@article{19490,
abstract = {Abstract. We study integral points on the quadratic twists ED : y2 = x3 −
D2x of the congruent number curve. We give upper bounds on the number of
integral points in each coset of 2ED(Q) in ED(Q) and show that their total is
(3.8)rank ED(Q). We further show that the average number of non-torsion
integral points in this family is bounded above by 2. As an application we also
deduce from our upper bounds that the system of simultaneous Pell equations
aX2 − bY 2 = d, bY 2 − cZ2 = d for pairwise coprime positive integers a, b, c, d,
has at most (3.6)ω(abcd) integer solutions.},
author = {Chan, Yik Tung},
issn = {1088-6850},
journal = {Transactions of the American Mathematical Society},
number = {9},
pages = {6675--6700},
publisher = {American Mathematical Society},
title = {{Integral points on the congruent number curve}},
doi = {10.1090/tran/8732},
volume = {375},
year = {2022},
}
@article{19491,
abstract = {Using a recent breakthrough of Smith [18], we improve the results of Fouvry and Klüners [4, 5] on the solubility of the negative Pell equation. Let D denote the set of positive squarefree integers having no prime factors congruent to 3 modulo 4 . Stevenhagen [19] conjectured that the density of d in D such that the negative Pell equation x2−dy2=−1 is solvable with x,y∈Z is 58.1% , to the nearest tenth of a percent. By studying the distribution of the 8 -rank of narrow class groups Cl+(d) of Q(√d) , we prove that the infimum of this density is at least 53.8% .},
author = {Chan, Yik Tung and Koymans, Peter and Milovic, Djordjo and Pagano, Carlo},
issn = {2050-5094},
journal = {Forum of Mathematics, Sigma},
publisher = {Cambridge University Press},
title = {{The 8-rank of the narrow class group and the negative Pell equation}},
doi = {10.1017/fms.2022.40},
volume = {10},
year = {2022},
}
@unpublished{15090,
abstract = {Given a locally finite set A⊆Rd and a coloring χ:A→{0,1,…,s}, we introduce the chromatic Delaunay mosaic of χ, which is a Delaunay mosaic in Rs+d that represents how points of different colors mingle. Our main results are bounds on the size of the chromatic Delaunay mosaic, in which we assume that d and s are constants. For example, if A is finite with n=#A, and the coloring is random, then the chromatic Delaunay mosaic has O(n⌈d/2⌉) cells in expectation. In contrast, for Delone sets and Poisson point processes in Rd, the expected number of cells within a closed ball is only a constant times the number of points in this ball. Furthermore, in R2 all colorings of a dense set of n points have chromatic Delaunay mosaics of size O(n). This encourages the use of chromatic Delaunay mosaics in applications.},
author = {Biswas, Ranita and Cultrera di Montesano, Sebastiano and Draganov, Ondrej and Edelsbrunner, Herbert and Saghafian, Morteza},
booktitle = {arXiv},
title = {{On the size of chromatic Delaunay mosaics}},
year = {2022},
}
@article{15131,
abstract = {RNA modifications are widespread in biology and abundant in ribosomal RNA. However, the importance of these modifications is not well understood. We show that methylation of a single nucleotide, in the catalytic center of the large subunit, gates ribosome assembly. Massively parallel mutational scanning of the essential nuclear GTPase Nog2 identified important interactions with rRNA, particularly with the 2′-O-methylated A-site base Gm2922. We found that methylation of G2922 is needed for assembly and efficient nuclear export of the large subunit. Critically, we identified single amino acid changes in Nog2 that completely bypass dependence on G2922 methylation and used cryoelectron microscopy to directly visualize how methylation flips Gm2922 into the active site channel of Nog2. This work demonstrates that a single RNA modification is a critical checkpoint in ribosome biogenesis, suggesting that such modifications can play an important role in regulation and assembly of macromolecular machines.},
author = {Yelland, James N. and Bravo, Jack Peter Kelly and Black, Joshua J. and Taylor, David W. and Johnson, Arlen W.},
issn = {1545-9985},
journal = {Nature Structural & Molecular Biology},
keywords = {Molecular Biology, Structural Biology},
pages = {91--98},
publisher = {Springer Nature},
title = {{A single 2′-O-methylation of ribosomal RNA gates assembly of a functional ribosome}},
doi = {10.1038/s41594-022-00891-8},
volume = {30},
year = {2022},
}
@article{15132,
abstract = {Clustered regularly interspaced short palindromic repeats - CRISPR-associated protein (CRISPR-Cas) systems are a critical component of the bacterial adaptive immune response. Since the discovery that they can be reengineered as programmable RNA-guided nucleases, there has been significant interest in using these systems to perform diverse and precise genetic manipulations. Here, we outline recent advances in the mechanistic understanding of CRISPR-Cas9, how these findings have been leveraged in the rational redesign of Cas9 variants with altered activities, and how these novel tools can be exploited for biotechnology and therapeutics. We also discuss the potential of the ubiquitous, yet often-overlooked, multisubunit CRISPR effector complexes for large-scale genomic deletions. Furthermore, we highlight how future structural studies will bolster these technologies.},
author = {Bravo, Jack Peter Kelly and Hibshman, Grace N and Taylor, David W},
issn = {0958-1669},
journal = {Current Opinion in Biotechnology},
keywords = {Biomedical Engineering, Bioengineering, Biotechnology},
publisher = {Elsevier},
title = {{Constructing next-generation CRISPR–Cas tools from structural blueprints}},
doi = {10.1016/j.copbio.2022.102839},
volume = {78},
year = {2022},
}
@article{15133,
abstract = {In the evolutionary arms race against phage, bacteria have assembled a diverse arsenal of antiviral immune strategies. While the recently discovered DISARM (Defense Island System Associated with Restriction-Modification) systems can provide protection against a wide range of phage, the molecular mechanisms that underpin broad antiviral targeting but avoiding autoimmunity remain enigmatic. Here, we report cryo-EM structures of the core DISARM complex, DrmAB, both alone and in complex with an unmethylated phage DNA mimetic. These structures reveal that DrmAB core complex is autoinhibited by a trigger loop (TL) within DrmA and binding to DNA substrates containing a 5′ overhang dislodges the TL, initiating a long-range structural rearrangement for DrmAB activation. Together with structure-guided in vivo studies, our work provides insights into the mechanism of phage DNA recognition and specific activation of this widespread antiviral defense system.},
author = {Bravo, Jack Peter Kelly and Aparicio-Maldonado, Cristian and Nobrega, Franklin L. and Brouns, Stan J. J. and Taylor, David W.},
issn = {2041-1723},
journal = {Nature Communications},
keywords = {General Physics and Astronomy, General Biochemistry, Genetics and Molecular Biology, General Chemistry, Multidisciplinary},
publisher = {Springer Nature},
title = {{Structural basis for broad anti-phage immunity by DISARM}},
doi = {10.1038/s41467-022-30673-1},
volume = {13},
year = {2022},
}
@article{15134,
abstract = {CRISPR-Cas systems are adaptive immune systems that protect prokaryotes from foreign nucleic acids, such as bacteriophages. Two of the most prevalent CRISPR-Cas systems include type I and type III. Interestingly, the type I-D interference proteins contain characteristic features of both type I and type III systems. Here, we present the structures of type I-D Cascade bound to both a double-stranded (ds)DNA and a single-stranded (ss)RNA target at 2.9 and 3.1 Å, respectively. We show that type I-D Cascade is capable of specifically binding ssRNA and reveal how PAM recognition of dsDNA targets initiates long-range structural rearrangements that likely primes Cas10d for Cas3′ binding and subsequent non-target strand DNA cleavage. These structures allow us to model how binding of the anti-CRISPR protein AcrID1 likely blocks target dsDNA binding via competitive inhibition of the DNA substrate engagement with the Cas10d active site. This work elucidates the unique mechanisms used by type I-D Cascade for discrimination of single-stranded and double stranded targets. Thus, our data supports a model for the hybrid nature of this complex with features of type III and type I systems.},
author = {Schwartz, Evan A. and McBride, Tess M. and Bravo, Jack Peter Kelly and Wrapp, Daniel and Fineran, Peter C. and Fagerlund, Robert D. and Taylor, David W.},
issn = {2041-1723},
journal = {Nature Communications},
keywords = {General Physics and Astronomy, General Biochemistry, Genetics and Molecular Biology, General Chemistry, Multidisciplinary},
publisher = {Springer Nature},
title = {{Structural rearrangements allow nucleic acid discrimination by type I-D Cascade}},
doi = {10.1038/s41467-022-30402-8},
volume = {13},
year = {2022},
}
@article{15136,
abstract = {CRISPR–Cas9 as a programmable genome editing tool is hindered by off-target DNA cleavage1,2,3,4, and the underlying mechanisms by which Cas9 recognizes mismatches are poorly understood5,6,7. Although Cas9 variants with greater discrimination against mismatches have been designed8,9,10, these suffer from substantially reduced rates of on-target DNA cleavage5,11. Here we used kinetics-guided cryo-electron microscopy to determine the structure of Cas9 at different stages of mismatch cleavage. We observed a distinct, linear conformation of the guide RNA–DNA duplex formed in the presence of mismatches, which prevents Cas9 activation. Although the canonical kinked guide RNA–DNA duplex conformation facilitates DNA cleavage, we observe that substrates that contain mismatches distal to the protospacer adjacent motif are stabilized by reorganization of a loop in the RuvC domain. Mutagenesis of mismatch-stabilizing residues reduces off-target DNA cleavage but maintains rapid on-target DNA cleavage. By targeting regions that are exclusively involved in mismatch tolerance, we provide a proof of concept for the design of next-generation high-fidelity Cas9 variants.},
author = {Bravo, Jack Peter Kelly and Liu, Mu-Sen and Hibshman, Grace N. and Dangerfield, Tyler L. and Jung, Kyungseok and McCool, Ryan S. and Johnson, Kenneth A. and Taylor, David W.},
issn = {1476-4687},
journal = {Nature},
number = {7900},
pages = {343--347},
publisher = {Springer Nature},
title = {{Structural basis for mismatch surveillance by CRISPR–Cas9}},
doi = {10.1038/s41586-022-04470-1},
volume = {603},
year = {2022},
}
@article{15144,
author = {Bravo, Jack Peter Kelly},
issn = {1937-8661},
journal = {Genetic Engineering & Biotechnology News},
keywords = {Management of Technology and Innovation, Biomedical Engineering, Bioengineering, Biotechnology},
number = {4},
pages = {12},
publisher = {Mary Ann Liebert},
title = {{SuperFi-Cas9 exceeds fidelity, matches speed of original Cas9}},
doi = {10.1089/gen.42.04.03},
volume = {42},
year = {2022},
}
@article{15203,
abstract = {The first X-ray pulsar, Cen X-3, was discovered 50 yr ago. Radiation from such objects is expected to be highly polarized due to birefringence of plasma and vacuum associated with propagation of photons in the presence of the strong magnetic field. Here we present results of the observations of Cen X-3 performed with the Imaging X-ray Polarimetry Explorer. The source exhibited significant flux variability and was observed in two states different by a factor of ∼20 in flux. In the low-luminosity state, no significant polarization was found in either pulse phase-averaged (with a 3σ upper limit of 12%) or phase-resolved (the 3σ upper limits are 20%–30%) data. In the bright state, the polarization degree of 5.8% ± 0.3% and polarization angle of 49fdg6 ± 1fdg5 with a significance of about 20σ were measured from the spectropolarimetric analysis of the phase-averaged data. The phase-resolved analysis showed a significant anticorrelation between the flux and the polarization degree, as well as strong variations of the polarization angle. The fit with the rotating vector model indicates a position angle of the pulsar spin axis of about 49° and a magnetic obliquity of 17°. The detected relatively low polarization can be explained if the upper layers of the neutron star surface are overheated by the accreted matter and the conversion of the polarization modes occurs within the transition region between the upper hot layer and a cooler underlying atmosphere. A fraction of polarization signal can also be produced by reflection of radiation from the neutron star surface and the accretion curtain.},
author = {Tsygankov, Sergey S. and Doroshenko, Victor and Poutanen, Juri and Heyl, Jeremy and Mushtukov, Alexander A. and Caiazzo, Ilaria and Di Marco, Alessandro and Forsblom, Sofia V. and González-Caniulef, Denis and Klawin, Moritz and La Monaca, Fabio and Malacaria, Christian and Marshall, Herman L. and Muleri, Fabio and Ng, Mason and Suleimanov, Valery F. and Sunyaev, Rashid A. and Turolla, Roberto and Agudo, Iván and Antonelli, Lucio A. and Bachetti, Matteo and Baldini, Luca and Baumgartner, Wayne H. and Bellazzini, Ronaldo and Bianchi, Stefano and Bongiorno, Stephen D. and Bonino, Raffaella and Brez, Alessandro and Bucciantini, Niccolò and Capitanio, Fiamma and Castellano, Simone and Cavazzuti, Elisabetta and Ciprini, Stefano and Costa, Enrico and Rosa, Alessandra De and Del Monte, Ettore and Gesu, Laura Di and Lalla, Niccolò Di and Donnarumma, Immacolata and Dovčiak, Michal and Ehlert, Steven R. and Enoto, Teruaki and Evangelista, Yuri and Fabiani, Sergio and Ferrazzoli, Riccardo and Garcia, Javier A. and Gunji, Shuichi and Hayashida, Kiyoshi and Iwakiri, Wataru and Jorstad, Svetlana G. and Karas, Vladimir and Kitaguchi, Takao and Kolodziejczak, Jeffery J. and Krawczynski, Henric and Latronico, Luca and Liodakis, Ioannis and Maldera, Simone and Manfreda, Alberto and Marin, Frédéric and Marinucci, Andrea and Marscher, Alan P. and Matt, Giorgio and Mitsuishi, Ikuyuki and Mizuno, Tsunefumi and Ng, Chi-Yung and O’Dell, Stephen L. and Omodei, Nicola and Oppedisano, Chiara and Papitto, Alessandro and Pavlov, George G. and Peirson, Abel L. and Perri, Matteo and Pesce-Rollins, Melissa and Petrucci, Pierre-Olivier and Pilia, Maura and Possenti, Andrea and Puccetti, Simonetta and Ramsey, Brian D. and Rankin, John and Ratheesh, Ajay and Romani, Roger W. and Sgrò, Carmelo and Slane, Patrick and Soffitta, Paolo and Spandre, Gloria and Tamagawa, Toru and Tavecchio, Fabrizio and Taverna, Roberto and Tawara, Yuzuru and Tennant, Allyn F. and Thomas, Nicholas E. and Tombesi, Francesco and Trois, Alessio and Vink, Jacco and Weisskopf, Martin C. and Wu, Kinwah and Xie, Fei and Zane, Silvia},
issn = {2041-8213},
journal = {The Astrophysical Journal Letters},
keywords = {Space and Planetary Science, Astronomy and Astrophysics},
number = {1},
publisher = {American Astronomical Society},
title = {{The x-ray polarimetry view of the accreting pulsar Cen X-3}},
doi = {10.3847/2041-8213/aca486},
volume = {941},
year = {2022},
}
@article{15204,
abstract = {Using observations of X-ray pulsar Hercules X-1 by the Imaging X-ray Polarimetry Explorer we report a highly significant (>17σ) detection of the polarization signal from an accreting neutron star. The observed degree of linear polarization of ~10% is far below theoretical expectations for this object, and stays low throughout the spin cycle of the pulsar. Both the degree and angle of polarization exhibit variability with the pulse phase, allowing us to measure the pulsar spin position angle 57(2) deg and the magnetic obliquity 12(4) deg, which is an essential step towards detailed modelling of the intrinsic emission of X-ray pulsars. Combining our results with the optical polarimetric data, we find that the spin axis of the neutron star and the angular momentum of the binary orbit are misaligned by at least ~20 deg, which is a strong argument in support of the models explaining the stability of the observed superorbital variability with the precession of the neutron star.},
author = {Doroshenko, Victor and Poutanen, Juri and Tsygankov, Sergey S. and Suleimanov, Valery F. and Bachetti, Matteo and Caiazzo, Ilaria and Costa, Enrico and Di Marco, Alessandro and Heyl, Jeremy and La Monaca, Fabio and Muleri, Fabio and Mushtukov, Alexander A. and Pavlov, George G. and Ramsey, Brian D. and Rankin, John and Santangelo, Andrea and Soffitta, Paolo and Staubert, Rüdiger and Weisskopf, Martin C. and Zane, Silvia and Agudo, Iván and Antonelli, Lucio A. and Baldini, Luca and Baumgartner, Wayne H. and Bellazzini, Ronaldo and Bianchi, Stefano and Bongiorno, Stephen D. and Bonino, Raffaella and Brez, Alessandro and Bucciantini, Niccolò and Capitanio, Fiamma and Castellano, Simone and Cavazzuti, Elisabetta and Ciprini, Stefano and De Rosa, Alessandra and Del Monte, Ettore and Di Gesu, Laura and Di Lalla, Niccolò and Donnarumma, Immacolata and Dovčiak, Michal and Ehlert, Steven R. and Enoto, Teruaki and Evangelista, Yuri and Fabiani, Sergio and Ferrazzoli, Riccardo and Garcia, Javier A. and Gunji, Shuichi and Hayashida, Kiyoshi and Iwakiri, Wataru and Jorstad, Svetlana G. and Karas, Vladimir and Kitaguchi, Takao and Kolodziejczak, Jeffery J. and Krawczynski, Henric and Latronico, Luca and Liodakis, Ioannis and Maldera, Simone and Manfreda, Alberto and Marin, Frédéric and Marinucci, Andrea and Marscher, Alan P. and Marshall, Herman L. and Matt, Giorgio and Mitsuishi, Ikuyuki and Mizuno, Tsunefumi and Ng, Chi-Yung and O’Dell, Stephen L. and Omodei, Nicola and Oppedisano, Chiara and Papitto, Alessandro and Peirson, Abel L. and Perri, Matteo and Pesce-Rollins, Melissa and Pilia, Maura and Possenti, Andrea and Puccetti, Simonetta and Ratheesh, Ajay and Romani, Roger W. and Sgrò, Carmelo and Slane, Patrick and Spandre, Gloria and Sunyaev, Rashid A. and Tamagawa, Toru and Tavecchio, Fabrizio and Taverna, Roberto and Tawara, Yuzuru and Tennant, Allyn F. and Thomas, Nicolas E. and Tombesi, Francesco and Trois, Alessio and Turolla, Roberto and Vink, Jacco and Wu, Kinwah and Xie, Fei},
issn = {2397-3366},
journal = {Nature Astronomy},
keywords = {Astronomy and Astrophysics},
number = {12},
pages = {1433--1443},
publisher = {Springer Nature},
title = {{Determination of X-ray pulsar geometry with IXPE polarimetry}},
doi = {10.1038/s41550-022-01799-5},
volume = {6},
year = {2022},
}
@article{15205,
abstract = {Magnetars are neutron stars with ultrastrong magnetic fields, which can be observed in x-rays. Polarization measurements could provide information on their magnetic fields and surface properties. We observed polarized x-rays from the magnetar 4U 0142+61 using the Imaging X-ray Polarimetry Explorer and found a linear polarization degree of 13.5 ± 0.8% averaged over the 2– to 8–kilo–electron volt band. The polarization changes with energy: The degree is 15.0 ± 1.0% at 2 to 4 kilo–electron volts, drops below the instrumental sensitivity ~4 to 5 kilo–electron volts, and rises to 35.2 ± 7.1% at 5.5 to 8 kilo–electron volts. The polarization angle also changes by 90° at ~4 to 5 kilo–electron volts. These results are consistent with a model in which thermal radiation from the magnetar surface is reprocessed by scattering off charged particles in the magnetosphere.},
author = {Taverna, Roberto and Turolla, Roberto and Muleri, Fabio and Heyl, Jeremy and Zane, Silvia and Baldini, Luca and González-Caniulef, Denis and Bachetti, Matteo and Rankin, John and Caiazzo, Ilaria and Di Lalla, Niccolò and Doroshenko, Victor and Errando, Manel and Gau, Ephraim and Kırmızıbayrak, Demet and Krawczynski, Henric and Negro, Michela and Ng, Mason and Omodei, Nicola and Possenti, Andrea and Tamagawa, Toru and Uchiyama, Keisuke and Weisskopf, Martin C. and Agudo, Ivan and Antonelli, Lucio A. and Baumgartner, Wayne H. and Bellazzini, Ronaldo and Bianchi, Stefano and Bongiorno, Stephen D. and Bonino, Raffaella and Brez, Alessandro and Bucciantini, Niccolò and Capitanio, Fiamma and Castellano, Simone and Cavazzuti, Elisabetta and Ciprini, Stefano and Costa, Enrico and De Rosa, Alessandra and Del Monte, Ettore and Di Gesu, Laura and Di Marco, Alessandro and Donnarumma, Immacolata and Dovčiak, Michal and Ehlert, Steven R. and Enoto, Teruaki and Evangelista, Yuri and Fabiani, Sergio and Ferrazzoli, Riccardo and Garcia, Javier A. and Gunji, Shuichi and Hayashida, Kiyoshi and Iwakiri, Wataru and Jorstad, Svetlana G. and Karas, Vladimir and Kitaguchi, Takao and Kolodziejczak, Jeffery J. and La Monaca, Fabio and Latronico, Luca and Liodakis, Ioannis and Maldera, Simone and Manfreda, Alberto and Marin, Frédéric and Marinucci, Andrea and Marscher, Alan P. and Marshall, Herman L. and Matt, Giorgio and Mitsuishi, Ikuyuki and Mizuno, Tsunefumi and Ng, Stephen C.-Y. and O’Dell, Stephen L. and Oppedisano, Chiara and Papitto, Alessandro and Pavlov, George G. and Peirson, Abel L. and Perri, Matteo and Pesce-Rollins, Melissa and Pilia, Maura and Poutanen, Juri and Puccetti, Simonetta and Ramsey, Brian D. and Ratheesh, Ajay and Romani, Roger W. and Sgrò, Carmelo and Slane, Patrick and Soffitta, Paolo and Spandre, Gloria and Tavecchio, Fabrizio and Tawara, Yuzuru and Tennant, Allyn F. and Thomas, Nicholas E. and Tombesi, Francesco and Trois, Alessio and Tsygankov, Sergey S. and Vink, Jacco and Wu, Kinwah and Xie, Fei},
issn = {1095-9203},
journal = {Science},
keywords = {Multidisciplinary},
number = {6620},
pages = {646--650},
publisher = {American Association for the Advancement of Science},
title = {{Polarized x-rays from a magnetar}},
doi = {10.1126/science.add0080},
volume = {378},
year = {2022},
}
@article{15206,
abstract = {We use the Relativistic Precession Model (RPM) and quasi-periodic oscillation (QPO) observations from the Rossi X-ray Timing Explorer to derive constraints on the properties of the black holes that power these sources and to test general relativity (GR) in the strong field regime. We build upon past techniques by using pairs of simultaneously measured QPOs, rather than triplets, and by including characteristic frequencies from the broad noise components of the power spectra in our fits. We find the inclusion of these broad noise components causes an overestimate in masses and underestimate in spins compared to values derived independently from optical spectra. We extend the underlying space-time metric to constrain potential deviations from the predictions of GR for astrophysical black holes. To do this, we modify the RPM model to a Kerr–Newman–deSitter space-time and model changes in the radial, ecliptic, and vertical frequencies. We compare our models with X-ray data of XTE J1550-564 and GRO J1655-40 using robust statistical techniques to constrain the parameters of the black holes and the deviations from GR. For both sources, using QPO and characteristic frequency data, we constrain particular deviations from GR to be less than one part per thousand.},
author = {Rink, Katherine and Caiazzo, Ilaria and Heyl, Jeremy},
issn = {1365-2966},
journal = {Monthly Notices of the Royal Astronomical Society},
keywords = {Space and Planetary Science, Astronomy and Astrophysics},
number = {1},
pages = {1389--1397},
publisher = {Oxford University Press},
title = {{Testing general relativity using quasi-periodic oscillations from X-ray black holes: XTE J1550-564 and GRO J1655-40}},
doi = {10.1093/mnras/stac2740},
volume = {517},
year = {2022},
}
@article{15207,
abstract = {Of more than a thousand known cataclysmic variables (CVs), where a white dwarf is accreting from a hydrogen-rich star, only a dozen have orbital periods below 75 minutes1,2,3,4,5,6,7,8,9. One way to achieve these short periods requires the donor star to have undergone substantial nuclear evolution before interacting with the white dwarf10,11,12,13,14, and it is expected that these objects will transition to helium accretion. These transitional CVs have been proposed as progenitors of helium CVs13,14,15,16,17,18. However, no known transitional CV is expected to reach an orbital period short enough to account for most of the helium CV population, leaving the role of this evolutionary pathway unclear. Here we report observations of ZTF J1813+4251, a 51-minute-orbital-period, fully eclipsing binary system consisting of a star with a temperature comparable to that of the Sun but a density 100 times greater owing to its helium-rich composition, accreting onto a white dwarf. Phase-resolved spectra, multi-band light curves and the broadband spectral energy distribution allow us to obtain precise and robust constraints on the masses, radii and temperatures of both components. Evolutionary modelling shows that ZTF J1813+4251 is destined to become a helium CV binary, reaching an orbital period under 20 minutes, rendering ZTF J1813+4251 a previously missing link between helium CV binaries and hydrogen-rich CVs.},
author = {Burdge, Kevin B. and El-Badry, Kareem and Marsh, Thomas R. and Rappaport, Saul and Brown, Warren R. and Caiazzo, Ilaria and Chakrabarty, Deepto and Dhillon, V. S. and Fuller, Jim and Gänsicke, Boris T. and Graham, Matthew J. and Kara, Erin and Kulkarni, S. R. and Littlefair, S. P. and Mróz, Przemek and Rodríguez-Gil, Pablo and Roestel, Jan van and Simcoe, Robert A. and Bellm, Eric C. and Drake, Andrew J. and Dekany, Richard G. and Groom, Steven L. and Laher, Russ R. and Masci, Frank J. and Riddle, Reed and Smith, Roger M. and Prince, Thomas A.},
issn = {1476-4687},
journal = {Nature},
number = {7932},
pages = {467--471},
publisher = {Springer Nature},
title = {{A dense 0.1-solar-mass star in a 51-minute-orbital-period eclipsing binary}},
doi = {10.1038/s41586-022-05195-x},
volume = {610},
year = {2022},
}
@article{15208,
abstract = {This year, a new era of observations of compact objects in X-ray polarization is commencing. Among the key targets for the Imaging X-ray Polarimetry Explorer mission are the magnetars 4U 0142+61 and 1RXS J170849.0-400910. Here, we present detailed predictions of the expected polarization from these sources that incorporate realistic models of emission physics at the surface (gaseous or condensed), the temperature distribution on the surface, general relativity, quantum electrodynamics, and scattering in the magnetosphere, accounting for the broad-band spectral energy distribution from below 1 keV to nearly 100 keV. We find that either atmospheres or condensed surfaces can account for the emission at a few keV. In both cases, either a small hot polar cap or scattering is required to account for the emission at 5–10 keV and, above 10 keV, scattering by a hard population of electrons can account for the rising power in the hard X-rays observed in many magnetars in quiescence. Although these different scenarios result in very similar spectral energy distributions, they generate dramatically different polarization signatures from 2 to 8 keV, which is the range of sensitivity of the Imaging X-ray Polarimetry Explorer. Observations of these sources in X-ray polarization will therefore probe the emission from magnetars in an essentially new way.},
author = {Caiazzo, Ilaria and González-Caniulef, Denis and Heyl, Jeremy and Fernández, Rodrigo},
issn = {1365-2966},
journal = {Monthly Notices of the Royal Astronomical Society},
keywords = {Space and Planetary Science, Astronomy and Astrophysics},
number = {4},
pages = {5024--5034},
publisher = {Oxford University Press},
title = {{Probing magnetar emission mechanisms with X-ray spectropolarimetry}},
doi = {10.1093/mnras/stac1571},
volume = {514},
year = {2022},
}
@article{15209,
abstract = {It has been recently suggested that white dwarfs generate magnetic fields in a process analogous to the Earth. The crystallization of the core creates a compositional inversion that drives convection, and combined with rotation, this can sustain a magnetic dynamo. We reanalyse the dynamo mechanism, arising from the slow crystallization of the core, and find convective turnover times tconv of weeks to months – longer by orders of magnitude than previously thought. With white dwarf spin periods P ≪ tconv, crystallization-driven dynamos are almost always in the fast-rotating regime, where the magnetic field B is at least in equipartition with the convective motion and is possibly further enhanced by a factor of B ∝ (tconv/P)1/2, depending on the assumed dynamo scaling law. We track the growth of the crystallized core using MESA and compute the magnetic field B(Teff) as a function of the white dwarf’s effective temperature Teff. We compare this prediction with observations and show that crystallization-driven dynamos can explain some – but not all – of the ∼MG magnetic fields measured for single white dwarfs, as well as the stronger fields measured for white dwarfs in cataclysmic variables, which were spun up by mass accretion to short P. Our B(Teff) curves might also explain the clustering of white dwarfs with Balmer emission lines around Teff ≈ 7500 K.},
author = {Ginzburg, Sivan and Fuller, Jim and Kawka, Adela and Caiazzo, Ilaria},
issn = {1365-2966},
journal = {Monthly Notices of the Royal Astronomical Society},
keywords = {Space and Planetary Science, Astronomy and Astrophysics},
number = {3},
pages = {4111--4119},
publisher = {Oxford University Press},
title = {{Slow convection and fast rotation in crystallization-driven white dwarf dynamos}},
doi = {10.1093/mnras/stac1363},
volume = {514},
year = {2022},
}
@article{15210,
abstract = {The maximum mass of a star that can produce a white dwarf (WD) is an important astrophysical quantity. One of the best approaches to establishing this limit is to search for WDs in young star clusters in which only massive stars have had time to evolve and where the mass of the progenitor can be established from the cooling time of the WD together with the age of the cluster. Searches in young Milky Way clusters have not thus far yielded WD members more massive than about 1.1 M⊙, well below the Chandrasekhar mass of 1.38 M⊙, nor progenitors with masses in excess of about 6 M⊙. However, the hunt for potentially massive WDs that escaped their cluster environs is yielding interesting candidates. To expand the cluster sample further, we used HST to survey four young and massive star clusters in the Magellanic Clouds for bright WDs that could have evolved from stars as massive as 10 M⊙. We located five potential WD candidates in the oldest of the four clusters examined, the first extragalactic single WDs thus far discovered. As these hot WDs are very faint at optical wavelengths, final confirmation will likely have to await spectroscopy with 30 m class telescopes.},
author = {Richer, Harvey B. and Cohen, Roger E. and Heyl, Jeremy and Kalirai, Jason and Caiazzo, Ilaria and Correnti, Matteo and Cummings, Jeffrey and Goudfrooij, Paul and Hansen, Bradley M. S. and Peeples, Molly and Sabbi, Elena and Tremblay, Pier-Emmanuel and Williams, Benjamin},
issn = {2041-8213},
journal = {The Astrophysical Journal Letters},
keywords = {Space and Planetary Science, Astronomy and Astrophysics},
number = {2},
publisher = {American Astronomical Society},
title = {{When do stars go boom?}},
doi = {10.3847/2041-8213/ac6585},
volume = {931},
year = {2022},
}
@article{15211,
abstract = {Over a dozen millisecond pulsars are ablating low-mass companions in close binary systems. In the original ‘black widow’, the eight-hour orbital period eclipsing pulsar PSR J1959+2048 (PSR B1957+20)1, high-energy emission originating from the pulsar2 is irradiating and may eventually destroy3 a low-mass companion. These systems are not only physical laboratories that reveal the interesting results of exposing a close companion star to the relativistic energy output of a pulsar, but are also believed to harbour some of the most massive neutron stars4, allowing for robust tests of the neutron star equation of state. Here we report observations of ZTF J1406+1222, a wide hierarchical triple hosting a 62-minute orbital period black widow candidate, the optical flux of which varies by a factor of more than ten. ZTF J1406+1222 pushes the boundaries of evolutionary models5, falling below the 80-minute minimum orbital period of hydrogen-rich systems. The wide tertiary companion is a rare low-metallicity cool subdwarf star, and the system has a Galactic halo orbit consistent with passing near the Galactic Centre, making it a probe of formation channels, neutron star kick physics6 and binary evolution.},
author = {Burdge, Kevin B. and Marsh, Thomas R. and Fuller, Jim and Bellm, Eric C. and Caiazzo, Ilaria and Chakrabarty, Deepto and Coughlin, Michael W. and De, Kishalay and Dhillon, V. S. and Graham, Matthew J. and Rodríguez-Gil, Pablo and Jaodand, Amruta D. and Kaplan, David L. and Kara, Erin and Kong, Albert K. H. and Kulkarni, S. R. and Li, Kwan-Lok and Littlefair, S. P. and Majid, Walid A. and Mróz, Przemek and Pearlman, Aaron B. and Phinney, E. S. and Roestel, Jan van and Simcoe, Robert A. and Andreoni, Igor and Drake, Andrew J. and Dekany, Richard G. and Duev, Dmitry A. and Kool, Erik C. and Mahabal, Ashish A. and Medford, Michael S. and Riddle, Reed and Prince, Thomas A.},
issn = {1476-4687},
journal = {Nature},
keywords = {Multidisciplinary},
number = {7908},
pages = {41--45},
publisher = {Springer Nature},
title = {{A 62-minute orbital period black widow binary in a wide hierarchical triple}},
doi = {10.1038/s41586-022-04551-1},
volume = {605},
year = {2022},
}
@article{15212,
abstract = {We determine the distribution of cooling ages of massive Gaia EDR3 white dwarfs identified with over 90 per cent probability within 200 pc and with mass in the range 0.95–1.25 M⊙. Using three sets of publicly available models, we consider sub-samples of these white dwarfs sorted into three equally spaced mass bins. Under the assumption of a constant white dwarf formation rate, we find an excess of white dwarfs, both along the Q branch and below it, corresponding respectively to stars that are in the process of freezing and those that are completely frozen. We compare the cooling age distributions for each of these bins to the recently determined time-varying star formation rate of Gaia DR2 main sequence stars. For white dwarfs in the two lightest mass bins, spanning the mass range 0.95–1.15 M⊙, we find that the cumulative cooling age distribution is statistically consistent with the expectation from the star formation rate. For white dwarfs in the heaviest mass bin, 1.15–1.25 M⊙, we find that their cumulative distribution is inconsistent with the star formation rate for all of the models considered; instead, we find that their cooling age distribution is well fitted by a linear combination of the distribution expected for single stellar evolution products and the distribution expected for double white dwarf merger products when approximately 40–50 per cent of the 1.15–1.25 M⊙ white dwarfs that formed over the past 4 Gyr are produced through double white dwarf mergers.},
author = {Fleury, Leesa and Caiazzo, Ilaria and Heyl, Jeremy},
issn = {1365-2966},
journal = {Monthly Notices of the Royal Astronomical Society},
keywords = {Space and Planetary Science, Astronomy and Astrophysics},
number = {4},
pages = {5984--5993},
publisher = {Oxford University Press},
title = {{The cooling of massive white dwarfs from Gaia EDR3}},
doi = {10.1093/mnras/stac458},
volume = {511},
year = {2022},
}
@article{15213,
abstract = {We searched through the entire Gaia EDR3 candidate white dwarf catalog for stars with proper motions and positions that are consistent with them having escaped from the Alpha Persei cluster within the past 81 Myr, the age of the cluster. In this search we found five candidate white dwarf escapees from Alpha Persei and obtained spectra for all of them. We confirm that three are massive white dwarfs sufficiently young to have originated in the cluster. All these are more massive than any white dwarf previously associated with a cluster using Gaia astrometry, and possess some of the most massive progenitors. In particular, the white dwarf Gaia EDR3 4395978097863572, which lies within 25 pc of the cluster center, has a mass of about 1.20 solar masses and evolved from an 8.5 solar-mass star, pushing the upper limit for white dwarf formation from a single massive star, while still leaving a substantial gap between the resulting white dwarf mass and the Chandrasekhar mass.},
author = {Miller, David R. and Caiazzo, Ilaria and Heyl, Jeremy and Richer, Harvey B. and Tremblay, Pier-Emmanuel},
issn = {2041-8213},
journal = {The Astrophysical Journal Letters},
keywords = {Space and Planetary Science, Astronomy and Astrophysics},
number = {2},
publisher = {American Astronomical Society},
title = {{The ultramassive white dwarfs of the Alpha Persei cluster}},
doi = {10.3847/2041-8213/ac50a5},
volume = {926},
year = {2022},
}