BRITE-Constellation reveals evidence for pulsations in the enigmatic binary η Carinae

Richardson, Noel D.; Pablo, H.; Sterken, C.; Pigulski, A.; Koenigsberger, Gloria; Moffat, A. F. J.; Madura, Thomas; Hamaguchi, Kenji; Corcoran, M. F.; Damineli, A.; Gull, Theodore R.; Hillier, D. J.; Weigelt, G.; Handler, G.; Wade, G. A.; Weiß, W. W.; Zwintz, K.

doi:10.1093/mnras/sty157

Cited by 16 publications

(12 citation statements)

References 58 publications

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“…In addition to the orbital-related periodicity of the short-lived peaks, van Genderen, de Groot, & Thé (1994) and Sterken et al (1996) found low amplitude (millimagnitude) variations with a period P = 58.58 d. Two decades later, Richardson et al (2018) confirmed this period using measurements made with the BRITE-Constellation nano-satellites. Thus the 58.8 day variability seems to be stable in frequency over at least four decades.…”

Section: Introductionmentioning

confidence: 84%

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Distinguishing circumstellar from stellar photometric variability in Eta Carinae

Damineli¹,

Lajús

Almeida

et al. 2019

Monthly Notices of the Royal Astronomical Society

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The interacting binary Eta Carinae remains one of the most enigmatic massive stars in our Galaxy despite over four centuries of observations. In this work, its light curve from the ultraviolet to the near-infrared is analysed using spatially resolved HST observations and intense monitoring at the La Plata Observatory, combined with previously published photometry. We have developed a method to separate the central stellar object in the ground-based images using HST photometry and applying it to the more numerous ground-based data, which supports the hypothesis that the central source is brightening faster than the almost-constant Homunculus. After detrending from longterm brightening, the light curve shows periodic orbital modulation (∆V ∼ 0.6 mag) attributed to the wind-wind collision cavity as it sweeps around the primary star and it shows variable projected area to our line-of-sight. Two quasi-periodic components with time scales of 2-3 and 8-10 yr and low amplitude, ∆V < 0.2 mag, are superimposed on the brightening light-curve, being the only stellar component of variability found, which indicates minimal stellar instability. Moreover, the light curve analysis shows no evidence of "shell ejections" at periastron. We propose that the long-term brightening of the stellar core is due to the dissipation of a dusty clump in front of the central star, which works like a natural coronagraph. Thus, the central stars appear to be more stable than previously thought since the dominant variability originates from a changing circumstellar medium. We predict that the brightening phase, due mainly to dust dissipation, will be completed around 2032 ± 4 yr, when the star will be brighter than in the 1600's by up to ∆V ∼ 1 mag.

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Section: Introductionmentioning

confidence: 84%

“…• The two short-period pulsations: Low-amplitude pulsations (milli-magnitude) with strict periodicity P = 58.8 d and P = 22.7 d, probably tidally excited (Richardson et al 2018).…”

Section: Discussionmentioning

confidence: 99%

Distinguishing circumstellar from stellar photometric variability in Eta Carinae

Damineli¹,

Lajús

Almeida

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…Breysacher (1997) and Sterken & Breysacher (1997) find a period of ∼6 h and an amplitude of 0.025 mag in data obtained shortly after the 1994 eruption and suggest that it might be due to pulsations in one of the two stars. As the oscillations persist through the eclipses, an alternative possibility is that they are associated with Star C. Although most O stars do not exhibit such variations, tidally excited oscillations (TEOs) have recently been reported in the OB-type system ι Orionis (Pablo et al 2017) and η Carinae (Richardson et al 2018). In red we show the spectrum of Star A while in blue we show the spectrum that would be obtained if Star A were occulted by a simple disc with radius 25.1 R .…”

Section: Short-term Variabilitymentioning

confidence: 99%

The enigmatic binary system HD 5980

Hillier

Koenigsberger

Nazé

et al. 2019

Monthly Notices of the Royal Astronomical Society

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The Small Magellanic Cloud multiple system HD 5980 contains a luminous blue variable (LBV) that underwent a major eruption in 1994, and whose current spectrum is that of a hydrogen-rich Wolf–Rayet (WR) star. Since the eruption, the wind mass-loss rate has been declining while wind speeds have been steadily increasing. Observations obtained in 2014 when Star A (the LBV) eclipses Star B indicate that the fitted mass-loss rate and luminosity have reached the lowest values ever determined for such spectra: $\dot{M}$ = 4.5 × 10−5$\mathrm{M}_\odot \, \hbox{yr}^{-1}$, L = 1.7 × 106 L⊙. In addition, the radius of the LBV’s continuum-emitting region is similar to that derived from the eclipse light curves of the late 1970s. Hence, it appears to have attained a similar ‘low’ state to that of the late 1970s. While a good fit to the emission spectrum is obtained using a cmfgen model, there are discrepancies in the UV. In particular, the extent of the observed absorption profiles is ∼1000 km s−1 greater than predicted by the emission-line intensities. Further, HST UV observations obtained in 2016, when Star A is eclipsed by Star B, show unusual P Cygni profiles that are not easily explained. Surprisingly the 2016 emission-line spectrum is similar to that at the opposite eclipse obtained in 2014. The complex UV profiles are likely to arise as a consequence of the dynamics of the wind–wind collision and radiative braking, both of which will cause significant departures from spherical symmetry, and have a strong orbital phase dependence. However, other scenarios, such as intrinsically aspherical winds, cannot be ruled out.

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“…We compile a list of 22 heartbeat binaries with TEOs: OB-type: HD 177863 (Willems and Aerts, 2002); ι Ori (Pablo et al, 2017); MACHO80.7443.1718 (Jayasinghe et al, 2019); QX Car and V1294 Sco (Kołaczek-Szymański et al, 2020); two possible candidates: η Car (Richardson et al, 2018); R81 (Tubbesing et al, 2002).…”

Section: Eccentric Binaries With Tidally Excited Oscillations (Teos)mentioning

confidence: 99%

Asteroseismology of Close Binary Stars: Tides and Mass Transfer

Guo

2021

Front. Astron. Space Sci.

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The study of stellar oscillations allows us to infer the properties of stellar interiors. Meanwhile, fundamental parameters such as mass and radius can be obtained by studying stars in binary systems. The synergy between binarity and asteroseismology can constrain the parameter space of stellar properties and facilitate the asteroseismic inference. On the other hand, binarity also introduces additional complexities such tides and mass transfer. From an observational perspective, we briefly review the recent advances in the study of tidal effects on stellar oscillations, focusing on upper main sequence stars (F-, A-, or OB- type). The effect can be roughly divided into two categories. The first one concerns the tidally excited oscillations (TEOs) in eccentric binaries where TEOs are mostly due to resonances between dynamical tides and gravity modes of the star. TEOs appear as orbital-harmonic oscillations on top of the eccentric ellipsoidal light curve variations (the “heartbeat” feature). The second category is regarding the self-excited oscillations perturbed by static tides in circularized and synchronized close binaries. It includes the tidal deformation of the propagation cavity and its effect on eigenfrequencies, eigenfunctions, and the pulsation alignment. We list binary systems that show these two types of tidal effect and summarize the orbital and pulsation observables. We also discuss the theoretical approaches used to model these tidal oscillations and relevant complications such as non-linear mode coupling and resonance locking. Further information can be extracted from the observations of these oscillations which will improve our understanding of tides. We also discuss the effect of mass transfer, the extreme result of tides, on stellar oscillations. We bring to the readers' attention: (1) oscillating stars undergoing mass accretion (A-, F-, and OB type pulsators and white dwarfs), for which the pulsation properties may be changed significantly by accretion; (2) post-mass transfer pulsators, which have undergone a stable or unstable Roche-Lobe overflow. These pulsators have great potential in probing detailed physical processes in stellar interiors and mass transfer, as well as in studying the binary star populations.

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BRITE-Constellation reveals evidence for pulsations in the enigmatic binary η Carinae

Cited by 16 publications

References 58 publications

Distinguishing circumstellar from stellar photometric variability in Eta Carinae

Distinguishing circumstellar from stellar photometric variability in Eta Carinae

The enigmatic binary system HD 5980

Asteroseismology of Close Binary Stars: Tides and Mass Transfer

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