The frequency-independent radio luminosity -- orbital/rotational period relation of RS CVn stars

Abstract

Radio emissions from RS CVn objects exhibit distinct characteristics at low and high frequencies, widely attributed to differing radiation mechanisms. The disparate processes of high-frequency gyrosynchrotron and low-frequency electron cyclotron maser emissions have traditionally suggested an absence of correlation in their radio luminosities. Our study presents a frequency-independent linear correlation between radio luminosity ($L_R$) and orbital/rotational periods ($P$) in RS CVn binaries. Analyzing the Sydney Radio Star Catalogue (SRSC) data, we derived orbital periods for 42 of 60 RS CVn sources using TESS light curves, revealing a strong positive correlation (PCC = 0.698, $P$ = 3.95e-7) between $\log_{10}L_R$ and $\log_{10}P$. This correlation remains across frequencies from 144-3000 MHz, showing uniform luminosity behavior. By combining light curve analysis with stellar mass-radius-luminosity relationships, we calculated parameters like binary mass, primary/secondary mass, Rossby number, and binary separation for eight RS CVn systems. The results show a notable correlation between radio luminosity and binary mass, primary mass, and separation (PCC = 0.663, 0.663, 0.719), with separation showing the strongest correlation. This suggests the radio emission may largely originate from the binary components' interaction, challenging existing models of RS CVn radio emission mechanisms and offering insights into the individual versus collective origins of these emissions.