Surface magnetic fields on two accreting T Tauri stars: CV Cha and CR Cha

Hussain, G. A. J.; Cameron, A. Collier; Jardine, M.; Dunstone, Nick; Velez, Jc Ramirez; Stempels, H. C.; Donati, J. F.; Semel, M.; Aulanier, G.; Harries, Tim J.; Bouvier, J.; Dougados, C.; Ferreira, J.; Carter, B. D.; Lawson, W. A.

doi:10.1111/j.1365-2966.2009.14881.x

Cited by 103 publications

(131 citation statements)

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“…Components of arcsecond-scale multiples are separated with a plus sign. C13 Casassus et al (2013); d1 Pontoppidan et al (2011); d2 Lombardi et al (2008); d3 Knude & Hog (1998) Torres et al (2012); d9 Andersson et al (2002); d10 Torres et al (2008); d11 Wichmann et al (1998); d12 Mamajek (2008); i1 Cox et al (2013); i2 Salyk et al (2014); i3 Koerner & Sargent (1995); i4 Simon et al (2000); i5 Espaillat et al (2007); i6 Hussain et al (2009); i7 Guilloteau et al (2011); i8 Guilloteau et al (1999); i9 Walsh et al (2014); i10 Malfait et al (1998); i11 Matter et al (2014); i12 Weinberger et al (1999); i13 Canovas et al (2013) Meeus et al (2012) which is a re-evaluation of the data reported by Panić et al (2010). For HD 100453, HD 169142, HD 36112 and HD 50138, the 2-1 limits are similar.…”

Section: Observational Resultsmentioning

confidence: 99%

Observations and modelling of CO and [C i] in protoplanetary disks

Kama

Bruderer

Carney

et al. 2016

A&A

111

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Context. The gas-solid budget of carbon in protoplanetary disks is related to the composition of the cores and atmospheres of the planets forming in them. The principal gas-phase carbon carriers CO, C 0 , and C + can now be observed regularly in disks. Aims. The gas-phase carbon abundance in disks has thus far not been well characterized observationally. We obtain new constraints on the [C]/[H] ratio in a large sample of disks, and compile an overview of the strength of [C ] and warm CO emission. Methods. We carried out a survey of the CO 6-5 line and the [C ] 1-0 and 2-1 lines towards 37 disks with the APEX telescope, and supplemented it with [C ] data from the literature. The data are interpreted using a grid of models produced with the DALI disk code.We also investigate how well the gas-phase carbon abundance can be determined in light of parameter uncertainties.

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Section: Observational Resultsmentioning

confidence: 99%

Observations and modelling of CO and [C i] in protoplanetary disks

Kama

Bruderer

Carney

et al. 2016

A&A

111

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“…The recently measured magnetic fields of CTTS stars CV Cha and CR Cha (Hussain et al 2009) show a complex structure consisting of a number of multipoles. In another CTTS, V2247 Oph, the magnetic field is complex and varies on the time-scale of weeks ; see also Smirnov et al 2005;Donati et al 2011).…”

Section: Conclusion and Discussionmentioning

confidence: 99%

Accretion onto stars with octupole magnetic fields: Matter flow, hot spots and phase shifts

2012

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Recent measurements of the surface magnetic fields of classical T Tauri stars (CTTSs) and magnetic cataclysmic variables show that their magnetic fields have a complex structure. Investigation of accretion onto such stars requires global three-dimensional (3D) magnetohydrodynamic (MHD) simulations, where the complexity of simulations strongly increases with each higher-order multipole. Previously, we were able to model disc accretion onto stars with magnetic fields described by a superposition of dipole and quadrupole moments. However, in some stars, like CTTS V2129 Oph and BP Tau, the octupolar component is significant and it was necessary to include the next octupolar component. Here, we show results of global 3D MHD simulations of accretion onto stars with superposition of the dipole and octupole fields, where we vary the ratio between components. Simulations show that if octupolar field strongly dominates at the disc-magnetosphere boundary, then matter flows into the ring-like octupolar poles, forming ring-shape spots at the surface of the star above and below equator. The light-curves are complex and may have two peaks per period. In case where the dipole field dominates, matter accretes in two ordered funnel streams towards poles, however the polar spots are meridionally-elongated due to the action of the octupolar component. In the case when the fields are of similar strengths, both, polar and belt-like spots are present. In many cases the light-curves show the evidence of complex fields, excluding the cases of small inclinations angles, where sinusoidal light-curve is observed and 'hides' the information about the field complexity.We also propose new mechanisms of phase shift in stars with complex magnetic fields. We suggest that the phase shifts can be connected with: (1) temporal variation of the star's intrinsic magnetic field and subsequent redistribution of main magnetic poles; (2) variation of the accretion rate, which causes the disc to interact with the magnetic fields associated with different magnetic moments. We use our model to demonstrate these phase shift mechanisms, and we discuss possible applications of these mechanisms to accreting millisecond pulsars and young stars.

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“…Assuming that each observation provides a coverage of 10% of the rotational period, we quantified the phase coverage of each data set as a fraction f of the full rotational cycle (see Table 1 The quality of ZDI mapping is reduced for the data sets with an insufficient phase-coverage. Yet, as demonstrated by numerical experiments (Donati & Brown 1997; and ZDI studies based on observations with poor phasecoverage (Donati 1999;Hussain et al 2009), it is still possible to extract useful information about the stellar surface features from just a few spectra and from observations covering only half of the stellar rotation cycle. Aiming to maintain consistency in our long-term ZDI analysis of II Peg, we performed magnetic inversions for all 12 epochs.…”

Section: Spectropolarimetric Observationsmentioning

confidence: 99%

Magnetic field topology of the RS CVn star II Pegasi

Kochukhov

Mantere

Hackman

et al. 2013

A&A

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Context. The dynamo processes in cool active stars generate complex magnetic fields responsible for prominent surface stellar activity and variability at different time scales. For a small number of cool stars magnetic field topologies were reconstructed from the time series of spectropolarimetric observations using the Zeeman Doppler imaging (ZDI) method, often yielding surprising and controversial results. Aims. In this study we follow a long-term evolution of the magnetic field topology of the RS CVn binary star II Peg using a more self-consistent and physically more meaningful modelling approach compared to previous ZDI studies. Methods. We collected high-resolution circular polarisation observations of II Peg using the SOFIN spectropolarimeter at the Nordic Optical Telescope. These data cover 12 epochs spread over 7 years, comprising one of the most comprehensive spectropolarimetric data sets acquired for a cool active star. A multi-line diagnostic technique in combination with a new ZDI code is applied to interpret these observations. Results. We have succeeded in detecting clear magnetic field signatures in average Stokes V profiles for all 12 data sets. These profiles typically have complex shapes and amplitudes of ∼10 −3 of the unpolarised continuum, corresponding to mean longitudinal fields of 50-100 G. Magnetic inversions using these data reveals evolving magnetic fields with typical local strengths of 0.5-1.0 kG and complex topologies. Despite using a self-consistent magnetic and temperature mapping technique, we do not find a clear correlation between magnetic and temperature features in the ZDI maps. Neither do we confirm the presence of persistent azimuthal field rings found in other RS CVn stars. Reconstruction of the magnetic field topology of II Peg reveals significant evolution of both the surface magnetic field structure and the extended magnetospheric field geometry on the time scale covered by our observations. From 2004 to 2010 the total field energy drastically declined and the field became less axisymmetric. This also coincided with the transition from predominantly poloidal to mainly toroidal field topology. Conclusions. A qualitative comparison of the ZDI maps of II Peg with the prediction of dynamo theory suggests that the magnetic field in this star is produced mainly by the turbulent α 2 dynamo rather than the solar αΩ dynamo. Our results do not show a clear active longitude system, nor is there evidence of the presence of an azimuthal dynamo wave.

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Surface magnetic fields on two accreting T Tauri stars: CV Cha and CR Cha

Cited by 103 publications

References 50 publications

Observations and modelling of CO and [C i] in protoplanetary disks

Observations and modelling of CO and [C i] in protoplanetary disks

Accretion onto stars with octupole magnetic fields: Matter flow, hot spots and phase shifts

Magnetic field topology of the RS CVn star II Pegasi

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