The X-Ray Life

of Stars:Low-Mass and

Pre-Main Sequence

The X-Ray Life

of Stars:Low-Mass and

Pre-Main Sequence

Manuel GüdelUniversity of Vienna

Manuel GüdelUniversity of Vienna

• On the main sequence: from the Sun back to ZAMS

• Younger still: Protoplanetary disks and accretion

• More massive: Herbig stars

• More embedded: Jets and outflows

• Eruptive variables

• Summary

Outline

α Cen AB: solar-like behavior (Ayres+ 2009)• cycles• rotational modulation, • slow changes in coronal T

The Sun behaves like a normal X-ray G2V star and therefore as an example and anchor for stellar X-ray astronomy.

The Sun Among Stars

YEAR

Line Shifts: Contact Binary

• no eclipse• near-polar• on primary• height 0.06-0.2 R*

(Huenemoerder+ 2006)

(composite, 15 lines in MEG)Rapidly Rotating Giant

(NeX 12.14A centroids, HEG)

(Drake+ 2008)

at rest redshift60-140 km/s

line shift,broadening,Doppler im., near-polarregion, ≤ 1R*(Drake+ 2008)

FK ComVV Cep

(Flaring) Coronal Structure from Fluorescence

Monte-Carlo modeling of fluorescent efficiency for different source heights (depending on flux > 7.11 keV):

h < 0.3R* (Testa+ 2008; see also Osten et al. 2007: alternatively electron impact but inefficient)

Beyond the Limit of Stars: Brown Dwarfs

(Berger+ 2010)

(Preibisch+ 2005)

* Young BDs (M6-M9): like stars (M6-M9): coronal activity depends on Teff, not mass!

* Old BDs: X-ray faint – but not radio faint! Magnetic activity persists, but coronal heating declines.

stars ----------------BDs---------------

LX/Lbol

log LX

log L(Hα)

log LR

Toward Forming Stars: Accretion and the

„High-Energy“ Environment

Shocks in accretion streams:

T = 3mHv2 / 16k

v vff = (2GM/R)1/2

T = a few MK

dM/dt = 4R2fvffnemp ne 1012-1014 cm-3

vff

f

Dense, cool plasma in accretion shocks?(Kastner+ 2002, Stelzer & Schmitt 2004, Schmitt+ 2005, Günther+ 2006, Argiroffi+ 2007, Robrade &

Schmitt 2006/07, Huenemoerder+ 2007, etc)

ne = 1012 cm-3

(Günther+ 2006)

r

i f

(Günther+ 2008)

OVIII 3-4 MK OVII 2 MKhot10-30 MK

1-2 MK

non-accreting

accreting

X-Ray Soft Excess (Güdel 2006; Telleschi+ 2007; G&T 2007)

MS stars

CTTS

WTTS

cool

Related to accretion AND coronal activity

L(OVII)

L(OVIII)

But Shocks are Complex...

• MX << Mopt: need right conditions: too fast: chromospheric absorption

too slow: T too low, no X-rays;mixture of structured flows (Sacco+2010)

(Curran+ 2011)

0.3

dex

2.5 dex

• MX nearly constant! Not correl. with Mopt.(Curran+ 2011): optical-depth effects increasing with accretion rate?

. . .

(Günther+ 2007)

MgXI NeIXOVII

Post-shock

Observations: (TW Hya, Brickhouse+ 2010)

• OVII lower density • OVII lower absorption:

OVII NH = 4.1x1020 cm-2

NeIX NH = 1.8x1021 cm-2

shoc

k

(Brickhouse+ 2010)

Problems with Cooling....

Shock-heated gas channeled back tothe corona? „Accretion-fed corona“(Brickhouse+ 2010)

(2D simulations by Orlando+ 2010; By=1 G, plasma-β >> 1)

Or fibril-structured accretion streams,dense core developing shock deeper in chromosphere: NeIX from deep, dense layers, OVII only from outer, low-dens layer(Sacco+ 2010)

shoc

kac

creti

on fl

ow

denser

chromos-phere

more NH

OVII, NeIX

NeIX

Fe K 6.4 keV

Fluorescence of cooldisk material

Disk Ionization by Stellar X-Rays: Fluorescence

Fe XXV 6.7 keV(30 – 100 MK)

(COUP, Tsujimoto+ 2005)

(flaring protostar in COUP)

6.4 keV

SXR flare

6.4 keV line during impulsive phase like HXR or radio: EW = 1.4 keV!!theoretical disks: <150 eV (George & Fabian 1991, Drake+ 2008)

K shell electron ejection bynonthermal electrons?

(Osten et al. 2007, Czesla & Schmitt 2007)

rather inefficient

(Czesla & Schmitt 2007)

Orion YSO (COUP):

(Drake+ 2008)

source height

EWcalc

6.4 keV

Irradiating hard source hidden:suppressed continuum:

CTTS

AB Aur (HAe)

• Soft spectrum• low density• high Teff (10 kK) h

(≈1600Å) photoexcitation X-ray source at R > 1.7R*

(Telleschi et al. 2007)

Herbig Ae/Be Stars

Magnetically Confined Winds in AB Aur? Accretion in HD 104237A?

NeIX: 1012 cm-3

(Testa+ 2008)

Jets in HD 163296?(Günther+ 2009)

And low-masscompanions in many others? (Stelzer+ 2009)

L1551 IRS 5: (observations 2001, 2005, 2009)Star absorbed, but inner jet X-ray strong

• Cooling jet, dominated by expansion• standing structure at 0.5-1”

(Schneider+ 2011)

Jets, Accretion Flows

cooling

time

DG Tau

hard/hot

Hard emission: coronalexcessively absorbed by dust-depleted accretion flows.

Jets, Accretion Flows

soft/cool:constant

low NH

high NH

>> NH(AV)

hard/hot:variable

DG Tau:

observations 2004, 2005/06, 2010 (Chandra LP; Güdel+ 2011)

TAX spectrumduring 1 week

ACIS-S image

similar spectrum:soft “stellar” component and jet

Offset in 2010 identical to 2005/06 (Schneider+): standing structure; collimation region?

1pixel = 0.0615”Deconvolution of SER-treated ACIS data (Güdel+ 2011)

0.17” (40 AU along jet)

2-8 keV

0.3-1.5 keV

n = 105 cm-3

(Günther+ 2009)

Eruptive Variables

FU Ori stars (FUors): disk dominates optical spectrum; large amplitude; yrs-decadesEX Lup stars (EXors): star dominates optical spectrum; less energetic, shorter

FUOrs not in immediate outburst: (Skinner+ 2009, 2011)• very hard spectra• excess absorption: due to accretion streams, winds, puffed-up inner disk?• possibly X-ray overluminous for known/estimated masses

(Skinner+ 2011)

companion FU Ori

V1118 Ori:moderate X-ray increase;disk inner radius 0.4 to 0.2 AU due to increased accretionpost-outburst: X-rays low

disruption of magnetosphereby narrower disk?

(Audard+ 2010)

V1647 Ori:strong X-ray increase;correlated with accretion rate?

induced magnetic reconnnection betweenstar and disk?

(Kastner+ 2006)

Z CMa:no X-ray change(Stelzer+ 2009)

EX Lup:correlated, accretion-funnelabsorbed hardspectrum + accretion-related soft spectrum(Grosso+ 2010)

X-rays

X-rays

Summary

Unexpected diversity of emission mechanisms and heating processes revealed in cool/pre-main sequence stars:

• Coronal radiation, T = 1-100 MK • accretion shocks ear photosphere in T Tauri stars• internal or bow shocks in jets of T Tauris and Herbigs• standing shocks (?) in jet collimation regions • magnetically confined winds in Herbig stars• protoplanetary disk ionisation and fluorescence• disk-magnetosphere interactions in eruptive variables

Rich field that has helped diagnose basic physical processes especially around young, pre-main sequence stars.

similar: Hamaguchi et al. (1.5 keV)

Irradiating hard source hidden (behind star, disk, etc):suppressed continuum, strong fluorescent line

NGC 2071 IRS1

(Skinner et al. 2007, 2010)

Extreme Fluorescence?

NGC 2071 IRS 1: - EW(6.4 keV) = 2.4 keV(Skinner+ 2007,10) - constant over years

- not accompanied by flares- no Fe XXV contribution!

XMM:

Chandra: