Spectroscopy,MOSTphotometry, and interferometry of MWC 314: is it an LBV or an interacting binary?

Abstract

MWC 314 is a bright candidate luminous blue variable that resides in a fairly close binary system, with an orbital period of 60.753±0.003 d. We observed MWC 314 with a combination of optical spectroscopy, broad-band ground-and space-based photometry, as well as with long baseline, near-infrared interferometry. We have revised the singlelined spectroscopic orbit and explored the photometric variability. The orbital light curve displays two minima each orbit that can be partially explained in terms of the tidal distortion of the primary that occurs around the time of periastron. The emission lines in the system are often double-peaked and stationary in their kinematics, indicative of a circumbinary disc. We find that the stellar wind or circumbinary disc is partially resolved in the K ′ -band with the longest baselines of the CHARA Array. From this analysis, we provide a simple, qualitative model in an attempt to explain the observations. From the assumption of Roche Lobe overflow and tidal synchronisation at periastron, we estimate the component masses to be M 1 ≈ 5M ⊙ and M 2 ≈ 15M ⊙ , which indicates a mass of the LBV that is extremely low. In addition to the orbital modulation, we discovered two pulsational modes with the MOST satellite. These modes are easily supported by a low-mass hydrogen-poor star, but cannot be easily supported by a star with the parameters of an LBV. The combination of these results provides evidence that the primary star was likely never a normal LBV, but rather is the product of binary interactions. As such, this system presents opportunities for studying mass-transfer and binary evolution with many observational techniques.

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

“…A second model, involving boosting the eccentricity of an orbit during mass transfer, showed the primary mass of MWC 314 was ∼ 14M⊙. The pulsational behavior of MWC 314 that was observed with MOST confirmed the low-mass nature of this system (Richardson et al 2016a). Similar short-period (∼ 6 hr) pulsations were observed in the HD 5980 system by Sterken & Breysacher (1997) after its LBV-like eruption, but the close orbit likely changes the observed stellar structure of these stars compared to other LBV stars.…”

“…The only similar star that has shown stable pulsations is the LBV candidate MWC 314 (Richardson et al 2016a), which exhibits two pulsations with periods close to 1 d. This star has a spectrum reminiscent of the LBVs like η Carinae, but many of the emission lines are double-peaked, forming in a circumbinary disk. In the case of MWC 314, Richardson et al (2016a) found that the binary was not a massive LBV as previously suggested by Muratorio et al (2008) and Lobel et al (2013), but rather was the evolutionary byproduct of a lower-mass binary interaction. The system was a close spectroscopic twin to the binary HDE 326823 (Richardson et al 2011) where mass transfer has hidden the mass gainer behind a thick accretion torus while leaving the lower mass donor star visible.…”

“…A spectrum of η Car taken near apastron fromRichardson et al (2016a) is shown with the BRITE-Constellation red filter transmission curve. The strong Hα profile dominates this portion of the spectrum, which is why the y-axis is shown in logarithmic units.…”

Mode couplings and resonance instabilities in dust clusters

“…An N-body code, box_tree [8,9,28,35,[51][52][53][54], was employed to model the dynamics of the dust system. Particles are trapped within a parabolic potential well in the horizontal direction and by a linear electric field and gravity in the vertical direction (see Eq.…”

Physics of Eclipsing Binaries. Ii. Toward the Increased Model Fidelity

“…Their components at periastron are separated by only a few stellar radii, giving rise to significant tidal forces that distort stellar surfaces. A total of 28 giants in heartbeat stars have been reported to date (Nicholls & Wood 2012;Gaulme et al 2013Gaulme et al , 2014Beck et al 2014;Richardson et al 2016); of these, there are 9 for which the authors developed a full model (Nicholls & Wood 2012;Beck et al 2014;Richardson et al 2016), all of them under the constant volume…”