Cyclotron Modeling Phase-Resolved Infrared Spectroscopy of Polars III: AM Herculis and ST Leo Minoris

TL;DR

This study presents phase-resolved infrared spectra of two polars, AM Her and ST LMi, revealing cyclotron emission features and modeling their magnetic and accretion properties with detailed spectral analysis.

Contribution

First phase-resolved IR spectra with comprehensive phase coverage for AM Her and ST LMi, enabling detailed cyclotron emission modeling and magnetic field estimation.

Findings

Cyclotron emission characterized for both objects.

Magnetic field strengths estimated at ~13 MG and ~12 MG.

Consistent accretion geometries derived from spectral modeling.

Abstract

We present phase-resolved low resolution infrared spectra of AM Her and ST LMi, two low-field polars that we observed with SPEX on the IRTF. Optical/NIR lightcurves are also published to help constrain the viewing geometry and brightness of the objects at the time they were observed. Currently, only limited IR spectra have been published for these objects, and none with the phase-coverage presented here. In both cases, the resulting spectra are dominated by emission from the secondary star in the NIR. However, the emission regions are also self-eclipsed, allowing us to isolate the cyclotron emission through subtraction of the dim-phase spectrum. We use a ``Constant Lambda'' prescription to model the changing cyclotron features seen in the resulting data. For AM Her, we find a best fit model of: B = 13.6 MG, kT = 4.0 keV, and logLambda = 5.0. The cyclotron derived accretion geometry is consistent with an orbital inclination of 50 degrees and a magnetic co-latitude of 85 degrees. For ST LMi, B = 12.1 MG, kT = 3.3 keV, and logLambda = 5.7 with an orbital inclination of 55 degrees and a magnetic co-latitude of 128 degrees.