Characterizing Variability in Bright Metallic-Line A (Am) Stars Using Data from the NASA TESS Spacecraft

TL;DR

This study investigates the variability and pulsation characteristics of bright metallic-line A (Am) stars using TESS data, revealing unexpected delta Scuti pulsations in some stars and emphasizing the need for further analysis.

Contribution

It provides the first extensive TESS-based photometric analysis of Am stars, identifying pulsators and variability patterns that challenge existing theories.

Findings

Discovered delta Scuti pulsations in some Am stars.

Identified variability possibly caused by rotation and starspots.

Highlighted the need for follow-up observations to confirm pulsations.

Abstract

Metallic-line A (Am) stars are main-sequence stars of around twice the mass of the Sun that show element abundance peculiarities in their spectra. The radiative levitation and diffusive settling processes responsible for these abundance anomalies should also deplete helium from the region of the envelope that drives delta Scuti pulsations. Therefore, these stars are not expected to be delta Scuti stars, which pulsate in multiple radial and nonradial modes with periods of around 2 hours. As part of the NASA TESS Guest Investigator Program, we proposed photometric observations in 2-minute cadence for samples of bright (visual magnitudes around 7-8) Am stars. Our 2020 SAS meeting paper reported on observations of 21 stars, finding one delta Scuti star and two delta Scuti / gamma Doradus hybrid candidates, as well as many stars with photometric variability possibly caused by rotation and starspots. Here we present an update including 34 additional stars observed up to February 2021, among them three delta Scuti stars and two delta Scuti / gamma Doradus hybrid candidates. Confirming the pulsations in these stars requires further data analysis and follow-up observations, because of possible background stars or contamination in the TESS CCD pixels with scale 21 arc sec per pixel. Asteroseismic modeling of these stars will be important to understand the reasons for their pulsations.