Accretion by the Secondary in η Carinae During the Spectroscopic Event. I. Flow Parameters

Soker, Noam

doi:10.1086/497389

Cited by 40 publications

(126 citation statements)

References 38 publications

(103 reference statements)

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“…Soker et al have discussed in a series of papers an accretion model for η Car, which argues for the opposite effect that we just stated (see, e.g., Soker 2005, Kashi & Soker 2008a2009b). In their scenario, the companion accretes mass from η Car during periastron.…”

Section: Possible Scenarios For the Observed Changes In η Carmentioning

confidence: 55%

Near-infrared evidence for a sudden temperature increase in Eta Carinae

Mehner¹,

Ishibashi²,

Whitelock³

et al. 2014

A&A

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Aims. Eta Car's ultra-violet, optical, and X-ray light curves and its spectrum suggest a physical change in its stellar wind over the last decade. It was proposed that the mass-loss rate decreased by a factor of about 2 in the last 15 years. We complement these recent results by investigating the past evolution and the current state of η Car in the near-infrared (IR). Results. The long-term brightening trends in η Car's JHKL light curves were discontinuous around the 1998 periastron passage. After 1998, the star shows excess emission above the extrapolated trend from earlier dates, foremost in J and H, and the blueward, cyclical progression in its near-IR colors is accelerated. The near-IR color evolution is strongly correlated with the periastron passages. After correcting for the secular trend we find that the color evolution matches an apparent increase in blackbody temperature of an optically thick near-IR emitting plasma component from about 3500 to 6000 K over the last 20 years. Conclusions. We suggest that the changing near-IR emission may be caused by variability in optically thick bremsstrahlung emission. Periastron passages play a key role in the observed excess near-IR emission after 1998 and the long-term color evolution. We thus propose as a hypothesis that angular momentum transfer (via tidal acceleration) during periastron passages leads to sudden changes in η Car's atmosphere resulting in a long-term decrease in the mass-loss rate.

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Section: Possible Scenarios For the Observed Changes In η Carmentioning

confidence: 55%

Near-infrared evidence for a sudden temperature increase in Eta Carinae

Mehner¹,

Ishibashi²,

Whitelock³

et al. 2014

A&A

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“…1948−2009, the wind-wind shocks were disrupted near each periastron passage. That allowed temporary accretion onto the secondary star (Soker 2003(Soker , 2005Soker & Behar 2006). Less far-UV radiation during each event resulted in the highexcitation lines to become temporarily weaker.…”

Section: Resultsmentioning

confidence: 99%

Eta Carinae’s 2014.6 spectroscopic event: Clues to the long-term recovery from its Great Eruption

Mehner¹,

Davidson²,

Humphreys³

et al. 2015

A&A

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Aims. Every 5.5 years, η Car's light curve and spectrum change remarkably across all observed wavelength bands. These so-called spectroscopic events are most likely caused by the close approach of a companion. We compare the recent spectroscopic event in mid-2014 to the events in 2003 and 2009 and investigate long-term trends. Methods. Eta Car was observed with HST STIS, VLT UVES, and CTIO 1.5 m CHIRON for a period of more than two years in 2012−2015. Archival observations with these instruments cover three orbital cycles and the events of 2003.5, 2009.1, and 2014.6. The STIS spectra provide high spatial resolution and include epochs during the 2014 event when observations from most ground-based observatories were not feasible. The strategy for UVES observations allows for a multidimensional analysis, because each location in the reflection nebula is correlated with a different stellar latitude. Results. Important spectroscopic diagnostics during η Car's events show significant changes in 2014 compared to previous events.While the timing of the first He ii λ4686 flash was remarkably similar to previous events, the He ii equivalent widths were slightly larger, and the line flux increased by a factor of ∼7 Conclusions. The basic character of η Car's spectroscopic events has changed in the past two to three cycles. The ionizing UV radiation dramatically weakened during each pre-2014 event but not in 2014. The strengthening of He i and N ii emission and the weakening of the lower-excitation Hα and Fe ii wind features in our direct line of sight implies a substantial change in the physical parameters of the emitting regions. The polar spectrum at FOS4 shows fewer changes in the broad wind emission lines, which may be explained by the latitude-dependent wind structure of η Car. The quick and strong recovery of the He ii emission in 2014 supports a scenario, in which the wind-wind shock may not have completely collapsed as was proposed for previous events. As a result, the companion did not accrete as much material as in previous events. All this may be the consequence of just one elementary change, namely a strong decrease in the primary's mass-loss rate. This would mark the beginning of a new phase, in which the spectroscopic events can be described as an occultation by the primary's wind.

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“…Davidson (2002) suggested that strong instabilities near periastron might cause the shocked gas to radiatively cool, reducing the emission at high energies. Soker (2005) and Akashi et al (2006) suggested that Bondi-Hoyle accretion of the primary star's wind by the companion star near periastron could suppress the companion's wind and thus reduce the emission from the colliding wind shock for a brief period. In optical observations, the He ii k4687 emission line, which is believed to arise near the WWC shock, decreased in concert with the X-ray drop (Steiner & Damineli 2004).…”

Section: The Absorber Around the Wwc Plasmamentioning

confidence: 99%

X‐Ray Spectral Variation of η Carinae through the 2003 X‐Ray Minimum

Hamaguchi

Corcoran

Gull

et al. 2007

ApJ

201

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We report the results of an observing campaign on Car around the 2003 X-ray minimum, mainly using the XMMNewton observatory. These are the first spatially resolved X-ray monitoring observations of the stellar X-ray spectrum during the minimum. The hard X-ray emission, associated with the wind-wind collision (WWC) in the binary system, varied strongly in flux on timescales of days, but not significantly on timescales of hours. The X-ray flux in the 2Y10 keV band seen by XMM-Newton was only 0.7% of the flux maximum seen by RXTE. The slope of the X-ray continuum above 5 keV did not vary in any observation, which suggests that the electron temperature of the hottest plasma did not vary significantly at any phase. Through the minimum, the absorption to the stellar source increased by a factor of 5Y10 to N H $ (3Y 4) ; 10 23 cm À2 . These variations were qualitatively consistent with emission from the WWC plasma entering into the dense wind of the massive primary star. During the minimum, X-ray spectra also showed significant excesses in the thermal Fe xxv emission line on the red side, while they showed only a factor of 2 increase in equivalent width of the Fe fluorescence line at 6.4 keV. These features are not fully consistent with the eclipse of the X-ray plasma and may suggest an intrinsic fading of the X-ray emissivity. The drop in the WWC emission revealed the presence of an additional X-ray component that exhibited no variation on timescales of weeks to years. This component may be produced by the collision of high-speed outflows at v $ 1000Y2000 km s À1 from Car with ambient gas within a few thousand AU from the star.

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Accretion by the Secondary in η Carinae During the Spectroscopic Event. I. Flow Parameters

Cited by 40 publications

References 38 publications

Near-infrared evidence for a sudden temperature increase in Eta Carinae

Near-infrared evidence for a sudden temperature increase in Eta Carinae

Eta Carinae’s 2014.6 spectroscopic event: Clues to the long-term recovery from its Great Eruption

X‐Ray Spectral Variation of η Carinae through the 2003 X‐Ray Minimum

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