Year: 2005
Type: article
Abstract: 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 α 2 ( t )/α 2 (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.
Source: The Astronomical Journal
DOI: 10.1086/430886
Authors: Dirk Grupe, Anil K. Pradhan, Stephan Frank
Institutions: Pennsylvania State University, The Ohio State University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
Funder: National Science Foundation
OpenAlex ID: W2005864572