Accretion-powered chromospheres in classical T Tauri stars

Петров, П. П.; Gahm, G. F.; Stempels, H. C.; Walter, Frederick M.; Artemenko, S. A.

doi:10.1051/0004-6361/201116721

Cited by 48 publications

(61 citation statements)

References 64 publications

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“…The diagram shows the anti-phase variations between stellar and NC velocities, as reported in Paper I, and is similar to what has been observed in several CTTS (e.g. Petrov et al 2001Petrov et al , 2011.…”

Section: Veiling Line Strength and Phasesupporting

confidence: 86%

Face to phase with RU Lupi

Gahm¹,

Stempels²,

Walter³

et al. 2013

A&A

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Context. Some classical T Tauri stars, with intense line and continuous excess emission, show extremely complex spectral variations. Aims. We aim to map and interpret the spectral variations in one such extreme T Tauri star, namely RU Lupi, and to explore how the changes are related to stellar brightness and rotational phase. Methods. We followed the star over three observing runs, each covering a few days, collecting high-resolution optical spectra. In connection to the third run, complementary NIR spectra, multicolour photometric data, and X-ray observations were obtained. Results. The stellar photospheric absorption line spectrum is weakened by superimposed emission, and this veiling becomes extremely high on occasion. Interpreted as a variable continuous excess emission, its contribution would amount to several times the stellar continuum brightness. However, the stellar brightness does not change much when the veiling changes, and we conclude that the veiling is dominated by narrow line emission that fills in the photospheric lines. Continuous emission, originating at the hot spot on the stellar surface, plays a dominant role only at lower degrees of veiling. The radial velocity of narrow emission components in lines of He  vary periodically in anti-phase with the stellar velocity, reflecting the location and motion of the accretion footprint. The blue-shifted wings in He , related to a stellar wind, are remarkably stable in equivalent width. This implies that the line flux responds directly to changes in the veiling, which in turn is related to the accretion rate close to the star. In contrast, the equivalent widths of the red-shifted wings change with rotational phase. From the pattern of variability we infer that these wings originate in accreting gas close to the star, and that the accretion funnels are bent and trail the hot spot. The profiles of the forbidden lines of [O I] and [S II] are very stable in strength and shape over the entire observing period, and like a system of narrow, blue-shifted absorption features seen in lines of Ca  and Na , they originate at larger distances from the star in the disk wind. Slightly blue-shifted emission components are present in the forbidden lines and might be related to a wide angle molecular disk wind proposed by others.

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Section: Veiling Line Strength and Phasesupporting

confidence: 86%

Face to phase with RU Lupi

Gahm¹,

Stempels²,

Walter³

et al. 2013

A&A

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“…In DR Tau, an inverse-P Cygni profile is detected in the Paγ and Paδ lines. Such a feature is observed also in the Hδ line while it is absent in the Hα and Hβ lines (Petrov et al 2011, Alencar et al 2001 which, on the contrary, are strongly peaked at red-shifted velocities. The high-n Brackett lines are more symmetric, consistent with their lower optical depth with respect to line emission from lower levels (e.g.…”

Section: Hydrogen Linesmentioning

confidence: 89%

High-resolution TNG spectra of T Tauri stars

Antoniucci

Nisini

Biazzo

et al. 2017

A&A

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Aims. We aim to characterise the star-disk interaction region in T Tauri stars that show photometric and spectroscopic variability. Methods. We used the GIANO instrument at the Telescopio Nazionale Galileo to obtain near-infrared high-resolution spectra (R∼ 50,000) of XZ Tau and DR Tau, which are two actively accreting T Tauri stars classified as EXors. Equivalent widths and profiles of the observed features are used to derive information on the properties of the inner disk, the accretion columns, and the winds. Results. Both sources display composite H i line profiles, where contributions from both accreting gas and high-velocity winds can be recognised. These lines are progressively more symmetric and narrower with increasing upper energy which may be interpreted in terms of two components with different decrements or imputed to self-absorption effects. XZ Tau is observed in a relatively high state of activity with respect to literature observations. The variation of the He i 1.08µm line blue-shifted absorption, in particular, suggests that the inner wind has undergone a dramatic change in its velocity structure, connected with a recent accretion event. DR Tau has a more stable wind as its He i 1.08µm absorption does not show variations with time in spite of strong variability of the emission component. The IR veiling in the two sources can be interpreted as due to blackbody emission at temperatures of 1600 K and 2300 K for XZ Tau and DR Tau, respectively, with emitting areas ∼ 30 times larger than the central star. While for XZ Tau these conditions are consistent with emission from the inner rim of the dusty disk, the fairly high temperature inferred for DR Tau might suggest that its veiling originates from a thick gaseous disk located within the dust sublimation radius. Strong and broad metallic lines, mainly from C i and Fe i, are detected in XZ Tau, similar to those observed in other EXor sources during burst phases. At variance, DR Tau shows weaker and narrower metallic lines, despite its larger accretion luminosity. This suggests that accretion is not the only driver of metallic line excitation. Conclusions. The presented observations demonstrate the potential of wide-band, high-resolution near-IR spectroscopy to simultaneously probe the different phenomena that occur in the interaction region between the stellar magnetosphere and the accretion disk, thus providing hints on how these two structures are linked to each other.

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“…Petrov et al (2011) found a smooth change of about 5 km s −1 in the radial velocity of the narrow emission component in the He  5875 Å line from August 14 to 17. This implies a lower limit of the period of about three days.…”

Section: Analysis: the Structure Of The Accretion Flowmentioning

confidence: 91%

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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Accretion-powered chromospheres in classical T Tauri stars

Cited by 48 publications

References 64 publications

Face to phase with RU Lupi

Face to phase with RU Lupi

High-resolution TNG spectra of T Tauri stars

Doppler probe of accretion onto a T Tauri star

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