IUE observation of strong UV absorption in the spectrum of the C2 white dwarf ion of LP 145-141.

Abstract

An absorption feature of exceptional strength has been observed by IUE around 1900 Å in the spectrum of the cool (7500 K) degenerate "λ467O" or "C₂" star LP 145-141. Molecule formation is shown to be favoured in helium-rich, high pressure white dwarf atmospheres, with CO, C₂ or O₂ dominant, depending on the He/C and C/O ratios (Table 1). The Schunann-Runge bands of O₂ should be extremely strong if C/O is solar, or, causing complete absorption beyond 2000 Å. However, since in the observed spectrum there is flux present not only around 1800 but also at 1500 Å, the absorption is more probably due to a hitherto unknown dissociation from the v" = 0 and 1 vibration level of ³π_u triplet ground state of C₂.