HD 112485 may rotate at different rates within its interior

The massive pulsating star HD 112485 is part of an eclipsing binary, where the two stars pass in front of each other from our viewpoint. Analysis of 65 such systems found tentative signs that HD 112485’s interior rotates at different rates. Across the sample, pulsation amplitude decreased as pulsation frequency increased, while neither frequency nor amplitude showed a significant link to the binary’s orbital period.

Star system: HD 112485 | Distance from the Sun: 5881 light years

HD 112485 is a massive pulsating star in an eclipsing binary, a system where the stars periodically pass in front of one another as seen from Earth. Its internal rotation may vary with depth: the analysis tentatively points to different rotation rates inside the star. The result comes from comparing the star’s pulsations with models of its interior and evolution.

The work examined TESS observations of 65 β Cephei stars in eclipsing binaries. These are massive stars that expand and contract in regular patterns, producing changes in brightness. Researchers looked for rotationally split modes, where rotation separates a pulsation signal into nearby frequencies. This pattern can help reveal a star’s interior rotation. They derived rotation rates for 14 systems where the splitting could be identified.

HD 112485 and EK Cru also received detailed modelling to match their observed pulsations with predicted stellar behaviour. HD 112485 is among the least evolved β Cephei stars modelled with this method. Its estimated core hydrogen mass fraction is 0.501, with an uncertainty of +0.009 and -0.013. This fraction indicates how much hydrogen remains in the star’s core. The analysis also found that pulsation amplitude tends to be lower at higher pulsation frequencies. Neither pulsation frequency nor amplitude had a statistically significant relationship with the binary orbital period.

Key findings
The sample included 65 β Cephei stars in eclipsing binaries, with interior rotation rates derived for 14 systems.
HD 112485 shows tentative evidence of different rotation rates within its interior.
Most systems with measured rotation were consistent with near-uniform rotation; CZ Vel was an exception.
HD 112485’s core hydrogen mass fraction was estimated as 0.501, with an uncertainty of +0.009 and -0.013.
Pulsation amplitude decreased as pulsation frequency increased, but neither pulsation frequency nor amplitude showed a significant link to orbital period.

Scientific study

Ensemble pulsational characteristics of eclipsing binaries containing β Cep stars observed by the TESS mission (external link)