Search Publications
Measurement of Magnetic Helicity Injection and Free Energy Loading into the Solar Corona
Kusano, K.; Sakurai, T.; Yokoyama, T. +1 more
We develop a new methodology that can determine magnetic helicity flux as well as Poynting flux across the photosphere based on magnetograph observation. By applying this method, we study the injection mechanism of magnetic helicity and magnetic free energy into the solar corona. In order to derive the helicity and energy fluxes, first the velocit…
Toward a Mass and Radius Determination of the Nearby Isolated Neutron Star RX J185635-3754
Walter, Frederick M.; Neuhäuser, Ralph; Lattimer, James M. +3 more
We discuss efforts to determine the mass, radius, and surface composition of the nearby compact object RX J185635-3754 from its multiwavelength spectral energy distribution. We compute nonmagnetized model atmospheres and emergent spectra for selected compositions and gravities and discuss efforts to fit existing and new observational data from ROS…
Large-Amplitude X-Ray Outbursts from Galactic Nuclei: A Systematic Survey using ROSAT Archival Data
Brandt, W. N.; Eracleous, Michael; Boller, Th. +1 more
In recent years, luminous X-ray outbursts with variability amplitudes as high as ~400 have been serendipitously detected from a small number of active and inactive galaxies. These outbursts may result from the tidal disruptions of stars by supermassive black holes, as well as accretion disk instabilities. In order to place the first reliable const…
The Luminosity Function of Star Clusters in Spiral Galaxies
Larsen, Søren S.
Star clusters in six nearby spiral galaxies are examined using archive images from the Wide Field Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope (HST). The galaxies have previously been studied from the ground and some of them are known to possess rich populations of ``young massive clusters.'' Comparison with the HST images indica…
Mid-Infrared line diagnostics of active galaxies. A spectroscopic AGN survey with ISO-SWS
Lutz, D.; Genzel, R.; Sturm, E. +5 more
We present medium resolution (R ~ 1500) ISO-SWS 2.4-45 mu m spectra of a sample of 29 galaxies with active nuclei. This data set is rich in fine structure emission lines tracing the narrow line regions and (circum-)nuclear star formation regions, and it provides a coherent spectroscopic reference for future extragalactic studies in the mid-infrare…
Coronal Holes and the High-Speed Solar Wind
Cranmer, Steven R.
Coronal holes are the lowest density plasma components of the Sun's outer atmosphere, and are associated with rapidly expanding magnetic fields and the acceleration of the high-speed solar wind. Spectroscopic and polarimetric observations of the extended corona, coupled with interplanetary particle and radio sounding measurements going back severa…
Doppler Shift Oscillations of Hot Solar Coronal Plasma Seen by SUMER: A Signature of Loop Oscillations?
Solanki, S. K.; Curdt, W.; Innes, D. E. +2 more
We report observations of strongly damped Doppler shift oscillations detected in a flare line, Fe XIX, with the Solar Ultraviolet Measurement of Emitted Radiation spectrometer. Spectra were recorded above an active region at the western limb of the Sun, from lines with formation temperatures ranging from 0.01 to 10 MK. However, the oscillations we…
Hubble Space Telescope and Chandra Monitoring of the Crab Synchrotron Nebula
Gallagher, J. S.; Mori, K.; Hester, J. J. +6 more
We report the results of coordinated Hubble Space Telescope and Chandra observations of the Crab synchrotron nebula. Similar dynamical structures, including equatorial wisps moving outward at ~0.5c, are seen in both passbands. The inner X-ray ring is a variable, irregular structure from which wisps and diffuse emission emerge. The X-ray/visible je…
The White Dwarf Cooling Sequence of the Globular Cluster Messier 4
Rich, R. Michael; Gibson, Brad K.; Stetson, Peter B. +7 more
We present the white dwarf sequence of the globular cluster M4, based on a 123 orbit Hubble Space Telescope exposure, with a limiting magnitude of V~30 and I~28. The white dwarf luminosity function rises sharply for I>25.5, consistent with the behavior expected for a burst population. The white dwarfs of M4 extend to approximately 2.5 mag faint…
XMM-Newton observation of the Lockman Hole. II. Spectral analysis
Hasinger, G.; Mainieri, V.; Rosati, P. +5 more
We present the results of the X-ray spectral analysis of the first deep X-ray survey with the XMM-Newton observatory during Performance Verification. The X-ray data of the Lockman Hole field and the derived cumulative source counts were reported by Hasinger et al. (2001). We restrict the analysis to the sample of 98 sources with more than 70 net c…