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X-Rays from Low and Intermediate Mass Stars

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X-Rays from Low and Intermediate Mass Stars X-rays from low and intermediate mass stars Jan Robrade Hamburger Sternwarte X-ray Universe, Dublin, 16-19 June 2014 The solar corona Sun in X-rays: SDO, Yohkoh, TRACE Solar corona is highly structured and dynamic Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 2 / 23 Stellar X-ray emission This talk: Low and intermediate mass stars X-ray generation mechanisms Time evolution of X-ray emission ’The X-ray HRD’ (G¨udel 2004) X-ray stars are (virtually) everywhere! Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 3 / 23 Cool stars in X-rays The solar neighborhood: 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 Stars 16.06.2014 4 / 23 Cool stars in X-rays Activity-dynamo relation (F - mid M) (Wright+ 2011) X-rays from magnetic activity, log LX/Lbol ≈ −3 ... −7 LX ∝ dynamo power; Ro = P/τc powerlaw (slope?) - saturation (level, breakpoint ?) - supersaturation (?) Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 4 / 23 Coronal dynamo regimes Activity regimes of stars (blue: Ro = 0.13, red: Rc /R∗ = 3, green: GX = 0.01) (Wright+ 2011) (also: Jeffries+ 2011) dynamo regimes depend on mass and rotation supersaturation: excess polar updraft vs. centrifugal stripping Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 5 / 23 X-ray activity at very low masses Very red dwarfs are faint... ...and fully convective! Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 6 / 23 Ultracool Dwarfs - magnetic activity at low masses ) 1 − 100 LHS 3003 (M7) 80 60 40 20 0 Rate (cts ks Rate (cts 0 10 20 30 40 50 ) 1 2.0 − SCR J1845-6357 (M8.5) 1.5 1.0 0.5 0.0 Rate (cts s 0 5 10 15 mod. active stars ) 1 35 log LX/Lbol ≈−4, − 30 LHS 2065 (M9) 25 20 TXqq = 1 − 5 MK 15 10 5 0 Rate (cts ks 0 10 20 30 40 Time (ks) X-ray light curves of very low mass stars (XMM-Newton, Chandra) quasi-quiescent X-ray emission, log LX/Lbol ≈−3.0 ···− 5.0 strong flares with hot plasma (& 10 MK) frequent Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 7 / 23 Ultracool Dwarfs - X-ray/radio connection 18 < M6.5 M6.5–M9.5 > M9.5 17 Benz & Güdel (1994) Upper limit New result Flare 16 15 14 g/s/Hz] [er R , L 13 10 log 12 11 Radio vs. X-ray luminosity (Williams+ 2014) 10 9 24 25 26 27 28 29 30 31 32 log10 LX [erg/s] X-ray bright and radio bright group (also Stelzer+ 2012) UCDs violate G¨udel-Benz relation Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 8 / 23 Ultracool Dwarfs - X-ray/radio connection 18 < M6.5 M6.5–M9.5 > M9.5 17 Benz & Güdel (1994) Upper limit New result Flare 16 15 14 g/s/Hz] [er R , (image by G. Hallinan) L 13 10 log 12 11 Radio vs. X-ray luminosity (Williams+ 2014) 10 9 24 25 26 27 28 29 30 31 32 log10 LX [erg/s] changing/bimodal dynamo mechanism, increasingly neutral atmospheres (e.g. Mohanty & Basri 2003, Reiners & Basri 2010) radio bright objects, fast rotators: ECME, aurorae (Hallinan+ 2007/08) Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 8 / 23 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 Stars 16.06.2014 9 / 23 X-ray activity at higher masses - A stars BSC sample: opt. brightness limited (Schr¨oder & Schmitt 2007) Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 9 / 23 X-ray activity at higher masses −1 keV −1 0.01 0.1 normalized counts s −3 10 0.5 1 Energy (keV) XMM spectra of Altair and Alderamin A7 IV-V, M = 1.8/2.0 M⊙, age: 1.2/0.8 Gyr ultra-fast rotators, Vsini ≈ 220/280 km/s, 60/80 % break-up virtual identical X-ray properties Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 10 / 23 X-ray activity at higher masses X-ray light curve and high-res spectrum of Altair (A7) (Robrade & Schmitt, 2009) 27 LX = 1.4 × 10 erg/s, log LX/Lbol = −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 Stars 16.06.2014 10 / 23 X-ray activity at higher masses 1.0 0.5 0.0 -0.5 North (milliarcseconds) -1.0 1.0 0.5 0.0 -0.5 -1.0 East (milliarcseconds) Surface images of Altair & Alderamin, CHARA (Monnier+ 2007, Zhao+09) oblate, gravity darkening ⇒ Teff ≈ 6800 K - 8500 K X-ray surface features at Teff . 7400 K ’equatorial bulge corona’ Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 10 / 23 The fading of X-ray activity 105 104 103 102 observation 101 ratio of count rates HRC-I/MOS 0 10 0.4 0.6 0.8 1.0 1.2 Temperature in MK β Pictoris (ESO, G¨unther+ 2012) β Pictoris - A6, young, debris disk (Hempel et al. 2005, G¨unther et al. 2012) X-rays: very soft (TX ≈ 1 MK), very faint (log LX ≈ 26.5) =⇒ No significant magnetic activity around A5 (or earlier) ...tight upper limits on Fomalhaut (A3) and Vega (A0) (log LX < 25.5) X-ray detections likely companions (e.g. VAST survey; De Rosa et al., 2011) Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 11 / 23 Ap/Bp stars – X-rays and the MCWS model MCWS model (Babel & Montmerle, 1997) MHD/RFHD advancements: (ud-Doula, Owocki, Townsend) rigid disks, dynamic phenomena Ap/Bp stars: magnetic intermediate mass stars, chemically peculiar, slow rotators fields: large-scale, stable, uncorrelated, rare (< 10 %), fossil IQ Aurigae: A0p, (Teff ≈ 14500 K, M = 4.0 M⊙, 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 Stars 16.06.2014 12 / 23 Ap/Bp stars – X-rays and the MCWS model MCWS model (Babel & Montmerle, 1997) MHD/RFHD advancements: (ud-Doula, Owocki, Townsend) rigid disks, dynamic phenomena 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 Stars 16.06.2014 12 / 23 Ap/Bp stars – IQ Aurigae −1 keV −1 0.01 0.1 1 normalized counts s −3 10 0.51 2 5 Energy (keV) Quasi-quiescent lightcurve & X-ray spectra - XMM (Robrade & Schmitt, 2011) −1 log LXqq = 29.6 erg s , log LX/Lbol ≈−6.5 X-rays from well above the stellar surface (O vii f /i ≈ 1, d & 7 R∗) 31 −1 flare: LXpeak = 3 × 10 erg s , very hot plasma: TX . 100 MK metallicity increase, moderately sized structure, L . 0.2 R∗ Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 13 / 23 Ap/Bp stars in X-rays HD 144334 1e+30 HD 34452 Lx/Lbol = -7 HD 12767 HD 146001 1e+29 HD 125823 HD 175362 HD 137509HD 142301F 1e+28 HD 133880 HD 184905 HD 22470 HD 54118 HD 147010 HD 122532 HD 143473 HD 28843 HD 27309 LX vs. Lbol 1e+27 HD 40312 X-ray luminosity (erg/s) A0 – B7, magnetic CP stars HD 112413 1e+26 (updated from Robrade & Schmitt (2011) 1.8 2 2.2 2.4 2.6 2.8 3 3.2 Stellar luminosity (log LSun) 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, radio-overluminous Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 14 / 23 Ap/Bp stars in X-rays 30 30 29 29 (erg/s) (erg/s) X 28 X 28 27 27 log L log L 26 26 2.5 3.0 3.5 4.0 4.5 5.0 5.5 4.0 4.1 4.2 4.3 M (MSun) log Teff (K) 30 30 29 29 (erg/s) (erg/s) X 28 X 28 27 27 log L log L 26 26 1.0 2.0 3.0 4.0 5.0 6.5 7.0 7.5 8.0 8.5 Beff (kG) log t (yr) LX vs. stellar parameter no correlation of LX with age or Beff unexplained scatter: magnetic field geometry, time variability, companions... Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 14 / 23 The temporal evolution of solar-like activity Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 15 / 23 The evolution of stellar rotation Envelope Core Rotation vs. age for solar-like stars in open clusters (Gallet & Bouvier 2013) large spread of initial rotation periods rotation is function of age and mass (Teff , color) Jan Robrade (Hamburger Sternwarte) X-rays from Stars 16.06.2014 16 / 23 X-ray activity as age indicator 1−20 Å 1000 20−100 Å 100−360 Å 360−920 Å 920−1200 Å 100 10 Relative flux (Sun=1) 1 0.1 0.1 0.2 0.3 0.40.5 1 2 3 4 5 6 7 8 Age (Gyr) X-ray/UV flux vs.
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