Categorizing and Searching for Rapidly Oscillating Ap Stars

by Dr Jacob Romeo (U. Hawaii Physics)

Thursday Sep 5, 2024, 3:30 PM → 4:30 PM Pacific/Honolulu

Room 112 (Watanabe Hall)

The night sky is full of stars and astronomers are still discovering new things about them every day! What helps astronomers in knowing their interior structures and compositions are pulsations in the star. There are different types of pulsations such as radial and non-radial. Radial pulsations expand and contract spherically with one period, making them a lot easier to study and observe. Where non-radial pulsations are waves traveling throughout the star, going in all directions in complex patterns with multiple periods, making them a lot more intricate to study. One of these non-radial pulsators is called a roAp, rapidly oscillating A-type peculiar star, which lies in the delta-scuti instability strip along with other non-radial pulsators.

There are approximately one-hundred known roAp stars, where most of the rapid pulsators in the instability strip get classified as gammadors or delta-scutis. Though they oscillate rapidly, with a period of a few seconds, their amplitudes are larger compared to roAps. This is what makes them so different as their amplitudes can be on the order of mmags. Due to their small amplitudes, it is very difficult to detect the oscillations in roAp stars. Sometimes detecting new pulsations or not seeing the repeated ones on different observation nights. Astronomers have theories to why they oscillate with such small amplitudes, with the best working theory being due to the metals in their atmospheres creating a strong magnetic field. In the outer layers of the star, the B-fields effect it directly through a restoring force action and indirectly by relations with the outer convection layer.  Another reason they are hard to resolve is that they are very dim due to being A, sometimes F,  type stars at about 1-2 solar masses. Sensitive equipment, in the visible range, is needed to be able to observe these stars, like the 1-meter observatory SARA-RM in the Canary Islands, which is 2400 meters above sea level with perfect conditions. The Mauna Kea observatory is an even better spot to observe roAp stars due to the pristine weather and size of the telescopes. Asteroseismologists have become aware that roAp stars are very important in studying the interiors of stars and their evolution. Which is why this research not only gathered more data on known roAps, but time was spent to also make a classification algorithm so that it is easier to find candidates.

The theoretical work on roAps is very interesting, but thorough and heavy. Which is why as an undergrad I was working on the classification algorithm to easier find these stars so that astronomers can learn more about them. The first piece of the python script is done, though a lot of updates are needed to make it more selective. Another goal is to make an A.I. algorithm to find the small oscillations in roAps on the Amplitude spectrum you get out of the data collection. The program would also learn the more data you fed it, allowing it to not only do the entire data analysis needed, but to also highlight certain pulsations in the data to confirm if the candidate is an roAp or not.

Jacob R. Romeo  jromeo@hawaii.edu   (352) 408-0098