The magnetorotational instability in debris-disc gas

Kral, Quentin; Latter, Henrik N.

doi:10.1093/mnras/stw1429

Cited by 38 publications

(41 citation statements)

References 45 publications

(60 reference statements)

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“…temperature, Σ n the neutral carbon density and f the ionisation fraction of carbon. We see that indeed, in HD 32297, for ionisation fraction lower than about 10 −2 (which is typical for shielded disks as shown in Kral et al 2018), the ambipolar parameter becomes lower than 100 and thus the ions and neutrals are not well coupled, which provides very low α values in MRI-simulations (see Kral & Latter 2016, and references therein). Our best fitting secondary gas models predict CO production rates of ∼0.005 M ⊕ /Myr and ∼0.035 M ⊕ /Myr for 49 Cet and HD 32297, respectively.…”

Section: Modelling Resultsmentioning

confidence: 58%

“…Using eq. 4 in Kral & Latter (2016), we calculate that the ambipolar parameter for carbon is ∼ 100( T 20K ) −1/2 ( Σn 10 −5 g/cm 2 )( f 10 −2 ), where T is the gas Figure 5. The mass evolution of 12 CO, 13 CO, C 18 O gas and C 0 gas components in representative secondary gas disk models of 49 Cet (left) and HD 32297 (right).…”

Section: Modelling Resultsmentioning

confidence: 99%

“…We note that in debris disks α values could be very different from those in protoplanetary disks for several reasons. Kral & Latter (2016) found that the magnetorotational instability could work in a debris disk environment and could even lead to high α values because of the high ionisation fraction that can be reached in unshielded disks (mostly made of ionised carbon, such as in β Pic, Cataldi et al 2018). In HD 32297 and 49 Cet, the ionisation fraction could be much lower because of the strong shielding leading to drastically lower α values.…”

Section: Upgraded Shielded Secondary Gas Disk Modelmentioning

confidence: 99%

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New Millimeter CO Observations of the Gas-rich Debris Disks 49 Cet and HD 32297

Moór

Kral

Ábrahám

et al. 2019

ApJ

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Previous observations revealed the existence of CO gas at nearly protoplanetary level in several dust-rich debris disks around young A-type stars. Here we used the ALMA 7m-array to measure 13 CO and C 18 O emission toward two debris disks, 49 Cet and HD 32297, and detected similarly high CO content (>0.01 M ⊕ ). These high CO masses imply a highly efficient shielding of CO molecules against stellar and interstellar ultraviolet photons. Adapting a recent secondary gas disk model that considers both shielding by carbon atoms and self-shielding of CO, we can explain the observed CO level in both systems. Based on the derived gas densities we suggest that, in the HD 32297 disk, dust and gas are coupled and the dynamics of small grains is affected by the gaseous component. For 49 Cet, the question of coupling remains undecided. We found that the main stellar and disk properties of 49 Cet and HD 32297 are very similar to those of previously identified debris disks with high CO content. These objects constitute together the first known representatives of shielded debris disks.

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Section: Modelling Resultsmentioning

confidence: 58%

Section: Modelling Resultsmentioning

confidence: 99%

Section: Upgraded Shielded Secondary Gas Disk Modelmentioning

confidence: 99%

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New Millimeter CO Observations of the Gas-rich Debris Disks 49 Cet and HD 32297

Moór

Kral

Ábrahám

et al. 2019

ApJ

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“…This choice of parametrization of ν is arbitrary, but it offers a form simple enough to understand the gas evolution. Note that we expect α to be smaller than unity, although its value has only been constrained between 10 −4 − 0.5 Kral & Latter 2016;Kral et al 2019;Moór et al 2019). The input of gas in the system happens through the release of volatile species that escape after the break up of volatile rich bodies in a collisional cascade.…”

Section: Modelmentioning

confidence: 87%

Population synthesis of exocometary gas around A stars

Marino

Flock

Henning

et al. 2020

Monthly Notices of the Royal Astronomical Society

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The presence of CO gas around 10-50 Myr old A stars with debris discs has sparked debate on whether the gas is primordial or secondary. Since secondary gas released from planetesimals is poor in H 2 , it was thought that CO would quickly photodissociate never reaching the high levels observed around the majority of A stars with bright debris discs. Kral et al. (2019) showed that neutral carbon produced by CO photodissociation can effectively shield CO and potentially explain the high CO masses around 9 A stars with bright debris discs. Here we present a new model that simulates the gas viscous evolution, accounting for carbon shielding and how the gas release rate decreases with time as the planetesimal disc loses mass. We find that the present gas mass in a system is highly dependant on its evolutionary path. Since gas is lost on long timescales, it can retain a memory of the initial disc mass. Moreover, we find that gas levels can be out of equilibrium and quickly evolving from a shielded onto an unshielded state. With this model, we build the first population synthesis of gas around A stars, which we use to constrain the disc viscosity. We find a good match with a high viscosity (α ∼ 0.1), indicating that gas is lost on timescales ∼ 1 − 10 Myr. Moreover, our model also shows that high CO masses are not expected around FGK stars since their planetesimal discs are born with lower masses, explaining why shielded discs are only found around A stars. Finally, we hypothesise that the observed carbon cavities could be due to radiation pressure or accreting planets.

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“…They show that gas drag could work to slow down these unbound grains when assuming that gas is produced from sublimation of grains for the age of the system. The amount of gas required is ∼5 × 10 −3 M ⊕ and could also be coming from gas produced farther away in the cold belt and viscously evolving to create an accretion disc up to the star [124,125].…”

Section: Trapping With Gasmentioning

confidence: 99%

Exozodiacal clouds: hot and warm dust around main sequence stars

Kral

Krivov

Defrère

et al. 2017

Astronomical Review

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A warm/hot dust component (at temperature >300 K) has been detected around ∼20% of A, F, G, K stars. This component is called 'exozodiacal dust' as it presents similarities with the zodiacal dust detected in our solar system, even though its physical properties and spatial distribution can be significantly different. Understanding the origin and evolution of this dust is of crucial importance, not only because its presence could hamper future detections of Earthlike planets in their habitable zones, but also because it can provide invaluable information about the inner regions of planetary systems. In this review, we present a detailed overview of the observational techniques used in the detection and characterisation of exozodiacal dust clouds ('exozodis') and the results they have yielded so far, in particular regarding the incidence rate of exozodis as a function of crucial parameters such as stellar type and age, or the presence of an outer cold debris disc. We also present the important constraints that have been obtained, on dust size distribution and spatial location, using state-of-the-art radiation transfer models on some of these systems. Finally, we investigate the crucial issue of how to explain the presence of exozodiacal dust around so many stars (regardless of their ages) despite the fact that such dust so close to its host star should disappear rapidly due to the coupled effect of collisions and stellar radiation forces. Several potential mechanisms have been proposed to solve this paradox and are reviewed in detail in this paper. The review finishes by presenting the future of this growing field.

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The magnetorotational instability in debris-disc gas

Cited by 38 publications

References 45 publications

New Millimeter CO Observations of the Gas-rich Debris Disks 49 Cet and HD 32297

New Millimeter CO Observations of the Gas-rich Debris Disks 49 Cet and HD 32297

Population synthesis of exocometary gas around A stars

Exozodiacal clouds: hot and warm dust around main sequence stars

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