Issue |
A&A
Volume 694, February 2025
|
|
---|---|---|
Article Number | A73 | |
Number of page(s) | 10 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361/202453039 | |
Published online | 04 February 2025 |
Examining the evolution of the supersoft X-ray source RX J0513.9 − 6951
Institut für Astronomie und Astrophysik, Kepler Center for Astro and Particle Physics, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
⋆ Corresponding author; tavleev@astro.uni-tuebingen.de
Received:
17
November
2024
Accepted:
1
January
2025
Context. Supersoft X-ray sources (SSSs) are thought to be accreting white dwarfs (WDs) in close binary systems, with thermonuclear burning on their surfaces. The SSS RX J0513.9 − 6951 in the Large Magellanic Cloud (LMC) exhibits cyclic variations between optical low and high states, which are anti-correlated with its X-ray flux. This behaviour is believed to be the result of the periodic expansion and contraction of the WD due to variations in the accretion rate in the system.
Aims. We analyse the eight high-resolution XMM and six grating Chandra spectra of RX J0513.9 − 6951 with our grid of model atmosphere spectra of hot WDs computed under the assumption of local thermodynamic equilibrium. Our aim is to test a contraction model of the source variability by tracking the evolution of the WD properties.
Methods. We use a recently computed grid of hot WD model atmospheres, spanning a wide range of effective temperatures (Teff = 100−1000 kK in steps of 25 kK) and eight values of surface gravity. The LMC chemical composition of the atmospheres was assumed.
Results. The obtained fitting parameters (effective temperature Teff, surface gravity log g, and bolometric luminosity L) evolve on the Teff − log g and Teff − L planes. This evolution follows the model tracks of WDs with masses of 1.05 − 1.15 M⊙ and thermonuclear burning on the surface. We show that, when the source has a relatively small photospheric radius and is optically bright, it lies below the stable-burning strip with a relatively low bolometric luminosity. Conversely, the fainter optical states correspond to higher bolometric luminosity and larger photospheric radii of the hot WD. RXJ0513 lies within the stable-burning strip during this state. This means that the optical brightness of the system is lower when the WD is larger, more luminous, and illuminates the accretion disc more effectively. These results contradict the contraction model, which predicts the opposite behaviour of the source. We use a model that assumes that the far UV/soft X-ray flux is reprocessed into the optical band due to multiple scattering in the cloud system above the accretion disc. More significant illumination can lead to rarefying of the cloud slab, thereby reducing the reprocessing efficiency and making the source fainter in the optical band.
Key words: novae / cataclysmic variables / white dwarfs / X-rays: individuals: RX J0513.9 − 6951
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article is published in open access under the Subscribe to Open model. Subscribe to A&A to support open access publication.
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.