Project F

Recovering the mass of the circumstellar nebula around a massive star at the end of its evolution

Claudia Agliozzo & Neil Phillips

(email advisors)

Massive stars live fast and die young! Whether at death they produce a Supernova or a Black Hole depends on how much of their mass they lose during their life, forming circumstellar nebulae. We will evaluate the mass of the nebula around a massive star near the end of its life.

The evolution of massive stars is governed by mass-loss, which determines the final remnant (neutron star, black hole). Theorists suggest that for stars more massive than 25 solar masses, a large fraction of the stellar mass is stripped-off quickly during their post-main sequence evolution (spent as a Blue Supergiant, BSG), before to become Wolf Rayet stars. Because this transition is very short, but also because of the rarity of massive stars compared to long lived, less massive stars, the mass-loss mechanism is poorly understood. Among the possibilities are strong interaction with a binary companion, and violent giant eruptions. 

Why is this important? Massive stars are major influencers of star formation and galaxy evolution, providing UV radiation, mechanical energy and newly formed chemical elements to their surroundings. They are expected to play an important role in the early Universe, when massive stars were more numerous than at the present epoch. Thus, understanding these stars is a key to improve our knowledge of the far Universe.

Several BSGs in the Milky Way are surrounded by massive circumstellar nebulae, composed of different emitting components (ionized and neutral gas, dust) and thus visible at different wavelengths (radio, IR, optical). Recently, our group obtained a rich dataset of circumstellar nebulae in the Magellanic Clouds, the closest galaxies to the Milky Way and a nearby laboratory that resembles the poor metallicity conditions of the distant early Universe.

We will estimate the nebular mass around a massive star near the end of its life, by evaluating different emitting components through ALMA sub-millimeter continuum and spectroscopic data. We will also analyse integral-field unit spectroscopic data to infer the nebula geometry and thus the mass-loss mechanism from the radial velocities of the brightest optical emission lines. We will test the very large mass loss inferred from modelling of the star, and thus define the evolutionary state of this star.

The student will analyse and model different astrophysical emission mechanisms observed in gaseous nebulae, and will derive meaningful astrophysical quantities. They will gain familiarity with multiwavelength data from different telescopes and instruments, and learn to adopt a multiwavelength approach.

#ALMA #GEMINI-South #spectroscopy #photometry #circumstellarnebula

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