Search Publications
A month in the life of NGC 4151: velocity-delay maps of the broad-line region
Horne, Keith; Ulrich, Marie-Helene
We analyse continuum and emission-line variability in NGC 4151 based on IUE spectra taken with nearly complete 1-d sampling over a 35-d interval during 1991 November-December. The 1320-Angstroms continuum undertook a bumpy exponential decline by a factor ~3 over 25 d, and then made a dramatic recovery in ~2d near the end of the campaign. The same …
Periodic UV modulation of X1850-087: a double degenerate binary in the globular cluster NGC 6712?
van Paradijs, J.; Charles, P. A.; Naylor, T. +3 more
We report the discovery with the Hubble Space Telescope (HST) of a short-period (20.6 min) UV modulation in X1850-087, the luminous X-ray source in the globular cluster NGC 6712. The low-amplitude modulation (0.044+/-0.007 mag) is not detected in archival X-ray observations with EXOSAT. We compare the properties of X1850-087 with the 11-min binary…
Optical and ultraviolet spectrophotometry of the ONeMg Nova V838 Herculis 1991
Shore, Steven N.; Sonneborn, George; Wagner, R. Mark +2 more
We present an analysis of optical and UV spectra of the fast nova V838 Herculis 1991. IUE observations began on 1991 March 25 and continued through 1991 August 20, while optical observations began on 1991 March 29 and continued through 1991 August 20. We determine a value for the reddening of E(B-V)~0.5+/-0.1 and a distance of ~3+/-1 kpc based bot…
Star counts in the Hubble Deep Field: constraining galactic structure models.
Minniti, D.; de Marchi, G.; Méndez, R. A. +2 more
Stellar sources are identified in the Hubble Deep Field, and accurate colours and magnitudes are presented. The predictions of a Galactic star counts model are compared with the faint stellar counts in this field. The model reproduces the observations very well in the magnitude range 21.0 < V ≤ 26.4, while it overpredicts the counts by a factor…
HST star counts at high galactic latitudes
Gilmore, Gerard; Elson, Rebecca A. W.; Santiago, Basilio X.
We use star counts from 17 deep fields imaged with the Wide Field Camera 2 (WFC-2) as part of the HST Medium Deep Survey key project in order to constrain the amount of dark matter in the Galaxy that can be in the form of low-mass main-sequence stars or white dwarfs. Based on the number of red stars found in our fields, we exclude the possibility …
The globular clusters in M87: a bimodal colour distribution
Elson, Rebecca A. W.; Santiago, Basilio X.
We present V and I photometry for ~150 globular clusters with 20<<e1>V<</e1>27 about 2.5 arcmin from the centre of M87, the cD galaxy in the Virgo cluster. The data were acquired with the Hubble Space Telescope which, with an effective resolution of 0.1 arcsec, allows us for the first time to distinguish between globular clusters…
HST photometry of 47 TUC and analysis of the stellar luminosity function in Milky Way clusters
Elson, Rebecca A. W.; Gilmore, Gerard F.; Santiago, Basilio X.
We present V and I photometry for over 1000 stars in a region 5 arcmin from the centre of the globular cluster 47 Tuc. The field was imaged with the Wide Field and Planetary Camera 2 (WFPC-2) as part of the Hubble Space Telescope's Medium Deep Survey key project. The luminosity function (LF) continually rises in the domain 5<~<e1>M_I<~…
Solving the mystery of the heavy-element opacity in the DA white dwarf GD 394.
Barstow, M. A.; Bruhweiler, F. C.; Holberg, J. B. +3 more
The white dwarf GD 394 is one of a very small number of bright hot DAs which have detectable quantities of highly ionized heavy elements in their spectra. Whether this material resides in the photosphere of GD 394 or is in the form of a circumstellar shell has been the subject of much debate, with the large discrepancy between the published radial…
Superhumps and ultraviolet superdips: HST observations of OY Car.
Marsh, T. R.; Horne, K.; Cheng, F. H. +5 more
HST observations of the cataclysmic variable OY Car in superoutburst show dips in its ultraviolet light curve coincident with the optical superhump. By analogy with the light curves of X-ray dippers, the authors believe this to be due to obscuration of the hottest regions of the disc by the vertical structure flaring up at the edge of the disc. Th…
Multifrequency observations of the eclipsing symbiotic triple system CH Cyg during the 1992-94 active phase.
Ivison, R. J.; Davis, R. J.; Chochol, D. +14 more
The authors present UBV photoelectric photometry, plus optical and ultraviolet low- and high-resolution spectroscopy and MERLIN, VLA and JCMT radio/mm-wave observations of the symbiotic star CH Cyg during the period 1989.7-1995.5 which covers the 1992 outburst. On 1990 July 22 the spectrum displayed only absorption features characterized by broad …