@article{21274,
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.
},
author = {Cristea, Andrei-Alexandru and Caiazzo, Ilaria and Cunningham, Tim and Raymond, John C. and Vennes, Stephane and Kawka, Adela and Desai, Aayush A and Miller, David R. and Hermes, J. J. and Fuller, Jim and Heyl, Jeremy and van Roestel, Jan and Burdge, Kevin B. and Rodriguez, Antonio C. and Pelisoli, Ingrid and Gänsicke, Boris T. and Szkody, Paula and Kenyon, Scott J. and Vanderbosch, Zach and Drake, Andrew and Ferrario, Lilia and Wickramasinghe, Dayal and Karambelkar, Viraj R. and Justham, Stephen and Pakmor, Ruediger and El-Badry, Kareem and Prince, Thomas and Kulkarni, S. R. and Graham, Matthew J. and Masci, Frank J. and Groom, Steven L. and Purdum, Josiah and Dekany, Richard and Bellm, Eric C.},
issn = {1432-0746},
journal = {Astronomy & Astrophysics},
publisher = {EDP Sciences},
title = {{A half ring of ionized circumstellar material trapped in the magnetosphere of a white dwarf merger remnant}},
doi = {10.1051/0004-6361/202556432},
volume = {706},
year = {2026},
}
@article{21725,
abstract = {The initial–final mass relation (IFMR) links a star’s birth mass to the mass of its white dwarf (WD) remnant, providing key constraints on stellar evolution. Open clusters offer the most straightforward way to empirically determine the IFMR, as their well-defined ages allow for direct progenitor lifetime estimates. We construct the most comprehensive open cluster WD IFMR to date by combining new spectroscopy of 22 WDs with an extensive literature review of WDs with strong cluster associations. To minimize systematics, we restrict our analysis to spectroscopically confirmed hydrogen-atmosphere (DA) WDs consistent with single-stellar origins. We separately analyze a subset with reliable Gaia-based astrometric membership assessments, as well as a full sample that adds WDs with strong cluster associations whose membership cannot be reliably assessed with Gaia. The Gaia-based sample includes 69 spectroscopically confirmed DA WDs, more than doubling the sample size of previous Gaia-based open cluster IFMRs. The full sample, which includes 53 additional literature WDs,
increases the total number of cluster WDs by over 50% relative to earlier works. We provide functional forms for both the Gaia-based and full-sample IFMRs. The Gaia-based result useful for Mi � 2.67 M⊙ is Mf = [0.179 0.100H (Mi 3.84 M )] × (Mi 3.84 M ) + 0.628 M , where H(x) is the Heaviside step function. Comparing our IFMR to recent literature, we identify significant deviations from best-fit IFMRs derived from both Gaia-based volume-limited samples of field WDs and double WD binaries, with the largest discrepancy occurring for initial masses of about 5 M⊙.},
author = {Miller, David R. and Caiazzo, Ilaria and Heyl, Jeremy and Richer, Harvey B. and Hollands, Mark A. and Tremblay, Pier Emmanuel and El-Badry, Kareem and Rodriguez, Antonio C. and Vanderbosch, Zachary P.},
issn = {1538-4357},
journal = {The Astrophysical Journal},
keywords = {White dwarf stars, Open star clusters, Compact objects, Stellar evolution},
number = {1},
publisher = {IOP Publishing},
title = {{The White Dwarf initial–final mass relation from open clusters in Gaia DR3}},
doi = {10.3847/1538-4357/ae18c8},
volume = {996},
year = {2026},
}
@article{21745,
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. },
author = {Elms, Abbigail K. and Bagnulo, Stefano and Tremblay, Pier Emmanuel and Cunningham, Tim and Munday, James and Landstreet, John and El-Badry, Kareem and Caiazzo, Ilaria and Melis, Carl and Pinter, Viktoria and Weinberger, Alycia},
issn = {1365-2966},
journal = {Monthly Notices of the Royal Astronomical Society},
number = {1},
publisher = {Oxford University Press},
title = {{Detection of a weak magnetic field in the Balmer emission line white dwarf WDJ1653−1001}},
doi = {10.1093/mnras/stag505},
volume = {548},
year = {2026},
}
@article{22270,
abstract = {The explosion of a white dwarf (WD) in a close binary can launch a surviving runaway star at
velocities of ≳ 1000 km s−1
. Such runaways provide a direct probe of thermonuclear supernovae (SNe)
in double-degenerate binaries. Several candidate runaways are known, but their evolutionary states
and the demographics of the broader population are uncertain. To enable robust population inference,
we carry out a systematic survey for hypervelocity runaways with a simple selection function, selecting
candidates based on large Gaia-inferred tangential velocities and blue colors. We classify 100% of the
resulting 92 candidates using a combination of spectroscopic follow-up and archival data. The search
yields ten suspected D6
stars and three LP 40-365 stars. Three D6
stars are new discoveries, including
two hot (Teff ≳ 50,000 K) objects and one cool (Teff ≈ 7,000 K) object. We forward-model our survey
under several proposed D6
star evolutionary models, coupling each to a Galactic model and the survey
selection function. No single model reproduces the observed diversity of D6
stars, which likely reflects
a range of remnant masses, ages, and heating mechanisms. Models in which runaway companions
are heated by SN shocks alone are too faint and short-lived to explain most of the observed sample,
while fully reheated models are too luminous and long-lived. Models with intermediate heating,
as occurs in some simulations of violent mergers and partially disrupted remnants, best match the
observed magnitude, distance, and kinematic-age distributions. The inferred D6
star birth rate is
model dependent, but the models that best match the observed population require rates of only a
few percent of the Galactic SN Ia rate, perhaps implying that most SNe Ia result from WD binaries
in which both components explode. If most SNe Ia do produce surviving runaways, these must be
fainter or shorter-lived than the currently known runaways.},
author = {El-Badry, Kareem and Werner, Klaus and Shen, Ken J. and Strader, Jay and Rodriguez, Antonio C. and Han, Jiwon Jesse and Chandra, Vedant and Chomiuk, Laura and Vanderbosch, Zachary P. and Blomberg, Lisa and Yamaguchi, Natsuko and Nagarajan, Pranav and Caiazzo, Ilaria and van Roestel, Joannes C and Glanz, Hila and Wong, Tin Long Sunny and Bhat, Aakash and Hollands, Mark A.},
issn = {2565-6120},
journal = {The Open Journal of Astrophysics},
keywords = {white dwarfs, binaries: close, stars: chemically peculiar},
publisher = {Maynooth Academic Publishing},
title = {{A systematic survey for hypervelocity runaways from thermonuclear supernovae}},
doi = {10.33232/001c.164326},
volume = {9},
year = {2026},
}
@article{22303,
abstract = {We present the discovery of AT 2024wpp (‘Whippet’), a fast and luminous 18cow-like transient. At a redshift of z = 0 . 0868 , revealed by Keck Cosmic Web Imager spectroscopy of its faint star-forming host, it is the fourth-nearest example of its class to date. Rapid identification of the source in the Zwicky Transient Facility data stream permitted ultraviolet-through- optical observations to be obtained prior to peak, allowing the first determination of the peak bolometric luminosity ( 2 ×1045 erg s−1 ), maximum photospheric radius ( 1015 cm), and total radiated energy ( 1051 erg) of an 18cow-like object. We present results from a comprehensive multiwavelength observing campaign, including a far-ultraviolet spectrum from the Cosmic Origins Spectrograph on the Hubble Space Telescope and deep imaging extending > 100 d post-explosion from the Very Large Telescope, Hubble Space Telescope , Very Large Array, and Atacama Large Millimetre Array. We interpret the observations under a model in which a rapidly accreting central engine blows a fast ( ∼0.2 c ) wind into the surrounding medium and irradiates it with X-rays. The high Doppler velocities and intense ionization within this wind prevent identifiable spectroscopic features from appearing in the ejecta or in the surrounding circumstellar material. Weak H and He signatures do emerge in the spectra after 35 d in the form of double-peaked narrow lines. Each peak is individually narrow (full width δv ∼3000 km s−1 ) but the two components are separated by v ∼6600 km s−1 , indicating stable structures of denser material, possibly representing streams of tidal ejecta or an ablated companion star.},
author = {Perley, Daniel A and Ho, Anna Y Q and McGrath, Zoë and Camilo, Michael and Sevilla, Cassie and Chen, Ping and Schroeder, Genevieve and Govreen-Segal, Taya and Bochenek, Aleksandra and Qin, Yu-Jing and Gillanders, James H and Amend, Benjamin and Anderson, Joseph P and Andreoni, Igor and Aryan, Amar and Bellm, Eric C and Bloom, Joshua S and de Boer, Thomas and Carney, Jonathan and Caiazzo, Ilaria and Chambers, Ken C and Charalampopoulos, Panos and Chen, Ting-Wan and Chen, Tracy X and Coughlin, Eric R and Coughlin, Michael and Dennefeld, Michel and Dimitriadis, Georgios and Fremling, Christoffer and Frostig, Danielle and Gal-Yam, Avishay and Galbany, Lluís and Gangopadhyay, Anjashay and Ghendrih, Melzie and Graham, Matthew J and Gromadzki, Mariusz and Groom, Steven L and Gutiérrez, Claudia P and Hinds, K -Ryan and Huber, Mark E and Inserra, Cosimo and Kaiser, Benjamin C and Kasliwal, Mansi M and Koivisto, Niilo E and Lin, Chien-Cheng and Liu, Chang and Lowe, Thomas B and Magnier, Eugene and Mahabal, Ashish A and Milligan, Andrew and Minguez, Paloma and Mo, Geoffrey and Müller-Bravo, Tomás E and Nicholl, Matt and Pessi, Priscila J and Pignata, Giuliano and Purdum, Josiah and Rehemtulla, Nabeel and Rich, R Michael and Sahu, Anwesha and Singh, Avinash and Smartt, Stephen J and Smith, Ian A and Sollerman, Jesper and Srinivasaragavan, Gokul and Srivastav, Shubham and Stein, Robert D and Schulze, Steve and Tweddle, Jack W and Wainscoat, Richard and Wise, Jacob L and Yan, Lin and Young, David R},
issn = {1365-2966},
journal = {Monthly Notices of the Royal Astronomical Society},
keywords = {stars: black holes, supernovae: individual: AT2024wpp, radio continuum: transients},
number = {1},
publisher = {Oxford University Press},
title = {{AT 2024wpp: An extremely luminous fast ultraviolet transient powered by accretion onto a black hole}},
doi = {10.1093/mnras/stag678},
volume = {549},
year = {2026},
}
@article{22675,
abstract = {Tidal disruption events (TDEs) have traditionally been discovered in optical sky surveys through targeted searches of nuclear transients. However, it is expected that some TDEs will occur outside the galaxy nucleus, arising from wandering black holes (BHs) originating in galaxy mergers. Here, we present observations of TDE 2025abcr, the first optical TDE discovered in the outskirts of a host galaxy. The TDE was identified by a custom “off-nuclear” implementation of the machine learning classifier tdescore, which classifies new ZTF transients based on their lightcurves. Follow-up observations confirm that TDE 2025abcr is a TDE-H+He, occurring 9
5 (9.3 kpc projected distance) from the nucleus of a massive galaxy (M⋆ = 1011.18±0.03M⊙) with a central BH mass of 108.82±0.65M⊙. TDE 2025abcr itself was likely disrupted by a much lighter BH (106.09±0.53M⊙, as estimated with peak luminosity scaling relations). The BH was either dynamically ejected from the nucleus or lies at the center of a very faint tidally stripped dwarf galaxy undergoing a minor merger. Late-time observations of TDE 2025abcr could confirm the origin of this apparent “wandering” BH. The rate of highly offset (≳3 kpc) TDEs can be constrained to <10% of the nuclear TDE rate, but our discovery implies that many dozens of similar sources will be detected by the Vera C. Rubin Observatory each year with resolvable offsets.},
author = {Stein, Robert and Carney, Jonathan and Ward, Charlotte and Margutti, Raffaella and Hall, Xander J. and Sfaradi, Itai and Andreoni, Igor and Charalampopoulos, Panos and Chornock, Ryan and Gezari, Suvi and Mo, Geoffrey and Yao, Yuhan and Anumarlapudi, Akash and Bellm, Eric C. and Bloom, Joshua S. and Busmann, Malte and Caiazzo, Ilaria and Cenko, S. Bradley and Graham, Matthew J. and Groom, Steven L. and Gruen, Daniel and Hammerstein, Erica and Kaiser, Benjamin C. and Kasliwal, Mansi M. and O’Connor, Brendan and Palmese, Antonella and Purdum, Josiah and Rastinejad, Jillian C. and Riddle, Reed and Rusholme, Ben and Sollerman, Jesper and Somalwar, Jean J. and Veilleux, Sylvain},
issn = {2041-8213},
journal = {The Astrophysical Journal Letters},
number = {2},
publisher = {IOP Publishing},
title = {{TDE 2025abcr: A tidal disruption event in the outskirts of a massive galaxy}},
doi = {10.3847/2041-8213/ae77f3},
volume = {1006},
year = {2026},
}
@article{21241,
abstract = {White dwarfs (WDs) showing transits from orbiting planetary debris provide significant insights into the structure and dynamics of debris disks, which are eventually accreted to produce metal pollution. This is a rare class of objects with only eight published systems. In this work, we perform a systematic search for such systems within 500 pc in the Gaia-eDR3 catalog of WDs using the light curves from the Zwicky Transient Facility (ZTF) and present six new candidates. Our selection process targets the top 1% most photometrically variable sources identified using a combined variability metric from ZTF and Gaia eDR3 photometry, boosted by a metric space we define using von Neumann statistics and Pearson-Skew as a novel discovery tool to identify these systems. This is followed by optical spectroscopic observations of visually selected variables to confirm metal pollution. Four of the six systems show long-timescale photometric variability spanning several months to years, resulting either from long-term evolution of transit activity or dust and debris clouds at wide orbits. Among them, WD J1013–0427 shows an indication of reddening during the long-duration dip. Interpreting this as dust extinction makes it the first system to indicate an abundance of dust grains with radius ≲0.3 μm in the occulting material. The same object also shows metal emission lines that map an optically thick eccentric gas disk orbiting within the star’s Roche limit. For each candidate, we infer the abundances of the photospheric metals and estimate accretion rates. We show that transiting debris systems tend to have higher inferred accretion rates compared to the general population of metal-polluted WDs. Growing the number of these systems will further illuminate such comparative properties in the near future. Separately, we also serendipitously discovered an AM Canis Venaticorum showing a very long-duration outburst—only the fourth such system to be known.},
author = {Bhattacharjee, Soumyadeep and Vanderbosch, Zachary P. and Hollands, Mark A. and Tremblay, Pier-Emmanuel and Xu, Siyi and Guidry, Joseph A. and Hermes, J.J. and Caiazzo, Ilaria and Rodriguez, Antonio C. and van Roestel, Jan and El-Badry, Kareem and Drake, Andrew J. and Roulston, Benjamin R. and Riddle, Reed and Rusholme, Ben and Groom, Steven L. and Smith, Roger and Toloza, Odette},
issn = {1538-3873},
journal = {Publications of the Astronomical Society of the Pacific},
number = {7},
publisher = {IOP Publishing},
title = {{A ZTF search for circumstellar debris transits in White Dwarfs: Six new candidates, one with gas disk emission, identified in a novel metric space}},
doi = {10.1088/1538-3873/ade0ea},
volume = {137},
year = {2025},
}
@article{21317,
abstract = {Accreting white dwarfs (WDs) in close binary systems, commonly known as cataclysmic variables (CVs), with orbital periods below the canonical period minimum (≈80 minutes) are rare. Such short periods can only be reached if the donor star in the CV is either significantly evolved before initiating mass transfer to the WD or is metal-poor. We present optical photometry and spectroscopy of Gaia19bxc, a high-amplitude variable identified as a polar CV with an exceptionally short orbital period of 64.42 minutes—well below the canonical CV period minimum. High-speed photometry confirms persistent double-peaked variability consistent with cyclotron beaming, thus indicating the presence of a magnetic WD. Phase-resolved Keck/Low-Resolution Imaging Spectrometer (LRIS) spectroscopy reveals strong hydrogen and helium emission lines but no donor features, indicating the accretor is a magnetic WD and the donor is hydrogen-rich, but cold and faint. The absence of a detectable donor and the low inferred temperature (≲3500 K) disfavor an evolved donor scenario. Instead, the short period and the system’s halo-like kinematics suggest Gaia19bxc may be the first known metal-poor polar. Because metal-poor donors are more compact than solar-metallicity donors of the same mass, they can reach shorter minimum periods. Gaia19bxc is one of only a handful of known metal-poor CVs below the canonical period minimum and has the shortest period of any such magnetic system discovered to date.},
author = {Galiullin, Ilkham and Rodriguez, Antonio C. and El-Badry, Kareem and Caiazzo, Ilaria and Szkody, Paula and Nagarajan, Pranav and Whitebook, Samuel},
issn = {2041-8213},
journal = {The Astrophysical Journal Letters},
number = {2},
publisher = {IOP Publishing},
title = {{Optical spectroscopy of the most compact accreting binary harboring a magnetic White Dwarf and a hydrogen-rich donor}},
doi = {10.3847/2041-8213/adff82},
volume = {990},
year = {2025},
}
@article{18851,
abstract = {We present volume-limited samples of cataclysmic variables (CVs) and AM CVn binaries jointly selected from SRG/eROSITA eRASS1 and Gaia DR3 using an X-ray + optical color–color diagram (the "X-ray Main Sequence"). This tool identifies all CV subtypes, including magnetic and low-accretion rate systems, in contrast to most previous surveys. We find 23 CVs, 3 of which are AM CVns, out to 150 pc in the Western Galactic Hemisphere. Our 150 pc sample is spectroscopically verified and complete down to LX = 1.3 × 1029 erg s−1 in the 0.2–2.3 keV band, and we also present CV candidates out to 300 pc and 1000 pc. We discovered two previously unknown systems in our 150 pc sample: the third nearest AM CVn and a magnetic period bouncer. We find the mean LX of CVs to be 〈LX〉 ≈ 4.6 × 1030 erg s−1, in contrast to previous surveys which yielded 〈LX〉 ∼ 1031−1032 erg s−1. We construct X-ray luminosity functions that, for the first time, flatten out at LX ∼ 1030 erg s−1. We infer average number, mass, and luminosity densities of ρN,CV = (3.7 ± 0.7) × 10−6pc−3, (math formular), and (math formular), respectively, in the solar neighborhood. Our uniform selection method also allows us to place meaningful estimates on the space density of AM CVns, ρN,AM CVn = (5.5 ± 3.7) × 10−7 pc−3. Magnetic CVs and period bouncers make up 35% and 25% of our sample, respectively. This work, through a novel discovery technique, shows that the observed number densities of CVs and AM CVns, as well as the fraction of period bouncers, are still in tension with population synthesis estimates.},
author = {Rodriguez, Antonio C. and El-Badry, Kareem and Suleimanov, Valery and Pala, Anna F. and Kulkarni, Shrinivas R. and Gaensicke, Boris and Mori, Kaya and Rich, R. Michael and Sarkar, Arnab and Bao, Tong and De Oliveira, Raimundo Lopes and Ramsay, Gavin and Szkody, Paula and Graham, Matthew and Prince, Thomas A. and Caiazzo, Ilaria and Vanderbosch, Zachary P. and Roestel, Jan Van and Das, Kaustav K. and Qin, Yu Jing and Kasliwal, Mansi M. and Wold, Avery and Groom, Steven L. and Reiley, Daniel and Riddle, Reed},
issn = {0004-6280},
journal = {Publications of the Astronomical Society of the Pacific},
number = {1},
publisher = {IOP Publishing},
title = {{Cataclysmic variables and AM CVn binaries in SRG/eROSITA + Gaia: Volume limited samples, X-ray luminosity functions, and space densities}},
doi = {10.1088/1538-3873/ada185},
volume = {137},
year = {2025},
}
@article{18852,
abstract = {Recent observations have found a growing number of hypervelocity stars with speeds of ≈1500 − 2500 km s−1 that could have only been produced through thermonuclear supernovae in white dwarf binaries. Most of the observed hypervelocity runaways in this class display a surprising inflated structure: their current radii are roughly an order of magnitude greater than they would have been as white dwarfs filling their Roche lobe. While many simulations exist studying the dynamical phase leading to supernova detonation in these systems, no detailed calculations of the long-term structure of the runaways have yet been performed. We used an existing AREPO hydrodynamical simulation of a supernova in a white dwarf binary as a starting point for the evolution of these stars with the one-dimensional stellar evolution code MESA. We show that the supernova shock is not energetic enough to inflate the white dwarf over timescales longer than a few thousand years, significantly shorter than the 105 − 6 year lifetimes inferred for observed hypervelocity runaways. Although they experience a shock from a supernova less than ≈0.02 R⊙ away, our models do not experience significant interior heating, and all contract back to radii of around 0.01 R⊙ within about 104 years. Explaining the observed inflated states requires either an additional source of significant heating or some other physics that is not yet accounted for in the subsequent evolution.},
author = {Bhat, Aakash and Bauer, Evan B. and Pakmor, Rüdiger and Shen, Ken J. and Caiazzo, Ilaria and Rajamuthukumar, Abinaya Swaruba and El-Badry, Kareem and Kerzendorf, Wolfgang E.},
issn = {1432-0746},
journal = {Astronomy & Astrophysics},
number = {1},
publisher = {EDP Sciences},
title = {{Supernova shocks cannot explain the inflated state of hypervelocity runaways from white dwarf binaries}},
doi = {10.1051/0004-6361/202451371},
volume = {693},
year = {2025},
}
@article{19439,
abstract = {White dwarfs (WDs) are the most abundant compact objects, and recent surveys have suggested that over a third of WDs in accreting binaries host a strong (B ≳ 1 MG) magnetic field. However, the origin and evolution of WD magnetism remain under debate. Two WD pulsars, AR Sco and J191213.72–441045.1 (J1912), have been found, which are non-accreting binaries hosting rapidly spinning (1.97 minutes and 5.30 minutes, respectively) magnetic WDs. The WD in AR Sco is slowing down on a (math formular) yr timescale. It is believed they will eventually become polars, accreting systems in which a magnetic WD (B ≈ 10−240 MG) accretes from a Roche lobe-filling donor spinning in sync with the orbit (≳78 minutes). Here, we present multiwavelength data and analysis of Gaia22ayj, which outbursted in 2022 March. We find that Gaia22ayj is a magnetic accreting WD that is rapidly spinning down (math formular
yr) like WD pulsars, but shows clear evidence of accretion, like polars. Strong linear polarization (40%) is detected in Gaia22ayj; such high levels have only been seen in the WD pulsar AR Sco and demonstrate the WD is magnetic. High speed photometry reveals a 9.36 minutes period accompanying a high amplitude (∼2 mag) modulation. We associate this with a WD spin or spin–orbit beat period, not an orbital period as was previously suggested. Fast (60 s) optical spectroscopy reveals a broad "hump," reminiscent of cyclotron emission in polars, between 4000 and 8000 Å. We find an X-ray luminosity of (math formular) in the 0.3–8 keV energy range, while two very large array radio campaigns resulted in a non-detection with a Fr < 15.8 μJy 3σ upper limit. The shared properties of both WD pulsars and polars suggest that Gaia22ayj is a missing link between the two classes of magnetic WD binaries.},
author = {Rodriguez, Antonio C. and El-Badry, Kareem and Hakala, Pasi and Rodríguez-Gil, Pablo and Bao, Tong and Galiullin, Ilkham and Kurlander, Jacob A. and Law, Casey J. and Pelisoli, Ingrid and Schreiber, Matthias R. and Burdge, Kevin and Caiazzo, Ilaria and Roestel, Jan Van and Szkody, Paula and Drake, Andrew J. and Buckley, David A.H. and Potter, Stephen B. and Gaensicke, Boris and Mori, Kaya and Bellm, Eric C. and Kulkarni, Shrinivas R. and Prince, Thomas A. and Graham, Matthew and Kasliwal, Mansi M. and Rose, Sam and Sharma, Yashvi and Ahumada, Tomás and Anand, Shreya and Viitanen, Akke and Wold, Avery and Chen, Tracy X. and Riddle, Reed and Smith, Roger},
issn = {0004-6280},
journal = {Publications of the Astronomical Society of the Pacific},
number = {2},
publisher = {IOP Publishing},
title = {{A link between White Dwarf pulsars and polars: Multiwavelength observations of the 9.36-minute period variable Gaia22ayj}},
doi = {10.1088/1538-3873/adb0f1},
volume = {137},
year = {2025},
}
@article{19840,
abstract = {We report the discovery of two new magnetic cataclysmic variables with brown dwarf companions and long orbital periods (P_{\rm orb}=95\pm1 and 104\pm2 min). This discovery increases the sample of candidate magnetic period bouncers with confirmed sub-stellar donors from four to six. We also find their X-ray luminosity from archival XMM–Newton observations to be in the range L_{\rm X}\approx10^{28}-10^{29} \mathrm{erg\,s^{-1}} in the 0.25–10 keV band. This low luminosity is comparable with the other candidates, and at least an order of magnitude lower than the X-ray luminosities typically measured in cataclysmic variables. The X-ray fluxes imply mass transfer rates that are much lower than predicted by evolutionary models, even if some of the discrepancy is due to the accretion energy being emitted in other bands, such as via cyclotron emission at infrared wavelengths. Although it is possible that some or all of these systems formed directly as binaries containing a brown dwarf, it is likely that the donor used to be a low-mass star and that the systems followed the evolutionary track for cataclysmic variables, evolving past the period bounce. The donor in long period systems is expected to be a low-mass, cold brown dwarf. This hypothesis is supported by near-infrared photometric observations that constrain the donors in the two systems to be brown dwarfs cooler than
1100 K (spectral types T5 or later), most likely losing mass via Roche Lobe overflow or winds. The serendipitous discovery of two magnetic period bouncers in the small footprint of the XMM–Newton catalogue implies a large space density of these type of systems, possibly compatible with the prediction of 40–70 per cent of magnetic cataclysmic variables to be period bouncers.},
author = {Cunningham, Tim and Caiazzo, Ilaria and Sienkiewicz, Gracjan and Wheatley, Peter J. and Gänsicke, Boris T. and El-Badry, Kareem and Arcodia, Riccardo and Charbonneau, David and Connor, Liam and De, Kishalay and Hakala, Pasi and Kenyon, Scott J. and Maheshwari, Sumit Kumar and Rodriguez, Antonio C. and Van Roestel, Jan and Tremblay, Pier Emmanuel},
issn = {1365-2966},
journal = {Monthly Notices of the Royal Astronomical Society},
number = {1},
pages = {633--649},
publisher = {Oxford University Press},
title = {{Discovery of two new polars evolved past the period bounce}},
doi = {10.1093/mnras/staf561},
volume = {540},
year = {2025},
}
@article{19964,
abstract = {It has been suggested that giant planet occurrence peaks for stars with M* ≈ 3 M⊙ at a value a factor of 4 higher than observed for solar-mass stars. This population of giant planets predicted to frequently orbit main-sequence B stars at a ≈ 10 au is difficult to characterize during the few hundred million years while fusion persists in their host stars. By the time those stars become massive, young white dwarfs, any giant planets present would still be luminous as a consequence of their recent formation. From an initial sample of 2195 Gaia-identified massive, young white dwarfs, we use homogeneous Spitzer Infrared Array Camera (IRAC) photometry to search for evidence of unresolved giant planets. For 30 systems, these IRAC data provide sensitivity to objects with M ≲ 10 MJup, and we identify one candidate with M ≈ 4 MJup orbiting the white dwarf GALEX J071816.4+373139. Correcting for the possibility that some of the white dwarfs in our sample result from mergers, we find a giant planet occurrence n GP = 0.11+0.13-0.07 for stars with initial masses M* ≳ 3 M⊙. Our occurrence inference is consistent with both the Doppler-inferred occurrence of giant planets orbiting M* ≈ 2 M⊙ giant stars and the theoretically predicted factor of 4 enhancement in the occurrence of giant planets orbiting M* ≈ 3 M⊙ stars relative to solar-mass stars. Future James Webb Space Telescope NIRCam observations of our sample would provide sensitivity to Saturn-mass planets and thereby a definitive estimate of the occurrence of giant planets orbiting stars with M* ≳ 3 M⊙.},
author = {Cheng, Sihao and Schlaufman, Kevin C. and Caiazzo, Ilaria},
issn = {1538-3881},
journal = {The Astronomical Journal},
number = {1},
publisher = {IOP Publishing},
title = {{A candidate giant planet companion to the massive, young White Dwarf GALEX J071816.4+373139 informs the occurrence of giant planets orbiting B stars}},
doi = {10.3847/1538-3881/addd21},
volume = {170},
year = {2025},
}
@article{20586,
abstract = {We present the discovery of deep, irregular, periodic transits toward the white dwarf ZTF J1944+4557 using follow-up time-series photometry and spectroscopy from Palomar, Keck, McDonald, Perkins, and Lowell observatories. We find a predominant period of 4.9704 hr, consistent with an orbit near the Roche limit of the white dwarf, with individual dips over 30% deep and lasting between 15 and 40 minutes. Similar to the first known white dwarf with transiting debris, WD 1145+017, the transit events are well-defined with prominent out-of-transit phases where the white dwarf appears unobscured. Spectroscopy concurrent with transit photometry reveals that the average Ca K equivalent width remains constant in and out of transit. The broadening observed in several absorption features cannot be reproduced by synthetic photospheric models, suggesting the presence of circumstellar gas. Simultaneous g + r- and g + i-band light curves from the CHIMERA instrument reveal no color dependence to the transit depths, requiring transiting dust grains to have sizes s ≳ 0.2 μm. The transit morphologies appear to be constantly changing at a rate faster than the orbital period. Overall transit activity varies in the system, with transit features completely disappearing during the seven months between our 2023 and 2024 observing seasons and then reappearing in 2025 March, still repeating at 4.9704 hr. Our observations of the complete cessation and resumption of transit activity provide a novel laboratory for constraining the evolution of disrupted debris and processes like disk exhaustion and replenishment timescales at white dwarfs.},
author = {Guidry, Joseph A. and Vanderbosch, Zachary P. and Hermes, J. J. and Veras, Dimitri and Hollands, Mark A. and Bhattacharjee, Soumyadeep and Caiazzo, Ilaria and El-Badry, Kareem and Kao, Malia L. and Ould Rouis, Lou Baya and Rodriguez, Antonio C. and Van Roestel, Jan},
issn = {1538-4357},
journal = {The Astrophysical Journal},
number = {2},
publisher = {IOP Publishing},
title = {{Transiting planetary debris near the Roche limit of a white dwarf on a 4.97 hr orbit—and its vanishing}},
doi = {10.3847/1538-4357/adfecb},
volume = {992},
year = {2025},
}
@article{20588,
abstract = {In this second paper on our variability survey of central stars of planetary nebulae (CSPNe) using the Zwicky Transient Facility (ZTF), we report 11 long-timescale variables with variability timescales ranging from months to years. We also present preliminary analyses based on spectroscopic and/or photometric follow-up observations for six of them. Among them is NGC 6833, which shows a 980 days periodic variability with strange characteristics: “triangle-shaped” brightening in r, i, and WISE bands but almost coincidental shallow dips in the g-band. The most plausible explanation is a wide binary with the photometric period being the orbital period. Long-period near-sinusoidal variability was detected in two other systems, NGC 6905 and Kn 26, with periods of 700 days and 230 days, respectively, making them additional wide-binary candidates. The latter also shows a short period at 1.18 hr. We then present CTSS 2 and K 3-5, which show brightening and significant reddening over the whole ZTF baseline. A stellar model fit to the optical spectrum of CTSS 2 reveals it to be one of the youngest post-AGB CSPNe known. Both show high-density emission-line cores. We propose these to be late-thermal-pulse candidates, currently evolving towards the AGB phase. We then present recent HST/COS ultraviolet spectroscopy of the known wide-binary candidate LoTr 1, showing that the hot star is a spectroscopic twin of the extremely hot white dwarf in UCAC2 46706450. Similar to this object, LoTr 1 also has a fast rotating wide subgiant companion. We suggest that the long photometric period of 11 yr is the binary orbital period. Finally, we briefly discuss the ZTF light curves of the remaining variables, namely Tan 2, K 3-20, WHTZ 3, Kn J1857+3931, and IPHAS J1927+0814. With these examples, we present the effectiveness of the von Neumann statistics and Pearson Skew-based metric space in searching for long-timescale variables.},
author = {Bhattacharjee, Soumyadeep and Reindl, Nicole and Bond, Howard E. and Werner, Klaus and Zeimann, Gregory R. and Jones, David and El-Badry, Kareem and Mackensen, Nina and Chornay, Nicholas and Kulkarni, S. R. and Caiazzo, Ilaria and Van Roestel, Jan and Rodriguez, Antonio C. and Prince, Thomas A. and Rusholme, Ben and Laher, Russ R. and Smith, Roger},
issn = {1538-3873},
journal = {Publications of the Astronomical Society of the Pacific},
number = {10},
publisher = {IOP Publishing},
title = {{Variability of central stars of planetary nebulae with the Zwicky Transient Facility. II. Long-timescale variables including wide binary and late thermal pulse candidates}},
doi = {10.1088/1538-3873/ae051e},
volume = {137},
year = {2025},
}
@article{19025,
abstract = {A complete understanding of the central stars of planetary nebulae (CSPNe) remains elusive. Over the past several decades, time-series photometry of CSPNe has yielded significant results including, but not limited to, discoveries of nearly 100 binary systems, insights into pulsations and winds in young white dwarfs, and studies of stars undergoing very late thermal pulses. We have undertaken a systematic study of optical photometric variability of cataloged CSPNe, using the light curves from the Zwicky Transient Facility (ZTF). By applying appropriate variability metrics, we arrive at a list of 94 highly variable CSPN candidates. Based on the timescales of the light-curve activity, we classify the variables broadly into short- and long-timescale variables. In this first paper in this series, we focus on the former, which is the majority class comprising 83 objects. We report periods for six sources for the first time, and recover several known periodic variables. Among the aperiodic sources, most exhibit a jitter around a median flux with a stable amplitude, and a few show outbursts. We draw attention to WeSb 1, which shows a different kind of variability: prominent deep and aperiodic dips, resembling transits from a dust/debris disk. We find strong evidence for a binary nature of WeSb 1 (possibly an F-type subgiant companion). The compactness of the emission lines and inferred high electron densities make WeSb 1 a candidate for either an EGB 6-type planetary nucleus, or a symbiotic system inside an evolved planetary nebula, both of which are rare objects. To demonstrate further promise with ZTF, we report three additional newly identified periodic sources that do not appear in the list of highly variable sources. Finally, we also introduce a two-dimensional metric space defined by the von Neumann statistics and Pearson Skew and demonstrate its effectiveness in identifying unique variables of astrophysical interest, like WeSb 1.},
author = {Bhattacharjee, Soumyadeep and Kulkarni, S. R. and Kong, Albert K.H. and Tam, M. S. and Bond, Howard E. and El-Badry, Kareem and Caiazzo, Ilaria and Chornay, Nicholas and Graham, Matthew J. and Rodriguez, Antonio C. and Zeimann, Gregory R. and Fremling, Christoffer and Drake, Andrew J. and Werner, Klaus and Rodriguez, Hector and Prince, Thomas A. and Laher, Russ R. and Chen, Tracy X. and Riddle, Reed},
issn = {0004-6280},
journal = {Publications of the Astronomical Society of the Pacific},
number = {2},
publisher = {IOP Publishing},
title = {{Variability of central stars of planetary nebulae with the zwicky transient facility. I. Methods, short-timescale variables, and the unusual nucleus of WeSb 1}},
doi = {10.1088/1538-3873/ada702},
volume = {137},
year = {2025},
}
@article{18866,
abstract = {Using JWST Near Infrared Camera (NIRCam) images of the globular cluster 47,Tucanæ, (or NGC,104), taken at two epochs just 7 months apart, we derived proper-motion membership down to F322W2 ∼ 27. We identified an intriguing feature at the very low-mass end of the main sequence, around ∼ 0.08,M_⋅, at magnitudes F322W2 ∼ 24 and m_ F150W2 ∼ 25. This feature, dubbed 'kink', is characterized by a prominent discontinuity in the slope of the main sequence. A similar discontinuity is seen in theoretical isochrones with oxygen-poor chemistries, related to the rapid onset of absorption. We therefore hypothesize that the cluster hosts disproportionately more oxygen-poor stars near the bottom of the main sequence compared to the upper main sequence and the red giant branch. Our results show no strong or conclusive evidence of a rise in the brown dwarf luminosity function at faint magnitudes, in contrast to previous findings likely affected by faint red background galaxies. In our analysis, we accounted for this contamination by using proper motion membership.},
author = {Scalco, M. and Gerasimov, R. and Bedin, L. R. and Vesperini, E. and Correnti, M. and Nardiello, D. and Burgasser, A. and Richer, H. and Caiazzo, Ilaria and Heyl, J. and Libralato, M. and Anderson, J. and Griggio, M.},
issn = {1432-0746},
journal = {Astronomy & Astrophysics},
publisher = {EDP Sciences},
title = {{JWST photometry and astrometry of 47 Tucanæ. Discontinuity in the stellar sequence at the star--brown dwarf transition}},
doi = {10.1051/0004-6361/202452907},
volume = {694},
year = {2025},
}
@article{15189,
abstract = {Cataclysmic variables (CVs) that have evolved past the period minimum during their lifetimes are predicted to be systems with a brown dwarf donor. While population synthesis models predict that around 40–70 per cent of the Galactic CVs are post-period minimum systems referred to as ‘period bouncers’, only a few dozen confirmed systems are known. We report the study and characterization of a new eclipsing CV, SRGeJ041130.3+685350 (SRGeJ0411), discovered from a joint SRG/eROSITA and ZTF programme. The optical spectrum of SRGeJ0411 shows prominent hydrogen and helium emission lines, typical for CVs. We obtained optical high-speed photometry to confirm the eclipse of SRGeJ0411 and determine the orbital period to be Porb ≈ 97.530 min. The spectral energy distribution suggests that the donor has an effective temperature of ≲ 1800 K. We constrain the donor mass with the period–density relationship for Roche lobe-filling stars and find that Mdonor ≲ 0.04 M⊙. The binary parameters are consistent with evolutionary models for post-period minimum CVs, suggesting that SRGeJ0411 is a new period bouncer. The optical emission lines of SRGeJ0411 are single-peaked despite the system being eclipsing, which is typically only seen due to stream-fed accretion in polars. X-ray spectroscopy hints that the white dwarf in SRGeJ0411 could be magnetic, but verifying the magnetic nature of SRGeJ0411 requires further investigation. The lack of optical outbursts has made SRGeJ0411 elusive in previous surveys, and joint X-ray and optical surveys highlight the potential for discovering similar systems in the near future.},
author = {Galiullin, Ilkham and Rodriguez, Antonio C and Kulkarni, Shrinivas R and Sunyaev, Rashid and Gilfanov, Marat and Bikmaev, Ilfan and Yungelson, Lev and van Roestel, Jan and Gänsicke, Boris T and Khamitov, Irek and Szkody, Paula and El-Badry, Kareem and Suslikov, Mikhail and Prince, Thomas A and Buntov, Mikhail and Caiazzo, Ilaria and Gorbachev, Mark and Graham, Matthew J and Gumerov, Rustam and Irtuganov, Eldar and Laher, Russ R and Medvedev, Pavel and Riddle, Reed and Rusholme, Ben and Sakhibullin, Nail and Sklyanov, Alexander and Vanderbosch, Zachary P},
issn = {1365-2966},
journal = {Monthly Notices of the Royal Astronomical Society},
keywords = {Space and Planetary Science, Astronomy and Astrophysics},
number = {1},
pages = {676--692},
publisher = {Oxford University Press},
title = {{A joint SRG/eROSITA + ZTF search: Discovery of a 97-min period eclipsing cataclysmic variable with evidence of a brown dwarf secondary}},
doi = {10.1093/mnras/stae012},
volume = {528},
year = {2024},
}
@article{15191,
abstract = {Despite their shared origin, members of globular clusters display star-to-star variations in composition. The observed pattern of element abundances is unique to these stellar environments and cannot be fully explained by any proposed mechanism. It remains unclear whether stars form with chemical heterogeneity or inherit it from interactions with other members. These scenarios may be differentiated by the dependence of chemical spread on stellar mass; however, obtaining a sufficiently large mass baseline requires abundance measurements on the lower main sequence, which is too faint for spectroscopy even in the nearest globular clusters. We developed a stellar modeling method to obtain precise chemical abundances for stars near the end of the main sequence from multiband photometry, and we applied it to the globular cluster 47 Tucanae. The computational efficiency is attained by matching chemical elements to the model components that are most sensitive to their abundance. We determined [O/Fe] for ∼5000 members below the main-sequence knee at the level of accuracy, comparable to the spectroscopic measurements of evolved members in the literature. The inferred distribution disfavors stellar interactions as the origin of chemical spread; however, an accurate theory of accretion is required to draw a more definitive conclusion. We anticipate that future observations of 47 Tucanae with the James Webb Space Telescope will extend the mass baseline of our analysis into the substellar regime. Therefore, we present predicted color–magnitude diagrams and mass–magnitude relations for the brown dwarf members of 47 Tucanae.},
author = {Gerasimov, Roman and Burgasser, Adam J. and Caiazzo, Ilaria and Homeier, Derek and Richer, Harvey B. and Correnti, Matteo and Heyl, Jeremy},
issn = {1538-4357},
journal = {The Astrophysical Journal},
keywords = {Space and Planetary Science, Astronomy and Astrophysics},
number = {1},
publisher = {American Astronomical Society},
title = {{Exploring the chemistry and mass function of the globular cluster 47 Tucanae with new theoretical color–magnitude diagrams}},
doi = {10.3847/1538-4357/ad08bf},
volume = {961},
year = {2024},
}
@article{18709,
abstract = {We measure the mass distribution of main-sequence (MS) companions to hot subdwarf B stars (sdBs) in post-common envelope binaries (PCEBs). We carried out a spectroscopic survey of 14 eclipsing systems ("HW Vir binaries") with orbital periods of 3.8 < Porb < 12 hr, resulting in a well-understood selection function and a near-complete sample of HW Vir binaries with G < 16. We constrain companion masses from the radial velocity curves of the sdB stars. The companion mass distribution peaks at MMS ≈ 0.15 M⊙ and drops off at MMS > 0.2 M⊙, with only two systems hosting companions above the fully convective limit. There is no correlation between Porb and MMS within the sample. A similar drop-off in the companion mass distribution of white dwarf (WD) + MS PCEBs has been attributed to disrupted magnetic braking (MB) below the fully convective limit. We compare the sdB companion mass distribution to predictions of binary evolution simulations with a range of MB laws. Because sdBs have short lifetimes compared to WDs, explaining the lack of higher-mass MS companions to sdBs with disrupted MB requires MB to be boosted by a factor of 20–100 relative to MB laws inferred from the rotation evolution of single stars. We speculate that such boosting may be a result of irradiation-driven enhancement of the MS stars' winds. An alternative possibility is that common envelope evolution favors low-mass companions in short-period orbits, but the existence of massive WD companions to sdBs with similar periods disfavors this scenario.},
author = {Blomberg, Lisa and El-Badry, Kareem and Breivik, Katelyn and Caiazzo, Ilaria and Nagarajan, Pranav and Rodriguez, Antonio and Van Roestel, Jan and Vanderbosch, Zachary P. and Yamaguchi, Natsuko},
issn = {0004-6280},
journal = {Publications of the Astronomical Society of the Pacific},
number = {12},
publisher = {IOP Publishing},
title = {{The companion mass distribution of post common envelope hot subdwarf binaries: Evidence for boosted and disrupted magnetic braking?}},
doi = {10.1088/1538-3873/ad94a2},
volume = {136},
year = {2024},
}