Eta Carinae Across the 2003.5 Minimum: Analysis in the Visible and Near-Infrared Spectral Region

Abstract

We present an analysis of the visible through near-infrared spectrum of Eta Carinae (η Car) and its ejecta obtained during the "η Car Campaign with the Ultraviolet and Visual Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT)." This is a part of larger effort to present a complete η Car spectrum, and extends the previously presented analyses with the Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS) in the UV (1240-3159 Å) to 10,430 Å. The spectrum in the mid-and near-UV is characterized by the ejecta absorption. At longer wavelengths, stellar wind features from the central source and narrow-emission lines from the Weigelt condensations dominate the spectrum. However, narrow absorption lines from the circumstellar shells are present. This paper provides a description of the spectrum between 3060 and 10,430 Å, including line identifications of the ejecta absorption spectrum, the emission spectrum from the Weigelt condensations and the P Cygni stellar wind features. The high spectral resolving power of VLT/UVES enables equivalent width measurements of atomic and molecular absorption lines for elements with no transitions at the shorter wavelengths. However, the ground-based seeing and contributions of nebular-scattered radiation prevent direct comparison of measured equivalent widths in the VLT/UVES and HST/STIS spectra. Fortunately, HST/STIS and VLT/UVES have a small overlap in wavelength coverage which allows us to compare and adjust for the difference in scattered radiation entering the instruments' apertures. This paper provides a complete online VLT/UVES spectrum with line identifications and a spectral comparison between HST/STIS and VLT/UVES between 3060 and 3160 Å.

The extended interacting wind structure of Eta Carinae

“…Studies of the STIS far‐UV and mid‐UV echelle spectra of η Car (Nielsen, Gull & Vieira Kober 2005) suggested a decline in highly excited atomic states beginning about 6 months before the X‐ray drop/spectroscopic minimum in 2003.5. Nielsen et al (2009) demonstrated that the major drop of the high‐ionization wind lines occurred with complementary growth of low‐ionization wind lines.…”

THE OPTICAL WIND LINE VARIABILITY OFηCARINAE DURING THE 2009.0 EVENT

“…Column 9 of Table 1 lists other features that blend with the line of interest and that complicate measurements. More complete listings of line blends can be found in the tables of Nielsen et al (2009) and Zethson et al (2012). Brief descriptions of the observed properties and variations follow in subsections for each line species.…”

Explaining the transient fast blue absorption lines in the massive binary system η Carinae

“…The complication is in that it is not simple to estimate the population of the relevant atomic state. Nielsen et al (2009) present high spectral resolution (R ∼ 80, 000) of the hydrogen Hδ line, as well as of the He I λ7067Å line, across the 2003.5 spectroscopic event. The He I λ7067Å line shows Doppler shift variations with the orbital phase that fit emission and absorption in the acceleration zone of the secondary wind (Kashi & Soker 2007, 2008b.…”

“…This may suggest that part of the absorption in the Hδ line is from the conical shell, in addition to an absorption component associated with the primary wind. Close to periastron (phase 1.001 in figure 5 of Nielsen et al 2009) the Hδ line shows an anomalous wide blue absorption wing, reaching velocities up to −v ≃ 900 km s −1 . At the closest observation times, phases 0.985 and 1.115, this broad absorption does not exist.…”

“…η Carinae (η Car) is a very massive stellar binary system, with an orbital period of 5.54 yr (Damineli 1996), as observed in all wavelengths (e.g. radio, Duncan & White 2003; IR, Whitelock et al 2004; visible, van Genderen et al 2006; Fernandez‐Lajus et al 2010; UV, Smith et al 2004; emission and absorption lines, Damineli et al 2008a,b; Nielsen et al 2009; X‐ray, Corcoran 2005; Corcoran et al 2010; Hamaguchi et al 2007). The high eccentricity of e ≃ 0.9 results in rapid changes in emission and absorption lines, as well as in the continuum, near each periastron passage.…”