The magnetic obliquity of accreting T Tauri stars

Abstract

Classical T Tauri stars (CTTS) accrete material from their discs through their magnetospheres. The geometry of the accretion flow strongly depends on the magnetic obliquity, i.e., the angle between the rotational and magnetic axes. We aim at deriving the distribution of magnetic obliquities in a sample of 10 CTTSs. For this, we monitored the radial velocity variations of the HeI$\lambda$5876 line in these stars' spectra along their rotational cycle. HeI is produced in the accretion shock, close to the magnetic pole. When the magnetic and rotational axes are not aligned, the radial velocity of this line is modulated by stellar rotation. The amplitude of modulation is related to the star's projected rotational velocity, $v\sin i$, and the latitude of the hotspot. By deriving $v\sin i$ and HeI$\lambda$5876 radial velocity curves from our spectra we thus obtain an estimate of the magnetic obliquities. We find an average obliquity in our sample of 11.4${}^{\circ }$ with an rms dispersion of 5.4${}^{\circ }$. The magnetic axis thus seems nearly, but not exactly aligned with the rotational axis in these accreting T Tauri stars, somewhat in disagreement with studies of spectropolarimetry, which have found a significant misalignment ($\gtrsim 20^{\circ }$) for several CTTSs. This could simply be an effect of low number statistics, or it may be due to a selection bias of our sample. We discuss possible biases that our sample may be subject to. We also find tentative evidence that the magnetic obliquity may vary according to the stellar interior and that there may be a significant difference between fully convective and partly radiative stars.

arXiv comment28 pages (including online material), 25 figures

References in corpus (50)

• Very Low Mass Stars and Brown Dwarfs in Taurus-Auriga
• Gaps and Rings in an ALMA Survey of Disks in the Taurus Star-forming Region
• X-Shooter spectroscopy of young stellar objects in Lupus: Accretion properties of class II and transitional objects
• An Optical Spectroscopic Study of T Tauri Stars. I. Photospheric Properties
• The Pisa pre-main sequence tracks and isochrones. A database covering a wide range of Z, Y, mass, and age values
• Magnetospheric accretion-ejection processes in the classical T Tauri star AA
• MHD Simulations of Disk-Magnetized Star Interactions in Quiescent Regime: Funnel Flows and Angular Momentum Transport
• A Millimeter Continuum Size-Luminosity Relationship for Protoplanetary Disks
• Magnetospheric accretion on the T Tauri star BP Tauri
• Magnetic fields and accretion flows on the classical T Tauri star V2129 Oph
• Can we predict the global magnetic topology of a pre-main sequence star from its position in the Hertzsprung-Russell diagram?
• The evolution of surface magnetic fields in young solar-type stars I: the first 250 Myr
• Accretion funnels onto weakly magnetized young stars
• Accretion dynamics and disk evolution in NGC 2264: a study based on the Corot photometric observations
• Magnetospheric accretion and spin-down of the prototypical classical T Tauri star AATau
• CSI 2264: Characterizing Accretion-Burst Dominated Light Curves for Young Stars in NGC 2264
• The large-scale magnetic field and poleward mass accretion of the classical T Tauri star TW Hya
• The SOPHIE search for northern extrasolar planets III. A Jupiter-mass companion around HD 109246
• CSI 2264: Probing the inner disks of AA Tau-like systems in NGC 2264
• Non-stationary dynamo & magnetospheric accretion processes of the classical T Tauri star V2129 Oph
• Resolved young binary systems and their disks
• Classical T Tauri stars: magnetic fields, coronae, and star-disc interactions
• Multidimensional models of hydrogen and helium emission line profiles for classical T Tauri Stars: method, tests and examples
• Observational constraints on dust disk sizes in tidally truncated protoplanetary disks in multiple systems in the Taurus region
• Spectral variability of classical T Tauri stars accreting in an unstable regime
• Surface magnetic fields on two accreting T Tauri stars: CV Cha and CR Cha
• Non-axisymmetric accretion on the classical TTS RW Aur A
• A Third Star in the T Tauri System
• Magnetometry of the classical T Tauri star GQ Lup: non-stationary dynamos & spin evolution of young Suns
• Warps, bending and density waves excited by rotating magnetized stars: results of global 3D MHD simulations
• Boundary between Stable and Unstable Regimes of Accretion. Ordered and Chaotic Unstable Regimes
• The close classical T Tauri binary V4046 Sgr: Complex magnetic fields & distributed mass accretion
• Complex magnetic topology and strong differential rotation on the low-mass T Tauri star V2247 Oph
• A Search for Giant Planet Companions to T Tauri Stars
• Faint disks around classical T Tauri stars: small but dense enough to form planets?
• The magnetic fields of intermediate-mass T Tauri stars : I. Magnetic detections and fundamental stellar parameters
• Magnetospheric accretion on the fully-convective classical T Tauri star DN Tau
• Dynamical Masses of Low Mass Stars in the Taurus and Ophiuchus Star Forming Regions
• The magnetic field and accretion regime of CI Tau
• The magnetic propeller accretion regime of LkCa 15
• TW Hya: Spectral Variability, X-Rays, and Accretion Diagnostics
• CSI 2264: Characterizing Young Stars in NGC 2264 with Stochastically Varying Light Curves
• The circumstellar environment of T Tau S at high spatial and spectral resolution
• Inner disk structure of the classical T Tauri star LkCa 15
• Accretion-powered chromospheres in classical T Tauri stars
• Interpretation of the Veiling of the Photospheric Spectrum for T Tauri Stars in Terms of an Accretion Model
• Rotation Effects in Classical T Tauri Stars
• The 2014-2017 outburst of the young star ASASSN-13db: A time-resolved picture of a very low-mass star between EXors and FUors
• The accretion dynamics of EX Lupi in quiescence:The star, the spot, and the accretion column
• Face to phase with RU Lupi

Cited by in corpus (13)

• The ODYSSEUS Survey. Motivation and First Results: Accretion, Ejection, and Disk Irradiation of CVSO 109
• Measuring the Density Structure of an Accretion Hot Spot
• Complex Modulation of Rapidly Rotating Young M Dwarfs: Adding Pieces to the Puzzle
• Star-disk interaction in the T Tauri star V2129 Oph: An evolving accretion-ejection structure
• Hydrogen Emission from Accretion and Outflow in T Tauri Stars
• The STAR-MELT Python package for emission line analysis of YSOs
• Stable accretion and episodic outflows in the young transition disk system GM Aurigae
• Long period modulation of the classical T Tauri star CI Tau: evidence for an eccentric close-in massive planet at 0.17 au
• Misalignment of the outer disk of DK Tau and a first look at its magnetic field using spectropolarimetry
• Accretion variability in RU Lup
• Spectroscopic and interferometric signatures of magnetospheric accretion in young stars
• Correlation between the optical veiling and accretion properties: A case study of the classical T Tauri star DK Tau
• ExoplaNeT accRetion mOnitoring sPectroscopic surveY (ENTROPY) - II. Time series of Balmer line profiles of Delorme 1(AB)b