Ssiss is sse titel

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X-Ray Spectroscopy of Cool Stars From Coronal
Heating to Accretion
Manuel Güdel Paul Scherrer Institut,
Switzerland Max-Planck-Institute for Astronomy,
Heidelberg, Germany
ESA
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Coronal statics Structure and extent of magnetic
fields
X-ray eclipse map (0.015 mas)
Radio VLBI (0.8 mas)
(UV Cet, Benz et al. 1998)
(? CrB, Guedel et al. 2003)
...but marginal or exceptional and always
challenging
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Coronal structure ? coronal heating
and dynamics
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First step toward coronal structure densities
and EM
(Audard et al. 2001, Ayres et al. 2001, Güdel et
al. 2001, Huenemoerder et al. 2001, Mewe et al.
2001, Ness et al. 2001, Phillips et al. 2001,
etc Surveys Nes et al. 2004, Testa et al.
2004)
(Testa et al. 2004)

• Coronal densities typically 1010 cm-3
  
• In active stars up to 1011 cm-3

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Combine - density at T (homogenous
assumption) and EM at T - reasonable scale
height at T (e.g., loop scaling laws) ? surface
filling factor for structures at T
(Testa et al. 2004)
(Ness et al. 2004)
activity
MgXI 7 MK
NeIX 3-4 MK
solar active regions
OVII
activity
cool fill up to 10 then add hot
plasma
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add cool plasma interactions between
more heating, higher T, active regions
flares more pasma, higher ne
Are flares heating active stellar
coronae? (e.g.,Güdel et
al. 1997, Drake et al. 2000, Ness et al. 2004)
?
?
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Composition of stellar coronae Indicator of mass
transport?
Solar analogs
active stars enhanced high-FIP inverse FIP
effect Brinkman et al. 2001, Güdel et al. 2001)
IFIP
activity
(?1 Ori, Telleschi et al. 2005)
Sun and inactive stars (Sun) enhanced low-FIP
FIP effect
FIP
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What determines IFIPness among most active stars?
Fe/Ne
weaker IFIP
IFIPness determined by the stellar
Teff Ionisation structure in chromosphere?
stronger IFIP
(XEST published values after Telleschi et al.
2007 EPIC Scelsi et al. 2007)
Teff
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Abundances as accretion indicators?

• 1. Metals like Fe, Mg, Si, C, O, may condense
  into grains and be retained
• in the disk (planets). Not so Ne and N (TW
  Hya, Herczeg et al. 2002 for Si/UV
• Stelzer Schmitt 2004 for Ne, N, C,
  Fe/X-rays)
• Accretion streams Fe-depleted / Ne- and N rich
• 2. But similar in other active stars
• old TW Hya Ne/O high
• young BP Tau Ne/O normal
• Grain growth toward planets
• retains metals only in old TW
• Hya disk. In younger CTTS, dust
• accretes as well (Drake et al. 2005).
• 3. MP Mus old, but low Ne!
• (Argiroffi et al. 2007)

ESA
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Proxima Centauri, quiescent
inactive star
...also Proxima Centauri average flare
active star
...not Proxima Centauri YY Gem, quiescent
similar active star
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Anything left for "quiescence"?
(Audard et al. 2003)
Flare distributions in light curves Favor
dominance of small flares All coronal heating
may be due to the sum of all flares.
(Audard et al. 1999, Kashyap et al. 2002, Guedel
et al. 2003, Arzner Guedel 2004, Stelzer et
al. 2007)
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(Guedel et al. 2003)
ne
average flare log ne 10.50 /-
0.28 quiescent YY Gem log ne 10.35 0.13
-0.45
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DEM steep on low-T side DEM
?T4 (static loops DEM ?T1.0-1.5)
(Laming Drake 1999)

• superposed flaring (heating - cooling)
• DEM ?T3-5
• from hydrodynamic decay
• (Guedel et al. 2003)

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• Flares bring
• new, chromospheric
• material into corona
• (cromospheric evaporation)
• Flares not directly responsible
• for IFIP in active stars
• IFIP composition builds up
• gradually
• (Nordon Behar 2006)

active star IFIP
activated (flaring) star relative FIP
inactive star FIP
flare
FIP
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How does accretion interact with the
high-energy environment?
Shocks in accretion streams
vff

• T 3?mHv2 / 16k
• v ? vff (2GM/R)1/2
• T a few MK (ltlt 10 MK)
• dM/dt 4?R2fvffnemp ? ne ? 1012-1014 cm-3

f
Can test these predictions using high-res X-ray
spectroscopy
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High-resolution X-ray spectroscopy of
classical T Tauri stars

• TW Hya BP Tau
• (Kastner et al. 02) (Schmitt et al. 05)
• very soft spectrum hard
• very high densities intermed. dens.
• (1013 cm-3, NeIX) (3x1011 cm-3)
• Hypothesis Shock-induced soft X-rays

NeIX
OVII
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r
T Tau
BP Tau
Dense, cool plasma in accretion shocks? Possible
for TW Hya, BP Tau, V4046 Sgr, MP Mus (Kastner
et al. 2002, Stelzer Schmitt 2004, Schmitt et
al. 2005, Günther et al. 2006, Argiroffi et al.
2007)
i
f

• But Not measured in XEST targets
• AB Aur
• T Tau
• Density lt few x 1010 cm-3 ltlt shock ne
• So, is accretion really important?

AB Aur
(Telleschi et al. 2007, Güdel et al. 2007)
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OVIII 3-4 MK
OVII 2 MK
10-30 MK
hot
WTTS non-accreting
CTTS accreting
1-2 MK
"SOFT EXCESS" (Telleschi et al. 2007, Güdel et
al. 2007)
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CTTS
Soft Excess
MS stars
2-3x
WTTS
hotter
(Güdel Telleschi 2007)
Accretion adds cool material in CTTS
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New insight into coronal statics and dynamics
from high-res spectroscopy

• Active coronae may be driven by magnetic
  explosive energy release
• density, temperatures, EM distributions
• Open questions what drives abundance
  anomalies?
• how are dynamic coronal systems
  structured?
• Coronal magnetic structures modified by
  accretion
• density, temperatures, abundances(?),
• soft excess
• Open questions how is soft excess
  achieved?
• what exactly do abundances reflect?

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