SEISMOLOGY OF STELLAR ATMOSPHERES

1. SEISMOLOGY OF STELLAR ATMOSPHERES Zdzislaw Musielak Physics Department University of Texas at Arlington (UTA)

2. OUTLINE • Stellar Activity in the H-R Diagram • Stellar Activity and Exoplanets • Atmospheric Oscillations • Models and Theoretical Predictions • Atmospheric Seismology

3. Active Sun

4. Solar Magnetogram

5. Solar structure

6. Model of the Solar Atmosphere Averett and Loeser (2008)

7. Forms of Stellar Activity • Chromospheric activity (Ca II, Mg II) • Transition-region activity (C IV, N V, O VI) • Coronal activity (X-rays, Fe XII, Fe XV) • Wind activity (tenuous and massive winds) • Atmospheric oscillations

8. The H-R Diagram

9. Chromospheric activity Rutten et al. (1987) and Schrijver et al. (1999)

10. Coronal and Wind Activity Haisch & Schmidt (1991)

11. Stellar Activity and Exoplanets • Enhancement of stellar activity by exoplanets (e.g., Ca II H+K and X-rays) • Interaction between the stellar and planetary magnetic fields Fint ~ Bs Bp1/3 Vc / d2 Rp2 FX1/6 Cuntz, Saar & Musielak (2000) Orbital modulations of Ca II in 3 systems Hot spot following the planet in HD179949 Shkolnik, Walker & Bohlender (2003)

12. White Dwarfs (WD) DAV and DBV – pulsating WD DAB – H + neutral He lines DAO – H + ionized He lines DC – no lines in optical DAZ – H + “metal” lines DQ – strong carbon lines

13. Activity of White Dwarfs • Chromospheric: GD 356 (DA) – Balmer lines in emission (Greenstein 1985) G 227-5 and G 35-26 (DQ) N I, O I, Si I and C I lines in emission (Shipman et al. 2003) • Coronal (X-rays) – NONE (Cavallo et al. 1993, Musielak et al. 1995, 2003) GD 356 Chandra X-ray image of GD 358 (DBV)

14. Energy Input From stellar photospheres: acoustic and magnetic waves Produced in situ: reconnective processes From stellar coronae: heat conduction

15. Tube Waves and Spectra Solar wave spectra Solar wave spectra

16. Wave Energy and Radiative Losses

17. Physical Model

18. Chromospheric Models • Purely Theoretical • Two-Component • Self-Consistent • Time-Dependent • Stellar parameters: effective temperature, gravity, metallicity and filling factor.

19. Models versus Observations • Base - acoustic waves • Middle - magnetic tube waves • Upper – other waves and / or non-wave heating Fawzy et al. (2002a, b, c) Heating gaps!

20. Other Heating Mechanisms • Energy carried by torsional tube waves • Magnetic reconnection at very small scales – “nanoflares” (Mendoza- Briceno et al. 2002; Parker 1988) • Magnetic carpet – flux tube tectonics (Priest et al. 2002; Schrijver et al. 1998)

22. Generation of Transverse Tube Waves The wave operator with , , The source function

23. Solutions Fourier transform in time and space Asymptotic Fourier transforms Turbulent velocity correlations Evaluation of convolution integrals

24. Turbulent velocity correlations Spatial turbulent energy spectrum – modified Kolmogorov turbulent spectrum Temporal turbulent energy spectrum – modified Gaussian frequency factor

25. Wave Energy Spectra and Fluxes Stellar wave fluxes Stellar wave spectra Linear transverse tube waves Musielak & Ulmschneider (2003)

26. Solar Chromospheric Oscillations • Response of the solar chromosphere to propagating acoustic waves – 3-min oscillations (Fleck & Schmitz 1991, Kalkofen et al. 1994, Sutmann et al. 1998) • Oscillations of solar magnetic flux tubes (chromospheric network) – 7 min oscillations (Hasan & Kalkofen 1999, Musielak & Ulmschneider 2002, 2003) Chromospheric oscillations are not cavity modes! P-modes

27. Excitation of Oscillations by Tube Waves I The wave operator for longitudinal tube waves is with , and the cutoff frequency (Defouw 1976)

28. Excitation of Oscillations by Tube Waves II The wave operator for transverse tube waves is with , and the cutoff frequency (Spruit 1982)

29. Initial Value Problems and IC: and BC: and Laplace transforms and inverse Laplace transforms

30. Solar Flux Tube Oscillations Longitudinal tube waves Transverse tube waves

31. Observation of Chromospheric Oscillations I Tritschler, Schmidt & Wedemeyer (2005)

32. Observation of Chromospheric Oscillations II 8.3-min 3-min 5-min Tritschler, Schmidt & Wedemeyer (2005)

33. Solar Atmospheric Oscillations • Solar Chromosphere: 100 – 250 s • Solar Transition Region: 200 – 400 s • Solar Corona: 2 – 600 s TRACE and SOHO

34. Observations • A German – UTA team A. Nesis, H. Schleicher and R. Hammer - Kiepenheuer Institut fur Sonnenphysik (KIS) in Freiburg, Germany Z.E. Musielakand S. Routh - UTA was granted time to observe solar oscillations by the Vacuum Tower Telescope (VTT) at the Observatorio del Teide, Tanerife, Spain, in October 2008. The data analysis will be performed at KIS and UTA.

35. Atmospheric Oscillations in Solar-Type Stars F5 V • Response of stellar chromospheres to a spectrum of propagating and non-propagating acoustic and magnetic tube waves • The chromospheres oscillate with the corresponding acoustic or tube cutoff frequency • Performed studies: F5 V with Teff = 6440 K G5 V with Teff = 5330 K M0 V with Teff = 3850 K Z = 0 km Z = 1000 km Z = 1500 km Fawzy, Musielak & Ulmschneider (2005)

36. Theoretical Predictions I F5 V star: 4.5 – 5.0 mHz (non-magnetic) 3.5 – 4.5 mHz (magnetic) G5 V star: 5.5 – 6.5 mHz (non-magnetic) 5.0 – 6.0 mHz (magnetic) M0 V star: 8.5 – 11.0 mHz (non-magnetic) 9.0 – 10.0 mHz (magnetic) Maximum amplitudes range from 0.4 km/s in F5 V to 0.2 km/s in M0 V

37. Stellar P-mode Oscillations P-mode oscillations have been observed in 3 main-sequence stars (Sun and α Cen A and B) 2 subgiants (α CMi or Procyon A and η Boo) and 2 giants (α UMa and Arcturus) The p-mode oscillations in Procyon A seem to be inconclusive! α Cen A The HAO group Procyon A Bonanno et al. (2003)

38. Stellar Atmospheric Oscillations • White-light oscillations with period of 220 s observed in a couple of RS CVn stars during flares Mathioudakis et al (2003, 2006) • X-ray oscillations with period of 750 s observed in an active M-dwarf Mitra-Kraev et al (2006)

39. Atmospheric Oscillations in White Dwarfs • Theory predicts large acoustic fluxes for white dwarfs (Bohm & Cassinelli 1971, Arcoragi & Fontaine 1980, Musielak 1982) • Atmospheric oscillations as a new indicator of chromospheric activity (Musielak, Winget & Montgomery 2005) • Performed studies: DA stars with convection zones DB stars with convection zones Acoustic waves DA star with log g = 8 and Teff = 12500 K

40. Theoretical Predictions II DA stars: log g = 7 and Teff = 11000 K has P = 2 s and LO / LS = 0.02 log g = 8 and Teff = 12000 K has P = 0.2 s and LO / LS = 0.004 DB stars: log g = 7 and Teff = 23000 K has P = 0.8 s and LO / LS = 0.01 log g = 8 and Teff = 21000 K has P = 0.08 sand LO / LS = 0.02 Best candidates:GD 356, G 227-5, G 35-26, BMP 17088 and SDSS J123410.37-022802.9

41. Atmospheric Seismology • Is atmospheric seismology possible? Sun – no problem! Late-type stars – stars with magnetic spots and giants White dwarfs – magnetic (GD 356)

42. CONCLUSIONS • Late-type dwarfs, subgiants, giant, supergiants and white dwarfs show chromospheric activity. The proximity of giant planets may increase this activity. • Current theoretical models of stellar chromospheres predict “heating gaps”, which can be explained by including transverse and torsional waves and reconnective events in the models. • Oscillations driven by longitudinal and transverse tube waves can account for 3-min oscillations in the lower chromosphere but cannot account for 7-min in the upper chromosphere. • Theoretical predictions of expected chromospheric oscillations in solar-type and DA and DB stars were made. We suggested that atmospheric oscillations in white dwarfs may become a new indicator of chromospheric activity in these stars. Supported by NSF, NASA, NATO and The Alexander von Humboldt Foundation