As a result of collective efforts of an Australian–New Zealand VLBI team, the first New Zealand VLBI system was developed, and a series of test observations between New Zealand and Australia ...conducted. The equipment and techniques used to conduct New Zealand's first VLBI observations are discussed and results of work in Australia and New Zealand to obtain fringes and the image of the source (PKS1921-231) are presented. The road map for New Zealand radio-astronomy as well as New Zealand involvement in the SKA is discussed.
•We observed the first central-flash occultation by Pluto.•Modeled Pluto’s upper atmosphere temperature and pressure.•Haze layer alone cannot explain central flash.
In July 2007, we observed a ...stellar occultation by Pluto from three sites in New Zealand and Australia. From these occultation observations, we find that Pluto’s atmospheric pressure is still at the increased level measured in 2002 and 2006 with a pressure at a radius of 1275km of 2.09±0.09μbar. One of the sites, Mt. John Observatory, was ∼70km from the shadow center and we recorded the first central-flash occultation by Pluto. We carried out a dual-wavelength observation from this site with two different cameras using filtered high-time resolution observations in the visible from the one-meter telescope at Mt. John Observatory. From our central-flash observations, we find the elliptical shape that best matches the data corresponds to a nearly prolate atmosphere with an ellipticity of 0.09. The flux observed in the central-flash data can be fit equally well with either a haze layer or a thermal gradient in the altitudes probed by the occultation. However, the star light contributing to the central-flash occultation for the haze layer model would pass through a radius of 1130km from Pluto’s center. Given our current best estimate of Pluto’s surface radius is greater than 1151km (Tholen, D.J., Buie, M.W. 1997. Bulk properties of Pluto and Charon. In: Stern, S.A., Tholen, D.J. (Eds.), Pluto and Charon. The University of Arizona Press), we prefer the thermal gradient solution or a combination of haze and thermal gradient to explain the occultation light curves.
Using data from the Complete Nearby (redshift z _host < 0.02) sample of Type Ia Supernovae (CNIa0.02), we find a linear relation between two parameters derived from the B − V color curves of Type Ia ...supernovae: the color stretch s _BV and the rising color slope ${s}_{0}^{* }(B-V)$ after the peak, and this relation applies to the full range of s _BV . The s _BV parameter is known to be tightly correlated with the peak luminosity, especially for fast decliners (dim Type Ia supernovae), and the luminosity correlation with s _BV is markedly better than with the classic light-curve width parameters such as Δ m _15 ( B ). Thus, our new linear relation can be used to infer peak luminosity from ${s}_{0}^{* }$ . Unlike s _BV (or Δ m _15 ( B )), the measurement of ${s}_{0}^{* }(B-V)$ does not rely on a well-determined time of light-curve peak or color maximum, making it less demanding on the light-curve coverage than past approaches.
Astrometric positions of radio-emitting active galactic nuclei (AGNs) can be determined with sub-milliarcsec accuracy using very long baseline interferometry (VLBI). The usually small apparent proper ...motion of distant extragalactic targets allow us to realize the fundamental celestial reference frame with VLBI observations. However, long-term astrometric monitoring may reveal extreme changes in some AGN positions. Using new VLBI observations in 2018-2021, we show here that four extragalactic radio sources (3C48, CTA21, 1144+352, 1328+254) have a dramatic shift in their positions by 20-130 milliarcsec over two decades. For all four sources, the apparent positional shift is caused by their radio structure change.
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