Hydrogen permitted lines in the first near-ir spectra of th 28 microjet: Accretion or ejection tracers?

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Title: Hydrogen permitted lines in the first near-ir spectra of th 28 microjet: Accretion or ejection tracers?
Authors: Coffey, DeirdreBacciotti, FrancescaPodio, LindaNisini, B.
Permanent link: http://hdl.handle.net/10197/11148
Date: 10-Aug-2010
Online since: 2019-10-16T15:08:55Z
Abstract: We report the first near-infrared detection of the bipolar microjet from T Tauri star ThA 15-28 (hereafter Th 28). Spectra were obtained with Very Large Telescope (VLT)/ISAAC for the slit both perpendicular and parallel to the flow to examine jet kinematics and gas physics within the first arcsecond from the star. The jet was successfully detected in bothmolecular and atomic lines. The H2 component was found to be entirely blueshifted around the base of the bipolar jet. It shows that only the blue lobe is emitting in H2 while light is scattered in the direction of the red lobe, highlighting an asymmetric extinction and/or excitation between the two lobes. Consistent with this view, the red lobe is brighter in all atomic lines. Interestingly, the jet was detected not only in [Fe ii], but also in Brγ and Paβ lines. Though considered tracers mainly of accretion, we find that these high excitation hydrogen permitted lines trace the jet as far as 150 AU from the star. This is confirmed in a number of ways: the presence of the [Fe ii] 2.13μm line which is of similarly high excitation; Hi velocities which match the jet [Fe ii] velocities in both the blue and red lobe; and high electron density close to the source of >6 × 104 cm-3 derived from the [Fe ii] 1.64, 1.60μm ratio. These near-infrared data complement Hubble Space Telescope Imaging Spectrograph (HST/STIS) optical and near-ultraviolet data for the same target which were used in a jet rotation study, although no rotation signature could be identified here due to insufficient angular resolution. The unpublished HST/STIS Hα emission is included here alongside the other Hi lines. Identifying Brγ and Paβ as tracers of ejection is significant because of the importance of finding strong near-infrared probes close to the star, where forbidden lines are quenched, which will help understand accretion ejection when observed with high spatial resolution instruments such as VLTI/AMBER. © 2010. The American Astronomical Society. All rights reserved.
Funding Details: European Commission
Irish Research Council
Type of material: Journal Article
Publisher: IOP Publishing
Journal: Astrophysical Journal
Volume: 719
Issue: 1
Start page: 505
End page: 514
Copyright (published version): 2010 American Astronomical Society
Keywords: ISMJetsOutflowsStarsFormationThA 15-28Pre-main sequence
DOI: 10.1088/0004-637X/719/1/505
Language: en
Status of Item: Peer reviewed
Appears in Collections:Physics Research Collection

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