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  • X-Shooting ULLYSES: Massive Stars at Low Metallicity

    Armagh Observatory and Planetarium, UK; Department of Physics & Astronomy, University of Sheffield, UK; Space Telescope Science Institute, Baltimore, USA; Centre for Astrobiology (CSIC-INTA), Torrejón de Ardoz, Madrid, Spain; Montpellier Universe and Particles Laboratory, Montpellier University, France; Las Campanas Observatory, Carnegie Observatories, Chile; Institute for Physics and Astronomy, University of Potsdam, Germany; Department of Physics, University of Montreal, Canada; Penn State Scranton, Dunmore, PA, USA; Astronomy Centre, Heidelberg University, Germany; et al. (The Messenger, 2024-03-01)
    The Hubble Space Telescope has devoted 500 orbits to observing 250 massive stars with low metallicity in the ultraviolet (UV) range within the framework of the ULLYSES program. The X-Shooting ULLYSES (XShootU) project enhances the legacy value of this UV dataset by providing high-quality optical and near-infrared spectra, which are acquired using the wide-wavelength- coverage X-shooter spectrograph at ESO's Very Large Telescope. XShootU emphasises the importance of combining UV with optical spectra for the consistent determination of key stellar parameters such as effective temperature, surface gravity, luminosity, abundances, and wind characteristics including mass-loss rates as a function of metallicity. Since uncertainties in these parameters have implications across various branches of astrophysics, the data and modelling generated by the XShootU project are poised to significantly advance our understanding of massive stars at low metallicity. This is particularly crucial for confidently interpreting James Webb Space Telescope (JWST) data of the earliest stellar generations, making XShootU a unique resource for comprehending individual spectra of low-metallicity stars.
  • Search for Stellar Companions of Exoplanet Host Stars with AstraLux/CAHA 2.2 m

    Astrophysikalisches Institut und Universitäts-Sternwarte Jena, Schillergässchen 2, D-07745 Jena, Germany; Armagh Observatory and Planetarium, College Hill, BT61 9DB Armagh, UK; Queen's University Belfast, School of Mathematics and Physics, Main Physics Building,University Road, BT7 1NN Belfast, UK; Astrophysikalisches Institut und Universitäts-Sternwarte Jena, Schillergässchen 2, D-07745 Jena, Germany; University of Galway, University Road, H91 TK33 Galway, Ireland; Research School of Astronomy & Astrophysics, Australian National University, Mount Stromlo Observatory Cotter Road, Weston Creek, Canberra, ACT, 2611, Australia; ARC Center of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Mount Stromlo Road, Stromlo, ACT, 2611, Australia; Instituto de Astrofísica de Andalucía CSIC, Glorieta de la Astronomia, Apartado 3004,18080 Granada, Spain; Schlagenhauf, Saskia; Mugrauer, Markus; Ginski, Christian; Buder, Sven; Fernández, Matilde; et al. (Monthly Notices of the Royal Astronomical Society, 2024-04-01)
    Stellar multiplicity is a key aspect of exoplanet diversity, as the presence of more than one star in a planetary system can have both devastating and positive effects on its formation and evolution. In this paper, we present the results of a Lucky Imaging survey of 212 exoplanet host stars performed with AstraLux at the 2.2 m telescope of the Centro Astronómico Hispano en Andalucía. The survey includes data from seven observing epochs between August 2015 and September 2020, and data for individual targets from four earlier observing epochs. The targets of this survey are nearby, bright, solar-like stars with high proper motions. In total, we detected 46 co-moving companions of 43 exoplanet host stars. Accordingly, this survey shows that the minimum multiplicity rate of exoplanet host stars is $20 \pm 3~{\rm per\ cent}$. In total, 33 binary and 10 hierarchical triple star systems with exoplanets have been identified. All companions were found to have a common proper motion with the observed exoplanet host stars, and with our astrometry we even find evidence of orbital motion for 28 companions. For all targets, we determine the detection limit and explore the detection space for possible additional companions of these stars. Based on the reached detection limit, additional co-moving companions beyond the detected ones can be excluded around all observed exoplanet host stars. The increasing number of exoplanets discovered in multiple stellar systems suggests that the formation of planets in such systems is by no means rare, but common. Therefore, our study highlights the need to consider stellar multiplicity in future studies of exoplanet habitability.
  • A study of galactic plane Planck galactic cold clumps observed by SCOPE and the JCMT plane survey

    Armagh Observatory and Planetarium, College Hill, Armagh, BT61 9DB, UK; Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, People's Republic of China; Astrophysics Research Institute, Liverpool John Moores University, Liverpool Science Park, iC2, 146 Brownlow Hill. Liverpool, L3 5RF, UK; NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Rd, Victoria, BC V9E 2E7, Canada; Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 2Y2, Canada; Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL, UK; Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejon 34055, Republic of Korea; University of Science and Technology, Korea (UST), 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea; National Astronomical Observatories, Chinese Academy of Sciences, Beijing, 100012, China; Key Laboratory of Radio Astronomy, Chinese Academy of Science, Nanjing 210008, China; Academia Sinica Institute of Astronomy and Astrophysics, 11F of AS/NTU Astronomy-Mathematics Building, No.1, Section 4, Roosevelt Rd, Taipei 10617, Taiwan; Department of Physics and Astronomy, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada; Nobeyama Radio Observatory, National Astronomical Observatory of Japan, National Institutes of Natural Sciences, Nobeyama, Minamimaki, Minamisaku, Nagano 384-1305, Japan; Astronomical Science Program, Graduate Institute for Advanced Studies, SOKENDAI, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; et al. (Monthly Notices of the Royal Astronomical Society, 2024-05-01)
    We have investigated the physical properties of Planck Galactic Cold Clumps (PGCCs) located in the Galactic Plane, using the JCMT Plane Survey (JPS) and the SCUBA-2 Continuum Observations of Pre-protostellar Evolution (SCOPE) survey. By utilising a suite of molecular-line surveys, velocities and distances were assigned to the compact sources within the PGCCs, placing them in a Galactic context. The properties of these compact sources show no large-scale variations with Galactic environment. Investigating the star-forming content of the sample, we find that the luminosity-to-mass ratio (L/M) is an order of magnitude lower than in other Galactic studies, indicating that these objects are hosting lower levels of star formation. Finally, by comparing ATLASGAL sources that are associated or are not associated with PGCCs, we find that those associated with PGCCs are typically colder, denser, and have a lower L/M ratio, hinting that PGCCs are a distinct population of Galactic Plane sources.
  • Modelling Time-dependent Convective Penetration in 1D Stellar Evolution

    Department of Astrophysics/IMAPP, Radboud University, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands; Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium; Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium; Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University, 1800 Sherman Avenue, Evanston, IL 60201, USA; Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106, USA; Center for Computational Astrophysics, Flatiron Institute, New York, NY 10010, USA; Center for Computational Astrophysics, Flatiron Institute, New York, NY 10010, USA; Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA; Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706, USA; Armagh Observatory and Planetarium, College Hill, Armagh, BT61 9DG, UK; Johnston, Cole; Michielsen, Mathias; Anders, Evan H.; et al. (The Astrophysical Journal, 2024-04-01)
    One-dimensional stellar evolution calculations produce uncertain predictions for quantities like the age, core mass, core compactness, and nucleosynthetic yields; a key source of uncertainty is the modeling of interfaces between regions that are convectively stable and those that are not. Theoretical and numerical work has demonstrated that there should be numerous processes adjacent to the convective boundary that induce chemical and angular momentum transport, as well as modify the thermal structure of the star. One such process is called convective penetration, wherein vigorous convection extends beyond the nominal convective boundary and alters both the composition and thermal structure. In this work, we incorporate the process of convective penetration in stellar evolution calculations using the stellar evolution software instrument MESA. We implement convective penetration according to the description presented by Anders et al. to to calculate a grid of models from the pre-main sequence to helium core depletion. The extent of the convective penetration zone is self-consistently calculated at each time step without introducing new free parameters. We find both a substantial penetration zone in all models with a convective core and observable differences to global stellar properties such as the luminosity and radius. We present how the predicted radial extent of the penetration zone scales with the total stellar mass, age, and metallicity of the star. We discuss our results in the context of existing numerical and observational studies.
  • NGTS-28Ab: a short period transiting brown dwarf

    School of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK; European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, NL-2201 AZ Noordwijk, the Netherlands; European Southern Observatory, Karl-Schwarzschildstr. 2, D-85748 Garching bei München, Germany; Département d'astronomie, Université de Genéve, 51 chemin Pegasi, CH-1290 Sauverny, Switzerland; NASA Ames Research Center, Moffett Field, CA 94035, USA; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA; NASA Exoplanet Science Institute, IPAC, California Institute of Technology, Pasadena, CA 91125, USA; NASA Ames Research Center, Moffett Field, CA 94035, USA; Bay Area Environmental Research Institute, Moffett Field, CA 94035, USA; Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C, B-4000 Liège, Belgium; Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA; Instituto de Astrofísica de Canarias (IAC), Calle Vía Láctea s/n, 38200, La Laguna, Tenerife, Spain; Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile; Centro de Astrofísica y Tecnologías Afines (CATA), Casilla 36-D, Santiago, Chile; Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK; Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK; et al. (Monthly Notices of the Royal Astronomical Society, 2024-05-01)
    We report the discovery of a brown dwarf orbiting a M1 host star. We first identified the brown dwarf within the Next Generation Transit Survey data, with supporting observations found in TESS sectors 11 and 38. We confirmed the discovery with follow-up photometry from the South African Astronomical Observatory, SPECULOOS-S, and TRAPPIST-S, and radial velocity measurements from HARPS, which allowed us to characterize the system. We find an orbital period of ~1.25 d, a mass of $69.0^{+5.3}_{-4.8}$ M<SUB>J</SUB>, close to the hydrogen burning limit, and a radius of 0.95 ± 0.05 R<SUB>J</SUB>. We determine the age to be &gt;0.5 Gyr, using model isochrones, which is found to be in agreement with spectral energy distribution fitting within errors. NGTS-28Ab is one of the shortest period systems found within the brown dwarf desert, as well as one of the highest mass brown dwarfs that transits an M dwarf. This makes NGTS-28Ab another important discovery within this scarcely populated region.
  • The wide-field, multiplexed, spectroscopic facility WEAVE: Survey design, overview, and simulated implementation

    Oxford Astrophysics, University of Oxford, Keble Road, Oxford OX1 3RH, UK; Kapteyn Astronomical Institute, Rijksuniversiteit Groningen, Landleven 12, 9747 AD Groningen, The Netherlands; RALSpace, STFC, Harwell, Didcot OX11 0QX, UK; SRON - Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands; Kapteyn Astronomical Institute, Rijksuniversiteit Groningen, Landleven 12, 9747 AD Groningen, The Netherlands; Oxford Astrophysics, University of Oxford, Keble Road, Oxford OX1 3RH, UK; RALSpace, STFC, Harwell, Didcot OX11 0QX, UK; Instituto de Astrofísica de Canarias, Calle Vía Láctea s/n, 38205 La Laguna, Santa Cruz de Tenerife, Spain; Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain; Centre for Astrophysics Research, University of Hertfordshire, Hatfield, Hertfordshire AL10 9AB, UK; Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK; Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK; Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Bd de l'Observatoire, CS 34229, 06304 Nice Cedex 4, France; INAF - Osservatorio Astronomico di Brera, Via Brera, 28, 20121 Milano, Italy; Aix Marseille Univ, CNRS, CNES, LAM, Laboratoire d'Astrophysique de Marseille, 13388 Marseille, France; INAF - Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy; et al. (Monthly Notices of the Royal Astronomical Society, 2024-05-01)
    WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, saw first light in late 2022. WEAVE comprises a new 2-deg 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 $R\sim 20\, 000$. After summarizing the design and implementation of WEAVE and its data systems, we present the organization, 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 ionized gas in z &lt; 0.5 cluster galaxies; (vi) survey stellar populations and kinematics in ${\sim} 25\, 000$ field galaxies at 0.3 ≲ z ≲ 0.7; (vii) study the cosmic evolution of accretion and star formation using &gt;1 million spectra of LOFAR-selected radio sources; and (viii) trace structures using intergalactic/circumgalactic gas at z &gt; 2. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator.
  • Spectroscopic diagnostics of lead stratification in hot subdwarf atmospheres

    Armagh Observatory and Planetarium, College Hill, Armagh, BT61 9DB, UK; Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK; Dr Karl Remeis-Observatory &amp; ECAP, Friedrich-Alexander University Erlangen-Nürnberg, Sternwartstr. 7, D-96049 Bamberg, Germany; Scott, L. J. A.; Jeffery, C. S.; Byrne, C. M.; Dorsch, M. (Monthly Notices of the Royal Astronomical Society, 2024-05-01)
    Heavy metal subdwarfs are a class of hot subdwarfs with very high abundances of heavy elements, typically around 10 000 times solar. They include stars, which are strongly enhanced in either lead or zirconium, as well as other elements. Vertical stratification of the enhanced elements, where the element is concentrated in a thin layer of the atmosphere, has been proposed as a mechanism to explain the apparent high abundances. This paper explores the effects of the vertical stratification of lead on the theoretical spectra of hot subdwarfs. The concentration of lead in different regions of the model atmosphere is found to affect individual lines in a broadly wavelength-dependent manner, with the potential for lines to display modified profiles depending on the location of lead enhancement in the atmosphere. This wavelength dependence highlights the importance of observations in both the optical and the UV for determining whether stratification is present in real stars.
  • Tracking the motion of a shock along a channel in the low solar corona

    Astronomy &amp; Astrophysics Section, DIAS Dunsink Observatory, Dublin Institute for Advanced Studies, Dublin, D15 XR2R, Ireland ; Armagh Observatory and Planetarium, College Hill, Armagh, BT61 9DG, N. Ireland, UK; School of Mathematics and Physics, Queen's University Belfast, University Road, Belfast, BT7 1NN, N. Ireland, UK; Astronomy &amp; Astrophysics Section, DIAS Dunsink Observatory, Dublin Institute for Advanced Studies, Dublin, D15 XR2R, Ireland; Armagh Observatory and Planetarium, College Hill, Armagh, BT61 9DG, N. Ireland, UK; Centre for Astrophysics and Relativity, School of Physical Sciences, Dublin City University, Dublin, D09 V209, Ireland; School of Mathematics and Physics, Queen's University Belfast, University Road, Belfast, BT7 1NN, N. Ireland, UK; Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, Tsarigradsko Chausee Blvd 72, Sofia, 1784, Bulgaria; Rigney, J.; Gallagher, P. T.; Ramsay, G.; Doyle, J. G.; Long, D. M.; et al. (Astronomy and Astrophysics, 2024-04-01)
    Context. Shock waves are excited by coronal mass ejections (CMEs) and large-scale extreme-ultraviolet (EUV) wave fronts and can result in low-frequency radio emission under certain coronal conditions. <BR /> Aims: In this work, we investigate a moving source of low-frequency radio emission as a CME and an associated EUV wave front move along a channel of a lower density, magnetic field, and Alfvén speed in the solar corona. <BR /> Methods: Observations from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, the Nançay Radio Heliograph (NRH), and the Irish Low Frequency Array (I-LOFAR) were analysed. Differential emission measure maps were generated to determine densities and Alfvén maps, and the kinematics of the EUV wave front was tracked using CorPITA. The radio sources' positions and velocity were calculated from NRH images and I-LOFAR dynamic spectra. <BR /> Results: The EUV wave expanded radially with a uniform velocity of ∼500 km s<SUP>−1</SUP>. However, the radio source was observed to be deflected and appeared to move along a channel of a lower Alfvén speed, abruptly slowing from 1700 km s<SUP>−1</SUP> to 250 km s<SUP>−1</SUP> as it entered a quiet-Sun region. A shock wave with an apparent radial velocity of &gt; 420 km s<SUP>−1</SUP> was determined from the drift rate of the associated Type II radio burst. <BR /> Conclusions: The apparent motion of the radio source may have resulted from a wave front moving along a coronal wave guide or by different points along the wave front emitting at locations with favourable conditions for shock formation.
  • EC 19529-4430: SALT identifies the most carbon- and metal-poor extreme helium star

    Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK; Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK; School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, UK; Australian Astronomical Optics - Macquarie, Faculty of Science and Engineering, Macquarie University, North Ryde, NSW 2113, Australia; Physics Department, University of Nebraska at Omaha, 6001 Dodge St, Omaha, NE 68182, USA; Jeffery, C. S.; Scott, L. J. A.; Philip Monai, A.; Miszalski, B.; Woolf, V. M. (Monthly Notices of the Royal Astronomical Society, 2024-05-01)
    EC 19529-4430 was identified as a helium-rich star in the Edinburgh-Cape (EC) Survey of faint-blue objects and subsequently resolved as a metal-poor extreme helium (EHe) star in the Southern African Large Telescope (SALT) survey of chemically peculiar hot subdwarfs. This paper presents a fine analysis of the SALT high-resolution spectrum. EC 19529-4430 has $T_{\rm eff} = 20\, 700 \pm 250$ K, $\log g /{\rm cm\, s^{-2}} = 3.49\pm 0.03$, and an overall metallicity some 1.3 dex below solar; surface hydrogen is $\approx 0.5~{{\ \rm per\ cent}}$ by number. The surface CNO ratio 1:100:8 implies that the surface consists principally of CNO-processed helium and makes EC 19529-4430 the coolest known carbon-poor and nitrogen-rich EHe star. Metal-rich analogues include V652 Her and GALEX J184559.8-413827. Kinematically, its retrograde orbit indicates membership of the Galactic halo. No pulsations were detected in TESS photometry and there is no evidence for a binary companion. EC 19529-4430 most likely formed from the merging of two helium white dwarfs, which themselves formed as a binary system some 11 Gyr ago.
  • Predicting the heaviest black holes below the pair instability gap

    Armagh Observatory and Planetarium (AOP), Armagh, College Hill, BT61 9DB, UK; School of Maths and Physics, Queen's University Belfast, Northern Ireland, University Road, BT7 1NN, UK; Armagh Observatory and Planetarium (AOP), Armagh, College Hill, BT61 9DB, UK; Winch, Ethan R. J.; Vink, Jorick S.; Higgins, Erin R.; Sabhahitf, Gautham N. (Monthly Notices of the Royal Astronomical Society, 2024-04-01)
    Traditionally, the pair instability (PI) mass gap is located between 50 and 130 M<SUB>⊙</SUB>, with stellar mass black holes (BHs) expected to 'pile up' towards the lower PI edge. However, this lower PI boundary is based on the assumption that the star has already lost its hydrogen (H) envelope. With the announcement of an 'impossibly' heavy BH of 85 M<SUB>⊙</SUB> as part of GW 190521 located inside the traditional PI gap, we realized that blue supergiant (BSG) progenitors with small cores but large hydrogen envelopes at low metallicity (Z) could directly collapse to heavier BHs than had hitherto been assumed. The question of whether a single star can produce such a heavy BH is important, independent of gravitational wave events. Here, we systematically investigate the masses of stars inside the traditional PI gap by way of a grid of 336 detailed MESA stellar evolution models calculated across a wide parameter space, varying stellar mass, overshooting, rotation, semiconvection, and Z. We evolve low Z stars in the range 10<SUP>-3</SUP> &lt; Z/Z<SUB>⊙</SUB> &lt; Z<SUB>SMC</SUB>, making no prior assumption regarding the mass of an envelope, but instead employing a wind mass-loss recipe to calculate it. We compute critical carbon-oxygen and helium core masses to determine our lower limit to PI physics, and we provide two equations for M<SUB>core</SUB> and M<SUB>final</SUB> that can also be of use for binary population synthesis. Assuming the H envelope falls into the BH, we confirm the maximum BH mass below PI is M<SUB>BH</SUB> ≃ 93.3 M<SUB>⊙</SUB>. Our grid allows us to populate the traditional PI gap, and we conclude that the distribution of BHs above the traditional boundary is not solely due to the shape of the initial mass function, but also to the same stellar interior physics (i.e. mixing) that which sets the BH maximum.
  • LISA Galactic Binaries with Astrometry from Gaia DR3

    Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany; Department of Physics and Astronomy, Texas Tech University, P.O. Box 41051, Lubbock, TX 79409, USA; Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Straße 1, 85741 Garching, Germany; Institute for Gravitational Wave Astronomy, School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT, UK; NASA Marshall Space Flight Center, Huntsville, AL 35811, USA; Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Callinstrasse 38, 30167 Hannover, Germany; Leibniz Universität Hannover, Institut für Gravitationsphysik, Callinstrasse 38, 30167 Hannover, Germany; Université de Paris, CNRS, Astroparticule et Cosmologie, 75013 Paris, France; IRFU, CEA, Université Paris-Saclay, F-91191, Gif-sur-Yvette, France; Department of Astrophysics/IMAPP, Radboud University, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands; South African Astronomical Observatory, P.O. Box 9, Observatory, 7935, Cape Town, South Africa; Department of Astronomy &amp; Inter-University Institute for Data Intensive Astronomy, University of Cape Town, Private Bag X3, 7701 Rondebosch, South Africa; Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK; Université de Paris, CNRS, Astroparticule et Cosmologie, 75013 Paris, France; Department of Astrophysics/IMAPP, Radboud University, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands; SRON, Netherlands Institute for Space Research, Niels Bohrweg 4, 2333 CA Leiden, The Netherlands; Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium; European Space Agency, European Space Astronomy Centre, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain; et al. (The Astrophysical Journal, 2024-03-01)
    Galactic compact binaries with orbital periods shorter than a few hours emit detectable gravitational waves (GWs) at low frequencies. Their GW signals can be detected with the future Laser Interferometer Space Antenna (LISA). Crucially, they may be useful in the early months of the mission operation in helping to validate LISA's performance in comparison to prelaunch expectations. We present an updated list of 55 candidate LISA-detectable binaries with measured properties, for which we derive distances based on Gaia Data Release 3 astrometry. Based on the known properties from electromagnetic observations, we predict the LISA detectability after 1, 3, 6, and 48 months using Bayesian analysis methods. We distinguish between verification and detectable binaries as being detectable after 3 and 48 months, respectively. We find 18 verification binaries and 22 detectable sources, which triples the number of known LISA binaries over the last few years. These include detached double white dwarfs, AM CVn binaries, one ultracompact X-ray binary, and two hot subdwarf binaries. We find that across this sample the GW amplitude is expected to be measured to ≈10% on average, while the inclination is expected to be determined with ≈15° precision. For detectable binaries, these average errors increase to ≈50% and ≈40°, respectively.
  • The Magnetic Field in the Colliding Filaments G202.3+2.5

    Shanghai Astronomical Observatory, Chinese Academy of Sciences, No. 80 Nandan Road, Xuhui, Shanghai 200030, People's Republic of China; , ,; National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan; Shanghai Astronomical Observatory, Chinese Academy of Sciences, No. 80 Nandan Road, Xuhui, Shanghai 200030, People's Republic of China; , ,; Shanghai Astronomical Observatory, Chinese Academy of Sciences, No. 80 Nandan Road, Xuhui, Shanghai 200030, People's Republic of China; , ,; Université de Franche-Comté, CNRS, Institut UTINAM, OSU THETA, F-25000 Besançon, France; National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Road, Chaoyang, Beijing 100101, People's Republic of China; Department of Physics, P.O. Box 64, FI-00014, University of Helsinki, Finland; Gemini Observatory/NSF's NOIRLab, 670 N. A'ohoku Place, Hilo, HI 96720, USA; Center for Astrophysics ∣ Harvard &amp; Smithsonian 60 Garden Street, Cambridge, MA 02138, USA; Academia Sinica Institute of Astronomy and Astrophysics No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan (R.O.C.); IRAP, Université de Toulouse, CNRS 9 avenue du Colonel Roche, BP 44346, F-31028 Toulouse Cedex 4, France; et al. (The Astrophysical Journal, 2024-03-01)
    We observe the magnetic field morphology toward a nearby star-forming filamentary cloud, G202.3+2.5, using James Clerk Maxwell Telescope/POL-2 850 μm thermal dust polarization observations with an angular resolution of 14.″4 (∼0.053 pc). The average magnetic field orientation is found to be perpendicular to the filaments, while showing different behaviors in the four subregions, suggesting various effects from the filaments' collision in these subregions. With the kinematics obtained by the ${{{\rm{N}}}_{2}{\rm{H}}}^{+}$ observation by IRAM, we estimate the plane-of-sky magnetic field strength by two methods, the classical Davis–Chandrasekhar–Fermi (DCF) method and the angular dispersion function (ADF) method, giving B <SUB>pos,dcf</SUB> and B <SUB>pos,adf</SUB> of ∼90 and ∼53 μG. We study the relative importance between the gravity (G), magnetic field (B), and turbulence (T) in the four subregions, and find G &gt; T &gt; B, G ≥ T &gt; B, G ∼ T &gt; B, and T &gt; G &gt; B in the north tail, west trunk, south root, and east wing, respectively. In addition, we investigate the projection effects on the DCF and ADF methods, based on a similar simulation case, and find the 3D magnetic field strength may be underestimated by a factor of ∼3 if applying the widely used statistical B <SUB>pos</SUB>-to-B <SUB>3D</SUB> factor when using the DCF or ADF methods, which may further underestimate/overestimate the related parameters.
  • Search for stellar companions of exoplanet host stars with AstraLux/CAHA 2.2 m

    Astrophysikalisches Institut und Universitäts-Sternwarte Jena, Jena, Germany; Armagh Observatory and Planetarium, Armagh, UK; Queen's University Belfast, UK; Astrophysikalisches Institut und Universitäts-Sternwarte Jena, Jena, Germany; University of Galway, Galway, Ireland; Research School of Astronomy &amp; Astrophysics, Australian National University, Canberra, Australian Capital Territory, Australia; ARC Center of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia; Instituto de Astrofísica de Andalucía CSIC, Glorieta de la Astronomia, Granada, Spain; Schlagenhauf, Saskia; Mugrauer, Markus; Ginski, Christian; Buder, Sven; Fernández, Matilde; et al. (Monthly Notices of the Royal Astronomical Society, 2024-02-01)
    Stellar multiplicity is a key aspect of exoplanet diversity, as the presence of more than one star in a planetary system can have both devastating and positive effects on its formation and evolution. In this paper, we present the results of a lucky imaging survey of 212 exoplanet host stars performed with AstraLux at CAHA 2.2 m. The survey includes data from seven observing epochs between August 2015 and September 2020, and data for individual targets from four earlier observing epochs. The targets of this survey are nearby, bright, solar-like stars with high proper motions. In total, we detected 46 co-moving companions of 43 exoplanet host stars. Accordingly, this survey shows that the minimum multiplicity rate of exoplanet host stars is $20 \pm 3~{{\%}}$. In total, 33 binary and ten hierarchical triple star systems with exoplanets have been identified. All companions were found to have a common proper motion with the observed exoplanet host stars, and with our astrometry we even find evidence of orbital motion for 28 companions. For all targets, we determined the detection limit and explore the detection space for possible additional companions of these stars. Based on the reached detection limit, additional co-moving companions beyond the detected ones can be excluded around all observed exoplanet host stars. The increasing number of exoplanets discovered in multiple stellar systems suggests that the formation of planets in such systems is by no means rare, but common. Therefore, our study highlights the need to consider stellar multiplicity in future studies of exoplanet habitability.
  • On the Scarcity of Dense Cores (n &gt; 10<SUP>5</SUP> cm<SUP>‑3</SUP>) in High-latitude Planck Galactic Cold Clumps

    Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, People's Republic of China; Department of Astronomy, School of Physics, Peking University, Beijing, 100871, People's Republic of China; Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, People's Republic of China; Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, People's Republic of China; Armagh Observatory and Planetarium, College Hill, Armagh, BT61 9DB, UK; Department of Physics, University of Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland; Yunnan Observatories, Chinese Academy of Sciences, 396 Yangfangwang, Guandu District, Kunming, 650216, People's Republic of China; Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, CAS, Beijing 100101, People's Republic of China; Departamento de Astronomía, Universidad de Chile, Las Condes, 7591245 Santiago, Chile; NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC, V9E 2E7, Canada; Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Elliot Building, Victoria, BC, V8P 5C2, Canada; Jet Propulsion Laboratory, California Institute of Technology, Pasadena CA 91109, USA; Departamento de Astronomía, Universidad de Chile, Las Condes, 7591245 Santiago, Chile; Indian Institute of Astrophysics, II Block, Koramangala, Bengaluru 560034, India; et al. (The Astrophysical Journal, 2024-03-01)
    High-latitude (∣b∣ &gt; 30°) molecular clouds have virial parameters that exceed 1, but whether these clouds can form stars has not been studied systematically. Using JCMT SCUBA-2 archival data, we surveyed 70 fields that target high-latitude Planck Galactic cold clumps (HLPCs) to find dense cores with density of 10<SUP>5</SUP>–10<SUP>6</SUP> cm<SUP>‑3</SUP> and size of &lt;0.1 pc. The sample benefits from both the representativeness of the parent sample and its coverage of the densest clumps at the high column density end (&gt;1 × 10<SUP>21</SUP> cm<SUP>‑2</SUP>). At an average rms of 15 mJy beam<SUP>‑1</SUP>, we detected Galactic dense cores in only one field, G6.04+36.77 (L183) while also identifying 12 extragalactic objects and two young stellar objects. Compared to the low-latitude clumps, dense cores are scarce in HLPCs. With synthetic observations, the densities of cores are constrained to be n <SUB> c </SUB> ≲ 10<SUP>5</SUP> cm<SUP>‑3</SUP> should they exist in HLPCs. Low-latitude clumps, Taurus clumps, and HLPCs form a sequence where a higher virial parameter corresponds to a lower dense-core detection rate. If HLPCs were affected by the Local Bubble, the scarcity should favor turbulence-inhibited rather than supernova-driven star formation. Studies of the formation mechanism of the L183 molecular cloud are warranted.
  • NGTS-28Ab: A short period transiting brown dwarf

    School of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK; European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands; European Southern Observatory, Karl-Schwarzschildstr. 2, D-85748 Garching bei München, Germany; Département d'astronomie, Université de Genéve, 51 chemin Pegasi, 1290 Sauverny, Switzerland; NASA Ames Research Center, Moffett Field, CA 94035, USA; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 USA; NASA Exoplanet Science Institute, IPAC, California Institute of Technology, Pasadena, CA 91125 USA; NASA Ames Research Center, Moffett Field, CA 94035, USA; Bay Area Environmental Research Institute, Moffett Field, CA 94035, USA; Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C, B-4000 Liège, Belgium; Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA; Instituto de Astrofísica de Canarias (IAC), Calle Vía Láctea s/n, 38200, La Laguna, Tenerife, Spain; Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile; Centro de Astrofísica y Tecnologías Afines (CATA), Casilla 36-D, Santiago, Chile; Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK; Dept. of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK; et al. (Monthly Notices of the Royal Astronomical Society, 2024-02-01)
    We report the discovery of a brown dwarf orbiting a M1 host star. We first identified the brown dwarf within the Next Generation Transit Survey data, with supporting observations found in TESS sectors 11 and 38. We confirmed the discovery with follow-up photometry from the South African Astronomical Observatory, SPECULOOS-S, and TRAPPIST-S, and radial velocity measurements from HARPS, which allowed us to characterise the system. We find an orbital period of ~1.25 d, a mass of $69.0^{+5.3}_{-4.8}$ M<SUB>J</SUB>, close to the Hydrogen burning limit, and a radius of 0.95 ± 0.05 R<SUB>J</SUB>. We determine the age to be &gt;0.5 Gyr, using model isochrones, which is found to be in agreement with SED fitting within errors. NGTS-28Ab is one of the shortest period systems found within the brown dwarf desert, as well as one of the highest mass brown dwarfs that transits an M dwarf. This makes NGTS-28Ab another important discovery within this scarcely populated region.
  • Rotation plays a role in the generation of magnetic fields in single white dwarfs

    Departamento de Física, Universidad Técnica Federico Santa María, Av. España 1680, Valparaíso, Chile; Millennium Nucleus for Planet Formation, NPF, Valparaíso 2340000, Chile; Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, Northern Ireland, UK; Department of Physics and Astronomy, University of Western Ontario, London, ON N6A 3K7, Canada; Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, Northern Ireland, UK; Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK; Department of Physics, Queens College, City University of New York, Flushing, NY-11367, USA; Hernandez, Mercedes S.; Schreiber, Matthias R.; Landstreet, John D.; Bagnulo, Stefano; Parsons, Steven G.; et al. (Monthly Notices of the Royal Astronomical Society, 2024-03-01)
    Recent surveys of close white dwarf binaries as well as single white dwarfs have provided evidence for the late appearance of magnetic fields in white dwarfs, and a possible generation mechanism, a crystallization and rotation-driven dynamo has been suggested. A key prediction of this dynamo is that magnetic white dwarfs rotate, at least on average, faster than their non-magnetic counterparts and/or that the magnetic field strength increases with rotation. Here we present rotation periods of ten white dwarfs within 40 pc measured using photometric variations. Eight of the light curves come from TESS observations and are thus not biased towards short periods, in contrast to most period estimates that have been reported previously in the literature. These TESS spin periods are indeed systematically shorter than those of non-magnetic white dwarfs. This means that the crystallization and rotation-driven dynamo could be responsible for a fraction of the magnetic fields in white dwarfs. However, the full sample of magnetic white dwarfs also contains slowly rotating strongly magnetic white dwarfs which indicates that another mechanism that leads to the late appearance of magnetic white dwarfs might be at work, either in addition to or instead of the dynamo. The fast-spinning and massive magnetic white dwarfs that appear in the literature form a small fraction of magnetic white dwarfs, and probably result from a channel related to white dwarf mergers.
  • Predicting the Heaviest Black Holes below the Pair Instability Gap

    Armagh Observatory and Planetarium (AOP), Armagh, College Hill, BT61 9DB; School of Maths and Physics, Queen's University Belfast, Northern Ireland, University Road, BT7 1NN; Armagh Observatory and Planetarium (AOP), Armagh, College Hill, BT61 9DB; Winch, Ethan R. J.; Vink, Jorick S.; Higgins, Erin R.; Sabhahit, Gautham N. (Monthly Notices of the Royal Astronomical Society, 2024-02-01)
    Traditionally, the pair instability (PI) mass gap is located between 50 and 130 M<SUB>⊙</SUB>, with stellar mass black holes (BHs) expected to pile up towards the lower PI edge. However, this lower PI boundary is based on the assumption that the star has already lost its hydrogen (H) envelope. With the announcement of an impossibly heavy BH of 85 M<SUB>⊙</SUB> as part of GW 190521 located inside the traditional PI gap, we realised that blue supergiant (BSG) progenitors with small cores but large Hydrogen envelopes at low metallicity (Z) could directly collapse to heavier BHs than had hitherto been assumed. The question of whether a single star can produce such a heavy BH is important, independent of gravitational wave events. Here, we systematically investigate the masses of stars inside the traditional PI gap by way of a grid of 336 detailed MESA stellar evolution models calculated across a wide parameter space, varying stellar mass, overshooting, rotation, semi-convection, and Z. We evolve low Z stars in the range 10<SUP>-3</SUP> &lt; Z/Z<SUB>⊙</SUB> &lt; Z<SUB>SMC</SUB>, making no prior assumption regarding the mass of an envelope, but instead employing a wind mass loss recipe to calculate it. We compute critical Carbon-Oxygen and Helium core masses to determine our lower limit to PI physics, and we provide two equations for M<SUB>core</SUB> and M<SUB>final</SUB> that can also be of use for binary population synthesis. Assuming the H envelope falls into the BH, we confirm the maximum BH mass below PI is M<SUB>BH</SUB> ≃ 93.3 M<SUB>⊙</SUB>. Our grid allows us to populate the traditional PI gap, and we conclude that the distribution of BHs above the gap is not solely due to the shape of the initial mass function (IMF), but also to the same stellar interior physics (i.e. mixing) that which sets the BH maximum.
  • Recent Advances in the Theoretical Modeling of Pulsating Low-mass He-core White Dwarfs

    Facultad de Ciencias Astronómicas y Geofísicas (UNLP), La Plata, Argentina;; Facultad de Ciencias Astronómicas y Geofísicas (UNLP), La Plata, Argentina; Institute of Space Sciences (IEEC-CSIC), Barcelona, Spain; Instituto de Física (UFRGS), Porto-Alegre, Brazil; Armagh Observatory, College Hill, UK; Córsico, A. H.; Althaus, L. G.; Calcaferro, L. M.; Serenelli, A. M.; Kepler, S. O.; et al. (20th European White Dwarf Workshop, 2017-03-01)
    Many extremely low-mass (ELM) white-dwarf (WD) stars are currently being found in the field of the Milky Way. Some of these stars exhibit long-period nonradial <P />g-mode pulsations, and constitute the class of ELMV pulsating WDs. In addition, several low-mass pre-WDs, which could be precursors of ELM WDs, have <P />been observed to show short-period photometric variations likely due to nonradial p modes and radial modes. They could constitute a new class of pulsating <P />low-mass pre-WD stars, the pre-ELMV stars. Here, we present the recent results of a thorough theoretical study of the nonadiabatic pulsation properties of <P />low-mass He-core WDs and pre-WDs on the basis of fully evolutionary models representative of these stars.
  • Constraining the progenitor evolution of GW 150914

    Armagh Observatory, and Planetarium, BT61 9DG Armagh, College Hill, Northern Ireland,; Vink, Jorick S. (High-mass X-ray Binaries: Illuminating the Passage from Massive Binaries to Merging Compact Objects, 2019-12-01)
    One of the largest surprises from the LIGO results regarding the first gravitational wave detection (GW 150914) was the fact the black holes (BHs) were heavy, of order 30 - 40 M<SUB>⊙</SUB>. The most promising explanation for this obesity is that the BH-BH merger occurred at low metallicity (Z): when the iron (Fe) contents is lower this is expected to result in weaker mass loss during the Wolf-Rayet (WR) phase. We therefore critically evaluate the claims for the reasons of heavy BHs as a function of Z in the literature. Furthermore, weaker stellar winds might lead to more rapid stellar rotation, allowing WR and BH progenitor evolution in a chemically homogeneous manner. However, there is as yet no empirical evidence for more rapid rotation amongst WR stars in the low Z environment of the Magellanic Clouds. Due to the intrinsic challenge of determining WR rotation rates from emission lines, the most promising avenue to constrain rotation-rate distributions amongst various WR subgroups is through the utilisation of their emission lines in polarised light. We thus provide an overview of linear spectro-polarimetry observations of both single and binary WRs in the Galaxy, as well as the Large and Small Magellanic Clouds, at 50% and 20% of solar Z, respectively. Initial results suggest that the route of chemically homogeneous evolution (CHE) through stellar rotation is challenging, whilst the alternative of a post-LBV or common envelope evolution is more likely.
  • The Of?p stars of the Magellanic Clouds: Are they strongly magnetic?

    Queen's University, Kingston, Ontario, Canada; Royal Military College, Kingston, Ontario, Canada; Université de Liège, 4000 Liège, Belgium; Armagh Observatory, Armagh BT61 9DG, Northern Ireland, UK; Universitätssternwarte, D-81679 München, Germany; Munoz, M.; Wade, G. A.; Nazé, Y.; Bagnulo, S.; Puls, J. (Contributions of the Astronomical Observatory Skalnate Pleso, 2018-01-01)
    All known Galactic Of?p stars have been shown to host strong, organized, magnetic fields. Recently, five Of?p stars have been discovered in the Magellanic Clouds. They posses photometric (Nazé et al., 2015) and spectroscopic (Walborn et al., 2015) variability compatible with the Oblique Rotator Model (ORM). However, their magnetic fields have yet to be directly detected. We have developed an algorithm allowing for the synthesis of photometric observables based on the Analytic Dynamical Magnetosphere (ADM) model by Owocki et al. (2016). We apply our model to OGLE photometry in order to constrain their magnetic geometries and surface dipole strengths. We predict that the field strengths for some of theses candidate extra-Galactic magnetic stars may be within the detection limits of the FORS2 instrument

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