Short-term variability and mass loss in Be stars - VI. Frequency groups in gamma Cas detected by TESS

Author(s)

Labadie-Bartz, Jonathan ^[1] ; Baade, Dietrich ^[2] ; Carciofi, Alex C. ^[1] ; Rubio, Amanda ^[1] ; Rivinius, Thomas ^[3] ; Borre, Camilla C. ^[4] ; Martayan, Christophe ^[3] ; Siverd, Robert J. ^[5]

Affiliation

^[1] Univ Sao Paulo, Inst Astron Geofis & Ciencias Atmosfer, Rua Matao 1226, Cidade Univ, BR-05508900 Sao Paulo, SP - Brazil

^[2] European Org Astron Res Southern Hemisphere ESO, Karl Schwarzschild Str 2, D-85748 Garching - Germany

^[3] European Org Astron Res Southern Hemisphere ESO, Casilla 19001, Santiago 19 - Chile

^[4] Aarhus Univ, Stellar Astrophys Ctr, Dept Phys & Astron, Ny Munkegade 120, DK-8000 Aarhus C - Denmark

^[5] NSFs NOIRLab, Gemini Observ, 670 N Aohoku Pl, Hilo, HI 96720 - USA

• Document type: Journal article
• Source: Monthly Notices of the Royal Astronomical Society; v. 502, n. 1, p. 242-259, MAR 2021.
• Web of Science Citations: 3

Abstract

In photometry of gamma Cas (B0.5 IVe) from the Solar Mass Ejection Imager (SMEI) and the BRIght Target Explorer (BRITE)-Constellation satellites, indications of low-order non-radial pulsation have recently been found, which would establish an important commonality with the class of classical Be stars at large. New photometry with the Transiting Exoplanet Survey Satellite (TESS) has detected three frequency groups near 1.0 (g1), 2.4 (g2), and 5.1 (g3) d(-1), respectively. Some individual frequencies are nearly harmonics or combination frequencies but not exactly so. Frequency groups are known from roughly three quarters of all classical Be stars and also from pulsations of beta Cep, slowly pulsating B (SPB), and gamma Dor stars and, therefore, firmly establish gamma Cas as a non-radial pulsator. The total power in each frequency group is variable. An isolated feature exists at 7.57 d(-1) and, together with the strongest peaks in the second and third groups ordered by increasing frequency (g2 and g3), is the only one detected in all three TESS sectors. The former long-term 0.82 d(-1) variability would fall into g1 and has not returned at a significant level, questioning its attribution to rotational modulation. Low-frequency stochastic variability is a dominant feature of the TESS light curve, possibly caused by internal gravity waves excited at the core-envelope interface. These are known to be efficient at transporting angular momentum outward, and may also drive the oscillations that constitute g1 and g2. The hard X-ray flux of gamma Cas is the only remaining major property that distinguishes this star from the class of classical Be stars. (AU)

• FAPESP's process: 17/23731-1 - Analysis and Modeling of a Large Sample of Galactic Be Stars
• Grantee: Jonathan Michael Labadie-Bartz
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 18/04055-8 - High precision spectroscopy: from the first stars to planets
• Grantee: Jorge Luis Melendez Moreno
• Support Opportunities: Research Projects - Thematic Grants