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: