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Magellanic cloud planetary nebula with suspected strong forbidden iron lines.
1Astronomy Department, University of California, Los Angeles, California 90024.
Summary
This study analyzes the Westerlund-Smith 25 nebula in the Large Magellanic Cloud, finding a normal helium abundance but depleted heavier elements compared to our galaxy. These findings offer insights into extragalactic chemical evolution.
Area of Science:
- Astronomy
- Astrophysics
- Spectroscopy
Background:
- The Westerlund-Smith 25 nebula in the Large Magellanic Cloud (LMC) is a high-excitation object.
- Previous studies suggest variations in elemental abundances in extragalactic nebulae.
Purpose of the Study:
- To determine the elemental abundances in the Westerlund-Smith 25 nebula.
- To compare these abundances with those in our galaxy and other LMC nebulae.
Main Methods:
- Spectroscopic observations using a vidicon detector at the Cerro Tololo 4-m telescopes.
- Analysis of prominent forbidden emission lines ([Ar IV], [Ne IV], [Ca V], [Fe V], [Fe VI], [Fe VII]).
Main Results:
- A nearly "normal" helium abundance was found.
- Significant depletions of nitrogen (N), oxygen (O), and neon (Ne) were observed relative to the Milky Way.
- Helium appears more abundant, oxygen depleted, and nitrogen, neon, and argon comparable when compared to other LMC diffuse nebulae or H II regions.
- Sulfur abundance remains uncertain.
- Gaseous iron is more abundant than in typical planetary nebulae.
Conclusions:
- The Westerlund-Smith 25 nebula exhibits a distinct chemical composition compared to galactic nebulae.
- Elemental abundance patterns in the LMC may differ from those in the Milky Way, particularly for heavier elements.
- Further investigation is needed to confirm sulfur abundance and refine understanding of iron's role.