Search Publications
Optical and UV spectroscopy of blue horizontal branch stars in the globular cluster NGC 6752.
Boksenberg, A.; Danziger, J.; Caloi, V. +4 more
Optical and far-UV spectra have been obtained for blue HB stars on both sides of the observed luminosity gap in NGC 6752. On this basis effective temperatures and absolute bolometric magnitudes are derived for six stars above the gap and four stars below it. The authors find that stars above the gap arrange themselves along a ZAHB locus. Across th…
Interstellar zinc revisited : possible depletion in high density sight-lines.
Harris, A. W.; Mas Hesse, J. M.
The question of the nondepletion of interstellar zinc has been reexamined in light of recent results which show that the depletions of many elements, including the volatile element chlorine, show better correlations with the mean volume density of hydrogen, than with hydrogen column density. Zinc abundances from an earlier study have been combined…
Flares on dMe stars : IUE and optical observations of AT MIC and comparison of far-ultraviolet stellar and solar flares.
Bromage, G. E.; Dufton, P. L.; Phillips, K. J. H. +1 more
Observations of AT Mic obtained before and/or during a large flare on Sept. 19, 1980, using the short-wave and long-wave cameras of the IUE satellite, a UBV photometer on the 0.5-m SAAO telescope, and a 380-510-nm Cassegrain spectrophotometer on the 1.9-m SAAO telescope are reported. The data are presented in tables and graphs and compared with da…
EXOSAT measurements of the quiescent X-ray spectrum of the burster 2S1636-536 : evidence for Comptonization in a hot corona.
King, A. R.; Courvoisier, T. J. -L.; Turner, M. J. L. +1 more
Measurement of the X-ray spectrum of the quiescent flux from the burster 2S 1636-536 with EXOSAT on 1983 July 17 - 18 gave as a best-fitting model a power law with a high-energy cut-off. The flux (2 - 10 keV) was seen to increase from 1.6×10-9erg cm-2s-1 to 2.5×10-9erg cm-2s-1 durin…
The spectra shape and variability of the blazar 3C 446.
Gear, W. K.; Robson, E. I.; McHardy, I. M. +5 more
The radio to X-ray spectrum and variability of 3C 446 are discussed, and it is shown that the entire infrared-ultraviolet wavelength region exhibits strongly correlated variations, with the infrared and optical fluxes varying together on a time-scale of weeks or less. The variations in spectral shape which occur in the submillimeter to optical wav…
NE III charge-exchange lines in the planetary nebula NGC 3918.
Harrington, J. P.; Clegg, R. E. S.; Storey, P. J.
The detection of Ne III triplet and quintet lines near 2600 Å in the planetary nebula NGC 3918 is reported. They are excited mainly by charge-transfer reactions between Ne3+ and H0. Empirical reaction rates for triplet and quintet exit channels, deduced from a photoionization model of the nebula and the line strengths, are wi…
X-ray and optical variability in the low-mass burst source X 1735-444.
Charles, P. A.; Corbet, R. H. D.; Smale, A. P. +2 more
The low-mass X-ray burst source X1735 - 444 was observed with Exosat for 9 hr on August 23, 1984. The source exhibited a high level of persistent X-ray emission throughout the observation, with variations of about 20 percent and one burst. In contrast to previous observations of this source, the softness of the X-ray emission was found to be corre…
The determination of the mass of a Magellanic Cloud planetary nebula by speckle interferometry.
Barlow, M. J.; Morgan, B. L.; Standley, C. +1 more
A Magellanic Cloud planetary nebula is resolved by speckle interferometry for the first time. The observations of SMC N2 show it to have a double-ring structure, the rings having angular radii of 0.22 and 0.38 arcsec, corresponding to absolute radii of 0.06 and 0.10 pc. The speckle observations of the galactic planetary nebula Vy 2-2 show a ring o…
The properties of the nuclei of the two hot SPOT galaxies NGC 1097 and 2997.
Walsh, J. R.; Nandy, K.; Meaburn, J. +1 more
NGC 1097 and 2997 are barred-spiral galaxies with hot spots in annuli around their central red nuclei. IUE low-dispersion spectra of two hot spots in NGC 1097 and of the ensemble of knots in the annulus around the central nucleus of NGC 2997 are presented. In addition, low-dispersion visible spectra of the hot spots and nuclei of both galaxies are…
The X-ray spectrum and variability of Markarian 421.
McHardy, I.; Warwick, R. S.; George, I. M. +1 more
The X-ray bright BL Lac object Markarian 421 (Mrk 421) was observed by Exosat four times over a period of 6 days in February 1984. The source exhibited a very soft power-law X-ray spectrum (photon spectral index is about 2.8) with an extremely low intrinsic column density (less than or equal to 10 to the 20th/sq cm). Significant X-ray variability …