High-resolution Hubble Space Telescope STIS spectra of CI and CO in the beta Pictoris circumstellar disk

High-resolution far-ultraviolet (FUV) echelle spectra showing absorption fe atures arising from C I and CO gas in the beta Pic circumstellar (CS) disk were obtained on 1997 December 6 and 19 using the Space Telescope Imaging S pectrograph (STIS). An unsaturated spin-forbidden line of C I at 1613.376 A ngstrom not previously seen in spectra of beta Pic was detected, allowing f or an improved determination of the column density of C I at zero velocity relative to the star (the stable component), N(P-3) = (2-4) x 10(16) cm(-2) Variable components with multiple velocities, which are the signatures of infalling bodies in the beta Pie CS disk, are observed in the C I lambda la mbda 1561 and 1657 multiplets. Also seen for the first time were two lines arising from the metastable D-1 level of carbon at 1931 Angstrom and 1463 A ngstrom. The results of analysis of the CO A-X (0-0), (1-0), and (2-0) band s are presented, including the bands arising from (CO)-C-13, with much bett er precision than has previously been possible, as a result of the very hig h resolution provided by the STIS echelle gratings. Only stable CO gas is o bserved, with a column density N(CO)= (6.3 +/- 0.3) x 10(14) cm(-2). An unu sual ratio of the column densities of (CO)-C-12 to (CO)-C-13 is found (R = 15 +/- 2). The large difference between the column densities of C I and CO indicates that photodissociation of CO is not the primary source of C I gas in the disk, contrary to previous suggestion.