THE OPTICAL WIND LINE VARIABILITY OFηCARINAE DURING THE 2009.0 EVENT

Abstract

We report on high-resolution spectroscopy of the 2009.0 spectroscopic event of η Carinae collected via SMARTS observations using the CTIO 1.5 m telescope and echelle spectrograph. Our observations were made almost every night over a two-month interval around the photometric minimum of η Car associated with the periastron passage of a hot companion. The photoionizing flux of the companion and heating related to colliding winds causes large changes in the wind properties of the massive primary star. Here we present an analysis of temporal variations in a sample of spectral lines that are clearly formed in the wind of the primary star. These lines are affected by a changing illumination of the flux of the secondary star during the periastron passage. We document the sudden onset of blueshifted absorption that occurred in most of the lines near or slightly after periastron, and we argue that these absorption components are seen when we view the relatively undisturbed wind of the foreground primary star. We present time series measurements of the net equivalent width of the wind lines and of the radial velocities of the absorption trough minima and the emission peak midpoints. Most lines decrease in emission strength around periastron, and those high excitation lines formed close to the primary exhibit a red-ward velocity excursion. We show how these trends can be explained using an illuminated hemisphere model that is based on the idea that the emission originates primarily from the side of the primary facing the hot companion.

Tov∞and beyond! The He i absorption variability across the 2014.6 periastron passage of η Carinae

“…The first column shows the He I λ4713 spectra leading up to and including the minimum, followed by its progression towards recovery (phases 12.89-13.17). While the data were interpolated to display this, no interpolation happened with a gap of more than 6 d. The key exception is the large data gap that exists between HJD 2, 456,887.5 and 2,456,944.9 (phases 13.0110-13.0349 coverage near the periastron passage is exquisite, we were not able to have coverage as long into the event as Richardson et al (2015) had for the 2009 event due to constraints on the telescope and the season in which periastron occurred in 2014. Nevertheless, these datasets are compatible as they integrate light over both the same kinematical region, as well as use the same entrance fibre for the spectrographs.…”

“…First, we did a direct comparison of the equivalent width to that of Richardson et al (2015). This integrates the profile from −1000 to +2000 km s −1 , which also includes the Na I D emission and absorption profiles entirely.…”

“…The secondary star has wind parameters indicative of either a WR or extreme O star, with the strongest constraints coming from the X-ray analysis (Pittard & Corcoran 2002;Parkin et al 2009), which points toṀ 2 ≈ 10 −5 M ⊙ yr −1 and v ∞,2 ∼ 3000 km s −1 . η Car has a high eccentricity (∼ 0.9) and an orbital period of 5.54 yr, and many observational phenomena are modulated on this time-scale, such as the X-ray emission (Corcoran 2005, Corcoran et al 2010, multi-wavelength photometry (Fernández-Lajús et al 2003, 2010Whitelock et al 2004), He I narrow emission (Damineli et al 1997), the Hα and other wind line profile morphologies (Richardson et al 2010(Richardson et al , 2015, He II emission from near the colliding winds (Steiner & Damineli 2004;Teodoro et al 2012Teodoro et al , 2016Mehner et al 2015;Davidson et al 2015), and spatiallyextended forbidden line emission (Gull et al 2009(Gull et al , 2011Teodoro et al 2013). The 2003 periastron passage was well-documented thanks to a large Treasury program with the Hubble Space Telescope (HST) and Space Telescope Imaging Spectrograph (STIS) 1 .…”

“…The more recent 2009 periastron passage was observed in the optical only with ground-based facilities due to a failure of the STIS that was repaired during Servicing Mission 4, after the 2009 periastron passage. However, this event brought about one of the most intense ground-based spectroscopic data-sets compiled, both for the He II emission (Teodoro et al 2012), and the optical spectrum and wind transitions (Richardson et al 2015), including the strong Hα profile (Richardson et al 2010) that is often saturated in groundbased observations. The intense time-series collected will allow for many future theoretical studies about the detailed system parameters.…”

“…This would allow for several variations we observe to be accounted for in the η Car system. For example, Richardson et al (2015) developed a simple cartoon model for the variability of the He I lines that allows for some fraction of the emission to be formed in an ionised hemisphere of the primary wind facing the secondary star. When coupled with the expected radial velocity variations of the primary, the model does fairly well at explaining the variations, but future 3D SPH models with simplex might better account for the variability.…”