Cambridge, July 11, 2007 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

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 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 ≈ cm -3 In active stars up to 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 OVII NeIX 3-4 MK activity solar active regions (Ness et al. 2004) (Testa et al. 2004) MgXI 7 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 n e 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 + published values; after Telleschi et al. 2007: EPIC: Scelsi et al. 2007) IFIPness determined by the stellar T eff : Ionisation structure in chromosphere? T eff 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 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 Proxima Centauri, quiescent...not Proxima Centauri: YY Gem, quiescent...also Proxima 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, x10 9 4x x x x10 10 OVII average flare log n e = / quiescent YY Gem log n e = (Guedel et al. 2003) nene

Cambridge, July 11, 2007 DEM steep on low-T side: DEM  T 4 (static loops: DEM  T ) superposed flaring (heating - cooling) DEM  T 3-5 from hydrodynamic decay (Guedel et al. 2003) (Laming & Drake 1999) T, EM, n e

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 = 3  m H v 2 / 16k v  v ff = (2GM/R) 1/2  T = a few MK (<< 10 MK) dM/dt = 4  R 2 fv ff n e m p  n e  cm -3 Can test these predictions using high-res X-ray spectroscopy v ff f

Cambridge, July 11, 2007 TW Hya BP Tau (Kastner et al. 02)(Schmitt et al. 05) very soft spectrumhard very high densities intermed. dens. (10 13 cm -3, NeIX) (3x10 11 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 cm -3 << shock n e So, is accretion really important? BP Tau AB Aur r i f (Telleschi et al. 2007, Güdel et al. 2007) T Tau

Cambridge, July 11, 2007 OVIII 3-4 MK OVII 2 MK "SOFT EXCESS" (Telleschi et al. 2007, Güdel et al. 2007) hot WTTS: non-accreting CTTS: accreting 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, 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