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The origin of hydrogen line emission for five Herbig Ae/Be stars spatially resolved by VLTI/AMBER spectro-interferometry

Kraus, S. and Hofmann, K.-H. and Benisty, M. and Berger, J.-P. and Chesneau, O. and Isella, A. and Malbet, F. and Meilland, A. and Nardetto, N. and Natta, A. and Preibisch, T. and Schertl, D. and Smith, M. and Stee, P. and Tatulli, E. and Testi, L. and Weigelt, G. (2008) The origin of hydrogen line emission for five Herbig Ae/Be stars spatially resolved by VLTI/AMBER spectro-interferometry. Astronomy and Astrophysics, 489 (3). pp. 1157-1173. ISSN 0004-6361.

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Context. Accretion and outflow processes are of fundamental importance for our understanding of the formation of stars and planetary systems. To trace these processes, diagnostic spectral lines such as the Brγ 2.166 μm line are widely used, although due to a lack of spatial resolution, the origin of the line emission is still unclear. Aims. Employing the AU-scale spatial resolution which can be achieved with infrared long-baseline interferometry, we aim to distinguish between theoretical models which associate the Brγ line emission with mass infall (magnetospheric accretion, gaseous inner disks) or mass outflow processes (stellar winds, X-winds, or disk winds). Methods. Using the VLTI/AMBER instrument, we spatially and spectrally (λ/Δλ = 1500) resolved the inner (≾5 AU) environment of five Herbig Ae/Be stars (HD163296, HD104237, HD98922, MWC297, V921 Sco) in the Brγ emission line as well as in the adjacent continuum. From the measured wavelength-dependent visibilities, we derive the characteristic size of the continuum and Brγ line-emitting region. Additional information is provided by the closure phase, which we could measure both in the continuum wavelength regime (for four objects) as well as in the spectrally resolved Brγ emission line (for one object). The spectro-interferometric data is supplemented by archival and new VLT/ISAAC spectroscopy. Results. For all objects (except MWC297), we measure an increase of visibility within the Brγ emission line, indicating that the Brγ-emitting region in these objects is more compact than the dust sublimation radius. For HD98922, our quantitative analysis reveals that the line-emitting region is compact enough to be consistent with the magnetospheric accretion scenario. For HD163296, HD104237, MWC297, and V921 Sco we identify an extended stellar wind or a disk wind as the most likely line-emitting mechanism. Since the stars in our sample cover a wide range of stellar parameters, we also search for general trends and find that the size of the Brγ-emitting region does not seem to depend on the basic stellar parameters (such as the stellar luminosity), but correlates with spectroscopic properties, in particular with the Hα line profile shape. Conclusions. By performing the first high-resolution spectro-interferometric survey on Herbig Ae/Be stars, we find evidence for at least two distinct Brγ line-formation mechanisms. Most significant, stars with a P-Cygni Hα line profile and a high mass-accretion rate seem to show particularly compact Brγ-emitting regions (R_(Brγ)/R_(cont) < 0.2), while stars with a double-peaked or single-peaked Hα-line profile show a significantly more extended Brγ-emitting region (0.6 ≾ R_(Brγ)/R_(cont) ≾ 1.4), possibly tracing a stellar wind or a disk wind.

Item Type:Article
Related URLs:
URLURL TypeDescription
Kraus, S.0000-0001-6017-8773
Benisty, M.0000-0002-7695-7605
Berger, J.-P.0000-0001-5025-0428
Isella, A.0000-0001-8061-2207
Smith, M.0000-0002-3321-1432
Testi, L.0000-0003-1859-3070
Additional Information:© ESO 2008. Received 10 April 2008 / Accepted 3 July 2008. We are grateful to A. Chelli and G. Duvert for carrying out independent checks on the AMBER data reduction. Furthermore, we would like to thank the referee for his comments, which helped to improve the paper. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. NSO/Kitt Peak FTS data used here were produced by NSF/NOAO.
Funding AgencyGrant Number
Subject Keywords:stars: pre-main sequence; stars: winds, outflows; planetary systems: protoplanetary disks; line: formation; accretion, accretion disks; techniques: interferometric
Issue or Number:3
Record Number:CaltechAUTHORS:20090519-111926638
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14267
Deposited By: Tony Diaz
Deposited On:25 Jun 2009 20:29
Last Modified:09 Mar 2020 13:19

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