@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{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{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{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}, } @article{13449, abstract = {Stars strongly impact their environment, and shape structures on all scales throughout the universe, in a process known as "feedback." Due to the complexity of both stellar evolution and the physics of larger astrophysical structures, there remain many unanswered questions about how feedback operates and what we can learn about stars by studying their imprint on the wider universe. In this white paper, we summarize discussions from the Lorentz Center meeting "Bringing Stellar Evolution and Feedback Together" in 2022 April and identify key areas where further dialog can bring about radical changes in how we view the relationship between stars and the universe they live in.}, author = {Geen, Sam and Agrawal, Poojan and Crowther, Paul A. and Keller, B. W. and de Koter, Alex and Keszthelyi, Zsolt and van de Voort, Freeke and Ali, Ahmad A. and Backs, Frank and Bonne, Lars and Brugaletta, Vittoria and Derkink, Annelotte and Ekström, Sylvia and Fichtner, Yvonne A. and Grassitelli, Luca and Götberg, Ylva Louise Linsdotter and Higgins, Erin R. and Laplace, Eva and You Liow, Kong and Lorenzo, Marta and McLeod, Anna F. and Meynet, Georges and Newsome, Megan and André Oliva, G. and Ramachandran, Varsha and Rey, Martin P. and Rieder, Steven and Romano-Díaz, Emilio and Sabhahit, Gautham and Sander, Andreas A. C. and Sarwar, Rafia and Stinshoff, Hanno and Stoop, Mitchel and Szécsi, Dorottya and Trebitsch, Maxime and Vink, Jorick S. and Winch, Ethan}, issn = {1538-3873}, journal = {Publications of the Astronomical Society of the Pacific}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, number = {1044}, publisher = {IOP Publishing}, title = {{Bringing stellar evolution and feedback together: Summary of proposals from the Lorentz Center workshop}}, doi = {10.1088/1538-3873/acb6b5}, volume = {135}, year = {2023}, }