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The region of Collinder 121
Kaltcheva, N. T.
The distribution of bright B-type stars in a field with a radius of 5° centred at the Galactic open cluster Cr 121 is studied utilizing Strömgren and Hβ photometry. All PPM stars earlier than spectral type A0 are used, revealing a loose nearby structure at a distance of 660-730pc, and a compact more distant group, which appears to be a genuine clu…
Nonequilibrium Ionization and First Ionization Potential Effect Diagnostics
Esser, Ruth; Edgar, Richard J.
We examine the accuracy of a common first ionization potential effect diagnostic, the ratio of Ne VI to Mg VI lines in the solar transition region. Since the two ions have quite similar contribution functions near their maxima in equilibrium, the ratio of these two ions is often taken to be the abundance ratio of Ne and Mg. First we compute nonequ…
The Occurrences of Coronal Mass Ejection at Solar Minimum and their Association with Surface Activity
Simnett, G. M.; Lewis, D. J.
We have developed a non-subjective technique for recording the occurrences of coronal mass ejection (CME) in data recorded by the Large Angle Spectrometric Coronagraph experiment (LASCO) aboard the Solar and Heliospheric Observatory spacecraft (SOHO). We have found evidence for, and quantified, an asymmetry in the apparent longitudes at which mass…
Near-infrared adaptive optics imaging of nuclear spiral structure in the Seyfert galaxy NGC 3227
Morris, Simon L.; Chapman, Scott C.; Walker, Gordon A. H.
We present high spatial resolution, near-infrared images in J, H and K of the nucleus of NGC 3227, obtained with the Adaptive Optics Bonnette on the Canada-France-Hawaii Telescope. The ~0.15arcsec (17pc) resolution allows structures to be probed in the core region. Dust obscuration becomes significantly less pronounced at longer wavelengths, revea…
An Observational Study of Helium in the Solar Corona with the EIT Instrument on Board the SOHO Spacecraft
Auchere, F.
Helium is the second most abundant element in the Universe. The understanding of the physicals processes associated with helium as well as the determination of the helium abundance both have implications in various research fields such as cosmology, stellar evolution or the physics of the solar wind. Helioseismology techniques give accurate measur…
Intercombinational Line Profiles in the UV Spectra of T Tauri Stars and Analysis of the Accretion Zone
Lamzin, S. A.
We have analyzed for the first time profiles of the SiIII 1892 Å and CIII 1909 Å intercombinational lines in HST spectra of the stars RY Tau and RU Lup. The widths of these optically thin lines exceeded 400 km/s, ruling out formation in the stellar chromosphere. Since the intensity of the Si line exceeds that of the C line, it is unlikely that a l…
Long-duration cosmic ray modulation from a Sun-Earth L1 orbit
Harrison, R. A.; Pike, C. D.
We analyse cosmic ray hits impacting the detector system of the Coronal Diagnostic Spectrometer aboard the Solar and Heliospheric Observatory spacecraft. These observations allow us to study the modulation of cosmic rays over a 4 year period (1996-2000) running from solar minimum to maximum, from a Sun-Earth L1 Lagrangian orbit. The modulation, at…
Age Difference between the Populations of Binary and Single F Stars Revealed from Hipparcos Data
Suchkov, A. A.
We have compared the kinematics and metallicity of the main-sequence binary and single uvby F stars from the Hipparcos catalog to see if the populations of these stars originate from the same statistical ensemble. The velocity dispersions of the known unresolved binary F stars have been found to be dramatically smaller than those of the single F s…
Optical, X-ray and radio observations of HD 61396: a probable new RS CVn-type binary
Singh, K. P.; Drake, S. A.; Pandey, S. K. +1 more
We have carried out BVR photometric and Hα spectroscopic observations of the star HD 61396 during 1998 March 20 to 1999 April 3. We have discovered regular optical photometric variability from this star, with an inferred period of 31.95+/-0.10d, and an amplitude of ~0.18mag. A possible period of 35.34+/-0.12d, as determined with Hipparcos, cannot …
Resolving SNR 0540-6944 from LMC X-1 with Chandra
Petre, Robert; Chu, You-Hua; Chen, C. -H. Rosie +1 more
We examine the supernova remnant SNR 0540-697 in the Large Magellanic Cloud (LMC) using data from the Chandra Advanced CCD Imaging Spectrometer. The X-ray emission from this supernova remnant (SNR) had previously been hidden in the bright emission of the nearby X-ray binary LMC X-1 however, new observations with Chandra can finally reveal the SNR'…