Recent Submissions

  • 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.
  • PDR Emission from the Arched-Filaments and Nearby Positions

    Instituto de Radioastronomía Milimétrica IRAM Av. Divina Pastora 7, 18012 Granada, Spain; I. Physikalisiches Institut, University of Cologne, Germany; University of Cincinnati, USA; Armagh Observatory and Planetarium, Northern Ireland; School of Physical Sciences, University of Adelaide, Australia; García, Pablo; Röllig, Markus; Abel, Nicholas; Steinke, Martin; Burton, Michael; et al. (The Multi-Messenger Astrophysics of the Galactic Centre, 2017-01-01)
    We investigate the physical conditions of the gas, atomic and molecular, in the filaments in the context of Photo-Dissociation Regions (PDRs) using the KOSMA-PDR mode of clumpy clouds. We also compare the [CII] vs. [NII] integrated intensity predictions in Abel et al. 2005 for HII regions and adjacent PDRs in the Galactic disk, and check for their applicability under the extreme physical conditions present in the GC. Our preliminary results show that observed integrated intensities are well reproduced by the PDR model. The gas is exposed to a relatively low Far-UV field between 10<SUP>2</SUP> - 10<SUP>3</SUP> Draine fields. The total volume hydrogen density is well constrained between 10<SUP>4</SUP> - 10<SUP>5</SUP> cm<SUP>-3</SUP>. The hydrogen ionization rate due to cosmic-rays varies between 10<SUP>-15</SUP> and 4× 10<SUP>-15</SUP> s<SUP>-1</SUP>, with the highest value ~ 10<SUP>-14</SUP> s<SUP>-1</SUP> found towards G0.07+0.04. Our results show that the line-of-sight contribution to the total distance of the filaments to the Arches Cluster is not negligible. The spatial distribution of the [CII]/[NII] ratio shows that the integrated intensity ratios are fairly homogeneously distributed for values below 10 in energy units. Calculations including variation on the [C/N] abundance ratio show that tight constraints on this ratio are needed to reproduce the observations.
  • Multimessenger science opportunities with mHz gravitational waves

    NASA Goddard Space Flight Center; Columbia University; Leiden University; Harvard University; The Pennsylvania State University; University of Cambridge; CITA, University of Toronto; California Institute of Technology; City University of New York/American Museum of Natural History; Princeton University; et al. (Bulletin of the American Astronomical Society, 2019-05-01)
    We review opportunities for multi-messenger science breakthroughs involving mHz gravitational waves with electromagnetic observations.
  • The Fornax3D Survey — A Magnitude-Limited Study of Galaxies in the Fornax Cluster with MUSE

    Armagh Observatory &amp; Planetarium, UK; INAF–Astronomical Observatory of Capodimonte, Napoli, Italy; -; Sarzi, M.; Iodice, E.; Fornax3D Collaboration (The Messenger, 2022-12-01)
    The Fornax galaxy cluster is an ideal nearby laboratory in which to study the impact of dense environments on the evolution of galaxies. The Fornax3D survey offers extended and deep integral-field spectroscopic observations for the brightest 33 galaxies within of virial radius of the Fornax cluster, obtained with the MUSE integral-field spectrograph, mounted on Unit Telescope 4 (Yepun) of ESO's Very Large Telescope in Chile. The Fornax3D data allowed us to reconstruct the formation of early-type galaxies in the cluster and to explore the link with spiral galaxies. Results have been published in 19 refereed papers since 2018. In this paper we review the broad goals of this campaign, its main results and the potential for future studies combining the MUSE data with the abundant multi-wavelength data coverage for Fornax.
  • 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 VLT-FLAMES Tarantula Survey

    Armagh Observatory, College Hill, BT61 9DG, Armagh, Northern Ireland; ATC, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ, UK; ARC, School of Mathematics and Physics, QUB, Belfast BT7 1NN, UK; Institute of Astrophysics, KU Leuven, Celestijnenlaan 200D, 3001, Leuven, Belgium; Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK; -; Vink, Jorick S.; Evans, C. J.; Bestenlehner, J.; McEvoy, C.; et al. (The Lives and Death-Throes of Massive Stars, 2017-11-01)
    We present a number of notable results from the VLT-FLAMES Tarantula Survey (VFTS), an ESO Large Program during which we obtained multi-epoch medium-resolution optical spectroscopy of a very large sample of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud (LMC). This unprecedented data-set has enabled us to address some key questions regarding atmospheres and winds, as well as the evolution of (very) massive stars. Here we focus on O-type runaways, the width of the main sequence, and the mass-loss rates for (very) massive stars. We also provide indications for the presence of a top-heavy initial mass function (IMF) in 30 Dor.
  • MOONS: The New Multi-Object Spectrograph for the VLT

    ESO; STFC, UK Astronomy Technology Centre, Royal Observatory Edinburgh, UK; Cavendish Laboratory, University of Cambridge, UK; Instituto de Astrofísica e Ciências do Espaço and Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Portugal; GEPI, Observatoire de Paris, PSL University, CNRS, France; Department of Physics, ETH Zurich, Switzerland; INAF-Osservatorio Astrofisico di Arcetri, Florence, Italy; Department of Astronomy, University of Geneva, Versoix, Switzerland; Pontificia Universidad Católica de Chile, Santiago, Chile; Department of Physics, University of Oxford, UK; et al. (The Messenger, 2020-06-01)
    MOONS is the new Multi-Object Optical and Near-infrared Spectrograph currently under construction for the Very Large Telescope (VLT) at ESO. This remarkable instrument combines, for the first time, the collecting power of an 8-m telescope, 1000 fibres with individual robotic positioners, and both low- and high-resolution simultaneous spectral coverage across the 0.64-1.8 μm wavelength range. This facility will provide the astronomical community with a powerful, world-leading instrument able to serve a wide range of Galactic, extragalactic and cosmological studies. Construction is now proceeding full steam ahead and this overview article presents some of the science goals and the technical description of the MOONS instrument. More detailed information on the MOONS surveys is provided in the other dedicated articles in this Messenger issue.
  • The Link between Hot and Cool Outflows

    Armagh Observatory and Planetarium, College Hill, BT61 9DG, Armagh, Northern Ireland,; Vink, Jorick S.; Sander, A. A. C.; Higgins, E. R.; Sabhahit, G. N. (The Origin of Outflows in Evolved Stars, 2022-01-01)
    The link between hot and cool stellar outflows is shown to be critical for correctly predicting the masses of the most massive black holes (BHs) below the so-called pair-instability supernova (PISN) mass gap. Gravitational Wave (GW) event 190521 allegedly hosted an "impossibly" heavy BH of 85 M <SUB>⊙</SUB>. Here we show how our increased knowledge of both metallicity Z and temperature dependent mass loss is critical for our evolutionary scenario of a low-Z blue supergiant (BSG) progenitor of an initially approx 100 M <SUB>⊙</SUB> star to work. We show using MESA stellar evolution modelling experiments that as long as we can keep such stars above 8000 K such low-Z BSGs can avoid strong winds, and keep a very large envelope mass intact before core collapse. This naturally leads to the Cosmic Time dependent maximum BH function below the PISN gap.
  • The origin and impact of Wolf-Rayet-type mass loss

    Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Mönchhofstr. 12-14, 69120 Heidelberg, Germany,; Armagh Observatory and Planetarium, College Hill, Armagh, BT61 9DG, N. Ireland; Anton Pannekoek Institute for Astronomy, Science Park 904, 1098 XH, Amsterdam, The Netherlands; Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24/25, D-14476 Potsdam, Germany; Sander, Andreas A. C.; Vink, Jorick S.; Higgins, Erin R.; Shenar, Tomer; Hamann, Wolf-Rainer; Todt, Helge (The Origin of Outflows in Evolved Stars, 2022-01-01)
    Classical Wolf-Rayet (WR) stars mark an important stage in the late evolution of massive stars. As hydrogen-poor massive stars, these objects have lost their outer layers, while still losing further mass through strong winds indicated by their prominent emission line spectra. Wolf-Rayet stars have been detected in a variety of different galaxies. Their strong winds are a major ingredient of stellar evolution and population synthesis models. Yet, a coherent theoretical picture of their strong mass-loss is only starting to emerge. In particular, the occurrence of WR stars as a function of metallicity (Z) is still far from being understood.