RECENT X-Ray VARIABILITY OF Η CARINAE: THE QUICK ROAD TO RECOVERY

Corcoran, M. F.; Hamaguchi, Kenji; Pittard, J. M.; Russell, Christopher M. P.; Owocki, Stan; Parkin, E. R.; Okazaki, Atsuo T.

doi:10.1088/0004-637x/725/2/1528

Cited by 72 publications

(111 citation statements)

References 27 publications

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“…A decrease in mass-loss rate was proposed (Mehner et al 2010). Kashi & Soker (2009a), Mehner et al (2010), and Corcoran et al (2010) also inferred a drop in η Car's mass-loss rate based on η Car's X-ray light curve.…”

Section: Discussionmentioning

confidence: 98%

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: Discussionmentioning

confidence: 98%

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

Mehner¹,

Ishibashi²,

Whitelock³

et al. 2014

A&A

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“…During the last three decades, it brightened by several magnitudes (Martin et al 2006;Smith & Frew 2011). Strong X-ray variability is seen as a result of dynamical changes in the wind collision zone (Corcoran et al 2010). The observed nearinfrared variability is probably related to the episodic formation of dust grains within compressed post-shock zones of the colliding winds (Smith 2010).…”

Section: The Far-infrared Spectral Energy Distribution Of η Carinaementioning

confidence: 99%

Herschelfar-infrared observations of the Carina Nebula complex

Gaczkowski

Preibisch

Ratzka

et al. 2012

A&A

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Context. The Carina Nebula represents one of the largest and most active star forming regions known in our Galaxy. It contains numerous very massive (M > ∼ 40 M ) stars that strongly affect the surrounding clouds by their ionizing radiation and stellar winds. Aims. Our recently obtained Herschel PACS and SPIRE far-infrared maps cover the full area (≈8.7 deg 2 ) of the Carina Nebula complex (CNC) and reveal the population of deeply embedded young stellar objects (YSOs), most of which are not yet visible in the mid-or near-infrared. Methods. We study the properties of the 642 objects that are independently detected as point-like sources in at least two of the five Herschel bands. For those objects that can be identified with apparently single Spitzer counterparts, we use radiative transfer models to derive information about the basic stellar and circumstellar parameters. Results. We find that about 75% of the Herschel-detected YSOs are Class 0 protostars. The luminosities of the Herschel-detected YSOs with SED fits are restricted to values of ≤5400 L , their masses (estimated from the radiative transfer modeling) range from ≈1 M to ≈10 M . Taking the observational limits into account and extrapolating the observed number of Herschel-detected protostars over the stellar initial mass function suggest that the star formation rate of the CNC is ∼0.017 M /year. The spatial distribution of the Herschel YSO candidates is highly inhomogeneous and does not follow the distribution of cloud mass. Rather, most Herschel YSO candidates are found at the irradiated edges of clouds and pillars. The far-infrared fluxes of the famous object η Car are about a factor of two lower than expected from observations with the Infrared Space Observatory obtained 15 years ago; this difference may be a consequence of dynamical changes in the circumstellar dust in the Homunculus Nebula around η Car. Conclusions. The currently ongoing star formation process forms only low-mass and intermediate-mass stars, but no massive (M > ∼ 20 M ) stars. The characteristic spatial configuration of the YSOs provides support to the picture that the formation of this latest stellar generation is triggered by the advancing ionization fronts.

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“…The WWC X-ray emission has been monitored intensively for 4 orbital cycles since 1996 (Corcoran et al 2010; M.F. Corcoran et al 2015, in preparation).…”

Section: Introductionmentioning

confidence: 99%

ETA CARINAE’S THERMAL X-RAY TAIL MEASURED WITH XMM-NEWTON AND NuSTAR

Hamaguchi

Corcoran

Gull

et al. 2016

ApJ

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The evolved, massive highly eccentric binary system, ηCar, underwent a periastron passage in the summer of 2014. We obtained two coordinated X-ray observations with XMM-Newton and NuSTAR during the elevated X-ray flux state and just before the X-ray minimum flux state around this passage. These NuSTAR observations clearly detected X-ray emission associated with ηCar extending up to ∼50 keV for the first time. The NuSTAR spectrum above 10 keV can be fit with the bremsstrahlung tail from a kT∼6 keV plasma. This temperature is ΔkT∼2 keV higher than those measured from the iron K emission line complex, if the shocked gas is in collisional ionization equilibrium. This result may suggest that the companion starʼs pre-shock wind velocity is underestimated. The NuSTAR observation near the X-ray minimum state showed a gradual decline in the X-ray emission by 40% at energies above 5 keV in a day, the largest rate of change of the X-ray flux yet observed in individual ηCar observations. The column density to the hardest emission component, N H ∼10 24 H cm −2 , marked one of the highest values ever observed for η Car, strongly suggesting increased obscuration of the wind-wind colliding X-ray emission by the thick primary stellar wind prior to superior conjunction. Neither observation detected the power-law component in the extremely hard band that INTEGRAL and Suzaku observed prior to 2011. If the nondetection by NuSTAR is caused by absorption, the power-law source must be small and located very near the windwind collision apex. Alternatively, it may be that the power-law source is not related to either ηCar or the GeV γ-ray source.

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RECENT X-Ray VARIABILITY OF Η CARINAE: THE QUICK ROAD TO RECOVERY

Cited by 72 publications

References 27 publications

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

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

Herschelfar-infrared observations of the Carina Nebula complex

ETA CARINAE’S THERMAL X-RAY TAIL MEASURED WITH XMM-NEWTON AND NuSTAR

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