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An Orbit for a Massive Wolf-Rayet Binary in the LMC: An Example of Binary Evolution
Authors:
Breelyn Cocke,
Philip Massey,
Nidia I. Morrell,
Laura R. Penny,
Kathryn F. Neugent,
Jan J. Eldridge,
Michal K. Szymanski,
Andrzej Udalski,
Laurella C. Marin
Abstract:
Wolf-Rayet (WR) stars are helium-burning, evolved massive stars which have had most of their hydrogen-rich outer layers removed either through stellar winds and/or binary stripping. Here we report on LMC173-1, a WN3+O binary located in the Large Magellanic Cloud (LMC). Using spectra obtained from the Magellan and Gemini-S telescopes, we have derived system parameters for this intriguing binary. Th…
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Wolf-Rayet (WR) stars are helium-burning, evolved massive stars which have had most of their hydrogen-rich outer layers removed either through stellar winds and/or binary stripping. Here we report on LMC173-1, a WN3+O binary located in the Large Magellanic Cloud (LMC). Using spectra obtained from the Magellan and Gemini-S telescopes, we have derived system parameters for this intriguing binary. The WR star's mass is only 43% that of its companion, and we argue that this requires binary evolution rather than mass loss by stellar winds alone, given the metallicity of the LMC. The stars are close enough to each other with their 3.52 day period that the O star is actually orbiting within the wind of the WR star, as is the case for other well-known WR+O systems, such as V444 Cyg. As a result, high precision OGLE photometry reveals a WR atmospheric eclipse, as well as a 7-8 millimag ellipsoidal modulation due primarily to the tidal distortion of the O star. Modeling the light curve allows us to estimate the orbital inclination. Derivation of stellar parameters suggests neither component is filling its Roche-lobe surface today. The O star is spinning much faster than synchronous rotation. Using BPASS v2.2 binary models, we discuss the probable evolutionary history of the system. The WR progenitor likely underwent Case A Roche-lobe overflow (RLOF) before leaving the main-sequence. As it lost its H-rich envelope, it became a WN-type WR. The resulting system is a binary with similar luminosities but very different radii, representing a post-RLOF phase.
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Submitted 11 March, 2026;
originally announced March 2026.
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GAMA 526784: the progenitor of a globular cluster-rich ultra-diffuse galaxy? II. Molecular gas, neutral gas and environment
Authors:
Maria Luisa Buzzo,
Anita Zanella,
Michael Hilker,
Kristine Spekkens,
Laura Hunter,
Laurella C. Marin
Abstract:
Aims. We investigate the gas reservoirs, star formation (SF) properties, and environment of the ultra-diffuse galaxy GAMA526784 to understand its formation history, the efficiency of molecular gas conversion into stars, and the possible role of an interacting companion in shaping its morphology. Methods. We analyse low and high-resolution CO observations to constrain the molecular gas content, com…
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Aims. We investigate the gas reservoirs, star formation (SF) properties, and environment of the ultra-diffuse galaxy GAMA526784 to understand its formation history, the efficiency of molecular gas conversion into stars, and the possible role of an interacting companion in shaping its morphology. Methods. We analyse low and high-resolution CO observations to constrain the molecular gas content, compare with HI data, and examine the SF efficiency of GAMA526784. The potential influence of a newly identified nearby dwarf galaxy is assessed using photometric and spatial information. Results. GAMA526784 exhibits a regular HI reservoir (M_HI/M* = 2.88) but only upper limits on its molecular gas mass (M_H2(5sigma)/M* < 0.23). The HI reservoir and CO non-detection can be explained by several mechanisms: (1) predominance of CO-dark H2, invisible to CO observations but contributing to SF; (2) a time delay in HI-to-H2 conversion following a recent interaction; or (3) elevated turbulence inhibiting gas collapse. An identified companion, found at a projected distance of 48 kpc, shows similar colours and lies in the direction of young star clusters in GAMA526784, indicating a possible association. We hypothesise this companion may have triggered the formation of star clusters in GAMA526784 through a high-velocity encounter. Conclusions. Our findings suggest GAMA526784 may have undergone an interaction that influenced its gas reservoirs and SF activity. The presence of a nearby companion agrees with predictions of a high-speed encounter, potentially offering a rare example of such an interaction in progress. We suggest this encounter may have shaped the system's recent evolution. Future observations, particularly targeting molecular gas tracers beyond CO and resolved HI maps, will be crucial in determining the extent of GAMA526784's cold gas reservoir and the nature of its recent star formation.
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Submitted 24 June, 2025;
originally announced June 2025.
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The Discovery of Three Galactic Wolf-Rayet Stars
Authors:
Laurella C. Marin,
Philip Massey,
Brian A. Skiff,
Kennedy A. Farrell
Abstract:
Wolf-Rayet stars (WRs) are evolved massive stars in the brief stage before they undergo core collapse. Not only are they rare, but they also can be particularly difficult to find due to the high extinction in the Galactic plane. This paper discusses the discovery of three new Galactic WRs previously classified as H$α$ emission stars, but thanks to Gaia spectra, we were able to identify the broad,…
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Wolf-Rayet stars (WRs) are evolved massive stars in the brief stage before they undergo core collapse. Not only are they rare, but they also can be particularly difficult to find due to the high extinction in the Galactic plane. This paper discusses the discovery of three new Galactic WRs previously classified as H$α$ emission stars, but thanks to Gaia spectra, we were able to identify the broad, strong emission lines that characterize WRs. Using the Lowell Discovery Telescope and the DeVeny spectrograph, we obtained spectra for each star. Two are WC9s, and the third is a WN6 + O6.5 V binary. The latter is a known eclipsing system with a 4.4 day period from ASAS-SN data. We calculate absolute visual magnitudes for all three stars to be between -7 and -6, which is consistent with our expectations of these subtypes. These discoveries highlight the incompleteness of the WR census in our local volume of the Milky Way and suggest the potential for future Galactic WR discoveries from Gaia low-dispersion spectra. Furthermore, radial velocity studies of the newly found binary will provide direct mass estimates and orbital parameters, adding to our knowledge of the role that binarity plays in massive star evolution.
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Submitted 20 August, 2024;
originally announced August 2024.