Cyclotron modeling phase-resolved infrared spectroscopy of polars I: EF Eridani

TL;DR

This study presents phase-resolved infrared spectra of EF Eridani, modeling cyclotron emission to understand magnetic field properties and emission mechanisms in this polar system.

Contribution

It introduces a two-component cyclotron emission model that better fits the infrared spectra of EF Eridani compared to single-component models.

Findings

A single cyclotron component with B=12.6 MG fits some spectral features.

A two-component model provides an excellent fit to the observed spectra.

A higher magnetic field model (B=115 MG) explains UV observations.

Abstract

We present phase-resolved low resolution infrared spectra of the polar EF Eridani obtained over a period of 2 years with SPEX on the IRTF. The spectra, covering the wavelength range 0.8 to 2.4 microns, are dominated by cyclotron emission at all phases. We use a ``Constant Lambda'' prescription to attempt to model the changing cyclotron features seen in the spectra. A single cyclotron emission component with B = 12.6 MG, and a plasma temperature of kT = 5.0 keV, does a reasonable job in matching the features seen in the H and K bands, but fails to completely reproduce the morphology shortward of 1.6 microns. We find that a two component model, where both components have similar properties, but whose contributions differ with viewing geometry, provides an excellent fit to the data. We discuss the implications of our models and compare them with previously published results. In addition, we show that a cyclotron model with similar properties to those used for modeling the infrared spectra, but with a field strength of B = 115 MG, can explain the GALEX observations of EF Eri.