Activity on T Tauri stars

Abstract. We present an XMM-Newton observation of the classical T Tauri star BP Tau. In the XMM-Newton RGS spectrum the O  triplet is clearly detected with a very weak forbidden line indicating high plasma densities and/or a high UV flux environment. At the same time concurrent UV data point to a small hot spot filling factor suggesting an accretion funnel shock as the site of the X-ray and UV emission. Together with the X-ray data on TW Hya these new observations suggest such funnels to be a general feature in classical T Tauri stars.

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“…An extensive overview of the optical properties of BP Tau is given by Gullbring et al (1996) and Errico et al (2001). (Bertout et al 1988).…”

Section: The Ctts Bp Tau: Optical and X-ray Propertiesmentioning

confidence: 99%

X-rays from accretion shocks in T Tauri stars: The case of BP Tau

Schmitt

Robrade

Ness

et al. 2005

A&A

124

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“…Variability amplitudes are typically modest (a few tenths of a magnitude) and last for 0.6 h to several hours. The gas heats only moderately, again in contrast to chromospheric gas in flares (Gullbring et al 1996). The induced variability may be explained by accretion rate changes of the order of 10%, which will then require a scale length of the inhomogeneities of 5 × 10 10 cm for the CTTS BP Tau and, combined with the free fall velocity, correctly explains the variability time scales (see Gullbring et al 1996, for further details).…”

mentioning

confidence: 92%

“…The gas heats only moderately, again in contrast to chromospheric gas in flares (Gullbring et al 1996). The induced variability may be explained by accretion rate changes of the order of 10%, which will then require a scale length of the inhomogeneities of 5 × 10 10 cm for the CTTS BP Tau and, combined with the free fall velocity, correctly explains the variability time scales (see Gullbring et al 1996, for further details). It is possible that these inhomogeneities reflect in variations of the softest X-ray flux if X-rays are produced in the accretion shock, but a dedicated monitoring study of BP Tau with ROSAT and ground-based UBVRI photometry revealed an absence of correlated events; X-ray variability may thus not be related to accretion-induced optical and UV variability (Gullbring et al 1997).…”

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confidence: 92%

X-rays from T Tauri: a test case for accreting T Tauri stars

Güdel¹,

Skinner

Melnikov

et al. 2007

A&A

104

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Context. The generation of X-rays in accreting T Tauri stars (TTS) is thought to be predominantly due to energy dissipation in magnetic fields, but alternative X-ray generation mechanisms have been proposed, such as heating in accretion shocks near the stellar surface, or in shocks forming in jets. Aims. We test models and trends discussed in the literature using X-ray data from the classical TTS T Tau. Methods. High-resolution spectroscopy from the Reflection Grating Spectrometers on XMM-Newton is used to infer electron densities, element abundances and the thermal structure of the X-ray source. We also discuss the ultraviolet light curve obtained by the Optical Monitor, and complementary ground-based photometry. A high-resolution image from Chandra constrains contributions from the two companions of T Tau N. Results. The X-ray grating spectrum is rich in emission lines, but shows an unusual mixture of features from very hot (≈30 MK) and very cool (1-3 MK) plasma, both emitted by similar amounts of emission measure. The cool plasma confirms the picture of a soft excess in the form of an enhanced O vii/O viii Lyα flux ratio, similar to that previously reported for other accreting TTS. Diagnostics from lines formed by this plasma indicate low electron densities ( < ∼ 10 10 cm −3 ). The Ne/Fe abundance ratio is consistent with a trend in pre-main sequence stars in which this ratio depends on spectral type, but not on accretion. Conclusions. On the basis of line density diagnostics, we conclude that the density of the cool "soft-excess" plasma is orders of magnitude below that predicted for an accretion shock, assuming previously determined accretion rates of (3−6) × 10 −8 M yr −1 . We argue that loading of magnetic field lines with infalling material suppresses the heating process in a part of the corona. We thus suggest that the X-ray production of T Tau is influenced by the accretion process although the X-rays may not form in the bulk of the accretion footpoints.

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“…The presence of hot spots or rings on the stellar surface has observable consequences. Periodic photometric variations will be produced as the star's rotation brings the spots into and out of view; periodic polarimetric variations have also been predicted (e.g., Gullbring & Gahm 1996) due to periodically varying illumination of the disk by the spots. We have investigated the photopolarimetric variability produced by such a theory (Wood et al 1996;Stassun & Wood 1998) where the hot accretion region was modeled as spots or rings on the stellar surface, and the polarization arises from the scattering of stellar and hot-spot radiation in the disk.…”

Section: Introductionmentioning

confidence: 99%

Scattered Light Signatures of Magnetic Accretion in Classical T Tauri Stars

Wood

Whitney

1998

The Astrophysical Journal

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The magnetic accretion model as applied to T Tauri stars predicts the formation of hot spots or rings on the stellar surface where accreting disk material impacts the stellar surface at or near the magnetic poles. When the magnetic poles are not aligned with the stellar rotation axis, or the hot spots are nonuniform, brightness variations arise as the hot spots rotate into and out of view. We have investigated the effects on the scattered light images of a T Tauri star-plus-disk system of nonaxisymmetric illumination of the circumstellar disk by hot starspots. We find that changes in the scattered light pattern occur during a stellar rotation period. These changes are observable with current high-resolution imagery and provide a further observational test of the magnetic accretion theory. The observed brightening and dimming of HH 30's scattered light disk may be explained by such a model, although further synoptic observations are required to confirm this.

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Activity on T Tauri stars

Cited by 36 publications

References 0 publications

X-rays from accretion shocks in T Tauri stars: The case of BP Tau

X-rays from accretion shocks in T Tauri stars: The case of BP Tau

X-rays from T Tauri: a test case for accreting T Tauri stars

Scattered Light Signatures of Magnetic Accretion in Classical T Tauri Stars

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