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- Nicholson, Rhana B, et al.
(författare)
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Rapid destruction of protoplanetary discs due to external photoevaporation in star-forming regions
- 2019
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 485, s. 4893-4905
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Tidskriftsartikel (refereegranskat)abstract
- We analyse N-body simulations of star-forming regions to investigate the effects of externalfar- and extreme-ultraviolet photoevaporation from massive stars on protoplanetary discs. Byvarying the initial conditions of simulated star-forming regions, such as the spatial distribution,net bulk motion (virial ratio), and density, we investigate which parameters most affect the rateat which discs are dispersed due to external photoevaporation. We find that disc dispersal due toexternal photoevaporation is faster in highly substructured star-forming regions than in smoothand centrally concentrated regions. Subvirial star-forming regions undergoing collapse alsoshow higher rates of disc dispersal than regions that are in virial equilibrium or are expanding.In moderately dense (∼100 M pc −3 ) regions, half of all protoplanetary discs with radii≥100 au are photoevaporated within 1 Myr, three times faster than is currently suggested byobservational studies. Discs in lower density star-forming regions (∼10 M pc −3 ) survive forlonger, but half are still dispersed on short time-scales (∼2 Myr). This demonstrates that theinitial conditions of the star-forming regions will greatly impact the evolution and lifetime ofprotoplanetary discs. These results also imply that either gas giant planet formation is extremelyrapid and occurs before the gas component of discs is evaporated, or gas giants only formin low-density star-forming regions where no massive stars are present to photoevaporate gasfrom protoplanetary discs.
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| 2. |
- Pinder, Adrian C., et al.
(författare)
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Mahseer (Tor spp.) fishes of the world : status, challenges and opportunities for conservation
- 2019
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Ingår i: Reviews in Fish Biology and Fisheries. - : Springer Science and Business Media LLC. - 0960-3166 .- 1573-5184. ; 29:2, s. 417-452
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Forskningsöversikt (refereegranskat)abstract
- The mahseer fishes (Tor spp.) represent an iconic genus of large-bodied species of the Cyprinidae family. Across the 16 recognised species in the genus, individual fish can attain weights over 50kg, resulting in some species being considered as premier sport fishes. Tor species also generally have high religious and cultural significance throughout South and Southeast Asia. Despite their economic and cultural importance, the status of Tor fishes has been increasingly imperilled through their riverine habitats being impacted by anthropogenic activities, such as hydropower dam construction and exploitation. Moreover, conservation efforts have been constrained by knowledge on the genus being heavily skewed towards aquaculture, with considerable knowledge gaps on their taxonomy, autecology, distribution and population status. Whilst taxonomic ambiguity has been a major constraint on conservation efforts, this has been partially overcome by recent, robust taxonomic revisions. This has enabled revision of the IUCN Red List status of Tor fishes; three species are now assessed as Near Threatened', one Vulnerable', three Endangered' and one Critically Endangered'. However, eight species remain Data deficient'. Here, information on these 16 Tor fishes is synthesised for the first time, outlining the current state of knowledge for each species, including their known distributions and population status. For each species, the outstanding gaps in knowledge are also identified, and their population threats and conservation prospects outlined. Consequently, this review provides the basis for researchers to challenge and enhance the knowledge base necessary to conserve these freshwater icons in an era of unprecedented environmental changes.
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