Radiative accretion shocks along nonuniform stellar magnetic fields in classical T Tauri stars

Orlando, S.; Bonito, R.; Argiroffi, C.; Reale, F.; Peres, G.; Miceli, M.; Matsakos, T.; Stehlé, C.; Ibgui, L.; Sá, Lionel de; Chièze, J. P.; Lanz, T.

doi:10.1051/0004-6361/201322076

Cited by 45 publications

(50 citation statements)

References 39 publications

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“…We estimate the apparent RV variation of the resulting absorption line by crosscorrelation. The modification of the stellar photosphere by the proximity of an accretion hot spot can be very complex, depending on plasma parameters, and can also contribute to powering a stellar wind (Orlando et al 2010(Orlando et al , 2013. Therefore, this analysis does not pretend to derive strong constraints on the properties of the line-dependent veiling, since it involves too many free (or poorly constrained) parameters, but to demonstrate that a simple accretion-plus-rotation model can explain simultaneously the observed RV signatures in the emission and the absorption lines.…”

Section: Dynamics Of Narrow and Broad Components And Their Rv Signaturesmentioning

confidence: 99%

Accretion dynamics of EX Lupi in quiescence

Sicilia‐Aguilar¹,

Fang²,

Roccatagliata³

et al. 2015

A&A

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Context. EX Lupi is a young, accreting M0 star and the prototype of EXor variable stars. Its spectrum is very rich in emission lines, including many metallic lines with narrow and broad components. The presence of a close companion has also been proposed, based on radial velocity signatures. Aims. We use the metallic emission lines to study the accretion structures and to test the companion hypothesis. Methods. We analyse 54 spectra obtained during five years of quiescence time. We study the line profile variability and the radial velocity of the narrow and broad metallic emission lines. We use the velocity signatures of different species with various excitation conditions and their time dependency to track the dynamics associated with accretion. Results. We observe periodic velocity variations in the broad and the narrow line components, consistent with rotational modulation. The modulation is stronger for lines with higher excitation potentials (e.g. He II), which are likely produced in a confined area very close to the accretion shock. Conclusions. We propose that the narrow line components are produced in the post-shock region, while the broad components originate in the more extended, pre-shock material in the accretion column. All the emission lines suffer velocity modulation due to the rotation of the star. The broad components are responsible for the line-dependent veiling observed in EX Lupi. We demonstrate that a rotationally modulated line-dependent veiling can explain the radial velocity signature of the photospheric absorption lines, making the close-in companion hypothesis unnecessary. The accretion structure is locked to the star and very stable during the five years of observations. Not all stars with similar spectral types and accretion rates show the same metallic emission lines, which could be related to differences in temperature and density in their accretion structure(s). The contamination of photospheric signatures by accretion-related processes can be turned into a very useful tool for determining the innermost details of the accretion channels in the proximity of the star. The presence of emission lines from very stable accretion columns will nevertheless be a very strong limitation for the detection of companions by radial velocity in young stars, given the similarity of the accretion-related signatures with those produced by a companion.

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Section: Dynamics Of Narrow and Broad Components And Their Rv Signaturesmentioning

confidence: 99%

Accretion dynamics of EX Lupi in quiescence

Sicilia‐Aguilar¹,

Fang²,

Roccatagliata³

et al. 2015

A&A

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“…Inside this radius, material is confined to flow along magnetic field lines where it impacts the stellar surface at magnetic footpoints, shockheating the photosphere (Orlando et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Accretion and Magnetic Reconnection in the Classical T Tauri Binary Dq Tau

Tofflemire

Ardila

Akeson

et al. 2017

ApJ

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The theory of binary star formation predicts that close binaries (a<100 au) will experience periodic pulsed accretion events as streams of material form at the inner edge of a circumbinary disk (CBD), cross a dynamically cleared gap, and feed circumstellar disks or accrete directly onto the stars. The archetype for the pulsed accretion theory is the eccentric, short-period, classical T Tauri binary DQ Tau. Low-cadence (∼daily) broadband photometry has shown brightening events near most periastron passages, just as numerical simulations would predict for an eccentric binary. Magnetic reconnection events (flares) during the collision of stellar magnetospheres near periastron could, however, produce the same periodic, broadband behavior when observed at a one-day cadence. To reveal the dominant physical mechanism seen in DQ Tau's low-cadence observations, we have obtained continuous, moderate-cadence, multiband photometry over 10 orbital periods, supplemented with 27 nights of minute-cadence photometry centered on four separate periastron passages. While both accretion and stellar flares are present, the dominant timescale and morphology of brightening events are characteristic of accretion. On average, the mass accretion rate increases by a factor of five near periastron, in good agreement with recent models. Large variability is observed in the morphology and amplitude of accretion events from orbit to orbit. We argue that this is due to the absence of stable circumstellar disks around each star, compounded by inhomogeneities at the inner edge of the CBD and within the accretion streams themselves. Quasiperiodic apastron accretion events are also observed, which are not predicted by binary accretion theory.

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“…Computing accretion can be performed through two main approaches: on the one hand, 2D and 3D simulations can include the influence of the magnetic field [9] as well as geometric or flow inhomogeneities effects [10,11]; on the other hand, 1D simulations can hardly deal with these effects 1 , but may include more refined physics, like time-dependent (non-LTE) ionization or radiative transfer.…”

Section: Hydro-radiative Simulations With the Code Astrolabementioning

confidence: 99%

Accretion shock stability on a dynamically heated YSO atmosphere with radiative transfer

Sá

Chièze

Stehlé

et al. 2014

EPJ Web of Conferences

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Abstract. Theory and simulations predict Quasi-Periodic Oscillations of shocks which develop in magnetically driven accretion funnels connecting the stellar disc to the photosphere of Young Stellar Objects (YSO). X-ray observations however do not show evidence of the expected periodicity. We examine here, in a first attempt, the influence of radiative transfer on the evolution of material impinging on a dynamically heated stellar atmosphere, using the 1D ALE-RHD code ASTROLABE. The mechanical shock heating mechanism of the chromosphere only slightly perturbs the flow. We also show that, since the impacting flow, and especially the part which penetrates into the chromosphere, is not treated as a purely radiating transparent medium, a sufficiently efficient coupling between gas and radiation may affect or even suppress the oscillations of the shocked column. This study shows the importance of the description of the radiation effects in the hydrodynamics and of the accuracy of the opacities for an adequate modeling.

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Radiative accretion shocks along nonuniform stellar magnetic fields in classical T Tauri stars

Cited by 45 publications

References 39 publications

Accretion dynamics of EX Lupi in quiescence

Accretion dynamics of EX Lupi in quiescence

Accretion and Magnetic Reconnection in the Classical T Tauri Binary Dq Tau

Accretion shock stability on a dynamically heated YSO atmosphere with radiative transfer

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