A measure of the size of the magnetospheric accretion region in TW Hydrae

Stars form by accreting material from their surrounding disks. There is a consensus that matter flowing through the disk is channelled onto the stellar surface by the stellar magnetic field. This is thought to be strong enough to truncate the disk close to the corotation radius, at which the disk rotates at the same rate as the star. Spectro-interferometric studies in young stellar objects show that hydrogen emission (a well known tracer of accretion activity) mostly comes from a region a few milliarcseconds across, usually located within the dust sublimation radius1–3. The origin of the hydrogen emission could be the stellar magnetosphere, a rotating wind or a disk. In the case of intermediate-mass Herbig AeBe stars, the fact that Brackett γ (Brγ) emission is spatially resolved rules out the possibility that most of the emission comes from the magnetosphere4–6 because the weak magnetic fields (some tenths of a gauss) detected in these sources7,8 result in very compact magnetospheres. In the case of T Tauri sources, their larger magnetospheres should make them easier to resolve. The small angular size of the magnetosphere (a few tenths of a milliarcsecond), however, along with the presence of winds9,10 make the interpretation of the observations challenging. Here we report optical long-baseline interferometric observations that spatially resolve the inner disk of the T Tauri star TW Hydrae. We find that the near-infrared hydrogen emission comes from a region approximately 3.5 stellar radii across. This region is within the continuum dusty disk emitting region (7 stellar radii across) and also within the corotation radius, which is twice as big. This indicates that the hydrogen emission originates in the accretion columns (funnel flows of matter accreting onto the star), as expected in magnetospheric accretion models, rather than in a wind emitted at much larger distance (more than one astronomical unit). The size of the inner disk of the T Tauri star TW Hydrae is determined using optical long-baseline interferometric observations, indicating that hydrogen emission comes from a region approximately 3.5 stellar radii across.

G. Zins | T. Paumard | L. Jocou | Dublin Institute for Advanced Studies | R. Abuter | K. Perraut | G. Duvert | A. Amorim | V. Coudé du Foresto | A. Eckart | G. Rousset | M. Habibi | R. Genzel | E. Wieprecht | H. Bonnet | P. Kervella | S. Gillessen | T. P. Ray | S. Scheithauer | J. Kolb | Y. Clénet | G. Perrin | C. Straubmeier | X. Haubois | Th. Henning | Z. Hubert | M. Wiest | L. Labadie | J. Woillez | F. Haussmann | E. van Dishoeck | S. Yazici | F. Eisenhauer | M. Bauböck | R. Garcia Lopez | F. Widmann | E. Wiezorrek | E. Gendron | A. Buron | W. Brandner | C. Dougados | O. Pfuhl | University College Dublin | T. Ott | E. Sturm | T. de Zeeuw | M. Koutoulaki | R. Fedriani | O. Straub | S. Lacour | Instituto Superior T'ecnico | H Germany | U. California | 17 Konigstuhl | Cnrs | G. Perrin | E. Observatory | P. Caselli | G. Rousset | Y. Clénet | R. Abuter | T. Henning | W. Brandner | S. Lacour | J. Kolb | J. Woillez | H. Bonnet | S. Leiden | T. Ray | E. V. Dishoeck | J. Berger | G. Duvert | A. Eckart | E. Gendron | M. F. Astronomy | R. Genzel | Observatoire de Paris | S. Hippler | F. Eisenhauer | T. Paumard | P. Kervella | U. G. Alpes | Ipag | Chile. | K. Perraut | M. Benisty | R. Grellmann | J. Bouquin | L. Labadie | S. Gillessen | Max Planck Institute for Extraterrestrial Physics | T. Ott | Centra | E. Sturm | O. Pfuhl | C. Dougados | F. Gao | A. Natta | M. Horrobin | M. Habibi | E. Wieprecht | E. Wiezorrek | I. Institut | U. Porto | Earth | Unidad Mixta Internacional Franco-Chilena de Astronom'ia | Lesia | P. Caselli | M. Benisty | J. P. Berger | P. Léna | S. Hippler | Department of Space | A. Natta | F. Gao | M. Horrobin | F. Vincent | P. Léna | V. C. D. Foresto | R. A. A. T. P. R. M. L. K. J. M. C. L. W. P. J. V. Th Garcia Lopez Natta Caratti o Garatti Ray Fedri | A. Caratti o Garatti | L. Klarmann | J. Sanchez-Bermudez | P. J. V. Garcia | R. Grellmann | W. de Wit | M. Filho | C. E. Garcia Dabo | A. Jimenez Rosales | J.-B. Le Bouquin | A. Ramirez | C. Rau | J. Shangguan | J. Stadler | S. von Fellenberg | Environment | C. U. Technology | L. Jocou | A. Amorim | M. Bauböck | P. Garcia | X. Haubois | J. Shangguan | S. Scheithauer | J. Stadler | O. Straub | C. Straubmeier | F. Vincent | F. Widmann | S. Yazici | Z. Hubert | A. Buron | F. Haussmann | A. Rosales | C. Rau | J. Sanchez-Bermudez | S. Fellenberg | M. Wiest | W. D. Wit | C. G. Dabo | U. Koln | I. D. Astronom'ia | Universidad Nacional Autnoma de M'exico | R. G. Lopez | L. Klarmann | M. Koutoulaki | M. Filho | A. C. O. Garatti | Centro de Astrof'isica e Gravitaccao | Universidade de Lisboa - Faculdade de Ciencias | F. Engenharia | A. Ramírez | I. Institut | R. Fedriani | D. Physics | T. Zeeuw | S. V. Fellenberg | L. Hall | G. W. S. O. Physics | Leiden University | Max Planck Institute for extraterrestrial Physics | J. L. Bouquin | T. Ott | A. Ramirez | G. R. S. O. Physics | M. Bauboeck | C. Technology

[1]  L. Hartmann,et al.  Emission-Line Diagnostics of T Tauri Magnetospheric Accretion. II. Improved Model Tests and Insights into Accretion Physics , 2001 .

[2]  Dublin Institute for Advanced Studies,et al.  Gas content of transitional disks: a VLT/X-Shooter study of accretion and winds , 2014, 1406.1428.

[3]  B. Swift,et al.  TIME-VARIABLE ACCRETION IN THE TW Hya STAR/DISK SYSTEM , 2010, 1009.1657.

[4]  S. Rabien,et al.  First light for GRAVITY: Phase referencing optical interferometry for the Very Large Telescope Interferometer , 2017, 1705.02345.

[5]  A. Amorim,et al.  GRAVITY data reduction software , 2014, Astronomical Telescopes and Instrumentation.

[6]  L. Hartmann,et al.  A Brγ Probe of Disk Accretion in T Tauri Stars and Embedded Young Stellar Objects , 1998 .

[7]  L. Hartmann,et al.  Disk Accretion Rates for T Tauri Stars , 1998 .

[8]  Origin of the wide-angle hot H2 in DG Tauri: New insight from SINFONI spectro-imaging , 2014, 1402.1160.

[9]  J. Donati,et al.  Global 3D simulations of disc accretion on to the classical T Tauri star V2129 Oph , 2009, 0912.1681.

[10]  T. Ray,et al.  CLASSICAL T TAURI-LIKE OUTFLOW ACTIVITY IN THE BROWN DWARF MASS REGIME , 2009, Proceedings of the International Astronomical Union.

[11]  S. Bonhomme,et al.  AMBER : Instrument description and first astrophysical results Special feature Near-infrared interferometry of η Carinae with spectral resolutions of 1 500 and 12 000 using AMBER / VLTI , 2006 .

[12]  D. Schertl,et al.  The origin of hydrogen line emission for five Herbig Ae/Be stars spatially resolved by VLTI/AMBER spectro-interferometry , 2008, 0807.1119.

[13]  U. Gorti,et al.  TRACING SLOW WINDS FROM T TAURI STARS VIA LOW-VELOCITY FORBIDDEN LINE EMISSION , 2016, 1608.06992.

[14]  T. Carroll,et al.  The prevalence of weak magnetic fields in Herbig Ae stars: the case of PDS 2. , 2015, 1502.05498.

[15]  Evolution of Disk Accretion , 1999, astro-ph/9902335.

[16]  Zhaohuan Zhu,et al.  CO and Dust Properties in the TW Hya Disk from High-resolution ALMA Observations , 2018, 1801.03948.

[18]  F. Ménard,et al.  The large-scale magnetic field and poleward mass accretion of the classical T Tauri star TW Hya , 2011, 1106.4162.

[19]  C. Bailer-Jones,et al.  Estimating Distance from Parallaxes. IV. Distances to 1.33 Billion Stars in Gaia Data Release 2 , 2018, The Astronomical Journal.

[20]  Belgium,et al.  Accretion funnels onto weakly magnetized young stars , 2007, 0712.2921.

[21]  C. Dominik,et al.  Passive Irradiated Circumstellar Disks with an Inner Hole , 2001, astro-ph/0106470.

[22]  Gerd Weigelt,et al.  Probing the accretion-ejection connection with VLTI/AMBER. High spectral resolution observations of the Herbig Ae star HD 163296 , 2015, 1502.03027.

[23]  Romain G. Petrov,et al.  Near-infrared interferometry of eta Carinae with spectral resolutions of 1 500 and 12 000 using AMBER/VLTI , 2007 .

[24]  M. Kürster,et al.  A young massive planet in a star–disk system , 2008, Nature.

[25]  J. S. Bloom,et al.  Near-Infrared Interferometric, Spectroscopic, and Photometric Monitoring of T Tauri Inner Disks , 2007, 0707.3833.

[26]  Tim J. Harries,et al.  Multidimensional models of hydrogen and helium emission line profiles for classical T Tauri stars: method, tests and examples , 2011, 1102.0828.

[27]  P. Hartigan,et al.  A New Look at T Tauri Star Forbidden Lines: MHD-driven Winds from the Inner Disk , 2018, The Astrophysical Journal.

[28]  Rafael Millan-Gabet,et al.  RADIAL STRUCTURE IN THE TW Hya CIRCUMSTELLAR DISK , 2011 .

[29]  L. Testi,et al.  A photoevaporative gap in the closest planet-forming disc , 2016, 1609.03903.

[30]  L. Testi,et al.  Probing the wind-launching regions of the Herbig Be star HD 58647 with high spectral resolution interferometry , 2016, 1601.02209.

[31]  G. Hussain,et al.  Classical T Tauri stars : magnetic fields, coronae, and star-disc interactions , 2013, 1310.8194.

[32]  Daniel T. Jaffe,et al.  Characterizing TW Hydra , 2017, 1712.04785.

[33]  W. Vacca,et al.  NEAR-INFRARED SPECTROSCOPY OF TW Hya: A REVISED SPECTRAL TYPE AND COMPARISON WITH MAGNETOSPHERIC ACCRETION MODELS , 2011, 1102.0535.

[34]  Julien H. Girard,et al.  Three Radial Gaps in the Disk of TW Hydrae Imaged with SPHERE , 2016, 1610.08939.

[35]  U. Gorti,et al.  THE PHOTOEVAPORATIVE WIND FROM THE DISK OF TW Hya , 2011, 1105.0045.

[36]  L. Testi,et al.  X-shooter spectroscopy of young stellar objects. IV. Accretion in low-mass stars and substellar objects in Lupus , 2013, 1310.2069.

[37]  D. Mourard,et al.  A disk wind in AB Aurigae traced with Hα interferometry , 2016 .

[38]  U. Gorti,et al.  Kinematic Links and the Coevolution of MHD Winds, Jets, and Inner Disks from a High-resolution Optical [ ] Survey , 2018, The Astrophysical Journal.

[39]  Laboratoire Lagrange,et al.  AMBER/VLTI high spectral resolution observations of the Brγ emitting region in HD 98922 - A compact disc wind launched from the inner disc region , 2015, 1508.00798.

[40]  Toulouse,et al.  The non-dipolar magnetic fields of accreting T Tauri stars , 2008, 0807.0758.

[41]  G. A. Wade,et al.  A high-resolution spectropolarimetric survey of Herbig Ae/Be stars – I. Observations and measurements , 2012, 1211.2907.

[42]  L. A. Hillenbrand,et al.  Spatially Resolving the Inner Disk of TW Hydrae , 2006, astro-ph/0601034.