On the Dynamics of Ultra Compact X-ray Binaries: 4U 1850-087, 4U 0513-40 and M15 X-2

TL;DR

This paper extends the dynamical analysis of ultra-compact X-ray binaries to three additional systems, modeling their long-term luminosity variations as oscillations in Kozai resonance, and provides constraints on their tidal dissipation factors.

Contribution

It applies the dynamical modeling approach used for 4U 1820-30 to three other UCXBs, offering insights into their long periodicities and tidal dissipation properties.

Findings

Long periods are modeled as oscillations in Kozai resonance.

Provides a lower limit on the tidal dissipation factor Q.

Similar dynamical behavior observed across studied UCXBs.

Abstract

In this work we extend our dynamical study of Ultra Compact X-ray Binaries (UCXB) 4U 1820-30 from Prodan and Murray 2012 to three more UCXBs in globular clusters: 4U 1850-087, 4U 0513-40 and M15 X-2. These three UCXBs have orbital periods < 20 mins. Two of them, 4U 1850-087 and 4U 0513-40, have suspected luminosity variations of order of ~ 1yr. There is insufficient observational data to make any statements regarding the long periodicity in the light curve of M15 X-2 at this point. The properties of these three systems are quite similar to 4U 1820-30, which prompt us to model their dynamics in the same manner. As in the case of 4U 1820-30, we interpret the suspected long periods as the period of small oscillations around a stable fixed point in the Kozai resonance. We provide a lower limit on the tidal dissipation factor Q which is in agreement with results obtained for the case of 4U 1820-30.