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Coronal mass ejections (CMEs) are large eruptions of magnetized plasma from the Sun that play an important role in space weather. The key to understanding the fundamental physics of a CME is measurement of the plasma properties within heliocentric distances of < 20 R ⊙ . Faraday rotation, a radioastronomical propagation measurement, is an extremely valuable diagnostic for studying CMEs. Faraday rotation measurements [RM] contain information on the magnetic field in the medium causing the Faraday rotation. Recent observations of CME-induced Faraday rotation (e.g., Howard et al. in Astrophys. J. 831 , 208, 2016 ; Kooi et al. in Solar Phys. 292 , 56, 2017 ; Bisi et al. in EGU General Assembly Conference Abstracts, 13243, 2017 ) have all been restricted to a single line of sight (LOS) and, therefore, limited to providing estimates of the magnetic field strength. Modeling by Liu et al. (Astrophys. J. 665 , 1439, 2007 ) and Jensen and Russell (Geophys. Res. Lett. 35 , L02103, 2008 ) demonstrated that multiple LOS are necessary to recover the magnetic field strength and structure of the observed CME. We report the first successful observations of Faraday rotation through a CME using multiple lines of sight: 13 LOS across seven target radio fields. We made these radio observations using the Karl G. Jansky Very Large Array (VLA) at 1 − 2 GHz frequencies in the triggered operation mode on 31 July 2015, using a constellation of cosmic radio sources through the solar corona at heliocentric distances of 8.2 − 19.5 R ⊙ . For LOS within 10 R ⊙ , the CME’s contribution to the measured RM was ≈ 0 to −20 rad m −2 , a significant enhancement over the coronal contribution. We assumed a force-free flux-rope structure for the CME’s magnetic field and explored three separate models for the CME’s plasma density: constant density, thin shell, and thick shell. The plasma densities and axial magnetic field strengths for the three models ranged over 5.4 − 6.4 × 10 3  cm −3 and 26 − 35 mG, respectively. Further, using all 13 LOS, we successfully determined the CME’s orientation and helicity.

The influence of aberration on the observational parameters of radio jets and estimates of their physical properties is studied. Aberration distorts the apparent shapes of radio sources. Two identical relativistic jets (whose spectra have maxima) moving approximately along the line of sight could be observed as a compact GPS radio source (jet) and an extended source with a power-law spectrum (counterjet). The apparent flux densities, shapes, and spectra of relativistic radio jets are distorted even when the jets lie in the plane of the sky (across the line of sight). Exact formulas are derived for the estimated physical parameters of relativistic radio jets, taking into account aberration.

The multi-epoch single-survey Planck satellite data have given a rare glimpse into how the radio spectra of active galactic nuclei (AGN) evolve in time. Using Planck and simultaneous auxiliary radio data ranging from 1 GHz to 857 GHz, spectra for 104 bright northern extragalactic radio sources (most of them AGN) have been assembled; in these, the various stages of flare development can be identified. The results are compared with theoretical models describing relativistic jets. Evidence for particularly flat high-frequency radio spectra is found, indicating a harder accelerated electron energy spectrum than usually assumed. A set of sources also shows signs of intrinsic cold dust.

Recent observations of the 1.35-centimeter line emission of water vapor from galactic sources show short-term variability in the spectra of several sources. Two additional sources, Cygnus 1 and NGC 6334N, have been observed, and the spectra of W49 and VY Canis Majoris were measured over a wider range of radial velocity.

The selection effects that apply to the identification of Galactic supernova remnants are reviewed together with the limitations that they impose on statistical studies. Emphasis is given to problems with recent discussions of the number, birthrate, and distribution of remnants within the Galaxy. The distribution of high-surface-brightness remnants is concentrated in a nuclear disk that is even more well-defined than that noted by van den Bergh 1988a,b. Also presented, as an Appendix, are revisions to the catalog of Galactic supernova remnants presented in Green 1988. The revised catalog contains 174 remnants.

UBV photometry is listed for 59 stars near 18 quasars and two unidentified radio sources and for 54 stars near ten Seyfert and four N-type galaxies. Some of the stars are suitable for use as secondary photoelectric standards. Many are faint enough so as to avoid large coincidence corrections for pulse counting with large telescopes. In some fields, the sequences are extensive enough to be used for calibration of photographic monitoring programs. Finding charts are given for all listed stars.

We measured the emission of water vapor at a wavelength of 1.35 centimeters from nine sources with the 120-foot (36.5-meter) Haystack antenna. Eight sources lie within 30 seconds of arc of the hydroxyl sources of 18 centimeters but not all hydroxyl sources produced detectable emission of water vapor. All sources are smaller than 30 seconds of arc in angular diameter, but we resolved at least three separate sources in the Orion Nebula. We do not find that the known hyperfine components are present with the equilibrium intensity distribution.

It is proposed that high-velocity pulsars are produced in extended galactic halos, and possibly in extragalactic space, from primordial (population III) stars. Such a population of neutron stars could provide an explanation for the gamma-ray bursters and would then accommodate the possibility that most bursters are not in the visible parts of galaxies.

The observational classification of active galaxies is reviewed and its likely meaning discussed. A large number of facts and ideas are examined, but a particular set of ideas is stressed as our best hope for a unified phenomenology, as follows. There is only one kind of Active Galactic Nucleus (AGN). The observed variety arises from three degrees of freedom: (1) Dust opacity, which produces the distinction between Type 1 and Type 2 AGN. (2) Viewing angle of a relativistic jet, which produces the distinction between blazars and Type 1 AGN. (3) Duty cycle of activity (i.e., fraction of time spent \"on\") which produces the distinction between radio-loud and radio-quiet AGN. The duty cycle may be related to the mass ofthe spheroidal component ofthe parent galaxy. A fourth degree of freedom is, of course, the overall luminosity. Also, it has recently become clear that there is considerable latitude in the physical condition of gas surrounding the nucleus. For theories of AGN to be presented with a real challenge, we need two things. First, a clear qualitative phenomenology, such as the possibility outlined above, must be decided upon. Second, we need to formulate a quantitative phenomenology.