Rotationally modulated X-ray emission from the accretion shock in CTTS

Rotationally modulated X-ray emission from the accretion shock in CTTS

Costanza Argiroffi The X-ray Universe - Berlin, 27 June 2011

V2129 Oph ProjectC. Argiroffi, E. Flaccomio, J. Bouvier, J.-F. Donati,

K. V. Getman, S. G. Gregory, G. A. J. Hussain,M. M. Jardine, M. B. Skelly and F. M. Walter

V4046 Sgr ProjectC. Argiroffi, A. Maggio, T. Montmerle,

D. P. Huenemoerder, E. Alecian, M. Audard, J. Bouvier,F. Damiani, J.-F. Donati, S. G. Gregory, M. Güdel,G. A. J. Hussain, J. H. Kastner and G. G. Sacco

ACCRETION IN YOUNG LOW MASS STARS

MAGNETOSPHERIC ACCRETION MODEL(Konigl 1991)

X-RAYS


X-rays from accretion in CTTS: predicted by Ulrich (1976) observational evidences by Kastner et al. (2002)

WHY STUDY X-RAYS FROM ACCRETION

Costanza Argiroffi INAF - OAPA, 27 April 2011

to constrain the total amount of X-rays emitted from CTTS

to set the energy balance of the accretion-shock region

to probe the properties (i.e. density, velocity) of the accretion stream

to probe the chemical composition of the inner disk

(to constrain the evolution of circumstellar disks)

(to infer the mass accretin rate)

(to understand how accretion occurs)

(to check the chemical evolution of circumstellar disks)

X-RAYS FROM ACCRETION: OPEN ISSUES

Costanza Argiroffi INAF - OAPA, 27 April 2011

Observed X-rays significantly lower than predicted

Density vs temperature pattern: observations vs models

Observability of the X-rays from accretion

AIMS: SEARCH FOR ROTATIONAL MODULATION IN X-RAYS

Expected periodic variations in:

plasma densities

plasma average temperatures

EM of plasma at temperatures of 1-5 MK

Observing programs:

Long X-ray monitoring of a CTTS

with simultaneous optical observations

Projects:

V2129 Ophiuchi

V4046 Sagittari


TARGETS: V2129 OPHIUCHI & V4046 SGR

Star V2129 Oph V4046 Sgr

single binary

Mass 1.35 Msun 0.91 + 0.88 Msun

ST K5 K5 + K5

Prot 6.53 days 2.42 days

age 3 Myr 10-15 Myr

i 60 deg 35 deg

B 4 kG 200 G

SFR Rho Ophiuchi Beta Pic

dist. 120 pc 72 pc

200 ks with Chandra/HETGS 360 ks with XMM


X-RAY MONITORING OF V2129 OPH

seg. 1 seg. 2

We have analyzed X-ray spectra integrated over: ~ 100 ks = 1 segment = 0.18 Prot


(Donati et al. 2011, Argiroffi et al. 2011)

VARIATIONS IN THE COOL EMD COMPONENT

Cool lines (long wavelengths) are stronger in seg.1 than in seg. 2

EMD1 > EMD2 at 3-4 MK


VARIATIONS IN PLASMA DENSITY

Densities are higher in seg.1 than in seg. 2


INTERPRETATION OF THE OBSERVED VARIABILITY

Results summary:

EM at ~4 MK is higher in seg.1 than seg.2

Ne at 4 MK is higher in seg. 1 than in seg. 2


(Argiroffi et al. 2011)

V4046 SAGITTARI

(Stempels & Gahm 2004)


X-RAY MONITORING OF V4046 SGR

Each segment is 120 ks

The X-ray observation covered 2.2 system rotations

We have analyzed X-ray spectra integrated over: ~25 ks = 0.12 Prot


TIME RESOLVED X-RAY SPECTROSCOPY


Lines detected at 1 sigma in all the time intervals

VARIABILITY: COOL LINES

Best fit period = 1.22 +/- 0.01 days

(rot. period = 2.42 days)


(Argiroffi et al. 2011, ApJ submitted)

VARIABILITY: HOT vs COOL LINES

Cool lines:

Hot lines:


V4046 SGR X-RAY MONITORING: RESULTS

Rot. modulation

Obs. period = half the system period

X-ray vs optical results

Cool plasma is not symmetrically distributed with respect to the stellar poles

Naturally explained if high-density cool plasma is located on both the stellar components

X-rays are likely produced only by a fraction of the accretion shock region


High density Cool plasma is compatible with being material heated in the accretion shock

CONCLUSIONS


CTTS display variability in their soft X-rays

This variability can be explained in terms of X-rays emitted in the accretion shock and seen with different viewing angles during stellar rotation.

Soft X-rays, like all the other accretion indicators, display rotational modulation

Documents

Rotationally modulated X-ray emission from the accretion shock in CTTS