ING Scientific Highlights in 1990
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ING Scientific Highlights
in 1990*

*Astronomical discoveries following from observations carried out with the ING telescopes


[ 1989 Scientific Highlights | 1991 Scientific Highlights ]


Schematic diagram of
BX Andromedae showing hotspot on secondary starContact binaries are composed of two low-mass intermediate type stars in rapid circular orbit around each other, with orbital periods between about 6 and 24 hours. Systems in true contact are joined at a neck, and a common convective envelope surrounds both stars, ensuring nearly uniform brightness over the common surface. As would then be expected, many contact binaries show stable and symmetric light curves as the stars orbit. However a few systems show very substantial changes in the shape of the light curve, on timescales of weeks to years. One hypothesis is that these systems are prone to extensive starspots.

BX And is such a system: orbital period changes indicate mass transfer 4×10-8 solar masses per year, and variable light curves can be explained by a hotspot located symmetrically about the line of centres covering about 20% of the secondary, perhaps a mass of gas floating on the secondary during the initial stages of transfer. Variations in the period are probably due to changes in the mass transfer rate, which also have an effect on the size and temperature of the hotspot and hence on the shape of the light curve. Once into contact, these systems continue to display enhanced magnetic activity in the form of starspots and active chromospheres, as demonstrated by recent INT observations of AG Vir and SS Ari.

More information

ING facilities involved:

  • Isaac Newton Telescope, using IDS
Some references: 
  • Bell, S.A. et al., 1990, "A photometric and spectroscopic study of BX Andromedae", MNRAS,244, 328
  • Hilditch, R.W. et al, 1990, "Spots on contact binary stars", GEMINI Newsletter Royal Greenwich Obs., 28, 16


Image of accretion disk around LX SerAccretion disks have aroused much interest in many different fields of astronomy. When they occur in binary star systems they can be studied particularly well since they are relatively nearby and bright, and because a reliable model of the geometry of the system is available. Among the most interesting type of binary system is the cataclysmic variable, which exhibits a spectacular variability on a wide range of timescales. This consists of a white dwarf primary and a cool secondary star. The cool star fills its Roche Lobe and mass from its outer layers falls towards the white dwarf. Because of its angular momentum, however, the infalling gas is forced into orbit around the white dwarf where it is stored in an accretion disk, which is responsible for a large proportion of the light emitted by the system. In some systems, the secondary star periodically eclipses parts of the accretion disk, producing a dip in the light curve typically lasting half an hour. The shape and colour of the eclipse curve reflects the intensity and temperature structure of the disk.

Using the Multipurpose Fotometer mounted on the JKT, researchers observed several eclipses of the eclipsing cataclysmic variable UX Uma in four wavebands and reconstructed the accretion disk structure using a maximum-entropy technique. The reconstruction shows that the bulk of the optical radiation comes from a more or less symmetric structure centered on the white dwarf, but that there is also a smaller spot, where the gas stream from the cool star hits the accretion disc.
Image of humps seen in spectrum of DP LeoAM Her systems are an important class of cataclysmic variables in which the secondary star loses material to a strongly magnetic white dwarf primary. The magnetic field on the primary is enormously strong, some tens of megagauss, so that the stream of material does not form a disk, but is captured by the field, and accretes on to the white dwarf in one or more shock regions at the magnetic poles. The energy of the system is released partly as X-rays in the shocks, and partly as optical cyclotron radiation from free electrons in the stream spiralling in the magnetic field. This radiation is emitted at low-order harmonics of the fundamental cyclotron frequency, broadened into humps by Doppler motion of the electrons in the emission region. Observing these humps in the spectra of AM Her systems is very difficult, but some reseachers using the WHT Faint Object Spectrograph were able to detect humps in a total of five systems. From the observations it is possible to determine the magnetic field strengths and temperatures of the emitting regions. The fields lie between 25 and 44 megagauss and the estimated temperatures lie between 5.0 and 23 keV. The data are now subject to detailed modelling.

More information

ING facilities involved:

  • Isaac Newton Telescope, using the Faint Object Spectrograph
  • Jacobus Kapteyn Telescope, with MPF
  • William Herschel Telescope, with FOS-2
Some references: 
  • Cropper, M. et al, 1990, "Cyclotron humps in AM-Herculis systems - variations around the orbit in DP-Leonis", MNRAS, 245, 760
  • Cropper, M. et al, 1989, "The magnetic field in four AM Her systems - Measurements from cyclotron humps", MNRAS, 236, 29
  • Rutten, R.G.M. et al, 1992, "Reconstruction of the accretion disk in six cataclysmic variable stars", A & A, 260, 213



Image of IRAS sources over the skyBright hight redshift quasars are important observation probes of the structure, evolution and early history of the Universe. The mere existence of the most luminous high-redshift quasars poses problems for currently popular models of the Universe, for example Cold Dark Matter, because the time available to form such massive energy sources since the Big Bang is uncomfortably short: only 1 billion years at a redshift of z=4. Their high optical luminosity means that they can be easily studied over very large cosmological distances, and they are particularly valuable as probes of the intervening gas clouds and galaxies, and for such fundamental investigations as the temperature of the microwave background, deuterium abundance and the large scale structure at early epochs. 

There are now 20 quasars known above a redshift of z=4, seven of which have had their nature and redshift confirmed using the INT. One third of the 36 highest known redshift quasars have been discovered by the ING.

Further problems with the Cold Dark Matter model were revealed in an analysis of large-scale galaxy clustering published recently. The researchers undertook an all-sky redshift survey of IRAS galaxies: 1211 new redshifts were obtained, the great majority with the WHT, with some from the INT and other telescopes. Other redshifts were obtained from the literarure or unpublished sources. The result was a uniform all-sky sample encompassing a larger volume of the Universe than any previous redshift survey and a map of the distribution of galaxies within a radius of 150h-1 Mpc. A clustering analysis of this map showed that the variation in density of galaxies over the Universe is inconsistent with the predictions of the Cold Dark Matter model.

The same reseachers used the map of the distibution of galaxies on the Local Group of Galaxies, and deduce the corresponding perculiar motion of the Local Group. They found that the acceleration acting on the Local Group is generated by a dozen or so clusters within 100h-1Mpc, and the velocity of the Local Group with respect to the microwave background radiation of 600 kms-1 can be explained provided the Universe has a density close to the critical value. No additional clusters located behind the galactic plane are needed to account for the Local Group motion, and there is no very large structure behind the Centaurus cluster capable of generating the claimed streaming motions of 1000kms-1, so the rationale for the 'Great Attractor' appears to have faded. 

More information

ING facilities involved: 

  • William Herschel Telescope, using FOS-2
  • Isaac Newton Telescope, using IPCS and FOS-1
Some references: 
  • Rowan-Robinson, M. et al, 1990, "A sparse-sample redshift surveyed of IRAS galaxies - Part One - The convergence of the IRAS dipole and the origin of our motion with respect to the microwave background", MNRAS, 247, 1 
  • Irwin, M. and McMahon, R., 1990, "Yet more z > 4 QSOs discovered using the INT", GEMINI Newsletter Royal Greenwich Obs., 30, 6 
  • Frenk, C.S. et al.,1991, "Is Cold Dark Matter Really Dead?", Nature, 351, 22 



2-D spectrum proving object is a background sourceGravitational lensing, the reimaging of a distant object by a massive intervening one, is a prediction of General Relativity which has only recently been observationally confirmed. Astronomers are seeking to use this phenomenon constructively to learn about the Universe. The most promising lenses are moderate redshift clusters of galaxies whose gravitational potential produces distorted arc-like images of remote background galaxies. The technique promises to reveal details of the high redshift universe unobtainable by conventional observations. One of the most challenging arc redshift determinations was achieved using ISIS on the WHT.

An exposure lasting over three hours was made of an extremely faint arc structure around the central galaxy of the rich cluster Abell 963 (redshift z=0.206) in 0.8 arcsecond seeing, revealing a single strong emission line at a wavelength of 6600Å. The interpretation of this observation is that the imaged object is a very distant spiral galaxy containing regions of active star formation: the emission line is [OII] redshifted to z=0.771. A second arc in this cluster proved too faint for spectroscopy, but INT images showed that the two arcs have similar unusually blue colours, indicating that they are two gravitational images of the same object.

More information

ING facilities involved: 

  • William Herschel Telescope, using ISIS
  • Isaac Newton Telescope, using the prime focus CCD
Some references: 
  • Ellis, R. et al, 1991, "Spectroscopy of arc in the rich cluster Abell 963", MNRAS, 249, 184


ISIS on the WHT was used to make the first optical follow up on a new ROSAT X-ray source and found a detached binary system. 

The globular cluster M15 is undergoing gravitational collapse and it has been a mystery as to how such clusters could survive this collapse. It is thought that this contraction could be halted through the formation of binary systems. The ISIS spectrograph and the WHT have been used to detect these binary systems and add weight to this theory. 

The INT has been used, with the Faint Object Spectrograph, to discover proto-planetary nebulae. The results showed high velocity stellar winds which had not previously been thought to form.

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Last modified: 13 December 2010