Accretion, Outflows, and Winds of Magnetized Stars

Romanova, M. M.; Owocki, S. P.

doi:10.1007/s11214-015-0200-9

Cited by 73 publications

(69 citation statements)

References 167 publications

(179 reference statements)

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“…Both observational and theoretical evidence clearly indicates that the magnetic field plays a major role in the accretion process of CTTS (see Romanova & Owocki 2015;Hartmann et al 2016, and references therein). The so-called magnetospheric accretion model predicts that the stellar magnetic field disrupts the inner disk, loads disk material in its flux tubes, and guides this material in its fall toward the star (e.g., Königl 1991;Calvet & Hartmann 1992;Hartmann et al 1994).…”

Section: Introductionmentioning

confidence: 99%

Redshifted X-rays from the material accreting onto TW Hydrae: Evidence of a low-latitude accretion spot

Argiroffi

Drake

Bonito

et al. 2017

A&A

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Context. High resolution spectroscopy, providing constraints on plasma motions and temperatures, is a powerful means to investigate the structure of accretion streams in classical T Tauri stars (CTTS). In particular, the accretion shock region, where the accreting material is heated to temperatures of a few million degrees as it continues its inward bulk motion, can be probed by X-ray spectroscopy. Aims. In an attempt to detect for the first time the motion of this X-ray-emitting post-shock material, we searched for a Doppler shift in the deep Chandra High Energy Transmission Grating observation of the CTTS TW Hya. This test should unveil the nature of this X-ray emitting plasma component in CTTS and constrain the accretion stream geometry. Methods. We searched for a Doppler shift in the X-ray emission from TW Hya with two different methods: by measuring the position of a selected sample of emission lines and by fitting the whole TW Hya X-ray spectrum, allowing the line-of-sight velocity to vary. Results. We found that the plasma at T ∼ 2 − 4 MK has a line-of-sight velocity of 38.3 ± 5.1 km s −1 with respect to the stellar photosphere. This result definitively confirms that this X-ray-emitting material originates in the post-shock region, at the base of the accretion stream, and not in coronal structures. The comparison of the observed velocity along the line of sight, 38.3 ± 5.1 km s −1 , with the inferred intrinsic velocity of the post shock of TW Hya, v post ≈ 110 − 120 km s −1 , indicates that the footpoints of the accretion streams on TW Hya are located at low latitudes on the stellar surface. Conclusions. Our results indicate that complex magnetic field geometries, such as those of TW Hya, permit low-latitude accretion spots. Moreover, since on TW Hya the redshift of the soft X-ray emission is very similar to that of the narrow component of the C iv resonance doublet at 1550 Å, then the plasma at 2 − 4 MK and that at 0.1 MK likely originate in the same post-shock regions.

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Section: Introductionmentioning

confidence: 99%

Redshifted X-rays from the material accreting onto TW Hydrae: Evidence of a low-latitude accretion spot

Argiroffi

Drake

Bonito

et al. 2017

A&A

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“…The region where the magnetic flux connects the disc with the star is very unstable, where magnetospheric ejections of plasma can take place (Goodson et al 1997;Zanni & Ferreira 2013). Magneto-hydrodynamic (MHD) simulations of the accretion and outflow processes in cTTS have been performed by several groups (see reviews by Bouvier et al (2007), Romanova & Owocki (2015) and references therein). The gas flows can be traced by analysis of emission line profiles in spectra of cTTS.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of wind and the dusty environments in the accreting T Tauri stars RY Tauri and SU Aurigae

Петров

Grankin

Gameiro

et al. 2018

Monthly Notices of the Royal Astronomical Society

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Classical T Tauri stars with ages of less than 10 Myr possess accretion discs. Magnetohydrodynamic processes at the boundary between the disc and the stellar magnetosphere control the accretion and ejections gas flows. We carried out a long series of simultaneous spectroscopic and photometric observations of the classical T Tauri stars RY Tau and SU Aur with the aim to quantify the accretion and outflow dynamics at time scales from days to years. It is shown that dust in the disc wind is the main source of photometric variability of these stars. In RY Tau we observed a new effect: during events of enhanced outflow the circumstellar extinction gets lower. The characteristic time of changes in outflow velocity and stellar brightness indicates that the obscuring dust is near the star. The outflow activity in both stars is changing on a time scale of years. Periods of quiescence in Hα profile variability were observed during 2015-2016 season in RY Tau and during 2016-2017 season in SU Aur. We interpret these findings in the framework of the magnetospheric accretion model, and discuss how the global stellar magnetic field may influence the long-term variations of the outflow activity.

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“…Outflows from these objects are the most efficient way to take away the angular momentum from the star-disc system and prevent the star from spinning up. Various theoretical outflow mechanisms which could drive outflows in young disc accreting stellar objects have been proposed in the literature (see reviews by Konigl & Pudritz 2000, p. 759;Pudritz & Banerjee 2005;Romanova & Owocki 2015).…”

Section: Introductionmentioning

confidence: 99%

EPISODIC HIGH-VELOCITY OUTFLOWS FROM V899 Mon: A CONSTRAINT ON THE OUTFLOW MECHANISMS*

Ninan

Ojha

Philip

2016

ApJ

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We report the detection of large variations in the outflow wind velocity from a young eruptive star, V899 Mon, during its ongoing high accretion outburst phase. Such large variations in the outflow velocity (from −722 to −425 km s −1 ) have never been reported previously in this family of objects. Our continuous monitoring of this source shows that the multi-component, clumpy, and episodic high velocity outflows are stable in the timescale of a few days, and vary over the timescale of a few weeks to months. We detect significant decoupling in the instantaneous outflow strength to accretion rate. From the comparison of various possible outflow mechanisms in magnetospheric accretion of young stellar objects, we conclude magnetically driven polar winds to be the most consistent mechanism for the outflows seen in V899 Mon. The large scale fluctuations in outflow over the short period makes V899 Mon the most ideal source to constrain various magnetohydrodynamics simulations of magnetospheric accretion.

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Accretion, Outflows, and Winds of Magnetized Stars

Cited by 73 publications

References 167 publications

Redshifted X-rays from the material accreting onto TW Hydrae: Evidence of a low-latitude accretion spot

Redshifted X-rays from the material accreting onto TW Hydrae: Evidence of a low-latitude accretion spot

Dynamics of wind and the dusty environments in the accreting T Tauri stars RY Tauri and SU Aurigae

EPISODIC HIGH-VELOCITY OUTFLOWS FROM V899 Mon: A CONSTRAINT ON THE OUTFLOW MECHANISMS*

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