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Searching for Strong Gravitational Lenses
Hezaveh, Yashar; Courbin, Frédéric; Leung, Calvin +9 more
Strong gravitational lenses provide unique laboratories for cosmological and astrophysical investigations, but they must first be discovered - a task that can be met with significant contamination by other astrophysical objects and asterisms. Here we review strong lens searches, covering various sources (quasars, galaxies, supernovae, FRBs, GRBs, …
Herbig Stars
Waters, L. B. F. M.; Brittain, Sean D.; Kamp, Inga +2 more
Herbig Ae/Be stars are young contracting stars on the radiative track in the HR diagram on their way to the main sequence. These stars provide a valuable link between high and low mass stars. Here we review the progress that has been made in our understanding of these fascinating objects and their disks since the last major review on this topic pu…
Extreme Solar Events: Setting up a Paradigm
Notsu, Yuta; Maehara, Hiroyuki; Dalla, Silvia +17 more
The Sun is magnetically active and often produces eruptive events on different energetic and temporal scales. Until recently, the upper limit of such events was unknown and believed to be roughly represented by direct instrumental observations. However, two types of extreme events were discovered recently: extreme solar energetic particle events o…
Navigation and Orbit Estimation for New Horizons' Arrokoth Flyby: Overview, Results and Lessons Learned
Weaver, Harold A.; Kavelaars, J. J.; Gwyn, Stephen D. J. +18 more
The New Horizons mission performed a successful flyby of Arrokoth, a distant Kuiper-Belt Object, on January 1, 2019, representing the farthest planetary encounter to date. The navigation strategy and performance required to deliver the spacecraft to the desired flyby target were driven by a number of challenges including those related to Arrokoth'…
Old-Aged Primary Distance Indicators
Salaris, Maurizio; Matsunaga, Noriyuki; Beaton, Rachael L. +8 more
Old-aged stellar distance indicators are present in all Galactic structures (halo, bulge, disk) and in galaxies of all Hubble types and, thus, are immensely powerful tools for understanding our Universe. Here we present a comprehensive review for three primary standard candles from Population II: (i) RR Lyrae type variables (RRL), (ii) type II Cep…
Modern Geometric Methods of Distance Determination
Pietrzyński, Grzegorz; Thévenin, Frédéric; Falanga, Maurizio +2 more
Building a 3D picture of the Universe at any distance is one of the major challenges in astronomy, from the nearby Solar System to distant Quasars and galaxies. This goal has forced astronomers to develop techniques to estimate or to measure the distance of point sources on the sky. While most distance estimates used since the beginning of the 20t…
Data Timing, Time Transfer and On-board Clock Monitoring for Space Astrometry with Gaia
Butkevich, Alexey G.; Klioner, Sergei A.; Geyer, Robin +1 more
The paper discusses the problematic of data timing in the framework of the space astrometry mission Gaia. For various reasons related both to astrometry and to the measuring principles of the Gaia instrument it is mandatory to assign a highly stable and accurate time tag for each observational point. For this purpose Gaia has a Rb clock on board. …