Spectral variability of classical T Tauri stars accreting in an unstable regime

Kurosawa, Ryuichi; Romanova, M. M.

doi:10.1093/mnras/stt365

Cited by 97 publications

(125 citation statements)

References 99 publications

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“…-The line velocity modulations observed for EX Lupi are suggestive of the stable accretion scenario proposed by Kurosawa & Romanova (2013). Our long-term monitoring is consistent with accretion occurring through remarkable stable channels, despite the frequent variations in the accretion rate.…”

Section: Discussionsupporting

confidence: 81%

“…The signature does not seem affected by the strong 2008 outburst (although there are only 3 points taken before the outburst), suggesting that the accretion structures infalling onto this star are extraordinarily well-fixed to the stellar structure/magnetic field. Even though the accretion rate varies in time and is probably very clumpy, it would be a case of remarkably stable accretion columns with very little instability (Kurosawa & Romanova 2013). Checking the long-term stability of the signal will be also a strong test for the proposed accretion column scenario.…”

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

confidence: 99%

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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: Discussionsupporting

confidence: 81%

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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“…Flux ratio of emission and absorption has a large span. As one of the physical interpretations see Kurosawa & Romanova (2013) for demonstration of the quasi-stationary appearance of the red-shifted absorption in T Tauri stars due to the unstable regime of the accretion.…”

Section: Description Of Morphological Categoriesmentioning

confidence: 99%

“…We refer the readers to Bonito et al (2013) and Reipurth et al (1996) for a discussion of the expected Hα profile features and their physical origin. Mechanisms that produce such multicomponent profiles are usually attributed to very young stars, cataclysmic variables, symbiotic stars, stars with massive outflows or inflows, and to many other types of active objects (Hamilton et al 2012;Kurosawa & Romanova 2013;Biazzo et al 2006;Lanzafame et al 2000).…”

Section: Introductionmentioning

confidence: 99%

TheGaia-ESO Survey: Catalogue of Hαemission stars

Traven

Zwitter

Eck

et al. 2015

A&A

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We discuss the properties of Hα emission stars across the sample of 22035 spectra from the Gaia-ESO Survey internal data release, observed with the GIRAFFE instrument and largely belonging to stars in young open clusters. Automated fits using two independent Gaussian profiles and a third component that accounts for the nebular emission allow us to discern distinct morphological types of Hα line profiles with the introduction of a simplified classification scheme. All in all, we find 3765 stars with intrinsic emission and sort their spectra into eight distinct morphological categories: single-component emission, emission blend, sharp emission peaks, double emission, P-Cygni, inverted P-Cygni, self-absorption, and emission in absorption. We have more than one observation for 1430 stars in our sample, thus allowing a quantitative discussion of the degree of variability of Hα emission profiles, which is expected for young, active objects. We present a catalogue of stars with properties of their Hα emission line profiles, morphological classification, analysis of variability with time and the supplementary information from the SIMBAD, VizieR, and ADS databases. The records in SIMBAD indicate the presence of Hα emission for roughly 25% of all stars in our catalogue, while at least 305 of them have already been more thoroughly investigated according to the references in ADS. The most frequently identified morphological categories in our sample of spectra are emission blend (23%), emission in absorption (22%), and self-absorption (16%). Objects with repeated observations demonstrate that our classification into discrete categories is generally stable through time, but categories P-Cygni and self-absorption seem less stable, which is the consequence of discrete classification rules, as well as of the fundamental change in profile shape. Such records of emission stars can be valuable for automatic pipelines in large surveys, where it may prove very useful for pinpointing outliers when calculating general stellar properties and elemental abundances. They can be used in studies of star formation processes, interacting binaries, and other fields of stellar physics.

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“…The results of global 3-D MHD simulations of matter flows in both stable and unstable accretion regimes are used in Kurosawa & Romanova (2013) to calculate time-dependent hydrogen line profiles and study their variability behaviors (see Fig. 2).…”

Section: Irregular Variability Caused By Accretion In An Unstable Regimementioning

confidence: 99%

Magnetospheric Accretions and the Inner Winds of Classical T Tauri Stars

Kurosawa¹,

Romanova²

2013

Proc. IAU

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Abstract. Recent spectropolarimetric observations suggest that young low-mass stars such as classical T Tauri stars (CTTSs) possess relatively strong (∼kG) magnetic field. This supports a scenario in which the final accretion onto the stellar surface proceeds through a magnetosphere, and the winds are formed in magnetohydrodynamics (MHD) processes. We examine recent numerical simulations of magnetospheric accretions via an inclined dipole and a complex magnetic fields. The difference between a stable accretion regime, in which accretion occurs in ordered funnel streams, and an unstable regime, in which gas penetrates through the magnetosphere in several unstable streams due to the magnetic Rayleigh-Taylor instability, will be discussed. We describe how MHD simulation results can be used in separate radiative transfer (RT) models to predict observable quantiles such as line profiles and light curves. The plausibility of the accretion flows and outflows predicted by MHD simulations (via RT models) can be tested against observations. We also address the issue of outflows/winds that arise from the innermost part of CTTSs. First, we discuss the line formations in a simple disk wind and a stellar wind models. We then discuss the formation of the conically shaped magnetically driven outflow that arises from the disk-magnetosphere boundary when the magnetosphere is compressed into an X-type configuration.

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Spectral variability of classical T Tauri stars accreting in an unstable regime

Cited by 97 publications

References 99 publications

Accretion dynamics of EX Lupi in quiescence

Accretion dynamics of EX Lupi in quiescence

TheGaia-ESO Survey: Catalogue of Hαemission stars

Magnetospheric Accretions and the Inner Winds of Classical T Tauri Stars

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