arXiv subjects

J. L. Verbena

Publications and source records attributed to J. L. Verbena.

3 recordsLinked to original sources

arXiv2026

Molecular cloud dispersal traced by the ionized carbon 158 micron line

Feedback from massive stars in the form of radiation and winds impacts the associated host molecular cloud. Feedback can disperse cloud material and lead to the destruction of the cloud. Recent observations of the ionized carbon CII 158 micron line in high-mass star-forming regions have demonstrated that this line is an excellent tracer of the gas dynamics in such environments. Expanding CII shells have been detected, along with high-velocity gas escaping the natal cloud through low-density channels. Motivated by these results, we conducted a systematic analysis of spectrally resolved CII maps obtained with SOFIA towards ten high-mass star-forming regions hosting at least one O-type star. Across all regions, we identify high-velocity CII line wings with velocities that exceed the cloud escape velocity, indicating that this gas is not gravitationally confined. We show that the high-velocity gas exhibits a complex velocity structure and cannot be attributed solely to a single, coherent expanding CII bubble. The amount of material in these erosion flows depends on the evolutionary stage of the molecular cloud and its associated HII region. Once the initial bubble around the cluster ruptures, typically after 0.1 Myr, gas is expelled from the cloud. The resulting cloud erosion timescales based on these directly observed mass ejection rates typically vary between 2 and 10 Myr after the formation of the first O stars, similar to other indirect measures of molecular cloud life times. These results suggest that stellar feedback is able to remove enough molecular gas to terminate the star formation in the host cloud.

astro-ph.GA↗

arXiv2019

Interferometric observations of SiO thermal emission in the inner wind of M-type AGB stars IK Tauri and IRC+10011

Context. AGB stars go through a process of strong mass-loss that involves pulsations of the atmosphere, which extends to a region where the conditions are adequate for dust grains to form. Radiation pressure acts on these grains which, coupled to the gas, drive a massive outflow. The details of this process are not clear, including which molecules are involved in the condensation of dust grains. Aims. To study the role of the SiO molecule in the process of dust formation and mass-loss in M-type AGB stars. Methods. Using the IRAM NOEMA interferometer we observed the $^{28}$SiO and $^{29}$SiO $J=3-2$, $v=0$ emission from the inner circumstellar envelope of the evolved stars IK Tau and IRC+10011. We computed azimuthally averaged emission profiles to compare the observations to models using a molecular excitation and ray-tracing code for SiO thermal emission. Results. We observed circular symmetry in the emission distribution. We also found that the source diameter varies only marginally with radial velocity, which is not the expected behavior for envelopes expanding at an almost constant velocity. The adopted density, velocity, and abundance laws, together with the mass-loss rate, which best fit the observations, give us information on the chemical behavior of the SiO molecule and its role in the dust formation process. Conclusions. The results indicate that there is a strong coupling between the depletion of gas phase SiO and gas acceleration in the inner envelope. This could be explained by the condensation of SiO into dust grains.

astro-ph.SR↗

arXiv2011

Outflow dynamics of dust-driven wind models and implications for cool envelopes of PNe

The density profiles of cool envelopes of young Planetary Nebulae (PNe) are reminiscent of the final AGB outflow history of the central star, so far as these have not yet been transformed by the hot wind and radiation of the central star. Obviously, the evolution of the mass loss rate of that dust-driven, cool wind of the former giant in its final AGB stages must have shaped these envelopes to some extent. Less clear is the impact of changes in the outflow velocity. Certainly, larger and fast changes would lead to significant complications in the reconstruction of the mass-loss history from a cool envelope's density profile. Here, we analyse the outflow velocity v_{\rm exp} in a consistent set of over 50 carbon-rich, dust-driven and well "saturated" wind models, and how it depends on basic stellar parameters. We find a relation of the kind of v_{\rm exp} \propto (L/M)^{0.6}. By contrast to the vast changes of the mass-loss rate in the final outflow phase, this relation suggest only very modest variations in the wind velocity, even during a thermal pulse. Hence, we conclude that the density profiles of cool envelopes around young PNe should indeed compare relatively well with their recent mass-loss history, when diluted plainly by the equation of continuity.

astro-ph.SR↗