Search Publications
γ-ray polarization constraints on Planck scale violations of special relativity
Ubertini, Pietro; Celotti, Annalisa; Maccione, Luca +2 more
Using recent polarimetric observations of the Crab Nebula in the hard X-ray band by INTEGRAL, we show that the absence of vacuum birefringence effects constrains O(E/M) Lorentz violation in QED to the level |ξ|<9×10-10 at 3σ CL, tightening by more than 3 orders of magnitude previous constraints. We show that planned X-ray polarimeter…
Long-Term Variability in the Optical Spectrum of the Seyfert Galaxy NGC 2992
Crenshaw, D. M.; Dietrich, M.; Trippe, M. L. +1 more
New spectra of NGC 2992 from the Cerro Tololo Inter-American Observatory show that this nearby active galactic nucleus changed its type classification to a Seyfert 2 in 2006. It was originally classified as a Seyfert 1.9, and has been previously seen as a Seyfert 1.5 with strong broad Hα emission. A comparison of the reddening and equivalent hydro…
The Radiometric and Pointing Calibration of SECCHI COR1 on STEREO
Thompson, W. T.; Reginald, N. L.
COR1 is the innermost coronagraph of the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) instrument suite aboard the twin Solar Terrestrial Relations Observatory (STEREO) spacecraft. The paired COR1 telescopes observe the white-light K-corona from 1.4 to 4 solar radii in a waveband 22.5 nm wide centered on the Hα line at 656 n…
Proto-Planetary Nebulae as Explosions: Bullets versus Jets and Nebular Shaping
Frank, Adam; Balick, Bruce; Blackman, Eric G. +3 more
Many proto-planetary nebulae (PPNs) appear as narrow collimated structures sometimes showing multiple, roughly aligned lobes. In addition, many PPN flows have been shown to have short acceleration times. In this paper we explore whether jet or "bullet" (a massive clump) models fit the observations of individual collimated lobes adequately by compa…
The defining characteristics of intermediate polars - the case of three-candidate systems
Ramsay, Gavin; Wheatley, Peter J.; Hakala, Pasi +2 more
Intermediate polars (IPs) are a group of cataclysmic variables (CVs) which are thought to contain white dwarfs which have a magnetic field strength in the range ~0.1-10MG. A significant fraction of the X-ray sources detected in recent deep surveys has been postulated to consist of IPs. Until now two of the defining characteristics of IPs have been…
Morphology and dynamics of Venus oxygen airglow from Venus Express/Visible and Infrared Thermal Imaging Spectrometer observations
Hueso, R.; Sánchez-Lavega, A.; Drossart, P. +5 more
Images obtained by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS)-M channel instrument onboard Venus Express have been used to retrieve maps and apparent motions of the O2 (1Δ) infrared nightglow on Venus at 1.27 µm. The nightglow distribution is highly inhomogeneous with the regions of brightest emissio…
Evolution of the flaring active region NOAA 10540 as a sequence of nonlinear force-free field extrapolations
Wiegelmann, T.; Thalmann, J. K.
Context: The solar corona is structured by magnetic fields. As direct measurements of the coronal magnetic field are not routinely available, it is extrapolated from photospheric vector magnetograms. When magnetic flux emerges from below the solar surface and expands into the corona, the coronal magnetic field is destabilized, leading to explosive…
Dynamics of Saturn's South Polar Vortex
Fletcher, Leigh N.; West, Robert A.; Porco, Carolyn C. +9 more
We present observations of Saturn's south polar vortex (SPV) showing that it shares some properties with terrestrial hurricanes: cyclonic circulation, warm central region (the eye) surrounded by a ring of high clouds (the eye wall), and convective clouds outside the eye. The polar location and the absence of an ocean are major differences. It also…
Temporal variations in the Sun's rotational kinetic energy
Antia, H. M.; Gough, D. O.; Chitre, S. M.
Aims: We study the variation of the angular momentum and the rotational kinetic energy of the Sun, and associated variations in the gravitational multipole moments, on a timescale of the solar cycle.
Methods: These quantities are determined by inverting helioseismic rotational splitting data obtained by the Global Oscillation Network Group and…
Variations of the solar granulation motions with height using the GOLF/SoHO experiment
Jiménez-Reyes, S. J.; García, R. A.; Mathur, S. +2 more
Context: Below 1 mHz, the power spectrum of helioseismic velocity measurements is dominated by the spectrum of convective motions (granulation and supergranulation) and it is difficult to detect the low-order acoustic modes and gravity modes.
Aims: We attempt to understand more clearly the behavior of solar granulation as a function of observi…