Multiepoch, multiwavelength study of accretion onto T Tauri

Schneider, P. C.; Günther, Hans Moritz; Robrade, J.; Schmitt, J. H. M. M.; Güdel, M.

doi:10.1051/0004-6361/201731613

Cited by 13 publications

(14 citation statements)

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“…Models successfully reproduce line ratios in the spectrum [137,141], although they do not describe the full temperature range of the shock accurately [139]. The FUV emission is formed at the bottom of the accretion column and in the gas around it [53,71], and yet, X-ray and FUV variability seem uncorrelated or even anti-correlated [142]. This finding clearly points to a fundamental problem in our current understanding of the accretion shock.…”

Section: Variabilitymentioning

confidence: 99%

The UV Perspective of Low-Mass Star Formation

Schneider¹,

Günther²

2020

Galaxies

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The formation of low-mass (M 2 M ) stars in molecular clouds involves accretion disks and jets, which are of broad astrophysical interest. Accreting stars represent the closest examples of these phenomena. Star and planet formation are also intimately connected, setting the starting point for planetary systems like our own. The ultraviolet (UV) spectral range is particularly suited to study star formation, because virtually all relevant processes radiate at temperatures associated with UV emission processes or have strong observational signatures in the UV. In this review, we describe how UV observations provide unique diagnostics for the accretion process, the physical properties of the protoplanetary disk, and jets and outflows.CTTSs were initially identified as a new class of objects due their optical variability. Very early on, it was realized that they also show signs of enhanced chromospheric activity, i.e., "emission lines resembling those of the solar chromosphere" [2]. These emission lines are superposed on a photospheric spectrum similar to main sequence stars of late spectral type. Initially, the source of emission in excess of a normal photosphere was speculated to be circumstellar or chromospheric in origin [3].The discovery that CTTSs are above and to the right of the main sequence in an HR-diagram demonstrated in conjunction with theoretical work [4], that these objects must be young and, thus, the progenitors of the large main sequence population [5,6]. This notion is corroborated by the presence of strong Li absorption, which requires ∼ 100× the Li abundance of the Sun [e.g. 7]. Because Li is depleted quickly in stellar interiors, the amount of surface lithium decreases with time in convective stars. Therefore, strong Li absorption can only be found in young stars and thus CTTS must be young [e.g. review by 8].Meanwhile the number of peculiarities found in CTTSs grew, but their established youth alone was insufficient to explain those peculiarities and the "mysteries" of CTTSs remained. Many features, like the origin of the "chromospheric emission" remained unexplained, until the early 1980s when a large variety of models were proposed to explain features of CTTSs including envelopes, outflows, infall, and dust disks.Specifically, the "ultraviolet excess" (measured around 3700 Å) and the "blue continuum", which go along with a weakening of photosperic absorption lines due to veiling [9,10], were shown to correlate with the strength of Hα [11,12]. Such a correlation indicates a common origin of both features as observed for chromospheric emission on the Sun. Thus, it was natural to ascribe the excess continuum emission at short wavelengths to a Balmer continuum, i.e., emission following the capture of a free electron by an ionized hydrogen atom. While that finding pinpoints neither the physical origin nor location of the emitting material, it paved the way for explanations involving a suitably tuned chromosphere for producing the observed (Balmer & Ca II H+K) line fluxes in CTTSs. Quantitative mod...

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Section: Variabilitymentioning

confidence: 99%

The UV Perspective of Low-Mass Star Formation

Schneider¹,

Günther²

2020

Galaxies

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“…The system has exhibited strong and highly variable circular polarization and non-thermal radio emission, serving as a demonstration for radio properties of inner magnetized outflows (Phillips et al 1993;Skinner & Brown 1994;Ray et al 1997;Johnston et al 2003;Smith et al 2003). Schneider et al (2018) used T Tau as an accretion laboratory to reveal that strong mass accretion affects the hot 10 6 K coronal emission, resulting in an observed anti-correlation between mass accretion and stellar X-Ray activity.…”

Section: A Historical Summary Of T Taurimentioning

confidence: 99%

“…Table 1 summarizes the observations presented in this study (top) and the archival datasets from the Chandra X-Ray Observatory, Hubble Space Telescope (HST) and Atacama Large Mm Array (ALMA) downloaded and presented here (bottom). The archival X-ray dataset from Chandra was presented and analyzed in detail by Schneider et al (2018) and the ALMA observations of T Tau were included in the 1.3mm dust continuum survey paper of Manara et al (2019). To the best of our knowledge, this is the first publication of the archival UV imaging dataset from the HST.…”

Section: Observationsmentioning

confidence: 99%

On the Nature of the T Tauri Triple System

Beck,

Schaefer,

Guilloteau

et al. 2020

Preprint

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We present a multi-wavelength analysis to reveal the nature of the enigmatic T Tauri triple star system. New optical and infrared measurements are coupled with archival X-ray, UV and mm datasets to show morphologies of disk material and outflow kinematics. A dark lane of obscuring material is seen in silhouette in several emission lines and in model-subtracted ALMA mm continuum dust residuals near the position of T Tau Sa+Sb, revealing the attenuating circumbinary ring around T Tau S. The flux variability of T Tau S is linked in part to the binary orbit; T Tau Sb brightens near orbital apastron as it emerges from behind circumbinary material. Outflow diagnostics confirm that T Tau N powers the blue-shifted western outflow, and the T Tau S binary drives the northwest-southeastern flow. Analysis of the southern outflow shows periodic arcs ejected from the T Tau system. Correlation of these arc locations and tangential kinematics with the orbit timing suggests that launch of the last four southern outflow ejections is contemporaneous with, and perhaps triggered by, the T Tau Sa+Sb binary periastron passage. We present a geometry of the T Tau triple that has the southern components foreground to T Tau N, obscured by a circumbinary ring, with mis-aligned disks and interacting outflows. Particularly, a wind from T Tauri Sa that is perpendicular to its circumstellar disk might interact with the circumbinary material, which may explain conflicting high contrast measurements of the system outflows in the literature. T Tauri is an important laboratory to understand early dynamical processes in young multiple systems. We discuss the historical and future characteristics of the system in this context.

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“…Previous work has provided observational evidence of varying density in hot spots 7 , but these observations were not sensitive to the radial density distribution. Attempts have been made to measure this distribution using X-ray observations [8][9][10] ; however, X-ray emission traces only a fraction of the hot spot 11,12 and also coronal emission 13,14 . Here we report periodic ultraviolet and optical light curves of the accreting star GM Aurigae, which have a time lag of about one day between their peaks.…”

mentioning

confidence: 99%

Measuring the density structure of an accretion hot spot

Espaillat

Robinson

Romanova

et al. 2021

Nature

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Magnetospheric accretion models predict that matter from protoplanetary disks accretes onto stars via funnel flows, which follow stellar magnetic field lines and shock on the stellar surfaces1–3, leaving hot spots with density gradients4–6. Previous work has provided observational evidence of varying density in hot spots7, but these observations were not sensitive to the radial density distribution. Attempts have been made to measure this distribution using X-ray observations8–10; however, X-ray emission traces only a fraction of the hot spot11,12 and also coronal emission13,14. Here we report periodic ultraviolet and optical light curves of the accreting star GM Aurigae, which have a time lag of about one day between their peaks. The periodicity arises because the source of the ultraviolet and optical emission moves into and out of view as it rotates along with the star. The time lag indicates a difference in the spatial distribution of ultraviolet and optical brightness over the stellar surface. Within the framework of a magnetospheric accretion model, this finding indicates the presence of a radial density gradient in a hot spot on the stellar surface, because regions of the hot spot with different densities have different temperatures and therefore emit radiation at different wavelengths.

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Multiepoch, multiwavelength study of accretion onto T Tauri

Cited by 13 publications

References 100 publications

The UV Perspective of Low-Mass Star Formation

The UV Perspective of Low-Mass Star Formation

On the Nature of the T Tauri Triple System

Measuring the density structure of an accretion hot spot

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