The Binarity of η Carinae Revealed from Photoionization Modeling of the Spectral Variability of the Weigelt Blobs B and D
Abstract
We focus on two Hubble Space Telescope Space Telescope Imaging Spectrograph (HST STIS) spectra of the Weigelt blobs B and D, extending from 1640 to 10400 Å, one recorded during the 1998 minimum (1998 March) and the other recorded in 1999 February, early in the following broad maximum. The spatially resolved spectra suggest two distinct ionization regions. One structure is the permanently low-ionization cores of the Weigelt blobs B and D, located several hundred AU from the ionizing source. Their spectra are dominated by emission from H I, [N II], Fe II, [Fe II], Ni II, [Ni II], Cr II, and Ti II. The second region, relatively diffuse in character and located between the ionizing source and the Weigelt blobs, is more highly ionized with emission from [Fe III], [Fe IV], N III], [Ne III], [Ar III], [Si III], [S III], and He I. Through photoionization modeling, we find that the radiation field from the more massive B-star companion supports the low-ionization structure throughout the 5.54 yr period. The radiation field of an evolved O star is required to produce the higher ionization emission seen across the broad maximum. This emission region is identified with slow-moving condensations photoionized by the O star and located in the extended mass flow emanating from the B-star primary. Comparison between the models and observations reveals that the high-ionization region is physically distinct (nH~107 cm-3 and Te~104 K) from the B and D blobs (nH~106 cm-3 and Te~7000 K).
Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.- Publication:
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The Astrophysical Journal
- Pub Date:
- May 2005
- DOI:
- 10.1086/429400
- arXiv:
- arXiv:astro-ph/0502106
- Bibcode:
- 2005ApJ...624..973V
- Keywords:
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- Atomic Data;
- ISM: H II Regions;
- ISM: Individual: Name: η Carinae;
- Line: Formation;
- Line: Identification;
- Astrophysics
- E-Print:
- 35 Pages, 5 figures. Accepted for the Astrophysical Journal