The formation of the magnetic symbiotic star FN Sgr

Belloni, Diogo; Mikołajewska, Joanna; Schreiber, Matthias R.

doi:10.1051/0004-6361/202449602

Cited by 2 publications

(1 citation statement)

References 118 publications

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“…It must have undergone interaction prior to the formation of the WD but its orbit is smaller than expected for a post-stable MT system. Meanwhile, its orbit is larger than PCEBs predicted by previous binary population synthesis codes (e.g., Zorotovic et al 2014), though it is consistent with some recent models of CEE from thermally pulsating AGB donors (e.g., Belloni et al 2024aBelloni et al , 2024bYamaguchi et al 2024a;Yamaguchi et al 2024b).…”

Section: Formation Historysupporting

confidence: 89%

No Longer Impossible: The Self-lensing Binary KIC 8145411 is a Triple

Yamaguchi,

El-Badry,

Ciardi

et al. 2024

PASP

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Five self-lensing binaries (SLBs) have been discovered with data from the Kepler mission. One of these systems is KIC 8145411, which was reported to host an extremely low mass (ELM; 0.2 M ⊙) white dwarf (WD) in a 456 days orbit with a solar-type companion. The system has been dubbed “impossible,” because evolutionary models predict that ∼0.2 M ⊙ WDs should only be found in tight orbits (P orb ≲ days). In this work, we show that KIC 8145411 is in fact a hierarchical triple system: it contains a WD orbiting a solar-type star, with another solar-type star ∼700 au away. The wide companion was unresolved in the Kepler light curves, was just barely resolved in Gaia DR3, and is resolved beyond any doubt by high-resolution imaging. We show that the presence of this tertiary confounded previous mass measurements of the WD for two reason: it dilutes the amplitude of the self-lensing pulses, and it reduces the apparent radial velocity (RV) variability amplitude of the WD’s companion due to line blending. By jointly fitting the system’s light curves, RVs, and multi-band photometry using a model with two luminous stars, we obtain a revised WD mass of (0.53 ± 0.01)M ⊙. Both luminous stars are near the end of their main-sequence evolution. The WD is thus not an ELM WD, and the system does not suffer the previously proposed challenges to its formation history. Similar to the other SLBs and the population of astrometric WD binaries recently identified from Gaia data, KIC 8145411 has parameters in tension with standard expectations for formation through both stable and unstable mass transfer (MT). The system’s properties are likely best understood as a result of unstable MT from an AGB star donor.

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Section: Formation Historysupporting

confidence: 89%

No Longer Impossible: The Self-lensing Binary KIC 8145411 is a Triple

Yamaguchi,

El-Badry,

Ciardi

et al. 2024

PASP

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Wide Post-common Envelope Binaries from Gaia: Orbit Validation and Formation Models

Yamaguchi,

El-Badry,

Rees

et al. 2024

PASP

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Astrometry from Gaia DR3 has enabled the discovery of a sample of 3000+ binaries containing white dwarfs (WD) and main-sequence (MS) stars in relatively wide orbits, with orbital periods P orb = (100–1000) days. This population was not predicted by binary population synthesis models before Gaia and—if the Gaia orbits are robust—likely requires very efficient envelope ejection during common envelope evolution (CEE). To assess the reliability of the Gaia solutions, we measured multi-epoch radial velocities (RVs) of 31 WD+MS binary candidates with P orb = (40–300) days and AstroSpectroSB1 orbital solutions. We jointly fit the RVs and astrometry, allowing us to validate the Gaia solutions and tighten constraints on component masses. We find a high success rate for the Gaia solutions, with only 2 out of the 31 systems showing significant discrepancies between their Gaia orbital solutions and our RVs. Joint fitting of RVs and astrometry allows us to directly constrain the secondary-to-primary flux ratio S , and we find S ≲ 0.02 for most objects, confirming the companions are indeed WDs. We tighten constraints on the binaries’ eccentricities, finding a median e ≈ 0.1. These eccentricities are much lower than those of normal MS+MS binaries at similar periods, but much higher than predicted for binaries formed via stable mass transfer. We present MESA single and binary evolution models to explore how the binaries may have formed. The orbits of most binaries in the sample can be produced through CEE that begins when the WD progenitor is an AGB star, corresponding to initial separations of 2–5 au. Roughly 50% of all post-common envelope binaries are predicted to have first interacted on the AGB, ending up in wide orbits like these systems.

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The formation of the magnetic symbiotic star FN Sgr

Abstract: There are several symbiotic stars (e.g.

Cited by 2 publications

References 118 publications

No Longer Impossible: The Self-lensing Binary KIC 8145411 is a Triple

No Longer Impossible: The Self-lensing Binary KIC 8145411 is a Triple

Wide Post-common Envelope Binaries from Gaia: Orbit Validation and Formation Models

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