New Tests of Magnetospheric Accretion in T Tauri Stars

Johns–Krull, Christopher M.; Gafford, April D.

doi:10.1086/340898

Cited by 70 publications

(76 citation statements)

References 58 publications

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“…correlated time variations of line flux (from the accretion columns) and continuum excess flux (from the accretion shocks) are not always observed (Ardila & Basri 2000. And some of the statistical correlations expected from MAMs for CTTS samples are not always fulfilled (Johns-Krull & Gafford 2002).…”

Section: Accretion Columns and Line Profilesmentioning

confidence: 98%

Magnetically Channeled Accretion in T Tauri Stars

Bouvier¹,

Alencar

Dougados³

2003

Open Issues in Local Star Formation

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Section: Accretion Columns and Line Profilesmentioning

confidence: 98%

Magnetically Channeled Accretion in T Tauri Stars

Bouvier¹,

Alencar

Dougados³

2003

Open Issues in Local Star Formation

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“…Bertout & Genova 2006) we obtain the following stellar parameters: L = 0.52 ± 0.15 L and R = 1.46 ± 0.20 R . Earlier published estimates of the radius range from 1.2 R (Bertout & Basri 1988) to 2.7 R (Johns-Krull & Gafford 2002).…”

Section: Stellar Parametersmentioning

confidence: 99%

Accretion-powered chromospheres in classical T Tauri stars

Петров

Gahm

Stempels

et al. 2011

A&A

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Context. Optical spectra of classical T Tauri stars (cTTS) are rich in emission lines of low-excitation species that are composed of narrow and broad components, which indicates the existence of two emitting regions with different kinematics, densities, and temperatures. The photospheric spectrum is often veiled by an excess continuous emission. This veiling is usually attributed to radiation from a heated region beneath the accretion shock. The broad emission lines of H i, He ii, Ca ii, Fe ii, and other species are thought to form in a larger volume of gas. Aims. The aim of this research is to clarify the nature of the veiling, and whether the narrow chromospheric lines of Fe i and other metals represent a standard chromosphere of a late-type star, or are induced by mass accretion. Methods. We carried out high-resolution spectroscopy of selected cTTS with a special focus on DR Tauri and followed variations of chromospheric features, such as narrow Fe i emission lines, and accretion signatures such as the veiling continuum and the He ii line emission. Results. We found that the amount of veiling in DR Tau varies from practically nothing to factors more than 10 times the stellar continuum intensity, and that the veiling is caused by both a non-photospheric continuum and chromospheric line emission filling in the photospheric absorption lines. The latter causes differential veiling because stronger lines are more veiled. We developed methods to separate the two sources of veiling. Several veiled T Tauri stars show a common effect: the radial velocities of photospheric and chromospheric lines vary in anti-phase. This is caused by an area with enhanced chromospheric emission, which is offset from the pole of rotation and is associated with the hot spot formed at the footprint of the magnetic funnel of mass accretion. Conclusions. The enhanced chromospheric emission in cTTS is linked not only to solar-like magnetic activity, but is powered to a greater extent by the accreting gas. We suggest that the area of enhanced chromospheric emission is induced by mass accretion, which modifies the local structure of stellar atmosphere in an area that is more extended than the hot accretion spot. The narrow emission lines from this extended area are responsible for the extra component in the veiling through line-filling of photospheric absorption lines.

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“…Typical values are about 1%, but the range is wide, reaching over 10% in the most active accretors (Calvet & Gullbring 1998;Johns-Krull & Gafford 2002, Ingleby et al 2013.…”

Section: Analysis: the Structure Of The Accretion Flowmentioning

confidence: 99%

Doppler probe of accretion onto a T Tauri star

Петров¹,

Gahm²,

Herczeg³

et al. 2014

A&A

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Context. The YY Ori stars are T Tauri stars with prominent time-variable redshifted absorption components that flank certain emission lines. S CrA, one of the brightest of these stars, affords the rare opportunity of directly probing the accretion processes on the line of sight to one of the components of this wide visual pair. Aims. We followed the spectral changes in S CrA to derive the physical structure of the accreting gas. Methods. A series of high-resolution spectra of the two components of S CrA was obtained during four nights with the UVES spectrograph at the Very Large Telescope. Results. We found that both stars are very similar with regard to surface temperature, radius, and mass. Variable redshifted absorption components are particularly prominent in the SE component. During one night, this star developed a spectrum unique among the T Tauri stars: extremely strong and broad redshifted absorption components appeared in many lines of neutral and ionized metals, in addition to those of hydrogen and helium. The absorption depths of cooler, low-ionization lines peak at low velocities -while more highly ionized lines have peak absorption depths at high velocities. The different line profiles indicate that the temperature and density of the accretion stream increase as material approaches the star. We derive the physical conditions of the flow at several points along the accretion funnel directly from the spectrum of the infalling gas. We estimated mass accretion rates of about 10 −7 M /yr, which is similar to that derived from the relation based on the strength of Hα emission line. Conclusions. This is the first time the density and temperature distributions in accretion flows around a T Tauri star have been inferred from observations. Compared with predictions from standard models of accretion in T Tauri stars, which assume a dipole stellar magnetic field, we obtained higher densities and a steeper temperature rise toward the star.

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New Tests of Magnetospheric Accretion in T Tauri Stars

Cited by 70 publications

References 58 publications

Magnetically Channeled Accretion in T Tauri Stars

Magnetically Channeled Accretion in T Tauri Stars

Accretion-powered chromospheres in classical T Tauri stars

Doppler probe of accretion onto a T Tauri star

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