FUSE observations of the Blue Compact Dwarf Galaxy Mrk 59

New FUSE far-UV spectroscopy of the nearby metal-deficient (Z⊙/8) cometary Blue Compact Dwarf (BCD) galaxy Markarian (Mrk) 59 is discussed. The data are used to investigate element abundances in its interstellar medium. The H i absorption lines are characterized by narrow cores which are interstellar in origin and by broad wings which are stellar in origin. The mean interstellar H i column density is ∼ 7 × 10 cm in Mrk 59. No H2 lines are seen and N(H2) is . 10 cm at the 10 σ level. The lack of diffuse H2 is due to the combined effect of a strong UV radiation field which destroys the H2 molecules and a low metallicity which leads to a scarcity of dust grains necessary for H2 formation. PCygni profiles of the S vi 933.4, 944.5 Å and O vi 1031.9, 1037.6 Å lines are seen, indicating the presence of very hot O stars and a stellar wind terminal velocity of ∼ 1000 km s. By fitting the line profiles with multiple components having each a velocity dispersion b = 7 km s and spanning a radial velocity range of 100 km s, some of which can be saturated, we derive heavy element abundances in the neutral gas. We find log N(O i)/N(H i) = –5.0±0.3 or [O i/H i] = –1.5 for the neutral gas, about a factor of 10 below the oxygen abundance of the supergiant H ii region, implying self-enrichment of the latter.