An Introduction to PlanetaryNebulae

Ryan Yamada6 March 2006

Overview

• Properties of Planetary Nebulae• Planetary Nebulae in IR• Observations with previous missions (ISO)

Introduction

• End-product of evolution of 1-8 solar mass stars• Detected by direct imaging or objective prism• ~1500 known; estimated > 23,000 in Milky Way• L ~ 104 Lsun, Tgas ~ 50,000 K for youngest Pne,

Tstar ~ 30,000 -100,000 K• Lifetime ~ 35,000 years

evolution• RGB

– Contraction of He core,degenerate for M < 2 Msun

– H-burning shell expands,outer convection zonedevelops

– Mass loss from stellar wind• Horizontal Branch

– He flash, T ~ 108 K• AGB

– C,O rich core– Outer envelope of AGB star

ejected

Location of PNe in Galaxy

Morphology

• Central hole due to high stages of ionizationof central gas

• Shape and latitude correlated!– Bipolar: within 3 degrees of galactic plane (A)– Elliptical: within 5 degrees of plane (F)– Spherical: within 12 degrees of plane (G)

Details of ejection depend on progenitor mass(and possibly rotation and magnetic field)

Circular/EllipticalNGC 6751 (“Dandelion Nebula”)Abell 39

Bipolar OutflowsM2-9 (“Twin Jet Nebula”)MZ 3 (“Ant Nebula”)

NGC 6543

Properties

• Ions of highest ionization potential have lowestmeasured expansion

• Degree of ionization decreases outward from star• Expansion velocity increases outward

– Gases ejected over a short period of time with a rangeof velocities, OR

– Uniform expansion modified by hydrodynamical forces(radiation pressure or expansion of hot gas into avacuum)

Why IR?

• Optical and UV only show lines of a fewionization stages of an element, while IRhas many lines

• IR lines originate from levels close toground, so they are not so sensitive totemperature - good for e- density!

• IR lines less affected by extinction

NGC 7027(Bernard-Salas et al., 2001)

Photo: H. Bond (ST Sci)

NGC 7027 ISO-SWS Spectra

NGC 7027

• F(Hβ) = 1.27 x10-9 erg cm-2 s-1

• ρe- = 50,000 cm-3 (assumed)• Te = 15,500 K

Abundances

Np = density of ionized HNe = electron densityIion/IHβ = normalized intensity of ionic lineλul = wavelength of lineλHβ = wavelength of HβαHβ = effective recombination coeff for Hβ

Aul = Einstein spontaneous transition rate

Conclusions

• Ionization correction factors based on similaritiesin ionization potential– Off by a lot! Ne/O different from Ne++/O++ by 58%,

N/O different from N+/O+ by 32%• Ne and Te correlated, consistent with simple

picture• No correlation between Ne and ions of high IP

PDRs in PNe

• Not all PNe have PDRs• Mass of ionized material ~ 10 times smaller

than mass of neutral and molecular mass• Gas in PDRs cool using far-infrared fine

structure lines from [C II], [O I], [Si II],[C I] and CO and H2.

PDRs (Bernard-Salas & Tielens, 2005)

• Observed 9 PNe (NGC 7027, NGC 6153,BD+30 3639, NGC 3918, Hb 5, Mz 3, K3-17, NGC 6543, NGC 6302)

• FIR-derived distances and luminositiesderived using H, He II Zanstra temperatures

• Best agreement with other observationsusing H temperatures (for those withcomplex geometries)

PDRs (Bernard-Salas & Tielens, 2005)

• PDR models useful for distinguishingbetween PDRs in different circumstellarenvironments (including PNe)

• Cannot be used to reliably derive thedensity in PNe because actual densitiesexceed critical densities

• Need to use different species with highercritical densities (e.g. high-level CO lines)

Summary

• IR observations of PNe can better determineelectron density, temperature

• PNe provide a way to probe nucleosynthesisin AGB stars

• Useful for testing models for outflows,plasmas, PDRs…

References

• Osterbrock and Ferland. Astrophysics ofGaseous Nebulae and Active Galactic Nuclei(Second Edition), 2006

• J. Bernard-Salas. Physica and Chemistry ofGas in Planetary Nebulae, Dissertation, 2003.

• Bernard Salas et al., A&A 367, 949 (2001)• Bernard-Salas & Tielens, A&A 431, 523

(2005)