Astronomers Measure Mass and Age of Beta Crucis A – Sci-News.com

Beta Crucis is represented in the flags of Australia, Brazil, New Zealand, Papua New Guinea and Samoa.

Beta Crucis. Image credit: Naskies at en.wikipedia / CC BY-SA 3.0.

Beta Crucis is a triple star system located at a distance of 280 light-years from the Earth.

Also known as HD 111123, HIC 62434, Becrux and Mimosa, it is the second-brightest object in the constellation of Crux and the 20th brightest star in the night sky.

The primary star in the system, beta Crucis A, is a beta Cephei variable star with rapid brightness changes.

The secondary, beta Crucis B, is a main sequence star with a stellar class of B2.

And the third companion is a low mass, pre-main sequence star.

To crack the age and mass of beta Crucis A, Dr. Daniel Cotton from the Australian National University and Monterey Institute for Research in Astronomy and his colleagues combined asteroseismology, the study of a stars regular movements, with polarimetry, the measurement of the orientation of light waves.

Asteroseismology relies on seismic waves bouncing around the interior of a star and producing measurable changes in its light, they explained.

Probing the interiors of heavy stars that will later explode as supernovae has traditionally been difficult.

In the study, the authors analyzed data from NASAs WIRE and TESS satellites, high-resolution spectroscopic data from ESO, and polarimetric data from Siding Spring Observatory and Western Sydney Universitys Penrith Observatory.

We wanted to investigate an old idea, Dr. Cotton said.

It was predicted in 1979 that polarimetry had the potential to measure the interiors of massive stars, but its not been possible until now.

The size of the effect is quite small, added Professor Jeremy Bailey, an astronomer at the University of New South Wales.

We needed the worlds best precision of the polarimeter we designed and built.

The team found beta Crucis A to be approximately 14.5 times as massive as the Sun and around 11 million years old, making it the heaviest star with an age determined from asteroseismology ever.

Analyzing the three types of long-term data together allowed us to identify Mimosas dominant mode geometries, said Professor Derek Buzasi, an astronomer at Florida Gulf Coast University.

This opened the road to weighing and age-dating the star using seismic methods.

This polarimetric study of Mimosa opens a new avenue for asteroseismology of bright massive stars, added Professor Conny Aerts, an astronomer with the Institute of Astronomy at KU Leuven, Radboud University Nijmegen, and the Max Planck Institute for Astronomy.

While these stars are the most productive chemical factories of our Galaxy, they are so far the least analyzed asteroseismically, given the degree of difficulty of such studies. The heroic efforts by the Australian polarimetrists are to be admired.

The teams paper was published in the journal Nature Astronomy.

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D.V. Cotton et al. Polarimetric detection of non-radial oscillation modes in the Cephei star Crucis. Nat Astron, published online December 6, 2021; doi: 10.1038/s41550-021-01531-9

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