Astronomical discoveries following from observations carried out with ING telescopes
SOLAR SYSTEM | |
First ever images of a neutral gas tail in a cometCoCAM WIDE FIELD INSTRUMENTWILLIAM HERSCHEL TELESCOPE JACOBUS KAPTEYN TELESCOPE Observations carried out to study the distribution of sodium atoms in comet Hale-Bopp led to the discovery of a new type of comet tail. Sodium atoms had previously been seen near the center of other comets, but these observations revealed for the first time a 6 degrees long straight tail of sodium. The discovery images were taken with the CoCAM wide-field CCD camera, built and operated by staff at the Isaac Newton Group, set up next to the 2.5m Isaac Newton Telescope. Members of the European Comet Hale-Bopp Team made several exposures of the comet through a narrow filter that isolates emission from sodium atoms, and to their great surprise the astronomers found that these atoms are distributed over enormous region in and around the comet. Contrary to earlier observations of bright comets near the Sun, the sodium was present not only in the region next to the cometary nucleus, but there were also large amounts in the region of the cometary tails. Following a careful analysis of the observed distribution of these atoms, the astronomers concluded that comet Hale-Bopp displays a third type of tail never seen before and consisting of sodium atoms. Whereas the well-known ion and dust tails so prominently displayed by Hale-Bopp show a large amount of structure, the new sodium tail has a completely different appearance. It takes the form of an approximately 600,000 km wide and 50 million km long tail, in a direction close but slightly different to that of the ion tail. While the electrically charged particles in the ion tail are accelerated to large velocities by the solar wind (very fast atomic particles emitted by the Sun), the sodium atoms are released from dust grains and then accelerated in the antisolar direction by simple fluorescence. These later conclusions were achieved thanks to observations carried out with the William Herschel Telescope. The European Comet Hale-Bopp Team also reported that high resolution observations taken with the Jacobus Kapteyn Telescope broadly revealed both spiral-jet and arc structures in the inner coma of comet Hale-Bopp. The astronomers took these pictures through a CN and a blue continuum filter and they obtained an expansion velocity for CN of 1.3 km/s.
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The sodium tail
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STARS | |
Nuevas enanas marrones
WILLIAM HERSCHEL TELESCOPE Desde que en 1995 se confirmó la naturaleza subestelar de la primera enana marrón descubierta, Teide 1, de 55 veces la masa de Júpiter, mediante las observaciones llevadas a cabo con el telescopio William Herschel y con el Keck I del Observatorio de Hawaii, la búsqueda de nuevas enanas marrones ha continuado sin cesar. Durante 1997, y como resultado de las observaciones realizadas a lo largo de 1996 en los telescopios del ORM, entre ellos los telescopios Isaac Newton y William Herschel, un equipo liderado por astrónomos del IAC dio a conocer el descubrimiento de nuevas enanas marrones en los cúmulos estelares jóvenes de las Pléyades y el Pesebre. En concreto, la enana marrón denominada Roque 4, con una masa de 45 veces la masa de Júpiter e I=19.75, resultó ser la enana marrón más fría y menos masiva jamás observada. Todas estas enanas marrones fueron descubiertas tras realizar fotometría óptica e infrarroja y estudiar tanto su emisión en H alpha como su tipo espectral. Asimismo, el dato de la velocidad radial fue fundamental para conocer su asociación con el cúmulo. En base a estos datos, los astrónomos del equipo descubridor concluyeron que el número de enanas marrones en nuestra Galaxia puede ser alto, lo cual representaría un resultado crucial para entender la estructura de la Vía Láctea. Picture
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New type of starWILLIAM HERSCHEL TELESCOPE A new type of star was discovered by an international team led by astronomers of the University of Wyoming. The astronomers used observations from some of the world's largest telescopes, including the William Herschel Telescope, and theoretical models run on supercomputers to develop new theories about the evolution of old binary systems. They found that in many binary systems, the initially more massive star ends its life and becomes a white dwarf, while the initially less massive star tries to evolve normally, but all the while loses mass to the white dwarf. Eventually, all that remains of the less massive star is an exposed stellar core with a size near that of the planet Jupiter and a mass of only 5/100th or so of its original value. Having used up or lost essentially all its hydrogen, this very small star has no remaining energy generation. It cannot ever become one of the usual stellar end-products. Therefore, it has a structure unlike any other kind of known star.
Picture
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 Doppler tomogram of IP Pegasi |
First detection of Spiral Waves in a stellar accretion discISAAC NEWTON TELESCOPE For the first time, astronomers detected spiral structure in the disc of gas that surrounds one of the stars in an interacting binary star system. The system they observed is known as IP Pegasi. IP Pegasi is an eclipsing dwarf nova (a subclass of cataclysmic variables) consisting of a K5 secondary star (0.5 solar masses) losing mass to a white dwarf (1.0 solar masses) in a 3.8-hour orbit. At semi-regular intervals of about three months the system brightens by 2 magnitudes as the mass transfer through the accretion disc suddenly increases. St Andrews University researchers observed the star in the first few days of one of these outbursts, when the disc was at its maximum extent. The disc is smaller than the radius of the Sun, so it is no possible to resolve it directly in any telescope. The technique they used involved measuring the velocity of the gas by looking at the Doppler shift in its spectrum. As the stars revolve around each other in their 3.8-hour orbit, the observers got successively different view of the disc. By using a technique called tomography, they were able to reconstruct a picture of the flow pattern of the gas. The results showed a two-armed trailing spiral in the outer part of the disc. Such spirals are thought to be created by tidal forces due to the gravitational pull of the normal star. The formation of such spirals had been predicted, but this is the first positive detection. This discovery was thanks to observations carried out at the Isaac Newton Telescope using SERVICE time. The SERVICE programme at the ING telescopes is well suited for undertaking a quick look on new cataclysmic variables or provide complimentary emission line information for old ones. But the programme's main advantage is that it offers the observers the opportunity of some flexibility over the predetermined schedule to cover unexpected events such as nova outbursts. Indeed the astronomers observed IP Pegasi while it was on the rise to outburst with the intermediate dispersion spectrograph on the Isaac Newton Telescope during SERVICE time, which resulted in the discovery of spiral structure in the binary's accretion disc.
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GALAXIES | |
Prueba observacional del origen por fusión de las galaxias elípticasISAAC NEWTON TELESCOPE Desde la década de los ochenta se conoce que las galaxias elípticas, tras su aparente simplicidad y uniformidad, esconden importantes peculiaridades. Casi la mitad de las elípticas estudiadas muestran tenues arcos luminosos, también llamados conchas. Entre un 20% y un 30% de las galaxias elípticas muestran núcleos que rotan en dirección opuesta u ortogonal a la del resto de la galaxia. Una fracción indeterminada de elípticas tiene anillos o discos polares con estrellas, gas y polvo. La existencia de tales estructuras sólo puede entenderse como resultado de procesos de acreción y/o fusión entre galaxias ya formadas, y no por un colapso monolítico en la etapa de formación. En concreto, la presencia de dos colas de marea contrapuestas es signo inequívoco de la fusión de dos galaxias de disco. El hecho de que las colas se diluyen con el tiempo hasta ser inobservables ha dificultado hasta ahora la realización de una prueba fundamental sobre el origen de las elípticas por fusión de espirales. Esta prueba fue encontrada gracias a las observaciones llevadas a cabo con el telescopio Isaac Newton de la galaxia elíptica peculiar NGC 3656. Esta galaxia había sido interpretada como el resultado de una fusión menor (una galaxia elíptica engulle a otra galaxia más pequeña) debido a la presencia de conchas fotométricas y de un núcleo con rotación ortogonal. Los datos del INT, tratados con un proceso especial de ecualización de la respuesta fotométrica del detector, han revelado un halo luminoso extenso y dos colas de marea. Tales colas son incompatibles con una fusión menor, y apuntan a una fusión mayor entre dos galaxias con disco de tamaño similar en órbita directa.
|  NGC 3656 and the two tidal tails |
COSMOLOGY | |
 Optical Counterpart of a Gamma-Ray Burst |
First Detection of the Optical Counterpart of a Gamma-Ray Burst
WILLIAM HERSCHEL TELESCOPE Since their discovery Gamma-Ray Bursts (GRBs) have been one of astronomy's great mysteries. For a long time it was expected that the detection of a counterpart at other wavelengths would provide the key to understanding the GRB phenomenon. However, such counterparts were not found, in spite of much effort during the last 25 years. The main problem for this was the lack of fast and accurate GRB positions. With the launch of the Wide Field Cameras (WFCs) on board the Italian-Dutch X-ray satellite BeppoSAX this has changed. For the first time GRB positions can be determined with accuracies of a few arcminutes within a few hours after the burst, unprecedented in GRB astronomy. Finally the situation changed dramatically on February 28, 1997 when a team of astronomers led by Jan van Paradijs of the University of Amsterdam and the University of Alabama in Huntsville pointed the William Herschel Telescope to the part of the sky where shortly before a new GRB had been detected (GRB 970228) by the Gamma-Ray Burst Monitor onboard BeppoSAX satellite. What the William Herschel Telescope saw was a faint optical source at the position on the sky determined by the X-ray satellite. Rapid follow-up with the William Herschel Telescope, and subsequent observations with the William Herschel and the Isaac Newton Telescopes revealed a fading optical source that was coincident with all the known error-boxes of GRB 970228. This led the discovery team to conclude that they had identified the first example of optical afterglow of a GRB.
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Discovery of the third most distant quasar and the highest redshift radio and X-ray source
WILLIAM HERSCHEL TELESCOPE During a CCD imaging phase of an investigation into the evolution of the space density of radio-loud quasars at high redshift, a quasar at z=4.72 was discovered. This quasar, GB1428+4217, is the third most distant quasar and the highest redshift radio and X-ray source currently known. Observations were carried out by astronomers from the University of California in Berkeley and the Institute of Astronomy in Cambridge using the Isaac Newton Telescope for imaging and the William Herschel Telescope for the spectroscopic follow-up.
|  GB1428+4217 quasar |
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Javier Méndez
18 November, 1997
jma@ing.iac.es