Search Publications
First-year continuous solar EUV irradiance from SOHO by the CELIAS/SEM during 1996 solar minimum
Galvin, A. B.; Judge, D. L.; Ogawa, H. S. +2 more
The CELIAS/SEM photodiode spectrometer aboard SOHO continuously monitors the full-disk EUV solar irradiance in an 8-nm wavelength band centered at 30.4 nm (first order), and in a broad wavelength band between 0.1 and 77 nm (central order). We present the absolute solar EUV irradiances for the 1996 solar EUV minimum year at 1 AU. The uncertainty in…
Monitoring Lyα Emission from the Blazar 3C 279
Urry, C. Megan; Koratkar, Anuradha; Pian, Elena +1 more
The blazar 3C 279 is well studied and shows frequent large continuum flares from radio to γ-ray wavelengths. There have been a number of multiwavelength observations of 3C 279, and hence there are extensive ultraviolet data for this object available in the UV archives. In this paper we present Lyα emission line measurements for 3C 279 using all th…
Resonance scattering of Lyman alpha from interstellar hydrogen
Brasken, Mats; Kyrola, Erkki
We derive a set of new line-of-sight (LOS) integrals and phase functions for the resonance scattering of unpolarized Lyman alpha light in the optically thin medium limit. To explicitly show the approximations done, and to indicate the range of validity of previously published formulas, we start by treating the general theory of resonance scatterin…
Coronal C+3 in the Large Magellanic Cloud: Evidence for a Hot Halo
Chu, You-Hua; Wakker, Bart; Points, Sean D. +2 more
Based on the detection of C IV absorption in five Large Magellanic Cloud (LMC) stars observed with the Goddard High-Resolution Spectrograph on the Hubble Space Telescope, we present the first unambiguous evidence that C+3 exists in the LMC away from regions where it could have been locally produced. We can exclude that this C+3
The Acoustic Moat and Thermal Transport in the Neighborhoods of Sunspots
Braun, D. C.; Lindsey, C.
Helioseismic holography of sunspots shows a remarkable acoustic anomaly surrounding the sunspot, which we call an ``acoustic moat.'' We used Solar and Heliospheric Observatory (SOHO) Michelson Doppler Imager observations of NOAA Active Region 7973 to render acoustic images of a typical sunspot. These images show a conspicuous halo, 70,000 km in di…
High resolution spectroscopy of symbiotic stars. IV. BX Monocerotis: orbital and stellar parameters
Schmutz, W.; Nussbaumer, H.; Shore, S. N. +4 more
We investigate the orbit and the components of the symbiotic BX Mon system with new high resolution spectroscopy, IUE spectra, published photographic magnitudes, and brightness estimates from the RASNZ. We review the available photometry and deduce a new binary period of 1401 days. We also find evidence in the IUE data that BX Mon is an eclipsing …
Measurements of Far-UV Emission from Elliptical Galaxies at Z = 0.375
Ferguson, Henry C.; Brown, Thomas M.; Deharveng, Jean-Michel +1 more
The ``UV upturn'' is a sharp rise in spectra of elliptical galaxies shortward of rest-frame 2500 Å. It is a ubiquitous phenomenon in nearby giant elliptical galaxies and is thought to arise primarily from low-mass evolved stars on the extreme horizontal branch and beyond. Models suggest that the UV upturn is a very strong function of age for these…
Mass-Loss Rate and He/H Abundance of the Erupting Component in the Small Magellanic Cloud System HD 5980
Schmutz, W.; Koenigsberger, G.; Peña, M. +1 more
The binary Wolf-Rayet system HD 5980 in the Small Magellanic Cloud underwent a major luminous blue variable-type eruptive event in 1994. It is the first such recorded event in which the apparent precursor transits from WNE to WNL spectral types prior to the eruption. In this paper we analyze the spectrum of the system obtained when the outburst wa…
Abundance analysis of the lambda Bootis stars HD 192640, HD 183324, and HD 84123
Heiter, U.; Paunzen, E.; Weiss, W. W. +2 more
The classification of lambda Bootis stars based on photometric indices or low resolution spectra is not sufficient for a final decision concerning a membership to this group. A detailed spectroscopic investigation is necessary to rule out stars with similar classification spectra but different abundance patterns. Therefore a program on abundance a…
Atomic Physics with the Goddard High Resolution Spectrograph on the Hubble Space Telescope. IV. Relative Oscillator Strengths for Singly Ionized Nickel
Federman, S. R.; Zsargó, J.
Absorption lines of trace metals like nickel are often used to measure the metallicity and depletion in H I regions within our Galaxy and others. Ultraviolet absorption lines from the dominant ion, Ni II, are generally weak, making them a convenient tool to study metallicity and depletion in these environments. As an aid for studies of dust evolut…