# SDSS J233325.92+152222.1 and the evolution of intermediate polars

## TL;DR

This study identifies SDSS J233325.92+152222.1 as the shortest orbital period intermediate polar, providing insights into the magnetic properties and evolution of such systems as they transition from long to short orbital periods.

## Contribution

It presents detailed spectroscopic and photometric analysis of SDSS J233325.92+152222.1, revealing its unique short orbital period and magnetic characteristics, supporting theories of magnetic moment conservation during evolution.

## Key findings

- SDSS J233325.92+152222.1 has an orbital period of 83.12 minutes.
- The white dwarf's magnetic moment is approximately 2 x 10^33 G cm^3.
- Long-period IPs likely evolve into short-period IPs while conserving magnetic moment.

## Abstract

Intermediate polars (IPs) are cataclysmic variables which contain magnetic white dwarfs with a rotational period shorter than the binary orbital period. Evolutionary theory predicts that IPs with long orbital periods evolve through the 2-3 hour period gap, but it is very uncertain what the properties of the resulting objects are. Whilst a relatively large number of long-period IPs are known, very few of these have short orbital periods. We present phase-resolved spectroscopy and photometry of SDSS J233325.92+152222.1 and classify it as the IP with the shortest known orbital period (83.12 +/- 0.09 min), which contains a white dwarf with a relatively long spin period (41.66 +/- 0.13 min). We estimate the white dwarf's magnetic moment to be mu(WD) \approx 2 x 10^33 G cm^3, which is not only similar to three of the other four confirmed short-period IPs but also to those of many of the long-period IPs. We suggest that long-period IPs conserve their magnetic moment as they evolve towards shorter orbital periods. Therefore the dominant population of long-period IPs, which have white dwarf spin periods roughly ten times shorter than their orbital periods, will likely end up as short-period IPs like SDSS J2333, with spin periods a large fraction of their orbital periods.