A half ring of ionized circumstellar material trapped in the magnetosphere of a white dwarf merger remnant

Cristea, Andrei-Alexandru; Caiazzo, Ilaria; Cunningham, Tim; Raymond, John C.; Vennes, Stephane; Kawka, Adela; Desai, Aayush A; Miller, David R.; Hermes, J. J.; Fuller, Jim; Heyl, Jeremy; van Roestel, Jan; Burdge, Kevin B.; Rodriguez, Antonio C.; Pelisoli, Ingrid; Gänsicke, Boris T.; Szkody, Paula; Kenyon, Scott J.; Vanderbosch, Zach; Drake, Andrew; Ferrario, Lilia; Wickramasinghe, Dayal; Karambelkar, Viraj R.; Justham, Stephen; Pakmor, Ruediger; El-Badry, Kareem; Prince, Thomas; Kulkarni, S. R.; Graham, Matthew J.; Masci, Frank J.; Groom, Steven L.; Purdum, Josiah; Dekany, Richard; Bellm, Eric C.

A half ring of ionized circumstellar material trapped in the magnetosphere of a white dwarf merger remnant

Cristea A-A, Caiazzo I, Cunningham T, Raymond JC, Vennes S, Kawka A, Desai AA, Miller DR, Hermes JJ, Fuller J, Heyl J, van Roestel J, Burdge KB, Rodriguez AC, Pelisoli I, Gänsicke BT, Szkody P, Kenyon SJ, Vanderbosch Z, Drake A, Ferrario L, Wickramasinghe D, Karambelkar VR, Justham S, Pakmor R, El-Badry K, Prince T, Kulkarni SR, Graham MJ, Masci FJ, Groom SL, Purdum J, Dekany R, Bellm EC. 2026. A half ring of ionized circumstellar material trapped in the magnetosphere of a white dwarf merger remnant. Astronomy & Astrophysics. 706, A188.

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DOI

10.1051/0004-6361/202556432

Journal Article | Published | English

Author

Cristea, Andrei-Alexandru^ISTA; Caiazzo, Ilaria^ISTA ; Cunningham, Tim; Raymond, John C.; Vennes, Stephane; Kawka, Adela; Desai, Aayush A^ISTA; Miller, David R.; Hermes, J. J.; Fuller, Jim; Heyl, Jeremy; van Roestel, Jan
All

Corresponding author has ISTA affiliation

Department

Caiazzo Group
Graduate School

Abstract

Many white dwarfs are observed in compact double white dwarf binaries, and through the emission of gravitational waves, a large fraction are destined to merge. The merger remnants that do not explode in a Type Ia supernova are expected to initially be rapidly rotating and highly magnetized. In this work, we present our discovery of the variable white dwarf ZTF J200832.79+444939.67, hereafter ZTF J2008+4449, as a likely merger remnant showing signs of circumstellar material without a stellar or substellar companion. The nature of ZTF J2008+4449 as a merger remnant is supported by its physical properties: it is hot (35 500 ± 300 K) and massive (1.12 ± 0.03 M ⊙ ), rapidly rotating with a period of ≈6.6 minutes, and likely possesses exceptionally strong magnetic fields (∼400−600 MG) at its surface. Remarkably, we detect a significant period derivative of (1.80 ± 0.09)×10 −12 s/s, indicating that the white dwarf is spinning down, and a soft X-ray emission that is inconsistent with photospheric emission. As the presence of a mass-transferring stellar or brown dwarf companion is excluded by infrared photometry, the detected spin-down and X-ray emission could be tell-tale signs of a magnetically driven wind or of interaction with circumstellar material, possibly originating from the fallback of gravitationally bound merger ejecta or from the tidal disruption of a planetary object. We also detect Balmer emission, which requires the presence of ionized hydrogen in the vicinity of the white dwarf, showing Doppler shifts as high as ≈2000 km s −1 . The unusual variability of the Balmer emission on the spin period of the white dwarf is consistent with the trapping of a half ring of ionized gas in the magnetosphere of the white dwarf.

Publishing Year

2026

Date Published

2026-02-10

Journal Title

Astronomy & Astrophysics

Publisher

EDP Sciences

Acknowledgement

We thank Lynne Hillenbrand and Soumyadeep Bhattacharjee for helpful discussions, and Kishalay De for his help with the WIRC reduction pipeline. IC was supported by NASA through grants from the Space Telescope Science Institute, under NASA contracts NASA.22K1813, NAS5- 26555 and NAS5-03127. TC was supported by NASA through the NASA Hubble Fellowship grant HST-HF2-51527.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 101020057). This work was based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grants No. AST-1440341, AST2034437, and currently Award #2407588. ZTF receives additional funding from the ZTF partnership. Current members include Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan, and OKC, University of Stockholm, Sweden. Operations are conducted by Caltech’s Optical Observatory (COO), Caltech/IPAC, and the University of Washington at Seattle, USA. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www. cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. The Pan-STARRS1 Surveys (PS1) and the PS1 public science archive have been made possible through contributions by the Institute for Astronomy, the University of Hawaii, the PanSTARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, the Queen’s University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation Grant No. AST–1238877, the University of Maryland, Eotvos Lorand University (ELTE), the Los Alamos National Laboratory, and the Gordon and Betty Moore Foundation. This work made use of Astropy (http://www.astropy.org): a community-developed core Python package and an ecosystem of tools and resources for astronomy (Astropy Collaboration 2013, 2018, 2022).

Volume

706

Article Number

A188

ISSN

0004-6361

eISSN

1432-0746

IST-REx-ID

21274

Cite this

Cristea A-A, Caiazzo I, Cunningham T, et al. A half ring of ionized circumstellar material trapped in the magnetosphere of a white dwarf merger remnant. Astronomy & Astrophysics. 2026;706. doi:10.1051/0004-6361/202556432

Cristea, A.-A., Caiazzo, I., Cunningham, T., Raymond, J. C., Vennes, S., Kawka, A., … Bellm, E. C. (2026). A half ring of ionized circumstellar material trapped in the magnetosphere of a white dwarf merger remnant. Astronomy & Astrophysics. EDP Sciences. https://doi.org/10.1051/0004-6361/202556432

Cristea, Andrei-Alexandru, Ilaria Caiazzo, Tim Cunningham, John C. Raymond, Stephane Vennes, Adela Kawka, Aayush A Desai, et al. “A Half Ring of Ionized Circumstellar Material Trapped in the Magnetosphere of a White Dwarf Merger Remnant.” Astronomy & Astrophysics. EDP Sciences, 2026. https://doi.org/10.1051/0004-6361/202556432.

A.-A. Cristea et al., “A half ring of ionized circumstellar material trapped in the magnetosphere of a white dwarf merger remnant,” Astronomy & Astrophysics, vol. 706. EDP Sciences, 2026.

Cristea, Andrei-Alexandru, et al. “A Half Ring of Ionized Circumstellar Material Trapped in the Magnetosphere of a White Dwarf Merger Remnant.” Astronomy & Astrophysics, vol. 706, A188, EDP Sciences, 2026, doi:10.1051/0004-6361/202556432.

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