On the origin of [Ne II] emission in young stars: mid-infrared and optical observations with the Very Large Telescope

Baldovin-Saavedra, C. (1,2), Audard, M. (1,2), Carmona, A. (1,2), Güdel, M. (3), Briggs, K. (3), Rebull, L. M. (4), Skinner, S. L. (5), and Ercolano, B. (6,7) ((1) ISDC Data Centre for Astrophysics, Université de Genéve, Chemin d’Ecogia 16, CH-1290 Versoix, Switzerland; (2) Observatoire Astronomique de l’Université de Genéve, Chemin de Maillettes 51, CH-1290 Sauverny, Switzerland; (3) University of Vienna, Department of Astrophysics, Türkenschanzstrasse 17, A-1180 Vienna, Austria; (4) Spitzer Science Center, California Institute of Technology, 220-6 1200 East California Boulevard, Pasadena, CA 91125 USA; (5) Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80309-0389, USA; (6) Universit¨ats-Sternwarte M¨unchen, Scheinerstrasse 1, 81679 M¨unchen, Germany; (7) Cluster of Excellence Origin and Structure of the Universe, Boltzmannstrasse 2, 85748 Garching, Germany)

We provide direct constraints on the origin of the [Ne II] emission in 15 young stars using high-spatial and spectral resolution observations with VISIR at the VLT that allow us to study the kinematics of the emitting gas. In addition we compare the [Ne II] line with optical forbidden lines observed for three stars with UVES. The [Ne II] line was detected in 7 stars, among them the first confirmed detection of [Ne II] in a Herbig Be star, V892 Tau. In four cases, the large blueshifted lines indicate an origin in a jet. In two stars, the small shifts and asymmetric profiles indicate an origin in a photo-evaporative wind. CoKu Tau 1, seen close to edge-on, shows a spatially unresolved line centered at the stellar rest velocity, although cross-dispersion centroids move within 10 AU from one side of the star to the other as a function of wavelength. The line profile is symmetric with wings extending up to about +-80 km/s. The origin of the [Ne II] line could either be due to the bipolar jet or to the disk. For the stars with VLT-UVES observations, in several cases, the optical forbidden line profiles and shifts are very similar to the profile of the [Ne II] line, suggesting that the lines are emitted in the same region. A general trend observed with VISIR is a lower line flux when compared with the fluxes obtained with Spitzer. We found no correlation between the line full-width at half maximum and the line peak velocity. The [Ne II] line remains undetected in a large part of the sample, an indication that the emission detected with Spitzer in those stars is likely extended.

Complete preprint ==> http://arxiv.org/abs/1205.2182

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