The companion mass distribution of post common envelope hot subdwarf binaries: evidence for boosted and disrupted magnetic braking?
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| Auteurs principaux: | , , , , , , , , |
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| Format: | Preprint |
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2024
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| _version_ | 1866917840738582528 |
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| author | Blomberg, Lisa El-Badry, Kareem Breivik, Katelyn Caiazzo, Ilaria Nagarajan, Pranav Rodriguez, Antonio van Roestel, Jan Vanderbosch, Zachary P. Yamaguchi, Natsuko |
| author_facet | Blomberg, Lisa El-Badry, Kareem Breivik, Katelyn Caiazzo, Ilaria Nagarajan, Pranav Rodriguez, Antonio van Roestel, Jan Vanderbosch, Zachary P. Yamaguchi, Natsuko |
| contents | We measure the mass distribution of main-sequence (MS) companions to hot subdwarf B stars (sdBs) in post-common envelope binaries (PCEBs). We carried out a spectroscopic survey of 14 eclipsing systems ("HW Vir binaries") with orbital periods of $3.8 < P_{\rm orb} < 12$ hours, resulting in a well-understood selection function and a near-complete sample of HW Vir binaries with $G < 16$. We constrain companion masses from the radial velocity curves of the sdB stars. The companion mass distribution peaks at $M_{\rm MS}\approx 0.15 M_{\odot}$ and drops off at $M_{\rm MS} > 0.2\,M_{\odot}$, with only two systems hosting companions above the fully-convective limit. There is no correlation between $P_{\rm orb}$ and $M_{\rm MS}$ within the sample. A similar drop-off in the companion mass distribution of white dwarf (WD) + MS PCEBs has been attributed to disrupted magnetic braking (MB) below the fully-convective limit. We compare the sdB companion mass distribution to predictions of binary evolution simulations with a range of MB laws. Because sdBs have short lifetimes compared to WDs, explaining the lack of higher-mass MS companions to sdBs with disrupted MB requires MB to be boosted by a factor of 20-100 relative to MB laws inferred from the rotation evolution of single stars. We speculate that such boosting may be a result of irradiation-driven enhancement of the MS stars' winds. An alternative possibility is that common envelope evolution favors low-mass companions in short-period orbits, but the existence of massive WD companions to sdBs with similar periods disfavors this scenario. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2408_15334 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | The companion mass distribution of post common envelope hot subdwarf binaries: evidence for boosted and disrupted magnetic braking? Blomberg, Lisa El-Badry, Kareem Breivik, Katelyn Caiazzo, Ilaria Nagarajan, Pranav Rodriguez, Antonio van Roestel, Jan Vanderbosch, Zachary P. Yamaguchi, Natsuko Solar and Stellar Astrophysics We measure the mass distribution of main-sequence (MS) companions to hot subdwarf B stars (sdBs) in post-common envelope binaries (PCEBs). We carried out a spectroscopic survey of 14 eclipsing systems ("HW Vir binaries") with orbital periods of $3.8 < P_{\rm orb} < 12$ hours, resulting in a well-understood selection function and a near-complete sample of HW Vir binaries with $G < 16$. We constrain companion masses from the radial velocity curves of the sdB stars. The companion mass distribution peaks at $M_{\rm MS}\approx 0.15 M_{\odot}$ and drops off at $M_{\rm MS} > 0.2\,M_{\odot}$, with only two systems hosting companions above the fully-convective limit. There is no correlation between $P_{\rm orb}$ and $M_{\rm MS}$ within the sample. A similar drop-off in the companion mass distribution of white dwarf (WD) + MS PCEBs has been attributed to disrupted magnetic braking (MB) below the fully-convective limit. We compare the sdB companion mass distribution to predictions of binary evolution simulations with a range of MB laws. Because sdBs have short lifetimes compared to WDs, explaining the lack of higher-mass MS companions to sdBs with disrupted MB requires MB to be boosted by a factor of 20-100 relative to MB laws inferred from the rotation evolution of single stars. We speculate that such boosting may be a result of irradiation-driven enhancement of the MS stars' winds. An alternative possibility is that common envelope evolution favors low-mass companions in short-period orbits, but the existence of massive WD companions to sdBs with similar periods disfavors this scenario. |
| title | The companion mass distribution of post common envelope hot subdwarf binaries: evidence for boosted and disrupted magnetic braking? |
| topic | Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2408.15334 |