Search Publications
Compton modelling of spectral variations observed in Z sources.
Wijers, R. A. M. J.; Schulz, N. S.
We present a simple model to fit the spectra of Z sources: a neutron star radiating at the centre of a hot scattering cloud. It is shown that the EXOSAT data of GX 17+2, GX 5-1, GX 340+0, and Sco X-2 (GX 349+2) in all branches of their Z profiles are represented well by this model. The neutron star temperature increases from the Horizontal Branch …
Intergalactic and galactic clouds on the line of sight to SN 1993J in M 81 seen in IUE spectra.
Bomans, D. J.; Fransson, C.; Kirshner, R. P. +4 more
High resolution IUE spectra of SN 1993J in M81 show the existence of several clouds on the line of sight. These include local galactic gas at 0 km s^-1^, gas in M81 at -130 km s^-1^, a cloud in the halo of the Milky Way near -45 km s^-1^, and an intergalactic cloud near +140 km s^-1^. Arguments for each of these locations are given. There is littl…
Core sub-structure of elliptical galaxies : the core resolution technique applied to NGC 1399.
Stiavelli, M.; Zeilinger, W. W.; Moller, P.
UBRJK' images, obtained with subarcsecond seeing, are presented and used to derive the core light profile of the elliptical galaxy NGC 1399. These data, combined with an HST PC V band exposure, and high- resolution velocity dispersion data obtained by us are used to show that NGC 1399 is likely to possess a central dark mass concentration. Models …
Spectral analysis of LSE 78 : an extreme helium star similar to BD -9 4395 and DY Centauri.
Jeffery, C. S.
LSE 78 is a hydrogen-deficient early-B supergiant, spectroscopically similar to the pulsating extreme helium star BD - 9 deg 4395 and the hot R CrB star DY Cen. The photospheric parameters of LSE 78 have been derived from optical high-resolution spectra by the method of fine analysis. The principal results are Teff = 18000 K, log g = 2.…
Variability of the Seyfert galaxy MKN 766 in the ROSAT all sky survey.
Molendi, S.; Maccacaro, T.; Schaeidt, S.
Results are presented from the ROSAT All Sky Survey (RASS) observation of the Seyfert galaxy Mkn 766. Using a technique specifically developed for the analysis of point sources in the RASS we show that Mkn 766 is highly variable. Comparison of the soft X-ray spectrum (0.1-2 keV) with EXOSAT Medium Energy archive data (2-10 keV) clearly shows that …
On the nature of the 25-min periodicity from 4U 0142+614 : a nearby, slowly spinning neutron star/Be system ?
Mereghetti, S.; Stella, L.; de Nile, F.
The unidentified X-ray source 4U 0142+614 has an unusually soft spectrum and has shown a periodic modulation at approximately 25 minutes, which could be interpreted as the orbital period of a Low Mass X-ray Binary. Recently a new X-ray source, probably a Be/neutron star system, has been discovered at an angular distance of only 24 arcmin from 4U 0…
Indications for common origin and gravitational interaction in three binary LMC clusters.
Kontizas, M.; Kontizas, E.; Michalitsianos, A.
Three close pair clusters of the LMC, NGC 2006/SL 538, NGC 2011a/b and NGC 2042a/b, have been studied in order to establish their binarity. The stellar content in the outer region of each cluster has been investigated by means of low resolution objective UK Schmidt prism spectra, the cores of the clusters have been examined using low resolution in…
Far infrared properties of late type dwarfs. Infrared fluxes of K and M dwarfs.
Doyle, J. G.; Mathioudakis, M.
IRAS fluxes/upper limits are presented for a large sample of K and M dwarfs. Good agreement is found between the 12 micrometer fluxes and those derived from the photospheric models of Mould (1976). Relationships between the optical and infrared colors are derived. The active dMe/dKe stars appear systematically brighter in the infrared compared wit…
Hard X-ray spectrum of 4U 1907+09.
Rao, A. R.; Chitnis, V. R.; Agrawal, P. C. +1 more
We have studied the binary X-ray source 4U 1907+09 in the energy range 20-100 keV, using a xenon-filled multilayer proportional counter telescope flown with balloons from Hyderabad in 1985 and 1991. Results of these observations are reported. The source was detected above 20 keV at a significance level of 13 sigma in 1985 and marginally detected i…
Rotational modulation and flares on RS Canum Venaticorum and BY Draconis stars. XVII. UV spectroscopy and optical photometry of AU Microscopii in 1986.
Doyle, J. G.; Quin, D. A.; Butler, C. J. +2 more
We present IUE spectroscopy and optical photometry of the active late type star AU Mic. The UV spectroscopy allow us to measure the chromospheric and transition region line fluxes. No detectable variations attributable to rotational modulation were evident in either the chromospheric lines or optical bands. We have produced an emission measure cur…