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Multiple retrograde substructures in the Galactic halo: A shattered view of Galactic history
Price-Whelan, Adrian M.; Helmi, Amina; Koppelman, Helmer H. +2 more
Aims: Several kinematic and chemical substructures have been recently found amongst Milky Way halo stars with retrograde motions. It is currently unclear how these various structures are related to each other. This Letter aims to shed light on this issue.
Methods: We explore the retrograde halo with an augmented version of the Gaia DR2 R…
Confirmation of the Gaia DR2 Parallax Zero-point Offset Using Asteroseismology and Spectroscopy in the Kepler Field
Huber, Daniel; Stello, Dennis; Pinsonneault, Marc H. +1 more
We present an independent confirmation of the zero-point offset of Gaia Data Release 2 parallaxes using asteroseismic data of evolved stars in the Kepler field. Using well-characterized red giant branch stars from the APOKASC-2 catalog, we identify a Gaia astrometric pseudocolor ({ν }eff})- and Gaia G-band magnitude-dependent zero-point…
Water vapour in the atmosphere of the habitable-zone eight-Earth-mass planet K2-18 b
Tsiaras, Angelos; Tinetti, Giovanna; Yurchenko, Sergey N. +2 more
In the past decade, observations from space and the ground have found water to be the most abundant molecular species, after hydrogen, in the atmospheres of hot, gaseous extrasolar planets1-5. Being the main molecular carrier of oxygen, water is a tracer of the origin and the evolution mechanisms of planets. For temperate, terrestrial p…
A dominant population of optically invisible massive galaxies in the early Universe
Elbaz, D.; Franco, M.; Shu, X. +9 more
Our current knowledge of cosmic star-formation history during the first two billion years (corresponding to redshift z > 3) is mainly based on galaxies identified in rest-frame ultraviolet light1. However, this population of galaxies is known to under-represent the most massive galaxies, which have rich dust content and/or old stella…
Massive runaway and walkaway stars. A study of the kinematical imprints of the physical processes governing the evolution and explosion of their binary progenitors
Renzo, M.; Zapartas, E.; de Mink, S. E. +6 more
We perform an extensive numerical study of the evolution of massive binary systems to predict the peculiar velocities that stars obtain when their companion collapses and disrupts the system. Our aim is to (i) identify which predictions are robust against model uncertainties and assess their implications, (ii) investigate which physical processes …
A Decade of Gamma-Ray Bursts Observed by Fermi-LAT: The Second GRB Catalog
Troja, E.; Caraveo, P. A.; Mirabal, N. +120 more
The Large Area Telescope (LAT) aboard the Fermi spacecraft routinely observes high-energy emission from gamma-ray bursts (GRBs). Here we present the second catalog of LAT-detected GRBs, covering the first 10 yr of operations, from 2008 to 2018 August 4. A total of 186 GRBs are found; of these, 91 show emission in the range 30-100 MeV (17 of which …
A year in the life of GW 170817: the rise and fall of a structured jet from a binary neutron star merger
Troja, E.; Piro, L.; van Eerten, H. +6 more
We present the results of our year-long afterglow monitoring of GW 170817, the first binary neutron star merger detected by Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo. New observations with the Australian Telescope Compact Array and the Chandra X-ray Telescope were used to constrain its late-time behavio…
Flare-productive active regions
Toriumi, Shin; Wang, Haimin
Strong solar flares and coronal mass ejections, here defined not only as the bursts of electromagnetic radiation but as the entire process in which magnetic energy is released through magnetic reconnection and plasma instability, emanate from active regions (ARs) in which high magnetic non-potentiality resides in a wide variety of forms. This revi…
The Spur and the Gap in GD-1: Dynamical Evidence for a Dark Substructure in the Milky Way Halo
Conroy, Charlie; Hogg, David W.; Price-Whelan, Adrian M. +1 more
We present a model for the interaction of the GD-1 stellar stream with a massive perturber that naturally explains many of the observed stream features, including a gap and an off-stream spur of stars. The model involves an impulse by a fast encounter, after which the stream grows a loop of stars at different orbital energies. At specific viewing …
The GALAH survey and Gaia DR2: dissecting the stellar disc's phase space by age, action, chemistry, and location
Lewis, Geraint F.; Ting, Yuan-Sen; Casey, Andrew R. +24 more
We use the second data releases of the European Space AgencyGaia astrometric survey and the high-resolution Galactic Archaeology with HERMES (GALAH) spectroscopic survey to analyse the structure of our Galaxy's disc components. With GALAH, we separate the α-rich and α-poor discs (with respect to Fe), which are superposed in both position and veloc…