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Soho Cds nis in-flight intensity calibration using a plasma diagnostic method
Mason, H. E.; Landini, M.; Landi, E. +1 more
The internal intensity calibration of the Coronal Diagnostic Spectrometer (CDS) - Normal Incidence Spectrometer (NIS) is studied using the Arcetri diagnostic method. A large number of spectral lines observed by the CDS-NIS 1 and NIS 2 windows in a solar active region is analysed in order to determine the intensity calibration curve for both channe…
On the evolutionary status of λ Bootis stars using HIPPARCOS data.
Paunzen, E.
We have used the Hipparcos data to derive absolute magnitudes and thus the evolutionary status for the group of λ Bootis stars. The origin for this small group of nonmagnetic, chemically peculiar stars, still remains a matter of debate. Using new evolutionary tracks, we are able to provide an age determination to distinguish between the two propos…
On the Relationship between the Periodic and Aperiodic Variability of Accreting X-Ray Pulsars
Stella, Luigi; Lazzati, Davide
Besides the narrow peaks originating from the periodic signal, the power spectra of accreting X-ray pulsars display continuum components usually increasing toward low frequencies; these arise from the source aperiodic variability. Most studies up to the present have adopted the view that the periodic and aperiodic variations are independent. Howev…
The Spectrum of the Large Magellanic Cloud Pulsar B0540-69
Boyd, Patricia T.; van Citters, G. W.; Taylor, M. J. +4 more
A prism spectrum of PSR B0540-69, the 50 ms pulsar in the Large Magellanic Cloud, was obtained with the Faint Object Spectrograph on the Hubble Space Telescope. This is only the second pulsar spectrum that has been observed in the optical. The 2500-5500 Å spectrum shows a smooth continuum with several broad emission lines. The lines are emitted by…
Ulysses observations of the northward extension of the heliospheric current sheet
Balogh, A.; Forsyth, R. J.; Smith, E. J. +1 more
After passing through the northern polar regions of the heliosphere during the summer of 1995, the Ulysses spacecraft has been gradually returning towards lower equatorial latitudes, reaching 30°N in August 1996 at about which time low speed solar wind from the streamer belt was once again observed. This paper reports on the Ulysses magnetic field…
Hubble Space Telescope WFPC Images of Emission Nebulosity near XZ Tauri
Ballester, Gilda E.; Krist, John E.; Crisp, David +14 more
XZ Tauri is a M3 V T Tauri star with a pre-main-sequence binary companion detected by infrared speckle interferometry at a projected separation of 0.3" (about 40 AU). Previous ground-based observations of the system have shown bipolar emission nebulosity, including a possible jet knot. Images obtained with the Wide Field and Planetary Camera 2 on …
HST-GHRS observations of candidate β Pictoris-like circumstellar gaseous disks.
Deleuil, M.; Ferlet, R.; Vidal-Madjar, A. +6 more
We present HST-GHRS observations of four stars in search of β Pictoris-like circumstellar gaseous disks. We detected gas around HR 10, HR 2174 and 51 Oph at large distances from the stars; this gas is circumstellar since the absorption lines from very excited levels require densities incompatible with those found in the diffuse interstellar medium…
A New Pulsation Spectrum and Asteroseismology of delta Scuti.
Templeton, Matthew R.; Bradley, Paul A.; Guzik, Joyce A. +3 more
We present the results of a five-year Strömgren y photometric campaign on δ Scuti. Our data set consists of 6515 discrete differential magnitudes, and spans the period of 1983 June to 1988 September. We found the primary pulsation mode at 59.731129±0.000002 µHz, in close agreement with the frequency determination of Fitch (1976, IAU Colloqui…
Galactic Cosmic-Ray Manganese: Ulysses High Energy Telescope Results
DuVernois, M. A.
The Ulysses High Energy Telescope (HET) allows for a study of Galactic cosmic-ray manganese because of the telescope's excellent mass resolution and large collecting area. The manganese isotopes in the cosmic rays provide a means of studying the parameters of the cosmic-ray propagation in the Galaxy. Each of the isotopes probes a separate aspect o…
Non-LTE model atmosphere analysis of the early ultraviolet spectra of Nova OS Andromedae 1986
Sonneborn, G.; Baron, E.; Shore, Steven N. +4 more
We analyse the early, optically thick, ultraviolet spectra of Nova OS And 1986 using a grid of spherically symmetric, non-LTE, line- blanketed, expanding model atmospheres and synthetic spectra with the following set of parameters: 5000<=T_model<=60000K, solar abundan ces, rho ~r^-3, v_max=2000 km s^-1, L=6x10^4Lsolar, and a statistical or m…