Birth of a Be star: an APOGEE search for Be stars forming through binary mass transfer

El-Badry, Kareem; Conroy, Charlie; Quataert, Eliot; Rix, Hans─Walter; Labadie-Bartz, Jonathan; Jayasinghe, T.; Thompson, Todd A.; Cargile, Phillip A.; Stassun, Keivan G.; Ilyin, I.

doi:10.1093/mnras/stac2422

Cited by 17 publications

(6 citation statements)

References 119 publications

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“…Several potential mass-transferring progenitors of classical Be stars have been identified, although the exact range of parameters required to form a Be star remains poorly constrained (Harmanec et al 2015;El-Badry et al 2022). The first case of the unstable Be + presubdwarf stage has been confirmed only recently (Frost et al 2022), and there are now six examples of this short-lived stage (Rivinius et al 2024).…”

Section: Introductionmentioning

confidence: 99%

The CHARA Array Interferometric Program on the Multiplicity of Classical Be Stars: New Detections and Orbits of Stripped Subdwarf Companions

Klement,

Rivinius,

Gies

et al. 2024

ApJ

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Rapid rotation and nonradial pulsations enable Be stars to build decretion disks, where the characteristic line emission forms. A major but unconstrained fraction of Be stars owe their rapid rotation to mass and angular momentum transfer in a binary. The faint, stripped companions can be helium-burning subdwarf OB-type stars (sdOBs), white dwarfs (WDs), or neutron stars. We present optical/near-infrared Center for High Angular Resolution Astronomy (CHARA) interferometry of 37 Be stars selected for spectroscopic indications of low-mass companions. From multiepoch H- and/or K-band interferometry plus radial velocities and parallaxes collected elsewhere, we constructed 3D orbits and derived flux ratios and absolute dynamical masses of both components for six objects, quadrupling the number of anchor points for evolutionary models. In addition, a new wider companion was identified for the known Be + sdO binary 59 Cyg, while auxiliary Very Large Telescope Interferometer/GRAVITY spectrointerferometry confirmed circumstellar matter around the sdO companion to HR 2142. On the other hand, we failed to detect any companion to the six Be stars with γ Cas–like X-ray emission, with sdOB and main-sequence companions of the expected spectroscopic mass being ruled out for the X-ray-prototypical stars γ Cas and π Aqr, leaving elusive WDs as the most likely companions, as well as a likely explanation of the X-rays. No low-mass main-sequence close companions were identified for the other stars.

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Section: Introductionmentioning

confidence: 99%

The CHARA Array Interferometric Program on the Multiplicity of Classical Be Stars: New Detections and Orbits of Stripped Subdwarf Companions

Klement,

Rivinius,

Gies

et al. 2024

ApJ

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“…A last case is HD 15124. The properties of its components were derived from simple SED fitting (El-Badry et al 2022) and appear rather similar to those of our targets, although the fast-rotating B-star belongs to the Be category, due to the presence of emissions linked to current accretion. However, for that system as for other post-interacting cases, the age is large: at least 200 Myr from evolutionary models, while our targets are young (<20 Myr).…”

Section: The Nature Of the Companionsmentioning

confidence: 82%

Extreme mass ratios and fast rotation in three massive binaries

Nazé,

Britavskiy,

Rauw

et al. 2023

Monthly Notices of the Royal Astronomical Society

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The origin of rapid rotation in massive stars remains debated, although binary interactions are now often advocated as a cause. However, the broad and shallow lines in the spectra of fast rotators make direct detection of binarity difficult. In this paper, we report on the discovery and analysis of multiplicity for three fast-rotating massive stars: HD 25631 (B3V), HD 191495 (B0V), and HD 46485 (O7V). They display strikingly similar TESS light curves, with two narrow eclipses superimposed on a sinusoidal variation due to reflection effects. We complement these photometric data by spectroscopy from various instruments (X-Shooter, Espadons, FUSE...), to further constrain the nature of these systems. The detailed analyses of these data demonstrates that the companions of the massive OB stars have low masses (∼1 M⊙) with rather large radii (2–4 R⊙) and low temperatures (<15 kK). These companions display no UV signature, which would exclude a hot subdwarf nature, but disentangling of the large set of X-Shooter spectra of HD 25631 revealed the typical signature of chromospheric activity in the companion’s spectrum. In addition, despite the short orbital periods (P = 3 − 7 d), the fast-rotating OB-stars still display non-synchronized rotation and all systems appear young (<20 Myr). This suggests that, as in a few other cases, these massive stars are paired in those systems with non-degenerate, low-mass PMS companions, implying that fast rotation would not be a consequence of a past binary interactions in their case.

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“…By querying the archive, we find 305 Be stars within 500 pc. Following the prescription of El-Badry et al (2022), this would imply that there are 28-170 hot subdwarf stars hiding behind classical Be stars in our 500 pc sample.…”

Section: Hot Subdwarfs As Companions To Be Starsmentioning

confidence: 89%

A 500 pc volume-limited sample of hot subluminous stars

Dawson,

Geier,

Heber

et al. 2024

A&A

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We present the first volume-limited sample of spectroscopically confirmed hot subluminous stars out to 500 pc, defined using the accurate parallax measurements from the Gaia space mission data release 3 (DR3). The sample comprises a total of 397 members, with 305 ($ 77<!PCT!>$) identified as hot subdwarf stars, including 83 newly discovered systems. Of these, we observe that 178 ($ are hydrogen-rich sdBs, 65 are sdOBs ($ 21<!PCT!>$), 32 are sdOs ($ 11<!PCT!>$), and 30 are He-sdO/Bs ($ 10<!PCT!>$). Among them, 48 ($ 16<!PCT!>$) exhibit an infrared excess in their spectral energy distribution fits, suggesting a composite binary system. The hot subdwarf population is estimated to be 90<!PCT!> complete, assuming that most missing systems are these composite binaries located within the main sequence (MS) in the Gaia colour-magnitude diagram (CMD). The remaining sources in the sample include cataclysmic variables (CVs), blue horizontal branch stars (BHBs), hot white dwarfs (WDs), and MS stars. We derived the mid-plane density $ $ and scale height $ h z $ for the non-composite hot subdwarf star population using a hyperbolic sechant profile (sech$^2$). The best-fit values are $ $ stars/pc3 and $ h z 62$ pc. When accounting for the composite-colour hot subdwarfs and their estimated completeness, the mid-plane density increases to $ $ stars/pc3. This corrected space density is an order of magnitude lower than predicted by population synthesis studies, supporting previous observational estimates.

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Birth of a Be star: an APOGEE search for Be stars forming through binary mass transfer

Cited by 17 publications

References 119 publications

The CHARA Array Interferometric Program on the Multiplicity of Classical Be Stars: New Detections and Orbits of Stripped Subdwarf Companions

The CHARA Array Interferometric Program on the Multiplicity of Classical Be Stars: New Detections and Orbits of Stripped Subdwarf Companions

Extreme mass ratios and fast rotation in three massive binaries

A 500 pc volume-limited sample of hot subluminous stars

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