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Physical conditions and chemical abundances of the variable planetary nebula IC 4997
Parthasarathy, M.; Danehkar, A.
The planetary nebula (PN) IC 4997 is one of a few rapidly evolving objects with variable brightness and nebular emission around a hydrogen-deficient star. In this study, we have determined the physical conditions and chemical abundances of this object using the collisionally excited lines (CELs) and optical recombination lines (ORLs) measured from…
Astrometry of variable compact radio sources: a search for Galactic black hole X-ray binaries
Maccarone, T. J.; Heinke, C. O.; Miller-Jones, J. C. A. +8 more
We use the Very Long Baseline Array to conduct high precision astrometry of a sample of 33 compact, flat spectrum, variable radio sources in the direction of the Galactic plane (Becker et al. 2010). Although Becker et al. (2010) ruled out a few potential scenarios for the origin of the radio emission, the study could not rule out that these source…
The Energetics of the Central Engine in the Powerful Quasar 3C 298
Schneider, Donald P.; Zeimann, Gregory R.; Hill, Gary J. +3 more
The compact steep-spectrum radio source 3C 298 (redshift of 1.44) has the largest 178 MHz luminosity in the Third Cambridge Revised Catalogue (3CR); its radio lobes are among the most luminous in the universe. The plasma state of the radio lobes is modeled with the aid of interferometric radio observations (in particular, the new Low Frequency Arr…
Signatures of extended discs and outflows in the circumgalactic medium using the Q0107 quasar triplet
Tejos, Nicolas; Beckett, Alexander; Morris, Simon L. +3 more
We use H I absorption along the lines-of-sight to the Q0107 quasar triplet in order to model potential disc and outflow structures in the circumgalactic medium of intervening galaxies at z ≲ 1, as well as the intergalactic medium on scales of up to a few virial radii. We consider a sample of twelve isolated galaxies in the Q0107 field with positio…
The Young Embedded Disk L1527 IRS: Constraints on the Water Snowline and Cosmic-Ray Ionization Rate from HCO+ Observations
Bergin, Edwin A.; Harsono, Daniel; Tobin, John J. +3 more
The water snowline in circumstellar disks is a crucial component in planet formation, but direct observational constraints on its location remain sparse owing to the difficulty of observing water in both young embedded and mature protoplanetary disks. Chemical imaging provides an alternative route to locate the snowline, and HCO+ isotop…
Searching for outbursts in the ground-based photometry of 67P/Churyumov-Gerasimenko
Gardener, Daniel; Snodgrass, Colin; Ligier, Nicolas
67P/Churyumov-Gerasimenko is a Jupiter-family comet that was the target of the Rosetta mission, the first mission to successfully orbit and land a probe on a comet. This mission was accompanied by a large ground-based observing campaign. We have developed a pipeline to calibrate and measure photometry of comet 67P during its 2016 perihelion passag…
Evidence of the Alfvén Transition Layer and Particle Precipitation in the Cusp Region: 3D Global PIC Simulation of the Solar Wind-Earth Magnetosphere Interaction
Lembège, B.; Cai, D. S.; Ekawati, Sri
A transition layer, named the Alfvénic transition layer (or ATL), has been clearly evidenced near the outer boundary of the cusp by experimental observations from the Cluster mission. This layer characterized by a local value of Log M A ~ 1, where M A is the Alfvén Mach number, allows the bulk flow to transit from super-Alfvé…
Solar Wind Electron Pressure Gradients, Suprathermal Spectral Hardness, and Strahl Localization Organized by Single-point Measurements of 0.1 nV m-1 Ambipolar E ∥
Scudder, Jack D.
A new, fast technique to measure the solar wind's ambipolar E ∥ routinely with 10% precision and accuracy is demonstrated using 4 yr of 1 au electron data from the Wind 3DP experiment. The 3DP electron instrument duty cycle determines E ∥ ≃ 0.1 nV m-1 from a single spectrum over much shorter time intervals than tho…
A Kepler K2 view of subdwarf A-type stars
Mösenlechner, G.; Paunzen, E.; Pelisoli, I. +3 more
Context. The spectroscopic class of subdwarf A-type (sdA) stars has come into focus in recent years because of their possible link to extremely low-mass white dwarfs, a rare class of objects resulting from binary evolution. Although most sdA stars are consistent with metal-poor halo main-sequence stars, the formation and evolution of a fraction of…
Estimating spectral photometric properties of the 67P/Churyumov-Gerasimenko comet nucleus
Statella, Thiago