@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{21705,
abstract = {We report the discovery of ATLAS J101342.5−451656.8 (hereafter ATLAS J1013−4516), an 8.56 minute orbital-period mass-transferring AM Canum Venaticorum (AM CVn) binary with a mean Gaia magnitude of G = 19.51, identified via periodic variability in light curves from the Asteroid Terrestrial-impact Last Alert System (ATLAS) of Gaia white dwarf candidates. Follow-up with the Large Lenslet Array Magellan Spectrograph shows a helium-dominated accretion disk, and high-speed ULTRACAM photometry reveals pronounced primary and secondary eclipses. We construct a decade-long timing baseline leveraging light curves from the ATLAS and Gaia surveys, as well as the high-speed imagers ULTRACAM on the New Energy Telescope and proto-Lightspeed on the Magellan Clay telescope. From this timing baseline, we measure an orbital period derivative of P 1.60 0.07 10 = ± × 12 s s−1. Interpreted in the context of stable mass transfer, the magnitude and sign of P indicate that the orbital evolution is governed by the interplay between gravitationalwave-driven angular-momentum losses and mass transfer, directly probing the donor’s structural response to mass loss. We constrain the accretor and donor mass based on stable mass-transfer arguments assuming angularmomentum loss dominated by gravitational-wave emission, allowing us to infer the characteristic gravitational
wave strain of the binary for future space-based GW observatories such as the Laser Interferometer Space Antenna (LISA). We predict a characteristic strain corresponding to a 4 yr LISA signal-to-noise ratio ≳10, establishing ATLAS J1013−4516 as a strong prospective LISA source that will probe long-term orbital evolution in the mass-transferring regime.},
author = {Chickles, Emma T. and Chakraborty, Joheen and Burdge, Kevin B. and Dhillon, Vik S. and Draghis, Paul and El-Badry, Kareem and Green, Matthew J. and Householder, Aaron and Hughes, Sarah and Layden, Christopher and Littlefair, Stuart P. and Munday, James and Pelisoli, Ingrid and Redden, Maya S. and Tonry, John and van Roestel, Joannes C and Angile, Francesco Elio and Brown, Alex J. and Segura, Noel Castro and Dinsmore, Jack and Dyer, Martin and Furesz, Gabor and Gabutti, Michelle and Garbutt, James and García-Mejía, Juliana and Jarvis, Daniel and Kennedy, Mark R. and Kerry, Paul and Mccormac, James and Mo, Geoffrey and Osip, Dave and Parsons, Steven and Pike, Eleanor and Piotrowski, John J. and Romani, Roger W. and Sahman, David and Simcoe, Rob},
issn = {1538-4357},
journal = {The Astrophysical Journal},
number = {2},
publisher = {IOP Publishing},
title = {{An eclipsing 8.56 minutes orbital period mass-transferring binary}},
doi = {10.3847/1538-4357/ae4871},
volume = {1000},
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{21780,
abstract = {It is predicted that half or more of all cataclysmic variables (CVs) should have evolved past the period minimum and now exist as so-called period bouncers where a white dwarf should be accreting from a Roche lobe filling substellar companion. However, this prediction stands in stark contrast to observations, where only a few per cent of CVs are found in this evolutionary phase. A potential solution to this discrepancy is that a magnetic field emerges from within the white dwarf after the system has reached the period minimum. The transfer of angular momentum from the spin of the white dwarf into the orbit then pushes the two stars apart, detaching them for potentially billions of years. Here we present the discovery of ZTF J021804.16+071152.93, a detached 0.69 +- 0.01 M, 19 MG magnetic white dwarf plus 37 +- 5MJup brown dwarf binary with an orbital period of 1.7 h. The kinematics of the system indicate that it is a high probability member of the Galactic thick disc. However, this strongly disagrees with the much younger age of the system obtained from the white dwarf parameters, implying that the system may have been accreting in the past. This system is therefore consistent with having detached as a result of the emergence of the magnetic field of the white dwarf when the system was still mass transferring, and may represent the ultimate fate for many (perhaps even most) CVs.},
author = {Parsons, S. G. and Brown, A. J. and Casewell, S. L. and Littlefair, S. P. and van Roestel, Joannes C and Rebassa-Mansergas, A. and Murillo-Ojeda, R. and Zorotovic, M. and Schreiber, M. R. and Bagnulo, S. and Stroet, M. A. and Castro Segura, N. and Dhillon, V. S. and Dyer, M. J. and Garbutt, J. A. and Green, M. J. and Jarvis, D. and Kennedy, M. R. and Kerry, P. and Mccormac, J. and Munday, J. and Pelisoli, I. and Pike, E. and Sahman, D. I. and Yates, A.},
issn = {1365-2966},
journal = {Monthly Notices of the Royal Astronomical Society},
number = {4},
publisher = {Oxford University Press},
title = {{ZTF J021804.16+071152.93: A dead cataclysmic variable and potential solution to the missing period bouncer cataclysmic variables}},
doi = {10.1093/mnras/stag521},
volume = {547},
year = {2026},
}
@article{21842,
abstract = {AM CVn stars are ultra-compact semi-detached binaries consisting of a white dwarf primary and a hydrogen-depleted secondary. In this
paper, we present spectroscopic and photometric results of 15 transient sources pre-classified as AM CVn candidates. Our analysis confirms
9 systems of the type AM CVn, 3 hydrogen-rich cataclysmic variables (accreting white dwarfs with near-main-sequence stars for donors),
and 3 systems that could be evolved cataclysmic variables. Eight of the AM CVn stars are analysed spectroscopically for the first time,
which increases the number of spectroscopically confirmed AM CVns by about 10%. TESS data revealed the orbital period of the AM CVn
star ASASSN-20pv to be Porb =27.282 min, which helps to constrain the possible values of its mass ratio. TESS also helped to determine
the superhump periods of one AM CVn star (ASASSN-19ct, Psh =30.94 min) and two cataclysmic variables we classify as WZ Sge stars
(Psh =90.77 min for ZTF18aaaasnn and Psh =91.6min for ASASSN-15na).We identified very different abundances in the spectra of theAM
CVns binaries ASASSN-15kf and ASASSN-20pv (both Porb ∼27.5min), suggesting different type of donors. Six of the studied AMCVns are
X-ray sources, which helped to determine their mass accretion rates. Photometry shows that the duration of all the superoutbursts detected
in the AM CVns is consistent with expectations from the disc instability model. Finally, we provide refined criteria for the identification of
new systems using all-sky surveys such as LSST.},
author = {Kára, Jan and Rivera Sandoval, Liliana and Mendoza, Wendy and Maccarone, Thomas and Pichardo Marcano, Manuel and Salazar Manzano, Luis E. and Oelkers, Ryan J. and van Roestel, Joannes C},
issn = {1448-6083},
journal = {Publications of the Astronomical Society of Australia},
publisher = {Cambridge University Press},
title = {{A study of transients from ground-based surveys reveals new ultra-compact accreting white dwarf binaries}},
doi = {10.1017/pasa.2026.10184},
volume = {43},
year = {2026},
}
@article{21897,
abstract = {Ultracompact binary systems, consisting of two compact objects in an orbit $\lesssim 0.5 {\rm R}_\odot$, should exhibit measurable rates of orbital period change ($\dot{P} \ne 0$) due to the emission of gravitational waves (GWs). Measurements of $\dot{P}$ have so far been limited to the shortest-period ultracompact binaries ($\lesssim 20$ min). Among the AM CVn-type subclass, several works have proposed the presence of extra angular momentum loss beyond GW emission, with magnetic braking being a widely discussed mechanism. If present, this magnetic braking would dominate the angular momentum loss of AM CVn-type binaries with orbital periods $\gtrsim 30$ min. In this work, we present a long-term eclipse timing study of two AM CVn-type binaries, YZ LMi and Gaia14aae, with respective orbital periods of 28.3 min and 49.7 min and continuous observations since 2006 and 2015. Both systems show $\dot{P}$ consistent with zero within $2\sigma$. Their $3\sigma$ upper limits are $1.1 \times 10^{-13}\, {\rm s \, s}^{-1}$ and $9.7 \times 10^{-14}\, {\rm s \, s}^{-1}$, respectively. These non-detections are most simply explained by a scenario in which secular angular momentum loss is not substantially stronger than GW emission at all orbital periods, but is combined with deviations from the secular $\dot{P}$ whose time-scales span decades but whose amplitude is $\lesssim 10^{-13}\, {\rm s \, s}^{-1}$. Our non-detections of $\dot{P}$ represent a limit on the strength of any enhanced angular momentum loss beyond pure GW emission.},
author = {Green, Matthew J and Marsh, Thomas R and van Roestel, Joannes C and Wong, Tin Long Sunny and Belloni, Diogo and Kilic, Mukremin and Breedt, Elmé and Brown, Alex and Copperwheat, Chris M and Chakpor, Anurak and Dhillon, V S and Segura, Noel Castro and Dyer, Martin J and Garbutt, James and Jarvis, Dan and Kengkriangkrai, Vasu and Kennedy, Mark R and Kerry, Paul and Kupfer, Thomas and Littlefair, S P and McCormac, James and Munday, James and Parsons, Steven G and Pike, Eleanor and Pelisoli, Ingrid and Rodríguez-Gil, Pablo and Sahman, David I and Yates, Amalie},
issn = {1365-2966},
journal = {Monthly Notices of the Royal Astronomical Society},
keywords = {binaries: close – stars, dwarf novae – novae, cataclysmic variables – white dwarfs},
number = {3},
publisher = {Oxford University Press},
title = {{No period change in two long-period AM CVn binaries}},
doi = {10.1093/mnras/stag673},
volume = {548},
year = {2026},
}
@article{21160,
abstract = {Context. AM Canum Venaticorum (AM CVn) stars are ultra-compact binary systems composed of a white dwarf primary accreting from a hydrogen-deficient donor. They play a crucial role in astrophysics as potential progenitors of Type Ia supernovae and as laboratories for gravitational wave studies. However, their formation and evolutionary history remain incomplete. Three formation channels have been discussed in the literature: the white dwarf, He-star, and cataclysmic variable channels.
Aims. The chemical composition of the accretor atmosphere reflects the material transferred from the donor. In this work we took the first accurate measurements of the fundamental parameters of the accreting white dwarf in ZTF J225237.05−051917.4, including the abundances of key elements such as carbon, nitrogen, and silicon, by analysing ultraviolet spectra obtained with the Hubble Space Telescope (HST). These measurements provide new insight into the evolutionary history of the system and, together with existing optical observations, establish it as a benchmark to develop our pipeline, paving the way for its application to a larger sample of AM CVn systems.
Methods. We determined the binary parameters through photometric analysis and constrained the atmospheric parameters of the white dwarf accretor, including its effective temperature, surface gravity, and chemical abundances, by fitting the HST ultraviolet spectrum with synthetic spectral models. We then inferred the system’s formation channel by comparing the results with theoretical evolutionary models.
Results. According to our measurements, the accretor’s effective temperature (Teff) is 23 300 ± 600 K and the surface gravity (log g) is 8.4 ± 0.3, which imply an accretor mass (MWD) of 0.86 ± 0.16 M⊙. We find a high nitrogen-to-carbon abundance ratio by mass of > 153.
Conclusions. The accretor is significantly hotter than previous estimates based on simplified blackbody fits to the spectral energy distribution, underscoring the importance of detailed spectral modelling for accurately determining system parameters. Our results show that ultraviolet spectroscopy is well suited to constraining the formation channels of AM CVn systems. Of the three proposed formation channels, the He-star channel can be excluded given the high nitrogen-to-carbon ratio. Our results are consistent with both the white dwarf and cataclysmic variable channels.},
author = {Yu, W. and Pala, A. F. and Kupfer, T. and Gänsicke, B. T. and Koester, D. and Belloni, D. and Wong, T. L.S. and Schreiber, M. R. and van Roestel, Joannes C and Brown, A. J. and Waagen, E. O. and González-Carballo, J. L. and Bednarz, S. and Bernacki, K. and De Martino, D. and Fernández Mañanes, E. and González Farfán, R. and Green, M. J. and Groot, P. J. and Hambsch, F. J. and Knigge, C. and Martin-Velasco, J. L. and Morales-Aimar, M. and Myers, G. and Naves Nogues, R. and Poggiani, R. and Popowicz, A. and Ramsay, G. and Reina-Lorenz, E. and Rodríguez-Gil, P. and Salto-González, J. L. and Sion, E. M. and Steeghs, D. and Szkody, P. and Toloza, O. and Tovmassian, G.},
issn = {1432-0746},
journal = {Astronomy & Astrophysics},
publisher = {EDP Sciences},
title = {{The evolutionary history of ultra-compact accreting binaries: I. Chemical abundances and the formation channel of the eclipsing AM CVn system ZTF J225237.05-051917.4 from HST spectroscopy}},
doi = {10.1051/0004-6361/202557568},
volume = {706},
year = {2026},
}
@article{21658,
abstract = {Dipolar (ℓ = 1) mixed modes have revealed a surprisingly weak differential rotation between the core and the envelope of evolved solar-like stars. Quadrupolar (ℓ = 2) mixed modes also contain information regarding internal dynamics but are very rarely characterised due to their low amplitude and the challenging identification of adjacent or overlapping rotationally split multiplets affected by near-degeneracy effects. We aim to extend the broadly used asymptotic seismic diagnostics beyond ℓ = 1 mixed modes by developing an analogue asymptotic description of ℓ = 2 mixed modes while explicitly accounting for near-degeneracy effects that distort their rotational multiplets. We have derived a new asymptotic formulation of near-degenerate mixed ℓ = 2 modes that describes off-diagonal terms representing the interaction between modes of adjacent radial orders. This formalism, expressed directly in the mixed-mode basis, provides analytical expressions for the near-degeneracy effects. We implemented the formalism within a global Bayesian mode-fitting framework for a direct fit of all ℓ = 0, 1, 2 modes in the power spectrum density. We were able to asymptotically model the asymmetric rotational splitting present in various radial orders of ℓ = 2 modes observed in young red giant stars without the need for any numerical stellar modelling. We applied our formalism to the Kepler target KIC 7341231, and it yielded core and envelope rotation rates consistent with previous numerical modelling while providing improved constraints from the global and model-independent approach. We also characterised the new target, KIC 8179973, measuring its rotation rate and mixed-mode parameters for the first time. As our framework relies on a direct global fit, it allows for much better precision on the asteroseismic parameters and rotation rate estimates than standard methods, yielding better constraints for rotation inversions. We have placed the first observational constraints on the asymptotic ℓ = 2 mixed-mode parameters (ΔΠ2, q2, and εg, 2), thus paving the way towards the use of asymptotic seismology beyond ℓ = 1 mixed modes.},
author = {Liagre, Bastien Raymond Bernard and Desai, Aayush A and Einramhof, Lukas and Bugnet, Lisa Annabelle},
issn = {1432-0746},
journal = {Astronomy & Astrophysics},
publisher = {EDP Sciences},
title = {{Near-degeneracy effects in quadrupolar mixed modes: From an asymptotic description to data fitting}},
doi = {10.1051/0004-6361/202558023},
volume = {707},
year = {2026},
}
@article{22263,
abstract = {Recent studies at high redshift have revealed an enigmatic class of little red dots (LRDs) with extreme Balmer breaks, stronger than in any stellar atmosphere. However, it is unclear whether such objects exist at lower redshift, especially given the low number of LRDs reported at z ≲ 2. Here, we report the discovery of PAN-BH*-1, an LRD with an extreme Balmer break at z = 1.73, identified from JWST/NIRCam pure-parallel imaging taken by the PANORAMIC survey, and confirmed by deep VLT/X-Shooter spectroscopy. The rest-optical to near-infrared spectral energy distribution of PAN-BH*-1 is consistent with a photospheric continuum with effective temperature Teff ≈ 4800 K. The broad Hα emission line shows remarkably deep absorption, stronger than previously measured in any LRD. The absorption trough spans from −520 to +267 km s−1 with respect to the systemic redshift. The presence of blue- and red-shifted absorption suggests complex dynamics of the obscuring gas along the line of sight. We speculate that the absorption trough can be produced by a thick wind launched from a thick, rotating photospheric disk, the latter being the source of the red optical continuum. While the source is unresolved in the rest-optical JWST data (reff < 47 pc), the rest-near-UV Hubble Space Telescope imaging shows an extended morphology with (formular displayed) kpc, which we interpret as a host galaxy with a stellar mass of ∼10^8 M⊙, in line with the narrow Hα emission. The discovery of this object at cosmic noon highlights the feasibility of systematic searches for extreme LRDs with wide-area facilities such as Euclid and Roman.},
author = {Torralba Torregrosa, Alberto and Matthee, Jorryt J and Weibel, Andrea and Naidu, Rohan P. and Ma, Yilun and Cloonan, Aidan P. and Desai, Aayush A and De Graaff, Anna and Greene, Jenny E. and Jespersen, Christian Kragh and Kramarenko, Ivan and Mascia, Sara and Oesch, Pascal A. and Sun, Wendy Q. and Williams, Christina C.},
issn = {2041-8213},
journal = {The Astrophysical Journal Letters},
number = {2},
publisher = {IOP Publishing},
title = {{A black hole star at cosmic noon: Extreme Balmer break, photospheric continuum, and broad absorption by thick winds in a Little Red Dot at z = 1.7}},
doi = {10.3847/2041-8213/ae7bfd},
volume = {1005},
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{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 Tucanae. Discontinuity in the stellar sequence at the star--brown dwarf transition}},
doi = {10.1051/0004-6361/202452907},
volume = {694},
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},
}