Hydrogen recombination continuum as the radiative model for stellar optical flares

Simões, P. J.A., Araújo, A., Válio, A. and Fletcher, L. (2024) Hydrogen recombination continuum as the radiative model for stellar optical flares. Monthly Notices of the Royal Astronomical Society, 528(2), pp. 2562-2567. (doi: 10.1093/mnras/stae186)

Abstract

The study of stellar flares has increased with new observations from CoRoT, Kepler, and TESS satellites, revealing the broad-band visible emission from these events. Typically, stellar flares have been modelled as 104 K blackbody plasma to obtain estimates of their total energy. In the Sun, white-light flares (WLFs) are much fainter than their stellar counterparts, and normally can only be detected via spatially resolved observations. Identifying the radiation mechanism for the formation of the visible spectrum from solar and stellar flares is crucial to understand the energy transfer processes during these events, but spectral data for WLFs are relatively rare, and insufficient to remove the ambiguity of their origin: photospheric blackbody radiation and/or Paschen continuum from hydrogen recombination in the chromosphere. We employed an analytical solution for the recombination continuum of hydrogen instead of the typically assumed 104 K blackbody spectrum to study the energy of stellar flares and infer their fractional area coverage. We investigated 37 events from Kepler-411 and five events from Kepler-396, using both radiation mechanisms. We find that estimates for the total flare energy from the H recombination spectrum are about an order of magnitude lower than the values obtained from the blackbody radiation. Given the known energy transfer processes in flares, we argue that the former is a physically more plausible model than the latter to explain the origin of the broad-band optical emission from flares.

• Item Type: Articles
• Additional Information: The authors acknowledge the partial financial support received from Fundac¸ao˜ de Amparo a` Pesquisa do Estado de Sao˜ Paulo (FAPESP) grants 2018/04055- 8, 2021/02120-0, 2022/15700-7, Conselho Nacional de Desenvolvimento Cient´ıfico e Tecnologico ´ (CNPq) grant 150817/2022-3, as well as Fundo Mackenzie de Pesquisa e Inovac¸ao˜ (MackPesquisa), project number 231017. PJAS acknowledges support from Conselho Nacional de Desenvolvimento Cient´ıfico e Tecnologico ´ (CNPq) grants 307612/2019-8 and 305808/2022-2. LF acknowledgessupport from UK Research and Innovation’s Science and Technology Facilities Council under grant award number ST/X000990/1.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Fletcher, Professor Lyndsay
• Authors: Simões, P. J.A., Araújo, A., Válio, A., and Fletcher, L.
• College/School: College of Science and Engineering > School of Physics and Astronomy
• Journal Name: Monthly Notices of the Royal Astronomical Society
• Publisher: Oxford University Press
• ISSN: 0035-8711
• ISSN (Online): 1365-2966
• Copyright Holders: Copyright: © 2024 The Author(s)
• First Published: First published in Monthly Notices of the Royal Astronomical Society 528(2): 2562-2567
• Publisher Policy: Reproduced under a Creative Commons licence

Project Code	Award No	Project Name	Principal Investigator	Funder's Name	Funder Ref	Lead Dept
317627		Solar Physics at the University of Glasgow	Lyndsay Fletcher	Science and Technology Facilities Council (STFC)	ST/X000990/1	P&S - Physics & Astronomy