524 research outputs found
Milli-arcsecond--scale Spectral Properties and Jet Motions in M87
We have combined high resolution VLBI Space Observatory Programme (VSOP) data
at 1.6 and 4.8 GHz with Very Long Baseline Array (VLBA) data at higher
frequencies and with similar resolutions to study the spectral properties of
the core of M87 with milliarcsecond resolution. The VSOP data allow a more
accurate measurement of the turn-over frequency, and hence more reliable
determination of associated physical parameters of the source. Comparison of
the images with previously published images yields no evidence for significant
motion of components in the parsec-scale jet. In addition, the brightness
temperatures obtained from model-fits to the core are well below the inverse
Compton limit, suggesting the radio emission we are observing is not strongly
Doppler boosted.
Colour version on http://www.vsop.isas.jaxa.jp/survey/publications/m87.ps.gzComment: To appear in PASJ VSOP special issue. Minor correction
The Vela Pulsar Wind Nebula at 6cm
Observations using the Australia Telescope Compact Array at a wavelength of 6
cm have uncovered the radio counterpart to the compact X-ray nebula surrounding
the Vela pulsar. Two lobes were found oriented about the spin axis of the
pulsar, starting at the edge of X-ray emission, they extend to three times the
size. The northern lobe has a bright, defined edge and an integrated flux of
0.14 Jy, while the southern lobe of 0.12 Jy is more diffuse.Comment: 4 pages, 3 figures. To appear in "Neutron Stars in Supernova
Remnants" (ASP Conference Proceedings), eds P. O. Slane and B. M. Gaensle
An Analysis of Principal Perceptions of the Primary Teaching Evaluation System Used in Eight U.S. States
This research examines how public school principals in eight U.S. states perceive their teacher evaluation systems which are based on Charlotte Danielson’s Framework for Teaching (FfT). States were selected to represent high, middle, and low scorers in the annual Education Week “Quality Counts” report (Education Week, 2016). 1,142 out of over 8,100 working principals in the eight states responded to an online survey, yielding a response rate of over 14%. Most principals were not satisfied with FfT and found implementing the system too cumbersome. Responses suggested an average of two changes to FfT desired by each principal; few wanted to keep their FfT as is. Targets for improvement included overhauling software used to enter teacher evaluations; eliminating student growth goals and student test scores (VAMs) as part of evaluations; reducing the time and paperwork required; and wanting more training for administrators and teachers on the use of FfT. Some states’ principals wanted to return control over teacher evaluation systems to local school districts. Most respondents agreed that their version of FfT has improved their school’s instructional program, and they prefer the new instrument over their previous evaluation instrument
(Ultra) Precise Astrometry today and tomorrow, with Next-generation Observatories
High precision astrometry provides the foundation to resolve many fundamental
problems in astrophysics. The application of astrometric studies spans a wide
range of fields, and has undergone enormous growth in recent years. This is as
a consequence of the increasing measurement precision and wide applicability,
which is due in turn to the development of new techniques. Forthcoming next
generation observatories have the potential to further increase the astrometric
precision, providing there is a matching improvement in the methods to correct
for systematic errors. The EVN and other observatories are providing
demonstrations of these and are acting as pathfinders for next-generation
telescopes such as the SKA and ngVLA. We will review the perspectives for the
coming facilities and examples of the current state-of-the-art for astrometry.Comment: ADS reference 2018evn..confE..54R from conference
https://pos.sissa.it/34
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