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Magnetic activity along the main sequence

Magnetic activity along the main sequence. Axel Brandenburg ( Nordita, Copenhagen ). Solar butterfly diagram. Typical cycle patterns. HD 81809: an old sun? B-V=0.64  0.80 P cyc =8yr, P rot =40d, logR HK =-4.91: inactive. The sun as a star B-V=0.66 P cyc =10yr, P rot =26d,

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Magnetic activity along the main sequence

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  1. Magnetic activity alongthe main sequence Axel Brandenburg (Nordita, Copenhagen)

  2. Solar butterfly diagram Main sequence magnetic activity

  3. Typical cycle patterns HD 81809: an old sun? B-V=0.64  0.80 Pcyc=8yr, Prot=40d, logRHK=-4.91: inactive The sun as a star B-V=0.66 Pcyc=10yr, Prot=26d, logRHK=-4.90: inactive Main sequence magnetic activity

  4. Inactive versus active stars HD 160346, B-V=0.96 Pcyc=7yr, Prot=36d, logRHK=-4.80: inactive HD156026, B-V=1.16 Pcyc=21yr, Prot=21d, logRHK=-4.48: active Main sequence magnetic activity

  5. Exceptions HD 115404, B-V=0.93 Pcyc=12yr, Prot=18d, logRHK=-4.48: active HD95735, B-V=1.51 flares Main sequence magnetic activity

  6. Any correlations? Period ratio vs dimensional rotation period (Baliunas, Nesme-Ribes, Sokoloff, & Soon 1996) Main sequence magnetic activity

  7. Cycle to rotation frequency ratio Slow rotator Short cycle Vaughan- Preston gap wcyc=2p/Pcyc W=2p/ Prot Fast rotator Long cycle Main sequence magnetic activity

  8. Good and excellentstars Brandenburg, Saar, Turpin (1998, ApJ 498, L51)

  9. Evolutionary diagram Stars begin on the active branch, then jump to the inactive branch. Main sequence magnetic activity

  10. Dynamointerpretation field strength • Along each branch, • increases with field strength!  antiquenching Main sequence magnetic activity

  11. Activity versus inverse Rossby Main sequence magnetic activity

  12. Frequency ratio vs inv Rossby Main sequence magnetic activity

  13. Importance of plotting nondimensional quantities Period ratio vs dimensional rotation period 2 branches mixed in one! (Baliunas, Nesme-Ribes, Sokoloff, & Soon 1996) Main sequence magnetic activity

  14. Expanded sample Saar & Brandenburg (1999, ApJ 524, 295)

  15. Predictions possible… HD 129333 (EK Dra) Prot=2.8d, Pcyc=1.4 or 39 yr (if on A or S branch) Main sequence magnetic activity

  16. Order out of disorder: Hale’s polarity law Main sequence magnetic activity

  17. Quenching of alpha • Isotropic box simulations: • ht is “catastrophically” quenched (Cattaneo & Vainshtein 1991, because 2D: Gruzinov & Diamond 1994) • a is “catastrophically” quenched (Vainshtein & Cattaneo 1992, Gruzinov & Diamond 1994, +others) • Astrophysical simulations: • a small even kinematically (Rm dependence?) • B is definitely strong does not exclude:- Main sequence magnetic activity

  18. Saturation behavior explained by magnetic helicity conservation Steady state, closed box Small scale and large scale current helicity in balance Main sequence magnetic activity

  19. Taking magnetic helicity seriously Two-scale assumption  Dynamical a-quenching (Kleeorin & Ruzmaikin 1982) Steady limit: consistent with VC92

  20. Conclusions • Stellar dynamos: rich, unexpected behavior • Important for development of theory • From theory: plot non-dimensional quantities • Mean-field theory  a-effect antiquenched • Different modes of operation (unclear) Main sequence magnetic activity

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