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So why is that star wearing a dusty belt?

Infrared image and model of the dusty disk around HD 62623, along with velocity data showing rotation.
Infrared image and model of the dusty disk around HD 62623, along with velocity data showing rotation. F. Millour et al.
/ Source: Discovery Channel

The hottest, most massive stars generate fierce stellar winds that affect their surroundings. So how is it that one such star can hold on to its dusty belt without it being blown away? A suite of optical telescopes borrowing a technique from radio astronomy may have provided the answer.

The star HD 62623 is a hot supergiant star between 2,000 and 3,000 light-years away. Previous observations in the infrared indicated that there was quite a bit of dust in the environment surrounding this energetic star

Astronomers at the Max Planck Institute for Radio Astronomy in Germany and the Joint Research Unit (UMR) in France decided to take a much closer look at the structure of this dust.

In order to do so, they needed very high spatial resolution in order to see fine details. They used the Very Large Telescope Interferometer (VLTI) in Chile, a system that can combine light from the site's four 8.2-meter telescopes and four 1.8-meter telescopes. By doing so, astronomers can achieve resolution of several milliarcseconds. (A milliarcsecond is like seeing an astronaut on the moon with your naked eye!) As you may imagine, doing this is not easy.

Radio astronomers have been using interferometry for decades (i.e. Very Large Array), so this team was able to borrow a powerful technique from radio in order to process the data.

Called self-calibration, it literally uses the target source itself as a calibrator to take out instrumental effects. Starting with a simple model, you iteratively make a better and better one as calibration improves. Once the astronomers were able to get the best image possible, they were able to model the system.

The dust ring is several astronomical units (AU) across, where 1 AU is the average distance between the sun and the Earth. The disk is likely held in place by a known but unseen companion star that is more like the mass of the sun.

This companion can slow down the intense stellar wind of HD 62623, allowing the disk to survive. The observations even show the disk to be rotating. However, the authors are still not clear how dust can survive in the first place around such an incredibly bright star to begin with, so more work is always needed.

This research has been accepted by Astronomy & Astrophysics, and a preprint is available at arxiv.org.