Detection of a weak magnetic field in the Balmer emission line white dwarf WDJ1653−1001

Elms, Abbigail K.; Bagnulo, Stefano; Tremblay, Pier Emmanuel; Cunningham, Tim; Munday, James; Landstreet, John; El-Badry, Kareem; Caiazzo, Ilaria; Melis, Carl; Pinter, Viktoria; Weinberger, Alycia

Detection of a weak magnetic field in the Balmer emission line white dwarf WDJ1653−1001

Elms AK, Bagnulo S, Tremblay PE, Cunningham T, Munday J, Landstreet J, El-Badry K, Caiazzo I, Melis C, Pinter V, Weinberger A. 2026. Detection of a weak magnetic field in the Balmer emission line white dwarf WDJ1653−1001. Monthly Notices of the Royal Astronomical Society. 548(1), stag505.

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DOI

10.1093/mnras/stag505

Journal Article | Published | English

Scopus indexed

Author

Elms, Abbigail K.; Bagnulo, Stefano; Tremblay, Pier Emmanuel; Cunningham, Tim; Munday, James; Landstreet, John; El-Badry, Kareem; Caiazzo, Ilaria^ISTA ; Melis, Carl; Pinter, Viktoria; Weinberger, Alycia

Department

Caiazzo Group

Abstract

The small DAHe and DAe spectral classes comprise isolated, hydrogen-dominated atmosphere white dwarfs that exhibit variable photometric flux and Balmer line emission. These mysterious systems offer unique insight into the complex interplay between magnetic fields, stellar rotation and atmospheric activity in single white dwarfs. DAHe stars have detectable magnetic fields through Zeeman-split spectral lines, whereas DAe stars lack such splitting. We report the first discovery and characterization of magnetism in the DAe white dwarf WD J165335.21−100116.33 with new time-resolved spectropolarimetry from FORS2. We detect a weak but variable longitudinal magnetic field with values Bz > −9.2 ± 2.4 kG and Bz < −2.2 ± 1.0 kG. Independent ZTF and ATLAS photometry reveal a consistent period of P = 80.3070 ± 0.0007 h. Time-resolved optical spectroscopy obtained with six ground-based instruments demonstrates strong modulation in the strength of the Hα and Hβ Balmer line emission with P = 80.2922 ± 0.0108 h. The photometric flux and Balmer emission strength vary in antiphase, with the strongest magnetic detections coinciding with phases of low photometric flux and strong line emission. These characteristicssupport the theory that a magnetically active, temperature-inverted spot/region is producing an optically thin chromospheric emission region. Comparison with other DAe and DAHe white dwarfsreveals all systems have a strikingly similar antiphase phenomenology, reinforcing the theory that they are subject to a unified physical mechanism. With the detection of a weak magnetic field, we reclassify WD J165335.21−100116.33 as a low-field DAHe white dwarf.

Publishing Year

2026

Date Published

2026-05-01

Journal Title

Monthly Notices of the Royal Astronomical Society

Publisher

Oxford University Press

Acknowledgement

This project has received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (Grant agreement numbers 101002408). The observationsfrom the FOcal Reducer/low dispersion Spectrograph 2 (FORS2) instrument were collected at the European Southern Observatory (ESO) under ESO programme(s) 113.26ES.001. 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/conso rtium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. 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 and AST-2034437 and a collaboration including current partners Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, IN2P3, University of Warwick, Ruhr University Bochum, Northwestern University and former partners the University of Washington, Los Alamos National Laboratories, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. This work has made use of data from the Asteroid Terrestrialimpact Last Alert System (ATLAS) project. The Asteroid Terrestrial-impact Last Alert System (ATLAS) project is primarily funded to search for near earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889, and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen’s University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile. This work makes use of observations from the Las Cumbres Observatory global telescope network. Research at Lick Observatory is partially supported by a generous gift from Google. A major upgrade of the Kast spectrograph on the Shane 3 m telescope at Lick Observatory was made possible through generous gifts from William and Marina Kast as well as the Heising–Simons Foundation. The Isaac Newton Telescope is operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile. Observations reported here were obtained at the Multiple Mirror Telescope (MMT) Observatory, a joint facility of the Smithsonian Institution and the University of Arizona. Based on observations collected at Centro Astronómico Hispano en Andalucía (CAHA) at Calar Alto, operated jointly by Junta de Andalucía and Consejo Superior de Investigaciones Científicas (IAA-CSIC).

Volume

548

Issue

Article Number

stag505

ISSN

0035-8711

eISSN

1365-2966

IST-REx-ID

21745

Cite this

Elms AK, Bagnulo S, Tremblay PE, et al. Detection of a weak magnetic field in the Balmer emission line white dwarf WDJ1653−1001. Monthly Notices of the Royal Astronomical Society. 2026;548(1). doi:10.1093/mnras/stag505

Elms, A. K., Bagnulo, S., Tremblay, P. E., Cunningham, T., Munday, J., Landstreet, J., … Weinberger, A. (2026). Detection of a weak magnetic field in the Balmer emission line white dwarf WDJ1653−1001. Monthly Notices of the Royal Astronomical Society. Oxford University Press. https://doi.org/10.1093/mnras/stag505

Elms, Abbigail K., Stefano Bagnulo, Pier Emmanuel Tremblay, Tim Cunningham, James Munday, John Landstreet, Kareem El-Badry, et al. “Detection of a Weak Magnetic Field in the Balmer Emission Line White Dwarf WDJ1653−1001.” Monthly Notices of the Royal Astronomical Society. Oxford University Press, 2026. https://doi.org/10.1093/mnras/stag505.

A. K. Elms et al., “Detection of a weak magnetic field in the Balmer emission line white dwarf WDJ1653−1001,” Monthly Notices of the Royal Astronomical Society, vol. 548, no. 1. Oxford University Press, 2026.

Elms, Abbigail K., et al. “Detection of a Weak Magnetic Field in the Balmer Emission Line White Dwarf WDJ1653−1001.” Monthly Notices of the Royal Astronomical Society, vol. 548, no. 1, stag505, Oxford University Press, 2026, doi:10.1093/mnras/stag505.

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