Diffuse Far-Ultraviolet Observations of the Taurus Region

Abstract

© 2006 The American Astronomical Society. All rights reserved. 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 A v > 1.5, obscures the background diffuse FUV radiation, while scattered FUV radiation is seen in and beyond the halo region, where A v < 1.5. The total intensity of H 2 fluorescence in the cloud halo is I H2 6.5 × 10 4 photons cm -2 s -1 sr -1 in the 1370-1670 Å wavelength band. A synthetic model of the H 2 fluorescent emission fits the present observation best with a hydrogen density n H = 50 cm -3 , H 2 column density N(H 2 )= 0.8 × 10 20 cm -2 , and incident FUV intensity I UV = 0.2. H 2 fluorescence is not seen in the core, presumably because the required radiation flux to induce fluorescence is unable to penetrate the core region.