Asynchronous Polars and Nearly Synchronous IPs

Polars and IPs are clearly related subclasses of magnetic CVs, and the distinction between the two classes are not always clear-cut, with subclasses such as diskless IPs and asynchronous polars (APs) muddying the water.

Here, we adopt a definition that APs are polars in a temporary state of asynchronism. That is, in APs, the equilibrium spin period is assumed to equal the orbital period, but the current spin period deviates from this equality. In the prototype, V1500 Cyg, we believe it was the 1975 nova eruption that caused this temporary asynchronism; observations since then have tracked its march back towards synchronicity, which is estimated to take of order 150 years. Systematic spin period change is also seen in another well-studied AP, V1432 Aql, although in this case the synchronization time scale is much longer at ~4 Myr (still much shorter than the evolutionary time scale of the binary).

When we adopt "temporary asynchronism" as the defining characteristic of APs, confirmation of membership requires a determination of spin period derivative: if the spin period is approaching synchronism over a time scale mush shorter than the evolutionary one, then it is a confirmed AP.

Table 1 of Littlefield et al. (2023) 9 APs and related systems, many of which do not have a good measurement of spin period derivative. We consider many of these to be AP candidates. However, we must question how realistic it is to knock off a polar far from synchronism (via nova eruptions or any other, hitherto unarticularted, mechanisms).

Here we adopt an arbitrary limit of 5% asynchronism as the outer boundary of APs and AP candidates. If a spin period of a magnetic CV is well over the canonical value of 10% but less than 95%, we will use the label "nearly synchronous IPs." Currently, this label applies to Swift J0503.7-2819 and 1RXS J052430.2+424449, nicknamed "Paloma,"

Please send your comments, suggestions etc. to Koji.Mukai@nasa.gov and/or Koji.Mukai@umbc.edu

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Asynchronous Polars and Nearly Synchronous IPs