UK Scientists Await
Last Updated on Monday, 08 March 2010 16:24
Published on Friday, 25 February 2005 00:00
The second refurbishment mission of the Hubble Space Telescope (HST) is scheduled for launch on 11 February. Astronomers in the UK are eagerly awaiting the upgrading of the HST's instruments to begin a series of observations which will cover celestial objects ranging from white dwarfs and Sun-like stars to colliding galaxies, gravitational lenses and quasars.
The HST will receive two new instruments. The Near-Infrared Camera and Multi- Object Spectrometer (NICMOS) will be the first of Hubble's instruments to probe the sky at infrared wavelengths. The Space Telescope Imaging Spectrograph (STIS) supersedes the Faint Object Spectrograph and the Goddard High Resolution Spectrograph, both of which will be brought back to Earth on board the shuttle Discovery. HST will continue to operate with its original European-built Faint Object Camera, which requires corrective optics, and a second generation Wide Field and Planetary Camera (WFCP2) which was installed during the previous refurbishment mission in 1993.
Future Research by UK Astronomers
Sixteen major research proposals from UK astronomers have been accepted by the Space Telescope Science Institute in Baltimore for the next cycle of HST observations.
Professor Carole Jordan of Oxford University will be studying the processes taking place in Epsilon Eridani, one of the closest stars to our Sun both in size and distance. She intends to use STIS to study the structure of the star's sparse outer atmosphere and the reasons why its temperature rises to around 3 million degrees. The results will be compared with those for other dwarf stars, since the level of stellar 'activity', depends on the stellar rotation rate and conditions deep in the convection zone below the photosphere, where the magnetic fields are generated by dynamo action.
Professor John Peacock of the Royal Observatory, Edinburgh, has been given observing time with WFPC2 and NICMOS to look at the two oldest known galaxies in the Universe. It is hoped to establish the ages, compositions and distances of these radio galaxies. If it can be established that these are something like normal elliptical galaxies at redshift 1.55, this will prove that at least some galaxies formed very close to the Big Bang, i.e. soon after the creation of the Universe.
Dr Ian McHardy of Southampton University will be studying BL Lacertae objects (low power radio galaxies). These are generally thought to lie in large elliptical galaxies but observations suggest that the BL Lacertae object, PKS1413+135 lies in a spiral galaxy. Dr. McHardy intends to use NICMOS to find out whether the BL Lac lies within the 'host' galaxy or behind it as a background quasar which is being gravitationally lensed by the apparent host. If the BL Lac turns out to be exactly centred on the underlying galaxy, the conventional theories will have to be re-thought.
Dr Nial Tanvir of Cambridge University has an interest in two proposals:
1) He is principal investigator for a project using NICMOS to obtain infrared magnitudes (brightnesses) for a sample of Cepheid variables in the galaxy M96. This should produce a more reliable estimate of the galaxy's distance and provide important data for the eventual determination of the expansion rate of the Universe - the Hubble constant.
2) He is a co-investigator on a US-led proposal to do infrared (NICMOS) and optical (STIS in imaging mode) observations of intergalactic stars in the Virgo cluster of galaxies. These stars were only discovered last year (with WFPC2) and are thought to have been ejected from galaxies during collisions. Information on their infrared colours will give a better idea of the types of stars involved. The STIS imaging observations are intended mainly to map the spatial distribution of the stars within the cluster.
Dr Max Pettini (Royal Greenwich Observatory) and Dr David Bowen (Royal Observatory Edinburgh) will be using STIS to estimate the mass of the Universe. They will measure with great precision how much deuterium (a heavy form of hydrogen) was manufactured in the Big Bang. Since deuterium was manufactured only in the Big Bang, the amount of deuterium is related to the total amount of matter in the Universe, so they will, in effect, be 'weighing' the entire Universe. Their studies will concentrate on a proto- galaxy, with only one fifth the age of our Milky Way, where deuterium is most likely to be in near-pristine proportion relative to other elements.
Dr Martin Still of the University of St Andrews is working with collaborators in Sussex and the United States to study an unusual white dwarf star. They will use STIS to obtain high resolution imaging of material which is being magnetically-propelled from the cataclysmic variable AE Aquarii, a close red dwarf / white dwarf binary where material is transferred from one star to the other. With a spin period of 33 seconds, AE Aquarii is the fastest-spinning white dwarf star known. This spin is so rapid that perhaps 99% of all accreting material is ejected from the system by the magnetic field. The result is a spectacular 'Catherine-wheel nebula' of outflowing material. The team hope to see the outflow from AE Aquarii as it traces a unique spiral pattern, caused by the orbital rotation of the system.
Dr Francis Keenan of Queen's University, Belfast will be using STIS for ultraviolet spectroscopy of gas found in the interstellar medium in the Magellanic Bridge, a region of material between two nearby galaxies, the Large and Small Magellanic Clouds. The observations will investigate the physical conditions within the Bridge gas and determine the chemical composition of important elements such as carbon, nitrogen, oxygen, magnesium, silicon, sulphur and iron. This will show whether the Bridge gas originated in the Small Magellanic Cloud, as current theory suggests. Studies of young B-type stars in the Bridge will also confirm whether star formation is still occurring in this region.
Dr Clive Tadhunter of Sheffield University will be using NICMOS to determine whether there is a quasar hidden in the core of the nearby radio galaxy, Cygnus A, the most powerful radio source in the local universe. Many astronomers believe that quasars and radio galaxies are the same object viewed from different directions. This would be possible if all radio sources have quasar nuclei which are surrounded by obscuring dust and gas. NICMOS will test this theory by searching for the quasar nuclei in radio galaxies at infrared wavelengths where there is less extinction caused by the dust. The high spatial resolution and stability of NICMOS make these measurements feasible for the first time.
Dr Gerry Gilmore of the Institute of Astronomy in Cambridge has four projects.
1) To study the ongoing interaction between the Milky Way and its nearest neighbour, the Sagittarius dwarf galaxy. This small interloper, only discovered in 1994, actually lies inside the Milky Way and is only about twice as far from the centre of the Galaxy as the Sun. It is probably being destroyed by the tides of the Milky Way, and merging into it. The Sagittarius galaxy has four globular clusters, some of the most massive and youngest known. Dr Gilmore intends to determine accurate ages for the clusters and to study the early evolution of the Sagittarius dwarf.
2) Data collected over 4 years will determine the motion of the Sagittarius galaxy across the sky. By determining its real orbit inside the Milky Way it will be possible to calculate when it will be finally destroyed. Both of these studies will use WFPC2.
3) The nature of the invisible dark material which seems to make up most of the Universe remains a mystery. One possibility involves a very large population of low mass stars. Extremely long exposure images of a nearby dwarf galaxy in Ursa Minor will look at its small, faint stars to see if they contribute to the dark matter. This project uses the new deep imaging capability of STIS, and the near infrared capability of NICMOS, to complement deep optical imaging with WFPC2.
4) To study the evolution and formation of globular star clusters in the vicinity of the Large Magellanic Cloud. Studies of these clusters, covering all ages from very young to the oldest known, will reveal their evolution with time. By using all three HST cameras at the same time, data will be fed into special-purpose computers to build the best available models of how the clusters should evolve.
Dr Neal Jackson of Jodrell Bank will be looking at the galaxies which cause gravitational lensing, creating multiple images of more distant objects. Optical images of some lensing galaxies obtained with the WFPC2 showed that these galaxies are quite elongated. This is unexpected because most galaxies responsible for lensing are thought to be quite round, massive elliptical systems. NICMOS will enable the team to look in the infrared so that they can see through dust around these galaxies and should give more information on whether the lensing galaxies are elliptical.
Dr Bob Thomson of the University of Hertfordshire and colleagues from Jodrell Bank and the University of Wales, Cardiff, have been awarded time on HST to observe the optical jet in the elliptical galaxy M87. Thomson's team will be using NICMOS to look for evidence of an interaction between the jet and the interstellar medium in M87. At a distance of only 50 million light years, M87 is the nearest active galaxy with an optical jet. The jet extends over 5000 light years from the bright central nucleus of the galaxy and is powered by a massive black hole at the centre.
Drs Anna Gatti, Janet Drew and Rene Oudmaijer from Imperial College, London, are planning to use WFPC2 to obtain near-ultraviolet and optical images of the unusual Abell 35 binary system. The aim is to measure the angular separation of the two stars. If the stars are distinguishable at a separation of a tenth or so of an arcsecond, it will confirm that the two stars cannot have emerged from a common envelope. STIS will provide ultraviolet spectra of the hot white dwarf. This cannot be done from the ground because its giant companion is so bright and because the ultraviolet can only be observed from space. The data will allow the white dwarf's effective temperature, mass and radial velocity to be determined and provide a valuable test of theories of binary star evolution.
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