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Hubble Space Telescope Imaging of a Peculiar Stellar Complex in NGC 6946
Elmegreen, Bruce G.; Hodge, Paul W.; Larsen, Søren S. +4 more
The stellar populations in a stellar complex in NGC 6946 are analyzed on images taken with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. The complex is peculiar because of its very high density of stars and clusters and semicircular shape. Its physical dimensions are about the same as for the local Gould Belt, but the stel…
April 2000 magnetic storm: Solar wind driver and magnetospheric response
Pulkkinen, Tuija I.; Palmroth, Minna; Pulkkinen, Antti +4 more
On 4 April 2000, a coronal mass ejection (CME) took place close to the western limb of the Sun. The shock front of the CME hit the Earth's magnetosphere on 6 April. A strong interplanetary southward BZ event in the sheath region caused a magnetic storm that was the second strongest in the year 2000 if quantified by the peak of the Dst i…
The Unusually Long Duration Gamma-Ray Burst GRB 000911: Discovery of the Afterglow and Host Galaxy
Axelrod, T. S.; Price, P. A.; Harrison, F. A. +18 more
Of all the well-localized gamma-ray bursts, GRB 000911 has the longest duration (T90=500 s) and ranks in the top 1% of BATSE bursts for fluence. Here we report the discovery of the afterglow of this unique burst. In order to simultaneously fit our radio and optical observations, we are required to invoke a model involving a hard electro…
X-ray and optical monitoring of the peculiar source 4U 1700+24/V934 Her
Cusumano, G.; Palazzi, E.; Frontera, F. +10 more
We report on ASCA and BeppoSAX X-ray broad band observations of the galactic low-luminosity X-ray source 4U 1700+24 performed on 1995 and 1998, respectively, and on (quasi-)simultaneous ground observations of its optical counterpart, V934 Her, from the Loiano 1.5-meter telescope. In order to better understand the nature of the source we also analy…
Emergence and Drastic Breakdown of a Twisted Flux Rope to Trigger Strong Solar Flares in NOAA Active Region 9026
Kurokawa, Hiroki; Ishii, Takako T.; Wang, Tongjiang
An emerging twisted flux rope model to explain the drastic evolution of a flare-productive NOAA Active Region 9026 is presented. The drastic changes in the δ-type sunspot configuration were found to start shortly before the big flares of 2000 June 6: (1) rapid proper motions of sunspots started at the both sides of the central δ sunspot about 7 hr…
Computing the Parallax of the Pleiades from the Hipparcos Intermediate Astrometry Data: An Alternative Approach
Makarov, Valeri V.
The inconsistency between the mean parallax of the Pleidaes open cluster from the Hipparcos catalog and that obtained from the stellar evolution theory and photometric measurements is probed by recomputing the Hipparcos data in a different way that reduces the propagation of the along-scan attitude errors. This is achieved by coupling observations…
Very Large Telescope and Hubble Space Telescope Observations of the Host Galaxy of GRB 990705
Le Floc'h, E.; Sanders, D. B.; Mereghetti, S. +6 more
We present Very Large Telescope spectroscopic observations of the GRB 990705 host galaxy and highlight the benefits provided by the prompt phase features of gamma-ray bursts (GRBs) to derive the redshifts of the latter. In the host spectrum, we indeed detect an emission feature that we attribute to the [O II] λλ3726, 3729 doublet and derive an una…
Infrared Space Observatory Observations of the Unidentified 30 Micron Feature in Proto-Planetary Nebulae
Volk, Kevin; Kwok, Sun; Szczerba, Ryszard +1 more
The intrinsic emission profile of the unidentified broad 30 µm emission feature is derived from Infrared Space Observatory (ISO) spectra of proto-planetary nebulae (PPNs). The feature is resolved into two components: a narrower feature at 26 µm and a broader feature at 33 µm. The intrinsic profiles of these two features and their…
Flare- and Shock-accelerated Energetic Particles in the Solar Events of 2001 April 14 and 15
Cohen, C. M. S.; Maclennan, C. G.; Mason, G. M. +5 more
We report heavy-ion composition and spectra for the solar energetic particle (SEP) events of 2001 April 14 and 15, using the combined capabilities of the Advanced Composition Explorer (ACE), Wind, and the Interplanetary Monitoring Platform 8 (IMP-8) to cover the energy range from ~30 keV nucleon-1 to ~400 MeV nucleon-1. These…
An advanced physical model of cometary activity
Fulle, M.; Szegő, K.; Rodionov, A. V. +2 more
We describe the present state of an advanced physical model aimed at the simulation of the environment of active cometary nuclei. The model can handle the complicated shapes of real cometary nuclei, and is ready to handle alternative assumptions concerning the nucleus composition and structure; its present version is based on the simple, but hithe…