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The 2008 outburst in the young stellar system Z CMa. I. Evidence of an enhanced bipolar wind on the AU-scale

Benisty, M. and Malbet, F. and Dougados, C. and Natta, A. and Le Bouquin, J. B. and Massi, F. and Bonnefoy, M. and Bouvier, J. and Chauvin, G. and Chesneau, O. and Garcia, P. J. V. and Grankin, K. and Isella, A. and Ratzka, T. and Tatulli, E. and Testi, L. and Weigelt, G. and Whelan, E. T. (2010) The 2008 outburst in the young stellar system Z CMa. I. Evidence of an enhanced bipolar wind on the AU-scale. Astronomy and Astrophysics, 517 . Art. No. L3. ISSN 0004-6361.

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Context. Accretion is a fundamental process in star formation. Although the time evolution of accretion remains a matter of debate, observations and modelling studies suggest that episodic outbursts of strong accretion may dominate the formation of the central protostar. Observing young stellar objects during these elevated accretion states is crucial to understanding the origin of unsteady accretion. Aims. Z CMa is a pre-main-sequence binary system composed of an embedded Herbig Be star, undergoing photometric outbursts, and a FU Orionis star. This system therefore provides a unique opportunity to study unsteady accretion processes. The Herbig Be component recently underwent its largest optical photometric outburst detected so far. We aim to constrain the origin of this outburst by studying the emission region of the HI Br_γ line, a powerful tracer of accretion/ejection processes on the AU-scale in young stars. Methods. Using the AMBER/VLTI instrument at spectral resolutions of 1500 and 12 000, we performed spatially and spectrally resolved interferometric observations of the hot gas emitting across the Br_γ emission line, during and after the outburst. From the visibilities and differential phases, we derive characteristic sizes for the Br_γ emission and spectro-astrometric measurements across the line, with respect to the continuum. Results. We find that the line profile, the astrometric signal, and the visibilities are inconsistent with the signature of either a Keplerian disk or infall of matter. They are, instead, evidence of a bipolar wind, maybe partly seen through a disk hole inside the dust sublimation radius. The disappearance of the Br_γ emission line after the outburst suggests that the outburst is related to a period of strong mass loss rather than a change of the extinction along the line of sight. Conclusions. Apart from the photometric increase of the system, the main consequence of the outburst is to trigger a massive bipolar outflow from the Herbig Be component. Based on these conclusions, we speculate that the origin of the outburst is an event of enhanced mass accretion, similar to those occuring in EX Ors and FU Ors.

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Additional Information:© ESO 2010. Received 12 April 2010. Accepted 26 June 2010. Published online 30 July 2010. Based on observations collected at the VLTI (ESO Paranal, Chile) with programs 282.C-5031, 082.C-0376, 084.C-0162. We thank the VLTI team at Paranal, as well as R. Cesaroni, S. Antoniucci, L. Podio, P. Stee and M. van den Ancker for fruitful discussions. We thank the anonymous referee for helpful comments. M.B. acknowledges funding from INAF (grant ASI-INAF I/016/07/0).
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Istituto Nazionale di Astrofisica (INAF)ASI-INAFI/016/07/0
Subject Keywords:circumstellar matter; stars: variables: T Tauri; herbig Ae/Be; stars: winds; outflows; methods: obsevational; stars: individual: Z CMa; techniques: interferometric
Record Number:CaltechAUTHORS:20100831-140037883
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Official Citation:The 2008 outburst in the young stellar system Z CMa - I. Evidence of an enhanced bipolar wind on the AU-scale M. Benisty, F. Malbet, C. Dougados, A. Natta, J. B. Le Bouquin, F. Massi, M. Bonnefoy, J. Bouvier, G. Chauvin, O. Chesneau, P. J. V. Garcia, K. Grankin, A. Isella, T. Ratzka, E. Tatulli, L. Testi, G. Weigelt and E. T. Whelan A&A 517 L3 (2010) DOI: 10.1051/0004-6361/201014776
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:19746
Deposited By: Tony Diaz
Deposited On:15 Sep 2010 20:21
Last Modified:26 Dec 2012 12:23

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