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Paper: Is the Distribution of Nitrogen in the Atmospheres of Hot DA White Dwarfs Inhomogeneous?
Volume: 334, 14th European Workshop on White Dwarfs
Page: 181
Authors: Chayer, P.; Vennes, S.; Dupuis, J.
Abstract: Unusually high nitrogen abundances in the atmospheres of the hot DA white dwarfs GD 659, RE J1032+532, and RE J1614-085 have been reported in the literature. Because of the strength of the NV λ1240 doublet and the absence of nitrogen absorption in extreme ultraviolet (EUV) spectra, it has been proposed that the nitrogen abundance as a function of depth should vary: The abundance should be low in deeper regions where the EUV continuum is formed, so that no photoionization edges of NIII, NIV, nor NV would be detected in that spectral range, while the abundance should be much higher in the upper layers of the atmosphere where the NV doublet is formed. By using NLTE model atmospheres and combining EUVE and HST observations, we reexamine the question, and show that our new nitrogen abundances based on the NV λλ 1238 and 1242 doublet do not support the stratified nitrogen model.
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