Showing papers by "T. J. Sumner published in 1992"
02 Jan 1992
TL;DR: In this article, the discovery of a new white dwarf as a bright extreme ultraviolet (EUV) source was reported during the first observations using the Wide Field Camera1 on the Rosat satellite.
Abstract: DETAILED understanding of the evolution of main-sequence stars into white dwarfs depends on knowledge of the chemical composition of white-dwarf atmospheres, but the hottest white dwarfs emit much of their radiation in the extreme ultraviolet (EUV), a part of the spectrum that has been generally inaccessible to astronomers. We report here the discovery of a new white dwarf as a bright EUV source found during the first observations using the Wide Field Camera1 on the Rosat satellite. Within the 1-arcmin error box of the EUV source is an unusually blue star, which we show to be a binary system consisting of a DA white dwarf and a cool companion in the classification range dM2–dM5. There are some similarities between this new object and the binary system Feige 24 (ref. 2), but spectral differences in the EUV emission can be attributed to significantly different atmospheric compositions for the two white dwarfs.
17 citations
01 Sep 1992
TL;DR: In this article, the diffuse soft X-ray background in the band between 90 and 188 eV was observed by the Wide Field Camera (WFC) on ROSAT during a 5-day period prior to the main all-sky survey and cover a great circle on the sky of width 5 deg passing through the ecliptic poles and near the Galactic poles.
Abstract: We present observations of the diffuse soft X-ray background in the band between 90 and 188 eV made by the Wide Field Camera (WFC) on ROSAT. The observations were made during a 5-day period prior to the main all-sky survey and cover a great circle on the sky of width 5 deg passing through the ecliptic poles and near the Galactic poles. A detailed discussion of the data reduction and background subtraction is given. The measured count rates are compared to those observed by previous missions using the Landini and Fossi (1990) thin plasma emission code. The results are shown to be consistent with emission from a single-component plasma with a temperature of about 10 exp 6 K.
6 citations
TL;DR: In this paper, it was shown that a white dwarf is unable to account for the emission, and the possibility of coronal emission on one of the four other faint objects within the WFC error circle and on the Am star can be rejected.
Abstract: The recent detection of the eclipsing metallic-lined binary δ Cap in the extreme ultraviolet as part of the Wide-Field Camera All-Sky Survey has prompted a reexamination of the available data in order to attempt to locate the source of the emission. It can be shown that a white dwarf is unable to account for the emission, and the possibility of coronal emission on one of the four other faint objects within the WFC error circle and on the Am star can be rejected. The available data are consistent with the visually unseen secondary being weakly active
3 citations
01 Dec 1992
TL;DR: In this article, an Adiabatic Demagnetization Refrigerator (ADR) backed by a mechanical pre-cooler is evaluated and a system design which is related to the present development status of mechanical coolers is presented.
Abstract: An Adiabatic Demagnetization Refrigerator (ADR) suitable for use in space would have applications in the fields of mm/submm and x-ray astronomy. Since ADR's operate in the absence of gravity without the need for highly complex modifications from established laboratory designs, they could offer a considerable advantage over He-3 refrigerators. The concept of an ADR backed by a mechanical pre-cooler is evaluated. Either a second ADR or a recycling Helium bath is used between the ADR and the mechanical cooler. This has the potential for both high reliability and very long operations. A system design which is related to the present development status of mechanical coolers is presented. The performance of such a system is evaluated. The operational parameters addressed include: achievable temperature and stability; hold and recycle times; and residual magnetic field strength.
1 citations
TL;DR: In this article, a balloon-borne gamma-ray detector was used to observe SN 1987A, which included a spark chamber to determine the arrival directions of the photons, was sensitive in the energy range 50-500 MeV and the 95 percent confidence upper limit to the flux on day 55 after the explosion has been established to be 11 x 10 exp -5 photons/sq cm/s.
Abstract: Analysis of the data obtained from two flights of a balloonborne gamma-ray detector to observe SN 1987A was completed The detector, which included a spark chamber to determine the arrival directions of the photons, was sensitive in the energy range 50-500 MeV The 95 percent confidence upper limit to the flux on day 55 after the explosion has been established to be 11 x 10 exp -5 photons/sq cm/s and on day 407 to be 34 x 10 exp -5 photons/sq cm/s These limits are compared with various theoretical predictions
1 citations