The dispersal of protoplanetary discs

Abstract

Protoplanetary discs are a natural consequence of the star formation process and as such are ubiquitous around low-mass stars. They are fundamental to planet formation as they hold the reservoir of material from which planets form. Their evolution and final dispersal and the timescales that regulate these process are therefore of particular interest. In this contribution I will review the observational evidence for the dispersal of discs being dominated by two timescales and for the final dispersal to occur quickly and from the inside out. I will discuss the current theoretical models, including X-ray photoevaporation, showing that the latter provides a natural explanation to the observed behaviour and review supporting and contrasting evidence. I will finally introduce a new mechanism based on the interaction between planet formation and photoevaporation that may explain a particular class of transition discs with large inner holes and high accretion rates that are problematic for photoevaporation models and planet formation models alone.

Testing the models of X-ray driven photoevaporation with accreting stars in the Orion Nebula Cluster

“…When using the older tracks from D'Antona & Mazzitelli (1994), the slope becomes 1.77 ± 0.22, which is in agreement with the findings of other studies. In particular, this slope agrees with the value of 1.66 ± 0.07 that Ercolano (2014) found in their total sample, which also contains the accretion rates we used in our analysis. According to the authors, slopes of 1.45 − 1.70 are expected in the context of X-ray driven photo-evaporative disk dispersal.…”

“…The slope is in agreement with the findings from Bustamante et al (2016) of 1.90±0.17 (Hα-sample), but higher than the value of 1.72 ± 0.17 (U-excess sample) and the value of 1.69 ± 0.11 found by Telleschi et al (2007) for stars in the Taurus molecular cloud. Furthermore, the slope is larger than the value of 1.28 ± 0.07 found by Ercolano (2014) for their total sample and the 1.44 ± 0.10 obtained by despite the fact that they used the same evolutionary tracks. Repeating the analysis with the mass estimates listed in the COUP table, the slope becomes 1.67 ± 0.21, in agreement with the slope reported by .…”

Signum and self: engraved gemstones and the expression of identity at Herculaneum

“…41 Nor do we know if the patterns of gem-wearing evident at the beachfront are representative of daily habits. 42 It is plausible that at least some of the individuals were carrying moreor lessthan they would normally have worn as they attempted to escape the city: two male skeletons, for example, were found in arch 12 on either side of a wooden casket containing an assemblage of different types of jewellery, including engraved gemstones, 43 that may represent the possessions of a nuclear family, 44 or perhaps the stock of a jeweller; 45 the presence of three earrings implies that at least some of the contents belonged to a woman. 46 At our most skeptical, we cannot even be certain that all of the jewellery in fact belonged to the individuals found wearing or carrying it.…”