XPN project

PROJECT SUMMARY
Planetary Nebulae (PN) are luminous emission line objects which are abundantly found with beautiful appearance throughout the Milky Way. In other galaxies, at distances beyond the LMC/SMC, extragalactic Planetary Nebulae (XPN) appear as point-like objects, which are relatively easy to detect with narrow-band imaging techniques. They have been found in large numbers out to the distance of galaxies in the Virgo Cluster, and also in the intracluster space of Virgo. Recently, intracluster XPN were even discovered as far away as in the Coma Cluster. Because of their bright emission lines, XPN are visible with good contrast with respect to the continuum light of the underlying population of unresolved stars in a galaxy, which is why they have become increasingly interesting as individually resolved tracers for low to intermediate mass (i.e. old) stellar populations - which otherwise can be studied only in the integrated light of very many unresolved individual stars.
The XPN Physics project attempts to verify, whether - and if yes: to which extent -, XPN are good probes for measuring chemical abundances from their parent stellar population.

THE TEAM

-Prof. Dr. Detlef Schönberner
-Dr. Matthias Steffen
-Dr. Martin M. Roth
-Dr. Christer Sandin
-Dr. Ana Monreal Ibero (previous member)
-Dr. Andreas Kelz

 

WORK PLAN
I. Theory
-Comparison of Cloudy and CORONA codes
-Extending CORONA
-Study of typical abundance patterns
-Modified treatment of central star wind
-Include recombination lines of metal ions
-Initial conditions of density structure
-Central star models
-Special case of WR central stars
-Model grid
-Plasma diagnostic analysis of model grid with common tools  
-Temperature fluctuations
Impact on [O III] luminosity function
II. Observation
-Reference data base of line intensities from known objects
-Expansion velocities of galactic halo and bulge PNe
-Expansion velocities in LMC/SMC
-Spectrophotometry of Milky Way Halo PNe
-XPN in local group dwarf galaxies
-XPN in M31 and M33
-XPN in Virgo cluster galaxies, and intracluster objects

 

PROBLEMS


PNe are ionised, expanding circumstellar shells around a dying star. Their beautiful and striking visual appearance is created by photoionisation of the circumstellar gas from the hot central star, which is emitting plenty of high-energy UV photons. Likewise, the hot stellar wind and the occurrency of shock waves plays an important role in shaping the ionized nebula. Conventional diagnostic analyses of PNe often neglect the time-dependence of these two important mechanisms, treating the nebula as a homogeneous and static object in energy and ionization equilibrium. In "XPN Physics", we use time-dependent hydrodynamical simulations in concert with selected observations to assess systematically, in how far common plasma diagnostic techniques are effected by density structure, dynamical evolution, and metallicities. This project is expected to yield important clues to justify qualitatively and quantitatively, in how far XPN are indeed useful probes for the study of resolved stellar populations in galaxies.
Important questions to address by a detailed hydrodynamic treatment of the PN evolution, confronted with new and existing observational data:
How are structure and expansion of a PN determined by its metallicity?
What is the influence of the extremely strong winds from [WC] central stars?
Does a minimum metallicity exist, necessary for the formation of a PN?
What are the quantitative differences if hydrodynamic simulations are used for the plasma diagnostic instead of static photoionization codes?
Which ionization factors follow from hydrodynamic models?

xpn.jpg

 

-Extragalaktische Nebel

 

 

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