Fe I in the β Pictoris circumstellar gas disk - I. Physical properties of the neutral iron gas A. Vidal-Madjar, F. Kiefer, A. Lecavelier des Etangs, V. Bourrier, D. Ehrenreich, R. Ferlet, G. Hébrard and P. A. Wilson A&A, 607 (2017) A25 Published online: 31 October 2017 DOI: 10.1051/0004-6361/201630040