Observations of the runaway HD 271791 Nucleosynthesis in a core-collapse supernova
Veronika Schaffenroth Institute for Astro- and Particle Physics, University of Innsbruck
18th Workshop on Nuclear Astrophysics Schloss Ringberg 18.03.16
Collaborators: Norbert Przybilla, Keith Butler, Andreas Irrgang, Uli Heber
Characteristics of massive runaway stars
massive and young Ø found in the halo of the Galaxy
Characteristics of massive runaway stars
massive and young Ø can only be formed in open clusters or associations found in the spiral arms (disk)
Ø far away from star forming regions ñ ejection event
Dynamical Ejection: Hills Mechanism
Hypervelocity stars – Unbound to the Galaxy Ejected by the super-massive black hole?
blender_slingshot.avi
Media File (video/avi)
Dynamical Ejection: Characteristics
• age same as age of the home cluster • not expected to show signs of binary evolution (high rotational velocities, different abundances)
• expected to be single in most cases
Supernova Explosion in a Binary System
blender_sn.avi
12 C,16 O
• high rotational velocities • rejuvenation via mass transfer • flight time smaller than the age, several Myr for the companion to explode in a supernova
• accretion of some of the material ejected in the core collapse-SN due to the small separation of the pre-SN binary ñ enhancement in α process elements and elements produced in the core collapse-SN
Motivation
studying runaway from supernova scenario
• Infer insights into explosive nucleosynthesis from an independent and so far unexploited indicator
• Derive observational constraints on theoretical supernova models
• first observational evidence for r-process elements in supernova ejecta?
ùñ quantitative spectral analysis • atmospheric parameters
• elemental abundances
HD271791 – the most extreme runaway known
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Schaffenroth 2015
• bright (12 mag), normal B star • Teff “ 18700 350 K, log g “ 3.16 0.1, Vrot “ 128 km s´1
M “ 12 0.5Md, R “ 15 1.5Rd, age = 18 2 Myr • but high radial velocity Vrad “ 443 1 km s´1 !
Position of HD272791
Schaffenroth 2015
• birthplace at the outskirts of the galaxy • current position in the halo, „ 10 kpc under the disk • 3D velocity from Vrad, proper motions and distance 22 4 kpc Ñ galactic restframe velocity 750 140 km s´1
• unbound to the galaxy
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Schaffenroth et al., in prep.
Monte Carlo simulation using formula from Tauris & Takens 1998 • post common-envelope system with separation of 12 Rd • primary is a Wolf-Rayet star with 20 Md, turns into a BH • ejection in direction of the Galactic rotation
B star abundances and gradients
Nieva et al. 2012
ATLAS 9 LTE model
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Spectrum of HD271791 in the Optical
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Spectrum of HD271791 in the Optical
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Spectrum of HD271791 in the Optical
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Spectrum of HD271791 in the Optical
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Spectrum of HD271791 in the Optical
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Spectrum of HD271791 in the Optical
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Spectrum of HD271791 in the Optical
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Spectrum of HD271791 in the Optical
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Abundances of HD271791
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Comparison with theoretical SN/HN calculations
Schaffenroth 2015 Ñ enhancement of the α elements Ñ HD271791 was ejected by a supernova ex- plosion Ñ heavier elements only visible in the UV!
assumptions: • wind accretion in progenitor system
• nucleosynthesis yields by Nomoto et al. 2006
• 10 % accretion efficiency
• partial mixing of accreted material with unpolluted matter approximated by diffusion
Spectrum synthesis in the UV
Cu III
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• our spectrum synthesis in the optical well advanced and tested
• extension to the UV line forest to derive abundances of heavier elements
• implementing of line-lists for all lines with data in the literature
Elements with some available data
not included in the model
included in NLTE
included in LTE
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Abundances from the UV for several comparison stars
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Conclusions
• most extreme runaway known HD271791 – ejected by a core-collapse supernova in a very tight binary system
• enhancement of the α-elements seen in the optical spectrum
• simulations show the extreme velocities can be explained by the scenario
• extension of spectrum synthesis to the UV to derive abundances of heavier elements
• limiting factor: missing atomic data and model atoms
• many blends due to high rotational velocities
Future Plans
• improvement of the spectrum synthesis in the UV with more model atoms for the iron group
• decreasing of the abundance scatter in individual lines
• differential abundance analysis to derive the tiny contribution of the heavier elements to the stellar lines
• more realistic assumptions of expected abundance pattern and supernova ejecta accretion
Runaway Stars
Analysis method