Si II emission line diagnostics

• Published in: Monthly notices of the Royal Astronomical Society Vol. 253; no. 1; pp. 123 - 128
• Main Authors: Judge, P. G., Carpenter, K. G., Harper, G. M.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford University Press 01.11.1991; Blackwell Science
• Subjects: Astronomy; Astrophysics; Atomic processes and interactions; Earth, ocean, space; Exact sciences and technology; Fundamental aspects of astrophysics; Fundamental astronomy and astrophysics. Instrumentation, techniques, and astronomical observations; Data analysis; Ultraviolet radiation; Flux density; Atomic process; Data table; Numerical simulation; Cool star; Emission line; Electron density; Silicon II
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/253.1.123

Ratios of Si II UV emission lines in a variety of objects are compared with computations based upon recently published collisional data of Dufton & Kingston. We analyse a high-quality spectrum of α Tau (K5 III) obtained by Carpenter et al. using the G270M mode of the GHRS on the Hubble Space Telescope, in addition to high-dispersion data from Skylab and IUE. Agreement betwen observation and theory is satisfactory for most lines with the exception of ratios within the $3{s}^{2}3p^{2}P^{0}\rightarrow 3s3{p}^{2}\,^{4}P\,(\text{UV}\,0.01)$ multiplier near 2335 Å. A blend with a line of Ni II accounts partially for the discrepancies and solves a problem with Si II) emission measures. However, a further problem remains which suggests that the computed collision strengths for the transitions $3s^{2} 3p ^{2}P^{0}_{1/2,3/2}\rightarrow 3s3p^{2}\,^{4}P_{5/2}$ may be too large by a factor of about 1.5.