X-Ray Spectroscopy of Cool Stars From Coronal Heating to Accretion

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) (UV Cet, Benz et al. 1998) ( CrB, Guedel et al. 2003) ...but marginal or exceptional and always challenging

Coronal structure  coronal heating and dynamics

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

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

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)  

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

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

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

Proxima Centauri, quiescent inactive star ...also Proxima Centauri: average flare active star ...not Proxima Centauri: YY Gem, quiescent similar active star

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)

OVII 5x109 4x1011 2x1010 4x1011 2x1010 (Guedel et al. 2003) ne average flare log ne = 10.50 +/- 0.28 quiescent YY Gem log ne = 10.35 +0.13 -0.45

T, EM, ne 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)

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

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 (<< 10 MK) dM/dt = 4R2fvffnemp ne  1012-1014 cm-3 f Can test these predictions using high-res X-ray spectroscopy

High-resolution X-ray spectroscopy of classical T Tauri stars • TW HyaBP 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

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 < few x 1010 cm-3 << shock ne • So, is accretion really important? AB Aur (Telleschi et al. 2007, Güdel et al. 2007)

OVII 2 MK OVIII 3-4 MK 10-30 MK hot WTTS: non-accreting CTTS: accreting 1-2 MK "SOFT EXCESS" (Telleschi et al. 2007, Güdel et al. 2007)

CTTS Soft Excess MS stars ≈ 2-3x WTTS hotter (Güdel & Telleschi 2007) “Accretion adds cool material in CTTS”

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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X-Ray Spectroscopy of Cool Stars From Coronal Heating to Accretion