Observations inspect double-lined spectroscopic binary HD 34736

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Using various telescopes, an international team of astronomers has conducted a comprehensive study of a double-lined spectroscopic binary known as HD 34736. The study, published November 6 in the Monthly Notices of the Royal Astronomical Society, delivers important insights into the properties of this system.

So far, the majority of binaries have been detected by Doppler shifts in their spectral lines, hence these systems are called spectroscopic binaries. Observations show that in some spectroscopic binaries, spectral lines from both stars are visible, and these lines are alternately double and single. These systems are known as double-lined spectroscopic binaries (SB2).

HD 34736 is an SB2 system consisting of two chemically peculiar late B-type stars, located some 1,215 light years away. Previous observations of HD 34736 have found that the system has an extraordinarily strong magnetic field exceeding 4.5 kG. The effective temperatures of the primary and secondary star were found to be 13,700 and 11,500 K, respectively.

In order to shed more light on the properties of HD 34736, a group of astronomers led by Eugene Semenko of the National Astronomical Research Institute of Thailand, decided to investigate this system in detail with various observing facilities worldwide.

"For this study, we organized a multi-site spectroscopic and spectropolarimetric monitoring campaign with observational facilities in Europe, Asia, and North America," the researchers wrote in the paper.

The observations found that the primary object in HD 34736 is a chemically peculiar helium-weak star with an effective temperature of 13,000 K and rotational velocity of 75 km/s.

When it comes to its companion, the collected data indicate that it is a chemically peculiar star exhibiting variability of magnesium and silicon emission lines, with an effective temperature of 11,500 K and rotational velocity of 110–180 km/s. The two components orbit each other on a highly eccentric orbit with an orbital period of 83.2 days.

According to the study, the primary star has a rotational period of approximately 1.28 days, which is lengthening at a rate of about 1.26 seconds per year. The secondary star's rotational period turned out to be shorter—about 0.52 days, reducing at a rate of 0.14 seconds per year.

Furthermore, the observations found that the primary star showcases a strongly asymmetric global magnetic field, whose strength varies from −6.0 to 5.0 kG. For the secondary star, the astronomers identified weak spectropolarimetric evidence of a magnetic field.

Based on the obtained data, the authors of the paper suppose that there may be a third cooler component in the HD 34736 system, likely a T Tauri variable star. However, further studies of the system are required in order to confirm this hypothesis.

More information: Eugene Semenko et al., HD 34736: An intensely magnetised double-lined spectroscopic binary with rapidly-rotating chemically peculiar B-type components, Monthly Notices of the Royal Astronomical Society (2024). DOI: 10.1093/mnras/stae2503. On arXiv: DOI: 10.48550/arxiv.2411.05376

Journal information: Monthly Notices of the Royal Astronomical Society , arXiv

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