Thesis Topic: Mass Loss from Cool Evolved Stars: Constraining Effects of Convection, Pulsation, and Binarity

Thesis Supervisors:

Markus Wittkowski (ESO)

Susanne Hoefner (University of Uppsala, Sweden)

Andrea Chiavassa (University of Nice, France)

Abstract

Mass loss from cool evolved stars is an important ingredient of the cosmic matter cycle, enriching the Universe with newly formed elements and dust. It is also important for the further stellar evolution of these stars toward planetary nebulae and core-collapse supernovae. For low-and-intermediate-mass asymptotic giant branch (AGB) stars, it has been shown that pulsation and convection lead to strongly extended molecular atmospheres, where the temperature is cool enough for dust to form. For massive red supergiants (RSGs), however, current dynamic model atmospheres, based on pulsation and convection alone, cannot explain observed atmospheric extensions by far. Moreover, close companions may have a considerable effect on the mass-loss process of the primary.

This PhD project includes interferometric monitoring and imaging observations of both AGB and RSG stars. These observations at high spatial resolution allow us to  image the stellar atmospheres, where the winds originate. We will use the PIONIER, GRAVITY, and MATISSE instruments of the Very Large Telescope Interferometer (VLTI), possibly complemented by ALMA observations. Data obtained with all VLTI instruments are already available. Further data will be proposed along the thesis and according to the interest of the student. The data will be compared to latest 1D and 3D dynamic models of the mass-loss process in collaboration with team members of the newly started advanced ERC grant EXWINGS ("Explaining the winds of cool giant and supergiant stars with global 3D models", PI Susanne Hoefner, University of Uppsala, Sweden, https://www.physics.uu.se/research/research-funding/european-research-council/exwings/). Project EXWINGS aims at a breakthrough in understanding the winds of cool giant and supergiant stars.

References

  • Wittkowski, M., et al., Precision Monitoring of Cool Evolved Stars: Constraining Effects of Convection and Pulsation, The Messenger, 2019, vol. 178 p. 34
  • Wittkowski, M., et al., VLTI-GRAVITY measurements of cool evolved stars. I. Variable photosphere and extended atmospherWittkowski, M., et al., Aperture synthesis imaging of the carbon AGB star R Sculptoris. Detection of a complex structure and a dominating spot on the stellar disk, A&A, 2017, Volume 601, A3
    e of the Mira star R Peg, A&A, 2018, Volume 613, L7
  • Hoefner, S. & Freytag, B., Exploring the origin of clumpy dust clouds around cool giants. A global 3D RHD model of a dust-forming M-type AGB star, A&A, 2019, Volume 623, A158
  • Bladh, S., et al.,  An extensive grid of DARWIN models for M-type AGB stars. I. Mass-loss rates and other properties of dust-driven winds, A&A, 2019, Volume 626, A100