The Multiple Continuum Components in the White Light Flare of 16 January 2009 on the dM4.5e Star YZ CMi

TL;DR

This study reveals that stellar white-light flares can have multiple continuum components, including blackbody and hydrogen recombination spectra, which exhibit anti-correlated evolution, advancing understanding of flare emission mechanisms.

Contribution

It provides the first evidence of multiple continuum components in stellar flares and models their anti-correlated behavior, bridging stellar and solar flare phenomena.

Findings

Detection of both blackbody-like and hydrogen recombination spectra in stellar flare continuum

Anti-correlation observed between the two continuum components during flare decay

Modeling suggests continuum veiling explains the anti-correlation

Abstract

The white light during M dwarf flares has long been known to exhibit the broadband shape of a T~10,000 K blackbody, and the white light in solar flares is thought to arise primarily from Hydrogen recombination. Yet, a current lack of broad wavelength coverage solar-flare spectra in the optical/near-UV prohibits a direct comparison of the continuum properties to determine if they are indeed so different. New spectroscopic observations of a secondary flare during the decay of a megaflare on the dM4.5e star YZ CMi have revealed multiple components in the white-light continuum of stellar flares, including both a blackbody-like spectrum and a hydrogen recombination spectrum. One of the most surprising findings is that these two components are anti-correlated in their temporal evolution. We combine initial phenomenological modeling of the continuum components with spectra from radiative-hydrodynamic models to show that continuum veiling gives rise to the measured anti-correlation. This modeling allows us to use the components' inferred properties to predict how a similar spatially resolved, multiple-component white-light continuum might appear using analogies to several solar flare phenomena. We also compare the properties of the optical stellar flare white light to Ellerman bombs on the Sun.