Matrà, L, Dent, WRF, Wyatt, MC et al. (9 more authors) (2017) Exocometary gas structure, origin and physical properties around β Pictoris through ALMA CO multitransition observations. Monthly Notices of the Royal Astronomical Society, 464 (2). pp. 1415-1433. ISSN 0035-8711
Abstract
Recent ALMA observations unveiled the structure of CO gas in the 23 Myr old β Pictoris planetary system, a component that has been discovered in many similarly young debris discs. We here present ALMA CO J = 2−1 observations, at an improved spectro-spatial resolution and sensitivity compared to previous CO J = 3−2 observations. We find that (1) the CO clump is radially broad, favouring the resonant migration over the giant impact scenario for its dynamical origin, (2) the CO disc is vertically tilted compared to the main dust disc, at an angle consistent with the scattered light warp. We then use position-velocity diagrams to trace Keplerian radii in the orbital plane of the disc. Assuming a perfectly edge-on geometry, this shows a CO scaleheight increasing with radius as R0.75, and an electron density [derived from CO line ratios through non-local thermodynamic equilibrium (NLTE) analysis] in agreement with thermodynamical models. Furthermore, we show how observations of optically thin line ratios can solve the primordial versus secondary origin dichotomy in gas-bearing debris discs. As shown for β Pictoris, subthermal (NLTE) CO excitation is symptomatic of H2 densities that are insufficient to shield CO from photodissociation over the system's lifetime. This means that replenishment from exocometary volatiles must be taking place, proving the secondary origin of the disc. In this scenario, assuming steady state production/destruction of CO gas, we derive the CO+CO2 ice abundance by mass in β Pic's exocomets to be at most ∼6 per cent, consistent with comets in our own Solar system and in the coeval HD181327 system.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Reproduced in accordance with the publisher's self-archiving policy. |
Keywords: | molecular processes, comets: general, circumstellar matter, stars: individual: β Pictoris, planetary systems, submillimetre: planetary systems |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Physics and Astronomy (Leeds) > Astrophysics (Leeds) |
Funding Information: | Funder Grant number Royal Society Not Known |
Depositing User: | Symplectic Publications |
Date Deposited: | 31 Mar 2017 11:13 |
Last Modified: | 31 Mar 2017 11:13 |
Published Version: | https://doi.org/10.1093/mnras/stw2415 |
Status: | Published |
Publisher: | Oxford University Press (OUP) |
Identification Number: | 10.1093/mnras/stw2415 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:114302 |