The distribution of accretion rates as a diagnostic of protoplanetary disc evolution

We show that the distribution of observed accretion rates is a powerful diagnostic of protoplanetary disc physics. Accretion due to turbulent ("viscous") transport of angular momentum results in a fundamentally different distribution of accretion rates than accretion driven by magnetised disc winds. We find that a homogeneous sample of $\gtrsim$300 observed accretion rates would be sufficient to distinguish between these two mechanisms of disc accretion at high confidence, even for pessimistic assumptions. Current samples of T Tauri star accretion rates are not this large, and also suffer from significant inhomogeneity, so both viscous and wind-driven models are broadly consistent with the existing observations. If accretion is viscous, the observed accretion rates require low rates of disc photoevaporation ($\lesssim$$10^{-9}$M$_{\odot}$yr$^{-1}$). Uniform, homogeneous surveys of stellar accretion rates can therefore provide a clear answer to the long-standing question of how protoplanetary discs accrete.Comment: 10 pages, 8 figures. Accepted for publication in MNRA

Evidence for ubiquitous carbon grain destruction in hot protostellar envelopes

Earth is deficient in carbon and nitrogen by up to ${\sim}4$ orders of magnitude compared with the Sun. Destruction of (carbon- and nitrogen-rich) refractory organics in the high-temperature planet forming regions could explain this deficiency. Assuming a refractory cometary composition for these grains, their destruction enhances nitrogen-containing oxygen-poor molecules in the hot gas ($\gtrsim 300$K) after the initial formation and sublimation of these molecules from oxygen-rich ices in the warm gas (${\sim}150$K). Using observations of $37$ high-mass protostars with ALMA, we find that oxygen-containing molecules (CH$_3$OH and HNCO) systematically show no enhancement in their hot component. In contrast, nitrogen-containing, oxygen-poor molecules (CH$_3$CN and C$_2$H$_3$CN) systematically show an enhancement of a factor ${\sim} 5$ in their hot component, pointing to additional production of these molecules in the hot gas. Assuming only thermal excitation conditions, we interpret these results as a signature of destruction of refractory organics, consistent with the cometary composition. This destruction implies a higher C/O and N/O in the hot gas than the warm gas, while, the exact values of these ratios depend on the fraction of grains that are effectively destroyed. This fraction can be found by future chemical models that constrain C/O and N/O from the abundances of minor carbon, nitrogen and oxygen carriers presented here.Comment: Accepted for publication in ApJ Letter

Suldat

Ġabra ta’ poeżiji u proża li tinkludi: Sursum Corda! ta’ R. M. B. – Tal-Qali ta’ Ġużè Ellul – Tfajla ta’ Dun Karm – Meta mort Għawdex bid-dawra ta’ Ġ. Cassar-Pullicino – Il-Maqdes tal-Mulej ta’ A. Buttigieg – Il-Barrakka ta’ Katrin ta’ P. Pawl Tabone – Ġlieġel ta’ Mary Meylak – Is-Suldat ta’ Ġużè Chetcuti.N/

Towards future pedestrian-vehicle interactions: Introducing theoretically-supported AR prototypes

The future urban environment may consist of mixed traffic in which pedestrians interact with automated vehicles (AVs). However, it is still unclear how AVs should communicate their intentions to pedestrians. Augmented reality (AR) technology could transform the future of interactions between pedestrians and AVs by offering targeted and individualized communication. This paper presents nine prototypes of AR concepts for pedestrian-AV interaction that are implemented and demonstrated in a real crossing environment. Each concept was based on expert perspectives and designed using theoretically-informed brainstorming sessions. Prototypes were implemented in Unity MARS and subsequently tested on an unmarked road using a standalone iPad Pro with LiDAR functionality. Despite the limitations of the technology, this paper offers an indication of how future AR systems may support future pedestrian-AV interactions

Investigating the Impact of Metallicity on Star Formation in the Outer Galaxy. I. VLT/KMOS Survey of Young Stellar Objects in Canis Major

The effects of metallicity on the evolution of protoplanetary disks may be studied in the outer Galaxy where the metallicity is lower than in the solar neighbourhood. We present the VLT/KMOS integral field spectroscopy in the near-infrared of $\sim$120 candidate young stellar objects (YSOs) in the CMa-$\ell$224 star-forming region located at a Galactocentric distance of 9.1 kpc. We characterise the YSO accretion luminosities and accretion rates using the hydrogen Br$\gamma$ emission and find the median accretion luminosity of $\log{(L_{\rm acc})} = -0.82^{+0.80}_{-0.82} L_\odot$. Based on the measured accretion luminosities, we investigate the hypothesis of star formation history in the CMa-$\ell$224. Their median values suggest that Cluster C, where most of YSO candidates have been identified, might be the most evolved part of the region. The accretion luminosities are similar to those observed toward low-mass YSOs in the Perseus and Orion molecular clouds, and do not reveal the impact of lower metallicity. Similar studies in other outer Galaxy clouds covering a wide range of metallicities are critical to gain a complete picture of star formation in the Galaxy.Comment: Accepted for publication in APJS, 51 pages, 37 figures, 6 table