X-ray shining stars Advances foreseen with ASTRO-H

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X-ray shining stars Advances foreseen with ASTRO-H Marc Audard (University of Geneva) ASTRO-H Special Session 8, EWASS 2012, Roma, 3 July 2012

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X-ray shining stars Advances foreseen with ASTRO-H. Marc Audard (University of Geneva). ASTRO-H Special Session 8, EWASS 2012, Roma, 3 July 2012. Introduction. Why should we care about stellar science with ASTRO-H? - PowerPoint PPT Presentation

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  • X-ray shining starsAdvances foreseen with ASTRO-HMarc Audard(University of Geneva)

    ASTRO-H Special Session 8, EWASS 2012, Roma, 3 July 2012

  • Introduction

    Why should we care about stellar science with ASTRO-H?

    Stars are nearby astrophysical cosmic plasmas ideal to study MHD physics, the importance of magnetic fields, stellar winds, and X-ray photons on the surrounding environment (chemical enrichment, energy input; habitability of planets; irradiation of accretion disks)

    Stars are rich line-emitters!

  • XMM-Newton/ChandraThe high-resolution grating spectra on-board XMM-Newton and Chandra have allowed excellent, new science to be done on stars:Abundance studies (FIP and inverse FIP effect)Average density & opacity measurementsEclipse & Doppler mapping of corona (limited)Density measurements in a handful of young stars (excitement! Accretion may produce sufficient X-rays)Detection of Fe Ka at 6.4 keV: information on source size, height, mechanism (but very limited!)Density variations during flares (rare! Low S/N)Line profiles in stellar windsEtc

  • Science with ASTRO-HThe effective area and spectral resolution above 1 keV of ASTRO-H will help:

    Dynamical MHD processes at the kilosecond time scaleProbe densities in accreting starsDetect Fe Ka emission and constrain geometries

    These are selected topics!

  • A dynamical pictureChromospheric evaporation can lead to mass motions into the corona with speeds of a few 100 km/sNon-equilibrium conditions in the fast rise phaseAudard et al. (2003)Flares of a few ksRise time < 100s

  • Gdel et al. (2002)Proxima CentauriF ~ ne2V V ~F/ne2 M ~ F/ne

  • Testa et al. (2008). See also Osten et al. (2007), Giardino et al. (2007), Drake et al. (2008)Same application for accretion disks

  • Czesla & Schmitt (2007)V1486 Ori (Czesla & Schmitt 2007):

    Evidence of very hot plasma > 10 keV

    Strong fluorescent Fe Ka line (EW1400 eV) in the initial phase of the flare rise

    Fluorescence models underpredict the observed Fe Ka flux (Czesla & Schmitt 2007)

    Other examples (e.g., Tsujimoto et al. 2005, Giardino et al. 2007; Stelzer et al. 2011)Fe Ka line also detected in quiescence

    Origin of line not definitive (fluorescence, electron impact ionization)

    ASTRO-H will allow to do reverbation mapping of the star-disk system

  • Detailed flare studiesModel: 1/6 of AB Dor flare (2-T; 20+80 MK; Maggio et al. 2000), i.e., about 10x quiescenceBai et al. (1979) model for Fe Ka

    SXS: 31.5 c/s

  • 100 km/s shiftEven better at 7keVOther lines of hot plasma at longer wavelengths usefulCaveat: moving flare plasma dominates the emission (but not so unreasonable for large flares)Caveat2: thermal broadeningCaveat3: line of sight!

  • Hard X-ray non-thermal flare emissionHard X-ray emission detected in a stellar flare

    Preferred explanation as non-thermal thick-target bremsstrahlung emission (also supported by Fe Ka emission)

    Superflare on II Peg; Osten et al. 2007. Previously inconclusive with BeppoSAX (Pallavicini et al. 2000) Osten et al. 2007Note that non-thermal X-rays must exist: evidence in the Sun and in non-thermal radio emission of stars in quiescence

  • SXS will not deblend the many Fe lines around the Ne IX triplet. Accurate modeling and atomic data will be required to derive the density.Problem less important for OVIIHotter plasma will also be probed (Mg XI, Si XIII, etc) but critical densities may be too high (except during flares)AB Dor in quiescence: 2.4 c/s (SXS)rifrifNe IXO VIIMg XIrifne 1011-12 cm-3ne 109-10 cm-3ne 1011.5-12.5 cm-3

  • High densities in accreting starsHigh i/f ratio in He-like triplets of TW Hya indicate ne1013 cm-3 (Kastner et al. 2002; Stelzer & Schmitt 2004). Also Fe XVII (Ness & Schmitt 2005)Plasma T3 MK consistent with adiabatic shocks from gas in free fall (v150-300 km s-1)High densities in accreting young stars (Schmitt et al. 2005; Robrade & Schmitt 2006; Gnther et al. 2006; Argiroffi et al. 2007), but not all (Telleschi et al. 2007; Gdel et al. 2007, Argiroffi et al. 2011; etc)

    Very limited sample (only 8 CTTS), with generally poor signal-to-noise ratio in grating spectra

  • Accretion in young starsVery small sample of accreting stars with gratingsSXS will allow us to measure densities in the critical range of 1011-12 cm-3, i.e., with the Ne IX and Mg XI tripletsMeasurement at lower densities (O VII) will be difficult due to NH (1020-1022 cm-2) and to the limited spectral resolution at 22 131ksSchmitt et al. (2005)ASTRO-H, SXS130ks, 0.03 c/sNH=6x1020 cm-2rif

  • Potential of ASTRO-H to observe several nearby (140pc) star forming regions also with SXS to obtain densitiesImportance to determine the contribution of accreting plasmaAccess to Ne IX (but blends with Fe) and Mg XI, crucial for accreting plasmas. Access to OVII will depend on column density (OK for NHAV=3m at 500pc) and spectral resolution.

    Hartmann (1997)Audard et al. (2010)During outbursts in young stars, due to the increase in accretion rate, the accretion disk closes in and may have disrupted the magnetic loops, modifying the magnetospheric configuration (Kastner et al. 2004; 2006; Grosso et al. 2005; Audard et al. 2005; 2010; Hamaguchi et al. 2012)Fx 10-15-10-14 erg s-1 cm-2

  • *X-ray emission from interacting wind massive binaries: what Astro-H can tell usThe interactions of stellar winds in massive binary systems produce X-ray emission due to heating of the winds in the interaction zone (e.g. Stevens et al. 1992, ApJ, 386, 265).

    Courtesy G. Rauw

  • *The morphology of the wind interaction zone depends on the ratio between the wind momenta:

    X-ray emission lines formed in the interaction region are expected to display a changing morphology depending on the shock properties and the orbital phase (e.g. Henley et al. 2003, MNRAS 346, 773). This provides important diagnostics on the wind interaction. Courtesy G. Rauw

  • Fe K is probably one of the best diagnostic lines for this purpose as it traces only the hottest plasma produced in the wind wind interaction zone.The spectral resolution of SXS (assumed value 5 eV equivalent to 225 km s-1) is just about right to resolve lines that are a few 1000 km s-1 wide.Observations at different orbital phases of a sample of such binaries will allow to probe the physics of wind interactions. *Courtesy G. Rauw

  • Hydrodynamic shocks in colliding wind systems are known to accelerate relativistic particles (seen through synchrotron radio emission in a subsample of massive binaries, e.g. De Becker 2007, A&ARv 14, 171).The copious photospheric UV radiation is expected to produce hard X-ray emission through inverse Compton scattering.This has been observed (so far) for Carinae (Leyder et al. 2008, A&A 477, L29) and WR140 (Sugawara et al. 2011, BSRSL 80, 724).Astro-H offers the ideal combination of instrumental capabilities to detect such a hard tail and simultaneously characterize the thermal emission of a colliding wind system (see also posters by De Becker et al. and Khangulyan et al. at this meeting).

    Courtesy G. Rauw

  • ConclusionsDynamical processes (flare physics) will be studied with good S/NStochastic processes, however, require some integration time (20-50 ks) to capture flares with sufficient energy and signalASTRO-H will also probe high densities in young accreting stars via the Ne IX and Mg XI tripletsASTRO-H will help constrain geometries via the Fe Ka lineThe SXI will also provide additional coverage in the field of stellar clusters, in particular star forming regionsASTRO-H SXS will also be useful for colliding wind binaries: it will resolve lines in shocks and trace the wind-wind shock zoneThe broad-band coverage of ASTRO-H will also help detect the non-thermal emission in stellar coronae and colliding wind binaries

    Count rates should not be too problematic except during very strong flares, and optical loading should be minimal but can be alleviated thanks to optical blocking filters

    NB: all sims with 5eV resolution and optical filter**Top figure: schematic illustration of the wind wind collision. The kinetic energy normal to the shock surface is converted into heat, thereby producing a substantial heating of the plasma inside the wind interaction zone.Bottom figure: hydrodynamical simulation (without orbital motion effects) of a wind-wind collision. The primary star is located at z=0, whilst the secondary is at z=2e13 cm. Left = density map, right = temperature map. Important comment: the hottest plasma is expected near the binary axis, because there the winds collide head-on.*Figure (left): to first order, the shape of the shock zone between the two winds is set by the value of R (= the wind momentum ratio = square root of the ratio of the products of mass-loss times terminal wind velocity). Figure (right): predicted line profile variations as a function of R and viewing angle (hence orbital phase).*Normal single massive stars do not display an Fe K line in their spectrum because the intrinsic X-ray emission of massive stars is not hot enough to produce a substantial emission in this line. Top left figure: orbital configuration of gamma Vel at the phases of three ASCA observations (SIS spectra shown on the right). Bottom left figure: predicted SXI spectrum of gamma Vel (based upon the spectral parameters inferred from the ASCA observation at phase 0.078). **