* Astronomy

Blobrana · L

RE: V4046 Sagitarii

Blobrana · L

Title: A Disk-based Dynamical Mass Estimate for the Young Binary V4046 Sgr
Authors: Katherine A. Rosenfeld, Sean M. Andrews, David J. Wilner, H. C. Stempels

We present sensitive, arcsecond-resolution Submillimeter Array observations of the 12CO J=2-1 line emission from the circumstellar disk orbiting the double-lined spectroscopic binary star V4046 Sgr. Based on a simple model of the disk structure, we use a novel Monte Carlo Markov Chain technique to extract the Keplerian velocity field of the disk from these data and estimate the total mass of the central binary. Assuming the distance inferred from kinematic parallax measurements in the literature (d is approximately 73 pc), we determine a total stellar mass M_star = 1.75^{+0.09}_{-0.06} solar masses and a disk inclination i_d = 33.5^{+0.7}_{-1.4} degrees from face-on. These measurements are in excellent agreement with independent dynamical constraints made from multi-epoch monitoring of the stellar radial velocities, confirming the absolute accuracy of this precise (~ few percent uncertainties) disk-based method for estimating stellar masses and reaffirming previous assertions that the disk and binary orbital planes are well aligned (with |i_d - i_star| \approx 0.1±1 degree). Using these results as a reference, we demonstrate that various pre-main sequence evolution models make consistent and accurate predictions for the masses of the individual components of the binary, and uniformly imply an advanced age of ~5-30 Myr. Taken together, these results verify that V4046 Sgr is one of the precious few nearby and relatively evolved pre-main sequence systems that still hosts a gas-rich accretion disk.

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Title: The close T Tauri binary system V4046 Sgr: Rotationally modulated X-ray emission from accretion shocks
Authors: C. Argiroffi (1,2), A. Maggio (2), T. Montmerle (3), D. P. Huenemoerder (4), E. Alecian (5), M. Audard (6,7), J. Bouvier (8), F. Damiani (2), J.-F. Donati (9), S. G. Gregory (10), M. Güdel (11), G. A. J. Hussain (12), J. H. Kastner (13), G. G. Sacco (13) ((1) Dip. di Fisica, Univ. di Palermo, Palermo, (2) INAF - Osservatorio Astronomico di Palermo, Palermo, Italy, (3) Institut d'Astrophysique de Paris, Paris, France, (4) MIT, Kavli Institute for Astrophysics and Space Research, Cambridge, MA, USA, (5) Observatoire de Paris, Meudon Principal Cedex, France, (6) ISDC Data Center for Astrophysics, University of Geneva, Versoix, Switzerland, (7) Observatoire de Genève, University of Geneva, Versoix, Switzerland, (8) UJF-Grenoble 1 / CNRS-INSU, Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Grenoble, France, (9) IRAP-UMR 5277, CNRS and Univ. de Toulouse, Toulouse, France, (10) California Institute of Technology, Pasadena, CA, USA, (11) University of Vienna, Department of Astronomy, Vienna, Austria (12) ESO, Garching bei München, Germany, (13) Center for Imaging Science, Rochester Institute of Technology, Rochester, NY, USA)

We report initial results from a quasi-simultaneous X-ray/optical observing campaign targeting V4046 Sgr, a close, synchronous-rotating classical T Tauri star (CTTS) binary in which both components are actively accreting. V4046 Sgr is a strong X-ray source, with the X-rays mainly arising from high-density (n_e ~ 10^(11-12) cm^(-3)) plasma at temperatures of 3-4 MK. Our multiwavelength campaign aims to simultaneously constrain the properties of this X-ray emitting plasma, the large scale magnetic field, and the accretion geometry. In this paper, we present key results obtained via time-resolved X-ray grating spectra, gathered in a 360 ks XMM-Newton observation that covered 2.2 system rotations. We find that the emission lines produced by this high-density plasma display periodic flux variations with a measured period, 1.22±0.01 d, that is precisely half that of the binary star system (2.42 d). The observed rotational modulation can be explained assuming that the high-density plasma occupies small portions of the stellar surfaces, corotating with the stars, and that the high-density plasma is not azimuthally symmetrically distributed with respect to the rotational axis of each star. These results strongly support models in which high-density, X-ray-emitting CTTS plasma is material heated in accretion shocks, located at the base of accretion flows tied to the system by magnetic field lines.

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