FIRST DETECTION OF KRYPTON AND XENON IN A WHITE DWARF

• Published in: Astrophysical journal. Letters Vol. 753; no. 1; pp. 1 - 5
• Main Authors: Werner, Klaus, Rauch, Thomas, RINGAT, ELLEN, Kruk, Jeffrey W
• Format: Journal Article
• Language: English
• Published: United States 01.07.2012
• Subjects: ASTROPHYSICS; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BINARY STARS; CAPTURE; DIFFUSION; ELEMENT ABUNDANCE; Evolutionary; FAR ULTRAVIOLET RADIATION; GALLIUM; HELIUM; HYDROGEN; IRON; KRYPTON; MOLYBDENUM; NEUTRON REACTIONS; NUCLEAR PHYSICS AND RADIATION PHYSICS; NUCLEOSYNTHESIS; PHOTOSPHERE; Stars; Ultraviolet; ULTRAVIOLET SPECTRA; WHITE DWARF STARS; XENON
• ISSN: 2041-8205; 2041-8213
• DOI: 10.1088/2041-8205/753/1/L7

We report on the first detection of the noble gases krypton (Z = 36) and xenon (54) in a white dwarf. About 20 Kr VI-VII and Xe VI-VII lines were discovered in the ultraviolet spectrum of the hot DO-type white dwarf RE 0503-289. The observations, performed with the Far Ultraviolet Spectroscopic Explorer, also reveal highly ionized photospheric lines from other trans-iron group elements, namely Ga (31), Ge (32), As (33), Se (34), Mo (42), Sn (50), Te (52), and I (53), from which gallium and molybdenum are new discoveries in white dwarfs, too. For Kr and Xe, we performed an NLTE analysis and derived mass fractions of log Kr = -4.3 + or - 0.5 and log Xe = -4.2 + or - 0.6, corresponding to an enrichment by factors of 450 and 3800, respectively, relative to the Sun. The origin of the large overabundances is unclear. We discuss the roles of neutron-capture nucleosynthesis in the precursor star and radiation-driven diffusion. It is possible that diffusion is insignificant and that the observed metal abundances constrain the evolutionary history of the star. Its hydrogen deficiency may be the consequence of a late helium-shell flash or a binary white dwarf merger.