SCIENTIFIC AND TECHNICAL AEROSPACE REPORTS
A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 44, ISSUE 13 - JULY 05, 2006
89 ASTRONOMY
Includes observations of celestial bodies; astronomical instruments and techniques; radio, gamma-ray, x-ray, ultraviolet, and infrared astronomy; and astrometry.
20060016495 Arizona Univ., Tucson, AZ USA
Spacewatch Survey for Asteroids and Comets
McMillan, Robert S; Nov 2005; 68 pp.; In English Contract(s)/Grant(s): F49620-03-1-0107 Report No.(s): AD-A443974; FRS-330820; No Copyright; ONLINE: http://hdl.handle.net/100.2/ADA443974; Avail.: CASI: A04, Hardcopy
Low-light-level telescopic imaging observations of the night sky were made with the 0.9-meter and 1.8-meter Spacewatch Telescopes on Kitt Peak mountain in the Tohono Oodham Nation, Arizona. Small bodies in the solar system were discovered and followed to improve knowledge of their orbits and analyze the distribution of their absolute magnitudes. During this grant interval, a total of 6,620 positional measurements of 1,352 Earth-approaching Asteroids (EAs) were made, 200 of which were objects newly discovered by this project. The other EAs were observed to improve their orbits. Spacewatch also discovered 5 Centaurs or Scattered Disk Objects, 3 Trans-Neptunian Objects (TNOs), and 12 comets during this report interval. The 0.9-meter telescope was automated during this grant interval, allowing unattended operation. The number of detections of EAs and the area of sky covered allowed a new determination of the number of EAs with absolute magnitudes greater than or equal 22 and their distribution with absolute magnitude to be made. New collaborations were formed between Spacewatch and the USAF-funded Pan-STARRS project in Hawaii and the NASA-funded WISE spacecraft mission. Updates on loose associations with a program of asteroid photometry in NWAustralia, and astronomers in Mongolia are also given. Spacewatch is described at http://spacewatch.lpl.arizona.edu. DTIC
Asteroids; Comets; Surveys; Telescopes
20060016950 Arizona Univ., Tucson, AZ USA
Study of Potiential Spacecraft Target Near-Earth Asteroids
Worden, Simon P; Feb 2006; 12 pp.; In English Contract(s)/Grant(s): FA9550-04-1-0459; F49620-02-1-0107; Proj-2311 Report No.(s): AD-A444533; No Copyright; Avail.: CASI: A03, Hardcopy
In support of AFRL's space vehicles directorate I conducted a series of observations and analysis. Beginning with three visits to AFRL/VS at Kirtland AFB, NM lab personnel led by Dr. Babu Singaraju we identified a critical space supenonty objective was the ability to detect and study small objects (microsatellites) at Geosynchronous altitudes. The PI (Simon Worden) in concert with faculty and staff at the University of Arizona and the Hawaii High Performance Computing Center were able to plan a series of observations using the Steward Observatory MMT telescope and its Adaptive Optics system of several large commercial Geosynchronous satellites. This data was additionally post-processed using methods developed at the University of Arizona and the Hawaii High Performance Computing Center. These results showed that small microsatellites (less than 1 square meter) could be easily detected at GEO altitudes. Further work to refine these methods have been proposed for direct AFRL funding. DTIC
Artificial Satellites; Asteroids; Deep Space; Detection; Situational Awareness; Targets
20060017029 NASA Ames Research Center, Moffett Field, CA, USA
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Improving Neural Network Generalization Ability Using Outlier Analysis and Voronoi Tessellation
Ho, Michelle; McIntosh, Dawn M.; Srivastava, Ashok N.; [2006]; 1 pp.; In English; American Astronomical Society, 8-12 Jan. 2006, Washington, DC, USA; Original contains black and white illustrations; No Copyright; Avail.: CASI: A01, Hardcopy
The data used in this study was obtained from the Sloan Digital Sky Survey (SDSS), which provides astronomers with what is currently the most extensive mapping of the universe, covering 25% of the sky and cataloging the spectral properties (e.g., luminosity, color, surface temperature) of over 100 million celestial objects. Images generated by the SDSS are collected through 5 filters named u, g, r, l, and z that have respective wavelengths of 3540, 4750, 6222, 7632, and 9049 A. By measuring the photometric redshifts of the aforementioned wavelengths of a galaxy, astronomers can ascertain the extent to which galaxy is receding from which the distance to the galaxy can be calculated. Data collected for a small select group of galaxies (approximately 30, 000) contains accurate measurements of the galaxies' redshifts, in addition to measurements of their spectral properties. The above dataset containing both redshift measurements as well as spectral properties of the selectedgalaxies served as the training set for the purposes of this study; the data set containing only the spectra properties of a separate group of galaxies served as the test set. Derived from text
Neural Nets; Sky Surveys (Astronomy); Red Shift; Galactic Clusters; Spectral Reflectance; Luminosity; Galaxies
20060017064 Hawaii Univ., Honolulu, HI, USA
An X-ray Observation of the L1251 Dark Cloud
Simon, Theodore; The Astronomical Journal; January 2006; Volume 131, pp. 501-511; In English Contract(s)/Grant(s): NAS5-26555; NNG04GF53G; NAGW-2166; Copyright; Avail.: Other Sources
An X-ray image of the L1251 dark cloud in Cepheus was obtained with the XMM-Newton telescope. More than three dozen sources were detected above a 3 delta limit in X-ray luminosity of L(sub X = 10(exp 29) ergs/s. Among the detection sare eight optically visible T Tauri stars, which had been identified in earlier work from their emission at H(alpha). The two strongest X-ray sources have steady luminosities of L(sub X) approx. 10(exp 31) ergs/s and are at the saturation limit or X-ray activity in late-type stars, L(sub X)/L(sub bol) approx. 10(exp -3). X-ray emission was also observed from two CO emission cores in L1251, core C (L1251A) and core E (L1251B). Both regions contain high-velocity molecular gas, bright IRAS sources (Class I protostars), thermal radio sources, and Herbig-Haro (HH) jets. In L1251A strong X-ray emission was discovered in close proximity to the near-inbred and radio source IRSA/VLA 7 and to IRAS 22343+7501. IRSA/VLA 7 thus appears to be the most likely source of the molecular and HH outflows in L1251A. In L1251B X-ray emission was observed from a visible T Tauri star, KP2-44, which is thought to be the driving source for HH 189. Also reported is the tentative detection of X-ray emission from VLA 3, a thermal radio continuum source in L1251B that is closely associated with the extreme Class I protostar IRAS 22376+7455. Author
Molecular Gases; X Ray Sources; XMM-Newton Telescope; Protostars; Luminosity; Herbig-Haro Objects; Emission; T Tauri Stars
20060017675 Alcatel Space Industries, Cannes la Bocca, France
Deployable Hexapod Using Tape-Springs
Blanchard, Laurent; Falzon, Frederic; Dupuis, Jean; Merlet, Jean-Pierre; Jul 13, 2005; 8 pp.; In English; Original contains color illustrations Report No.(s): AD-A445185; No Copyright; Avail.: CASI: A02, Hardcopy
In the near future of space observation systems several technical challenges come into light like multi-pupil systems conceived as free flyers or extremely high resolution (EHR) systems with large dimensions and high agility requirements. To be able to face these challenges the Alcatel Space Research Department is studying innovative structural concepts for future observation instruments. One of these concepts is based on an hexapod whose legs are deployable coiled tape-springs. This hexapod is stowed in a favorable mechanical configuration for launch and self- deployed once in orbit. The deployment errors and long-term instabilities can be corrected thanks to six actuators located under the feet of the hexapod and the final optical performance is reached thanks to adaptive optics. The main advantages of this concept compared to classical hyper-stable telescope structures are: -a reduced volume during launch allowing large systems design -a very strong reduction of dimensional stability requirements during launch thanks to the actuators and the adaptive optics which will correct the geometric instabilities of the structure after deployment. This allows to build very light structures sized only by orbital life with quite classical CFRP or metallic materials. - a mass and inertia reduction which leads to an agility gain of the system. This concept is currently examined with ESA Innovative Triangle Initiative support. The goal of this study is to develop and build a representative breadboard of an hexapod using this technology and to evaluate its deployment precision and correction capabilities. This paper presents the optimal design algorithm based on interval analysis and used to define the geometry of the breadboard in order to maximize its correction capabilities and to insure its workspace. Then the structure design and the 6 tape-spring mechanisms are described. The paper ends with the results of the deployment and correction tests. DTIC
Actuators; Deployment; Telescopes
20060018299 NASA Goddard Space Flight Center, Greenbelt, MD, USA
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Gamma Ray Burst Discoveries with the Swift Mission
Marshall, F. E.; [2006]; 1 pp.; In English; Third International Conference on Particle and Fundamental Physics in Space, 19-21 Apr. 2006, Beijing, China; No Copyright; Avail.: Other Sources; Abstract Only
Gamma Ray Bursts are the largest explosions in the Universe, and the recently launched Swift mission is a multi-wavelength observatory that has greatly expanded our ability to study them.
Swift's wide-field gamma-ray camera is detecting about 100 bursts per year that are quickly viewed with sensitive X-ray and UV/optical telescopes on the observatory.
Positions are rapidly released to the world to enable ground-based observations.
Results from the first year of observations will be presented.
The mystery of short GRBs has been solved, very high redshift bursts discovered, and enormous X-ray flares found in afterglows.
These and other results will be discussed. Author
Swift Observatory; Gamma Ray Bursts; Afterglows; Explosions; Gamma Rays
20060018818 Nuclear Research Center of Grenoble, Grenoble, France
New Technological Development for Far Infrared Bolometer Arrays
Mottin, E; Agnese, Patrick; Peytavit, E; Beguin, A; Rey, P; Jul 13, 2005; 11 pp.; In English; Original contains color illustrations Report No.(s): AD-A445745; No Copyright; Avail.: CASI: A03, Hardcopy
Since 1997, CEA/SAP and CEA/LETI/SLIR have been developing monolithic Si bolometer arrays sensitive in the far infrared and submillimeter range for space observations. Two focal planes, 32x64 and 16x32 pixel arrays, are designed and manufactured for the PACS (Photodetector Array Camera and Spectrometer) instrument of the Herschel observatory, to be launched in 2007. The two arrays cover respectively the 60-130 micrometer and 130-210 micrometer ranges. The goal of these large bolometer arrays is to achieve observations in a background limited NEP around 10(to the negative 16th power)W.Hz(to the negative 1/2 power). The detector physics and manufacture techniques of the different stages of these arrays are first presented. Then we describe the read-out and multiplexing cold electronics (300mK) that make possible several functional modes (temporal and fixed pattern noise reduction, etc.). The latest experimental measurements carried out with the complete detector system at the nominal temperature are presented and performances are discussed. DTIC
Astronomical Observatories; Bolometers; Far Infrared Radiation
20060019124 Gemini Observatory, Hilo, HI, USA
Gemini Focus: Newsletter of the Gemini Observatory
Michaud, Peter, Editor; Fisher, Scott, Editor; Petersen, Carolyn Collins, Editor; Johnson, Rachel, Editor; June 2006; 68 pp.; In English; See also 20060019125 - 20060019132; Original contains color illustrations; Copyright; Avail.: Other Sources Articles included in the recent newsletter are: The Supernova Legacy Survey; Comets Hiding in the Main Asteroid Belt; Gemini Maps Gas Streaming Toward Black Hole in NGC 1097; Phoenix Measures a Brown-Dwarf Binary; Active Galaxy NGC 1068; Globular Clusters as Star Formation and Kinematic Tracers; Phoenix Gives New View of Eta Carinae; and Image Quality Refinements and Monitoring. Derived from text
Black Holes (Astronomy); Globular Clusters; Star Formation; Supernovae; Kinematics; Asteroid Belts; Brown Dwarf Stars
20060019125 Colorado Univ., USA
Phoenix Gives New View of Eta Carinae
Smith, Nathan; Gemini Focus: Newsletter of the Gemini Observatory; June 2006, pp. 38-40; In English; See also 20060019124; Copyright; Avail.: Other Sources
New spectra obtained with the high- resolution infrared Phoenix spectrograph on Gemini South provide striking insight to the structure of the so-called ''Homuncu1us' nebula around the massive southern hemisphere star Eta Carinae. In addition, they help produce the first definitive three-dimensional picture of the nebula's geometry. This bipolar nebula (Figures i and 2) was ejected by the massive star at its heart in the mid-nineteenth century. During that outburst, Eta Carinae was briefly the second-brightest star in the night sky, despite its distance of 2.3 kiloparsecs (about 7,500 light-years). The star faded after 15 - 20 years, but today its luminosity is re-radiated in the thermal infrared by dust formed in the nebula. This makes Eta Carinae the brightest io-micron object in the sky outside the solar system. The outburst ejected a huge amount of mass-more than ten times that of our Sun-and almost 105' ergs of kinetic energy, as inferred from observations in 2003 of emission from its dust. (That is about a billion times more energy than our Sun gives off in a year). The cause of the event and the mechanism that launched such a huge amount of mass off the star (while allowing the star to survive) remains unknown, but the structure of the fossil nebula it created holds important clues. Derived from text
Massive Stars; Southern Hemisphere; Infrared Radiation; Spectrographs; Io; Luminosity
20060019126 Vanderbilt Univ., USA
Phoenix Measures a Brown-Dwarf Binary
Stassun, Keivan Guadalupe; Gemini Focus: Newsletter of the Gemini Observatory; June 2006, pp. 25-28; In English; See also 20060019124; Copyright; Avail.: Other Sources
Observations of a newly discovered brown-dwarf eclipsing binary using the high-resolution near-infrared Phoenix spectrograph on Gemini South provide the first direct, accurate measurements of the fundamental physical properties of two young brown dwarfs. These measurements have important implications for theories about how such objects form and evolve. Brown dwarfs are 'failed stars' that span the divide between stars and planets. They serve as a critical link between theories of star and planet formation. Yet, even the most fundamental physical properties of brown dwarfs-their masses and radii-have so far eluded direct measurement. Prior to our observations, the mass of only one brown dwarf had been measured with sufficient accuracy to demonstrate that the object was, indeed, a brown-dwarf. In no case had a brown dwarf s radius been measured directly. We have discovered the object 2MO535-05 to be a brown-dwarf eclipsing binary-the first of its kind-in the young (about a million years old) Orion Nebula Cluster. This discovery was made as part of an ongoing long-term program to identify and study new eclipsing binaries in nearby star-forming regions by repeatedly imaging thousands of young stars and searching for those that exhibit periodic diminutions of flux. The I-band (0.8-micron) light curve (Figure 1) clearly shows the eclipsing nature of the system and provides a precise measure of the orbital period (about 9.8 days). Derived from text
Brown Dwarf Stars; Eclipsing Binary Stars; Star Formation; Imaging Techniques; Planetary Evolution; Star Clusters
20060019127 Gemini Observatory, Hilo, HI, USA
Gemini's Look at Active Galaxy NGC 1068
Mason, Rachel; Gemini Focus: Newsletter of the Gemini Observatory; June 2006, pp. 29-32; In English; See also 20060019124; Copyright; Avail.: Other Sources
Active galactic nuclei (AGNs) are regions of galaxies that emit copious amounts of energy from very energetic x-rays to lung-wavelength radio waves. In addition, they usually contain large amounts of hot, fast-moving gas swirling in a disk around the central region. Studying the properties of gas and dust in such environments allows astronomers to understand the nature and evolution of the massive black holes at the centers of active galaxies. Even a casual glance at the astronomy literature reveals a bewildering variety of AGN, with a nomenclature to match. They range from types 1 and 2 Seyfert galaxies to broad absorption-line quasars and blazars, taking in broad- and narrow-line radio galaxies and low-ionization nuclear emission-line region galaxies along the way. In fact, it has recently been estimated that there are as many as 60 different classes of AGN. This variety calls for some sort of model to help astronomers understand their formation, evolution, and activity. Astronomers can breathe a sigh of relief that we have the so-called 'unified model' of AGNs to bring some order to the zoo of active galaxies. In its most basic form, this model proposes that the accreting supermassive black hole that is the powerhouse of an AGN is surrounded by a doughnut-shaped 'torus' of dust and gas which obscures the nucleus from certain angles, but leaves it exposed from others. The detection of broad emission lines in polarized light scattered from the hidden nuclei of several Type 2 galaxies demonstrates the basic validity of the unified model. However, plenty of questions remain as to the nature of the obscuring material (its origin, geometry, composition, extent) and the extent to which this simple model can really explain the differences between many flavors of AGNs. Derived from text
Active Galaxies; Black Holes (Astronomy); Blazars; High Temperature Gases; Seyfert Galaxies; Radio Waves; Absorption Spectra; Active Galactic Nuclei; Radio Galaxies
20060019128 Oxford Univ., Oxford, UK
The Supernova Legacy Survey
Hook, Isobel; Gemini Focus: Newsletter of the Gemini Observatory; June 2006, pp. 17-21; In English; See also 20060019124; Copyright; Avail.: Other Sources
Gemini Observatory, the Canada-France-Hawaii Telescope (CFHT), the W.M. Keck Observatory, the Very Large Telescope (VLT) and other observatories have been working together since 2003 on a major observing program called the Supernova Legacy Survey (SNLS). The goal of this ambitious project is to determine the nature of a mysterious form of energy in the universe called 'Dark Energy.' The project follows up on a startling 1998 discovery made by two teams of astronomers working independently of each other. They were making measurements of distant Type Ia supernovae and found that the expansion of the universe is accelerating, contrary to the deceleration that would be expected from the pull of gravity. the results implied that there is some form of energy dominating the dynamics of the universe, which is pushing the universe apart. Today we still do not know what this energy is, and so its name reflects our ignorance of its nature. How do supernova explosions help us understand dark matter? Type Ia supernovae (SNe Ia) are believed to be thermonuclear explosions of white dwarf stars which have accreted matter from their stellar companions to the point where they can no longer support themselves. These outbursts appear to us as new point-like optical sources lasting only a few weeks. SNe Ia have two important properties that allow them to be used for cosmological tests. First, they are bright (sometimes outshining a whole galaxy), so can be observed at cosmological distances. Second, their uniform peak brightness allows them to be used as 'standard candles.' Derived from text
Astronomical Observatories; Cosmology; Dark Matter; Supernovae; Surveys; Thermonuclear Explosions; White Dwarf Stars; Gravitation; Brightness
20060019129 Gemini Observatory, Hilo, HI, USA
Comets Hiding in the Main Asteroid Belt
Fisher, Scott; Gemini Focus: Newsletter of the Gemini Observatory; June 2006, pp. 15-16; In English; See also 0060019124; Copyright; Avail.: Other Sources
Comets are among the most recognizable objects in the sky. Due to the classic chevron shape and ephemeral nature of these celestial objects, humans have observed comets with awe, and sometimes with fear, for the entirety of written history. Far from being harbingers of doom (as they were once portrayed), we now know that comets are icy bodies that become active as they approach the Sun. The main source of this activity is due to sublimation of the ices that hold a comet's nucleus together. This process causes jets and outbursts that form the ion and dust tails we see streaming away from comets as they pass near the Sun.
There are two broad classifications of comets based on where they originate in the solar system. The first are the so-called 'short-period' or Jupiter-family comets (JFCs for short). These are believed to have formed in the Kuiper Belt justbeyond Neptune (between 30 and 50 astronomical units (AU) from the Sun). The second are the 'long-period' (or Halley Family) comets. These are thought to originate in the much more distant Oort cloud, which lies about 3,000-5,000 AU from the Sun. Even though the vast majority of the comets we observe today come from these two reservoirs, astronomers have long suspected that other populations of solar system objects may also be rich in water ice (which dominates the ice component of most comets).
Astronomers seeking to explain the origin of our planet's oceans have often invoked the bombardment of the infant Earth by ice-rich objects such as comets as a plausible source of the water. To prove this theory, it s important to identify the populations of comets that could supply the amount of material needed to form all of the bodies of water on Earth. In support of this endeavor, recent observations made with the Gemini Multi-Object Spectrograph at Gemini North helped Henry Hsieh and David Jewitt of the University of Hawaii Institute for Astronomy uncover a new class of comet that orbits in the main asteroid belt. Hsieh and Jewitt were motivated to perform a survey of about 300 small (a few kilometers in size) asteroids after the object 133P/Elst-Pizarro was observed to exhibit a dust coma similar to that of a classical comet during its perihelion passages of 1996 and 2002. During this survey, two more objects-P/2005 U1 Read and asteroid 118401-were found to be active with comet-like morphologies. Together, these three objects form a new class of comets that have stable orbits completely within the main asteroid belt: the Main-Belt Comets (MBCs).
Imaging with Gemini (as well as 1- to 2-meter telescopes in Chile and Taiwan) leaves no doubt that these objects are physically cometary in nature (Figure i), but dynamically they are bona fide asteroids with orbits unlike any other known comet. Derived from text
Comets; Kuiper Belt; Surveys; Asteroid Belts; Classifications; Comet Nuclei; Halley's Comet
20060019130 Gemini Observatory, Chile
Image Quality Refinements and Monitoring
Boccas, Maxime; Michaud, Peter; Gemini Focus: Newsletter of the Gemini Observatory; June 2006, pp. 43-48; In English; See also 20060019124; Copyright; Avail.: Other Sources
As standing members on the list of the 'Top 10' biggest telescopes in the world, each of the Gemini primary mirrors has a suriace area of about 50 square meters. With such large areas to control, the challenge of maintaining the shape (or figure) of the mirrors, as well as the alignment of the entire optical system, requires enormous quantities of technology, ingenuity, and effort.Arecent paper by Gemini s Optics Group summarizes the ongoing campaign of Gemini s Engineering staff to refine the optical performance of both telescopes to take full advantage of nights when atmospheric conditions allow the telescopes to operate at or near the diffraction limit. (See Performance and Upgrades of Active Optics on Gemini Telescopes by Maxime Boccas and Tomislav Vucina, Proceedings of SPIE, 6273, May 2006).
A main challenge of producing excellent image quality (IQ) stems from the fact that the Gemini primary mirrors are meniscus mirrors. This type of mirror is relatively thin (approx. 20 cm) for its width (approx. 800 cm), which allows it to slump against its supports as the telescope tracks targets across thesky. Naturally, any deformation of the surface induces aberrations into the optical shape of the mirror, and therefore into any data obtained by the telescope. To mitigate these aberrations, Gemini (like all 8- to io-meter-class telescopes) uses active optics (aO) to continuously maintain and optimize the optical surface and alignment of the elements in the massive seven-story-high optical system. Given the active nature of the a 0 system, many of the engineering and optimization tests of the system components require real (on-sky) data, taken when atmospheric conditions are at their absolute best (to assess the performance of the system). Because these sky conditions are both rare and much coveted by PIs around the partnership, the testing procedures must be done with great efficiency as to minimize the impact on the science productivity of both telescopes. Derived from text
Telescopes; Image Resolution; Diffraction; Io; Menisci
20060019131 Rochester Inst. of Tech., NY, USA
Gemini Maps Gas Streaming Toward Black Hole in NGC 1097
Fathi, Kambiz; Bergmann, Thaisa Storchi; Gemini Focus: Newsletter of the Gemini Observatory; June 2006, pp. 22-24; In English; See also 20060019124; Copyright; Avail.: Other Sources
Current galaxy evolution theories postulate two main processes to account for how galaxies change over time: strong interactions between galaxies and/or internal evolution due to gravitational perturbations. The evolution often results in morphological distortions (changes in a galaxy s overall shape) or other kinds of transformations. In the absence of an interacting companion, the signatures of these evolutionary changes include the emergence of spiral arms, the creation of bars, as well as formation and feeding of an active nucleus.
Due to concentrations of mass towards the central gravitational potential well in galaxies, galactic nuclear regions are suitable environments for the formation of supermassive black holes (between a million and a billion solar masses). We now believe that there are supermassive black holes at the centers of most galaxies, or at least the ones with significant bulge components. Recent research shows that the mass of the supermassive black hole is proportional to that of the bulge. This relation implies a possible relation between the large-scale properties of galaxies and the nuclear properties such as the mass of the supermassive black hole.
Gas infall into such a supermassive black hole gives rise to energy output from the nucleus of the galaxy (which is known as an active galaxy). As long as gas is being fed to the black hole, the galaxy remains active. However, once the inflow of gas has ceased, the galaxy activity slows or stops. In this context, measuring the speed at which gas is falling from the outer parts of a galaxy towards the center, as well as the rate of the gas infall, allows us to calculate supermassive black hole s growth rate and the lifetime of the active phase. One of the long-standing problems in the study of nuclear activity in galaxies has been to understand the process by which gas is transferred from galactic scales (large regions of space) to nuclear scales (smaller areas within the galaxy). This process requires a huge loss of angular momentum.
Some pioneering research seems to suggest that the gas is transferred to the nuclear region by large-scale bars, but observational studies have not found an excess of bars among active galaxies when compared with control samples. Recent morphological studies have found an excess of nuclear dusty spiral structures in active galaxies instead, while recent theoretical works have shown that such nuclear spirals could be channels by which gas is transferred to the nucleus. But until the present date there were no kinematical studies to provide observational evidence that gas was indeed flowing along these small-scale spiral arms towards the active nucleus. Derived from text
Active Galaxies; Black Holes (Astronomy); Nuclear Structure; Gravitational Fields; Stellar Mass; Spiral Galaxies; Angular Momentum; Galaxies
20060019132 Swinburne Univ. of Technology, Australia
Globular Clusters as Star Formation and Kinematic Tracers
Pierce, Michael; Gemini Focus: Newsletter of the Gemini Observatory; June 2006, pp. 33-37; In English; See also 20060019124; Copyright; Avail.: Other Sources
The study of galaxy formation continue to be one of the main thrusts in astronomy. However, many global uncertainties cloud our understanding of the details, raising questions in particular about the early chemical history, the role of minor star formation, and galaxy merger histories. Even more uncertain, for elliptical galaxies especially, is quantifying the dark matter content at large radii. These uncertainties are all important issues, particularly those that deal with the existence of dark matter halos. We hope to clarify them by studying galaxies and their associated star clusters. Complex mixes of stellar populations in the central regions of galaxies make disentangling different star formation epochs and chemical enrichment histories a difficult problem. Low stellar surface brightness in the outer regions makes obtaining velocity measurements prohibitively time-consuming. Our team uses the spectra of globular clusters (GCs) to probe both the star-formation histories and gravitational potentials of elliptical galaxies. Globular clusters are suited to this purpose for several reasons. First, they are single stellar populations, which means that their stars are characterized by a single formation age and metallicity. Second, they are found around all galaxy types. Third, their high surface brightnesses makes them possible to observe to large distances. Author
Globular Clusters; Star Formation; Galactic Evolution; Dark Matter; Star Clusters; Halos; Gravitational Fields; Brightness
Source: NASA
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