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LSV 46°21: The Central White Dwarf Star of Sh 2-216

The central star of Sh 2-216 (source of PN) is the white dwarf WE 0441+467 or LSV 46°21. Interstellar extinction often inhibits far-ultraviolet (FUV) spectral analysis of such stars given the planetary envelope, but NASA’s Far Ultraviolet Spectroscopic Explored (FUSE) satellite was used to examine many FUV sources over its lifetime (1999 – 2007). I’ve indicated the position of LSV 46°21 in my image as it’s quite a bright WD. I’ve also attached a link to the paper by Thomas Rauch, Klaus Werner, Marc Ziegler, Jeffrey W. Kruk and Cristina M. Oliveira “Spectral Analysis of Central Stars of Planetary Nebulae” which presents two very interesting atmospheric models, one with TMAP and one with OWENS.

Section 2 is wort a read as it presents a nice overview of the analysis techniques and typical  compositions of small, hot central stars. White dwarfs are fascinating objects with very complex elemental and molecular compositions. Fig. 4 of the paper, for instance, is a plot of the relative abundance of elements in LSV 46°21’s photosphere. The graph is in two parts, but the upper part plots abundance versus mass fraction. You can see the high abundance of heavy metals relative to the solar abundance values, obviously indicating significant dredge up.   

https://arxiv.org/pdf/0709.0041

 

White Dwarfs:

A white dwarf is the compact stellar remnant produced by the evolution of low- to intermediate-mass stars (≈0.8–8 solar masses), such as the Sun. It represents the final evolutionary stage for the vast majority of stars in the universe.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Formation and Evolution

During the main-sequence phase, a star generates energy through hydrogen fusion in its core. Once core hydrogen is exhausted, the star evolves into a red giant, undergoing shell burning and substantial mass loss. The outer layers are expelled into the surrounding interstellar medium, frequently forming a planetary nebula. The residual core—no longer capable of sustaining nuclear fusion—contracts under gravity until it is supported by electron degeneracy pressure, producing a white dwarf.

Physical Properties

White dwarfs are characterized by:

• High density: Masses comparable to that of the Sun are confined within a radius similar to that of Earth, yielding average densities on the order of 106 to 107 g/cm3

• Degenerate matter: Their internal structure is supported by quantum mechanical degeneracy pressure rather than thermal pressure.
• Composition: Most consist primarily of carbon and oxygen, though helium or oxygen–neon cores are possible depending on progenitor mass.
• High initial temperature: Newly formed white dwarfs can have surface temperatures exceeding 100,000 K.
• Absence of fusion: They radiate residual thermal energy and gradually cool over billions of years.

White dwarfs obey an inverse mass–radius relation: more massive white dwarfs have smaller radii. Their maximum stable mass is limited by the Chandrasekhar limit (approximately 1.4 solar masses), beyond which electron degeneracy pressure can no longer counteract gravitational collapse.

Solar Evolution

Stellar evolution models predict that the Sun will evolve into a red giant in approximately 5 billion years and ultimately leave behind a carbon–oxygen white dwarf.

 

Location of Sh 2-216

Location of Sh 2-216 Central Star (CS), the White Dwarf WE 0441+467 or LSV 46°21

Astrophysics News Stellar Evolution LSV 46 21 Star Forming Westerhout 5

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