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D. G. Smillie (Space and Atmospheric Physics Group, Blackett Lab., Imperial College, UK; Harvard-Smithsonian CfA), J. C. Pickering (Space and Atmospheric Physics Group, Blackett Lab., Imperial College, UK), P. L. Smith (Harvard-Smithsonian CfA)
Exciting new astrophysical spectra provided by both space-based (such as STIS, Hubble) and ground-based spectrographs (such as HIRES, Keck-1 telescope) are unable to be fully interpreted due to deficiencies in the database of laboratory measured atomic data such as transition wavelengths and oscillator strengths. The transition elements, particularly the Iron (3d) group, are extremely important for stellar astrophysics providing much of the observed stellar opacity, and the doubly ionized species dominate the spectra of hot (B-type) stars [1]. Transition wavelengths with uncertainties of ~1:107 and oscillator strengths with uncertainties of ~10% are required to fully interpret the astrophysical spectra.
At Imperial College, we use a Penning discharge lamp with our unique Fourier transform spectrometer (FTS) [1] capable of measurements from the visible to the VUV (down to 135nm) at high resolution (typical wavenumber uncertainty ~1:108). These measurements are supplemented by IR FTS spectra and grating spectra (beyond the 135nm limit) taken at the National Institute of Standards and Technology (NIST), USA. The spectra are analyzed to provide intensity and wavenumber calibrated linelists. This allows term analysis (calculating energy levels from the measured transition line wavelengths) and branching ratios (which can be combined with level lifetimes to produce oscillator strengths) to be determined.
FTS measurements of Fe III in the UV and IR have been completed at Imperial and NIST and grating measurements are planned at NIST to complete the Fe III work. Similarly, Co III and Cr III measurements are currently ongoing at both Imperial and NIST. After completion of the analysis, the data will be disseminated to atomic databases (such as the NIST Atomic Spectra Database and the Vienna Atomic Line Database).
This work is supported in part by NASA Grant NAG5-12668, PPARC and the Royal Society of the UK.
[1] J. C. Pickering, Vibrational Spectroscopy, 29, 27-43 (2002)
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.