Supersoft X-Ray Source CAL 83: A Possible AE Aqr-like System

A Odendaal,P A Charles,P J Meintjes,A F Rajoelimanana

doi:10.14311/app.2015.02.0094

A Odendaal, P A Charles + Show 2 more

Open Access

https://doi.org/10.14311/app.2015.02.0094

Copy DOI

Abstract

CAL83 is a close binary supersoft X-ray source in the Large Magellanic Cloud. A ~67 s periodicity detected in supersoft X-rays is most probably associated with the spin period of a highly spun-up white dwarf (WD). The variability in the period is ascribed to the obscuration of the WD by the hydrogen burning envelope surrounding it, rotating with a period that is close to, but not quite synchronized with, the WD rotation period. Optical spectra obtained with SALT exhibit accretion disc emission lines with broad wing structures and P Cyg profiles, indicating mass outflows. Timing analysis of photometrical observations performed at the South African Astronomical Observatory (SAAO) revealed variable signals at ≤1 mHz which are thought to be associated with quasi-periodic oscillations from an accretion disc. The short spin period inferred for CAL83 can be the result of spin-up by accretion disc torques during a long mass transfer history, placing this source on a similar evolutionary track as the cataclysmic variable AE Aqr.

Highlights

Supersoft X-ray sources (SSS) are highly luminous in the supersoft X-ray band, with >90% of the unabsorbed X-ray flux being below ∼0.5 keV
Van den Heuvel et al (1992) showed that the low effective temperatures and high luminosities of SSS can be explained by the nuclear burning of hydrogen on the surface of a white dwarf (WD) accreting from a binary companion
The accretion rate required for steady nuclear burning is ∼ 1 − 4 × 10−7 M yr−1

Summary

Introduction

Supersoft X-ray sources (SSS) are highly luminous in the supersoft X-ray band, with >90% of the unabsorbed X-ray flux being below ∼0.5 keV. CAL 83 is a close binary SSS in the Large Magellanic Cloud It is not a persistent X-ray source and several X-ray off-states have been observed, with long-term optical variability anti-correlated with the long-term X-ray variability, as described by e.g. The optical spectrum of CAL 83 is characterized by Balmer and He ii accretion disc emission lines (Co98 and references therein). The He ii λ4686 emission line has a broad, variable wing structure that has been observed in some of the Balmer lines. Preliminary results of the analysis of optical data are presented in §2.2 and §2.3

Observations and Results

Optical spectroscopy with SALT

Fast photometry with SHOC

The Evolution of CAL 83

DISCUSSION