Variable Polarization of WR 31a: Binary Companion or Corotating Interaction Region?
WR 31a (Hen 3-519) is likely a postluminous blue variable (LBV) star that is evolving to become a classical Wolf–Rayet star. Multicolor (UBVR) photopolarimetric observations of WR 31a were obtained over nine nights in early-2007. The linear polarization data of WR 31a trace a “loop” structure in a S...
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IOP Publishing
2025-01-01
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| Online Access: | https://doi.org/10.3847/1538-3881/add2ed |
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| author | Christiana Erba Richard Ignace Faith Simmons Ben Davies |
| author_facet | Christiana Erba Richard Ignace Faith Simmons Ben Davies |
| author_sort | Christiana Erba |
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| description | WR 31a (Hen 3-519) is likely a postluminous blue variable (LBV) star that is evolving to become a classical Wolf–Rayet star. Multicolor (UBVR) photopolarimetric observations of WR 31a were obtained over nine nights in early-2007. The linear polarization data of WR 31a trace a “loop” structure in a Stokes Q − U diagram, which is similar in all four passbands. After mean subtraction, the four loops align to form a single overall pattern. Such loops can be expected to arise from binary systems. We test the binary hypothesis with two models. The data are fitted for a strictly circular orbit to derive an orbital period of 16.7 days, requiring a high inclination perspective of i ∼ 80°. We also consider an elliptical orbit under simplifying assumptions, yielding a match for i ∼ 75° with eccentricity e ∼ 0.5 and a longer orbital period of about 70 days. The prevalence of binarity among massive stars is well known; the prospect of detecting a binary companion during the post-LBV stage of WR 31a would add to an emerging narrative of diverse interactions between massive multiple components as a function of the evolutionary stage. However, if the loop originates because of a corotating interaction region, then the rotation period could be 8.5 days or 17 days. This would give an estimated equatorial rotation speed of 95 or 190 km s ^−1 . Either of these is a significant fraction of the estimated critical speed of rotational break-up at 320 km s ^−1 (for an Eddington factor of Γ = 0). |
| format | Article |
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| institution | Kabale University |
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| language | English |
| publishDate | 2025-01-01 |
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| spelling | doaj-art-d5b2c3f9312249be822fb197e0cafa3d2025-08-20T03:26:35ZengIOP PublishingThe Astronomical Journal1538-38812025-01-0117011010.3847/1538-3881/add2edVariable Polarization of WR 31a: Binary Companion or Corotating Interaction Region?Christiana Erba0https://orcid.org/0000-0003-1299-8878Richard Ignace1https://orcid.org/0000-0002-7204-5502Faith Simmons2Ben Davies3Space Telescope Science Institute , 3700 San Martin Drive, Baltimore, MD 21218, USA ; christi.erba@gmail.com; Department of Physics and Astronomy, East Tennessee State University , Johnson City, TN 37663, USADepartment of Physics and Astronomy, East Tennessee State University , Johnson City, TN 37663, USADepartment of Physics and Astronomy, East Tennessee State University , Johnson City, TN 37663, USAIndependent ResearcherWR 31a (Hen 3-519) is likely a postluminous blue variable (LBV) star that is evolving to become a classical Wolf–Rayet star. Multicolor (UBVR) photopolarimetric observations of WR 31a were obtained over nine nights in early-2007. The linear polarization data of WR 31a trace a “loop” structure in a Stokes Q − U diagram, which is similar in all four passbands. After mean subtraction, the four loops align to form a single overall pattern. Such loops can be expected to arise from binary systems. We test the binary hypothesis with two models. The data are fitted for a strictly circular orbit to derive an orbital period of 16.7 days, requiring a high inclination perspective of i ∼ 80°. We also consider an elliptical orbit under simplifying assumptions, yielding a match for i ∼ 75° with eccentricity e ∼ 0.5 and a longer orbital period of about 70 days. The prevalence of binarity among massive stars is well known; the prospect of detecting a binary companion during the post-LBV stage of WR 31a would add to an emerging narrative of diverse interactions between massive multiple components as a function of the evolutionary stage. However, if the loop originates because of a corotating interaction region, then the rotation period could be 8.5 days or 17 days. This would give an estimated equatorial rotation speed of 95 or 190 km s ^−1 . Either of these is a significant fraction of the estimated critical speed of rotational break-up at 320 km s ^−1 (for an Eddington factor of Γ = 0).https://doi.org/10.3847/1538-3881/add2edWolf-Rayet starsLuminous blue variable starsStellar windsPolarimetryStellar mass loss |
| spellingShingle | Christiana Erba Richard Ignace Faith Simmons Ben Davies Variable Polarization of WR 31a: Binary Companion or Corotating Interaction Region? The Astronomical Journal Wolf-Rayet stars Luminous blue variable stars Stellar winds Polarimetry Stellar mass loss |
| title | Variable Polarization of WR 31a: Binary Companion or Corotating Interaction Region? |
| title_full | Variable Polarization of WR 31a: Binary Companion or Corotating Interaction Region? |
| title_fullStr | Variable Polarization of WR 31a: Binary Companion or Corotating Interaction Region? |
| title_full_unstemmed | Variable Polarization of WR 31a: Binary Companion or Corotating Interaction Region? |
| title_short | Variable Polarization of WR 31a: Binary Companion or Corotating Interaction Region? |
| title_sort | variable polarization of wr 31a binary companion or corotating interaction region |
| topic | Wolf-Rayet stars Luminous blue variable stars Stellar winds Polarimetry Stellar mass loss |
| url | https://doi.org/10.3847/1538-3881/add2ed |
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