Salvatore Sciortino - University of Leicester · S. Sciortino – Ringberg 11.03.2005 Fluorescence: observations and statistics 'Cold' Fe 6.4 keV line thus far detected in a number

S. Sciortino – Ringberg 11.03.2005

X-rays as a probe of YSO physicsRecent XMM-Newton and Chandra results

Salvatore SciortinoINAF – Oss. Astronomico di Palermo Giuseppe S. Vaiana

(& lots of colleagues!)(e.g. Palermo, PennState, ESTEC, Grenoble, MIT, Hamburg

Observatory)


Long (two decades) Standing Questions

Is the Young Stellar Objects (YSOs) X-ray emission always a scaled up version of solar one ?

Can we distinguish between “pure” solar-like coronal and star-disk interaction activity ?

What is the interplay between accretion and X-ray emission in YSOs ?

“More Recently”: What is the effects of X-rays on small (planetary) and large (mol. cloud) scale evolution ?

To answer we need top quality data


Further open issues ....

Accretion in YSOsHow is it channeled?How is it regulated?

Feedback processes?Chemistry of protoplanetary disks

How do complex molecules form?Catalyst processes and molecules?

Isotopic ratios?


X-rays as a diagnostic of processes in YSOs, Why ?

Accreting (Class I, Class II) and non-accreting (Class III) YSOs are strong X-ray sourcesClass 0 not yet firmly detected in X-rays X-rays excellent for studying embedded YSOs

Absorption at 1 keV = at 1 µmThey provide an excellent diagnostics of key processes in YSOs


A Shallow (34 ksec) XMM-Newton observation of the ρ Oph core

Next Step will (hopefully) be

DROXO, ADeep (500 ksec)Rho Oph XMM-NewtonObservation

(PI: S. Sciortino)

Ozawa, Grosso & Montmerle 2004


The Chandra Orion Ultradeep Project (COUP)

Central 8x8 arcmin ofCOUP

(PI: E. Feigelson)

A COUP MOVIE


Recent topics explored

X-ray fluorescence from YSOsFlares and sizes of magnetic structures in YSOsX-ray Emission from Class 0 YSOs Shock-driven X-ray emission in YSOs


X-ray emission from (low-mass) accreting YSOs

Very X-ray luminousAt 1 Msun, log(LX) = 30-31 (Sun: log(LX)=26.5-27.5)

Very hotPlasma at 10's MK normally present, up to >100 MK (Sun: >= 10 MK only during flares)

Highly time variableStochastic variability, flares, rotational modulation

Often low metal abundance in emitting plasmaClass I/II hotter X-ray spectra than Class III


Fluorescence

Emission of X-ray radiation from photo-ionized cold material

Photo-ionizing photons come from star, cold material in circumstellar disk

Fluorescence is an obvious tracer of 'intimate relationships' between hard X-rays and cold materialIt can give important clues to the geometry of the circumstellar material


Fluorescence: what lines?

Best observable line is the Fe I Kα line at 6.4 keVHighest yieldFe abundant

Fe I photoionized by photons with E > 7.11 keVHigh-energy X-rays needed

Needs to be resolved from nearby Fe XXV Kα line at 6.7 keV


Fluorescence: observations and statistics

'Cold' Fe 6.4 keV line thus far detected in a number of casesOne detection in YLW16A in ρ Oph during an intense X-ray flare (Imanishi et al. 2001)7 cases of fluorescence in ONC YSOs (Tsujimoto et al. 2005) during intense X-ray flaringOne detection in Elias 29 in ρ Oph during quiescence and flaring (Favata et al. 2005)

Lbol

= 26 Lbol,sun

, Lacc

= 15-18 Lbol,sun

(very high)


Elias 29, Chandra and XMM light curves

Chandra

XMM-Newton


Elias 29, fluorescence

Chandra

XMM-Newton


Elias 29, equivalent width

Classic analysis by George and Fabian (1991) for a power law exciting spectrum (I ~ A E

o-Г ph keV-1)

Equivalent width function of incident spectrum (known) and cold material geometry (including viewing angle)Incident spectrum (Г ~ 2.6) and EW

obs=160 ev rules

out reflection from a cold slab EW

pred < 100 ev for Г >2


Elias 29, equivalent width

● EW(6.4 keV) = 150 eV requires a centrally illuminated disk and face-on viewing geometry

● IR observations (Boogert et al. 2002) indicate face-on disk

● Chiavassa et al. (2005) observe calcite around Elias 29, => liquid water from X-ray heated ice on grain surface

● Ceccarelli et al. (2002) find superheated gas in disk, likely UV/X-ray induced


Fluorescence in ONC YSOs

Chandra observations


X-ray fluorescence in ONC YSOs

EW(6.4 keV) = 110 – 250 eVUncertainties due to low statistics

These sources must be sources with face-on disksCOUP 649 and 1040 have no NIR (JHK)excess

Fluorescence requires disksX-rays can “see” disks with no NIR excessCan help constraining the inclination


Fluorescence, conclusions

Fluorescence important diagnostic of disk presence, geometry, etc.Likely a common intrinsic occurrence in YSOsX-rays interaction in the disk important for chemistry, etc.

Fluorescence one of the few direct tracers of such processes

Fluorescence can see disks with no evident JHK excess


Fluorescence, future work

Measurement of Fe 6.4 keV line at high S/N important diagnostic of disk structureDROXO (centered near Elias 29) will provide new high quality, time resolved spectraDetailed modeling of fluorescence line in order to provide disk density profileTime delay?


X-ray flares and size of magnetic structures

X-ray flares are classic tool to derive physical parameters of emitting regionUse of dynamical information (decay time, etc.) allows derivation of physical characteristics of flaring regionFlaring plasma must be magnetically confined, thus this allows to measure the size of individual magnetic structures


Example: solar flares


Some math...


Temperature-density evolution of solar flares


What if decay is not free?

Equation for L assumes that one measures the intrinsic decay time scale of loopIf heating is present during decay, τlc > τth

The loop will appear longer than it isThe slope ζ of the flare decay in the log(T)-log(n) diagram is a sensitive diagnostic of the presence of significant heating


Results from past flare analyses

Large number of intense flares analyzed with this technique:

RS CvnAlgol systemsFlare starsYoung solar-type stars

Invariably L R* : flaring structures are small and confined to the immediate photospheric surroundings


Enter the Orion Nebula Cluster Chandra observation (COUP)13 days non-stop observation

Except for orbit gaps every 48 hrUnique opportunity to study long-lasting flaring eventsUnique opportunity to measure the size of magnetic structures in accreting YSOs1600 X-ray sources detected32 flares with sufficient statistics for detailed analysis


Analysis of COUP flares

COUP 1343, results:long lasting (τ ≈40 ks)very hot plasma (100s MK)almost free decay fast temperature decay steep ζLong loop 2 × 1012 cm (≈ 0.1 AU!)Confining B field 150 G


Analysis of COUP flares

COUP 28, results:very long lasting (τ ≈80 ks)moderate T plasma (≤100 MK)sustained heating slow temperature decay shallow ζLongish loop 1 × 1012 cm (L/2 ≈ 2.5 R*)Confining B field 180 G


How can these long loops be structured?

Never seen in more evolved starsStability problem respect to centrifugal force

Orion YSOs are fast rotators (P ≈ 3-6 d)Co-rotation radius typically at 3-4 R*Long loops anchored on star only would be ripped open

Solution: loops connecting star and disk (at corotation radius)

Postulated by magnetospheric accretion scenario


Magnetospheric accretion


Flaring structures in ONC YSOs

Study of flaring structures in ONC YSOs has provided direct evidence of long magnetic structures in YSOsFirst “direct” determination of their size and B value

Extrapolation to photosphere compatible with Zeeman-measured fields (up to 5-6 kG)

Also, smaller ('normal coronal') structures present as shown from firm detection of X-ray rotational modulation in YSOs (Flaccomio et al. 2005, ApJS in press)Hint that large flaring structures present only in non-accreting systems (but statistics is limited ...)


R Corona Australis SFR in X-rays

@ 170 pcThe six blue sources are protostars seen with XMM-Newton

Hamaguchi et al. 2005, ApJ in press


The same YSOs seen in X-rays and infrared light. N

H ~ 3 10^23, Av ~ 180 m

XW

counterpart of IRS7 X

E: no counterpart down to

K ~19.4 m / Class O I If X-rays from Class 0

confirmed as a general occurrence Magnetic effects become an essential ingredient for understanding star formation process. Magnetic field structures can moderate the cloud collapse

X-ray from a Class 0 YSO ?

XE

XW


Summary

X-rays provide new, unique diagnostics of YSOs physicsDisk heating, chemistry, orientation

FluorescenceSize and location of magnetic structures funnelling accreting plasma

Flare analysisX-rays from Class 0 imply a key role of magnetic field in regulating star formation processPhysics and structure of accretion stream

He-like triplet study

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Salvatore Sciortino - University of Leicester · S. Sciortino – Ringberg 11.03.2005 Fluorescence: observations and statistics 'Cold' Fe 6.4 keV line thus far detected in a number