SEISMOLOGY OF STELLAR ATMOSPHERES

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SEISMOLOGY OF STELLAR ATMOSPHERES

• Zdzislaw Musielak
• Physics Department
• University of Texas at Arlington (UTA)

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OUTLINE

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

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Active Sun
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Solar Magnetogram
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Solar structure
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Model of the Solar Atmosphere
Averett and Loeser (2008)
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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

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The H-R Diagram
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Chromospheric activity
Rutten et al. (1987) and Schrijver et al. (1999)
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Coronal and Wind Activity
Haisch Schmidt (1991)
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Stellar Activity and Exoplanets

• Enhancement of stellar activity
• by exoplanets (e.g., Ca II HK 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)
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White Dwarfs (WD)
DAB H neutral He lines
DAV and DBV pulsating WD
DAO H ionized He lines
DC no lines in optical
DAZ H metal lines
DQ strong carbon lines
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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)
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Energy Input

• From stellar photospheres
• acoustic and magnetic waves
• Produced in situ
• reconnective processes
• From stellar coronae
• heat conduction

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Tube Waves and Spectra
Solar wave spectra
Solar wave spectra
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Wave Energy and Radiative Losses
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Physical Model
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Chromospheric Models

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

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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!
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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)

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Generation of Transverse Tube Waves
The wave operator
with
,
,
The source function
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Solutions
Fourier transform in time and space
Asymptotic Fourier transforms Turbulent
velocity correlations Evaluation of convolution
integrals
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Turbulent velocity correlations
Spatial turbulent energy spectrum modified
Kolmogorov
turbulent spectrum
Temporal turbulent energy spectrum modified
Gaussian
frequency factor
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Wave Energy Spectra and Fluxes
Stellar wave fluxes
Stellar wave spectra
Linear transverse tube waves
Musielak Ulmschneider (2003)
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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
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Excitation of Oscillations by Tube Waves I
The wave operator for longitudinal tube waves is
with
,
and the cutoff frequency (Defouw 1976)
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Excitation of Oscillations by Tube Waves II
The wave operator for transverse tube waves is
with
,
and the cutoff frequency (Spruit 1982)
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Initial Value Problems
and
IC
and
BC
and

Laplace transforms and inverse Laplace transforms
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Solar Flux Tube Oscillations
Longitudinal tube waves
Transverse tube waves
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Observation of Chromospheric Oscillations I
Tritschler, Schmidt Wedemeyer (2005)
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Observation of Chromospheric Oscillations II
8.3-min
3-min
5-min
Tritschler, Schmidt Wedemeyer (2005)
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Solar Atmospheric Oscillations

• Solar Chromosphere 100 250 s
• Solar Transition Region 200 400 s
• Solar Corona 2 600 s
• TRACE and SOHO

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Observations

• A German UTA team
• A. Nesis, H. Schleicher and R. Hammer -
  Kiepenheuer Institut fur Sonnenphysik (KIS) in
  Freiburg, Germany
• Z.E. Musielak and 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.

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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)
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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
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Stellar P-mode Oscillations

• P-mode oscillations have been observed in
• 3 main-sequence stars (Sun and a Cen A and
  B)
• 2 subgiants (a CMi or Procyon A and ? Boo)
• and 2 giants (a UMa and
• Arcturus)
• The p-mode oscillations in
• Procyon A seem to be
• inconclusive!

a Cen A
The HAO group
Procyon A
Bonanno et al. (2003)
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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)

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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
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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 s
  and LO / LS 0.02
• Best candidates GD 356, G 227-5, G 35-26, BMP
  17088
• and SDSS
  J123410.37-022802.9

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Atmospheric Seismology

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

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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