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LASCO observations of an Earth-directed coronal mass ejection on May 12, 1997
St. Cyr, O. C.; Plunkett, S. P.; Michels, D. J. +5 more
Coronal mass ejections (CMEs) that occur near the center of the solar disk are most likely to impact Earth. Detection of such events as ‘halos’ in white-light coronagraphs has been somewhat controversial in recent years. We present observations from the LASCO coronagraphs on SOHO that provide convincing evidence of the detection of an Earth-direct…
Transient Effects and Disturbed Conditions
Wibberenz, G.; Potgieter, M. S.; Bieber, J. W. +1 more
In the present phase of the solar cycle no big transients leading to strong modulation had been observed after 1991. Apart from a few minor disturbances cosmic rays were still recovering to a new intensity maximum. It was suggested, therefore, that existing literature from previous cycles should be critically reviewed. The scene was set by the int…
Solar wind radial and latitudinal structure: Electron density and core temperature from Ulysses thermal noise spectroscopy
Moncuquet, Michel; Issautier, Karine; Meyer-Vernet, Nicole +1 more
We present new in situ solar wind plasma measurements obtained during Ulysses fast transit from the south solar pole to the north one, which took place 1 year before the 1996 sunspot minimum. The data were obtained with the radio receiver of the Unified Radio and Plasma Wave Experiment, using the method of quasi-thermal noise spectroscopy, which i…
The nitrogen spectra of Wolf-Rayet stars. A grid of models and its application to the Galactic WN sample
Hamann, W. -R.; Koesterke, L.
Adopting the ``standard model'' for Wolf-Rayet atmospheres, non-LTE radiation transfer calculations are performed which account for helium and nitrogen. Grids of theoretical models are presented for the whole relevant parameter range. The WN classification criteria are employed in order to identify the subtype domains, and inconsistencies are disc…
Effects of errors in the solar radius on helioseismic inferences
Basu, Sarbani
Frequencies of intermediate-degree f modes of the Sun seem to indicate that the solar radius is smaller than what is normally used in constructing solar models. We investigate the possible consequences of an error in radius on results for solar structure obtained using helioseismic inversions. It is shown that solar sound speed will be overestimat…
Wolf-Rayet stars and O-star runaways with HIPPARCOS. I. Kinematics
van der Hucht, K. A.; Moffat, A. F. J.; van den Heuvel, E. P. J. +9 more
Reliable systemic radial velocities are almost impossible to secure for Wolf-Rayet stars, difficult for O stars. Therefore, to study the motions - both systematic in the Galaxy and peculiar - of these two related types of hot, luminous star, we have examined the Hipparcos proper motions of some 70 stars of each type. We find that (a) both groups f…
Systematics of RR Lyrae Statistical Parallax. III. Apparent Magnitudes and Extinctions
Gould, Andrew; Popowski, Piotr
We sing the praises of the central limit theorem. Having previously removed all other possible causes of significant systematic error in the statistical-parallax determination of RR Lyrae absolute magnitudes, we investigate systematic errors from two final sources of input data: apparent magnitudes and extinctions. We find corrections due to each …
Modeling the Brightness Profiles of the Orion Proplyds
Henney, W. J.; Arthur, S. J.
We investigate whether simple models of a photoevaporated flow from an externally ionized neutral clump or wind can reproduce the observed Hα intensity profiles of the proplyds in the inner Orion Nebula. We find that models fitted to the bright ``cusp'' at the head of each proplyd successfully predict the brightness distribution of the extended di…
Photoionization of Disk Winds
Chiang, J.; Murray, N.
The disk-wind model suggests that the broad emission lines of a quasar are emitted from the surface of the accretion disk feeding the central black hole. In this paper, we assume that a line-driven wind emerges from the illuminated face of the disk and calculate the line emission produced by this wind. The location and mass-loss rate of the wind a…
The nucleus and inner coma of Comet 46P/Wirtanen
Jorda, L.; Lamy, P. L.; Toth, I. +2 more
We report the detection of the nucleus of comet 46P/Wirtanen from analysis of images taken with the Planetary Camera (WFPC2) of the Hubble Space Telescope (HST) on 28 August 1996. The high spatial resolution (a WFPC2 pixel projects to 50 km at the distance of the comet) allowed us to separate the signal of the nucleus from that of the coma and to …