An infrared diagnostic for magnetism in hot stars

TL;DR

This study explores the use of infrared hydrogen recombination lines as a new method to detect and analyze magnetic fields in hot stars, especially useful in obscured regions and for lower-density environments.

Contribution

It demonstrates the viability of IR hydrogen lines as magnetic diagnostics in hot stars, expanding detection capabilities beyond traditional optical and UV methods.

Findings

IR hydrogen lines show variable emission features in magnetic B2V stars

IR diagnostics can detect circumstellar material more easily due to lower stellar flux contribution

IR methods enable study of magnetic hot stars in obscured regions

Abstract

Magnetospheric observational proxies are used for indirect detection of magnetic fields in hot stars in the X-ray, UV, optical, and radio wavelength ranges. To determine the viability of infrared (IR) hydrogen recombination lines as a magnetic diagnostic for these stars, we have obtained low-resolution (R~1200), near-IR spectra of the known magnetic B2V stars HR 5907 and HR 7355, taken with the Ohio State Infrared Imager/Spectrometer (OSIRIS) attached to the 4.1m Southern Astrophysical Research (SOAR) Telescope. Both stars show definite variable emission features in IR hydrogen lines of the Brackett series, with similar properties as those found in optical spectra, including the derived location of the detected magnetospheric plasma. These features also have the added advantage of a lowered contribution of stellar flux at these wavelengths, making circumstellar material more easily detectable. IR diagnostics will be useful for the future study of magnetic hot stars, to detect and analyze lower-density environments, and to detect magnetic candidates in areas obscured from UV and optical observations, increasing the number of known magnetic stars to determine basic formation properties and investigate the origin of their magnetic fields.