Search Publications
The 1998 May 2-3 Magnetic Cloud: An Interplanetary ``Highway'' for Solar Energetic Particles Observed with SOHO/ERNE
Riihonen, Esa; Kocharov, Leon; Torsti, Jarmo
Using the Energetic and Relativistic Nuclei and Electron (ERNE) instrument on the Solar and Heliospheric Observatory (SOHO), we have measured the 17-22 MeV proton flux anisotropy during the 1998 May 2-3 solar energetic particle (SEP) event, when SOHO was inside a magnetic cloud associated with a previous coronal mass ejection (CME). The ability of…
Dynamical Mass Estimates for Five Young Massive Stellar Clusters
Brodie, Jean P.; Hunter, Deidre A.; Larsen, Søren S.
We have obtained high-dispersion spectra for four massive star clusters in the dwarf irregular galaxies NGC 4214 and NGC 4449, using the HIRES spectrograph on the Keck I telescope. Combining the velocity dispersions of the clusters with structural parameters and photometry from images taken with the Hubble Space Telescope, we estimate mass-to-ligh…
The Small Blue Straggler Star Population in the Dense Galactic Globular Cluster NGC 6752
Sabbi, E.; Ferraro, F. R.; Rood, R. T. +1 more
We used high-resolution Hubble Space Telescope (HST)-WFPC2 and wide-field ground-based observations to construct a catalog of blue straggler stars (BSSs) that spans the entire radial extent of the globular cluster NGC 6752. The BSS sample is the most extensive ever obtained for this cluster. Although NGC 6752 is a high-density cluster with a large…
The nuclei of comets 126P/IRAS and 103P/Hartley 2
Jorda, L.; Lamy, P.; Groussin, O. +1 more
We report the detection of the nucleus of 126P/IRAS and 103P/Hartley 2 with the Infrared Camera of the Infrared Space Observatory (ISOCAM). 126P/IRAS was observed on 12 November 1996, when it was at r_h=1.71 AU from the Sun and Δ=1.32 AU from the Earth. 103P/Hartley 2 was observed on 5 February 1998, when it was at r_h=1.21 AU from the Sun and Δ=0…
NGC 604, the Scaled OB Association (SOBA) Prototype. I. Spatial Distribution of the Different Gas Phases and Attenuation by Dust
Mas-Hesse, J. M.; Pérez, E.; Maíz-Apellániz, J.
We have analyzed Hubble Space Telescope and ground-based data to characterize the different gas phases and their interaction with the massive young cluster in NGC 604, a giant H II region in M33. The warm ionized gas is made out of two components: a high-excitation, high surface brightness H II surface located at the faces of the molecular clouds …
X-Ray Observations of Stellar Clusters Near the Galactic Center
Yusef-Zadeh, F.; Law, C.
We report the first detection of X-ray emission from the Quintuplet star cluster and compare its X-ray emission to that of the Arches star cluster. Four point sources are significantly detected near the core of the Quintuplet cluster with a total absorption-corrected luminosity of ~1×1033 ergs s-1. Diffuse, thermal emission i…
A Snapshot Survey for Gravitational Lenses among z>=4.0 Quasars. I. The z>5.7 Sample
Strauss, Michael A.; Brinkmann, J.; Fan, Xiaohui +7 more
Over the last few years, the Sloan Digital Sky Survey (SDSS) has discovered several hundred quasars with redshift between 4.0 and 6.4. Including the effects of magnification bias, one expects a priori that an appreciable fraction of these objects are gravitationally lensed. We have used the Advanced Camera for Surveys on the Hubble Space Telescope…
Long-term variability in the X-ray emission of RX J0720.4-3125
de Vries, C. P.; Vink, J.; Verbunt, F. +1 more
We detect a gradual, long-term change in the shape of the X-ray spectrum of the isolated neutron star RX J0720.4-3125, such that the spectrum of the source can no longer be described as a blackbody spectrum. The change is accompanied by an energy-dependent change in the pulse profile. If the X-ray emission is influenced by the magnetic field of th…
Evidence of Magnetic Reconnection along Coronal Hole Boundaries
Doyle, J. G.; Madjarska, M. S.; van Driel-Gesztelyi, L.
The present study reveals for the first time the existence of bidirectional jets, which are a signature of magnetic reconnection, occurring along coronal hole boundaries. The Solar Ultraviolet Measurement of Emitted Radiation spectrometer observations obtained in the N IV 765.15 Å (1.3×105 K) and Ne VIII 770.42 Å (6×105 K) em…
Properties of the background of EPIC-pn onboard XMM-Newton
Freyberg, M. J.; Matsushita, K.; Takahashi, I. +2 more
We have investigated the background properties of EPIC-pn onboard XMM-Newton to establish the background subtraction method. Count rates of the background vary violently by two orders of magnitude at the maximum, while during the most quiet period, these are stable within 8% at a 1σ level. The overall spectrum is dominated by particle events above…