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Light-Element Abundance Patterns in the Orion Association. I.Hubble Space Telescope Observations of Boron in G Dwarfs
Cunha, Katia; Smith, Verne V.; Lambert, David L. +1 more
The boron abundances for two young solar-type members of the Orion association, BD -6°1250 and HD 294297, are derived from Hubble Space Telescope STIS spectra of the B I transition at 2496.771 Å. The best-fit boron abundances for the target stars are 0.13 and 0.44 dex lower than the solar meteoritic value of logɛ(B)=2.78. An anticorrelation of bor…
In-Flight Determination of the Plate Scale of the Extreme-Ultraviolet Imaging Telescope
Auchère, F.; Artzner, G.; DeForest, C. E.
Using simultaneous observations of the Michelson Doppler Imager and Extreme-Ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory spacecraft, we determined in flight the plate scale of the EIT. We found a value of 2.629"+/-0.001" pixel-1, in fair agreement with the 2.627"+/-0.001" pixel-1 value d…
Optical Observations of the Binary Pulsar System PSR B1718-19: Implications for Tidal Circularization
Kulkarni, S. R.; van Kerkwijk, M. H.; Lyne, A. G. +3 more
We report on Keck and Hubble Space Telescope optical observations of the eclipsing binary pulsar system PSR B1718-19, in the direction of the globular cluster NGC 6342. These reveal a faint star (mF702W=25.21+/-0.07 Vega system) within the pulsar's 0.5" radius positional error circle. This may be the companion. If it is a main-sequence …
Precise Interplanetary Network Localization of the Bursting Pulsar GRO J1744-28
Cline, T.; Hurley, K.; Kouveliotou, C. +8 more
We analyze 426 observations of the bursting pulsar GRO J1744-28 by Ulysses and BATSE. Triangulating each burst and statistically combining the triangulation annuli, we obtain a 3 σ error ellipse whose area is 532 arcsec2. The accuracy of this statistical method has been independently verified with observations of the soft gamma repeater…
The Variability of Seyfert 1.8 and 1.9 Galaxies at 1.6 Microns
Rieke, G. H.; Alonso-Herrero, A.; Quillen, A. C. +4 more
We present a study of Seyfert 1.5-2.0 galaxies observed at two epochs with the Hubble Space Telescope (HST) at 1.6 µm. We find that unresolved nuclear emission from nine of 14 nuclei varies at the level of 10%-40% on timescales of 0.7-14 months, depending upon the galaxy. A control sample of Seyfert galaxies lacking unresolved sources and ga…
An Ultraviolet Fe II Image of SN 1885 in M31
Fesen, Robert A.; Hamilton, Andrew J. S.
Ultraviolet imaging of the remnant of supernova (SN) 1885 in M31 with the Hubble Space Telescope using the F255W filter on the WFPC2 reveals a dark spot of Fe II absorption at the remnant's known position in the bulge of M31. The diameter of the absorbing spot, ~0.5", is consistent with the 0.70"+/-0.05" diameter measured in the higher quality WFP…
The HE II Emitting Nebula N44C in the Large Magellanic Cloud: Optical/Ultraviolet Spectroscopy of the Nebula and Its Ionizing Star
Garnett, Donald R.; Chu, You-Hua; Galarza, Vanessa C.
We present HST spectroscopy and imaging, along with new ground-based spectroscopy and ROSAT HRI imaging, of the He II emitting nebula N44C and its ionizing star. A GHRS spectrogram of the ionizing star yields a spectral type of about O7 for the star. The lack of P Cygni profiles for Si IV and C IV indicates that the star is not a supergiant. The n…
Temperature Structure of the Quiet Corona: An SXT-SUMER Discrepancy
Lemen, J.; Sturrock, P. A.; Wolfson, Richard +2 more
The Soft X-ray Telescope (SXT) on Yohkoh and the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) are both capable of providing measures of temperature in the solar corona. A recent SUMER-based study of a quiet coronal region suggests an isothermal plasma in the range from 1.…
The Relationship of Solar Abundance Measurements to the Electron Temperature in a Polar Coronal Hole
Doschek, G. A.; Laming, J. M.
We discuss the behavior of the intensity of the Mg VI λ1191.64 spectral line relative to the intensity of the Ne VI λ1005.78 spectral line as a function of height above the limb in the solar north polar coronal hole. The intensities of Mg VI lines relative to Ne VI lines have been shown to be excellent indicators of element abundance variations du…
Extreme-Ultraviolet Flares in an F2 Star
Mullan, D. J.; Mathioudakis, M.
We report on the coronal properties of two early F dwarfs. For both stars, spectroscopic data reveal a hot corona with material at temperatures as high as 107.1-107.2 K. The EUV photometric observations of one of the stars (HR 120: F2) reveal two large flares with rapid decay times. The rapid decays are in striking contrast w…