0000000000530456
AUTHOR
S. G. Gregory
The close classical T Tauri binary V4046 Sgr: Complex magnetic fields & distributed mass accretion
We report here the first results of a multi-wavelength campaign focussing on magnetospheric accretion processes within the close binary system V4046 Sgr, hosting two partly-convective classical T Tauri stars of masses ~0.9 Msun and age ~12 Myr. In this paper, we present time-resolved spectropolarimetric observations collected in 2009 September with ESPaDOnS at the Canada-France-Hawaii Telescope (CFHT) and covering a full span of 7d or ~2.5 orbital/rotational cycles of V4046 Sgr. Small circularly polarised Zeeman signatures are detected in the photospheric absorption lines but not in the accretion-powered emission lines of V4046 Sgr, thereby demonstrating that both system components host lar…
Surface and Atmospheric Structure on the T Tauri Star V2129 Oph
We provide an overview of a multi-wavelength observing campaign focusing on the accretion and coronal processes in the young star V2129 Oph. V2129 Oph is a classical T Tauri star with a 6.5 day rotation period in the ρ Oph star forming region. On 27-29 June 2009 we obtained two 100 ksec Chandra HETG exposures, aiming at opposite hemispheres of the star. We discuss the X-ray data elsewhere. In order to place the coronal X-ray emission in context, we obtained contemporaneous optical and near-IR photometry and high dispersion optical spectroscopy. The photometry shows the existence of dark photospheric spots. The Hα line profiles show a modulation of the mean Hα velocity and the presence of re…
Multi-wavelength observing of a forming solar-like star
V2129 Oph is a 1.35 solar mass classical T Tauri star, known to possess a strong and complex magnetic field. By extrapolating from an observationally derived magnetic surface map, obtained through Zeeman-Doppler imaging, models of V2129 Oph's corona have been constructed, and used to make predictions regarding the global X-ray emission measure, the amount of modulation of X-ray emission, and the density of accretion shocks. In late June 2009 we will under take an ambitious multi-wavelength, multi-observing site, and near contemporaneous campaign, combining spectroscopic optical, nIR, UV, X-ray, spectropolarimetric and photometric monitoring. This will allow the validity of the 3D field topo…
Coordinated Optical/X-ray observations of the CTTS V2129 Oph The Chandra View
Young low-mass accreting stars (classical T Tauri stars; CTTSs) possess strong magnetic fields that are responsible for the regulation of the accretion and outflow processes, and the confinement and heating of coronal plasma. Understanding the physics of CTTS magnetospheres and of their interaction with circumstellar disks can elucidate the history and evolution of our own Sun and Solar System, at the stage when planets were being formed. In June 2009 we have conducted an extensive multi-wavelength observing campaign of V2129 Oph, a K5 CTTS in the ρ Ophiuchi molecular cloud, with the goal of obtaining a synoptic view of its photosphere, magnetic field, coronal plasma, and of its accretion s…
The magnetosphere of the close accreting PMS binary V4046 Sgr AB
We present a preliminary 3D potential field extrapolation model of the joint magnetosphere of the close accreting PMS binary V4046 Sgr. The model is derived from magnetic maps obtained as part of a coordinated optical and X-ray observing program.
Modeling X-ray emission from stellar coronae
By extrapolating from observationally derived surface magnetograms of low-mass stars we construct models of their coronal magnetic fields and compare the 3D field geometry with axial multipoles. AB Dor, which has a radiative core, has a very complex field, whereas V374 Peg, which is completely convective, has a simple dipolar field. We calculate global X-ray emission measures assuming that the plasma trapped along the coronal loops is in hydrostatic equilibrium and compare the differences between assuming isothermal coronae, or by considering a loop temperature profiles. Our preliminary results suggest that the non-isothermal model works well for the complex field of AB Dor, but not for the…