Intermediate Mass Stars in X-rays From coronae to wind shocks

Transcription

1 Intermediate Mass Stars in X-rays From coronae to wind shocks Jan Robrade Hamburger Sternwarte COSPAR Moscow, 08. August 2014

2 Stellar X-ray emission high-mass stars: wind shocks This talk: Intermediate mass stars: coronae in A stars young HAeBe stars magnetic Ap/Bp stars low-mass stars: magnetic activity The X-ray HRD (Güdel 2004) Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

3 The solar corona Sun in X-rays: SDO, TRACE Corona & Aurora (K. van Gorp, J. Jussila) Solar corona is highly structured and dynamic Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

4 Cool stars in X-rays The solar neighborhood: ROSAT/volume limited (Schmitt 1997) X-ray surface flux varies by orders of magnitude at given B-V Sun weakly active, coronal holes describe lower limit X-ray activity declines towards hotter stars Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

5 X-rays and dynamos Activity-dynamo relation (F - mid M) (Wright+ 2011) X-rays from magnetic activity, logl X /L bol L X dynamo power; Ro = P/τ c (interplay of convective motion & differential rotation) strong evolution of activity during stellar MS lifetime powerlaw (slope?) - saturation (level, breakpoint?) - supersaturation (?) Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

6 X-ray activity at higher masses - A stars A stars are optically bright... but what about X-rays? Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

7 X-ray activity at higher masses - A stars RASS/BSC sample: brightness limited (Schröder & Schmitt 2007) Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

8 X-ray activity at higher masses normalized counts s 1 kev Energy (kev) 1 XMM spectra of Altair (αaql,5 pc) and Alderamin (αcep,15 pc) A7 IV-V, T eff 7800 K, M = 1.8/2.0 M, age: 1.2/0.8 Gyr ultra-fast rotators, vsini 220/280 kms 1, 60/80 % break-up virtual identical X-ray properties Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

9 X-ray activity at higher masses X-ray light curve and high-res spectrum of Altair (A7) (Robrade & Schmitt, 2009) L X = erg/s, logl X /L bol = 7.4 minor activity, rotational modulation, long-term stable corona coronal properties similar to inactive Sun dominated by cool 1 4 MK plasma solar-like abundance pattern (FIP effect, Ne/O ratio) O vii f/i-ratio high (UV sensitive) Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

10 X-ray activity at higher masses 1.0 North (milliarcseconds) East (milliarcseconds) Surface images of Altair & Alderamin, CHARA (Monnier+ 2007, Zhao+09) oblate, gravity darkening T eff 6800K K X-ray surface features at T eff 7400 K equatorial bulge corona Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

11 The fading of X-ray activity 10 5 ratio of count rates HRC-I/MOS observation Temperature in MK β Pictoris (ESO, Günther+ 2012) β Pictoris - A6, young, debris disk (Hempel et al. 2005, Günther et al. 2012) X-rays: very soft (T X 1 MK), very faint (logl X 26.5) = No significant magnetic activity around A5 (or earlier)...tight upper limits on Fomalhaut (A3) and Vega (A0) (logl X < 25.5) X-ray detections likely companions (e.g. VAST survey; De Rosa et al., 2011) HR A5 (ka5hf0ma5v λ Boo), logl X = 28.1, T eff 7450 K (Robrade & Schmitt, 20 Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

12 X-rays from YSOs The youth of intermediate mass stars Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

13 HAeBe stars young intermediate mass stars YSO evolution M (Alecian+ 2013) IR excess, magnetic activity, accretion/outflow processes stellar structure depends on mass and evolutionary state IMTTS (F- & G-type) at lower masses/younger age (RY Tau, SU Aur, T Tau...) Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

14 HAeBe stars magnetic fields HAeBe with magnetic field detections (red) (Alecian+ 2013) strong, large-scale fields rare (< 10%), in slow rotators magn. field & rotation properties like Ap/Bp stars PMS origin of large-scale field Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

15 X-rays from HAeBe stars normalized counts s 1 kev normalized counts s 1 kev Energy (kev) Energy (kev) X-ray spectra of HAe stars: HD & AB Aur L X vs. L bol (Stelzer et al., 2009) variety of X-ray luminosities & activity levels strong soft component, accretion or wind shocks (MCWS/jets) magnetic activity present, often weak few studied in detail with high-res X-ray spectra e.g. HD (Günther& Schmitt, 2009); AB Aur (Telleschi et al., 2007) Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

16 X-rays from ApBp stars Surface magnetic field distribution of α 2 CVn (Kochukov & Wade, 2010) Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

17 Ap/Bp stars X-rays and the MCWS model MCWS model (Babel & Montmerle, 1997) MHD/RFHD advancements: (ud-doula, Owocki, Townsend) Ap/Bp stars: magnetic intermediate mass stars, chemically peculiar, slow rotators fields: large-scale, stable, uncorrelated, rare (< 10%), fossil IQ Aurigae: A0p, (T eff K, M = 4.0M, age 60 Myr) ROSAT detection: X-ray bright, soft spectrum X-rays via magnetically confined wind-shocks (MCWS) Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

18 The MCWS model: massive magnetic stars R A < R K L X ṀV B 0.4, T X K( V sh ) kms 1 (BM97) magnetically channeled line driven stellar winds (dynamic models. incl. stellar rotation) η B 2 eqr 2 /ṀV (magnetic confinement, ud-doula et al. 2002) η >> 1: rigid disk structures + centrifugal breakouts W = Vrot V orb, V orb = GM/R (rotation parameter, ud-doula et al. 2008) η,w R A,R K Standard model for magnetic hot stars invoked to explain: X-ray overluminosity, hard spectral components, flares, rotational modulation... DM forced corotation CM DM R K < R A Petit et al θ 1 OriC, O5 (Gagné et al. 2005), τ Sco, B0.2 (Cohen et al. 2003), σ OriE, B2p (Townsend et al. 2005), β Cep, B2III (Favata et al. 2009), MiMeS sample (Petit et al. 2013)... Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

19 The MCWS model: massive magnetic stars R A < R K L X ṀV B 0.4, T X K( V sh ) kms 1 (BM97) magnetically channeled line driven stellar winds (dynamic models. incl. stellar rotation) η B 2 eqr 2 /ṀV (magnetic confinement, ud-doula et al. 2002) η >> 1: rigid disk structures + centrifugal breakouts W = Vrot V orb, V orb = GM/R (rotation parameter, ud-doula et al. 2008) η,w R A,R K DM forced corotation CM DM Caveats: models tuned for more massive stars, smaller η fails to describe details for several stars R K < R A Petit et al MCWS overall successful, continuous improvement... (e.g. ud-doula et al. 2014) Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

20 Ap/Bp stars X-rays from IQ Aur XMM-Newton lightcurve of IQ Aur (Robrade & Schmitt, 2011) hot plasma in quasi-quiescence & large flare strong soft X-ray component magnetic activity + wind shocks Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

21 Ap/Bp stars IQ Aurigae normalized counts s 1 kev Energy (kev) Quasi-quiescent lightcurve & X-ray spectra (flare/qq) (Robrade & Schmitt, 2011) logl Xqq = 29.6 ergs 1, logl X /L bol 6.5 stable X-ray emission over decades no clear rotational modulation very hot flare with L Xpeak = ergs 1, E X = erg Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

22 IQ Aur - Pt. II top: soft excess (quasi-quiescence) right: flare evolution high-resolution spectrum: density/uv-field & temperature diagnostics Ovii f/i-ratio: X-rays from well above the stellar surface (f/i 1, d 7 R ) Oviii vs. Ovii excess of cool plasma moderate flare: light curve and time resolved spectral analysis T X 100 MK, metallicity increase, moderately sized structure L 0.2R Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

23 Ap/Bp stars HD Rate (cts s 1 ) HD XMM/pn Time (ks) normalized counts s 1 kev Energy (kev) X-ray lightcurve and spectra of HD (B9p) New XMM observation 2014: logl X = 30.2 ergs 1, logl X /L bol 5.9 hot plasma dominant: /20 MK, short-term variability cool component at 2 MK weak (10% EM)...but many Ap/Bp stars remained undetected in X-rays Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

24 Ap/Bp stars in X-rays X-ray luminosity (erg/s) 1e+30 1e+29 1e+28 1e+27 1e+26 HD HD HD HD HD HD HD HD HD HD HD HD HD HD HD HD HD HD F Lx/Lbol = -7 HD L X vs. L bol A0 B7, magnetic CP stars (updated from Robrade & Schmitt (2011) Stellar luminosity (log L Sun ) X-rays predominantly in more luminous Ap/Bp stars (L 200L ) sufficient mass loss & wind speed, strong magnetic confinement (η 1) weak trend with opt. brightness...but large scatter X-ray/ Radio relation violated in all cases, Ap/Bp stars are radio-overluminous presence of non-coronal sources Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

25 Ap/Bp stars in X-rays Pt. II log L X (erg/s) log L X (erg/s) M (M Sun ) log L X (erg/s) log L X (erg/s) log T eff (K) B eff (kg) log t (yr) L X vs. stellar parameter no correlation of L X with age or B eff unexplained scatter: magnetic field geometry, time variability, companions... Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22

26 S u m m a r y Very diverse picture - many different X-ray phenomena Main Sequence - A stars X-rays from magnetic activity in late A stars weakly active stars, X-ray properties resemble quiescent sun ZAMS: very low, residual activity possible at mid A Magnetic Main Sequence - Ap/Bp stars X-rays from magnetically channeled stellar wind + rigid disk? predominantly in more luminous, more massive stars compatible with extended MCWS model YSO - IMTTS, HAeBe stars magnetic activity (outer convection zone stars) accretion/wind shocks, jets Future project: erosita/srg German-Russian X-ray all-sky survey Jan Robrade (Hamburger Sternwarte) X-rays from Intermediate Mass Stars / 22