Search Publications
The Needles in the Haystack Survey: searching for X-ray-selected normal galaxies
Georgantopoulos, I.; Plionis, M.; Georgakakis, A. E. +2 more
In this paper we present the first results from an ongoing serendipitous survey aiming to identify X-ray-selected `normal' galaxies [i.e. not dominated by active galactic nuclei (AGNs)] by combining archival XMM-Newton data with the Sloan Digital Sky Survey. In the first 4.5 deg2 of this program, we have identified a total of 11 `normal…
Abundances of Neutron-Capture Elements in the Hot Extreme Helium Stars V1920 Cygni and HD 124448
Rao, N. Kameswara; Lambert, David L.; Pandey, Gajendra +1 more
Analysis of Hubble Space Telescope Space Telescope Imaging Spectrograph ultraviolet spectra of two hot extreme helium (EHe) stars, V1920 Cyg and HD 124448, provides the first measurements of abundances of neutron-capture elements for EHe stars. Although the two stars have similar abundances for elements up through the iron group, they differ strik…
The XMM-Newton/2dF survey - III. Comparison between optical and X-ray cluster detection methods
Georgakakis, A.; Georgantopoulos, I.; Plionis, M. +4 more
We directly compare X-ray and optical techniques of cluster detection by combining Sloan Digital Sky Survey photometric data with a wide-field (~1.6 deg2) XMM-Newton survey near the North Galactic Pole region. The optical cluster detection procedure is based on merging two independent selection methods: a smoothing + percolation techniq…
GIRAFFE multiple integral field units at VLT: A unique tool to recover velocity fields of distant galaxies
Flores, H.; Hammer, F.; Puech, M. +2 more
The GIRAFFE spectrograph is unique in providing the integral field spectroscopy of fifteen distant galaxies at the same time. It has been successfully implemented at the second VLT unit within the FLAMES facility. We present GIRAFFE observations acquired during the Guaranteed Time Observation of the Paris Observatory, using total exposure times ra…
CLUSTER observations of lower hybrid waves excited at high altitudes by electromagnetic whistler mode signals from the HAARP facility
Pickett, J. S.; Inan, U. S.; Platino, M. +3 more
We report new observations from the CLUSTER spacecraft of strong excitation of lower hybrid (LH) waves by electromagnetic (EM) whistler mode waves at altitudes >=20,000 km outside the plasmasphere. Previous observations of this phenomenon occurred at altitudes <=7000 km. The excitation mechanism appears to be linear mode coupling in the pres…
Cluster observations in the magnetotail during sudden and quasiperiodic solar wind variations
Balogh, A.; Lucek, E.; Kim, K. -H. +5 more
A clear bipolar (negative/positive) signature in the Ey component was observed by three spacecraft on Cluster in the magnetotail during the passage of a solar wind discontinuity on October 11, 2001 (day 284), which caused a sudden commencement (sc) on the ground. The positive Ey perturbation was accompanied by the northward/d…
Short-Period Variable Be Stars Discovered or Confirmed through Self-Correlation Analysis of Hipparcos Epoch Photometry
Percy, John R.; Harlow, Christopher D. W.; Wu, Alice P. S.
We have surveyed 277 bright Be stars for short-period (0.2-2 day) photometric variability using self-correlation analysis of Hipparcos epoch photometry. This extends the work of Percy et al.; the methods are as described there. We report the discovery, timescale, and amplitude of short-period variability in: HD 7636 (V764 Cas), HD 11606 (V777 Cas)…
A cometary neutral gas simulator for gas dynamic sensor and mass spectrometer calibration
Wurz, P.; Altwegg, K.; Balsiger, H. +6 more
The goal of the European Space Agency's Rosetta mission is a rendezvous with the Edgewood-Kuiper Belt comet 67P/Churyumov-Gerasimenko. After the initial encounter the spacecraft will accompany the comet for one to two years toward the Sun and throughout the perihelion passage. For the calibration of the onboard comet mass spectrometers a calibrati…
The Phoenix Deep Survey: the radio properties of the hard X-ray-selected sample
Georgakakis, A.; Sullivan, M.; Mobasher, B. +3 more
The radio properties of hard (2-8 keV) X-ray-selected sources are explored by combining a single 50-ks XMM-Newton pointing with the ultradeep and homogeneous Phoenix radio (1.4-GHz) survey. A total of 43 sources are detected above the X-ray flux limit fX(2-8 keV) = 7.7 × 10-15 erg s-1 cm-2, with 14 of th…
Numerical Magnetohydrodynamic Experiments for Testing the Physical Mechanisms of Coronal Mass Ejections Acceleration
Liu, Yang; Feng, Xueshang; Zhang, T. X. +3 more
Analysis of observations from both space-borne (LASCO/SOHO, Skylab and Solar Maximum Mission) and ground-based (Mauna Loa Observatory) instruments show that there are two types of coronal mass ejections (CMEs), fast CMEs and slow CMEs. Fast CMEs start with a high initial speed, which remains more or less constant, while slow CMEs start with a low …