The Core-Wing Anomaly of Cool Ap Stars: Abnormal Balmer Profiles

TL;DR

This paper investigates the abnormal Balmer line profiles in cool Ap stars, revealing that their atmospheres are atypical and cannot be explained by standard LTE models, indicating unique atmospheric properties.

Contribution

It identifies and characterizes the core-wing anomaly in Balmer profiles of cool Ap stars, challenging previous assumptions of normal stellar atmospheres.

Findings

Balmer profiles show broad wings with narrow cores in cool Ap stars

Standard LTE models cannot explain the observed profiles

The atmospheres of these stars are abnormal and not 'normal'

Abstract

Paper by Cowley et al. The Core-Wing Anomaly Etc. The profiles of H$\alpha$ in a number of cool Ap stars are anomalous. Broad wings, indicative of temperatures in the range 7000-8000K end abruptly in narrow cores. The widths of these cores are compatible with those of dwarfs with temperatures of 6000K or lower. This profile has been known for Przybylski's star, but it is seen in other cool Ap's. The H$\beta$ profile in several of these stars shows a similar core-wing anomaly (CWA). In Przybylski's star, the CWA is probably present at higher Balmer members. We are unable to account for these profiles within the context of LTE and normal dwarf atmospheres. We conclude that the atmospheres of these stars are not ``normal.'' This is contrary to a notion that has long been held.