More Like this

1. Maximum temperatures in evolving protoplanetary discs and composition of planetary building blocks

   https://doi.org/10.1093/mnras/stab837  

   Li, Min; Huang, Shichun; Zhu, Zhaohuan; Petaev, Michail I; Steffen, Jason H (April 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT The maximum temperature and radial temperature profile in a protoplanetary disc are important for the condensation of different elements in the disc. We simulate the evolution of a set of protoplanetary discs from the collapse of their progenitor molecular cloud cores as well as the dust decoupling within the discs as they evolve. We show how the initial properties of the cloud cores affect the thermal history of the protoplanetary discs using a simple viscous disc model. Our results show that the maximum mid-plane temperature in the disc occurs within 0.5 au. It increases with the initial cloud temperature and decreases with its angular velocity and the viscosity of the disc. From the observed properties of the molecular cloud cores, we find the median value of the maximum temperature is around 1250 K, with roughly 90 per cent of them being less than 1500 K – a value that is lower than the 50 per cent condensation temperatures of most refractory elements. Therefore, only cloud cores with high initial temperatures or low-angular velocities and/or low viscosities within the planet-forming discs will result in refractory-rich planetesimals. To reproduce the volatile depletion pattern of CM, CO, and CV chondrites and the terrestrial planets in Solar system, one must either have rare properties of the initial molecular cloud cores like high core temperature, or other sources of energy to heat the disc to sufficiently high temperatures. Alternatively, the volatile depletion observed in these chondrites may be inherited from the progenitor molecular cloud. 

   more » « less
2. Seven white dwarfs with circumstellar gas discs I: white dwarf parameters and accreted planetary abundances

   https://doi.org/10.1093/mnras/stad3557  

   Rogers, L. K.; Bonsor, A.; Xu, S.; Dufour, P.; Klein, B. L.; Buchan, A.; Hodgkin, S.; Hardy, F.; Kissler-Patig, M.; Melis, C.; et al (November 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Observations of planetary material polluting the atmospheres of white dwarfs are an important probe of the bulk composition of exoplanetary material. Medium- and high-resolution optical and ultraviolet spectroscopy of seven white dwarfs with known circumstellar dust and gas emission are presented. Detections or meaningful upper limits for photospheric absorption lines are measured for: C, O, Na, S, P, Mg, Al, Si, Ca, Ti, Cr, Fe, and Ni. For 16 white dwarfs with known observable gaseous emission discs (and measured photospheric abundances), there is no evidence that their accretion rates differ, on average, from those without detectable gaseous emission. This suggests that, typically, accretion is not enhanced by gas drag. At the effective temperature range of the white dwarfs in this sample (16 000–25 000 K) the abundance ratios of elements are more consistent than absolute abundances when comparing abundances derived from spectroscopic white dwarf parameters versus photometric white dwarf parameters. Crucially, this highlights that the uncertainties on white dwarf parameters do not prevent white dwarfs from being utilized to study planetary composition. The abundances of oxygen and silicon for the three hydrogen-dominated white dwarfs in the sample with both optical and ultraviolet spectra differ by 0.62 dex depending on if they are derived from the optical or ultraviolet spectra. This optical/ultraviolet discrepancy may be related to differences in the atmospheric depth of line formation; further investigations into the white dwarf atmospheric modelling are needed to understand this discrepancy. 

   more » « less
3. Composition constraints of the TRAPPIST-1 planets from their formation

   https://doi.org/10.1093/mnras/stad2110  

   Childs, Anna_C; Shakespeare, Cody; Rice, David_R; Yang, Chao-Chin; Steffen, Jason_H (July 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We study the formation of the TRAPPIST-1 (T1) planets starting shortly after Moon-sized bodies form just exterior to the ice line. Our model includes mass growth from pebble accretion and mergers, fragmentation, type-I migration, and eccentricity and inclination dampening from gas drag. We follow the composition evolution of the planets fed by a dust condensation code that tracks how various dust species condense out of the disc as it cools. We use the final planet compositions to calculate the resulting radii of the planets using a new planet interior structure code and explore various interior structure models. Our model reproduces the broader architecture of the T1 system and constrains the initial water mass fraction of the early embryos and the final relative abundances of the major refractory elements. We find that the inner two planets likely experienced giant impacts and fragments from collisions between planetary embryos often seed the small planets that subsequently grow through pebble accretion. Using our composition constraints, we find solutions for a two-layer model, a planet comprised of only a core and mantle, that match observed bulk densities for the two inner planets b and c. This, along with the high number of giant impacts the inner planets experienced, is consistent with recent observations that these planets are likely desiccated. However, two-layer models seem unlikely for most of the remaining outer planets, which suggests that these planets have a primordial hydrosphere. Our composition constraints also indicate that no planets are consistent with a core-free interior structure. 

   more » « less
4. The Ophiuchus DIsc Survey Employing ALMA (ODISEA) – III. The evolution of substructures in massive discs at 3–5 au resolution

   https://doi.org/10.1093/mnras/staa3787  

   Cieza, Lucas A; González-Ruilova, Camilo; Hales, Antonio S; Pinilla, Paola; Ruíz-Rodríguez, Dary; Zurlo, Alice; Casassus, Simón; Pérez, Sebastián; Cánovas, Hector; Arce-Tord, Carla; et al (January 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We present 1.3 mm continuum ALMA long-baseline observations at 3–5 au resolution of 10 of the brightest discs from the Ophiuchus DIsc Survey Employing ALMA (ODISEA) project. We identify a total of 26 narrow rings and gaps distributed in 8 sources and 3 discs with small dust cavities (r <10 au). We find that two discs around embedded protostars lack the clear gaps and rings that are ubiquitous in more evolved sources with Class II SEDs. Our sample includes five objects with previously known large dust cavities (r >20 au). We find that the 1.3 mm radial profiles of these objects are in good agreement with those produced by numerical simulations of dust evolution and planet–disc interactions, which predict the accumulation of mm-sized grains at the edges of planet-induced cavities. Our long-baseline observations resulted in the largest sample of discs observed at ∼3–5 au resolution in any given star-forming region (15 objects when combined with Ophiuchus objects in the DSHARP Large Program) and allow for a demographic study of the brightest $$\sim\! 5{{\ \rm per\ cent}}$$ of the discs in Ophiuchus (i.e. the most likely formation sites of giant planets in the cloud). We use this unique sample to propose an evolutionary sequence and discuss a scenario in which the substructures observed in massive protoplanetary discs are mainly the result of planet formation and dust evolution. If this scenario is correct, the detailed study of disc substructures might provide a window to investigate a population of planets that remains mostly undetectable by other techniques. 

   more » « less
5. Dust–gas dynamics driven by the streaming instability with various pressure gradients

   https://doi.org/10.1093/mnras/stae272  

   Baronett, Stanley A; Yang, Chao-Chin; Zhu, Zhaohuan (February 2024, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The streaming instability, a promising mechanism to drive planetesimal formation in dusty protoplanetary discs, relies on aerodynamic drag naturally induced by the background radial pressure gradient. This gradient should vary in discs, but its effect on the streaming instability has not been sufficiently explored. For this purpose, we use numerical simulations of an unstratified disc to study the non-linear saturation of the streaming instability with mono-disperse dust particles and survey a wide range of gradients for two distinct combinations of the particle stopping time and the dust-to-gas mass ratio. As the gradient increases, we find most kinematic and morphological properties increase but not always in linear proportion. The density distributions of tightly coupled particles are insensitive to the gradient whereas marginally coupled particles tend to concentrate by more than an order of magnitude as the gradient decreases. Moreover, dust–gas vortices for tightly coupled particles shrink as the gradient decreases, and we note higher resolutions are required to trigger the instability in this case. In addition, we find various properties at saturation that depend on the gradient may be observable and may help reconstruct models of observed discs dominated by streaming turbulence. In general, increased dust diffusion from stronger gradients can lower the concentration of dust filaments and can explain the higher solid abundances needed to trigger strong particle clumping and the reduced planetesimal formation efficiency previously found in vertically stratified simulations. 

   more » « less