Evaluating the Origin of Chemical Anomalies in Am Stars
Mbarara University of Science and Technology,
Date & Time :
Using the high-precision Kepler data, interesting phenomena such as spots, and ''hump and spike''; features were observed in the light curves of some normal A and metallic lined A stars (Am stars). However, the connection between such phenomena and the chemical peculiarity of the Am stars is still unclear. In order to make progress on these issues, it's important to: use the ultraprecise Kepler data to determine the spot and rotational properties of such stars, collect high-resolution spectroscopic data to determine their fundamental parameters, and individual chemical abundances, and compare the results with the theory. Using the ``hump and spike'' features, spot, and rotational properties were determined. In comparison with G, K, and M stars, spots in normal A and Am/Fm stars are weak, which may indicate the presence of a weak magnetic field. Using data collected with the High Efficiency and Resolution Mercator Echelle Spectrograph (HERMES), the spectral type, and the atmospheric stellar parameters such as effective temperatures, surface gravities, projected rotational, microturbulent, and radial velocities of a subsample of stars were determined. A detailed individual chemical abundance analysis for each target in the subsample was also performed. KIC 3459226 and KIC 6266219 were classified as Am stars, KIC 9349245 as marginal Am star, while KIC4567097, KIC 4818496, KIC 5524045, KIC 5650229, KIC 7667560, and KIC 9272082 are non-Am stars. Based on their spectral classification and chemical abundance pattern, KIC 6266219 (previously treated as chemically normal) was reclassified as an Am star (kA3hA7mF1) and KIC\,9272082 (previously treated as Am) as non-Am. Using the MESA evolution code, the evaluation of the transport processes indicates that radiative diffusion, combined with turbulent mixing, thermohaline convection, and slow to moderate rotation can account for most of the chemical peculiarities found in Am stars. However, discrepancies in abundances also imply that there are other processes, currently unknown, which contribute to the observed chemical peculiarities in Am stars.
About Speaker :
Trust Otto is a Ph.D. student at Mbarara University of Science and Technology, Mbarara, Uganda. This seminar is a part of the activities commemorating "75 years of India's Independence: Azadi ka Amrit Mahotsav" at ARIES.