The circumstellar environment of HD 50138 revealed by VLTI/AMBER at high angular resolution

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Title: The circumstellar environment of HD 50138 revealed by VLTI/AMBER at high angular resolution
Authors: Koutoulaki, Maria-KalliopiGarcia Lopez, R.Natta, A.Coffey, Deirdreet al.
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Date: 22-Jun-2018
Online since: 2019-10-15T15:33:22Z
Abstract: Context. HD 50138 is a Herbig B[e] star with a circumstellar disc detected at infrared and millimeter wavelength. Its brightness makes it a good candidate for near-infrared interferometry observations. Aims. We aim to resolve, spatially and spectrally, the continuum and hydrogen emission lines in the 2.12–2.47 micron region, to shed light on the immediate circumstellar environment of the star. Methods. VLTI/AMBER K-band observations provide spectra, visibilities, differential phases, and closure phases along three long baselines for the continuum, and H I emission in Brγ and five high-n Pfund lines. By computing the pure line visibilities, we derive the angular size of the different line-emitting regions. A simple local thermodynamic equilibrium (LTE) model was created to constrain the physical conditions of H I emitting region. Results. The continuum region cannot be reproduced by a geometrical two-dimensional (2D) elongated Gaussian fitting model. We estimate the size of the region to be 1 au. We find the detected hydrogen lines (Brγ and Pfund lines) come from a more compact region of size 0.4 au. The Brγ line exhibits an S-shaped differential phase, indicative of rotation. The continuum and Brγ line closure phases show offsets of ~ −25 ± 5° and 20 ± 10° respectively. This is evidence of an asymmetry in their origin, but with opposing directions. We find that we cannot converge on constraints for the HI physical parameters without a more detailed model. Conclusions. Our analysis reveals that HD 50138 hosts a complex circumstellar environment. Its continuum emission cannot be reproduced by a simple disc brightness distribution. Similarly, several components must be evoked to reproduce the interferometric observables within the Brγ line. Combining the spectroscopic and interferometric data of the Brγ and Pfund lines favours an origin in a wind region with a large opening angle. Finally, although we cannot exclude the possibility that HD 50138 is a young star our results point to an evolved source.
Funding Details: European Commission Horizon 2020
European Research Council
Irish Research Council
Science Foundation Ireland
metadata.dc.description.othersponsorship: ESO Fellowship Programme
Type of material: Journal Article
Publisher: EDP Sciences
Journal: Astronomy and Astrophysics
Volume: 614
Copyright (published version): 2018 ESO
Keywords: InterferometricHD 50138WindsOutflowsEmission-linePre-main sequenceInfrared
DOI: 10.1051/0004-6361/201832814
Language: en
Status of Item: Peer reviewed
Appears in Collections:Physics Research Collection

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