Showing papers by "Mike Irwin published in 1985"

Automatic Analysis of Crowded Fields

Abstract: There are many important 2D data reduction problems in Astronomy that are not amenable to conventional automatic analysis. Typically these problem areas arise in fields where the number density of images is high and where the local sky background may vary rapidly. Examples of such crowded fields are to be found in globular clusters, nearby resolved galaxies or even in deep frames of data well away from obvious concentrations of objects. Within such regions the image number density becomes so high that the majority of images overlap, aven at relatively high isophotes, and simple image analysis algorithms become confused. The confusion can be so bad that even an apparently simple objective like number counting will fail (Irwin & Trimble 1984).

A blue stellar population in the HI bridge between the two Magellanic Clouds

Abstract: Radio observations have shown1 that a common HI cloud surrounds the Magellanic Cloud system. However, no stellar link between the two galaxies has previously been found. The furthest known stellar extension eastward of the Small Magellanic Cloud (SMC) is the blue association of stars found by Kunkel2, which lie close to the extreme tip of the ‘wing’ of the SMC. The SMC wing was discovered by Shapley3, who described it as “a large cloud of faint stars extending eastward from the SMC toward the LMC [Large Magellanic Cloud]”. More recently, Westerlund4 described the brighter (V<20.0) stellar population of the wing as being a mixture of extreme Population I, OB associations, HII regions and both blue and yellow supergrants. The rest of the Magellanic system shows a strong correlation between HI density and the presence of stellar condensations, and this has led to speculation that stellar associations may be present in the HI extension of the optical wing (the HI bridge indicated in Fig. 1) and also independently in regions of high HI density in the Magellanic stream5. Deep Hα photography6 shows weak diffuse emission between the Magellanic Clouds., supporting the possible existence of an optical counterpart to the HI bridge, but star counts near the eastern tip of the wing7 failed to reveal any link and indeed corroborated earlier work on the structure of the wing8. We now report the discovery of several hundred blue main-sequence stars in an area reaching 9° east of the SMC, coinciding with the HI ridge extending from the wing. These stare lie midway between the two Clouds and are more than 2 kpc further east than what was believed to be the eastern tip of the SMC wing. The apparent magnitudes of the brightest main-sequence stars suggest an age of ∼100 Myr, similar to ages of associations in the wing.

Automated analysis of objective-prism spectra – I. Quasar detection

Abstract: On decrit un systeme entierement automatique pour la localisation, la mesure et l'analyse de grands nombres de spectres de basse resolution obtenus au prisme objectif. Application a l'identification de candidats quasars

A digital technique for the separation of the eclipses of a white dwarf and an accretion disc

Abstract: On presente une methode permettant d'extraire la composante naine blanche d'une eclipse a partir de la courbe de lumiere d'une etoile variable cataclysmique a eclipses