Search Publications
What Are the Hot R Coronae Borealis Stars?
De Marco, Orsola; Clayton, Geoffrey C.; Clark, J. S. +3 more
We investigate the evolutionary status of four stars: V348 Sgr, DY Cen, and MV Sgr in the Galaxy and HV 2671 in the LMC. These stars have in common random deep declines in visual brightness, which are characteristic of R Coronae Borealis (RCB) stars. RCB stars are typically cool hydrogen-deficient supergiants. The four stars studied in this paper …
High-resolution observations and mass modelling of the CLASS gravitational lens B1152+199
Biggs, A. D.; Browne, I. W. A.; Wilkinson, P. N. +5 more
We present a series of high-resolution radio and optical observations of the CLASS gravitational lens system B1152+199 obtained with the Multi-Element Radio-Linked Interferometer Network, Very Long Baseline Array and Hubble Space Telescope . Based on the milliarcsecond-scale substructure of the lensed radio components and precise optical astrometr…
The Galaxy Octopole Moment as a Probe of Weak-Lensing Shear Fields
Natarajan, Priyamvada; Goldberg, David M.
In this paper, we introduce the octopole moment of the light distribution in galaxies as a probe of the weak-lensing shear field. While traditional ellipticity estimates of the local shear derived from the quadrupole moment are limited by the width of the intrinsic ellipticity distribution of background galaxies, the dispersion in the intrinsic oc…
On electron acceleration at CIR related shock waves
Mann, G.; Keppler, E.; Roelof, E. C. +1 more
The interaction of fast and slow speed solar wind streams leads to the formation of so-called corotating interaction regions (CIRs) in the heliosphere. These CIRs are often associated with shock waves, at which electrons are accelerated as observed by the Ulysses spacecraft. A correlation between the ratio of energetic electron fluxes at the cross…
Nuclear Stellar Disks in Spiral Galaxies
Scarlata, C.; Stiavelli, M.; Morelli, L. +4 more
We report evidence for nuclear stellar disks in three early-type spirals, namely, NGC 1425, NGC 3898, and NGC 4698, revealed by Wide Field Planetary Camera 2 F606W images out of a sample of 38 spiral galaxies, selected from the Hubble Space Telescope data archive. Adopting the photometric method introduced by Scorza & Bender, we derived their …
The status of Galactic field λ Bootis stars in the post-Hipparcos era
Kamp, I.; Paunzen, E.; Iliev, I. Kh. +1 more
The λ Bootis stars are Population I, late B- to early F-type stars, with moderate to extreme (up to a factor 100) surface underabundances of most Fe-peak elements and solar abundances of lighter elements (C, N, O and S). To put constraints on the various existing theories that try to explain these peculiar stars, we investigate the observational p…
On the origin of radial magnetic fields in the heliosphere
Gosling, J. T.; Skoug, R. M.
Numerous examples of events wherein the heliospheric magnetic field (HMF) measured at a fixed point in space remains nearly radial for many hours have been reported in the literature. Such events are observed both in the normal solar wind and within disturbances driven by coronal mass ejections (CMEs). A very large fraction of these extended, near…
Timing analysis of the isolated neutron star RX J0720.4-3125
Cropper, Mark; Zavlin, Vyacheslav E.; Haberl, Frank +4 more
We present a combined analysis of XMM-Newton, Chandra and ROSAT observations of the isolated neutron star RX J0720.4-3125, spanning a total period of ~7yr. We develop a maximum likelihood periodogram for our analysis based on the ΔC statistic and the maximum likelihood method, which are appropriate for the treatment of sparse event lists. Our resu…
Probing the mass loss history of carbon stars using CO line and dust continuum emission
Ryde, N.; Olofsson, H.; Schöier, F. L.
An extensive modelling of CO line emission from the circumstellar envelopes around a number of carbon stars is performed. By combining radio observations and infrared observations obtained by ISO the circumstellar envelope characteristics are probed over a large radial range. In the radiative transfer analysis the observational data are consistent…
Including stereoscopic information in the reconstruction of coronal magnetic fields
Wiegelmann, T.; Neukirch, T.
We present a method to include stereoscopic information about the three-dimensional structure of flux tubes into the reconstruction of the coronal magnetic field. Due to the low plasma beta in the corona we can assume a force-free magnetic field, with the current density parallel to the magnetic field lines. Here we use linear force-free fields fo…