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1. The Nature of a Recently Discovered Wolf–Rayet Binary: Archetype of Stripping?*

   https://doi.org/10.3847/1538-4357/ad8a59  

   Massey, Philip; Neugent, Kathryn_F; Morrell, Nidia_I; Hillier, Desmond_John; Penny, Laura_R (December 2024, The Astrophysical Journal)

   Abstract LMCe055-1 was recently discovered in a survey for Wolf–Rayets (WRs) in the Large Magellanic Cloud, and classified as a WN4/O4, a lower-excitation version of the WN3/O3 class discovered as part of the same survey. Its absolute magnitude precluded it from being a WN4+O4 binary. Optical Gravitational Lensing Experiment photometry shows shallow primary and secondary eclipses with a 2.2 days period. The spectral characteristics and short period pointed to a possible origin due to binary stripping. Such stripped WR binaries should be common but have proven elusive to identify conclusively. In order to establish its nature, we obtained Hubble Space Telescope ultraviolet and Magellan optical spectra, along with imaging. Our work shows that the WR emission and Heiiabsorption arise in one star, and the Heiabsorption in another. The Heicontributor is the primary of the 2.2 days system and exhibits ∼300 km s⁻¹radial velocity variations on that timescale. However, the WR star shows 30–40 km s⁻¹radial velocity variations, with a likely 35 days period and a highly eccentric orbit. Possibly LMCe055-1 is a physical triple, but that would require the 2.2 days pair to have been captured by the WR star. A more likely explanation is that the WR star has an unseen companion in a 35 days orbit and that the 2.2 days pair is in a longer-period orbit about the two. Such examples of multiple systems are well known among massive stars, such as HD 5980. Regardless, we argue that it is highly unlikely that the WR component of the LMCe055-1 system resulted from stripping. 

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2. Constraints on the Binarity of the WN3/O3 Class of Wolf–Rayet Stars*

   https://doi.org/10.3847/1538-4357/acc5ed  

   Massey, Philip; Neugent, Kathryn F.; Morrell, Nidia I. (April 2023, The Astrophysical Journal)

   Abstract The WN3/O3 Wolf–Rayet (WR) stars were discovered as part of our survey for WRs in the Magellanic Clouds. The WN3/O3s show the emission lines of a high-excitation WN star and the absorption lines of a hot O-type star, but our prior work has shown that the absorption spectrum is intrinsic to the WR star. Their place in the evolution of massive stars remains unclear. Here we investigate the possibility that they are the products of binary evolution. Although these are not WN3+O3 V binaries, they could still harbor unseen companions. To address this possibility, we have conducted a multiyear radial velocity study of six of the nine known WN3/O3s. Our study finds no evidence of statistically significant radial velocity variations, and allows us to set stringent upper limits on the mass of any hypothetical companion star: for probable orbital inclinations, any companion with a period less than 100 days must have a mass <2M_⊙. For periods less than 10 days, any companion would have to have a mass <1M_⊙. We argue that scenarios where any such companion is a compact object are unlikely. The absorption lines indicate a normal projected rotational velocity, making it unlikely that these stars evolved with the aid of a companion star that has since merged. The modest rotation also suggests that these stars are not the result of homogenous evolution. Thus it is likely that these stars are a normal but short-lived stage in the evolution of massive stars. 

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3. Accretion geometry of the neutron star low mass X-ray binary Cyg X-2 from X-ray polarization measurements

   https://doi.org/10.1093/mnras/stac3726  

   Farinelli, R; Fabiani, S; Poutanen, J; Ursini, F; Ferrigno, C; Bianchi, S; Cocchi, M; Capitanio, F; De Rosa, A; Gnarini, A; et al (January 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We report spectro-polarimetric results of an observational campaign of the bright neutron star low-mass X-ray binary Cyg X-2 simultaneously observed by IXPE, NICER, and INTEGRAL. Consistently with previous results, the broad-band spectrum is characterized by a lower-energy component, attributed to the accretion disc with kTin ≈ 1 keV, plus unsaturated Comptonization in thermal plasma with temperature kTe = 3 keV and optical depth τ ≈ 4, assuming a slab geometry. We measure the polarization degree in the 2–8 keV band P = 1.8 ± 0.3 per cent and polarization angle ϕ = 140° ± 4°, consistent with the previous X-ray polarimetric measurements by OSO-8 as well as with the direction of the radio jet which was earlier observed from the source. While polarization of the disc spectral component is poorly constrained with the IXPE data, the Comptonized emission has a polarization degree P = 4.0 ± 0.7 per cent and a polarization angle aligned with the radio jet. Our results strongly favour a spreading layer at the neutron star surface as the main source of the polarization signal. However, we cannot exclude a significant contribution from reflection off the accretion disc, as indicated by the presence of the iron fluorescence line. 

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4. To binary or not to binary: An analysis of WR 71’s polarized line profiles

   Johnson, R.A. (January 2021, Bulletin of the American Astronomical Society)

   null (Ed.)

   Massive Wolf-Rayet (WR) stars in binary systems may produce supernovae capable of emitting long duration gamma ray bursts. Characterizing the structure of the colliding winds in these systems may help constrain the mass loss and transfer properties and help predict their future evolution. I will present new spectropolarimetric data for the possible WR+O binary system WR 71, collected using RSS at the Southern African Large Telescope. WR 71 is a WN6 whose binary status is unknown, but it displays similar spectropolarimetric variations to the known WR+O binary system V444 Cygni. I investigate the orbital and rotational velocity of WR 71's winds by analyzing its polarized emission line profiles as a function of phase, the first analysis of its kind. I compare the line polarization behavior with predictive models of both colliding wind binaries and single stars with co-rotating interaction regions. Describing the wind structure of WR 71 will help determine the rate of mass loss from the system, an important indicator for LGRB progenitors, and shed light on its binary status. 

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5. Multiwavelength Observations of a Jet Launch in Real Time from the Post-changing-look Active Galaxy 1ES 1927+654

   https://doi.org/10.3847/1538-4357/adaea0  

   Laha, Sibasish; Meyer, Eileen T; Sadaula, Dev R; Ghosh, Ritesh; Sengupta, Dhrubojyoti; Masterson, Megan; Shuvo, Onic I; Guainazzi, Matteo; Ricci, Claudio; Begelman, Mitchell C; et al (March 2025, The Astrophysical Journal)

   Abstract We present results from a high-cadence multiwavelength observational campaign of the enigmatic changing-look active galactic nucleus 1ES 1927+654 from 2022 May to 2024 April, coincident with an unprecedented radio flare (an increase in flux by a factor of ∼60 over a few months) and the emergence of a spatially resolved jet at 0.1–0.3 pc scales. Companion work has also detected a recurrent quasi-periodic oscillation (QPO) in the 2–10 keV band with an increasing frequency (1–2 mHz) over the same period. During this time, the soft X-rays (0.3–2 keV) monotonically increased by a factor of ∼8, while the UV emission remained nearly steady with <30% variation and the 2–10 keV flux showed variation by a factor ≲2. The weak variation of the 2–10 keV X-ray emission and the stability of the UV emission suggest that the magnetic energy density and accretion rate are relatively unchanged and that the jet could be launched owing to a reconfiguration of the magnetic field (toroidal to poloidal) close to the black hole. Advecting poloidal flux onto the event horizon would trigger the Blandford–Znajek mechanism, leading to the onset of the jet. The concurrent softening of the coronal slope (from Γ = 2.70 ± 0.04 to Γ = 3.27 ± 0.04), the appearance of a QPO, and the low coronal temperature ( $k{T}_e=8_{-3}^{+8}\mathrm{keV}$) during the radio outburst suggest that the poloidal field reconfiguration can significantly impact coronal properties and thus influence jet dynamics. These extraordinary findings in real time are crucial for coronal and jet plasma studies, particularly as our results are independent of coronal geometry. 

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