First detections of 610 MHz radio emission from hot magnetic stars

TL;DR

This study presents the first low-frequency radio detections of magnetic B-type stars, revealing their magnetospheric properties and variability, with implications for understanding stellar wind absorption and coherent emission processes.

Contribution

It provides the first low-frequency radio measurements of hot magnetic stars, expanding observational data into previously unexplored frequency regimes.

Findings

Detected five B-type stars at 610 and 1390 MHz.

No detections for O-type stars due to free-free absorption.

Observed rapid variability in one star, HD 133880.

Abstract

We have carried out a study of radio emission from a small sample of magnetic O- and B-type stars using the Giant Metrewave Radio Telescope, with the goal of investigating their magnetospheres at low frequencies. These are the lowest frequency radio measurements ever obtained of hot magnetic stars. The observations were taken at random rotational phases in the 1390 and the 610 MHz bands. Out of the 8 stars, we detect five B-type stars in both the 1390 and the 610 MHz bands. The O-type stars were observed only in the 1390 MHz band, and no detections were obtained. We explain this result as a consequence of free-free absorption by the free-flowing stellar wind exterior to the closed magnetosphere. We also study the variability of individual stars. One star - HD 133880 - exhibits remarkably strong and rapid variability of its low frequency flux density. We discuss the possibility of this emission being coherent emission as reported for CU Vir by Trigilio et al. (2000).