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Peculiar Multimodality on the Horizontal Branch of the Globular Cluster NGC 2808
Rich, R. Michael; Renzini, Alvio; Piotto, Giampaolo +6 more
We present distributions of colors of stars along the horizontal branch (HB) of the globular cluster NGC 2808, from Hubble Space Telescope Wide Field Planetary Camera 2 imaging in B, V, and an ultraviolet filter (F218W). This cluster's HB is already known to be strongly bimodal, with approximately equal-sized HB populations widely separated in the…
Performance and Early Results from the GOLF Instrument Flown on the SOHO Mission
Baudin, F.; Christensen-Dalsgaard, J.; García, R. A. +21 more
GOLF in-flight commissioning and calibration was carried out during the first four months, most of which represented the cruise phase of SOHO towards its final L1 orbit. The initial performance of GOLF is shown to be within the design specification, for the entire instrument as well as for the separate sub-systems. Malfunctioning of the polarising…
Wind variability of B supergiants. III. Corotating spiral structures in the stellar wind of HD 64760.
Owocki, S. P.; Cranmer, S. R.; Prinja, R. K. +2 more
Fourier analysis of two spectroscopic time series obtained with the IUE observatory confirm that the ultraviolet stellar wind profiles of HD 64760 (B0.5 Ib) are periodically variable. The periodic component consists of modulations that extend over most of the P Cygni absorption trough, and can frequently be traced through the emission lobe. The mo…
First View of the Extended Green-Line Emission Corona At Solar Activity Minimum Using the Lasco-C1 Coronagraph on SOHO
Llebaria, A.; St. Cyr, O. C.; Plunkett, S. P. +21 more
The newly developed C1 coronagraph as part of the Large-Angle Spectroscopic Coronagraph (LASCO) on board the SOHO spacecraft has been operating since January 29, 1996. We present observations obtained in the first three months of operation. The green-line emission corona can be made visible throughout the instrument's full field of view, i.e., fro…
The Hubble Space Telescope Extragalactic Distance Scale Key Project. VII. The Discovery of Cepheids in the Leo I Group Galaxy NGC 3351
Kelson, Daniel D.; Illingworth, Garth D.; Huchra, John P. +20 more
We report of the discovery and properties of Cepheid variable stars in the barred spiral galaxy NGC 3351 which is a member of the Leo I group of galaxies. NGC 3351 is one of 18 galaxies being observed as part of the Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale which aims to determine the Hubble constant to 10% accur…
Physical Conditions of the Coronal Line Region in Seyfert Galaxies
Ferland, Gary J.; Korista, Kirk T.; Ferguson, Jason W.
The launch of the Infrared Space Observatory and new atomic data have opened a window for the study of high-ionization gas in active galactic nuclei (AGNs). We present the results of a large number of photoionization simulations of the ``coronal line'' region in AGNs, employing new atomic data from the Opacity and Iron Projects. Our grid of line e…
Measurements of Frequencies of Solar Oscillations from the MDI Medium-l Program
Kosovichev, A. G.; Scherrer, P. H.; Schou, J. +2 more
Inversions of solar internal structure employ both the frequencies and the associated uncertainties of the solar oscillation modes as input parameters. In this paper we investigate how systematic errors in these input parameters may affect the resulting inferences of the sun's internal structure. Such systematic errors are likely to arise from ina…
Structure function measurements of the intermittent MHD turbulent cascade
Balogh, A.; Horbury, T. S.
The intertmittent nature of turbulence within solar wind plasma has been demonstrated by several studies of spacecraft data. Using magnetic field data taken in high speed flows at high heliographic latitudes by the Ulysses probe, the character of fluctuations within the inertia] range is discussed. Structure functions are used extensively. A simpl…
The stellar population of the globular cluster M 3. II. CCD photometry of additional 10,000 stars.
Cacciari, C.; Carretta, E.; Buonanno, R. +5 more
We present BVI CCD photometry for more than 10,000 stars in the innermost region (0.3'<r<~4') of the globular cluster M 3. When added to the previous photographic photometry by Buonanno et al. (1994A&A...290...69B) reaching as far as r~7', this results in an homogeneous data-set including about 19,000 stars measured in this cluster, whic…
Hubble Space Telescope Ultraviolet Observations of the Cores of M3 and M13
Ferraro, Francesco R.; Paltrinieri, Barbara; Fusi Pecci, Flavio +3 more
We present preliminary results from Hubble Space Telescope (HST)/WFPC2 observations of the central regions of the of the Galactic globular clusters M13 and M3. The clusters are almost identical in most respects, including chemical composition, but there are dramatic differences in both the horizontal-branch (HB) and blue straggler populations. The…