Diffuse Far-ultraviolet Observations of the Taurus Region

Diffuse far-ultraviolet (FUV: 1370–1670 Å) flux from the Taurus molecular cloud region has been observed with the SPEAR/FIMS imaging spectrograph. An FUV continuum map of the Taurus region, similar to the visual extinction maps, shows a distinct cloud core and halo region. The dense cloud core, where the visual extinction is Av > 1.5, obscures the background diffuse FUV radiation, while a scattered FUV radiation is seen in and beyond the halo region where Av < 1.5. The total intensity of H2 fluorescence in the cloud halo is IH2 = 6.5 ×10 4 photons cm s sr in the 1370–1670 Å wavelength band. A synthetic model of the H2 fluorescent emission fits the present observation best with a hydrogen density nH = 50 cm , H2 column density N(H2) = 0.8 ×10 cm, and an incident FUV intensity IUV = 0.2. H2 fluorescence is not seen in the core presumably because the required radiation flux to induce fluorescence is unable to penetrate the core region. Subject headings: ISM: individual (Taurus) — ISM: lines and bands — ultraviolet: ISM