Studying the variation of the fine-structure constant using emission-line multiplets.
GRUPE D., PRADHAN A.K. and FRANK S.
Abstract (from CDS):
As an extension of the method by Bahcall and coworkers to investigate the time dependence of the fine-structure constant, we describe an approach based on new observations of forbidden-line multiplets from different ionic species. We obtain optical spectra of fine-structure transitions in [Ne III], [Ne V], [O III], [O I], and [S II] multiplets from a sample of 14 Seyfert 1.5 galaxies in the low-z range 0.035<z<0.281. Each source and each multiplet is independently analyzed to ascertain possible errors. Averaging over our sample, we obtain a conservative value α2(t)/α2(0)=1.0030±0.0014. However, our sample is limited in size and our fitting technique simplistic, as we primarily intend to illustrate the scope and strength of emission-line studies of the time variation of the fine-structure constant. The approach can be further extended and generalized to a ``many-multiplet emission-line method'' analogous in principle to the corresponding method using absorption lines. With that aim, we note that the theoretical limits on emission-line ratios of selected ions are precisely known and provide well-constrained selection criteria. We also discuss several other forbidden and allowed lines that may constitute the basis for a more rigorous study using high-resolution instruments on the next generation of 8 m class telescopes.
Atomic Data - Cosmology: Miscellaneous - Galaxies: Active