Search

We present temporal and time-resolved spectral analyses of all the thermonuclear X-ray bursts observed from the neutron star low-mass X-ray binary 4U 1728-34 with NICER from 2017 June to 2019 September. In total, we detected 11 X-ray bursts from the source and performed time-resolved spectroscopy. Unlike some of the earlier results for other bursting sources from NICER, our spectral results indicate that the use of a scaling factor for the persistent emission is not statistically necessary. This is primarily a result of the strong interstellar absorption in the line of sight toward 4U 1728-34, which causes the count rates to be significantly lower at low energies. We also searched for burst oscillations and detected modulations in six different bursts at around the previously known burst oscillation frequency of 363 Hz. Finally, we report the detection of oscillations prior to two bursts at 356 and 359 Hz, respectively. This is the first time in the literature where burst oscillations are detected before the rapid rise in X-ray flux, from any known burster. These oscillations disappear as soon as the burst starts to rise and occur at a somewhat lower frequency than the oscillations we detect during the bursts., We thank the referee for valuable comments and suggestions that improved the manuscript. This work is supported by the Scientific Research Projects Coordination Unit of Istanbul University (ADEP Project No: FBA-2023-39409) and the Turkish Republic, Presidency of Strategy and Budget project, 2016K121370. Y.C. acknowledges support from the grant RYC2021-032718-I, financed by MCIN/AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR. This work was supported by NASA through the NICER mission and the Astrophysics Explorers Program., Peer Reviewed, Postprint (published version)

Magnetic activity and rotation are related to the age of low-mass main-sequence stars. To further constrain these relations, we study a sample of 574 main-sequence stars members of common proper motion pairs with white dwarfs, identified thanks to Gaia astrometry. We use the white dwarfs as age indicators, while the activity indexes and rotational velocities are obtained from the main-sequence companions using standard procedures. We find that stars older than 5 Gyr do not display H a nor Ca II H&K emission unless they are fast rotators due to tidal locking from the presence of unseen companions and that the rotational velocities tend to decrease over time, thus supporting the so-called gyrochronology. However, we also find moderately old stars (2–6 Gyr) that are active presumably because they rotate faster than they should for their given ages. This indicates that they may be suffering from weakened magnetic braking or that they possibly evolved through wind accretion processes in the past. The activity fractions that we measure for all stars younger than 5 Gyr range between 10 and 40 per cent. This is line with the expectations, since our sample is composed of F, G, K, and early M stars, which are thought to have short (<2 Gyr) activity lifetimes. Finally, we observe that the H a fractional luminosities and the RHK indexes for our sample of (slowly rotating) stars show a spread (-4 >log(LH a/Lbol); log(RHK) > -5) typically found in inactive M stars or weakly active/inactive F, G, K stars., This work has been partially supported by the (Spanish Ministerio de Asuntos Economicos ´ y Transformacion´ Digital) MINECO grant PID2020-117252GB-I00 and by the AGAUR/Generalitat de Catalunya grant SGR-386/2021. RR acknowledges support from Grant RYC2021-030837-I funded by MCIN/(Agencia Estatal de Investigacion) ´ AEI/ 10.13039/501100011033 and by ‘European Union NextGenerationEU/PRTR’. MEC acknowledges grant RYC2021-032721-I, funded by MCIN/AEI/10.13039/501100011033 and by the ‘European Union NextGenerationEU/PRTR’. MAH was supported by grant ST/V000853/1 from the Science and Technology Facilities Council (STFC). This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 101020057)., Peer Reviewed, Postprint (published version)

The next years will see the completion of several new facilities at Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali del Sud (LNS) opening up new possibilities in the fields of nuclear structure, nuclear dynamics, nuclear astrophysics and applications. These include a new line for high-intensity cyclotron beams, a new facility for in-flight production of radioactive ion beams, the PANDORA plasma trap for multidisciplinary studies and a high-power laser for basic science and applied physics. The nuclear physics community has organized a workshop to discuss the new physics opportunities that will be possible in the middle term (5–7 years) by employing state-of-the-art detection systems. A detailed discussion of the outcome from the workshop is presented in this report., Postprint (published version)

Classical novae are thermonuclear explosions in stellar binary systems, and important sources of 26Al and 22Na. While ¿ rays from the decay of the former radioisotope have been observed throughout the Galaxy, 22Na remains untraceable. Its half-life (2.6 yr) would allow the observation of its 1.275 MeV ¿-ray line from a cosmic source. However, the prediction of such an observation requires good knowledge of its nucleosynthesis. The 22Na(p,¿¿)23Mg reaction remains the only source of large uncertainty about the amount of 22Na ejected. Its rate is dominated by a single resonance on the short-lived state at 7785.0(7) keV in 23Mg. Here, we propose a combined analysis of particle-particle correlations and velocity-difference profiles to measure femtosecond nuclear lifetimes. The application of this method to the study of the 23Mg states, places strong limits on the amount of 22Na produced in novae and constrains its detectability with future space-borne observatories., Postprint (published version)

This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly notices of the Royal Astronomical Society following peer review. The version of record Vincentelli, F., et al. Sub-second infrared variability from the archetypal accreting neutron star 4U 1728-34. Monthly notices of the Royal Astronomical Society, October 2023, vol. 525, n. 2, p. 2509-2518. is available online at: https://doi.org/10.1093/mnras/stad2414, We report on the first simultaneous high-time resolution X-ray and infrared (IR) observations of a neutron star low mass X-ray binary in its hard state. We performed ¿h of simultaneous observations of 4U 1728-34 using HAWK-I@VLT, XMM–Newton, and NuSTAR. The source displayed significant X-ray and IR variability down to sub-second time-scales. By measuring the cross-correlation function between the IR and X-ray lightcurves, we discovered a significant correlation with an IR lead of ¿ms with respect to the X-rays. We analysed the X-ray energy dependence of the lag, finding a marginal increase towards higher energies. Given the sign of the lag, we interpret this as possible evidence of Comptonization from external seed photons. We discuss the origin of the IR seed photons in terms of cyclo-synchrotron radiation from an extended hot flow. Finally, we also observed the IR counterpart of a type-I X-ray burst, with a delay of ¿s. Although some additional effects may be at play, by assuming that this lag is due to light travel time between the central object and the companion star, we find that 4U 1728-34 must have an orbital period longer than ¿h and an inclination higher than 8¿., This work benefited from the discussions done during the ISSI meeting in Bern "Looking at the disc-jet coupling from different angles". FMV acknowledges support from the grant FJC2020-043334-I financed by MCIN/AEI/10.13039/501100011033 and Next Generation EU/PRTR. This work is supported by the Spanish Ministry of Science under grants PID2020–120323GB–I00, PID2021–124879NB-I00, and EUR2021–122010 TMB acknowledges financial contribution from grant PRIN INAF 2019 n.15. YC acknowledges support from the grant RYC2021-032718-I, financed by MCIN/AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR. LS acknowledges financial contributions from ASI-INAF agreements 2017-14-H.O and I/037/12/0; from “iPeska” research grant (P.I. Andrea Possenti) funded under the INAF call PRIN-SKA/CTA (resolution 70/2016), from PRIN-INAF 2019 no. 15 and from the Italian Ministry of University and Research (MUR), PRIN 2020 (prot. 2020BRP57Z) "GEMS". This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France (DOI : 10.26093/cds/vizier). The original description of the VizieR service was published in 2000, A&AS 143, 23", Peer Reviewed, Postprint (author's final draft)

This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly notices of the Royal Astronomical Society following peer review. The version of record Córsico, A.H., et al. General relativistic pulsations of ultra-massive ZZ Ceti stars. Monthly notices of the Royal Astronomical Society, October 2023, vol. 524, n. 4, p. 5929-5943 is available online at: https://doi.org/10.1093/mnras/stad2248, Ultra-massive white dwarf stars are currently being discovered at a considerable rate, thanks to surveys such as the Gaia space mission. These dense and compact stellar remnants likely play a major role in Type Ia supernova explosions. It is possible to probe the interiors of ultra-massive white dwarfs through asteroseismology. In the case of the most massive white dwarfs, general relativity could affect their structure and pulsations substantially. In this work, we present results of relativistic pulsation calculations employing relativistic ultra-massive ONe-core white dwarf models with hydrogen-rich atmospheres and masses ranging from 1.29 to 1.369 M¿ with the aim of assessing the impact of general relativity on the adiabatic gravity (g)-mode period spectrum of very high mass ZZ Ceti stars. Employing the relativistic Cowling approximation for the pulsation analysis, we find that the critical buoyancy (Brunt–Väisälä) and acoustic (Lamb) frequencies are larger for the relativistic case, compared to the Newtonian case, due to the relativistic white dwarf models having smaller radii and higher gravities for a fixed stellar mass. In addition, the g-mode periods are shorter in the relativistic case than those in the Newtonian computations, with relative differences of up to ~50 per¿cent for the highest mass models (¿1.369 M¿ ¿) and for effective temperatures typical of the ZZ Ceti instability strip. Hence, the effects of general relativity on the structure, evolution, and pulsations of white dwarfs with masses larger than ~1.29 M¿ cannot be ignored in the asteroseismological analysis of ultra-massive ZZ Ceti stars., Part of this work was supported by AGENCIA through the Programa de Modernización Tecnológica BID 1728/OC-AR, by the PIP 112-200801- 00940 grant from CONICET, by the National Science Foundation under grants AST-2205736, PHY-2110335, the National Aeronautics and Space Administration under grant 80NSSC22K0479, and the US DOE under contract DE-AC05-00OR22725. ST acknowledges support from MINECO under the PID2020-117252GB-I00 grant and by the AGAUR/Generalitat de Catalunya grant SGR386/2021. MC acknowledges grant RYC2021-032721-I, funded by MCIN/AEI/10.13039/ 501100011033 and by the European Union NextGenerationEU/PRTR. This research has made use of NASA Astrophysics Data System., Peer Reviewed, Postprint (author's final draft)

Context. The characterization of white dwarf atmospheres is crucial for accurately deriving stellar parameters such as effective temperature, mass, and age. However, the inclusion of physical processes such as convective mixing and convective dilution in current white dwarf atmospheric models offers a prediction of the spectral evolution of these objects. To constrain these models, accurate observational data and analyses are necessary. Aims. We aim to classify the population of white dwarfs up to 500 pc into hydrogen-rich or hydrogen-deficient atmospheres based on Gaia spectra and to derive an accurate spectral type-temperature distribution, namely, the ratio between the number of non-DAs to the total number of white dwarfs as a function of the effective temperature for the largest observed unbiased sample of these objects. Methods. We took advantage of the recent Gaia low-resolution spectra available for 76 657 white dwarfs up to 500 pc. We calculated the synthetic J-PAS narrow-band photometry and fit the spectral energy distribution of each object with up-to-date models for hydrogen-rich and helium-rich white dwarf atmospheres. We estimated the probability for a white dwarf to have a hydrogen-rich atmosphere and validated the results using the Montreal White Dwarf Database. Finally, precise effective temperature values were derived for each object using La Plata evolutionary models. Results. We successfully classified a total of 65 310 white dwarfs (57 155 newly classified objects) into DAs and non-DAs with an accuracy of 94%. An unbiased subsample of nearly 34 000 objects was built, from which we computed a precise spectral distribution spanning an effective temperature range from 5500 to 40 000 K, while accounting for potential selection effects. Conclusions. Some characteristic features of the spectral evolution, such as the deficit of helium-rich stars at Teff ˜ 35 000 - 40 000 K and in the range of 22 000 ¿ Teff ¿ 25 000 K, as well as a gradual increase from, We acknowledge support from MINECO under the PID2020-117252GB-I00 grant and by the AGAUR/Generalitat de Catalunya grant SGR-386/2021. P.C. acknowledges financial support from the Govern- ment of Comunidad Autónoma de Madrid (Spain) via postdoctoral grant ‘Atrac- ción de Talento Investigador’ 2019-T2/TIC-14760. R.M.O. is funded by INTA through grant PRE-OBSERVATORIO. MC acknowledges grant RYC2021- 032721-I, funded by MCIN/AEI/10.13039/501100011033 and by the Euro- pean Union NextGenerationEU/PRTR. RR acknowledges support from Grant RYC2021-030837-I funded by MCIN/AEI/ 10.13039/501100011033 and by “European Union NextGenerationEU/PRTR”. F.J.E. acknowledges support from ESA through the Faculty of the European Space Astronomy Centre (ESAC) – Funding reference 4000139151/22/ES/CM. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www. cosmos.esa.int/gaia), processed by the Gaia Data Processing and Anal- ysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/ consortium). Funding for the DPAC has been provided by national insti- tutions, in particular the institutions participating in the Gaia Multilateral Agreement. This work has made use of the Python package GaiaXPy, devel- oped and maintained by members of the Gaia Data Processing and Analy- sis Consortium (DPAC) and in particular, Coordination Unit 5 (CU5), and the Data Processing Centre located at the Institute of Astronomy, Cambridge, UK (DPCI). This publication makes use of VOSA, developed under the Spanish Virtual Observatory (https://svo.cab.inta-csic.es) project funded by MCIN/AEI/10.13039/501100011033/ through grant PID2020-112949GB-I00. We extensively made used of Topcat (Taylor 2005). This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France. We acknowledge use of the ADS bibliographic services., Peer Reviewed, Postprint (published version)

Planetary nebulae in Galactic open star clusters are rare objects; only three are known to date. They are of particular interest because their distance can be determined with high accuracy, allowing one to characterize the physical properties of the planetary nebula and its ionizing central star with high confidence. Here we present the first quantitative spectroscopic analysis of a central star in an open cluster, namely the faint nucleus of IPHASX J055226.2+323724 in M37. This cluster contains 14 confirmed white dwarf members, which were previously used to study the initial-to-final-mass relation of white dwarfs, and six additional white dwarf candidates. We performed an atmosphere modeling of spectra taken with the 10m Gran Telescopio Canarias. The central star is a hot hydrogen-deficient white dwarf with an effective temperature of 90 000 K and spectral type PG1159 (helium- and carbon-rich). We know it is about to transform into a helium-rich DO white dwarf because the relatively low atmospheric carbon abundance indicates ongoing gravitational settling of heavy elements. The star belongs to a group of hot white dwarfs that exhibit ultrahigh-excitation spectral lines possibly emerging from shock-heated material in a magnetosphere. We find a relatively high stellar mass of M = 0.85-0.14+0.13 M¿. This young white dwarf is important for the semi-empirical initial-final mass relation because any uncertainty related to white-dwarf cooling theory is insignificant with respect to the pre-white-dwarf timescale. Its post-asymptotic-giant-branch age of 170 000–480 000 yr suggests that the extended planetary nebula is extraordinarily old. We also performed a spectroscopic analysis of the six other white dwarf candidates of M37, confirming one as a cluster member., We thank the referee for a constructive report. NR issupported by the Deutsche Forschungsgemeinschaft (DFG) through grantsGE2506/17-1 and RE3915/2-1. MG and LRB acknowledge partial supportby MIUR under PRIN programme #2017Z2HSMF and by PRIN-INAF 2019.MEC acknowledges grant RYC2021-032721-I, funded by MCIN/AEI/10.13039/501100011033 and by the European Union NextGenerationEU/PRTR. PG thanksMarcel Drechsler and Sven Eklund for their contribution to PN imaging. RRacknowledges support from Grant RYC2021-030837-I funded by MCIN/AEI/10.13039/501100011033 and by “European Union NextGenerationEU/PRTR”.This work was partially supported by the AGAUR/Generalitat de Catalunya grantSGR-386/2021 and by the Spanish MINECO grant PID2020-117252GB-I00. TheTMAD tool (http://astro.uni-tuebingen.de/~TMAD) used for this paperwas constructed as part of the activities of the German Astrophysical VirtualObservatory. Based on observations made with the Gran Telescopio Canarias(GTC), installed at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, on the island of La Palma. The Starlinksoftware (Berry et al. 2022) is currently supported by the East Asian Observa-tory. Some of the data presented in this paper were obtained from the MikulskiArchive for Space Telescopes (MAST). This research has made use of NASA’sAstrophysics Data System and the SIMBAD database, operated at CDS, Stras-bourg, France. This research has made use of the VizieR catalogue access tool,CDS, Strasbourg, France. This work has made use of data from the EuropeanSpace Agency (ESA) missionGaia., Peer Reviewed, Postprint (published version)

The third data release of Gaia has provided low resolution spectra for 100 000 white dwarfs (WDs) that, together with the excellent photometry and astrometry, represent an unrivalled benchmark for the study of this population. In this work, we first built a highly-complete volume-limited sample consisting in 12 718 WDs within 100 pc from the Sun. The use of VOSA tool allowed us to perform an automated fitting of their spectral energy distributions to different atmospheric models. In particular, the use of spectrally derived J-PAS photometry from Gaia spectra led to the classification of DA and non-DA WDs with an accuracy ¡ 90%, tested in already spectroscopically labelled objects. The excellent performance achieved was extended to practically the whole population of WDs with effective temperatures above 5500 K. Our results show that, while the A branch of the Gaia WD Hertzsprung-Russell diagram is practically populated by DA WDs, the B branch is largely formed by non-DAs (65%). The remaining 35% of DAs within the B branch implies a second peak at 0.8 M in the DA- mass distribution. Additionally, the Q branch and its extension to lower temperatures can be observed for both DA and non-DA objects due to core crystallisation. Finally, we derived a detailed spectral evolution function, which confirms a slow increase of the fraction of non-DAs as the effective temperature decreases down to 10 500 K, where it reaches a maximum of 36% and then decreases for lower temperatures down to 31%, We are greatly indebted to Detlev Koester for providing us with his white dwarf model atmosphere spectra. ST acknowledges fruitful discussion and data provided by Carlos López-Sanjuan. We also thank to the referee Dr Jay Holberg for his valuable comments. FJE acknowledges financial support from the Servicio P ¨ublico de Empleo Estatal, Spain. PC acknowledges financial support from the Government of Comunidad Autónoma de Madrid (Spain) via postdoctoral grant ‘Atracción de Talento Investigador’ 2019-T2/TIC-14760. ST and ARM acknowledge support from MINECO under the PID2020-117252GB-I00 grant. ARM acknowledges support from Grant RYC-2016-20254 funded by MCIN/AEI/10.13039/501100011033 and by ESF Investing in your future. RMO is funded by INTA through grant PRE- OBSERVATORIO. MEC acknowledges support from NASA grants (HGC) 80NSSC17K0008 and (LWS) 80NSSC20K0193 and the University of Colorado Boulder., Peer Reviewed, Postprint (published version)

WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, will see first light in late 2022. WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable ‘mini’ integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366-959 nm at R ~ 5000, or two shorter ranges at R ~ 20¿000. After summarising the design and implementation of WEAVE and its data systems, we present the organisation, science drivers and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy’s origins by completing Gaia’s phase-space information, providing metallicities to its limiting magnitude for ~3 million stars and detailed abundances for ~1.5 million brighter field and open-cluster stars; (ii) survey ~0.4 million Galactic-plane OBA stars, young stellar objects and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey ~400 neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionised gas in z < 0.5 cluster galaxies; (vi) survey stellar populations and kinematics in ~25¿000 field galaxies at 0.3 ¿ z ¿ 0.7; (vii) study the cosmic evolution of accretion and star formation using >1 million spectra of LOFAR-selected radio sources; (viii) trace structures using intergalactic/circumgalactic gas at z > 2. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator., Postprint (published version)

Flux variability is a remarkable property of black hole (BH) accreting systems and a powerful tool to investigate the multi-scale structure of the accretion flow. The X-ray band is where some of the most rapid variations occur, pointing to an origin in the innermost regions close to the BH. The study of fast time variability provides us with means to explore the accretion flow around compact objects in ways which are inaccessible via spectral analysis alone and to peek at regions which cannot be imaged with the currently available instrumentation. In this chapter we will discuss fast X-ray variability in stellar-mass BH systems, namely, binary systems containing a star and a BH, occasionally contrasting it with observations of supermassive BHs in active galactic nuclei. We will explore how rapid variations of the X-ray flux have been used in multiple studies as a diagnostic of the innermost regions of the accretion flow in these systems. To this aim we will provide an overview of the currently most used analysis approaches for the study of X-ray variability, describe observations of both aperiodic and quasi-periodic phenomena, and discuss some of the proposed models., Peer Reviewed, Postprint (published version)

In the past few years, we have undertaken an extensive investigation of star clusters and their stellar populations in the Large and Small Magellanic Clouds (LMC and SMC) based on archival images collected with the Hubble Space Telescope. We present photometry and astrometry of stars in 101 fields observed with the Wide Field Channel of the Advanced Camera for Surveys and the Ultraviolet and Visual Channel and the Near-Infrared Channel of Wide Field Camera 3. These fields comprise 113 star clusters. We provide differential-reddening maps for those clusters with significant reddening variations across the field of view. We illustrate various scientific outcomes that arise from the early inspection of the photometric catalogs. In particular, we provide new insights into the extended main-sequence turnoff (eMSTO) phenomenon: (i) We detected eMSTOs in two clusters, KMHK 361 and NGC 265, which had no previous evidence of multiple populations. This finding corroborates the conclusion that the eMSTO is a widespread phenomenon among clusters younger than ~2 Gyr. (ii) The homogeneous color-magnitude diagrams (CMDs) of 19 LMC clusters reveal that the distribution of stars along the eMSTO depends on cluster age. (iii) We discovered a new feature along the eMSTO of NGC 1783, which consists of a distinct group of stars on the red side of the eMSTO in CMDs composed of UV filters. Furthermore, we derived the proper motions of stars in the fields of view of clusters with multi-epoch images. Proper motions allowed us to separate the bulk of bright field stars from cluster members and investigate the internal kinematics of stellar populations in various LMC and SMC fields. As an example, we analyze the field around NGC 346 to disentangle the motions of its stellar populations, including NGC 364 and BS 90, young and pre-main-sequence stars in the star-forming region associated with NGC 346, and young and old field stellar populations of the SMC. Based on these results and the fields a, We thank the anonymous referee for various suggestions that improved the quality of the manuscript. This work has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research innovation programme (Grant Agreement ERC-StG 2016, No. 716082 ’GALFOR’, PI: Milone, http://progetti.dfa.unipd. it/GALFOR) and from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No. 101034319 and from the European Union – NextGenerationEU, beneficiary: Ziliotto. A.P.M., M.T., and E.D. acknowledge support from MIUR through the FARE project R164RM93XW SEMPLICE (PI: Milone). A.P.M. and M.T. have been supported by MIUR under PRIN program 2017Z2HSMF (PI: Bedin). This research was supported in part by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) through project number CE170100013. This work is based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute (STScI). STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555., Peer Reviewed, Postprint (published version)

Context. The high-quality photometric and astrometric capabilities of the ESA Gaia space mission have revealed a bifurcation of the white dwarf sequence on the color magnitude diagram with two branches: A and B. While the A branch consists mostly of white dwarfs with hydrogen(H)-rich atmospheres, the B branch is not completely understood. Although it has been proposed that the B branch is populated mainly by helium (He)-rich white dwarfs, this branch overlaps with a ~0.8 M evolutionary track with a pure He envelope, which would imply an unexpected peak in the white dwarf mass distribution. Aims. In cold He-rich white dwarfs, it is expected that the outer convective zone penetrates into deep carbon (C) -rich layers, leading to a slight C contamination in their surfaces at ~10 000 K. In this paper we aim to study the Gaia bifurcation as the natural consequence of C dredge-up by convection in cold He-dominated white dwarfs. Methods. Relying on accurate atmosphere models, we provide a new set of evolutionary models for He-rich white dwarfs, which employ different prescriptions for the C enrichment. On the basis of these models, we carried out a population synthesis study of the Gaia 100 pc white dwarf sample to constrain the models that best fit the bifurcation. Results. Our study shows that He-rich white dwarf models with a slight C contamination below the optical detection limit can accurately reproduce the Gaia bifurcation. We refer to these stars as “stealth DQ” white dwarfs because they do not exhibit detectable C signatures in their optical spectra, but the presence of C in their atmosphere produces a continuum absorption favoring the emission in bluer wavelengths, thereby creating the B branch of the bifurcation. Furthermore, our study shows that the white dwarf mass distribution obtained when a stealth C contamination is taken into account presents a peak at ~0.6 M , which is consistent with the mass distribution for H-rich white dwarfs and with the standard evo, The authors acknowledge the expert referee S. O. Kepler. MC acknowledges grant RYC2021-032721-I, funded by MCIN/AEI/10.13039/501100011033 and by the European Union NextGenerationEU/PRTR. MAH is supported by grant ST/V000853/1 from the Science and Technology Facilities Council (STFC). RR acknowledges support from Grant RYC2021-030837-I funded by MCIN/AEI/ 10.13039/501100011033 and by “European Union NextGenerationEU/PRTR”. This work was partially supported by the AGAUR/Generalitat de Catalunya grant SGR-386/2021 and by the Spanish MINECO grant PID2020-117252GB-I00. This research made use of NASA Astrophysics Data System. This work made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement., Peer Reviewed, Postprint (published version)

This article has been accepted for publication in Monthly notices of the Royal Astronomical Society ©: 2023 Scaringi, S. et al. XGAPS: a sub-arcsec cross-match of galactic plane surveys. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved., We present a sub-arcsec cross-match of Gaia Data Release 3 (DR3) against the INT Galactic Plane Surveys (IGAPS) and the United Kingdom Infrared Deep Sky Survey (UKIDSS). The resulting cross-match of Galactic Plane Surveys (XGAPS) provides additional precise photometry (URGO, g, r, i, Ha, J, H, and K) to the Gaia photometry. In building the catalogue, proper motions given in Gaia DR3 are wound back to match the epochs of the IGAPS constituent surveys (INT Photometric HaSurvey of the Northern Galactic Plane, IPHAS, and the UV-Excess Survey of the Northern Galactic Plane, UVEX) and UKIDSS, ensuring high-proper motion objects are appropriately cross-matched. The catalogue contains 33¿987¿180 sources. The requirement of >3s parallax detection for every included source means that distances out to 1–1.5¿kpc are well covered. In producing XGAPS, we have also trained a Random Forest classifier to discern targets with problematic astrometric solutions. Selection cuts based on the classifier results can be used to clean colour-magnitude and colour–colour diagrams in a controlled and justified manner, as well as producing subsets of astrometrically reliable targets. We provide XGAPS as a 111 column table. Uses of the catalogue include the selection of Galactic targets for multi-object spectroscopic surveys as well as identification of specific Galactic populations., MM work was funded by the Spanish MICIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe” by the “European Union” through grant RTI2018-095076-B-C21, and the Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia “María de Maeztu”) through grant CEX2019-000918-M. ARM acknowledges support from Grant RYC2016-20254 funded by MCIN/AEI/10.13039/501100011033 and by ESF Investing in your future, and from MINECO under the PID2020-117252GB-I00 grant., Peer Reviewed, Postprint (published version)

We present a UV spectroscopic study of ionized outflows in 21 active galactic nuclei (AGN), observed with the Hubble Space Telescope (HST). The targets of the Supermassive Black Hole Winds in X-rays (SUBWAYS) sample were selected with the aim to probe the parameter space of the underexplored AGN between the local Seyfert galaxies and the luminous quasars at high redshifts. Our targets, spanning redshifts of 0.1–0.4 and bolometric luminosities (Lbol) of 1045–1046 erg s-1, have been observed with a large multi-wavelength campaign using XMM-Newton, NuSTAR, and HST. Here, we model the UV spectra and look for different types of AGN outflows that may produce either narrow or broad UV absorption features. We examine the relations between the observed UV outflows and other properties of the AGN. We find that 60% of our targets show a presence of outflowing H¿I absorption, while 40% exhibit ionized outflows seen as absorption by either C¿IV, N¿V, or O¿VI. This is comparable to the occurrence of ionized outflows seen in the local Seyfert galaxies. All UV absorption lines in the sample are relatively narrow, with outflow velocities reaching up to -3300 km s-1. We did not detect any UV counterparts to the X-ray ultra-fast outflows (UFOs), most likely due to their being too highly ionized to produce significant UV absorption. However, all SUBWAYS targets with an X-ray UFO that have HST data demonstrate the presence of UV outflows at lower velocities. We find significant correlations between the column density (N) of the UV ions and Lbol of the AGN, with NH I decreasing with Lbol, while NO VI is increasing with Lbol. This is likely to be a photoionization effect, where toward higher AGN luminosities, the wind becomes more ionized, resulting in less absorption by neutral or low-ionization ions and more absorption by high-ionization ions. In addition, we find that N of the UV ions decreases as their outflow velocity increases. This may be explained by a mechanical power that is eva, Peer Reviewed, Postprint (published version)

Context. X-Ray bursts (XRBs) are powerful thermonuclear events on the surface of accreting neutron stars (NSs) where nucleosynthesis of intermediate-mass elements occurs. The high surface gravity of an NS prevents the ejection of material by the XRB thermonuclear explosion. However, the predicted and observed XRB luminosities sometimes exceed Eddington’s value, and some of the material may escape by means of stellar wind. Aims. This work aims to determine the mass-loss and chemical composition of the material ejected through radiation-driven winds and its significance for Galactic abundances. It also reports on the evolution of observational quantities during the wind phase, which can help constrain the mass-radius relation in NSs. Methods. A non-relativistic radiative wind model was implemented, with modern opacity tables and treatment of the critical point, and linked through a new technique to a series of XRB hydrodynamic simulations that include over 300 isotopes. This allowed us to construct a quasi-stationary time evolution of the wind during the XRB. Results. In the models we studied, the total mass ejected by the wind was about 6 × 10^19 g; the average ejected mass per burst represented 2.6% of the accreted mass between bursts, with 0.1% of the envelope mass ejected per burst; and approximately 90% of the ejecta was composed by 60Ni, 64Zn, 68Ge, and 58Ni. The ejected material also contained a small fraction (10^-4 - 10^-5) of some light p-nuclei, but not enough to account for their Galactic abundances. Additionally, the observable magnitudes during the wind phase showed remarkable correlations, partly due to the fact that photospheric luminosity stays close to the Eddington limit. Some of these correlations involve wind parameters, such as energy and mass outflows, that are determined by the conditions at the base of the wind envelope. Conclusions. The simulations resulted in the first realistic quantification of mass-loss for each isotope synthesized in the, Peer Reviewed, Postprint (author's final draft)

Many astrophysical and terrestrial scenarios involving magnetic fields can be approached in axial geometry. Although the smoothed particle hydrodynamics (SPH) technique has been successfully extended to magneto-hydrodynamics (MHD), a well-verified, axisymmetric MHD scheme based on such technique does not exist yet. In this work we fill that gap in the scientific literature and propose and check a novel axisymmetric MHD hydrodynamic code, that can be applied to physical problems which display the adequate geometry. We show that the hydrodynamic code built following these axisymmetric hypothesis is able to produce similar results than standard 3D-SPMHD codes with equivalent resolution but with much lesser computational load., Peer Reviewed, Postprint (author's final draft)

The 25Al(p,¿) reaction has long been highlighted as a possible means to bypass the production of 26Al cosmic ¿ rays in classical nova explosions. However, uncertainties in the properties of key resonant states in 26Si have hindered our ability to accurately model the influence of this reaction in such environments. We report on a detailed ¿-ray spectroscopy study of 26Si and present evidence for the existence of a new, likely l=1, resonance in the 25Al + p system at Er=153.9(15) keV. This state is now expected to provide the dominant contribution to the 25Al(p,¿) stellar reaction rate over the temperature range, T˜0.1-0.2 GK. Despite a significant increase in the rate at low temperatures, we find that the final ejected abundance of 26Al from classical novae remains largely unaffected even if the reaction rate is artificially increased by a factor of 10. Based on new, galactic chemical evolution calculations, we estimate that the maximum contribution of novae to the observed galactic abundance of 26Al is ˜0.2M¿. Finally, we briefly highlight the important role that super-asymptotic giant branch stars may play in the production of 26Al., Postprint (published version)

We present the first reliable determination of the orbital period of the recurrent nova V2487 Oph (Nova Oph 1998). We derived a value of 0.753 ± 0.016 d (18.1 ± 0.4 h) from the radial velocity curve of the intense He¿II ¿4686 emission line as detected in time-series X-shooter spectra. The orbital period is significantly shorter than earlier claims, but it makes V2487 Oph one of the longest period cataclysmic variables known. The spectrum of V2487 Oph is prolific in broad Balmer absorptions that resemble a white dwarf spectrum. However, we show that they come from the accretion disc viewed at low inclination. Although highly speculative, the analysis of the radial velocity curves provides a binary mass ratio q ˜ 0.16 and a donor star mass M2 ˜ 0.21 M¿, assuming the reported white dwarf mass M1 = 1.35 M¿. A subgiant M-type star is tentatively suggested as the donor star. We were lucky to inadvertently take some of the spectra when V2487 Oph was in a flare state. During the flare, we detected high-velocity emission in the Balmer and He¿II ¿4686 lines exceeding -2000 km s-1 at close to orbital phase 0.4. Receding emission up to 1200 km s-1 at about phase 0.3 is also observed. The similarities with the magnetic cataclysmic variables may point to magnetic accretion on to the white dwarf during the repeating flares., Peer Reviewed, Postprint (published version)

Planets orbiting close to hot stars experience intense extreme-ultraviolet radiation, potentially leading to atmosphere evaporation and to thermal dissociation of molecules. However, this extreme regime remains mainly unexplored due to observational challenges. Only a single known ultra-hot giant planet, KELT-9b, receives enough ultraviolet radiation for molecular dissociation, with a day-side temperature of ~4,600¿K. An alternative approach uses irradiated brown dwarfs as hot-Jupiter analogues. With atmospheres and radii similar to those of giant planets, brown dwarfs orbiting close to hot Earth-sized white dwarf stars can be directly detected above the glare of the star. Here we report observations revealing an extremely irradiated low-mass companion to the hot white dwarf WD¿0032–317. Our analysis indicates a day-side temperature of ~8,000¿K, and a day-to-night temperature difference of ~6,000¿K. The amount of extreme-ultraviolet radiation (with wavelengths 100–912¿Å) received by WD 0032–317B is equivalent to that received by planets orbiting close to stars as hot as late B-type stars, and about 5,600 times higher than that of KELT-9b. With a mass of ~75–88¿Jupiter masses, this near-hydrogen-burning-limit object is potentially one of the most massive brown dwarfs known., This work was supported by a Benoziyo-prize postdoctoral fellowship (N.H.). This work was supported by a grant from the European Research Council (ERC) under the European Union’s FP7 Programme, Grant No. 833031 (D.M.). A.G.I. acknowledges support from the Netherlands Organisation for Scientific Research (NWO). C.B. acknowledges support from the National Science Foundation grant AST-1909022. E.B. acknowledges support from the Science and Technology Facilities Council (STFC) grant no. ST/S000623/1. B.T.G. acknowledges support from the UK’s Science and Technology Facilities Council (STFC), grant ST/T000406/1. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 101020057). A.R.M. acknowledges support from the Spanish MINECO grant PID2020-117252GB-I00 and from the AGAUR/Generalitat de Catalunya grant SGR-386/2021. F.M. acknowledges support from the INAF Large Grant “Dual and binary supermassive black holes in the multi-messenger era: from galaxy mergers to gravitational waves” (Bando Ricerca Fondamentale INAF 2022), from the INAF project “VLT-MOONS” CRAM 1.05.03.07., Peer Reviewed, Postprint (author's final draft)

We report on the 2019 XMM-Newton+NuSTAR monitoring campaign of the Seyfert galaxy NGC 2992, observed at one of its highest flux levels in the X-rays. The time-averaged spectra of the two XMM-Newton orbits show ultrafast outflows (UFOs) absorbing structures above 9 keV with >3s significance. A detailed investigation of the temporal evolution on a ~5 ks timescale reveals UFO absorption lines at a confidence level >95% (2s) in 8 out of 50 XMM-Newton segments, estimated via Monte Carlo simulations. We observe a wind variability corresponding to a length scale of 5 Schwarzschild radii rS. Adopting the novel Wind in the Ionized Nuclear Environment model, we estimate the outflowing gas velocity (v = 0.21–0.45c), column density (NH = 4–8 × 1024 cm-2) and ionization state ($\mathrm{log}({\xi }_{0}/\mathrm{erg}\ \mathrm{cm}\ {{\rm{s}}}^{-1})=3.7\mbox{--}4.7$), taking into account geometrical and special relativity corrections. These parameters lead to instantaneous mass outflow rates of ${\dot{M}}_{\mathrm{out}}\simeq 0.3\mbox{--}0.8$M¿ yr-1, with associated outflow momentum rates ${\dot{p}}_{\mathrm{out}}\simeq 20\mbox{--}90$LBol/c and kinetic energy rates ${\dot{E}}_{{\rm{K}}}\simeq 2\mbox{--}25$LBol. We estimate a wind duty cycle of ˜12% and a total mechanical power of ˜2 times the active galactic nuclei (AGN) bolometric luminosity, suggesting that the wind may drive significant feedback effects between the AGN and the host galaxy. Notably, we also provide an estimate for the wind launching radius and density of ˜5rS, 1011 cm-3, respectively., Peer Reviewed, Postprint (published version)

The 20Ne(p,¿)21Na reaction is the slowest in the NeNa cycle and directly affects the abundances of the Ne and Na isotopes in a variety of astrophysical sites. Here we report the measurement of its direct capture contribution, for the first time below Ec.m.=352 keV, and of the contribution from the Ec.m.=368 keV resonance, which dominates the reaction rate at T=0.03–1.00 GK. The experiment was performed deep underground at the Laboratory for Underground Nuclear Astrophysics, using a high-intensity proton beam and a windowless neon gas target. Prompt ¿ rays from the reaction were detected with two high-purity germanium detectors. We obtain a resonance strength ¿¿=(0.112±0.002stat±0.005sys)meV, with an uncertainty a factor of 3 smaller than previous values. Our revised reaction rate is 20% lower than previously adopted at T<0.1 GK and agrees with previous estimates at temperatures T=0.1 GK. Initial astrophysical implications are presented., Postprint (published version)

We present a new X-ray spectroscopic study of 22 luminous (2 × 1045 ¿ Lbol/erg s-1 ¿ 2 × 1046) active galactic nuclei (AGNs) at intermediate redshifts (0.1 ¿ z ¿ 0.4), as part of the SUpermassive Black hole Winds in the x-rAYS (SUBWAYS) sample, mostly composed of quasars and type 1 AGNs. Here, 17 targets were observed with XMM-Newton in 2019–2020, and the remaining 5 are from previous observations. The aim of this large campaign (1.45 Ms duration) is to characterise the various manifestations of winds in the X-rays driven from supermassive black holes in AGNs. In this paper we focus on the search for and characterisation of ultra-fast outflows (UFOs), which are typically detected through blueshifted absorption troughs in the Fe K band (E > 7 keV). By following Monte Carlo procedures, we confirm the detection of absorption lines corresponding to highly ionised iron (e.g. Fe¿XXV Ha and Fe¿XXVI Lya) in 7 out of 22 sources at the ¿95% confidence level (for each individual line). The global combined probability of such absorption features in the sample is > 99.9%. The SUBWAYS campaign, based on XMM-Newton, extends to higher luminosities and redshifts than previous local studies on Seyferts. We find a UFO detection fraction of ~30% of the total sample, which is in agreement with previous findings. This work independently provides further support for the existence of highly ionised matter propagating at mildly relativistic speeds (¿0.1c) in a considerable fraction of AGNs over a broad range of luminosities, which is believed to play a key role in the self-regulated AGN feeding-feedback cycle, as also supported by hydrodynamical multi-phase simulations., Peer Reviewed, Postprint (published version)

The Type 1 active galactic nucleus (AGN) ESO 511-G030, a formerly bright and soft excess dominated source, was observed in 2019 in the context of a multi-wavelength monitoring campaign. In the new exposures, the source was found to be in a flux state approximately ten times lower than archival exposures and without any trace of the soft excess. Interestingly, the X-ray weakening observed in the 2019 data corresponds to a comparable fading of the UV flux, suggesting a strong link between these two components. The UV-X-ray spectral energy distribution (SED) of ESO 511-G030 shows remarkable variability. We tested both phenomenological and physically motivated models on the data, finding that the overall emission spectrum of ESO 511-G030 in this extremely low flux state is due to the superposition of a power-law-like continuum (G ~ 1.7) and two reflection components emerging from hot and cold matter. Both the primary X-ray continuum and relativistic reflection are produced in the inner regions close to the supermassive black hole. The prominent variability of ESO 511-G030 and the lack of a soft excess can be explained by the dramatic change in the observed accretion rate, which dropped from an L/LEdd of 2% in 2007 to one of 0.2% in 2019. The X-ray photon index also became harder during the low flux observations from 2019, perhaps as a result of a photon starved X-ray corona., Peer Reviewed, Postprint (published version)

This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly notices of the Royal Astronomical Society following peer review. The version of record Althaus, L.G., et al. Carbon-oxygen ultra-massive white dwarfs in general relativity. Monthly notices of the Royal Astronomical Society, August 2023, vol. 523, n. 3, p. 4492-4503 is available online at: https://doi.org/10.1093/mnras/stad1720, We employ the La Plata stellar evolution code, lpcode, to compute the first set of constant rest-mass carbon–oxygen ultra-massive white dwarf evolutionary sequences for masses higher than 1.29 M¿ that fully take into account the effects of general relativity on their structural and evolutionary properties. In addition, we employ the lp-pul pulsation code to compute adiabatic g-mode Newtonian pulsations on our fully relativistic equilibrium white dwarf models. We find that carbon–oxygen white dwarfs more massive than 1.382 M¿ become gravitationally unstable with respect to general relativity effects, being this limit higher than the 1.369 M¿ we found for oxygen–neon white dwarfs. As the stellar mass approaches the limiting mass value, the stellar radius becomes substantially smaller compared with the Newtonian models. Also, the thermo-mechanical and evolutionary properties of the most massive white dwarfs are strongly affected by general relativity effects. We also provide magnitudes for our cooling sequences in different passbands. Finally, we explore for the first time the pulsational properties of relativistic ultra-massive white dwarfs and find that the period spacings and oscillation kinetic energies are strongly affected in the case of most massive white dwarfs. We conclude that the general relativity effects should be taken into account for an accurate assessment of the structural, evolutionary, and pulsational properties of white dwarfs with masses above ~1.30 M¿., We thank Domingo García-Senz for valuable comments about the possible impact of our models on Type Ia Supernovae and Detlev Koester for providing atmosphere models to the high surface gravities that characterise our relativistic ultra-massive white dwarf models. Part of this work was supported by PICT-2017-0884 from ANPCyT, PIP 112-200801-00940 grant from CONICET, and by the Spanish project PID 2019-109363GB-100. MEC acknowledges Grant RYC2021-032721-I funded by MCIN/AEI/10.13039/501100011033 and by the European Union NextGenerationEU/PRTR. ST, RR and ARM acknowledge support from MINECO under the PID2020-117252GB-I00 grant and from the AGAUR/Generalitat de Catalunya grant SGR-386/2021. RR acknowledges support from Grant RYC2021-030837-I funded by MCIN/AEI/ 10.13039/501100011033 and by “European Union NextGenerationEU/PRTR”. This research has made use of NASA Astrophysics Data System. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement., Postprint (author's final draft)

Context. Obscuration events in type I active galactic nuclei (AGN) have been detected more frequently in recent years. The strong flux decrease in the soft X-ray band between observations has been caused by clouds with large column densities transiting our line of sight (LOS) and covering the central AGN. Another event has been captured in NGC 3227 at the end of 2019, which was observed with XMM-Newton, NuSTAR, and the Hubble Space Telescope. Aims. We aim to determine the nature and origin of the observed spectral variability in the 2019 obscuration event. Methods. We study the evolution of the obscurer by splitting the two XMM-Newton observations from 2019 into timing bins of length ~10 ks. We used the SPEX code to analyse the 0.35–10 keV EPIC-PN spectra of each timing bin. Results. In the first observation (Obs 1), there is a strong anti-correlation between the column density (NH) of the obscurer and the continuum normalisations of the X-ray power law and soft Comptonisation components (Npow and Ncomt, respectively). The power-law continuum models the hard X-rays produced by the corona, and the Comptonisation component models the soft X-ray excess and emission from the accretion disk. Through further testing, we conclude that the continuum is likely to drive the observed variability, but we cannot rule out a possible contribution from NH of the obscurer if it fully transverses across the ionising source within our LOS during the observation. The ionisation parameter (¿) of the obscurer is not easily constrained, and therefore it is not clear whether it varies in response to changes in the ionising continuum. The second observation (Obs 2) displays a significantly lower count rate due to the combination of a high NH and covering fraction of the obscurer, and a lower continuum flux. Conclusions. The observed variability seen during the obscuration event of NGC 3227 in 2019 is likely driven by the continuum, but the obscurer varies at the same time, making it difficu, Peer Reviewed, Postprint (published version)

Accretion disks around compact objects are expected to enter an unstable phase at high luminosity1. One instability may occur when the radiation pressure generated by accretion modifies the disk viscosity, resulting in the cyclic depletion and refilling of the inner disk on short timescales2. Such a scenario, however, has only been quantitatively verified for a single stellar-mass black hole3,4,5. Although there are hints of these cycles in a few isolated cases6,7,8,9,10, their apparent absence in the variable emission of most bright accreting neutron stars and black holes has been a continuing puzzle11. Here we report the presence of the same multiwavelength instability around an accreting neutron star. Moreover, we show that the variability across the electromagnetic spectrum—from radio to X-ray—of both black holes and neutron stars at high accretion rates can be explained consistently if the accretion disks are unstable, producing relativistic ejections during transitions that deplete or refill the inner disk. Such a new association allows us to identify the main physical components responsible for the fast multiwavelength variability of highly accreting compact objects., The authors thank the referees for the constructive comments which improved the manuscript. The interpretation of the FV thank R. Arcodia, P. Casella, G. Marcel, G. Mastroserio, N. Scepi and L. Stella for insightful discussions. The interpretation of the results benefited from discussions held during the meeting ‘Looking at the disc-jet coupling from different angles’ held at the International Space Science Institute in Bern, Switzerland. FV was supported by the NASA awards 80NSSC19K1456, 80NSSC21K0526 and from grant FJC2020-043334-I financed by MCIN/AEI/10.13039/501100011033 and NextGenerationEU/PRTR. JN acknowledges support by the SAO award GO1-22036X. AJT acknowledges support for this work was provided by NASA through the NASA Hubble Fellowship grant #HST–HF2–51494.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5–26555. D.A. and N.C.S. acknowledges support from the Science and Technology Facilities Council (STFC) grant ST/V001000/1. FV, MAP and VC acknowledge support from the Spanish Ministry of Science and Innovation research project PID2020-120323GB-I00. MAP acknowledges support from the Consejería de Economía, Conocimiento y Empleo del Gobierno de Canarias and the European Regional Development Fund (ERDF) under grant with reference ProID2021010132 ACCISI/FEDER, UE. TMB acknowledges financial contribution from the agreement ASI-INAF n.2017- 14-H.0 and from PRIN-INAF 2019 N.15. TMD acknowledges support from the Spanish Ministry of Science and Innovation project PID2021-124879NB-I00, and the Europa Excelencia grant (EUR2021-122010). TDR acknowledge financial contribution from the agreement ASIINAF n.2017-14-H.0., Peer Reviewed, Postprint (author's final draft)

The radioisotope 26Al is a key observable for nucleosynthesis in the Galaxy and the environment of the early Solar System. To properly interpret the large variety of astronomical and meteoritic data, it is crucial to understand both the nuclear reactions involved in the production of 26Al in the relevant stellar sites and the physics of such sites. These range from the winds of low- and intermediate-mass asymptotic giant branch stars; to massive and very massive stars, both their Wolf–Rayet winds and their final core-collapse supernovae (CCSN); and the ejecta from novae, the explosions that occur on the surface of a white dwarf accreting material from a stellar companion. Several reactions affect the production of 26Al in these astrophysical objects, including (but not limited to) 25Mg(p, ¿)26Al, 26Al(p, ¿)27Si, and 26Al(n, p/a). Extensive experimental effort has been spent during recent years to improve our understanding of such key reactions. Here we present a summary of the astrophysical motivation for the study of 26Al, a review of its production in the different stellar sites, and a timely evaluation of the currently available nuclear data. We also provide recommendations for the nuclear input into stellar models and suggest relevant, future experimental work., Postprint (published version)

The future of deep space communications encompasses a challenging situation where the current facilities used to communicate with different spacecraft may become saturated as a result of an increasing number of missions and their complexity. From this forecast, the present study intends to provide a solution to saturation problems through strategically-located upgradable relays for Earth-Mars communications. The foremost goal of this paper is to quantitatively uncover the potential enhancements coming from relay placement in strategic orbits between Earth and Mars. Herein, two relay configurations –a.k.a. network topologies– are analyzed: the Lagrange-relays network topology and a circular, homogeneously-distributed satellite constellation, acknowledged here as pearl constellation. The first uses the Earth-Sun system Lagrange points L3, L4 and L5 as potential locations for the relays, whilst the second defines an optimized orbit between Earth and Mars with 3 or 4 relay satellites. To aid in the analysis, the authors developed an open-sourced piece of software that obtains the link availability as well as the data rate at which two nodes may communicate, taking as a reference the Deep Space Network for Earth, and the Mars Reconnaissance Orbiter for Mars. For complex topologies with more than two communicating nodes, the software outputs the end-to-end bit rate and optimal communication route at each time step. Moreover, this product is extensible to analyze and optimize any network topology and could be adapted to be used for contact management and mission planning in the future. The results show that the network-topology proposals are an advantageous option to significantly increase the link availability of Earth-Mars communications. Nevertheless, the Direct-To-Earth link always outperforms the multi-hop path due to the limited telecommunication system’s capabilities of both the spacecraft and the relays. As a result of this, the study includes an analysis on the re, Peer Reviewed, Postprint (published version)

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2023 A. J. Brown et al. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved., Wide-field time-domain photometric sky surveys are now finding hundreds of eclipsing white dwarf plus M dwarf binaries, a population encompassing a wealth of information and potential insight into white dwarf and close binary astrophysics. Precise follow-up observations are essential in order to fully constrain these systems and capitalize on the power of this sample. We present the first results from our programme of high-speed multiband photometric follow-up. We develop a method to measure temperatures, (model-dependent) masses, and radii for both components from the eclipse photometry alone and characterize 34 white dwarf binaries, finding general agreement with independent estimates using an alternative approach while achieving around a factor of 2 increase in parameter precision. In addition to these parameter estimates, we discover a number of interesting systems – finding four with sub-stellar secondaries, doubling the number of eclipsing examples, and at least six, where we find the white dwarf to be strongly magnetic, making these the first eclipsing examples of such systems and key to investigating the mechanism of magnetic field generation in white dwarfs. We also discover the first two pulsating white dwarfs in detached and eclipsing post-common-envelope binaries – one with a low-mass, likely helium core, and one with a relatively high mass, towards the upper end of the known sample of ZZ Cetis. Our results demonstrate the power of eclipse photometry, not only as a method of characterizing the population, but as a way of discovering important systems that would have otherwise been missed by spectroscopic follow-up., SGP acknowledges the support of the UK’s Science and Technology Facilities Council (STFC) Ernest Rutherford Fellowship. ARM acknowledges support from Grant RYC-2016-20254 funded by MCIN/AEI/10.13039/501100011033 and by ESF Investing in your future and from MINECO under the PID2020-117252GB-I00 grant. VSD, HiPERCAM, and ULTRACAM are supported by the STFC. IP and TRM acknowledge support from the STFC, grant ST/T000406/1 and a Leverhulme Research Fellowship. JM was supported by funding from a Science and Technology Facilities Council (STFC) studentship. Based on observations collected at the European Southern Observatory under ESO programme 0106.D-0824. Based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in the island of La Palma. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript version arising. We thank the anonymous referee for their helpful comments., Peer Reviewed, Postprint (published version)

Primordial black holes in the asteroid-mass window, which might constitute all the dark matter, can be captured by stars when they traverse them at low enough velocity. After being placed on a bound orbit during star formation, they can repeatedly cross the star if the orbit happens to be highly eccentric, slow down by dynamical friction and end up in the stellar core. The rate of these captures is highest in halos of high dark matter density and low velocity dispersion, when the first stars form at redshift ¿ 20. We compute this capture rate for low-metallicity stars of 0¿3 to 1 M , and find that a high fraction of these stars formed in the first dwarf galaxies would capture a primordial black hole, which would then grow by accretion up to a mass that may be close to the total star mass. We show the capture rate of primordial black holes does not depend on their mass over this asteroid-mass window, and should not be much affected by external tidal perturbations. These low-mass stellar black holes could be discovered today in low-metallicity, old binary systems in the Milky Way containing a surviving low-mass main- sequence star or a white dwarf, or via gravitational waves emitted in a merger with another compact object. No mechanisms in standard stellar evolution theory are known to form black holes below the Chandrasekhar mass, so detecting a low-mass black hole would fundamentally impact our understanding of stellar evolution, dark matter and the early Universe., We would like to acknowledge helpful discussions and advice fromN. Bellomo, J. L. Bernal, A. Escrivà, C. Germani, and J. Sal-vadó. This work was supported in part by Spanish grants CEX-2019-000918-M funded by MCIN/AEI/10.13039/501100011033,AYA2015-71091-P, and PID2019-108122GB-C32., Peer Reviewed, Postprint (author's final draft)

The white dwarf binary pathways survey is dedicated to studying the origin and evolution of binaries containing a white dwarf and an intermediate-mass secondary star of the spectral type A, F, G, or K (WD+AFGK). Here we present CPD-65 264, a new post common envelope binary with an orbital period of 1.37 days that contains a massive white dwarf (0¿86 0¿06 M ) and an intermediate-mass (1¿00 0¿05 M ) main-sequence secondary star. We characterized the secondary star and measured the orbital period using high-resolution optical spectroscopy. The white dwarf parameters are determined from HST spectroscopy. In addition, TESS observations revealed that up to 19 percent of the surface of the secondary is covered with starspots. Small period changes found in the light curve indicate that the secondary is the second example of a G-type secondary star in a post common envelope binary with latitudinal differential rotation. Given the relatively large mass of the white dwarf and the short orbital period, future mass transfer will be dynamically and thermally stable and the system will evolve into a cataclysmic variable. The formation of the system can be understood assuming common envelope evolution without contributions from energy sources besides orbital energy. CPD-65 264 is the seventh post common envelope binaries with intermediate-mass secondaries that can be understood assuming a small efficiency in the common envelope energy equation, in agreement with findings for post common envelope binaries with M-dwarf or sub-stellar companions., MSH and MRS acknowledge support by ANID, – Millennium Sci- ence Initiative Program – NCN19_171. MRS and MZ were also supported by FONDECYT (grant 1221059). SGP acknowledges the support of the STFC Ernest Rutherford Fellowship. BTG was sup- ported by the UK STFC grant ST/T000406/1. OT was supported by a Leverhulme Trust Research Project Grant and FONDECYT grant 3210382. ARM acknowledges support from Grant RYC-2016- 20254 funded by MCIN/AEI/10.13039/501100011033 and by ESF Investing in your future, and from MINECO under the PID2020- 117252GB-I00 grant. RR has received funding from the postdoctoral fellowship programme Beatriu de Pinós, funded by the Secretary of Universities and Research (Government of Catalonia) and by the Horizon 2020 programme of research and innovation of the Euro- pean Union under the Maria Skłodowska-Curie grant agreement No 801370. For the purpose of open access, the author has applied a cre- ative commons attribution (CC BY) licence to any author accepted manuscript version arising., Peer Reviewed, Postprint (published version)

The evolution of white dwarfs is essentially a gravothermal process of cooling in which the basic ingredients for predicting their evolution are well identified, although not always well understood. There are two independent ways to test the cooling rate. One is the luminosity function of the white dwarf population, and another is the secular drift of the period of pulsation of those individuals that experience variations., This work has been funded by the Spanish Ministry of Science and Innovation and FEDER UE (MCI-AEI-FEDER, UE) through grants PID2019-108709GB-I00 and the program Unidad de Excelencia María de Maeztu CEX2020-001058-M (JI), by the MINECO grant AYA\-2017-86274-P, and the grant RyC-2016-20254 (AR-M), by grant 2014 SGR 1458 and CERCA Programe of the Generalitat de Catalunya (JI), and by a URICI- CSIC grant, Postprint (published version)

Ultra-massive white dwarfs (M? & 1.05M ) are of utmost importance in view of the role they play in type Ia supernovae explosions, merger events, the existence of high magnetic field white dwarfs, and the physical processes in the Super Asymptotic Giant Branch phase. Aims. We present the first set of constant rest-mass ultra-massive oxygen/neon white dwarf cooling tracks with masses M? > 1.29M which fully take into account the effects of general relativity on their structural and evolutionary properties. Methods. We have computed the full evolution sequences of 1.29, 1.31, 1.33, 1.35, and 1.369 M white dwarfs with the La Plata stellar evolution code, LPCODE. For this work, the standard equations of stellar structure and evolution have been modified to include the effects of general relativity. Specifically, the fully general relativistic partial differential equations governing the evolution of a spherically symmetric star are solved in a way they resemble the standard Newtonian equations of stellar structure. For comparison purposes, the same sequences have been computed but for the Newtonian case. Results. According to our calculations, the evolutionary properties of the most massive white dwarfs are strongly modified by general relativity effects. In particular, the resulting stellar radius is markedly smaller in the general relativistic case, being up to 25% smaller than predicted by the Newtonian treatment for the more massive ones. We find that oxygen/neon white dwarfs more massive than 1.369 M become gravitationally unstable with respect to general relativity effects. When core chemical distribution due to phase separation on crystallization is considered, such instability occurs at somewhat lower stellar masses, & 1.36M . In addition, cooling times for the most massive white dwarf sequences result in about a factor of two smaller than in the Newtonian case at advanced stages of evolution. Finally, a sample of white dwarfs has been identified as ideal candidat, We thank Detlev Koester for extending his atmospheremodels to the high surface gravities that characterize our relativistic ultra-massive white dwarf models. We also thank the comments of an anony-mous referee that improved the original version of this paper. Part ofthis work was supported by PICT-2017-0884 from ANPCyT, PIP 112-200801-00940 grant from CONICET, grant G149 from University of LaPlata, NASA grants 80NSSC17K0008 and 80NSSC20K0193. ST and ARMacknowledge support from MINECO under the PID2020-117252GB-I00grant. ARM acknowledges support from Grant RYC-2016-20254 funded byMCIN/AEI/10.13039/501100011033 and by ESF Investing in your future. RRhas received funding from the postdoctoral fellowship program Beatriu de Pinós,funded by the Secretary of Universities and Research (Government of Catalonia)and by the Horizon 2020 programme of research and innovation of the Euro-pean Union under the Maria Skłodowska-Curie grant agreement No 801370.This research has made use of NASA Astrophysics Data System. This workhas made use of data from the European Space Agency (ESA) mission Gaia(https://www.cosmos.esa.int/gaia), processed by the Gaia Data Process-ing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by na-tional institutions, in particular the institutions participating in the Gaia Mul-tilateral Agreement., Peer Reviewed, Postprint (published version)

We verified for photometric stability a set of DA white dwarfs with Hubble Space Telescope magnitudes from thenear-ultraviolet to the near-infrared and ground-based spectroscopy by using time-spaced observations from theLas Cumbres Observatory network of telescopes. The initial list of 38 stars was whittled to 32final ones, whichcomprise a high-quality set of spectrophotometric standards. These stars are homogeneously distributed around thesky and are all fainter thanr~16.5 mag. Their distribution is such that at least two of them would be available tobe observed from any observatory on the ground at any time at airmass less than 2. Light curves and differentvariability indices from the Las Cumbres Observatory data were used to determine the stability of the candidatestandards. When available, Pan-STARRS1, Zwicky Transient Facility, and TESS data were also used to confirmthe star classification. Our analysis showed that four DA white dwarfs may exhibit evidence of photometricvariability, while afifth is cooler than our established lower temperature limit, and a sixth star might be a binary. Insome instances, due to the presence of faint nearby red sources, care should be used when observing a few of thespectrophotometric standards with ground-based telescopes. Light curves andfinding charts for all the stars areprovided., This study was supportedby NASA through grant O1904 from the Space TelescopeScience Institute, which is operated by AURA, Inc., underNASA contract NAS 5-26555 and the Space Telescope ScienceInstitute. The analysis was also supported by the DDRF grantD0001.82481. E.O. was also partially supported by the NSFthrough grant AST-1815767. R.R. received funding from thepostdoctoral fellowship program Beatriu de Pinós, funded bythe Secretary of Universities and Research(Government ofCatalonia)and by the Horizon 2020 program of research andinnovation of the European Union under the Maria Skło-dowska-Curie grant agreement No. 801370. C.S. is supportedby the US DOE through award DE-SC0007881. This work hasmade use of data from the European Space Agency(ESA)mission Gaia(https://www.cosmos.esa.int/gaia), processedby the Gaia Data Processing and Analysis Consortium(DPAC;https://www.cosmos.esa.int/web/gaia/dpac/consortium).Funding for the DPAC has been provided by nationalinstitutions, in particular the institutions participating in theGaia Multilateral Agreement. This publication makes use ofVOSA, developed under the Spanish Virtual Observatoryproject supported by the Spanish MINECO through grantAyA2017-84089. VOSA has been partially updated by usingfunding from the European Union’s Horizon 2020 Research andInnovation Programme, under grant Agreement No. 776403(EXOPLANETS-A). This work includes data from the AsteroidTerrestrial-impact Last Alert System(ATLAS)project. ATLAS isprimarily funded to search for near-earth asteroids through NASAgrants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575;byproducts of the NEO search include images and catalogs fromthe survey area. The ATLAS science products have been madepossible through the contributions of the University of HawaiiInstitute for Astronomy, the Queen’s University Belfast, the SpaceTelescope Science Institute, and the South African AstronomicalObservatory. G.N. and K.M. gratefully acknowledge support fromNASA under grant 80NSSC20K04, Peer Reviewed, Postprint (published version)

Context. NGC 5548 is an X-ray bright Seyfert 1 active galaxy. It exhibits a variety of spectroscopic features in the soft X-ray band, in particular including the absorption by the active galactic nucleus (AGN) outflows of a broad range of ionization states, with column densities up to 1027 m-2, and having speeds up to several thousand kilometers per second. The known emission features are in broad agreement with photoionized X-ray narrow and broad emission line models. Aims. We report on an X-ray spectroscopic study using 1.1 Ms XMM-Newton and 0.9 Ms Chandra grating observations of NGC 5548 spanning two decades. The aim is to search and characterize any potential spectroscopic features in addition to the known primary spectral components that are already modeled in high precision. Methods. For each observation, we modeled the data using a global fit including an intrinsic spectral energy distribution of the AGNs and the known distant X-ray absorbers and emitters. We utilized as much knowledge from previous studies as possible. The fit residuals were stacked and scanned for possible secondary features. Results. We detect a weak unidentified excess emission feature at ~18.4 Å (18.1 Å in the restframe). The feature is seen at > 5s statistical significance taking the look-elsewhere effect into account. No known instrumental issues, atomic transitions, or astrophysical effects can explain this excess. The observed intensity of the possible feature seems to anticorrelate in time with the hardness ratio of the source. However, even though the variability might not be intrinsic, it might be caused by the time-variable obscuration by the outflows. An intriguing possibility is the line emission from charge exchange between a partially ionized outflow and a neutral layer in the same outflow, or in the close environment. Other possibilities, such as emission from a highly ionized component with high outflowing speed, cannot be fully ruled out., Peer Reviewed, Postprint (published version)

Novae are caused by runaway thermonuclear burning in the hydrogen-rich envelopes of accreting white dwarfs, which leads to a rapid expansion of the envelope and the ejection of most of its mass1,2. Theory has predicted the existence of a ‘fireball’ phase following directly on from the runaway fusion, which should be observable as a short, bright and soft X-ray flash before the nova becomes visible in the optical3,4,5. Here we report observations of a bright and soft X-ray flash associated with the classical Galactic nova YZ Reticuli 11¿h before its 9¿mag optical brightening. No X-ray source was detected 4¿h before and after the event, constraining the duration of the flash to shorter than 8¿h. In agreement with theoretical predictions4,6,7,8, the source’s spectral shape is consistent with a black-body of 3.27+0.11-0.33¿×¿105¿K (28.2+0.9-2.8¿eV), or a white dwarf atmosphere, radiating at the Eddington luminosity, with a photosphere that is only slightly larger than a typical white dwarf., Peer Reviewed, Postprint (author's final draft)

Aims. The third Gaia data release provides low-resolution spectra for around 200 million sources. It is expected that a sizeable fraction of them contain a white dwarf (WD), neither isolated, or in a binary system with a main-sequence (MS) companion, that is a white dwarf-main sequence (WDMS) binary. Taking advantage of a consolidated Random Forest algorithm used in the classification of WDs, we extend it to study the feasibility of classifying Gaia WDMS binary spectra. Methods. The Random Forest algorithm is first trained with a set of synthetic spectra generated by combining individual WD and MS spectra for the full range of effective temperatures and surface gravities. Moreover, with the aid of a detailed population synthesis code, we simulate the Gaia spectra for the abovementioned populations. For evaluating the performance of the models, a set of metrics are applied to our classifications. Results. Our results show that for resolving powers above ~300 the accuracy of the classification depends exclusively on the S/R of the spectra, while below that value the S/R should be increased as the resolving power is reduced to maintain a certain accuracy. The algorithm is then applied to the already classified SDSS WDMS catalog, revealing that the automated classification exhibits an accuracy comparable (or even higher) to previous classification methods. Finally, we simulate the Gaia spectra, showing that our algorithm is able to correctly classify nearly 80% the synthetic WDMS spectra. Conclusions. Our algorithm represents a useful tool in the analysis and classification of real Gaia WDMS spectra. Even for those spectra dominated by the flux of the MS stars, the algorithm reaches a high degree of accuracy (60%)., This work was partially supported by the MINECO grant PID2020-117252GB-I00. A.R.M. acknowledges support from grant RYC-2016-20254 funded by MCIN/AEI/10.13039/501100011033 and by ESF Investing in your future. We would also like to acknowledge the fruitful information provided by M. Carrasco and J. de Bruijne, Peer Reviewed, Postprint (published version)

Hot, compact, hydrogen-deficient pre-white dwarfs (pre-WDs) with effective temperatures of Teff > 70,000 K and a surface gravity of 5.0 < log g < 7.0 are rather rare objects despite recent and ongoing surveys. It is believed that they are the outcome of either single star evolution (late helium-shell flash or late helium-core flash) or binary star evolution (double WD merger). Their study is interesting because the surface elemental abundances reflect the physics of thermonuclear flashes and merger events. Spectroscopically they are divided in three different classes, namely PG1159, O(He), or He-sdO. We present a spectroscopic analysis of five such stars that turned out to have atmospheric parameters in the range Teff = 70,000-80,000 K and log g = 5.2-6.3. The three investigated He-sdOs have a relatively high hydrogen mass fraction (10%) that is unexplained by both single (He core flash) and binary evolution (He-WD merger) scenarios. The O(He) star JL9 is probably a binary helium-WD merger, but its hydrogen content (6%) is also at odds with merger models. We found that RL 104 is the 'coolest' (Teff = 80,000 K) member of the PG1159 class in a pre-WD stage. Its optical spectrum is remarkable because it exhibits C IV lines involving Rydberg states with principal quantum numbers up to n = 22. Its rather low mass (0.48 +0.03/-0.02 Msun) is difficult to reconcile with the common evolutionary scenario for PG1159 stars due to it being the outcome of a (very) late He-shell flash. The same mass-problem faces a merger model of a close He-sdO plus CO WD binary that predicts PG1159-like abundances. Perhaps RL 104 originates from a very late He-shell flash in a CO/He WD formed by a merger of two low-mass He-WDs., We thank Uli Heber for putting his CASPEC spectrum of JL 9 at our disposal and useful comments on an earlier version of the manuscript, and Max Pritzkuleit for his support of the HOTFUSS project. M.D. acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG) through grant HE1356/71-1. R.R. has received funding from the postdoctoral fellowship programme Beatriu de Pinós, funded by the Secretary of Universities and Research (Government of Catalonia) and by the Horizon 2020 programme of research and innovation of the European Union under the Maria Skłodowska-Curie grant agreement No 801370. The TMAD tool (http://astro.uni-tuebingen.de/ ~TMAD) used for this paper was constructed as part of the activities of the German Astrophysical Virtual Observatory. Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). This research has made use of NASA’s Astrophysics Data System and the SIMBAD database, operated at CDS, Strasbourg, France. This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France. This work has made use of data from the European Space Agency (ESA) mission Gaia., Peer Reviewed, Postprint (author's final draft)

We identify Gaia 0007–1605 A,C as the first inner brown dwarf–white dwarf binary of a hierarchical triple system in which the outer component is another white dwarf (Gaia 0007–1605 B). From optical/near-infrared spectroscopy obtained at the Very Large Telescope with the X-Shooter instrument and/or from Gaia photometry plus spectral energy distribution fitting, we determine the effective temperatures and masses of the two white dwarfs (12,018 ± 68 K and 0.54 ± 0.01 M¿ for Gaia 0007–1605 A and 4445 ± 116 K and 0.56 ± 0.05 M¿ for Gaia 0007–1605 B) and the effective temperature of the brown dwarf (1850 ± 50 K; corresponding to spectral type L3 ± 1). By analyzing the available TESS light curves of Gaia 0007–1605 A,C we detect a signal at 1.0446 ± 0.0015 days with an amplitude of 6.25 ppt, which we interpret as the orbital period modulated from irradiation effects of the white dwarf on the brown dwarf's surface. This drives us to speculate that the inner binary evolved through a common-envelope phase in the past. Using the outer white dwarf as a cosmochronometer and analyzing the kinematic properties of the system, we conclude that the triple system is about 10 Gyr old., Postprint (published version)

Transitional millisecond pulsars (tMSPs) have emerged in the last decade as a unique class of neutron stars at the crossroads between accretion- and rotation-powered phenomena. In their (sub-luminous) accretion disc state, with X-ray luminosities of order 1033–1034 erg s-1, they switch rapidly between two distinct X-ray modes: the disc-high (DH) and disc-low (DL) states. We present a systematic XMM–Newton and Chandra analysis of the aperiodic X-ray variability of all three currently known tMSPs, with a main focus on their disc state and separating DH and DL modes. We report the discovery of flat-topped broad-band noise in the DH state of two of them, with break frequencies of 2.8 mHz (PSR J1023 + 0038) and 0.86 mHz (M28-I). We argue that the lowest frequency variability is similar to that seen in disc-accreting X-ray binaries in the hard state, at typical luminosities at least two orders of magnitude higher than tMSPs. We find strong variability in the DH state around 1 Hz, not typical of hard state X-ray binaries, with fractional rms amplitudes close to 30 per¿cent. We discuss our results and use them to constrain the properties of the accretion disc, assuming that the X-ray variability is produced by fluctuations in mass accretion rate, and that the break frequency corresponds to the viscous time-scale at the inner edge of the disc. In this context, we find that the newly found break frequencies are broadly consistent with a disc truncated close to the light cylinder with M¿¿1013-5×1014 g s-1 and a viscosity parameter a ¿ 0.2., Peer Reviewed, Postprint (author's final draft)

White dwarfs are the most common stellar remnants. Furthermore, as being old objects, their study could shed new light on different questions related to the history, formation and evolution of the Galaxy. Despite these objects have been broadly studied from a theoretical point of view, the observational data has been limited to a poor statistical sample, due to the intrinsic low luminosity of white dwarfs. However, thanks to the recent Gaia EDR3, for the first time, a significant sample of the White dwarf population of our Galaxy, containing around 13,000 objects up to 100 pc from the Sun, has been obtained. Such data, in particular its color-magnitude diagram, provides the ideal scenario for extracting the maximum information. This communication reports a work-in-progress of a widely applied technique for recovering the star formation history of galaxies through its color-magnitude diagram applied, in this case, for first time to the local White dwarf population., Peer Reviewed, Postprint (published version)

The origins of Type Ia supernovae (SNe Ia) are still debated. Some of the leading scenarios involve a double detonation in double white dwarf (WD) systems. In these scenarios, helium shell detonation occurs on top of a carbon-oxygen (CO) WD, which then drives the detonation of the CO core, producing an SN Ia. Extensive studies have been done on the possibility of a double helium detonation, following a dynamical helium mass-transfer phase onto a CO-WD. However, 3D self-consistent modeling of the double-WD system, the mass transfer, and the helium shell detonation have been little studied. Here we use 3D hydrodynamical simulations to explore this case in which a helium detonation occurs near the point of Roche lobe overflow of the donor WD and may lead to an SN Ia through the dynamically driven double-degenerate double-detonation (D6) mechanism. We find that the helium layer of the accreting primary WD does undergo a detonation, while the underlying CO core does not, leading to an extremely rapid and faint nova-like transient instead of a luminous SN Ia event. This failed core detonation suggests that D6 SNe Ia may be restricted to the most massive CO primary WDs. We highlight the nucleosynthesis of the long-lived radioisotope 44Ti during explosive helium burning, which may serve as a hallmark both of successful as well as failed D6 events, which subsequently detonate as classical double-degenerate mergers., Peer Reviewed, Postprint (published version)

Presolar stardust grains found in primitive meteorites are believed to retain the isotopic composition of stellar outflows at the time of grain condensation. Therefore, laboratory measurements of their isotopic ratios represent sensitive probes for investigating open questions related to stellar evolution, stellar explosions, nucleosynthesis, mixing mechanisms, dust formation, and galactic chemical evolution. For a few selected presolar grains, classical novae have been discussed as a potential source. For SiC, silicate, and graphite presolar grains, the association is based on the observation of small N(12C)/N(13C) and N(14N)/N(15N) number abundance ratios compared to solar values, and abundance excesses in 30Si relative to 29Si, as previously predicted by models of classical novae. We report on a direct measurement of the 29Si(p,¿)30P reaction, which strongly impacts simulated d29Si values from classical novae. Our new experimental 29Si(p,¿)30P thermonuclear reaction rate differs from previous results by up to 50% in the classical nova temperature range (T = 100–400 MK), while the rate uncertainty is reduced by up to a factor of 3. Using our new reaction rate in Monte Carlo reaction network and hydrodynamic simulations of classical novae, we estimate d29Si values with much reduced uncertainties. Our results establish d29Si values measured in presolar grains as a sensitive probe for assessing their classical nova paternity. We also demonstrate that d30Si values from nova simulations are currently not a useful diagnostic tool unless the large uncertainty of the 30P(p,¿)31S reaction rate can be significantly reduced., Postprint (published version)

The 30P(p,¿)31S reaction plays an important role in understanding the nucleosynthesis of A=30 nuclides in oxygen-neon novae. The Gaseous Detector with Germanium Tagging was used to measure 31Cl ß-delayed proton decay through the key Jp=3/2+, 260-keV resonance. The intensity I260ßp=8.3+1.2-0.9×10-6 represents the weakest ß-delayed, charged-particle emission ever measured below 400 keV, resulting in a proton branching ratio of Gp/G=2.5+0.4-0.3×10-4. By combining this measurement with shell-model calculations for G¿ and past work on other resonances, the total 30P(p,¿)31S rate has been determined with reduced uncertainty. The new rate has been used in hydrodynamic simulations to model the composition of nova ejecta, leading to a concrete prediction of 30Si:28Si excesses in presolar nova grains and the calibration of nuclear thermometers., Postprint (author's final draft)

MAXI J1820+070 is a low-mass X-ray binary with a black hole (BH) as a compact object. This binary underwent an exceptionally bright X-ray outburst from 2018 March to October, showing evidence of a non-thermal particle population through its radio emission during this whole period. The combined results of 59.5 h of observations of the MAXI J1820+070 outburst with the H.E.S.S., MAGIC and VERITAS experiments at energies above 200 GeV are presented, together with Fermi-LAT data between 0.1 and 500 GeV, and multiwavelength observations from radio to X-rays. Gamma-ray emission is not detected from MAXI J1820+070, but the obtained upper limits and the multiwavelength data allow us to put meaningful constraints on the source properties under reasonable assumptions regarding the non-thermal particle population and the jet synchrotron spectrum. In particular, it is possible to show that, if a high-energy (HE) gamma-ray emitting region is present during the hard state of the source, its predicted flux should be at most a factor of 20 below the obtained Fermi-LAT upper limits, and closer to them for magnetic fields significantly below equipartition. During the state transitions, under the plausible assumption that electrons are accelerated up to ~500 GeV, the multiwavelength data and the gamma-ray upper limits lead consistently to the conclusion that a potential HE and very-HE gamma-ray emitting region should be located at a distance from the BH ranging between 1011 and 1013 cm. Similar outbursts from low-mass X-ray binaries might be detectable in the near future with upcoming instruments such as CTA., Peer Reviewed, Postprint (author's final draft)

Context. Kinematic and chemical tagging of stellar populations have both revealed much information on the past and recent history of the Milky Way, including its formation history, merger events, and mixing of populations across the Galactic disk and halo. Aims. We present the first detailed 3D kinematic analysis of a sample of 3133 white dwarfs that used Gaia astrometry plus radial velocities, which were measured either by Gaia or by ground-based spectroscopic observations. The sample includes either isolated white dwarfs that have direct radial velocity measurements, or white dwarfs that belong to common proper motion pairs that contain nondegenerate companions with available radial velocities. A subset of common proper motion pairs also have metal abundances that have been measured by large-scale spectroscopic surveys or by our own follow-up observations. Methods. We used the white dwarfs as astrophysical clocks by determining their masses and total ages through interpolation with dedicated evolutionary models. We also used the nondegenerate companions in common proper motions to chemically tag the population. Combining accurate radial velocities with Gaia astrometry and proper motions, we derived the velocity components of our sample in the Galactic rest frame and their Galactic orbital parameters. Results. The sample is mostly located within ~300 pc from the Sun. It predominantly contains (90–95%) thin-disk stars with almost circular Galactic orbits, while the remaining 5–10% of stars have more eccentric trajectories and belong to the thick disk. We identified seven isolated white dwarfs and two common proper motion pairs as halo members. We determined the age – velocity dispersion relation for the thin-disk members, which agrees with previous results that were achieved from different white dwarf samples without published radial velocities. The age – velocity dispersion relation shows signatures of dynamical heating and saturation after 4–6 Gyr. We observed a m, Postprint (published version)

This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly notices of the Royal Astronomical Society following peer review. The version of record Hernandez, S. [et al.]. The white dwarf binary pathways survey - VI. Two close post-common envelope binaries with TESS light curves. "Monthly notices of the Royal Astronomical Society", 7 Març 2022, vol. 512, núm. 2, p. 1843-1856 is available online at: doi.org/10.1093/mnras/stac604., Establishing a large sample of post-common-envelope binaries (PCEBs) that consist of a white dwarf plus an intermediate mass companion star of spectral type AFGK, offers the potential to provide new constraints on theoretical models of white dwarf binary formation and evolution. Here, we present a detailed analysis of two new systems, TYC¿110-755-1 and TYC¿3858-1215-1. Based on radial velocity measurements, we find the orbital periods of the two systems to be ~0.85 and ~1.64¿d, respectively. In addition, HST spectroscopy of TYC¿110-755-1 allowed us to measure the mass of the white dwarf in this system (0.78 M¿). We furthermore analysed TESS high-time-resolution photometry and find both secondary stars to be magnetically extremely active. Differences in the photometric and spectroscopic periods of TYC¿110-755-1 indicate that the secondary in this system is differentially rotating. Finally, studying the past and future evolution of both systems, we conclude that the common envelope efficiency is likely similar in close white dwarf plus AFGK binaries and PCEBs with M-dwarf companions and find a wide range of possible evolutionary histories for both systems. While TYC¿3858-1215-1 will run into dynamically unstable mass transfer that will cause the two stars to merge and evolve into a single white dwarf, TYC¿110-755-1 is a progenitor of a cataclysmic variable system with an evolved donor star., MSH acknowledges the Fellowship for National PhD students from ANID, grant number 21170070. MRS acknowledges FONDECYT for the financial support (grant 1181404). SGP acknowledges the support of the STFC Ernest Rutherford Fellowship. BTG was supported by the UK STFC grant ST/T000406/1. OT was supported by a Leverhulme Trust Research Project Grant and FONDECYT grant 3210382. GT acknowledges support from PAPIIT project IN110619. MZ acknowledges financial support from FONDECYT (Programa de Iniciación, grant 11170559). FL was supported by the ESO studentship and the National Agency for Research and Development (ANID) Doctorado nacional, grant number 21211306. RR has received funding from the postdoctoral fellowship program Beatriu de Pinós, funded by the Secretary of Universities and ReMNRAS 000, 1–14 (2019) Two PCEBs with TESS light curve 13 search (Government of Catalonia) and by the Horizon 2020 program of research and innovation of the European Union under the Maria Skłodowska-Curie grant agreement No 801370. ARM acknowledges support from the MINECO grant AYA2017-86274-P and by the AGAUR (SGR-661/2017). Grant RYC-2016-20254 funded by MCIN/AEI/10.13039/501100011033 and by ESF Investing in your future. JJR acknowledges the support of the National Natural Science Foundation of China 11903048 and 11833006. We acknowledge the use of public data from the Swift data archive., Peer Reviewed, Postprint (author's final draft)

Stellar models and nucleosynthetic yields of primordial to extremely metal-poor (EMP) stars are crucial to interpret the surface abundances of the most metal-poor stars observed and, ultimately, to better understand the earliest stellar populations. In addition, they are key ingredients of Galactic chemical evolution models. Aims. We aim to better characterise the evolution and fates, and determine updated nucleosynthetic yields of intermediate-mass stars between primordial and EMP metallicity (Z = 10-10, 10-8, 10-7, 10-6, and 10-5). We also probed uncertainties in the nucleosynthesis of the oldest intermediate-mass stars, namely those related to the treatment of convection and convective boundaries and those related to wind prescriptions during the asymptotic giant branch (AGB) phase. Methods. We analyse the evolution of models from their main sequence, through the thermally pulsing AGB (TP-AGB), to the latest stages of their evolution, using the Monash-Mount Stromlo stellar evolution code MONSTAR. The results were post-processed with the code MONSOON, which allowed for the determination of the nucleosynthetic yields of 77 species up to 62Ni. By comparing them to similar calculations existing in the literature, we inspected the effects of input physics on the nucleosynthesis of EMP models. Results. From the evolutionary point of view, as reported in former works, we identified proton ingestion episodes (PIEs) in our lowest-mass lowest-metallicity models. Models of Z = 10-10 and Z = 10-8 in a narrow initial mass range around 5 M experience the cessation of thermal pulses, and their final fates as type-I1/2 supernovae cannot be discarded. However, the initial mass range of models eventually leading to the formation of type-I1/2 and electron-capture supernovae is considerably reduced compared to former works. All the models of initial mass & 6-7 M experience a corrosive second dredge-up and, analogously to those experiencing PIEs, undergo significant metal enrichment, We thank the anonymous referee for their useful comments and clarifications. This work was supported by the Spanish project PID 2019-109363GB-100, and by the German Deutsche Forschungsgemeinschaft, DFG project number Ts 17/2–1. S.W.C. acknowledges federal funding from the Australian Research Council through a Future Fellowship (FT160100046) and Discovery Project (DP190102431). This research was supported by use of the Nectar Research Cloud, a collaborative Australian research platform supported by the National Collaborative Research Infrastructure Strategy (NCRIS)., We thank the anonymous referee for their useful comments and clarifications. This work was supported by the Spanish project PID 2019-109363GB-100, and by the German Deutsche Forschungsgemeinschaft, DFG project number Ts 17/2–1. S.W.C. acknowledges federal funding from the Australian Research Council through a Future Fellowship (FT160100046) and Discovery Project (DP190102431). This research was supported by use of the Nectar Research Cloud, a collaborative Australian research platform supported by the National Collaborative Research Infrastructure Strategy (NCRIS)., Peer Reviewed, Postprint (updated version)

The Gaia mission has provided an unprecedented wealth of information about the white dwarf population of our Galaxy. In particular, our studies show that the sample up to 100\,pc from the Sun can be considered as practically complete. This fact allows us to estimate a precise fraction of double-degenerate (1.18±0.10\%) and white dwarf plus main-sequence stars (6.31±0.23\%) among all white dwarfs through comoving pairs identification. With the aid of a detailed population synthesis code we are able to reproduce synthetic white dwarf populations with nearly identical fractions as the observed ones, thus obtaining valuable information about the binary fraction, fb, initial mass ratio distribution, n(q), and initial separation distribution, f(a), among other parameters. Our best-fit model is achieved within a 1s confidence level for f(a)¿a-1, n(q)¿qnq, with nq=-1.13+0.12-0.10 and fb=0.32±0.02. The fraction of white dwarf mergers generated by this model is 9~16%, depending on the common-envelope treatment. As sub-products of our modelling we find that around 1~3% of the white dwarf population are unresolved double-degenerates and that only ~1% of all white dwarfs contain a He-core. Finally, only a mild kick during white dwarf formation seems to be necessary for fitting the observed sky separation of double-degenerate systems., We acknowledge our anonymous referee for his/her positive com- ments and the resulting improvement of the paper. This work was partially supported by the MINECO grant PID2020-117252GB-I00. AR-M acknowledges support from grant RYC-2016-20254 funded by MCIN/AEI/10.13039/501100011033 and by ESF Investing in your future. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gai a), processed by the Gaia Data Processing and Analysis Consor- tium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortiu m). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. FJE acknowledges financial support from the Spanish MINECO/FEDER through the grant AYA2017-84089 and MDM- 2017-0737 at Centro de Astrobiología (CSIC-INTA), Unidad de Ex- celencia María de Maeztu, and from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement no. 824064 through the ESCAPE - The European Science Cluster of Astronomy & Particle Physics ESFRI Research Infrastructures project. This research has made use of the Spanish Virtual Ob- servatory (http://svo.cab.inta-csic.es) supported from Ministerio de Ciencia e Innovaci ón through grant PID2020-112949GB-I00. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France., Peer Reviewed, Postprint (published version)