Photoionization feedback in massive star formation Bert - - PowerPoint PPT Presentation

Photoionization feedback in massive star formation

Bert Vandenbroucke (bv7@st-andrews.ac.uk) Kenneth Wood (St Andrews) Kristin Lund (St Andrews) Nina Sartorio (São José dos Campos) Diego Falceta-Gonçalves (São Paulo) Eric Keto (Harvard) Ian Bonnell (St Andrews)

27/06/2019 EWASS 2019, Lyon, S10: The feedback in the star formation process

Massive stars

https://en.wikipedia.org/wiki/List_of_most_massive_stars https://en.wikipedia.org/wiki/Initial_mass_function

𝑁⋆ > 100 M⊙

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Massive stars (2)

Palla & Stahler (1993)

fusion accretion Massive stars join the main sequence before they have reached their final mass!

Keto (2003)

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Photoionization

Vandenbroucke & Sartorio (in prep.)

Very massive stars emit copious amounts

• f photoionizing radiation

that heats their environment hot, ionised gas cold, neutral gas

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Photoheating: D-type expansion

Image courtesy of N. Sartorio

Photoheating causes an outward moving shock that shuts down accretion

Bisbas et al. (2015), STARBENCH Slide 5 of 14

However...

Image courtesy of N. Sartorio Mestel (1954), Keto (2002,2003)

Gravity can trap an HII region: accretion continues for longer

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Trapped HII regions

See Vandenbroucke et al. (2019) for an analytic expression

Lund et al. (2019) Slide 7 of 14

Not as stable as we thought...

Vandenbroucke et al. (2019) Slide 8 of 14

Small density perturbations lead to a periodic disturbance of the ionization front

From trapped to expanding

Lund et al. (2019) Keto (2002)

Transition from trapped HII region to D-type expansion past the ionised sonic point

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Non-spherical case

Sartorio et al. (2019)

Angular momentum conservation leads to the formation of an accretion torus with a different density structure

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D-type expansion in torus

Sartorio et al. (2019)

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Trapped HII regions

Sartorio et al. (2019)

Non-spherical trapped and semi-trapped HII regions also possible

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Critical luminosity

Sartorio et al. (2019)

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Summary

• Spherical HII regions grow as the mass (and luminosity)

increases => accretion shuts down

• Non-spherical HII regions are embedded in an accretion torus:

– can keep accreting through torus plane – torus structure changes with mass; unclear if evolution from trapped to D-type expansion still possible – stable accretion only possible for dense torus

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