High-resolution X-ray spectroscopy of T Tauri stars in the Taurus-Auriga complex

Telleschi, A.; Güdel, M.; Briggs, K. R.; Audard, M.; Scelsi, L.

doi:10.1051/0004-6361:20066193

Cited by 79 publications

(176 citation statements)

References 87 publications

(199 reference statements)

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“…The important result is that the model EMD has a pronounced peak at T ∼ 3 MK, which is exactly the feature that we observe in MP Mus and TW Hya, while no cool peak is present in the EMD of the WTTS TWA 5. The cool peak that we found in the EMD of the two CTTS TW Hya and MP Mus explains, in terms of EMD, the soft flux excess observed in the X-ray spectra of CTTS in the XEST survey Telleschi et al 2007). …”

Section: Soft X-rays From Shock-heated Plasma: Emdsupporting

confidence: 58%

“…The idea of accretion-driven X-rays from CTTS is superficially supported by a soft X-ray excess found in highresolution X-ray spectra of CTTS with respect to similar spectra of WTTS by Telleschi et al (2007) and . However, and noted that this soft X-ray excess is significantly lower than that predicted by simple models of X-ray emission from accretion shocks.…”

Section: Article Published By Edp Sciencesmentioning

confidence: 93%

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X-ray optical depth diagnostics of T Tauri accretion shocks

Argiroffi

Maggio

Peres

et al. 2009

A&A

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Context. In classical T Tauri stars, X-rays are produced by two plasma components: a hot low-density plasma, with frequent flaring activity, and a high-density lower temperature plasma. The former is coronal plasma related to the stellar magnetic activity. The latter component, never observed in non-accreting stars, could be plasma heated by the shock formed by the accretion process. However its nature is still being debated. Aims. Our aim is to probe the soft X-ray emission from the high-density plasma component in classical T Tauri stars to check whether this plasma is heated in the accretion shock or whether it is coronal plasma. Methods. High-resolution X-ray spectroscopy allows us to measure individual line fluxes. We analyze X-ray spectra of the classical T Tauri stars MP Muscae and TW Hydrae. Our aim is to evaluate line ratios to search for optical depth effects, which are expected in the accretion-driven scenario. We also derive the plasma emission measure distributions EMD, to investigate whether and how the EMD of accreting and non accreting young stars differ. The results are compared to those obtained for the non-accreting weakline T Tauri star TWA 5. Results. We find evidence of resonance scattering in the strongest lines of MP Mus, supporting the idea that soft X-rays are produced by plasma heated in the accretion shock. We also find that the EMD of MP Mus has two peaks: a cool peak at temperatures expected for plasma heated in the accretion shock, and a hot peak typical of coronal plasma. The shape of the EMD of MP Mus appears to be the superposition of the EMD of a pure coronal source, like TWA 5, and an EMD alike that of TW Hya, which is instead dominated by shock-heated plasma.

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Section: Soft X-rays From Shock-heated Plasma: Emdsupporting

confidence: 58%

Section: Article Published By Edp Sciencesmentioning

confidence: 93%

X-ray optical depth diagnostics of T Tauri accretion shocks

Argiroffi

Maggio

Peres

et al. 2009

A&A

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“…1) derived with the PINTofALE spectral code (Kashyap & Drake 2000) with the APED V1.3 atomic line database (Smith et al 2001), assuming the same metal abundances as before (as deduced from X-ray observations of CTTSs; Telleschi et al 2007). We use the ideal gas law, P = (γ − 1)ρ .…”

Section: Mhd Modelingmentioning

confidence: 99%

X-ray emitting MHD accretion shocks in classical T Tauri stars

Orlando¹,

Sacco

Argiroffi

et al. 2010

A&A

103

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Context. Plasma accreting onto classical T Tauri stars (CTTS) is believed to impact the stellar surface at free-fall velocities, generating a shock. Current time-dependent models describing accretion shocks in CTTSs are one-dimensional, assuming that the plasma moves and transports energy only along magnetic field lines (β 1). Aims. We investigate the stability and dynamics of accretion shocks in CTTSs, considering the case of β > ∼ 1 in the post-shock region. In these cases the 1D approximation is not valid and a multi-dimensional MHD approach is necessary. Methods. We model an accretion stream propagating through the atmosphere of a CTTS and impacting onto its chromosphere by performing 2D axisymmetric MHD simulations. The model takes into account the stellar magnetic field, the gravity, the radiative cooling, and the thermal conduction (including the effects of heat flux saturation). Results. The dynamics and stability of the accretion shock strongly depend on the plasma β. In the case of shocks with β > 10, violent outflows of shock-heated material (and possibly MHD waves) are generated at the base of the accretion column and intensely perturb the surrounding stellar atmosphere and the accretion column itself (therefore modifying the dynamics of the shock). In shocks with β ≈ 1, the post-shock region is efficiently confined by the magnetic field. The shock oscillations induced by cooling instability are strongly influenced by β: for β > 10, the oscillations may be rapidly dumped by the magnetic field, approaching a quasi-stationary state, or may be chaotic with no obvious periodicity due to perturbation of the stream induced by the post-shock plasma itself; for β ≈ 1 the oscillations are quasi-periodic, although their amplitude is smaller and the frequency higher than those predicted by 1D models.

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“…Preibisch et al 2005;Telleschi et al 2007b). Drake et al (2009) suggested that it is not the accretion of the CTTS that causes their low luminosity but rather, the low luminosity that allows the disk to approach the star more closely, i.e., weaker emitters to accrete and become CTTS.…”

Section: Varying Absorption?mentioning

confidence: 99%

The disk-bearing young star IM Lupi

Guenther¹,

Schmitt²,

Guêdel³

et al. 2010

A&A

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Context. Classical T Tauri stars (CTTS) differ in their X-ray signatures from older pre-main sequence stars, e.g., weak-lined TTS (WTTS). CTTS exhibit a soft excess and deviations from the low-density coronal limit in the He-like triplets. Aims. We test whether these features correlate with either accretion or the presence of a disk by observing IM Lup, a disk-bearing object apparently in transition between CTTS and WTTS without obvious accretion. Methods. We analyse a Chandra grating spectrum and additional XMM-Newton data of IM Lup and accompanying optical spectra, some of which where taken simultaneously with the X-ray observations. We fit the X-ray emission lines and decompose the Hα emission line into different components. Results. In X-rays, IM Lup has a bright and hot active corona, where elements with low first-ionisation potential are depleted. The He-like Ne ix triplet is in the low-density state, but because of the small number of counts in the data a high-density scenario cannot be excluded at the 90% confidence level. In terms of all its X-ray properties, IM Lup resembles a main-sequence star, but is also compatible with CTTS signatures at the 90% confidence level, thus we cannot decide whether the soft excess and deviations from the low-density coronal limit for the He-like triplets in CTTS are produced by accretion or only the presence of a disk. The star IM Lup is chromospherically active, which accounts for most of its emission in Hα. Despite its low equivalent width, the complexity of the Hα line profile is reminiscent of CTTS. We estimate the mass accretion rate to be 10 −11 M yr −1 .

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High-resolution X-ray spectroscopy of T Tauri stars in the Taurus-Auriga complex

Cited by 79 publications

References 87 publications

X-ray optical depth diagnostics of T Tauri accretion shocks

X-ray optical depth diagnostics of T Tauri accretion shocks

X-ray emitting MHD accretion shocks in classical T Tauri stars

The disk-bearing young star IM Lupi

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