Gas and dust around A-type stars at tens of Myr: signatures of cometary breakup
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Discs of dusty debris around main-sequence stars indicate fragmentation of orbiting planetesimals,and for a few A-type stars, a gas component is also seen that may come from collisionally released volatiles. Here we find the sixth example of a CO-hosting disc, around the ~30 Myr-old A0-star HD 32997. Two more of these CO-hosting stars, HD 21997 and 49 Cet, have also been imaged in dust with SCUBA-2 within the SCUBA-2 Survey of Nearby Stars project. A census of 27 A-type debris hosts within 125 pc now shows 7/16 detections of carbon-bearing gas within the 5-50 Myr epoch, with no detections in 11 older systems. Such a prolonged period of high fragmentation rates corresponds quite well to the epoch when most of the Earth was assembled from planetesimal collisions. Recent models propose that collisional products can be spatially asymmetric if they originate at one location in the disc, with CO particularly exhibiting this behaviour as it can photodissociate in less than an orbital period. Of the six CO-hosting systems, only β Pic is in clear support of this hypothesis. However, radiative transfer modelling with the ProDiMo code shows that the CO is also hard to explain in a proto-planetary disc context.
Greaves , J S , Holland , W S , Matthews , B C , Marshall , J P , Dent , W R F , Woitke , P , Wyatt , M C , Matrà , L & Jackson , A 2016 , ' Gas and dust around A-type stars at tens of Myr: signatures of cometary breakup ' Monthly Notices of the Royal Astronomical Society , vol 461 , no. 4 , pp. 3910-3917 . DOI: 10.1093/mnras/stw1569
Monthly Notices of the Royal Astronomical Society
© 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at: https://dx.doi.org/10.1093/mnras/stw1569
JSG and PW thank the ERC for funding for project DiscAnalysis, under the grant FP7-SPACE-2011 collaborative project 284405. JPM is supported by a UNSW Vice- Chancellor’s postdoctoral fellowship. MCW and LM acknowledge the support of the European Union through ERC grant 279973.