Evolution of dust in protoplanetary disks of eruptive stars

Abstract

Aims. Luminosity bursts in young FU Orionis-type stars warm up the surrounding disks of gas and dust, thus inflicting changes on their morphological and chemical composition. In this work, we aim at studying the effects that such bursts may have on the spatial distribution of dust grain sizes and the corresponding spectral index in protoplanetary disks. Methods. We use the numerical hydrodynamics code FEOSAD, which simulates the co-evolution of gas, dust, and volatiles in a protoplanetary disk, taking dust growth and back reaction on gas into account. The dependence of the maximum dust size on the water ice mantles is explicitly considered. The burst is initialized by increasing the luminosity of the central star to 100–300 L⊙ for a time period of 100 yr. Results. The water snowline shifts during the burst to a larger distance, resulting in the drop of the maximum dust size interior to the snowline position because of more efficient fragmentation of bare grains. After the burst, the water snowline shifts quickly back to its preburst location followed by renewed dust growth. The timescale of dust regrowth after the burst depends on the radial distance so that the dust grains at smaller distances reach the preburst values faster than the dust grains at larger distances. As a result, a broad peak in the radial distribution of the spectral index in the millimeter dust emission develops at ≈10 au, which shifts further out as the disk evolves and dust grains regrow to preburst values at progressively larger distances. This feature is most pronounced in evolved axisymmetric disks rather than in young gravitationally unstable counterparts, although young disks may still be good candidates if gravitational instability is suppressed. We confirmed our earlier conclusion that spiral arms do not act as strong dust accumulators because of the Stokes number dropping below 0.01 within the arms, but this trend may change in low-turbulence disks. Conclusions. We argue that, depending on the burst strength and disk conditions, a broad peak in the radial distribution of the spectral index can last for up to several thousand years after the burst has ended and can be used to infer past bursts in otherwise quiescent protostars. The detection of a similar peak in the disk around V883 Ori, an FU Orionis-type star with an unknown eruption date, suggests that such features may be common in the post-outburst objects.

Fast methods for tracking grain coagulation and ionization

“…First, they are the seeds of planet formation. While their characteristic size is submicron in the interstellar medium (ISM) (Mathis et al 1977), they grow by coagulation during the collapse and can reach sizes larger than 10 µm in the early stages of protostellar collapse (Guillet et al 2020;Silsbee et al 2020;Tsukamoto et al 2021;Vorobyov et al 2022;Bate 2022). Observations also suggest they reach these sizes (and possibly larger ones) in the envelopes of Class 0-I objects (Kwon et al 2009;Miotello et al 2014;Le Gouellec et al 2019;Galametz et al 2019).…”

“…The dust evolution used to be pre-processed or post-processed with no self-consistent feedback on the dynamics (Rossi et al 1991;Dullemond & Dominik 2005;Zhao et al 2016;Marchand et al 2020). Recently, more and more studies include the growth of grains in their hydrodynamics simulations (Tsukamoto et al 2021;Vericel et al 2021;Vorobyov et al 2022;Bate 2022). In Marchand et al (2021, hereafter Paper I), we presented a simple and fast method to track coagulation in a self-consistent way that is particularly suited for modeling star formation.…”

Sustained FU Orionis-type outbursts from colliding discs in stellar flybys

“…While we did not include ices in our calculations, the motion of the 𝑇 = 105 K iso-temperature line in our simulations is consistent with these observations. The water snow-line has a non-circular shape, which has also been found for outbursts in gravitationally unstable discs Vorobyov et al (2022). This is a crude comparison though as in practice the snow-line depends on the temperature as well as the pressure (see e.g.…”

The influence of metallicity on a combined stellar and disk evolution

“…Variable dust component: The dust-to-gas mass ratio, f dust , in this study is kept constant at the respective stellar metallicity value trough out the simulation and over the disk's radial extent. While this assumption might be reasonable in the first step, the dust fraction can differ within the disk over time due to a great number of processes, such as coagulation, drift, fragmentation, and vertical settling (e.g., Testi et al 2014;Vorobyov et al 2022).…”