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

QuickTime™ and aPhoto decompressor

are needed to see this picture.

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

Cambridge, July 11, 2007

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

Cambridge, July 11, 2007

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

Cambridge, July 11, 2007

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