5.3. Abundance Results
Table 1 shows the results of applying this analysis to two bona fide intrinsic absorbers, namely, the za ze NALs in UM 675 (Hamann 1997; Hamann et al. 1997b) and the BALs in PG 1254+047 (Hamann 1998). The ionic column densities listed for both sources follow from direct integration of the apparent optical depths in the absorption line troughs (see Section 5.4 below). For UM 675, I adjusted the optical depths for a 50% coverage fraction in all of the metal ions and 100% coverage in HI. These adjustments do not change the derived HI column density, but the columns in the metal ions are roughly doubled. Note that the relatively low column densities in both systems (and the lack of a significant HI Lyman edge in UM 675) support the assumption of low continuum optical depths in the calculations above (Hamann 1997).
The ionization states in both cases are uncertain, so the table lists the conservatively low metal-to-hydrogen ratios, [M/H]p, assuming each metal line forms at the peak in its f (Mi) curve. The table also lists the firm lower limits, [M/H]min, derived from the minimum correction factors in Hamann (1997). The uncertainties in the table indicate the range of values derived for a reasonable range of ionizing continuum shapes. Keep in mind that these M/H estimates are limiting values that need not agree between ions. The [M/H] quantities are typically higher (and more realistic) for the low-ionization metals because the HI lines tend to form with these ions. The [M/H]p results provide our best guess at the actual abundances in UM 675; the overall metallicity is roughly twice solar (Z 2 Z) based on [C/H], with nitrogen several times more enhanced. The result for Z Z is typical of za ze NALs and occurs without exception in the intrinsic systems (Petitjean et al. 1994, Wampler et al. 1993, Tripp et al. 1996 and 1997, Savage & Tripp 1998, Hamann 1997, Hamann et al. 1997c). The NALs thus support the independent evidence from BELs for Z Z and enhanced nitrogen (Section 4 above).
The derived BAL column densities lead to much more extreme abundances, with [Si/H] 1.8 and [P/C] +2.2 in PG 1254+047. These results are roughly typical of BALs (Turnshek 1988, Turnshek et al. 1996, Korista et al. 1996, Junkkarinen et al. 1997, Hamann 1997). They are too extreme to be compatible with well-mixed interstellar gas enriched by normal stellar populations. Shields (1996) noted that the BAL estimates are similar to the abundances measured in novae. He proposed that novae might dominate the enrichment of BAL regions if the nova rates are enhanced by white dwarfs gaining mass as they plunge through the QSO accretion disk. However, this unusual mechanism is not needed because there appear to be serious problems with the BAL column densities.