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Observing, Modeling, and Understanding Stellar Granulation

Published online by Cambridge University Press:  08 February 2017

Dainis Dravins
Dainis Dravins*
Affiliation:
Lund Observatory Box 43 S-22100 Lund Sweden

Abstract

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Numerical simulations of the three-dimensional structure and time evolution of stellar surface convection are now possible, at least for solar-type stars. Using the output from such simulations as sets of spatially and temporally varying model atmospheres, synthetic granulation images and spectral line profiles are computed, and compared to observations. Thus obtained disk-integrated data agree with observed lineshapes and bisector patterns in different stars, and also permit stellar rotation to be determined. Such simulations represent the first generation of models that are free from the classical ad hoc parameters of ‘mixing-length’, ‘micro-’ or ‘macro-turbulence’, parameters which in the past have characterized and limited stellar astrophysics.

To infer the surface structure also in more exotic stars, simpler and parametrized models must still be used to interpret observed line asymmetries. Such models suggest that rapidly rising ‘granules’ cover only a small surface fraction on early-type stars, a situation opposite to that in solar-type ones, and one likely to affect magnetic fields and stellar activity. Theoretical challenges for the future include detailed modeling also of early-type, giant, and other non-solar type stars of different rotational velocities; the hydrodynamics of entire stellar envelopes (including the interaction with global oscillations); and the interaction with magnetic fields (including their generation). Greatly increased computing power will be needed for such detailed modeling throughout the Herzsprung-Russell diagram, possibly requiring custom-designed computers.

Signatures of stellar granulation are primarily observed as asymmetries and wavelength shifts in photospheric absorption lines. Observational challenges include achieving sufficient spectral resolution to fully resolve such asymmetries; identifying granulation signatures throughout the HR-diagram (including the blended spectra of cool stars); observing how line asymmetries for a given spectral type depend on stellar rotational velocity, measuring wavelength shifts between groups of different lines in the same star, and between different stars; monitoring lineshift variations during stellar activity cycles; and ultimately high-resolution spectroscopy of spatially resolved granulation structures across stellar disks. The latter will require active optics on future very large telescopes, or the use of long-baseline optical interferometers.

Type
VII. Convection and Magnetic Fields in Solar-type Stars
Information
Symposium - International Astronomical Union , Volume 138: Solar Photosphere: Structure, Convection and Magnetic Fields , 1990 , pp. 397 - 415
Copyright
Copyright © Kluwer 1990 

References

Antia, H.M., Chitre, S.M., Narashima, D.: 1984, Astrophys. J. 282, 574 Google Scholar
Atroshchenko, I.N., Gadun, A.S., Kostik, R.I.: 1989, in Rutten, R.F., Severino, G., eds. Solar and Stellar Granulation , Kluwer, p. 521 Google Scholar
Bowler, K.C., Bruce, A.D., Kenway, R.D., Pawley, G.S., Wallace, D.J.: 1987, Physics Today 40, No. 10, p. 40 Google Scholar
Bray, R.J., Loughhead, R.E.: 1978, Astrophys. J. 224, 276 Google Scholar
Deming, D., Espenak, F., Jennings, D.E., Brault, J.W., Wagner, J.: 1987, Astrophys. J. 316, 771 Google Scholar
Dravins, D.: 1981, Astron. Astrophys. 98, 367 Google Scholar
Dravins, D.: 1982, Ann. Rev. Astron. Astrophys. 20, 61 Google Scholar
Dravins, D.: 1987a, Astron. Astrophys. 172, 200 Google Scholar
Dravins, D.: 1987b, Astron. Astrophys. 172, 211 Google Scholar
Dravins, D.: 1989, in Rutten, R.J., Severino, G., eds. Solar and Stellar Granulation , Kluwer, p. 493 Google Scholar
Dravins, D., Larsson, B., Nordlund, Å.: 1986, Astron. Astrophys. 158, 83 Google Scholar
Dravins, D., Lindegren, L., Nordlund, Å.: 1981, Astron. Astrophys. 96, 345 Google Scholar
Dravins, D., Nordlund, Å.: 1989a, Astron. Astrophys. , in press Google Scholar
Dravins, D., Nordlund, Å.: 1989b, Astron. Astrophys. , in press Google Scholar
Dupree, A.K., Baliunas, S.L., Guinan, E.F.: 1984, Bull. AAS 16, 797 Google Scholar
Gigas, D.: 1989, in Rutten, R.F., Severino, G., eds. Solar and Stellar Granulation , Kluwer, p.533 Google Scholar
Gray, D.F.: 1986, Publ. Astron. Soc. Pacific 98, 319 Google Scholar
Gray, D.F.: 1988, Lectures on Spectral-Line Analysis: F, G, and K Stars , The Publisher, Arva (Ontario)Google Scholar
Gray, D.F., Nagel, T.: 1989, preprint Google Scholar
Gray, D.F., Toner, C.G.: 1985, Publ. Astron. Soc. Pacific 97, 543 Google Scholar
Gray, D.F., Toner, C.G.: 1986, Publ. Astron. Soc. Pacific 98, 499 Google Scholar
Gray, D.F., Toner, C.G.: 1985, Publ. Astron. Soc. Pacific 97, 543 Google Scholar
Jiménez, A., Pallé, P.L., Régulo, C., Roca Cortés, T., Elsworth, Y.P., Isaak, G.R., Jefferies, S.M., McLeod, C.P., New, R., van der Raay, H.B.: 1988, in Christensen-Dalsgaard, J., Frandsen, S., eds. Advances in Helio- and Asteroseismology , Reidel, IAU symp 123, p. 215 Google Scholar
Livingston, W.C.: 1983, in Stenflo, J.O., ed. Solar and Stellar Magnetic Fields: Origins and Coronal Effects , Reidel, IAU symp. 102, p. 149 Google Scholar
Livingston, W., Huang, Y.R.: 1986, in Giampapa, M.S., ed. The SHIRSHOG Workshop , National Solar Observatory, Tucson, p. 1 Google Scholar
Nadeau, D.: 1988, Astrophys. J. 325, 480 Google Scholar
Nadeau, D., Maillard, J.P.: 1988, Astrophys. J. 327, 321 Google Scholar
Nelson, G.D.: 1980, Astrophys. J. 238, 659 Google Scholar
Nordlund, Å.: 1982, Astron. Astrophys. 107, 1 Google Scholar
Nordlund, Å.: 1985, Solar Phys. 100, 209 Google Scholar
Nordlund, Å., Dravins, D.: 1989, Astron. Astrophys. , in press Google Scholar
Schwarzschild, M.: 1975, Astrophys. J. 195, 137 Google Scholar
Smith, MA., Huang, Y.R., Livingston, W.: 1987, Publ. Astron. Soc. Pacific 99, 297 Google Scholar
Smith, MA., Karp, A.H.: 1978, Astrophys. J. 219, 522 Google Scholar
Smith, MA., Karp, A.H.: 1979, Astrophys. J. 230, 156 Google Scholar
Toner, C.G., Gray, D.F.: 1988, Astrophys. J. , 334, 1008 Google Scholar
Wallace, L., Huang, Y.R., Livingston, W.: 1988, Astrophys. J. 327, 399 Google Scholar
Wayte, R.C., Ring, J.: 1977, Monthly Notices Roy. Astron. Soc. 181, 131 Google Scholar
Winkler, K.HA., Chalmers, J.W., Hodson, S.W., Woodward, P.R., Zabusky, N.J.: 1987, Physics Today 40, No. 10, p. 28 Google Scholar