Hostname: page-component-cd9895bd7-gvvz8 Total loading time: 0 Render date: 2024-12-26T04:50:05.138Z Has data issue: false hasContentIssue false
  • English
  • Français

Theoretical Interpretation of Solar and Stellar Irradiance Variations

Published online by Cambridge University Press:  12 April 2016

Henk C. Spruit
Henk C. Spruit*
Affiliation:
Max-Planck-Institut für Astrophysik, Postfach 1523, D-85740 Garching bei München, Germany

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

The main cause of variability of solar type stars are their varying magnetic fields. To compute irradiance variations one has to compute the magnetic field (the dynamo problem), and from this the irradiance effects. The second problem is considered here. The theoretical work of the past decade has shown that the dominant effect of magnetic fields is a surface effect: a change of effective emissivity of the magnetic parts of the surface while the nonmagnetic part of the surface contributes very little to the irradiance variation on almost all time scales. No other processes have yet been found that would cause variations exceeding (at the current level of magnetic activity) the observed 0.1% irradiance fluctuation of the Sun. This implies that a knowledge of the surface magnetic fields [separated into its bright small scale (faculae, network) and dark large scale (spots) components] is sufficient for pre- or postdicting the solar irradiance. It is hypothesized that the discrepancy remaining between the measured irradiance variations and values reconstructed from proxies is due to the difficulty of finding a proxy that accurately correlates with the continuum contrast of a dispersed small scale magnetic field. Stellar structure theory predicts that the variations in the solar radius associated with magnetic activity are quite small. For stars, color and brightness variations should primarily be interpreted in terms of variations in the fraction of the surface covered by magnetic patches. Their (long term) displacement from the main sequence is not very large.

Type
Solar and Stellar Oscillations, Irradiance Variations, and their Interpretation
Information
International Astronomical Union Colloquium , Volume 143: The Sun as a Variable Star: Solar and Stellar Irradiance Variations , 1994 , pp. 270 - 279
Copyright
Copyright © Kluwer 1994

References

Arendt, S. 1992 Large-scale flows and solar luminosity variations. Astrophys. J 389, 421–427.CrossRefGoogle Scholar
Byrne, P.B. & Mullan, D.J. 1992 Influence of starspots on internal stellar structure. In Lecture Notes in Physics 397, 78–84. Spring-Verlarg.Google Scholar
Chapman, G.A., Herzog, A.D., Lawrence, J.K. & Shelton, J.C. 1984 Solar luminosity fluctuations and active region photometry. Astrophys. J. 282, L99–L101.CrossRefGoogle Scholar
Chiang, W.H. & Foukal, P.V. 1984 The influence of lacuale on sunspot heat blocking. Solar Phys. 97, 9–20.Google Scholar
D’silva, S. & Choudhuri, A.R. 1993 A theoretical model for tilts of bipolar magnetic regions. Astron. Astrophys. 272, 621–633.Google Scholar
D’Silva, &: Howard, R.A. 1993 Limits on the magnetic field strength at the base of the solar convective zone. Solar Phys. 148, 1–9.Google Scholar
bitem[] Endal, A.S., Sofia, S. & Twigg, L.W. 1982 Changes of solar luminosity and radius following secular perturbations in the convective envelope. Astrophys. J. 290, 748–757.Google Scholar
Foukal, P.V., & Lean, J. 1990 An empirical model of total solar irradiance variations between 1874 and 1988. Science 247, 556–558.Google Scholar
Foukal, P., Fowler, L.A. & Livshits, M. 1983 A thermal model of sunspot influence on solar luminosity. Astrophys. J. 267, 863–871.Google Scholar
Fox, P., Sofia, S., Chan, K.L. 1991 Convective flows around sunspot-like objects. Solar Phys. 135, 15–42.Google Scholar
Fröhlich, .C. 1990 Irradiance variability of the Sun. In Climate Impact of Solar Variability (ed. Schatten, K.H. & Arking, A.) NASA CP 3086, pp. 269–278.Google Scholar
Fröhlich, C., Foukal, P.V., Hickey, J.R. & Hudson, H.S., Willson, R.C. 1991 Solar irradiance variability from modem measurements. In The Sun in Time (ed. Sonett, C., Giampapa, M. & Matthews, M.), pp. 11–29. University of Arizona, Tucson, AZ, USA.Google Scholar
Gilliland, R.L. 1988 In Solar radiative output variation, Cambridge Research & Instrumentation Inc., Foukal, P., ed., 21 Erie st. Cambridge, MA 02139, pp. 239.Google Scholar
Kasting, J.F., & Grinspoon, D.H. 1991 The faint young Sun problem. In The Sun in Time (ed. Sonnett, C., Giampapa, M. & Matthews, M.). University of Arizona, Tucson, pp. 447–462.Google Scholar
Keller, C.U. 1992 Resolution of magnetic flux tubes on the Sun Nature 359, 307–308.Google Scholar
Knölker, M. Grossmann-Doerth, U., Schüssler, M., Weisshaar, E. 1991 Adv. Sp. Res. 11, 285. Google Scholar
Kuhn, J. 1994 Brightness observations of the Sun. In The Sun as a Variable Star: Solar and Stellar Irradiance Variations (ed. Pap, J.M., Fröhlich, C., Hudson, H.S. & Solanki, S.K.). Cambridge University Press, in press.Google Scholar
Lean, J., Skumanich, A. & White, O.R. 1992 Estimating the Sun’s radiative output during the Maunder Minimum. Geophys. Res. Lett. 19, 1595–1598.Google Scholar
Lean, J., Skumanich, A., White, O.R. & Rind, D. 1994 Estimating solar forcing of climate change during the Maunder Minimum. In The Sun as a Variable Star: Solar and Stellar Irradiance Variations (ed. Pap, J.M., Fröhlich, C., Hudson, H.S. & Solanki, S.K.). Cambridge University Press, in press.Google Scholar
Parker, E.N. 1979 Cosmical Magnetic Fields Oxford, Clarendon Press.Google Scholar
Parker, E.N. 1984 Magnetic buoyancy and the escape of magnetic fields from stars. Astrophys. J. 281, 839–845.Google Scholar
Schatten, K.H. & Mayr, H.G. 1985 On the maintenance of sunspots - An ion hurricane mechanism. Astrophys. J. 299, 1051–1062.Google Scholar
Schüssler, M. 1991 Geophys. Astrophys. Fluid Dyn. 62, 271.Google Scholar
Sofia, S. Schatten, K.H. & Oster, L. 1982 Solar irradiance modulation by active regions during 1980. Solar Phys. 80, 87–98.Google Scholar
Spiegel, E.A. & Weiss, N.O. 1980 Magnetic activity and variations in solar luminosity. Nature 287, 616–617.Google Scholar
Spruit, H.C. 1976 Pressure equilibrium and energy balance of small photospheric flux tubes. Solar Phys. 50, 269–295.Google Scholar
Spruit, H.C. 1977 Heat flow near obstacles in the solar convective zone. Solar Phys. 55, 3–34.Google Scholar
Spruit, H.C. 1982a Effect of spots on a star’s radius and luminosity. Astron. Astrophys. 108, 348–355.Google Scholar
Spruit, H.C. 1982b The flow of heat near a spot. Astron. Astrophys. 108, 356–360.Google Scholar
Spruit, H.C. 1991 In The Sun in Time (ed. Sonett, C., Giampapa, M. & Matthews, M.S.), pp. 118–158. University of Arizona Press, Tucson, AZ, USA.Google Scholar
Spruit, H.C. & Zwaan, C. 1981 The size dependence of contrasts and numbers of small magnetic flux tubes in an active region. Solar Phys. 70, 207–228.Google Scholar
Spruit, H.C. & Van Ballegooijen, A.A. 1982 Stability of toroidal flux tubes in stars. Astron. Astrophys. 106, 58–66, Erratum in 113, 350.Google Scholar
Spruit, H.C. & Weiss, A. 1986 Colors and luminosities of stars. Astron. Astrophys. 166, 167–176.Google Scholar
Zwaan, C. 1978 On the appearance of magnetic flux in the solar photosphere. Solar Phys. 60, 213–240.Google Scholar