Issue |
A&A
Volume 675, July 2023
|
|
---|---|---|
Article Number | A140 | |
Number of page(s) | 9 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361/202345935 | |
Published online | 11 July 2023 |
Recurrent mini-outbursts and a magnetic white dwarf in the symbiotic system FN Sgr
1
Advanced Technologies Research Institute, Faculty of Materials Science and Technology in Trnava, Slovak University of Technology in Bratislava, Bottova 25, 917 24 Trnava, Slovakia
e-mail: jozef.magdolen@stuba.sk
2
Department of Astronomy, University of Wisconsin, 475 N. Charter Str., Madison, WI 53706, USA
3
INAF – Astronomical Observatory Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
4
Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warsaw, Poland
5
Kleinkaroo Observatory, Calitzdorp, Western Cape, South Africa
6
Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
Received:
18
January
2023
Accepted:
31
May
2023
Aims. We investigated the optical variability of the symbiotic binary FN Sgr with photometric monitoring over a period of ≃55 years and with a high-cadence Kepler light curve lasting 81 days.
Methods. The data obtained in the V and I bands were reduced with standard photometric methods. The Kepler data were divided into subsamples and were analysed with the Lomb-Scargle algorithm.
Results. The V and I band light curves show a phenomenon never before observed with such recurrence in any symbiotic system, namely short outbursts starting between orbital phases 0.3 and 0.5 and lasting about 1 month, with a fast rise, a slower decline, and amplitudes of 0.5–1 mag. In the Kepler light curve, we discovered three frequencies with sidebands. We attribute a stable frequency of 127.5 d−1 (corresponding to a period of 11.3 min) to the white dwarf rotation. We suggest that this detection probably implies that the white dwarf accretes through a magnetic stream, as in intermediate polars. The small outbursts may be ascribed to the stream–disc interaction. Another possibility is that they are due to localised thermonuclear burning, perhaps confined by the magnetic field, such as those recently inferred in intermediate polars, albeit on different timescales. We also measured a second frequency around 116.9 d−1 (corresponding to about 137 min), which is much less stable and has a drift. This latter may be due to rocky detritus around the white dwarf, but is more likely caused by an inhomogeneity in the accretion disc. Finally, there is a third frequency close to the first one that appears to correspond to the beating between the rotation and the second frequency.
Key words: accretion, accretion disks / binaries: symbiotic / stars: individual: FN Sgr
© The Authors 2023
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.