Fe VII lines in the spectrum of RR Telescopii

Free access article

Issue		A&A Volume 432, Number 2, March III 2005


Page(s)		665 - 670
Section		Stellar atmospheres
DOI		http://dx.doi.org/10.1051/0004-6361:20042033

A&A 432, 665-670 (2005)
DOI: 10.1051/0004-6361:20042033

Fe VII lines in the spectrum of RR Telescopii

P. R. Young¹, K. A. Berrington² and A. Lobel³

¹ CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK
e-mail: p.r.young@rl.ac.uk
² School of Science and Mathematics, Sheffield Hallam University, Sheffield S1 1WB, UK
³ Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138, USA

(Received 21 September 2004 / Accepted 15 November 2004 )

Abstract
Thirteen transitions within the ground $3{\rm d}^2$ configuration of Fe VII are identified in ultraviolet and optical spectra of the symbiotic star RR Telescopii obtained with the STIS instrument of the Hubble Space Telescope. The line fluxes are compared with theoretical data computed with the recent atomic data of Berrington et al., and high resolution optical spectra from VLT/UVES are used to identify blends. Seven branching ratios are measured, with three in good agreement with theory and one affected by blending. The $\lambda$ 5277/ $\lambda$ 4943 branching ratio is discrepant by > $3\sigma$ , indicating errors in the atomic data for the $\lambda$ 5277 line. A least-squares minimization scheme is used to simultaneously derive the temperature, T, and density, $N_{\rm e}$ , of the RR Tel nebula, and the interstellar extinction, E(B-V), towards RR Tel from the complete set of emission lines. The derived values are: $\log\,T/{\rm K}=4.50$ $\pm$ 0.23, $\log\,N_{\rm e}/{\rm cm}^{-3}=7.25$ $\pm$ 0.05, and $E(B-V)\le 0.27$ . The extinction is not well-constrained by the Fe VII lines, but is consistent with the more accurate value E(B-V)=0.109^+0.052_-0.059 derived here from the Ne V $\lambda$ 2974/ $\lambda$ 1574 ratio in the STIS spectrum. Large differences between the K. A. Berrington et al. electron excitation data and the earlier F. P. Keenan & P. H. Norrington data-set are demonstrated, and the latter is shown to give worse agreement with observations.

Key words: stars: binaries: symbiotic -- stars: individual: RR Telescopii -- ultraviolet: stars -- atomic data

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