19 research outputs found
Extreme radio-wave scattering associated with hot stars
We use data on extreme radio scintillation to demonstrate that this
phenomenon is associated with hot stars in the solar neighbourhood. The ionized
gas responsible for the scattering is found at distances up to 1.75pc from the
host star, and on average must comprise 1.E5 distinct structures per star. We
detect azimuthal velocities of the plasma, relative to the host star, up to 9.7
km/s, consistent with warm gas expanding at the sound speed. The circumstellar
plasma structures that we infer are similar in several respects to the cometary
knots seen in the Helix, and in other planetary nebulae. There the ionized gas
appears as a skin around tiny molecular clumps. Our analysis suggests that
molecular clumps are ubiquitous circumstellar features, unrelated to the
evolutionary state of the star. The total mass in such clumps is comparable to
the stellar mass.Comment: 9 pages, 1 figure, to appear in Ap
Constraints on the massive graviton dark matter from pulsar timing and precision astrometry
The effect of a narrow-band isotropic stochastic GW background on pulsar
timing and astrometric measurements is studied. Such a background appears in
some theories of gravity. We show that the existing millisecond pulsar timing
accuracy () strongly constrains possible observational
consequences of theory of massive gravity with spontaneous Lorentz braking
\cite{dtt:2005}, essentially ruling out significant contribution of massive
gravitons to the local dark halo density. The present-day accuracy of
astrometrical measurements () sets less stringent
constraints on this theory.Comment: 4 pages, 1 figure; changes in content, references added, accepted for
publication in PR
Optical study of PKS B1322-110, the intra-hour variable radio source
Observations with the Australia Telescope Compact Array revealed intra-hour variations in the radio source PKS B1322-110 (Bignall et al. 2019). As part of an optical follow-up, we obtained Gemini Hα and Hα continuum (HαC) images of the PKS B1322-110 field. A robust 19 σ detection of PKS B1322- 110 in the Hα−HαC image prompted us to obtain the first optical spectrum of PKS B1322-110. With the Gemini spectrum we determine that PKS B1322-110 is a flat-spectrum radio quasar at a redshift of z = 3.007 ± 0.002. The apparent flux detected in the Hα filter is likely to originate from He ii emission redshifted precisely on the Galactic Hα narrow-band filter. We set upper limits on the emission measure of the Galactic plasma, for various possible cloud geometries