Search Publications
The region of Collinder 121
Kaltcheva, N. T.
The distribution of bright B-type stars in a field with a radius of 5° centred at the Galactic open cluster Cr 121 is studied utilizing Strömgren and Hβ photometry. All PPM stars earlier than spectral type A0 are used, revealing a loose nearby structure at a distance of 660-730pc, and a compact more distant group, which appears to be a genuine clu…
Near-infrared adaptive optics imaging of nuclear spiral structure in the Seyfert galaxy NGC 3227
Morris, Simon L.; Chapman, Scott C.; Walker, Gordon A. H.
We present high spatial resolution, near-infrared images in J, H and K of the nucleus of NGC 3227, obtained with the Adaptive Optics Bonnette on the Canada-France-Hawaii Telescope. The ~0.15arcsec (17pc) resolution allows structures to be probed in the core region. Dust obscuration becomes significantly less pronounced at longer wavelengths, revea…
Optical, X-ray and radio observations of HD 61396: a probable new RS CVn-type binary
Singh, K. P.; Drake, S. A.; Pandey, S. K. +1 more
We have carried out BVR photometric and Hα spectroscopic observations of the star HD 61396 during 1998 March 20 to 1999 April 3. We have discovered regular optical photometric variability from this star, with an inferred period of 31.95+/-0.10d, and an amplitude of ~0.18mag. A possible period of 35.34+/-0.12d, as determined with Hipparcos, cannot …
The space density of low-redshift active galactic nuclei
Boyle, B. J.; Londish, D.; Schade, D. J.
We present a new determination of the optical luminosity function (OLF) of active galactic nuclei (AGN) at low redshifts (z<0.15) based on Hubble Space Telescope (HST) observations of X-ray-selected AGN. The HST observations have allowed us to derive a true nuclear luminosity function for these AGN. The resulting OLF illustrates a two power-law…
Angular diameter and effective temperature of a sample of 15M giants at 2.2µm from lunar occultation observations
Tej, Anandmayee; Chandrasekhar, T.
High angular resolution measurements of a sample of 15M giants at 2.2µm by the technique of lunar occultation are presented in this paper. We obtain angular diameters for 11 sources of which five are the first diameter measurements. For these resolved sources we have estimated the effective temperatures, which are consistent with previous ca…
High time-resolution spectroscopic imaging using intensified CCD detectors
Much, R.; Kawakami, H.; Fordham, J. L. A. +2 more
The micro-channel plate intensified CCD photon counting detector developed at University College London has been upgraded to allow time-resolved spectroscopic optical data to be acquired on periodical sources such as pulsars. First observing trials have been carried out, acquiring spectroscopic data on the Crab pulsar. The detector was phase locke…
Source of excitation of low-l solar p modes: characteristics and solar-cycle variations
Chaplin, W. J.; Elsworth, Y.; Appourchaux, T. +3 more
We investigate various properties of the excitation source that is responsible for driving the acoustic p-mode oscillations of the Sun. Current prejudice places this in the superadiabatic layer of the convection zone. We consider in detail how the precise nature of the resonant mode spectrum is modified: (i) as a result of the impact of different …
Using Hubble Space Telescope images to identify straight segments in galaxy nuclear spirals
Chernin, A. D.
This Letter reports the discovery of straight segments of nuclear spiral arms. Hubble Space Telescope images of Seyfert galaxies are used. The morphology of the straight features on scales of few hundred parsecs proves to be similar to the morphology of disc-wide polygonal spirals and rings. This suggests that the straight structures on both nucle…
Interstellar CO towards X Persei (HD 24534) - I. One-component model
Kaczmarczyk, Grzegorz
Data on molecular CO in absorbing gas towards X Per, from the International Ultraviolet Explorer (IUE) and the echelle mode of the Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope, are reported. A statistical equilibrium model is used to recreate equivalent widths of CO bands and reproduce high-resolution GHRS spectra.…
The spectral variations of the O-type runaway supergiant HD 188209
Galeev, A.; Herrero, A.; Kaufer, A. +4 more
We report spectral time series of the late O-type runaway supergiant HD 188209. Radial velocity variations of photospheric absorption lines with a possible quasi-period of ~6.4d have been detected in high-resolution echelle spectra. Night-to-night variations in the position and strength of the central emission reversal of the Hα profile occurring …