Using asteroseismic1 techniques, an international team searched for pulsations in a subsample of five thousand stars, from the 32 thousand observed in short cadence in the first two sectors (roughly the first two months of science operations) of NASA‘s Transiting Exoplanet Survey Satellite (TESS), and found five rare rapidly oscillating Ap (roAp2) stars. These results were accepted for publication in the journal Monthly Notices of the Royal Astronomical Society.
Among the stellar data, the team found the fastest known roAp pulsator, which completes one pulsation every 4.7 minutes. Two of these five stars were found to be particularly challenging to the currently understanding of the field, one because it is cooler than theoretically expected for a roAp star and the other because it exhibits pulsation frequencies that are unexpectedly high.
First author Margarida Cunha (Instituto de Astrofísica e Ciências do Espaço – IA and Universidade do Porto), explains the importance of studying these stars: “The TESS data shows that less than 1% of all A-type stars are likely to be rapidly oscillating Ap stars. Yet, the discovery of these rare pulsators can contribute greatly to the correct modelling of stellar evolution, because roAp stars are unique testbeds for the modelling of the physical processes responsible for chemical element segregation, such as atomic diffusion and radiative levitation.”
- Asteroseismology is the study of stellar interiors, by measuring seismic oscillations at the star’s surface. In seismology, the different vibration modes from an Earthquake can be used to study the Earth’s interior, in order to get data from the composition and depth of its different layers. In a similar fashion, oscillations at the star’s surface can be used to infer the internal structure and composition of a star.
- Rapidly oscillating Ap stars, also known as roAp stars, are rare stellar objects. They are found among the chemically peculiar Ap stars, which are characterised by surface spots with enhanced abundances of Si, Cr, Sr, or Eu, up to a million times the solar value. Ap stars have strong magnetic fields and a small fraction exhibits low amplitude pulsations, at frequencies similar to those seen in our sun.