CoRoT's view on variable B8/9 stars: spots versus pulsations: Evidence for differential rotation in HD 174648

TL;DR

This study uses CoRoT data to investigate variability in B stars near the A and B-star instability zones, revealing evidence of spots and differential rotation in HD 174648 and highlighting challenges in distinguishing pulsations from rotational effects.

Contribution

It provides new evidence for spots and differential rotation in a B star, combining photometry, spectroscopy, and asteroseismic modeling to analyze variability.

Findings

Evidence of spots and differential rotation in HD 174648

Difficulty distinguishing pulsations from rotational modulation in light curves

Insights into variability mechanisms in B stars near the instability strip

Abstract

Context. There exist few variability studies of stars in the region in the Hertzsprung-Russell diagram between the A and B-star pulsational instability strips. With the aid of the high precision continuous measurements of the CoRoT space satellite, low amplitudes are more easily detected, making a study of this neglected region worthwhile. Aims. We collected a small sample of B stars observed by CoRoT to determine the origin of the different types of variability observed. Methods. We combine literature photometry and spectroscopy to measure the fundamental parameters of the stars in the sample, and compare asteroseismic modelling of the light curves with (differentially rotating) spotted star models. Results. We found strong evidence for the existence of spots and differential rotation in HD 174648, and formulated hypotheses for their origin. We show that the distinction between pulsations and rotational modulation is difficult to make solely based on the light curve, especially in slowly rotating stars.