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- ItemMassive stars in extremely metal-poor galaxies: a window into the past(Dordrecht [u.a.] : Springer Science + Business Media B.V, 2021) Garcia, Miriam; Evans, Christopher J.; Bestenlehner, Joachim M.; Bouret, Jean Claude; Castro, Norberto; Cerviño, Miguel; Fullerton, Alexander W.; Gieles, Mark; Herrero, Artemio; de Koter, Alexander; Lennon, Daniel J.; van Loon, Jacco Th.; Martins, Fabrice; de Mink, Selma E.; Najarro, Francisco; Negueruela, Ignacio; Sana, Hugues; Simón-Díaz, Sergio; Szécsi, Dorottya; Tramper, Frank; Vink, Jorick S.; Wofford, AidaCosmic history has witnessed the lives and deaths of multiple generations of massive stars, all of them invigorating their host galaxies with ionizing photons, kinetic energy, fresh material, and stellar-mass black holes. Ubiquitous engines as they are, astrophysics needs a good understanding of their formation, evolution, properties and yields throughout the history of the Universe, and with decreasing metal content mimicking the environment at the earliest epochs. Ultimately, a physical model that could be extrapolated to zero metallicity would enable tackling long-standing questions such as “What did the first, very massive stars of the Universe look like?” or “What was their role in the re-ionization of the Universe?” Yet, most of our knowledge of metal-poor massive stars is drawn from one single point in metallicity. Massive stars in the Small Magellanic Cloud (SMC, ∼1/5Z⊙ ) currently serve as templates for low-metallicity objects in the early Universe, even though significant differences with respect to massive stars with poorer metal content have been reported. This White Paper summarizes the current knowledge on extremely (sub-SMC) metal poor massive stars, highlighting the most outstanding open questions and the need to supersede the SMC as standard. A new paradigm can be built from nearby extremely metal-poor galaxies that make a new metallicity ladder, but massive stars in these galaxies are out of reach to current observational facilities. Such a task would require an L-size mission, consisting of a 10m-class space telescope operating in the optical and the ultraviolet ranges. Alternatively, we propose that ESA unites efforts with NASA to make the LUVOIR mission concept a reality, thus continuing the successful partnership that made the Hubble Space Telescope one of the greatest observatories of all time.
- ItemExoClock project: an open platform for monitoring the ephemerides of Ariel targets with contributions from the public(Dordrecht [u.a.] : Springer Science + Business Media B.V, 2021) Kokori, Anastasia; Tsiaras, Angelos; Edwards, Billy; Rocchetto, Marco; Tinetti, Giovanna; Wünsche, Anaël; Paschalis, Nikolaos; Agnihotri, Vikrant Kumar; Bachschmidt, Matthieu; Bretton, Marc; Caines, Hamish; Caló, Mauro; Casali, Roland; Crow, Martin; Dawes, Simon; Deldem, Marc; Deligeorgopoulos, Dimitrios; Dymock, Roger; Evans, Phil; Falco, Carmelo; Ferratfiat, Stephane; Fowler, Martin; Futcher, Stephen; Guerra, Pere; Hurter, Francois; Jones, Adrian; Kang, Wonseok; Kim, Taewoo; Lee, Richard; Lopresti, Claudio; Marino, Antonio; Mallonn, Matthias; Mortari, Fabio; Morvan, Mario; Mugnai, Lorenzo V.; Nastasi, Alessandro; Perroud, Valère; Pereira, Cédric; Phillips, Mark; Pintr, Pavel; Raetz, Manfred; Regembal, Francois; Savage, John; Sedita, Danilo; Sioulas, Nick; Strikis, Iakovos; Thurston, Geoffrey; Tomacelli, Andrea; Tomatis, AlbertoThe Ariel mission will observe spectroscopically around 1000 exoplanets to further characterise their atmospheres. For the mission to be as efficient as possible, a good knowledge of the planets’ ephemerides is needed before its launch in 2028. While ephemerides for some planets are being refined on a per-case basis, an organised effort to collectively verify or update them when necessary does not exist. In this study, we introduce the ExoClock project, an open, integrated and interactive platform with the purpose of producing a confirmed list of ephemerides for the planets that will be observed by Ariel. The project has been developed in a manner to make the best use of all available resources: observations reported in the literature, observations from space instruments and, mainly, observations from ground-based telescopes, including both professional and amateur observatories. To facilitate inexperienced observers and at the same time achieve homogeneity in the results, we created data collection and validation protocols, educational material and easy to use interfaces, open to everyone. ExoClock was launched in September 2019 and now counts over 140 participants from more than 15 countries around the world. In this release, we report the results of observations obtained until the 15h of April 2020 for 120 Ariel candidate targets. In total, 632 observations were used to either verify or update the ephemerides of 84 planets. Additionally, we developed the Exoplanet Characterisation Catalogue (ECC), a catalogue built in a consistent way to assist the ephemeris refinement process. So far, the collaborative open framework of the ExoClock project has proven to be highly efficient in coordinating scientific efforts involving diverse audiences. Therefore, we believe that it is a paradigm that can be applied in the future for other research purposes, too.
- ItemThe high energy Universe at ultra-high resolution: the power and promise of X-ray interferometry(Dordrecht [u.a.] : Springer Science + Business Media B.V, 2021) Uttley, Phil; Hartog, Roland den; Bambi, Cosimo; Barret, Didier; Bianchi, Stefano; Bursa, Michal; Cappi, Massimo; Casella, Piergiorgio; Cash, Webster; Costantini, Elisa; Dauser, Thomas; Trigo, Maria Diaz; Gendreau, Keith; Grinberg, Victoria; Herder, Jan-Willem den; Ingram, Adam; Kara, Erin; Markoff, Sera; Mingo, Beatriz; Panessa, Francesca; Poppenhäger, Katja; Różańska, Agata; Svoboda, Jiri; Wijers, Ralph; Willingale, Richard; Wilms, Jörn; Wise, MichaelWe propose the development of X-ray interferometry (XRI), to reveal the Universe at high energies with ultra-high spatial resolution. With baselines which can be accommodated on a single spacecraft, XRI can reach 100 μ as resolution at 10 Å (1.2 keV) and 20 μ as at 2 Å (6 keV), enabling imaging and imaging-spectroscopy of (for example) X-ray coronae of nearby accreting supermassive black holes (SMBH) and the SMBH ‘shadow’; SMBH accretion flows and outflows; X-ray binary winds and orbits; stellar coronae within ∼100 pc and many exoplanets which transit across them. For sufficiently luminous sources XRI will resolve sub-pc scales across the entire observable Universe, revealing accreting binary SMBHs and enabling trigonometric measurements of the Hubble constant with X-ray light echoes from quasars or explosive transients. A multi-spacecraft ‘constellation’ interferometer would resolve well below 1 μ as, enabling SMBH event horizons to be resolved in many active galaxies and the detailed study of the effects of strong field gravity on the dynamics and emission from accreting gas close to the black hole.
- ItemThe STIX Aspect System (SAS): The Optical Aspect System of the Spectrometer/Telescope for Imaging X-Rays (STIX) on Solar Orbiter(Dordrecht [u.a.] : Springer Science + Business Media B.V, 2020) Warmuth, A.; Önel, H.; Mann, G.; Rendtel, J.; Strassmeier, K.G.; Denker, C.; Hurford, G.J.; Krucker, S.; Anderson, J.; Bauer, S.-M.; Bittner, W.; Dionies, F.; Paschke, J.; Plüschke, D.; Sablowski, D.P.; Schuller, F.; Senthamizh Pavai, V.; Woche, M.; Casadei, D.; Kögl, S.; Arnold, N.G.; Gröbelbauer, H.-P.; Schori, D.; Wiehl, H.J.; Csillaghy, A.; Grimm, O.; Orleanski, P.; Skup, K.R.; Bujwan, W.; Rutkowski, K.; Ber, K.The Spectrometer/Telescope for Imaging X-rays (STIX) is a remote sensing instrument on Solar Orbiter that observes the hard X-ray bremsstrahlung emission of solar flares. This paper describes the STIX Aspect System (SAS), a subunit that measures the pointing of STIX relative to the Sun with a precision of ±4′′, which is required to accurately localize the reconstructed X-ray images on the Sun. The operating principle of the SAS is based on an optical lens that images the Sun onto a plate that is perforated by small apertures arranged in a cross-shaped configuration of four radial arms. The light passing through the apertures of each arm is detected by a photodiode. Variations of spacecraft pointing and of distance from the Sun cause the solar image to move over different apertures, leading to a modulation of the measured lightcurves. These signals are used by ground analysis to calculate the locations of the solar limb, and hence the pointing of the telescope.
- ItemVortex Motions in the Solar Atmosphere: Definitions, Theory, Observations, and Modelling(Dordrecht [u.a.] : Springer Science + Business Media B.V, 2023) Tziotziou, K.; Scullion, E.; Shelyag, S.; Steiner, O.; Khomenko, E.; Tsiropoula, G.; Canivete Cuissa, J.R.; Wedemeyer, S.; Kontogiannis, I.; Yadav, N.; Kitiashvili, I. N.; Skirvin, S.J.; Dakanalis, I.; Kosovichev, A.G.; Fedun, V.Vortex flows, related to solar convective turbulent dynamics at granular scales and their interplay with magnetic fields within intergranular lanes, occur abundantly on the solar surface and in the atmosphere above. Their presence is revealed in high-resolution and high-cadence solar observations from the ground and from space and with state-of-the-art magnetoconvection simulations. Vortical flows exhibit complex characteristics and dynamics, excite a wide range of different waves, and couple different layers of the solar atmosphere, which facilitates the channeling and transfer of mass, momentum and energy from the solar surface up to the low corona. Here we provide a comprehensive review of documented research and new developments in theory, observations, and modelling of vortices over the past couple of decades after their observational discovery, including recent observations in Hα, innovative detection techniques, diverse hydrostatic modelling of waves and forefront magnetohydrodynamic simulations incorporating effects of a non-ideal plasma. It is the first systematic overview of solar vortex flows at granular scales, a field with a plethora of names for phenomena that exhibit similarities and differences and often interconnect and rely on the same physics. With the advent of the 4-m Daniel K. Inouye Solar Telescope and the forthcoming European Solar Telescope, the ongoing Solar Orbiter mission, and the development of cutting-edge simulations, this review timely addresses the state-of-the-art on vortex flows and outlines both theoretical and observational future research directions.