scieee AI-readable full text Open interactive document viewer

A study of stochastic low-frequency variability in 50 O- and B-type stars

Pedersen, May Gade; Bildsten, Lars

Publisher
Zenodo
DOI
10.5281/zenodo.17282962
Repository
zenodo.org
Language
en

Abstract

With a rapidly increasing number of photometric time series becoming available for O- and B-type stars, especially since the launch of TESS, it has become clear that stochastic low-frequency (SLF) variability is a common type of variability found in massive stars. This type of variability is seen as an increase in power towards low frequencies, as characteristic of red noise, and has been suggested to be caused by internal gravity waves, subsurface convection zones, radiatively driven stellar winds, or a combination thereof. Here we present the analysis and characterization of the SLF variability of 50 O- and B-type stars observed by TESS, of which 49 are found in six different Cygnus OB associations and one is in the Small Magellanic Cloud. We adopt two different methods for characterizing the signal. For the first we fit a Lorentzian-like function to the power density spectrum of the stars. Our second model-independent method uses the root-mean-square of the photometric variability and the cumulative integrated power density to characterize the variability. We compare our results to predictions from 2D and 3D simulations of internal gravity waves, subsurface convection, and stellar winds, finding good agreement between the observed characteristic frequencies of our sample and the predictions from sub-surface convection.

Full text

TASC9/KASC16, 11 July 2025 A study of stochastic low-frequency variability in 50 Oand B-type stars May Gade Pedersen Collaborator: Lars Bildsten (KITP) OB association Open cluster Globular cluster Scorpius Centaurus Credit: Akira Fuji NGC 299 Credit: ESA/Hubble & NASA M80 Credit: ESA/Hubble & NASA Similar “age” and chemical composition Formed from the “same” molecular cloud Stellar associations and clusters 10-1000 stars (10-100 OB) Unbound Very young (< 200 Myrs) ~few 1000 stars Loosely bound Young (Myrs - Gyrs) stars Tightly bound Very old (Gyrs) 105−106 Stellar associations and clusters OB association Open cluster Globular cluster Scorpius Centaurus Credit: Akira Fuji NGC 299 Credit: ESA/Hubble & NASA M80 Credit: ESA/Hubble & NASA Credit: ESA 300.0302.5305.0307.5310.0 RA [degrees] 34 36 38 40 42 44 Dec [degrees] Group A Group B Group C Group D Group E Group F 0.0 0.5 1.0 1.5 2.0 2.5 E(B-V) > 655 OB stars Pedersen et al. (in prep) Sample from Quintana & Wright (2021) What is stochastic low-frequency variability? Pulsating star Stochastic low-frequency variability Eclipsing binary Light curve Periodogram Pulsating star Eclipsing binary What is stochastic low-frequency variability? Stochastic low-frequency variability Light curve How we typically look at the SLF variability log-log scale + unit conversion Periodogram SLF variability is ubiquitous in massive stars After 2019 Before 2019 Sources: Blomme+2011, Ramiaramanantsoa+2018, Bowman+2019ab, Pedersen+2019, Burssens+2020, Dorn-Wallenstein+2020, Dong-Xiang+2024, Ma+2024, Bowman+2024, Pedersen+2025 What causes SLF variability? Surface convection? Sub-surface convection? Internal gravity waves? Stellar winds? Credit: NSO/AURA/NSF Edelmann et al. (2019) Sun 3D simulation3D simulation Schultz et al. (2022) Simulated spectrum Schultz et al. (2022) Jimenez et al. (2002) Observed spectrum VIRGO Red data Simulated spectrum Edelmann et al. (2019) Simulated spectrum Krticka & Feldmeier (2021) Debnath et al. (2024) 2D simulation Introducing: SLF variables in Cygnus OB +1 SMC SLF +53 known SLF variables Cygnus OB associations 655 O/B type stars 49 SLF variables Small Magellanic Cloud 13 O type stars “1” SLF variable (Bouret et al. 2021) Comparison sample 53 known SLF variables (Bowman et al. 2020) ⇒ ⇒ 49 SLF variables (91%) Take away Stochastic low-frequency variability is ubiquitous in massive stars . We propose a new model-independent method to characterise the variability . Parameter correlations with spectroscopic luminosity consistent with known SLF variables . The lower metallicity SMC star has similar characteristics as Galactic SLF variables . We find good agreements between the observations and simulations for sub-surface convection (in some places also for internal gravity waves) Future work Analyse the light curves using Gaussian processes and compare to our new method TASC9/KASC16, 11 July 2025 A study of stochastic low-frequency variability in 50 Oand B-type stars May Gade Pedersen Collaborator: Lars Bildsten (KITP)