Searching for Diamagnetic Blob Accretion in the 74 day K2 Observation of V2400 Ophiuchi

TL;DR

This study analyzes 74 days of K2 photometry of V2400 Ophiuchi, revealing complex accretion behavior and proposing diamagnetic blob accretion as a plausible mechanism due to observed incoherence and variability.

Contribution

The paper provides detailed power spectral analysis of V2400 Oph's light curve and introduces diamagnetic blob accretion as a new model for its peculiar behavior.

Findings

Beat and spin periods measured at ~1003s and ~928s.

Power spectrum shows a break frequency at ~100 cycles/day.

Incoherent periodic signals suggest complex accretion dynamics.

Abstract

Since its discovery in 1995, V2400 Ophiuchi (V2400 Oph) has stood apart from most known intermediate polar cataclysmic variables due to its proposed magnetic field strength (9-27 MG) and disk-less accretion. To date, the exact accretion mechanism of the system is still unknown, and standard accretion models fail to accurately predict the peculiar behavior of its lightcurve. We present the K2 Campaign~11 light curve of V2400 Oph recording 74.19 days of photometric data cadenced at 1 minute. The light curve is dominated by aperiodic flickering and quasi-periodic oscillations, which make the beat and spin signals inconspicuous on short timescales. Notably, a log-log full power spectrum shows a break frequency at $\sim10^2$ cycles~d$^{-1}$ similar to some disk-fed systems. Through power spectral analysis, the beat and spin periods are measured as $1003.4\pm0.2$ seconds and $ 927.7\pm 0.1$ seconds respectively. A power spectrum of the entire K2 observation demonstrates beat period dominance. However, time-resolved power spectra reveals a strong dependence between observation length and the dominant frequency of the light curve. For short observations (2-12 hrs) the beat, spin, or first beat harmonic can be observed as the dominant periodic signal. Such incoherence and variability indicate a dynamical accretion system more complex than current intermediate polar theories can explain. We propose that a diamagnetic blob accretion model may serve as a plausible explanation for the accretion mechanism.