Recent Submissions

  • Multiwavelength High-resolution Observations of Chromospheric Swirls in the Quiet Sun

    Centre of Fusion, Space and Astrophysics, University of Warwick, Coventry CV4 7AL, UK; ASI—Italian Space Agency, Via del Politecnico snc, Rome, Italy ; INAF-OAR National Institute for Astrophysics, I-00078 Monte Porzio Catone (RM), Italy; High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder CO 80307-3000, USA; Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK; Department of Mathematics & Information Sciences, Northumbria University, Newcastle Upon Tyne, NE1 8ST, UK; Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, NO-0315, Oslo, Norway ; Rosseland Centre for Solar Physics, University of Oslo, P.O. Box 1029 Blindern, NO-0315, Oslo, Norway; Shetye, Juie; Verwichte, Erwin; Stangalini, Marco; Judge, Philip G.; et al. (The Astrophysical Journal, 2019-08-01)
    We report observations of small-scale swirls seen in the solar chromosphere. They are typically 2 Mm in diameter and last around 10 minutes. Using spectropolarimetric observations obtained by the CRisp Imaging Spectro-Polarimeter at the Swedish 1 m Solar Telescope, we identify and study a set of swirls in chromospheric Ca II 8542 Å and Hα lines as well as in the photospheric Fe I line. We have three main areas of focus. First, we compare the appearance, morphology, dynamics, and associated plasma parameters between the Ca II and Hα channels. Rotation and expansion of the chromospheric swirl pattern are explored using polar plots. Second, we explore the connection to underlying photospheric magnetic concentration (MC) dynamics. MCs are tracked using the SWAMIS tracking code. The swirl center and MC remain cospatial and share similar periods of rotation. Third, we elucidate the role swirls play in modifying chromospheric acoustic oscillations and found a temporary reduction in wave period during swirls. We use cross-correlation wavelets to examine the change in period and phase relations between different wavelengths. The physical picture that emerges is that a swirl is a flux tube that extends above an MC in a downdraft region in an intergranular lane. The rotational motion of the MC matches the chromospheric signatures. We could not determine whether a swirl is a gradual response to the photospheric motion or an actual propagating Alfvénic wave.
  • Photospheric Observations of Surface and Body Modes in Solar Magnetic Pores

    Astrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, Belfast, BT7 1NN, UK ; Solar Physics and Space Plasma Research Centre (SP2RC), University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, UK;; Mathematics and Information Sciences, Northumbria University, Newcastle Upon Tyne, NE1 8ST, UK; Astrophysics Research Centre, School of Mathematics and Physics, Queen's University, Belfast, BT7 1NN, UK ; Department of Physics and Astronomy, California State University Northridge, Northridge, CA 91330, USA; Solar Physics and Space Plasma Research Centre (SP2RC), University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, UK; Astrophysics Research Centre, School of Mathematics and Physics, Queen's University, Belfast, BT7 1NN, UK; School of Mathematics and Statistics, University of St Andrews, St Andrews, KY16 9SS, UK; Armagh Observatory & Planetarium, College Hill, Armagh, BT61 9DG, UK; Department of Physics and Astronomy, California State University Northridge, Northridge, CA 91330, USA; Solar Physics and Space Plasma Research Centre (SP2RC), University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, UK; Debrecen Heliophysical Observatory (DHO), Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, 4010 Debrecen, P.O. Box 30, Hungary; Keys, Peter H.; et al. (The Astrophysical Journal, 2018-04-01)
    Over the past number of years, great strides have been made in identifying the various low-order magnetohydrodynamic wave modes observable in a number of magnetic structures found within the solar atmosphere. However, one aspect of these modes that has remained elusive, until now, is their designation as either surface or body modes. This property has significant implications for how these modes transfer energy from the waveguide to the surrounding plasma. Here, for the first time to our knowledge, we present conclusive, direct evidence of these wave characteristics in numerous pores that were observed to support sausage modes. As well as outlining methods to detect these modes in observations, we make estimates of the energies associated with each mode. We find surface modes more frequently in the data, as well as that surface modes appear to carry more energy than those displaying signatures of body modes. We find frequencies in the range of ∼2-12 mHz, with body modes as high as 11 mHz, but we do not find surface modes above 10 mHz. It is expected that the techniques we have applied will help researchers search for surface and body signatures in other modes and in differing structures from those presented here.
  • Polarimetric view of the changing type Seyfert galaxy ESO 362-G018.

    Centro de Astrobiología (CSIC-INTA), Dep. de Astrofíica, Villanueva de la Cañada, E-28692, Madrid, Spain; Armagh Observatory, College Hill, Armagh BT61 9 DG, UK; Institut d'Astrophysique et de Géophysique, Université de Liége, Allée du 6 Août 19c, B5c, 4000 Liége, Belgium; Agís-González, B.; Bagnulo, S.; Hutsemékers, D.; Montesinos, B.; Miniutti, G.; Sanfrutos, M. (Highlights on Spanish Astrophysics IX, 2017-03-01)
    ESO362-G018 is an active galactic nucleus (AGN) which is classified as a Seyfert 1.5 galaxy e.g. by Bennert et al. (2006), (black data set on figure 1). However, Parisi et. al (2009) found an optical spectrum of this source which was taken during the 6dF Galaxy Survey, but it does not show the broad Balmer lines required to classify it as Seyfert 1 galaxy (red data set on figure 1). On the other hand, the results obtained by Agis-Gonzalez et al. (2014❩ in a X-ray analysis of this same source reveal that the inclination of ESO362- G018 i = 53° ± 5° is consistent with the picture of an AGN looked through the upper layers of a clumpy, dusty torus. Thus, according to the Unification Models of AGN and the clumpy nature of the torus, our interpretation of the different spectra is the following one. On 30th of January of 2003 (when the spectrum belonging to the 6dF survey was obtained), our line of sight intercepted a (or several aligned) torus clump(s) with much greater column density than its environment. Accordingly, the nucleus and the broad line region (❨BLR)❩ would be obscured. This allowed only the narrow emission lines to emerge from the narrow line region (NRL). Otherwise, on 18th of September of 2004 (when the spectrum by Bennert et al. 2006 was obtained) there is no clump to intercept and the BLR is not obscured so that the broad Balmer emission lines could be detected.
  • TESS Photometry of AM Her and AR UMa: Binary Parameters, Cyclotron Emission Modeling, and Mass Transfer Duty Cycles

    New Mexico State University, MSC 3DA, Las Cruces, NM 88003, USA; Picture Rocks Observatory, 1025 S. Solano Dr. Suite D., Las Cruces, NM 88001, USA; Finnish Centre for Astronomy with ESO, Quantum, Vesilinnantie 5, FI-20014, University of Turku, Finland; Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Surrey RH5 6NT, UK; Department of Physics, The George Washington University, Washington, DC 20052, USA; Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK; Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warsaw, Poland; Bay Area Environmental Research Institute, Moffett Field, CA 94035, USA; Picture Rocks Observatory, 1025 S. Solano Dr. Suite D., Las Cruces, NM 88001, USA; Instituto Nacional de Pesquisas Espaciais, Av. dos Astronautas 1758, São José dos Campos, SP 12227-010, Brazil; Department of Physics, University of Notre Dame, Notre Dame, IN 46556, USA; Department of Astronomy, University of Washington, Seattle, WA 98195, USA; et al. (The Astrophysical Journal, 2024-04-01)
    Transiting Exoplanet Survey Satellite (TESS) photometry of the polars AM Herculis (AM Her) and AR Ursae Majoris (AR UMa) is presented, along with high-speed photometry. AM Her shows a variety of high states with frequent transitions between them. TESS photometry of AR UMa in the low state reveals no evidence of accretion, while the McDonald 2.1 m telescope caught AR UMa in its high accretion state. Roche-lobe overflow is shut off during low states of AR UMa, while accretion often still takes place during low states of AM Her. We derive inclinations of 50° and 70° for AM Her and AR UMa respectively. To model the high-state light curves of AM Her, we employ a self-organized map light-curve classification scheme to establish common accretion configurations. The cyclotron radiation properties then allow the production of emission region maps on the surface of the white dwarf. The accretion geometry of AM Her is most consistent with a multipolar field structure. The high-state photometry of AR UMa has stochastic accretion flaring, which we attribute to magnetically buffeted mass transfer through the inner Lagrangian point L1. To consider this possibility, we examine the magnetism of both stars and argue that the local magnetic field near L1 can initiate short-lived accretion events and affect transitions between high and low accretion states in both AM Her and AR UMa. In particular, AR UMa has the low state as its default, while AM Her and most other active polars are in the high state by default.
  • Trajectory analysis for combined missions to mars and its Trojan Asteroids

    German Aerospace Center (DLR), Institute of Planetary Research, Rutherfordstr. 2, Berlin, Germany; Technical University of Berlin, Berlin, Germany; Armagh Observatory and Planetarium, Armagh, Northern Ireland, United Kingdom; Wickhusen, Kai; Oberst, Jürgen; Christou, Apostolos; Damme, Friedrich (Planetary and Space Science, 2023-04-01)
    While standalone missions to the Trojan Asteroids of Mars are costly, we analyze flyby scenarios of Mars Trojans, which can be achieved in combination with missions to Mars. <P />We find several trajectory options within the time window 2025-2050, which allow flybys at seven of the known Trojan asteroids located at L5 (trailing by approximately 60° behind Mars) with a low demand for additional delta-v of 0.02-1 km/s compared to a nominal Mars mission. On the other hand, the minimal cruise duration from Earth to the Trojan and from the Trojan to Mars adds up to at least 2 years as more than one revolution about the sun is required for the spacecraft. <P />For the unique L4 Trojan no practical trajectory solution was found. <P />All Trojans have a significant inclination of more than 10° relative to the orbital plane of Mars, which implies high flyby velocities (v = 6-13 km/s) for spacecraft approaching from within this plane.
  • Orbital Modification of the Himalia Family during an Early Solar System Dynamical Instability

    dli@arm.ac.uk; Armagh Observatory and Planetarium College Hill, Armagh, BT61 9DG, UK; School of Mathematics and Physics, Queen's University Belfast University Road, Belfast, BT7 1NN, UK; ;; Armagh Observatory and Planetarium College Hill, Armagh, BT61 9DG, UK; Li, Daohai; Christou, Apostolos A. (The Astronomical Journal, 2017-11-01)
    Among the irregular satellites orbiting Jupiter, the Himalia family is characterized by a high velocity dispersion δ v of several hundred ms<SUP>-1</SUP> among its members, inconsistent with a collisional origin. Efforts to account for this through internecine gravitational interactions do not readily reproduce this feature. Here, we revisit the problem in the context of recent cosmogonical models, where the giant planets migrated significantly through interaction with a planetesimal disk and suffered encounters with planetesimals and planet-sized objects. Our starting assumption is that family formation either predated this phase or occurred soon after its onset. We simulate numerically the diffusive effect of three distinct populations of perturbers on a set of test particles representing the family: Moon-sized (MPT) and Pluto-sized (PPT) planetesimals, and planetary-mass objects (PMO) with masses typical of ice-giant planets. We find that PPT flybys are inefficient, but encounters with MPTs raise the δ v of ∼60% of our test particles to &gt; 200 ms<SUP>-1</SUP> with respect to Himalia, in agreement with observations. As MPTs may not have been abundant in the disk, we simulate encounters between Jupiter and PMOs. We find that too few encounters generate less dispersion than MPTs while too many essentially destroy the family. For PMO masses in the range 5-20 m<SUB>\oplus</SUB>, the family orbital distribution is reproduced by a few tens of encounters.
  • New Evidence for a Physical Link between Asteroids (155140) 2005 UD and (3200) Phaethon

    Lowell Observatory, 1400 W. Mars Hill Rd., Flagstaff, AZ 86001, USA; Department of Physics, P.O. Box 64, FI-00014 University of Helsinki, Finland; Department of Astronomy &amp; Planetary Science, Northern Arizona University, P.O. Box 6010, Flagstaff, AZ 86011, USA; Las Cumbres Observatory, CA, USA; Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK; Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, 72, Tsarigradsko Chaussèe Blvd., Sofia BG-1784, Bulgaria; Aerospace Engineering, Nihon University, 7-24-1 Narashinodai, Funabashi, Chiba 2748501, Japan; Planetary Exploration Research Center, Chiba Institute of Technology, Narashino, Japan; Department of Physics, P.O. Box 64, FI-00014 University of Helsinki, Finland; Astrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, UK; Space sciences, Technologies &amp; Astrophysics Research (STAR) Institute University of Liège Allée du 6 Août 19, B-4000 Liège, Belgium; Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, F-13388, Marseille, France; Space sciences, Technologies, France; Department of Physics, P.O. Box 64, FI-00014 University of Helsinki, Finland; Division of Space Technology, Luleå University of Technology, Box 848, SE-98128 Kiruna, Sweden; et al. (The Planetary Science Journal, 2020-06-01)
    In 2018, the near-Earth object (155140) 2005 UD (hereafter UD) experienced a close fly by of the Earth. We present results from an observational campaign involving photometric, spectroscopic, and polarimetric observations carried out across a wide range of phase angles (0°7-88°). We also analyze archival NEOWISE observations. We report an absolute magnitude of H<SUB>V</SUB> = 17.51 ± 0.02 mag and an albedo of p<SUB>V</SUB> = 0.10 ± 0.02. UD has been dynamically linked to Phaethon due their similar orbital configurations. Assuming similar surface properties, we derived new estimates for the diameters of Phaethon and UD of D = 5.4 ± 0.5 km and D = 1.3 ± 0.1 km, respectively. Thermophysical modeling of NEOWISE data suggests a surface thermal inertia of ${\rm{\Gamma }}={300}_{-110}^{+120}$ and regolith grain size in the range of 0.9-10 mm for UD and grain sizes of 3-30 mm for Phaethon. The light curve of UD displays a symmetric shape with a reduced amplitude of Am(0) = 0.29 mag and increasing at a linear rate of 0.017 mag/° between phase angles of 0° and ∼25°. Little variation in light-curve morphology was observed throughout the apparition. Using light-curve inversion techniques, we obtained a sidereal rotation period P = 5.235 ± 0.005 hr. A search for rotational variation in spectroscopic and polarimetric properties yielded negative results within observational uncertainties of ∼10% μm<SUP>-1</SUP> and ∼16%, respectively. In this work, we present new evidence that Phaethon and UD are similar in composition and surface properties, strengthening the arguments for a genetic relationship between these two objects. <SUP>*</SUP> Partially based on data collected with 2 m RCC telescope at Rozhen National Astronomical Observatory.
  • Can a robot be a scientist? Developing students' epistemic insight through a lesson exploring the role of human creativity in astronomy

    LASAR Research Centre, Canterbury Christ Church University, North Holmes Road, Canterbury, CT1 1QU; Simon Langton Grammar School for Boys, Langton Lane, Canterbury CT47AS; Armagh Observatory, College Hill, Armagh BT619DM; Billingsley, Berry; Heyes, Joshua M.; Lesworth, Tim; Sarzi, Marc (Physics Education, 2023-01-01)
    Artificial intelligence is transforming the practice of science worldwide. Breakthroughs in machine learning are enabling, for example, the discovery of potentially habitable exoplanets beyond our solar system. The growing role of artificial intelligence (AI) in science raises questions for scientists, philosophers, computer scientists … and educators. How will the scholarship and practice of science education respond to the growing role of artificial intelligence in science? Questions like 'Can a robot be a scientist?' can help stimulate students' epistemic curiosity, about the nature of scientific knowledge, including the value and importance of apparently uniquely human attributes such as creativity. In this article we explain the development and delivery of a science lesson using the question 'can a robot be a scientist?' to explore the role of human creativity in scientific observation and classification, using resources and activities created for the citizen scientist project 'Galaxy Zoo'.
  • Zeeman Doppler Maps: Always Unique, Never Spurious?

    Armagh Observatory, College Hill, Armagh BT61 9DG, UK; Università degli Studi di Catania, Osservatorio Astrofisico di Catania, via S. Sofia 78, I-95123 Catania, Italy; Stift, Martin J.; Leone, Francesco (The Astrophysical Journal, 2017-01-01)
    Numerical models of atomic diffusion in magnetic atmospheres of ApBp stars predict abundance structures that differ from the empirical maps derived with (Zeeman) Doppler mapping (ZDM). An in-depth analysis of this apparent disagreement investigates the detectability by means of ZDM of a variety of abundance structures, including (warped) rings predicted by theory, but also complex spot-like structures. Even when spectra of high signal-to-noise ratio are available, it can prove difficult or altogether impossible to correctly recover shapes, positions, and abundances of a mere handful of spots, notwithstanding the use of all four Stokes parameters and an exactly known field geometry; the recovery of (warped) rings can be equally challenging. Inversions of complex abundance maps that are based on just one or two spectral lines usually permit multiple solutions. It turns out that it can by no means be guaranteed that any of the regularization functions in general use for ZDM (maximum entropy or Tikhonov) will lead to a true abundance map instead of some spurious one. Attention is drawn to the need for a study that would elucidate the relation between the stratified, field-dependent abundance structures predicted by diffusion theory on the one hand, and empirical maps obtained by means of “canonical” ZDM, I.e., with mean atmospheres and unstratified abundances, on the other hand. Finally, we point out difficulties arising from the three-dimensional nature of the atomic diffusion process in magnetic ApBp star atmospheres.
  • Diffuse X-Ray Emission in the Cygnus OB2 Association

    Universidad de Río Negro, Sede Atlántica, Viedma CP8500, Argentina; Smithsonian Astrophysical Observatory, 60 Garden St., Cambridge, MA 02138, USA; INAF-Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, I-90134 Palermo, Italy; Astrophysics Group, Keele University, Keele, Staffordshire ST5 5BG, UK; Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, D-21029, Hamburg, Germany; School of Physics, Astronomy &amp; Mathematics, University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB, UK; Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK; I. Physik. Institut, University of Cologne, D-50937 Cologne, Germany; Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK; Albacete-Colombo, J. F.; et al. (The Astrophysical Journal Supplement Series, 2023-11-01)
    We present a large-scale study of diffuse X-ray emission in the nearby massive stellar association Cygnus OB2 as part of the Chandra Cygnus OB2 Legacy Program. We used 40 Chandra X-ray ACIS-I observations covering ~1.0 deg<SUP>2</SUP>. After removing 7924 point sources detected in our survey and applying adaptive smoothing to the background-corrected X-ray emission, the adaptive smoothing reveals large-scale diffuse X-ray emission. Diffuse emission was detected in the subbands soft (0.5-1.2 keV) and medium (1.2-2.5 keV) and marginally in the hard (2.5-7.0 keV) band. From X-ray spectral analysis of stacked spectra we compute a total (0.5-7.0 keV) diffuse X-ray luminosity of ${L}_{{\rm{X}}}^{\mathrm{diff}}\approx $ 4.2 × 10<SUP>34</SUP> erg s<SUP>-1</SUP>, characterized by plasma temperature components at kT ≈ 0.11, 0.40, and 1.18 keV, respectively. The H I absorption column density corresponding to these temperatures has a distribution consistent with N <SUB>H</SUB> = (0.43, 0.80, 1.39) × 10<SUP>22</SUP> cm<SUP>-2</SUP>. The extended medium-band energy emission likely arises from O-type stellar winds thermalized by wind-wind collisions in the most populated regions of the association, while the soft-band emission probably arises from less energetic termination shocks against the surrounding interstellar medium. Supersoft and soft diffuse emission appears more widely dispersed and intense than the medium-band emission. The diffuse X-ray emission is generally spatially coincident with low-extinction regions that we attribute to the ubiquitous influence of powerful stellar winds from massive stars and their interaction with the local interstellar medium. Diffuse X-ray emission is volume filling, rather than edge brightened, oppositely to other star-forming regions. We reveal the first observational evidence of X-ray halos around some evolved massive stars.
  • Photoevaporation and Close Encounters: How the Environment around Cygnus OB2 Affects the Evolution of Protoplanetary Disks

    INAF-Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, I-90134, Palermo, Italy; Smithsonian Astrophysical Observatory, MS-67, 60 Garden Street, Cambridge, MA 02138, USA; Smithsonian Astrophysical Observatory, MS-67, 60 Garden Street, Cambridge, MA 02138, USA; Smithsonian Astrophysical Observatory, MS-67, 60 Garden Street, Cambridge, MA 02138, USA; Astrophysics Group, Keele University, Keele ST5 5BG, UK; Sede Atlantica de la Universidad Nacional de Rio Negro, Don Bosco y Leloir s/n, 8500 Viedma RN, Argentina; Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK; Universitäts-Sternwarte München, Scheinerstrasse 1, D-81679 München, Germany; Excellence Cluster Universe, Boltzmannstr. 2, D-85748 Garching, Germany; INAF-Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, I-90134, Palermo, Italy; School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK; Physik Institut, University of Cologne, D-50937 Cologne, Germany; Armagh Observatory, College Hill, Armagh BT61 9DG, UK; et al. (The Astrophysical Journal Supplement Series, 2023-11-01)
    In our Galaxy, star formation occurs in a variety of environments, with a large fraction of stars formed in clusters hosting massive stars. OB stars have an important feedback on the evolution of protoplanetary disks orbiting around nearby young stars and likely on the process of planet formation occurring in them. The nearby massive association Cyg OB2 is an outstanding laboratory to study this feedback. It is the closest massive association to our Sun and hosts hundreds of massive stars and thousands of low-mass members, both with and without disks. In this paper, we analyze the spatial variation of the disk fraction (i.e., the fraction of cluster members bearing a disk) in Cyg OB2 and study its correlation with the local values of far-ultraviolet (FUV) and extreme-ultraviolet (EUV) radiation fields and the local stellar surface density. We present definitive evidence that disks are more rapidly dissipated in the regions of the association characterized by intense local UV fields and large stellar density. In particular, the FUV radiation dominates disk dissipation timescales in the proximity (i.e., within 0.5 pc) of the O stars. In the rest of the association, EUV photons potentially induce a significant mass loss from the irradiated disks across the entire association, but the efficiency of this process is reduced at increasing distances from the massive stars owing to absorption by the intervening intracluster material. We find that disk dissipation due to close stellar encounters is negligible in Cyg OB2 and likely to have affected 1% or fewer of the stellar population. Disk dissipation is instead dominated by photoevaporation. We also compare our results to what has been found in other young clusters with different massive populations, concluding that massive associations like Cyg OB2 are potentially hostile to protoplanetary disks but that the environments where disks can safely evolve in planetary systems are likely quite common in our Galaxy.
  • Discovery of Magnetically Guided Metal Accretion onto a Polluted White Dwarf

    Armagh Observatory &amp; Planetarium, College Hill, Armagh BT61 9DG, UK; Department of Physics and Astronomy, University College London, London WC1E 6BT, UK; Armagh Observatory &amp; Planetarium, College Hill, Armagh BT61 9DG, UK; Department of Physics &amp; Astronomy, University of Western Ontario, 1151 Richmond St. N, London N6A 3K7, Ontario, Canada; Tartu Observatory, University of Tartu, Observatooriumi 1, Tõravere, 61602, Estonia; Bagnulo, Stefano; Farihi, Jay; Landstreet, John D.; Folsom, Colin P. (The Astrophysical Journal, 2024-03-01)
    Dynamically active planetary systems orbit a significant fraction of white dwarf stars. These stars often exhibit surface metals accreted from debris disks, which are detected through infrared excess or transiting structures. However, the full journey of a planetesimal from star-grazing orbit to final dissolution in the host star is poorly understood. Here, we report the discovery that the cool metal-polluted star WD 0816–310 has cannibalized heavy elements from a planetary body similar in size to Vesta, and where accretion and horizontal mixing processes have clearly been controlled by the stellar magnetic field. Our observations unveil periodic and synchronized variations in metal line strength and magnetic field intensity, implying a correlation between the local surface density of metals and the magnetic field structure. Specifically, the data point to a likely persistent concentration of metals near a magnetic pole. These findings demonstrate that magnetic fields may play a fundamental role in the final stages of exoplanetary bodies that are recycled into their white dwarf hosts.
  • Scientific problems addressed by the Spektr-UV space project (world space Observatory—Ultraviolet)

    Institute of Astronomy, Russian Academy of Sciences, Moscow, Russia; Southern Federal University, Rostov-on-Don, Russia; Astro Space Center, Lebedev Physical Institute, Russian Academy of Sciences, Moscow, Russia; St. Petersburg State University, St. Petersburg, Russia; Universidad Complutense de Madrid, Madrid, Spain; Sternberg Astronomical Institute, Lomonosov Moscow State University, Moscow, Russia; Observational Astronomy, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden; University of Colorado, Boulder, Colorado, USA; Leibniz Institut für Astrophysik Potsdam, Potsdam, Germany; Armagh Observatory, College Hill, Armagh, United Kingdom; et al. (Astronomy Reports, 2016-01-01)
    The article presents a review of scientific problems and methods of ultraviolet astronomy, focusing on perspective scientific problems (directions) whose solution requires UV space observatories. These include reionization and the history of star formation in the Universe, searches for dark baryonic matter, physical and chemical processes in the interstellar medium and protoplanetary disks, the physics of accretion and outflows in astrophysical objects, from Active Galactic Nuclei to close binary stars, stellar activity (for both low-mass and high-mass stars), and processes occurring in the atmospheres of both planets in the solar system and exoplanets. Technological progress in UV astronomy achieved in recent years is also considered. The well advanced, international, Russian-led Spektr-UV (World Space Observatory—Ultraviolet) project is described in more detail. This project is directed at creating a major space observatory operational in the ultraviolet (115-310 nm). This observatory will provide an effective, and possibly the only, powerful means of observing in this spectral range over the next ten years, and will be an powerful tool for resolving many topical scientific problems.
  • 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.
  • 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.
  • Mode Identification in a Pulsating Subdwarf B Star EPIC 212707862 Observed with K2

    Pedagogical University of Cracow, Mt. Suhora Observatory, ul. Podchorążych 2, 30-084 Cracow, Poland; Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, United Kingdom; Missuori State University, Department of Physics, Astronomy, and Materials Science, 901 S. National Av., Springfield, MO 65897, USA; Nordic Optical Telescope, Rambla Josè Ana Fernàndez Pèrez 7, 38711 Breña Baja, Spain; Nordic Optical Telescope, Rambla Josè Ana Fernàndez Pèrez 7, 38711 Breña Baja, Spain, Tartu Observatory: Observatooriumi 1, 61602 Tøravere, Estonia; Bachulski, S.; Baran, A. S.; Jeffery, C. S.; Østensen, R. H.; Reed, M. D.; et al. (Acta Astronomica, 2016-12-01)
    We present an analysis of K2 observations of EPIC 212707862, a pulsating subdwarf B star. We detected 13 significant frequencies from an 81 day run during Campaign 6. Our goal was to find features that could help us to identify pulsation modes. We could not identify any multiplets, which would also have enabled us to precisely derive a rotation period. Based on amplitude modulation we estimated that period to be around 80 days. We found two period-spacing sequences, and successfully identified modal degrees for 11 out of 13 detected frequencies. We assigned six of them to l=1, and another five to l=2. These results will facilitate future theoretical modeling. This star brings to 19 the number of pulsating subdwarf B stars observed with K2. Radial velocities obtained to date and the spectral energy distribution are consistent with EPIC 212707862 being a single hot subdwarf. Analysis of the spectrum gives atmospheric parameters: T<SUB>eff</SUB>=28 298±162 K, log g[cm/s<SUP>2</SUP>]=5.479±0.025 and log (n(He)/n(H))=-2.752±0.069.
  • Origin of impulsive plasma outflows due to magnetoacoustic shocks

    Department of Physics, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005, India; Armagh Observatory, College Hill, Armagh, Northern Ireland, BT61 9DG, United Kingdom; Rao, Y. K.; Srivastava, A. K.; Doyle, J. G.; Dwivedi, B. N. (Monthly Notices of the Royal Astronomical Society, 2017-09-01)
    We study an impulsive plasma outflow in the quiet-Sun using multiwavelength observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) on 2011 March 30. The outflow rises to the upper solar atmosphere with a high terminal speed of 1250 km s<SUP>- 1</SUP>. Emissions from multiple SDO/AIA channels (log T (K) = 4.7 to log T (K) = 7.0), peak at the same time indicating its highly impulsive origin. We obtain the line-of-sight differential emission measure maps and find that the outflow is made up of multitemperature plasma. Investigation of SDO/HMI magnetic field data at its footpoint shows that the emerging flux of negative polarity is oscillating at the period of 442 s. The oscillations are also observed in the intensity of 1600 Å almost co-temporally at the base of the outflow with the almost same period (≈416 s). The ∼7.0 min periodicity in the magnetic flux and 1600 Å flux is present both prior to and during the onset, and even after the outflows for the duration of ≈1 h. This indicates that the magnetoacoustic waves are generated and present at the base of the outflow and interact with the localized small-scale current sheet and associated X-point. Magnetoacoustic waves encounter with the discontinuity at the X-point that may further develop into the fast magnetic shocks leading to the formation of the observed shock cusp and triggering of the impulsive plasma outflows.
  • Ultraviolet spectral synthesis of Iota Herculis

    Department of Physics and Astronomy, The University of Western Ontario, London N6A 3K7, Canada; Department of Physics and Astronomy, The University of Western Ontario, London N6A 3K7, Canada; Armagh Observatory, College Hill, Armagh BT91 6DG, Northern Ireland; Golriz, S. S.; Landstreet, J. D. (Monthly Notices of the Royal Astronomical Society, 2017-04-01)
    The atmospheric abundances of elements provide essential insights into the formation and evolution history of stars. The visible wavelength window has been used almost exclusively in the past to determine the abundances of chemical elements in B-type stars. However, some elements do not have useful spectral lines in the visible spectrum. A high-resolution spectrum of ι Herculis is available from 999 to 1400 Å. In this project, we investigate the chemicalabundance determination in the ultraviolet (UV). We identify the elements whose abundances can be tested, and search for elements whose abundances can be determined in the UV to add to those in the current literature. We also investigate the completeness of the Vienna Atomic Line Database line-list in this region, and the adequacy of local thermodynamic equilibrium (LTE) modelling in the UV for this star. We have used the LTE spectrum synthesis code ZEEMAN to model the UV spectrum of ι Herculis for elements with 5 ≤ Z ≤ 80. Abundances or upper limits are derived for 24 elements. We find that most of our results are in reasonable agreement with previous results. We estimate a value or an upper limit for the abundance of nine elements in this star that were not detected in the visible spectrum. LTE UV spectral synthesis is found to be a useful tool for abundance determination, even though limitations such as incomplete and uncertain atomic data, uncertain continuum normalization and scattered light, and severe blending can introduce difficulties. The high abundance of two heavy elements may be a sign of radiative levitation.
  • Spurious Doppler maps from noisy spectra and zero-field inversions<SUP>★</SUP>

    Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland; Università di Catania, Dipartimento di Fisica e Astronomia, Sezione Astrofisica, Via S. Sofia 78, I-95123 Catania, Italy; INAF - Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95123 Catania, Italy; Stift, M. J.; Leone, F. (Monthly Notices of the Royal Astronomical Society, 2017-03-01)
    Empirical abundance maps derived with the help of Zeeman Doppler mapping are found to be at variance with the predictions of numerical models of atomic diffusion in magnetic atmospheres of ApBp stars. Although theory has often been made responsible for this lack of agreement, direct spectral synthesis based on the published abundance maps reveals that all the chemical inhomogeneities claimed for HD 3980 are entirely spurious, and those of HD 50773 to a large extent. In the former case, this is shown to be due to the neglect of a strong magnetic field, and in the latter case, due to noisy spectra in combination with considerable rotational broadening and ensuing strong line blending. Doppler maps for other magnetic ApBp stars could be affected by similar problems. It is also pointed out that the patchy, extreme overabundances in HD 3980 cannot be reconciled with the theory of stellar atmospheres.
  • 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.

View more