radiation in stellar atmospheres Important physical processes:

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An introduction to the MULTI radiative transfer code

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  1. An introduction to the MULTI radiative transfer code Lars Heggland Institute of Theoretical Astrophysics, University of Oslo Kwasan Observatory, Kyoto University

  2. Radiative transfer • The study of generation and transport of radiation in stellar atmospheres • Important physical processes: • Absorption • Emission / reemission • Scattering • Formation of spectral lines

  3. Why is this important? • Radiation is one of the few ways to directly collect information about a star • Spectral line formation is highly dependent on physical parameters such as: • Temperature (ionisation states, intensity) • Velocity fields (Doppler shifts)

  4. Why is this important? • Thus, a wealth of information is contained in spectral lines • By studying specific lines, we can get information about conditions from the photosphere (neutral or singly ionised lines, 5-10000 K) to the corona (highly ionised metal lines, 1 MK ++)

  5. Numerical radiative transfer • The aim: using theoretical models to explain and reproduce observations • OR: using models to predict future observations • The problem is non-trivial due to the complexity of the physical processes and of the atmosphere; simplifications required

  6. Numerical radiative transfer • Real atoms have hundreds of different energy levels • Very computationally intensive • Many levels have little effect on the studied line • Make simplified, smaller atomic models • Compute one element at a time

  7. The MULTI code • A non-LTE radiative transfer code written by Mats Carlsson • Written in standard compliant Fortran-77; designed for portability • Freely available for use: http://www.astro.uio.no/~matsc/mul22/index.html

  8. The MULTI code • Works in 1D; multi-dimensional analysis can be done by computing several different rays • Uses a given background atmosphere; dynamics (waves etc.) can be taken into account by running a simulation for each timestep

  9. The MULTI code • Powerful, but complex • The amount of input data and parameters is high • Patience required, experience very useful • Impressive amounts of output data make it worth it

  10. Documentation • Main: A computer program for solving multi-level non-LTE radiative transfer problems in moving or static atmospheres (available on Carlsson’s website, 46 pages plus appendices) • Update: mul22.ps (included in distribution) • multi.help, variables.doc (included)

  11. Input files CA 2 * ABUND AWGT 6.3304 40.08 *NK NLIN NCNT NFIX 6 5 0 5 * E G ION 0.00000 2.00000 'CA II 3P6 4S 2SE ' 2 13650.248 4.00000 'CA II 3P6 3D 2DE 3/2' 2 13710.900 6.00000 'CA II 3P6 3D 2DE 5/2' 2 25191.535 2.00000 'CA II 3P6 4P 2PO 1/2' 2 25414.465 4.00000 'CA II 3P6 4P 2PO 3/2' 2 95785.470 1.00000 'CA III GROUND TERM ' 3 * F NQ QMAX Q0 IW GA GVW GS 4 1 3.3000E-01 40 300. 3. 0 1.48E08 1.62 3.0E-06 5 1 6.6000E-01 40 300. 3. 0 1.50E08 1.61 3.0E-06 4 2 4.4200E-02 40 75. .3 0 1.48E08 2.04 3.0E-06 5 2 8.8300E-03 40 75. .3 0 1.50E08 2.01 3.0E-06 5 3 5.3000E-02 40 75. .3 0 1.50E08 2.01 3.0E-06 * J I P A0 TRAD ITRAD 6 1 1 2.0363E-19 5915. 2 6 2 1 6.1484E-18 5755. 2 6 3 1 6.1484E-18 5755. 2 6 4 1 2.3823E-18 4925. 2 6 5 1 2.3823E-18 4925. 2 * COLL CA2COL 1.71E-07 1.71E-07 4.27E-07 2.92E-07 1.31E-06 2.08E-07 2.92E-07 2.93E-07 1.29E-06 3.05E-07 1.45E-10 1.88E-10 1.88E-10 2.68E-10 2.68E-10 • ATOM: Atomic model (example: 6-level calcium) • Complex, but needs only be done once

  12. Input files • ATMOS: Model atmosphere (example: truncated VAL3C) • Specified on lg column mass, lg optical depth (500) or geometrical depth scale VAL3C MASS SCALE * LG G 4.44 * NDEP 52 *LG COLUMN MASS TEMPERATURE NE V VTURB -5.279262E+00 4.470000E+05 1.205000E+09 0. 1.128000E+01 -5.270430E+00 1.410000E+05 3.839000E+09 0. 9.870000E+00 -5.269783E+00 8.910000E+04 5.961000E+09 0. 9.820000E+00 -5.268492E+00 5.000000E+04 9.993000E+09 0. 9.760000E+00 -5.267285E+00 3.700000E+04 1.318000E+10 0. 9.730000E+00 * HYDROGEN POPULATIONS * NH(1) NH(2) NH(3) NH(4) NH(5) NP 2.3841E+03 7.9839E-04 2.0919E-04 2.3110E-04 2.9470E-04 1.0030E+09 5.3401E+04 1.8790E-02 7.4560E-03 8.1751E-03 1.0430E-02 3.1990E+09 2.4030E+05 7.5740E-02 2.9400E-02 3.1550E-02 4.0101E-02 5.0310E+09 2.7390E+06 6.7709E-01 1.7230E-01 1.7180E-01 2.1430E-01 9.0170E+09 1.3850E+07 3.2580E+00 4.7581E-01 4.3231E-01 5.2440E-01 1.1970E+10 3.6271E+07 9.2240E+00 8.6389E-01 7.2180E-01 8.5328E-01 1.3710E+10

  13. Input files • DSCALE: Depth scale to use for calculations • Does not need to use the same values as the atmosphere model; interpolation is performed MV45C3 MASS SCALE 45 -6.672232 -5.22498 -5.21206 -5.20977 -5.20795 -5.20536 -5.20078 -5.19238

  14. Input files • INPUT: Run and output options • Controls starting approximation, number of iterations, convergence limit… • Trial and error required for best results DIFF=5.0,ELIM1=0.01,ELIM2=0.001,QNORM=12.85,THIN=0.1, IATOM2=0,ICONV=1,IHSE=0,ILAMBD=0,IOPAC=1,ISTART=2,ISUM=0, ITMAX=300,ITRAN=0,NMU=3, IWABND=0,IWATMS=0,IWATOM=0,IWCHAN=0,IWDAMP=0,IWEMAX=1,IWEQW=0, IWEVEC=0,IWHEAD=0,IWHSE=0,IWLGMX=1,IWLINE=0,IWLTE=0,IWN=0,IWNIIT=0, IWOPAC=0,IWRAD=0,IWRATE=0,IWSTRT=0,IWTAUQ=0,IWTEST=0,IWWMAT=0, IWARN=2,IOPACL=0,ISCAT=0,INCRAD=0,INGACC=1,ICRSW=0, IDL1=1,IDLNY=1,IDLCNT=1

  15. Input files • ABUND, ABSDAT: used to calculate background opacities • Should not need to be changed in a solar photosphere/chromosphere model • …maybe in the corona and in other stars

  16. Output • Lots of data! (See variables.doc) • Intensity, flux, line source functions, population densities, transition rates… • Data written to be readable by IDL; reading and analysis routines are included in the distribution

  17. Sample output: C I line in transition zone (pdf file)

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