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Evidence for a signature of the galactic bar in the solar neighbourhood
Udry, S.; Raboud, D.; Grenon, M. +2 more
Using available kinematical data for a subsample of NLTT stars from the HIPPARCOS mission we confirm the existence of a previously reported local anomaly in the (u,v) plane: the mean motion /line{u} for old disc stars, with v < -30 km s(-1) , is largely positive (+19 +/- 9 km s(-1) w.r.t. the Galactic Center). With the use of the newest global …
The Rapid Decay of the Optical Emission from GRB 980326 and Its Possible Implications
Piro, L.; Veilleux, S.; Pian, E. +39 more
We report the discovery of the optical counterpart to GRB 980326. Its rapid optical decay can be characterized by a power law with exponent -2.10+/-0.13 and a constant underlying source at Rc=25.5+/-0.5. Its optical colors 2.1 days after the burst imply a spectral slope of -0.66+/-0.70. The γ-ray spectrum as observed with BATSE shows th…
Properties of the quiet Sun EUV network
Keenan, F. P.; Phillips, K. J. H.; Gallagher, P. T. +1 more
Observations of the quiet Sun network in a small region at Sun centre taken with the Coronal Diagnostic Spectrometer (CDS) on board SOHO are reported for EUV lines with T_e between ~ 10(4) and 10(6) K. The changing structure of the network in the upper chromosphere, transition region, up to the corona was examined using intensity distributions whi…
The binary star population of the young cluster NGC 1818 in the Large Magellanic Cloud
Gilmore, Gerard; Elson, Rebecca A. W.; Sigurdsson, Steinn +2 more
We determine the binary star fraction as a function of radius in NGC 1818, a young rich cluster in the Large Magellanic Cloud, using Hubble Space Telescope images in bands F336W (~U) and F555W (~V). Our sample includes binaries with M_primary~2-5.5M_solar and M_secondary>~0.7M_primary. The binary fraction increases towards the cluster centre, f…
A Circumstellar Disk in a Pre-main-sequence Binary Star
Koresko, Chris D.
New high-resolution images of HK T Tauri B, the companion to the 106 yr old classical T Tauri star HK Tauri A, show it to be surrounded by an optically thick, edge-on circumstellar disk that extends to a radius of at least 50 AU. The images were taken using a modified speckle technique to achieve a linear resolution of 8 AU. The disk is…
Sirius B: A New, More Accurate View
Barstow, M. A.; Bruhweiler, F. C.; Holberg, J. B. +2 more
Long-standing questions regarding the temperature, gravity, mass, and radius of the well-known white dwarf Sirius B are considered in light of new data. Recently obtained Extreme Ultraviolet Explorer (EUVE) observations and reprocessed IUE NEWSIPS data have produced a new, well-defined effective temperature of 24,790 +/- 100 K and a surface gravit…
Do the Infrared Emission Features Need Ultraviolet Excitation?
Werner, M.; Sellgren, K.; Uchida, K. I.
We present the results of imaging spectroscopy of the reflection nebula vdB 133, obtained with the infrared camera and circular variable filter wheel on the Infrared Space Observatory. Our observations reveal the infrared emission features (IEFs), at 6.2, 7.7, 8.7, 11.3, and 12.7 µm, and associated 5-15 µm continuum emission. The stell…
Neutral Hydrogen Column Depths in Prominences Using EUV Absorption Features
Andretta, V.; Kucera, T. A.; Poland, A. I.
Observations of prominence regions in hot coronal lines (≳106 K) at wavelengths below the hydrogen Lyman absorption limit show what appear to be absorption features. Other authors have suggested that these observed features may be due to H and He continuum absorption. But there has, as yet, been no conclusive evidence that this is indeed the case.…
Cradle to grave tracking of the January 6-11,1997 Sun-Earth connection event
Thompson, B. J.; Fox, N. J.; Peredo, M.
During the interval January 6-11, 1997, the satellites and ground facilities of the International Solar-Terrestrial Physics (ISTP) “Observatory” tracked a solar eruption from the Sun to the Earth. The resulting Coronal Mass Ejection (CME) took four days to travel through interplanetary space before arriving at Earth, where it caused electromagneti…
Cataclysmic Variables and a New Class of Faint Ultraviolet Stars in the Globular Cluster NGC 6397
Bailyn, Charles D.; Cool, Adrienne M.; Cohn, Haldan N. +2 more
We present evidence that the globular cluster NGC 6397 contains two distinct classes of centrally concentrated UV-bright stars. Color-magnitude diagrams constructed from U336, B439, V555, and I814 data obtained with the Hubble Space Telescope Wide Field Planetary Camera 2 reveal seven UV-bright stars fai…