Search Publications
Atomic fine-structure lines in the ISO-SWS spectra of the supergiants alpha Orionis and alpha Scorpii
Waters, L. B. F. M.; Justtanont, K.; Tielens, A. G. G. M. +3 more
We report the detection of infrared fine-structure lines of [Fe II] and [Si II] in the ISO-SWS spectra of two supergiants, alpha Ori and alpha Sco. From the observed intensities we infer that the emitting regions have temperatures in the range 1200-1800 K and are located within about 20 R_{*} from the star. This is interior to the region where dus…
Models of X-Ray Photoionization in LMC X-4: Slices of a Stellar Wind
Raymond, John; Vrtilek, S. D.; McCray, Richard +2 more
We show that the orbital variation in the UV P Cygni lines of the X-ray binary LMC X-4 results when X-rays photoionize nearly the entire region outside of the X-ray shadow of the normal star. We fit models to Goddard High Resolution Spectrograph (GHRS) observations of N V and C IV P Cygni line profiles. Analytic methods assuming a spherically symm…
An infrared image of the dust disc around beta PIC
Walker, H. J.; Lemke, D.; Klaas, U. +2 more
The star beta Pictoris is a normal main-sequence star with a remnant disc of cool dust around it. We present observations of the beta Pic dust disc in the far-infrared, obtained using the photometer (ISOPHOT) on the Infrared Space Observatory (ISO) satellite. We resolve the edge-on disc using high-resolution scans, with full widths at half-maximum…
300-580 Nanometer Long-Slit Spectroscopy of Comet Tabur (C/1996 Q1)
Smith, Graeme H.; Turner, Neal J.
Comets Liller (C/1988 A1) and Tabur (C/1996 Q1) have similar orbits and are thought to have been a single comet until they split at a previous perihelion passage. Long-slit spectra of comet Tabur were obtained on consecutive nights around 45 days before perihelion. Nuclear production rate ratios for NH/CN, C3/CN, and C2/CN, d…
Forward modeling of the coronal response to reconnection in an X-ray bright point
Longcope, Dana; Kankelborg, Charles
We use MDI magnetic field observations and the theory of reconnection through a separator to constrain a numerical simulation of an X-ray bright point observed in EUV by TRACE. A gasdynamic model is employed to describe the corona and transition region in the bright point loop. Nonlocal effects such as opacity and ambipolar diffusion are important…
Multiple CME Events Observed With LASCO
Simnett, G. M.; Lyons, M. A.
Observations are reported of two multiple CME events which were detected on 2-3 June 1997 and 9-10 June 1998, using the LASCO instrument on board SOHO. Each event consists of a group of four related CMEs which emerge from progressively higher latitudes over a time period of approximately 16 hours. In both cases there is on-disk activity visible in…
A Comparison of Measurements of Solar Extreme-Ultraviolet Spectral Line Intensities Emitted by C, N, O, and S Ions with Theoretical Calculations
Wilhelm, K.; Doschek, G. A.; Feldman, U. +2 more
Atomic data for ionized atoms are important for many astrophysical applications. The launch of the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) extreme-ultraviolet (EUV) spectrometer aboard the Solar and Heliospheric Observatory (SOHO) allows us to test the accuracy of certain computed relative excitation rate coefficients and trans…
V2109 Cygni, a second overtone field RR Lyrae star
Thomson, J. R.; Kiss, L. L.; Csák, B. +1 more
We present the first (as of February, 1999) UBV and uvby photometric measurements for the short period variable star V2109 Cyg discovered by the Hipparcos satellite and classified as a field RRc variable. We have obtained new times of maxima and the period change has been studied. We determined the fundamental physical parameters using the geometr…
A Time-Series IUE Archival Study of the White Dwarf in the Ultrashort-Period Dwarf Nova WZ Sagittae
Sion, E. M.; Cheng, F. H.; Slevinsky, R. J. +2 more
The IUE archive offers a series of far-UV spectra of the ultrashort-period dwarf nova WZ Sge over a long time baseline and hence the opportunity to monitor the ongoing accretion, the cooling of the white dwarf, and temporal variations in the line spectra. We have carried out a quantitative analysis of these spectra including model atmosphere simul…
UBV photometry, UV spectroscopy and radio observations of the peculiar binary V Sagittae
Eyres, S. P. S.; Naylor, T.; Wood, Janet H. +2 more
We have performed high-speed UBV photometric observations on the peculiar binary V Sagittae. Using three new eclipse timings we update the orbital ephemeris and convert it to a dynamical time-scale (TDB). We also searched for quasi-periodic oscillations but did not detect them. Using the Wilson-Devinney algorithm we have modelled the light curve t…