Mass Accretion onto T Tauri Stars

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Mass Accretion onto T Tauri Stars
Scott Gregory, Moira Jardine University of St.
Andrews, UK
Classical T Tauri Star (Goodson et al. 1997)
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Non-dipolar Magnetic Fields?

• Spectropolarimetry rules out a global dipole
  field at the stellar surface.
• (Valenti Johns-Krull 2004)

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Potential Field Extrapolations

• LQ Hya/AB Dor surface maps.
• Potential field extrapolation with source
  surface.
• Isothermal corona in hydrostatic equilibrium.

(Donati et al 2001 McIvor et al 2004 Gregory et
al. 2006, submitted)
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COUP X-ray Christmas Tree

• COUP (Chandra Orion Ultra-deep Project).
• Time lapse movie of observations many flares.
• Credit NASA/CXC/Penn State/E.Feigelson
  K.Getman et al.

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Coronal Extent and Stellar Mass
(Jardine et al. 2006, accepted)
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Coronal Field and X-ray Emission
Lower mass star where the presence of a disc
limits the size of the corona.
Higher mass star where the pressure of the hot
coronal gas limits the size of the corona.
(Jardine et al. 2006, accepted)
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X-ray Emission Measure and Mass
Observed Calculated
(Jardine et al. 2006, accepted)
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Accreting Field Extrapolations and Hot Spots
Latitude
Longitude
Latitude
Longitude
(Gregory et al. 2006, submitted)
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Mass Accretion and Stellar Mass

• Increase in mass accretion rate with stellar
  mass.
• Large scatter in mass accretion rate at any
  particular mass.

(Gullbring et al 1998 Rebull et al 2000 White
Ghez 2001 Gómez Persi 2002 Rebull et al
2002 White Basri 2003 Muzerolle et al
2003 Natta et al 2004 Calvet et al 2004 Muzerolle
et al 2005)
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Mass Accretion and Stellar Mass

• Red squares mass accretion rates calculated
  using COUP stars with estimates of R, M, Prot,
  Tcorona and EW(Ca II) lt 1Å.
• Equivalent width of Ca II 8542 Å used as an
  accretion indicator (Preibisch et al 2005)

(Gregory et al. 2006, submitted)
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Summary

• T Tauri stars have magnetic fields which are more
  extended than main sequence stars, but not as
  extended as dipolar fields.
• Accretion filling factors of order 1.
• Hot spots at a range of latitudes and longitudes.
• Accretion along open field lines significant.