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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
Costanza Argiroffi The X-ray Universe - Berlin, 27 June 2011
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
Costanza Argiroffi The X-ray Universe - Berlin, 27 June 2011
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
Costanza Argiroffi The X-ray Universe - Berlin, 27 June 2011
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
Costanza Argiroffi The X-ray Universe - Berlin, 27 June 2011
(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
Costanza Argiroffi The X-ray Universe - Berlin, 27 June 2011
VARIATIONS IN PLASMA DENSITY
Densities are higher in seg.1 than in seg. 2
Costanza Argiroffi The X-ray Universe - Berlin, 27 June 2011
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
Costanza Argiroffi The X-ray Universe - Berlin, 27 June 2011
(Argiroffi et al. 2011)
V4046 SAGITTARI
(Stempels & Gahm 2004)
Costanza Argiroffi The X-ray Universe - Berlin, 27 June 2011
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
Costanza Argiroffi The X-ray Universe - Berlin, 27 June 2011
TIME RESOLVED X-RAY SPECTROSCOPY
Costanza Argiroffi The X-ray Universe - Berlin, 27 June 2011
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)
Costanza Argiroffi The X-ray Universe - Berlin, 27 June 2011
(Argiroffi et al. 2011, ApJ submitted)
VARIABILITY: HOT vs COOL LINES
Cool lines:
Hot lines:
Costanza Argiroffi The X-ray Universe - Berlin, 27 June 2011
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
Costanza Argiroffi The X-ray Universe - Berlin, 27 June 2011
High density Cool plasma is compatible with being material heated in the accretion shock
CONCLUSIONS
Costanza Argiroffi The X-ray Universe - Berlin, 27 June 2011
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