Photometric Analysis of the eclipsing Polar MN Hya

TL;DR

This study analyzes the eclipsing polar MN Hya over several years, revealing a decreasing orbital period, mass loss during state changes, and insights into accretion processes and flickering behavior, challenging existing models.

Contribution

It provides new eclipse timings, refines the ephemeris, and offers observational evidence of period decrease and mass loss mechanisms in MN Hya, with implications for accretion physics.

Findings

Orbital period decreased during state change.

At least 60% of transferred mass was lost, likely as stellar wind.

Flickering intensity reduces with higher accretion rate.

Abstract

As an eclipsing polar with 3.39 hrs orbital period, MN Hya was going through state change when we observed it during 2009-2016. 10 new mid-eclipse times, along with others obtained from literature, allow us to give a new ephemeris. The residuals of linear fit show that period decreased during the phase of state change. It means angular momentum was lost during this phase. The X-ray observation indicates the mass accretion rate as about $3.6\times10^{-9}M_{\odot}yr^{-1}$. The period decrease gives that at least 60 percent of mass being transfered from secondary was lost, maybe in form of the spherically symmetric stellar wind. In high state, the data shows the intensity of the flickering reduced when system had higher accretion rate, and that flickering sticks out with primary timescale about 2 minutes, which implies the position of the threading point as about 30 radius of the white dwarf above the surface of it. The trend of light curves of the system in high state follows that of low state for a large fraction of phase interval from phase 0 to phase 0.4 since which the cyclotron feature is visible, and the primary intensity hump of light curves near phase 0.7 when the system is in high state did not appear on the curve when it is in low state. Those facts contradict the predictions of the two-pole model.