HD 42477: coupled r modes, g modes, and a p mode in an A0Vnne star. Issue 3 (21st March 2023)

• Record Type: Journal Article
• Authors: Kurtz, D W; Jayaraman, R; Sowicka, P; Handler, G; Saio, H; Labadie-Bartz, J; Lee, U
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 521:Issue 3(2023)
• Page Start: 4765
• Page End: 4774
• Publication Date: 2023-03-21
• Subjects: asteroseismology -- stars: emission-line, Be -- stars: individual: (TIC 294125876 HD 42477) -- stars: oscillations; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stad858
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Several studies have shown that a number of stars pulsating in p modes lie between the β Cep and δ Sct instability strips in the Hertzsprung–Russell (HR) Diagram. At present, there is no certain understanding of how p modes can be excited in this T eff range. The goal of this work is to disprove the conjecture that all stars pulsating in p modes and lying in this T eff range are the result of incorrect measurements of T eff, contamination, or the presence of unseen cooler companions lying in the δ Sct instability strip (given the high binary fraction of stars in this region of the HR Diagram). Using TESS data, we show that the A0Vnne star HD 42477 has a single p mode coupled to several r modes and/or g modes. We rule out a contaminating background star with a pixel-by-pixel examination, and we essentially rule out the possibility of a companion δ Sct star in a binary. We model the pulsations in HD 42477, and suggest that the g modes are excited by overstable convective core modes. We also conjecture that the single p mode is driven by coupling with the g modes, or that the oblateness of this rapidly-rotating star permits driving by He ii ionization in the equatorial region.