x-ray spectroscopy of cool stars from coronal heating to accretion
DESCRIPTION
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. Coronal statics: Structure and extent of magnetic fields. X-ray eclipse map (0.015 mas). Radio VLBI (0.8 mas). - PowerPoint PPT PresentationTRANSCRIPT
Cambridge, July 11, 2007
X-Ray Spectroscopy of Cool Stars
From Coronal Heating to Accretion
Manuel Güdel
Paul Scherrer Institut, SwitzerlandMax-Planck-Institute for Astronomy, Heidelberg, Germany
ESA
Cambridge, July 11, 2007
Coronal statics: Structure and extent of magnetic fields
...but marginal or exceptional and always challenging
Radio VLBI (0.8 mas)X-ray eclipse map (0.015 mas)
(UV Cet, Benz et al. 1998) ( CrB, Guedel et al. 2003)
Cambridge, July 11, 2007
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Coronal structure coronal heating and dynamics
Cambridge, July 11, 2007
(Testa et al. 2004)
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):
• Coronal densities typically ≈ 1010 cm-3 • In active stars up to 1011 cm-3
Cambridge, July 11, 2007
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
NeIX3-4 MK
solar active
regions
(Ness et al. 2004) (Testa et al. 2004)
MgXI7 MK
cool: fill up to 10% then: add hot plasma
“activity”
Cambridge, July 11, 2007
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)
Cambridge, July 11, 2007
Composition of stellar coronae: Indicator of mass transport?
Sun and inactive
stars (+Sun) enhanced low-
FIP:
FIP effect
(1 Ori, Telleschi et al. 2005)
active stars enhanced high-FIP :
inverse FIP effect
Brinkman et al. 2001, Güdel et al. 2001)
IFIP
FIP
Solar analogs
activity
Cambridge, July 11, 2007
What determines IFIPness among most active stars?
(XEST + publishedvalues; afterTelleschi et al. 2007:EPIC: Scelsi et al. 2007)
IFIPnessdetermined by
the stellar Teff:
Ionisation structure in chromosphere?
Teff
Fe/Ne
stronger IFIP
weaker IFIP
Cambridge, July 11, 2007
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
Cambridge, July 11, 2007
inactive star
similar active star
active star
Proxima Centauri,quiescent
...notProxima Centauri:
YY Gem, quiescent
...alsoProxima Centauri:
average flare
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Anything left for "quiescence"?
(Audard et al. 2003)
(Audard et al. 1999, Kashyap et al. 2002, Guedel et al. 2003, Arzner & Guedel 2004, Stelzer et al. 2007)
Flare distributions in light curves: Favor dominance of small flares:All coronal heating may be due to the sum of all flares.
Cambridge, July 11, 2007
5x109 4x1011 2x1010 4x1011 2x1010
OVII
average flare log ne = 10.50 +/- 0.28
quiescent YY Gem log ne = 10.35 +0.13 -0.45
(Guedel et al. 2003)
ne
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DEM steep on low-T side:
DEM T4
(static loops: DEM T1.0-1.5)
superposed flaring (heating - cooling)
DEM T3-5
from hydrodynamic decay
(Guedel et al. 2003)
(Laming & Drake 1999)
T, EM, ne
Cambridge, July 11, 2007
active star:
IFIP
• 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)
inactive star:
FIP
“activated” (flaring) star: relative FIP
flare
FIP
Cambridge, July 11, 2007
How does accretion interact with the „high-energy“ environment?
Shocks in accretion streams:
T = 3mHv2 / 16k
v vff = (2GM/R)1/2
T = a few MK (<< 10 MK)
dM/dt = 4R2fvffnemp ne 1012-1014 cm-3
Can test these predictions using high-res X-ray spectroscopy
vff
f
Cambridge, July 11, 2007
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
High-resolution X-ray spectroscopy of classical T Tauri stars
NeIX
OVII
Cambridge, July 11, 2007
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)
But: Not measured in XEST targets
• AB Aur• T Tau
Density < few x 1010 cm-3
<< shock ne
So, is accretion really important?
BP Tau
AB Aur
ri
f
(Telleschi et al. 2007,Güdel et al. 2007)
T Tau
Cambridge, July 11, 2007
OVIII3-4 MK
OVII 2 MK
"SOFT EXCESS" (Telleschi et al. 2007, Güdel et al. 2007)"SOFT EXCESS" (Telleschi et al. 2007, Güdel et al. 2007)
hot
WTTS:non-accreting
CTTS:accreting
10-30 MK
1-2 MK
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MS stars
CTTS
WTTS
(Güdel & Telleschi 2007)
Soft Excess
≈ 2-3x
hotter
“Accretion adds cool material in CTTS”
Cambridge, July 11, 2007
- 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?
New insight into coronal statics and dynamics from high-res spectroscopy:
Cambridge, July 11, 2007
end