Study reveals properties of fast-spinning magnetic star HD 345439

Using the Nanshan One-Meter Wide-Field Telescope (NOWT), Chinese astronomers have made multicolored photometric observations of a rapidly rotating magnetic star known as HD 345439. The results of this campaign observation, published November 1 on the arXiv preprint server, sheds more light on the properties of this star.

Magnetic stars of spectral type O, B and A (OBA) are relatively rare – for example, only 11 magnetic stars of type O are known to date. Observations show that they exhibit unique phenomena, such as the cyclic variability of line profile morphologies. Since the mechanism of formation of magnetic fields in these stars is not yet fully understood, the study of objects of this type is essential to advance our knowledge of this process.

Located approximately 7,000 light-years from Earth, HD 345439 is a massive helium-rich magnetic star exhibiting extremely strong, large-scale magnetic fields and rapid rotation. Recent observations have shown that the star is about seven times larger and almost nine times more massive than the sun. HD 345439 has longitudinal magnetic fields exhibiting periodic variability with an amplitude of about 2-3 kG, and the polar magnetic force of this star reaches 10 kG.

In order to better understand the properties of this particular star, a team of astronomers led by Dong-Xiang Shen from Xinjiang University in Urumqi, China made photometric observations of HD 345439 in late 2020.

“Here, we aim to provide more detailed features of the rapidly rotating magnetic early-type star HD 345439 using NOWT photometric observations,” the researchers wrote in the paper.

According to the study, the shapes of the light curves from the photometric observations of HD 345439 show a typical double-asymmetric S-wave characteristic originating from the star’s magnetic clouds. The researchers speculate that such a characteristic may be caused by a mismatch between the center of the dipole magnetic fields and the axis of rotation.

In general, the light curve profiles and amplitudes were found to be approximately consistent with archival data. The new observations found no evidence of pulsating behavior in HD 345439.

The NOWT data allowed Shen’s team to derive the rotation period of HD 345439. It has been calculated that it takes this star nearly 18.5 hours to rotate around its axis, which is consistent with previous estimates.

New research has revealed that HD 345439 is smaller and less massive than previously thought, having a radius of about 5.6 solar radii and a mass of eight solar masses. The results suggest the star is about 26.8 million years old, has an effective temperature of about 22,000 K, and its metallicity is at a level of -0.5. The distance to HD 345439 has been estimated at 6,982 light-years.

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