Protostellar Chimney Flues: Are Jets and Outflows Lifting Submillimeter Dust Grains from Disks into Envelopes?
L. Cacciapuoti,
L. Testi,
L. Podio
et al.
Abstract:Low dust opacity spectral indices (β < 1) measured in the inner envelopes of class 0/I young stellar objects (age ∼104–5 yr) have been interpreted as the presence of (sub-)millimeter dust grains in these environments. The density conditions and the lifetimes of collapsing envelopes have proven unfavorable for the growth of solids up to millimeter sizes. As an alternative, magnetohydrodynamical simulations suggest that protostellar jets and outflows might lift grains from circumstellar disks and diffuse them… Show more
“…The estimate of R given above is critically dependent on the (poorly known) properties of grains in the outflow. Indeed, it assumes that grains are present in protostellar outflows-as suggested by Cacciapuoti et al (2024) and references therein-and moreover that their properties are similar to those in the dense interstellar medium. The water abundance required to explain a given value of f w scales linearly with the adopted value of σ abs (Lyα).…”
Using the MIRI medium-resolution spectrometer on JWST, we have detected pure rotational, suprathermal OH emissions from the vicinity of the intermediate-mass protostar HOPS 370 (OMC2/FIR3). These emissions are observed from shocked knots in a jet/outflow and originate in states of rotational quantum number as high as 46 that possess excitation energies as large as E
U
/k = 4.65 × 104 K. The relative strengths of the observed OH lines provide a powerful diagnostic of the ultraviolet radiation field in a heavily extinguished region (A
V
∼ 10–20) where direct UV observations are impossible. To high precision, the OH line strengths are consistent with a picture in which the suprathermal OH states are populated following the photodissociation of water in its
B
˜
−
X
band by ultraviolet radiation produced by fast (∼80 km s−1) shocks along the jet. The observed dominance of emission from symmetric (
A
′
) OH states over that from antisymmetric (A″) states provides a distinctive signature of this particular population mechanism. Moreover, the variation of intensity with rotational quantum number suggests specifically that Lyα radiation is responsible for the photodissociation of water, an alternative model with photodissociation by a 104 K blackbody being disfavored at a high level of significance. Using measurements of the Brα flux to estimate the Lyα production rate, we find that ∼4% of the Lyα photons are absorbed by water. Combined with direct measurements of water emissions in the ν
2 = 1 − 0 band, the OH observations promise to provide key constraints on future models for the diffusion of Lyα photons in the vicinity of a shock front.
“…The estimate of R given above is critically dependent on the (poorly known) properties of grains in the outflow. Indeed, it assumes that grains are present in protostellar outflows-as suggested by Cacciapuoti et al (2024) and references therein-and moreover that their properties are similar to those in the dense interstellar medium. The water abundance required to explain a given value of f w scales linearly with the adopted value of σ abs (Lyα).…”
Using the MIRI medium-resolution spectrometer on JWST, we have detected pure rotational, suprathermal OH emissions from the vicinity of the intermediate-mass protostar HOPS 370 (OMC2/FIR3). These emissions are observed from shocked knots in a jet/outflow and originate in states of rotational quantum number as high as 46 that possess excitation energies as large as E
U
/k = 4.65 × 104 K. The relative strengths of the observed OH lines provide a powerful diagnostic of the ultraviolet radiation field in a heavily extinguished region (A
V
∼ 10–20) where direct UV observations are impossible. To high precision, the OH line strengths are consistent with a picture in which the suprathermal OH states are populated following the photodissociation of water in its
B
˜
−
X
band by ultraviolet radiation produced by fast (∼80 km s−1) shocks along the jet. The observed dominance of emission from symmetric (
A
′
) OH states over that from antisymmetric (A″) states provides a distinctive signature of this particular population mechanism. Moreover, the variation of intensity with rotational quantum number suggests specifically that Lyα radiation is responsible for the photodissociation of water, an alternative model with photodissociation by a 104 K blackbody being disfavored at a high level of significance. Using measurements of the Brα flux to estimate the Lyα production rate, we find that ∼4% of the Lyα photons are absorbed by water. Combined with direct measurements of water emissions in the ν
2 = 1 − 0 band, the OH observations promise to provide key constraints on future models for the diffusion of Lyα photons in the vicinity of a shock front.
Signposts of early planet formation are ubiquitous in substructured young discs. Dense, hot, and high-pressure regions that formed during the gravitational collapse process, integral to star formation, facilitate dynamical mixing of dust within the protostellar disc. This provides an incentive to constrain the role of gas and dust interaction and resolve potential zones of dust concentration during star and disc formation stages. We explore whether the thermal and dynamical conditions that developed during protostellar disc formation can generate gas flows that efficiently mix and transport the well-coupled gas and dust components. We simulated the collapse of dusty molecular cloud cores with the hydrodynamics code PLUTO augmented with radiation transport and self-gravity. We used a two-dimensional axisymmetric geometry and followed the azimuthal component of the velocity. The dust was treated as Lagrangian particles that are subject to drag from the gas, whose motion is computed on a Eulerian grid. We considered 1, 10, and 100 micron-sized neutral, spherical dust grains. Importantly, the equation of state accurately includes molecular hydrogen dissociation. We focus on molecular cloud core masses of 1 and 3 $M_ odot $ and explore the effects of different initial rotation rates and cloud core sizes. Our study underlines mechanisms for the early transport of dust from the inner hot disc regions via the occurrence of two transient gas motions, namely meridional flow and outflow. The vortical flow fosters dynamical mixing and retention of dust, while the thermal pressure driven outflow replenishes dust in the outer disc. Notably, these phenomena occur regardless of the initial cloud core mass, size, and rotation rate. Young dynamical precursors to planet-forming discs exhibit regions with complex hydrodynamical gas features and high-temperature structures. These can play a crucial role in concentrating dust for subsequent growth into protoplanets. Dust transport, especially, from sub-au scales surrounding the protostar to the outer relatively cooler parts, offers an efficient pathway for thermal reprocessing during pre-stellar core collapse.
The origin of the chemical diversity observed around low-mass protostars probably resides in the earliest history of these systems. We aim to investigate the impact of protostellar feedback on the chemistry and grain growth in the circumstellar medium of multiple stellar systems. In the context of the ALMA Large Program FAUST, we present high-resolution (50 au) observations of CH$_3$OH, H$_2$CO, and SiO and continuum emission at 1.3 mm and 3 mm towards the Corona Australis star cluster. Methanol emission reveals an arc-like structure at sim 1800 au from the protostellar system IRS7B along the direction perpendicular to the major axis of the disc. The arc is located at the edge of two elongated continuum structures that define a cone emerging from IRS7B. The region inside the cone is probed by H$_2$CO, while the eastern wall of the arc shows bright emission in SiO, a typical shock tracer. Taking into account the association with a previously detected radio jet imaged with JVLA at 6 cm, the molecular arc reveals for the first time a bow shock driven by IRS7B and a two-sided dust cavity opened by the mass-loss process. For each cavity wall, we derive an average H$_2$ column density of sim 7times 1021 cm$^ $, a mass of sim 9times 10$^ $ M$_ and a lower limit on the dust spectral index of $1.4$. These observations provide the first evidence of a shock and a conical dust cavity opened by the jet driven by IRS7B, with important implications for the chemical enrichment and grain growth in the envelope of Solar System analogues
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