Astronomy & Astrophysics

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Issue		A&A Volume 419, Number 1, May III 2004
Page(s)		215 - 224
Section		Interstellar and circumstellar matter
DOI		10.1051/0004-6361:20035647

A&A 419, 215-224 (2004)
DOI: 10.1051/0004-6361:20035647

Identification of emission lines in the low-ionization strontium filament near Eta Carinae

H. Hartman¹, T. Gull², S. Johansson¹, N. Smith³ and HST Eta Carinae Treasury Project Team³

¹ Atomic Astrophysics, Lund Observatory, Lund University, Box 43, 221 00 Lund, Sweden
² Laboratory for Astronomy and Solar Physics, Code 681, Goddard Space Flight Center, Greenbelt, MD 20771, USA
³ CASA, 389 UCB, University of Colorado, Boulder, CO 80309, USA

(Received 7 November 2003 / Accepted 10 February 2004)

Abstract
We have obtained deep spectra from 1640 to 10 100 Å with the Space Telescope Imaging Spectrograph (STIS) of the strontium filament, a largely neutral emission nebulosity lying close to the very luminous star Eta Carinae and showing an uncommon spectrum. Over 600 emission lines, both permitted and forbidden, have been identified. The majority originates from neutral or singly-ionized iron group elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni). Sr is the only neutron capture element detected. The presence of Sr II, numerous strong $\ion{ii}$ and $\ion{V}{ii}$ lines and the dominance of $\ion{i}$ over $\ion{ii}$ are notable discoveries. While emission lines of hydrogen, helium, and nitrogen are associable with other spatial structures at other velocities within the Homunculus, no emission lines from these elements correspond to the spatial structure or velocity of the $\ion~$ filament. Moreover, no identified $\ion~$ filament emission line requires an ionization or excitation energy above approximately 8 eV. Ionized gas extends spatially along the aperture, oriented along the polar axis of the Homunculus, and in velocity around the strontium filament. We suggest that the strontium filament is shielded from ultraviolet radiation at energies above 8 eV, but is intensely irradiated by the central star at wavelengths longward of 1500 Å.

Key words: line: identification -- stars: circumstellar matter -- stars: kinematics -- stars: individual: Eta Carinae

Offprint request: H. Hartman, henrik.hartman@astro.lu.se

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