An observed population of intermediate-mass helium stars that have been stripped in binaries

Drout, M. R.; Götberg, Y.; Ludwig, B. A.; Groh, J. H.; de Mink, S. E.; O’Grady, A. J. G.; Smith, N.

doi:10.1126/science.ade4970

Cited by 20 publications

(3 citation statements)

References 143 publications

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“…This issue could be mitigated by using BPASS spectral synthesis (Eldridge et al 2017) as the BPASS SSP at this age and metallicity produces a stronger UV emission at the fixed Q H . However, we caution that there is significant uncertainty in the ionizing and UV fluxes of massive metal-poor stars (e.g., Olivier et al 2022;Umeda et al 2022;Drout et al 2023). In the next section, we propose a solution that does not require >80% dominance by nebular emission.…”

Section: Inferred Ionizing Spectramentioning

confidence: 97%

No Top-heavy Stellar Initial Mass Function Needed: The Ionizing Radiation of GS9422 Can Be Powered by a Mixture of an Active Galactic Nucleus and Stars

Li 李,

Leja,

Johnson

et al. 2024

ApJL

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JWST is producing high-quality rest-frame optical and UV spectra of faint galaxies at z > 4 for the first time, challenging models of galaxy and stellar populations. One galaxy recently observed at z = 5.943, GS9422, has nebular line and UV continuum emission that appears to require a high ionizing photon production efficiency. This has been explained with an exotic stellar initial mass function (IMF; Cameron et al. 2023a), 10–30x more top-heavy than a Salpeter IMF. Here we suggest an alternate explanation to this exotic IMF. We use a new flexible neural net emulator for CLOUDY, Cue, to infer the shape of the ionizing spectrum directly from the observed emission line fluxes. By describing the ionizing spectrum with a piecewise power law, Cue is agnostic to the source of the ionizing photons. Cue finds that the ionizing radiation from GS9422 can be approximated by a double power law characterized by Q HeII Q H = − 1.5 , which can be interpreted as a combination of young, metal-poor stars and a low-luminosity active galactic nucleus with F ν ∝ λ 2 in a 65%/35% ratio. This suggests a significantly lower nebular continuum contribution to the observed UV flux (24%) than a top-heavy IMF (≳80%), and hence, necessitates a damped Lyα absorber to explain the continuum turnover bluewards of ∼1400 Å. While current data cannot rule out either scenario, given the immense impact the proposed top-heavy IMF would have on models of galaxy formation, it is important to propose viable alternative explanations and to further investigate the nature of peculiar high-z nebular emitters.

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Section: Inferred Ionizing Spectramentioning

confidence: 97%

No Top-heavy Stellar Initial Mass Function Needed: The Ionizing Radiation of GS9422 Can Be Powered by a Mixture of an Active Galactic Nucleus and Stars

Li 李,

Leja,

Johnson

et al. 2024

ApJL

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“…A similar problem is also seen in z ∼ 2-4 He II emitters (Nanayakkara et al 2019;Saxena et al 2020), where the He II equivalent widths are usually underpredicted by the BPASS models (Xiao et al 2018) with more realistic metallicities (Z = 0.005, 0.1, 1 Z e ). Consequently, additional ionizing sources, such as Wolf-Rayet stars and stripped helium stars (Drout et al 2023), might still be needed to reproduce the observed line strengths.…”

Section: Uv Line Diagnosticsmentioning

confidence: 99%

Characterizing the Average Interstellar Medium Conditions of Galaxies at z ∼ 5.6–9 with Ultraviolet and Optical Nebular Lines

Hu,

Papovich,

Dickinson

et al. 2024

ApJ

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Ultraviolet (UV; rest-frame ∼1200–2000 Å) spectra provide a wealth of diagnostics to characterize fundamental galaxy properties, such as their chemical enrichment, the nature of their stellar populations, and their amount of Lyman-continuum (LyC) radiation. In this work, we leverage publicly released JWST data to construct the rest-frame UV-to-optical composite spectrum of a sample of 63 galaxies at 5.6 < z < 9, spanning a wavelength range from 1500 to 5200 Å. Based on the composite spectrum, we derive an average dust attenuation E ( B − V ) gas = 0.10 − 0.11 + 0.10 from Hβ/Hγ, an electron density n e = 570 − 290 + 510 cm−3 from the [O ii] doublet ratio, an electron temperature T e = 16700 − 1500 + 1500 K from the [O iii] λ4363/[O iii] λ5007 ratio, and an ionization parameter log ( U ) = − 2.15 − 0.03 + 0.03 from the [O iii]/[O ii] ratio. Using a direct T e method, we calculate an oxygen abundance 12 + log ( O / H ) = 7.67 ± 0.08 and a carbon-to-oxygen (C/O) abundance ratio log ( C / O ) = − 0.86 − 0.10 + 0.13 . This C/O ratio is smaller than compared to z = 0 and z = 2–4 star-forming galaxies, albeit with moderate significance. This indicates the reionization-era galaxies might be undergoing a rapid buildup of stellar mass with high specific star formation rates. A UV diagnostic based on the ratios of C iii] λ λ1907, 1909/He ii λ1640 versus O iii] λ1666/He ii λ1640 suggests that the star formation is the dominant source of ionization, similar to the local extreme dwarf galaxies and z ∼ 2–4 He ii–detected galaxies. The [O iii]/[O ii] and C iv/C iii] ratios of the composite spectrum are marginally larger than the criteria used to select galaxies as LyC leakers, suggesting that some of the galaxies in our sample are strong contributors to the reionizing radiation.

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“…The resulting stripped star first contracts as a hot helium star. Drout et al (2023) and Götberg et al (2023) recently presented the discovery and analysis of such stars, which so far had been missing.…”

Section: Introductionmentioning

confidence: 99%

Explosions in Roche-lobe Distorted Stars: Relativistic Bullets in Binaries

DuPont,

MacFadyen,

de Mink

2024

ApJ

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State-of-the-art surveys reveal that most massive stars in the Universe evolve in close binaries. Massive stars in such systems are expected to develop aspherical envelopes due to tidal interactions and/or rotational effects. Recently, it was shown that point explosions in oblate stars can produce relativistic equatorial ring-like outflows. Moreover, since stripped-envelope stars in binaries can expand enough to fill their Roche lobes anew, it is likely that these stars die with a greater degree of asphericity than the oblate spheroid geometry previously studied. We investigate the effects of this asymmetry by studying the gas dynamics of axisymmetric point explosions in stars in various stages of filling their Roche lobes. We find that point explosions in these pear-shaped stars produce transrelativistic ejecta that coalesce into bullets pointed both toward and away from the binary companion. We present this result and comment on key morphological differences between core-collapse explosions in spherical versus distorted stars in binary systems, effects on gravitational wave sources, and observational signatures that could be used to glean these explosion geometries from current and future surveys.

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An observed population of intermediate-mass helium stars that have been stripped in binaries

Cited by 20 publications

References 143 publications

No Top-heavy Stellar Initial Mass Function Needed: The Ionizing Radiation of GS9422 Can Be Powered by a Mixture of an Active Galactic Nucleus and Stars

No Top-heavy Stellar Initial Mass Function Needed: The Ionizing Radiation of GS9422 Can Be Powered by a Mixture of an Active Galactic Nucleus and Stars

Characterizing the Average Interstellar Medium Conditions of Galaxies at z ∼ 5.6–9 with Ultraviolet and Optical Nebular Lines

Explosions in Roche-lobe Distorted Stars: Relativistic Bullets in Binaries

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