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Discovery of 18 Stars with -3.10 < [Fe/H] < -1.45 in the Sagittarius Dwarf Galaxy
Frebel, Anna; Chiti, Anirudh; Hansen, Kylie Y.
Studies of the early chemical evolution of some larger dwarf galaxies (>107 M⊙) are limited by the small number of stars known at low metallicities in these systems. Here we present metallicities and carbon abundances for eighteen stars with metallicities between -3.08 ≤ [Fe/H] ≤ -1.47 in the Sagittarius dwarf spheroidal g…
Hubble Space Telescope Astrometry in the Orion Nebula Cluster: Census of Low-mass Runaways
Gennaro, Mario; Bellini, Andrea; Strampelli, Giovanni +6 more
We present a catalog of high-precision proper motions in the Orion Nebula Cluster (ONC), based on Treasury Program observations with the Hubble Space Telescope's (HST) ACS/WFC camera. Our catalog contains 2454 objects in the magnitude range of 14.2 < mF775W < 24.7, thus probing the stellar masses of the ONC from ∼0.4 M⊙…
The κ-cookbook: a novel generalizing approach to unify κ-like distributions for plasma particle modelling
Fichtner, H.; Scherer, K.; Lazar, M. +1 more
In the literature different so-called κ-distribution functions are discussed to fit and model the velocity (or energy) distributions of solar wind species, pickup ions, or magnetospheric particles. Here, we introduce a generalized (isotropic) κ-distribution as a 'cookbook', which admits as special cases, or 'recipes', all the other known versions …
Detection of ultra-high-energy gamma rays from the Crab Nebula: physical implications
Aharonian, Felix; Khangulyan, Dmitry; Arakawa, Masanori
The Crab Nebula is an extreme particle accelerator that boosts the energy of electrons up to a few PeV (10^{15} eV), close to the maximum energy allowed theoretically. The physical conditions in the acceleration site and the nature of the acceleration process itself remain highly uncertain. The key information about the highest-energy accelerated …
HST/COS Observations of Quasar Outflows in the 500-1050 Å Rest Frame. III. Four Similar Outflows in 2MASS J1051+1247 with Enough Energy to Be Major Contributors to AGN Feedback
Xu, Xinfeng; Kriss, Gerard A.; Arav, Nahum +2 more
We detect four very energetic outflows in the Hubble Space Telescope/Cosmic Origins Spectrograph spectra of quasar 2MASS J1051+1247 with a combined kinetic luminosity (\dot{E}_{K}) of 1046 erg s-1. Remarkable similarities are seen in these outflows: velocity centroids between 4900 and 5700 km s-1, distances from th…
The Streamer Blowout Origin of a Flux Rope and Energetic Particle Event Observed by Parker Solar Probe at 0.5 au
Luhmann, J. G.; Lario, D.; Arge, C. N. +18 more
The distribution of spacecraft in the inner heliosphere during 2019 March enabled comprehensive observations of an interplanetary coronal mass ejection (ICME) that encountered Parker Solar Probe (PSP) at 0.547 au from the Sun. This ICME originated as a slow (∼311 km s-1) streamer blowout (SBO) on the Sun as measured by the white-light c…
Detection of the Red Supergiant Wind from the Progenitor of Cassiopeia A
Chevalier, Roger A.; Raymond, John C.; Milisavljevic, Dan +4 more
Cassiopeia A (Cas A) is one of the best studied young Galactic supernova remnants. While it provides a rare opportunity to study in detail the remnant of a supernova (SN) type IIb, questions remain regarding the nature of its progenitor, its mass-loss history, and its pre-SN evolution. Here we present an optical investigation of the circumstellar …
HST/COS Observations of Quasar Outflows in the 500-1050 Å Rest Frame. V. Richness of Physical Diagnostics and Ionization Potential-dependent Velocity Shift in PKS J0352-0711
Xu, Xinfeng; Kriss, Gerard A.; Arav, Nahum +2 more
We analyze absorption troughs from two outflows within PKS J0352-0711 (S1 at -1950 km s-1 and S2 at -3150 km s-1) from spectra taken with Hubble Space Telescope/Cosmic Origins Spectrograph, which cover the diagnostic-rich 585-900 Å rest-frame wavelength range. In S2, for the first time we clearly detect absorption troughs fro…
Cyclotron line energy in Hercules X-1: stable after the decay
Harrison, F.; Ducci, L.; Wilms, J. +6 more
We summarize the results of a dedicated effort made between 2012 and 2019 to follow the evolution of the cyclotron line in Her X-1 through repeated NuSTAR observations. The previously observed nearly 20-year-long decay of the cyclotron line energy has ended in 2012: from then on, the pulse-phase-averaged flux-corrected cyclotron line energy has re…
The pulsation properties of λ bootis stars I. the southern TESS sample
Paunzen, E.; Huber, D.; Bedding, T. R. +2 more
We analyse TESS light curves for 70 southern λ Boo stars to identify binaries and to determine which of them pulsate as δ Scuti stars. We find two heartbeat stars and two eclipsing binaries among the sample. We calculate that 81 per cent of λ Boo stars pulsate as δ Sct variables, which is about twice that of normal stars over the same parameter sp…