Variable Polarization of WR~31a: Binary Companion or Co-Rotating Interaction Region?
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arXiv
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| Autori principali: | , , , |
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| Natura: | Preprint |
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2025
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| _version_ | 1866915268120281088 |
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| author | Erba, Christiana Ignace, Richard Simmons, Faith Davies, Ben |
| author_facet | Erba, Christiana Ignace, Richard Simmons, Faith Davies, Ben |
| contents | WR 31a (Hen 3-519) is likely a post-luminous 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 fit for a strictly circular orbit to derive an orbital period of 16.7 d, requiring a high inclination perspective of $i\sim 80^\circ$. We also consider an elliptical orbit under simplifying assumptions, yielding a match for $i\sim 75^\circ$ with eccentricity $e\sim 0.5$ and a longer orbital period of about 70 d. 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 evolutionary stage. However, if the loop originates because of a co-rotating interaction region (CIR), then the rotation period could be 8.5 d or 17 d. This would give an estimated equatorial rotation speed of 95 or 190 km/s. Either of these is a significant fraction of the estimated critical speed of rotational break-up at 320 km/s (for an Eddington factor of $Γ=0$). |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2505_00183 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Variable Polarization of WR~31a: Binary Companion or Co-Rotating Interaction Region? Erba, Christiana Ignace, Richard Simmons, Faith Davies, Ben Solar and Stellar Astrophysics WR 31a (Hen 3-519) is likely a post-luminous 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 fit for a strictly circular orbit to derive an orbital period of 16.7 d, requiring a high inclination perspective of $i\sim 80^\circ$. We also consider an elliptical orbit under simplifying assumptions, yielding a match for $i\sim 75^\circ$ with eccentricity $e\sim 0.5$ and a longer orbital period of about 70 d. 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 evolutionary stage. However, if the loop originates because of a co-rotating interaction region (CIR), then the rotation period could be 8.5 d or 17 d. This would give an estimated equatorial rotation speed of 95 or 190 km/s. Either of these is a significant fraction of the estimated critical speed of rotational break-up at 320 km/s (for an Eddington factor of $Γ=0$). |
| title | Variable Polarization of WR~31a: Binary Companion or Co-Rotating Interaction Region? |
| topic | Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2505.00183 |