Chaplin W.J.,University of Birmingham |
Appourchaux T.,CNRS Paris Institute of Astrophysics |
Elsworth Y.,University of Birmingham |
Garcia R.A.,University Paris Diderot |
And 116 more authors.
Astrophysical Journal Letters | Year: 2010
We present preliminary asteroseismic results from Kepler on three G-type stars. The observations, made at one-minute cadence during the first 33.5days of science operations, reveal high signal-to-noise solar-like oscillation spectra in all three stars: about 20 modes of oscillation may be clearly distinguished in each star. We discuss the appearance of the oscillation spectra, use the frequencies and frequency separations to provide first results on the radii, masses, and ages of the stars, and comment in the light of these results on prospects for inference on other solar-type stars that Kepler will observe. © 2010. The American Astronomical Society. All rights reserved.
Stello D.,University of Sydney |
Basu S.,Yale University |
Bruntt H.,French National Center for Scientific Research |
Mosser B.,French National Center for Scientific Research |
And 49 more authors.
Astrophysical Journal Letters | Year: 2010
Asteroseismology of stars in clusters has been a long-sought goal because the assumption of a common age, distance, and initial chemical composition allows strong tests of the theory of stellar evolution. We report results from the first 34days of science data from the Kepler Mission for the open cluster NGC 6819 - one of the four clusters in the field of view. We obtain the first clear detections of solar-like oscillations in the cluster red giants and are able to measure the large frequency separation, Δν, and the frequency of maximum oscillation power, νmax. We find that the asteroseismic parameters allow us to test cluster membership of the stars, and even with the limited seismic data in hand, we can already identify four possible non-members despite their having a better than 80% membership probability from radial velocity measurements. We are also able to determine the oscillation amplitudes for stars that span about 2 orders of magnitude in luminosity and find good agreement with the prediction that oscillation amplitudes scale as the luminosity to the power of 0.7. These early results demonstrate the unique potential of asteroseismology of the stellar clusters observed by Kepler. © 2010. The American Astronomical Society. All rights reserved.
Metcalfe T.S.,High Altitude Observatory |
Monteiro M.J.P.F.G.,University of Porto |
Thompson M.J.,High Altitude Observatory |
Thompson M.J.,University of Sheffield |
And 62 more authors.
Astrophysical Journal | Year: 2010
The primary science goal of the Kepler Mission is to provide a census of exoplanets in the solar neighborhood, including the identification and characterization of habitable Earth-like planets. The asteroseismic capabilities of the mission are being used to determine precise radii and ages for the target stars from their solar-like oscillations. Chaplin et al. published observations of three bright G-type stars, which were monitored during the first 33.5 days of science operations. One of these stars, the subgiant KIC 11026764, exhibits a characteristic pattern of oscillation frequencies suggesting that it has evolved significantly. We have derived asteroseismic estimates of the properties of KIC 11026764 from Kepler photometry combined with ground-based spectroscopic data. We present the results of detailed modeling for this star, employing a variety of independent codes and analyses that attempt to match the asteroseismic and spectroscopic constraints simultaneously. We determine both the radius and the age of KIC 11026764 with a precision near 1%, and an accuracy near 2% for the radius and 15% for the age. Continued observations of this star promise to reveal additional oscillation frequencies that will further improve the determination of its fundamental properties. © 2010. The American Astronomical Society.
News Article | December 12, 2016
HOUSTON - (Dec. 12, 2016) - Rice University astronomers and their colleagues have for the first time mapped gases in three dark rings around a distant star. The rings mark spaces where planets are thought to have formed from dust and gas around the star. All the rings around HD 163296 are devoid of dust, and the international team of researchers led by Rice astronomer Andrea Isella is sure that planets, probably gas giants with masses comparable to Saturn, are responsible for clearing the outermost ones. But the inner ring has far more carbon monoxide than the other two, leading them to believe no planet exists there. That remains unexplained, he said. "The inner gap is mysterious," Isella said. "Whatever is creating the structure is removing the dust but there's still a lot of gas." The work appears this week in Physical Review Letters. Only 20 years after the first exoplanet was spotted, astronomers are beginning to learn how planets form. Thousands of planets are now in the database, and scientists continue to improve their ability to analyze them for life-supporting characteristics. One aim of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, the world's largest radio telescope used in the research, is to study protoplanetary systems. Their mechanics will help scientists understand how the planets like Earth formed. (Radio telescopes detect the unique electromagnetic waves emitted by elements and compounds in space, allowing them to be identified and measured.) The Rice-led team's target star, nearly 400 light years away and best observed from the Southern hemisphere, is one of many known to have a large disk of dust and gas, Isella said. "Of the material that formed this disk, about 1 percent is dust particles and 99 percent is gas," Isella said. "So if you only see the dust, you cannot tell if a ring was formed by a planet or another phenomenon. In order to distinguish and really tell if there are planets or not, you need to see what the gas is doing, and in this study, for the first time, we can see both the dust and the gas." The outer rings are 100 and 160 astronomical units from HD 163296. (One unit is the distance from the center of the sun to Earth.) That's much farther from the star than previously thought possible for planet formation. The star is too far from Earth for direct observation of the planets, yet evidence from the new study shows they are likely to be there, clearing dust and gas from the outer rings much like orbiting asteroids called shepherd satellites clear space between the rings around Saturn, Isella said. The inner ring, 60 astronomical units from its star, showed a much greater concentration of the three carbon monoxide isotopes measured relative to dust. "Theoreticians have proposed other phenomena that can form dark rings without planets," Isella said. The researchers suspect one in particular: a lack of turbulence among non-ionized gas molecules in a magnetorotational instability "dead zone" that allows gas and dust to condense into a Saturn-like ring at the edge of the dark zone rather than a planet. The ring may also appear at the carbon monoxide frost line where the gas becomes cold enough to condense. The results laid the foundation for a new round of observations just starting at ALMA. Isella's initiative to study 20 stars with protoplanetary disks is one of two "large programs" (from 24 proposals) accepted by the telescope. "'Large program' means that you ask for a lot of telescope time, more than 50 hours," Isella said. "The other one they accepted will look at the emissions from a galaxy at the beginning of the universe. "It means our topic is considered by the astronomical community to be one of its highest priorities," he said. Isella said the researchers will also return to HD 163296 to learn what other elements are in the disk and rings. Taking inventory will help them determine what kind of a planet might form from material that's readily available. "If we know the chemistry of the material forming a planet, we can understand the chemistry of the planet," he said. Proximity to the star is also important. For example, water has to be far enough from a star to freeze around grains and allow them to aggregate. There is a chance that systems like HD 163296 and HL Tauri, two of the first three (with TW Hydrae) observed by ALMA to show protoplanetary rings, are anomalies, he said. "Now the question is whether all the protoplanetary disks are like this. Do they all have this structure? There is the concern that this object and HL Tauri are freaks," Isella said. Answers should come when the 20-star survey is completed. "We won't begin to get the data until next September, but it will tell us a lot," he said. Co-authors are Greta Guidi of the Arcetri Astrophysical Observatory in Firenze, Italy; Leonardo Testi of the Arcetri Observatory and the European Southern Observatory, Munich; Shangfei Liu of Rice and Los Alamos National Laboratory; Hui Li and Shengtai Li of Los Alamos; Erik Weaver and Yann Boehler of Rice; John Carperter and Itziar De Gregorio-Monsalvo of the Joint ALMA Observatory; Carlo Manara of the European Space Research and Technology Center, Noordwijk, The Netherlands; Antonella Natta of Arcetri and the Dublin Institute for Advanced Studies, Ireland; Laura Pérez of the Max Planck Institute for Radio Astronomy, Bonn, Germany; Luca Ricci of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.; Anneila Sargent of the California Institute of Technology, Pasadena, Calif.; Marco Tazzari of the European Southern Observatory, and Neal Turner of the Jet Propulsion Laboratory, California Institute of Technology. The National Science Foundation, NASA, the National Radio Astronomy Observatory, the European Space Agency and Los Alamos National Laboratory supported the research. This news release can be found online at http://news. NRAO press release: ALMA Finds Compelling Evidence for Pair of Infant Planets around Young Star Rice University researchers led the first mapping of gases in rings around a distant star with the powerful ALMA radio telescope. Clockwise from upper left: Yann Boehler, Shanfei Liu, Andrea Isella, Luca Ricci and Erik Weaver. (Credit: Jeff Fitlow/Rice University) An ALMA image of the star HD 163296 and its protoplanetary disk as seen in dust. New observations suggested that two planets, each about the size of Saturn, are in orbit around the star. These planets, which are not yet fully formed, revealed themselves in the dual imprint they left in both the dust and the gas portions of the star's protoplanetary disk. (Credit: ALMA [ESO/NAOJ/NRAO]/Andrea Isella/B. Saxton [NRAO/AUI/NSF]) A composite image of the star HD 163296. The inner red area shows the dust of the protoplanetary disk. The broader blue disk is the carbon monoxide gas in the system. ALMA observed that in the outer two gaps in the dust, there was a significant dip in the concentration of carbon monoxide, suggesting two planets are forming there. (Credit: ALMA [ESO/NAOJ/NRAO]/Andrea Isella/B. Saxton [NRAO/AUI/NSF]) An artist's impression of the protoplanetary disk surrounding the young star HD 163296. By studying the dust (ruddy brown) and carbon monoxide gas (light blue) profiles of the disk, astronomers led by Rice University's Andrea Isella discovered tantalizing evidence that two planets are forming in the outer two dust gaps in the disk. (Credit: B. Saxton/NRAO/AUI/NSF) Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,910 undergraduates and 2,809 graduate students, Rice's undergraduate student-to-faculty ratio is 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for happiest students and for lots of race/class interaction by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to http://tinyurl. .
News Article | December 4, 2015
At the core of most massive galaxies in the universe is a supermassive black hole – a concentration of matter so dense that it attracts anything nearby, including light. Such black holes have masses from millions to billions of times that of the Sun and are generally idle, only accreting the occasional star or gas cloud that ventures too close to the galaxy's centre. A small fraction of them are, however, extremely active, devouring matter at a very high rate, causing the surrounding material to shine brightly across the electromagnetic spectrum, from radio waves to X-rays and gamma rays. In some cases, emission from matter in the vicinity of the black hole is so intense that the core of the galaxy outshines the stars. These objects appear as point sources in the sky, like stars, and are known as quasars – short for quasi-stellar sources. Quasars allow scientists to study gravity in the very strong field of the supermassive black holes. In addition, comparing the properties of quasars with those of other galaxies that host either active or passive black holes can reveal interesting aspects about the evolution of galaxies over cosmic history. But one other aspect piqued the interest of two scientists from the Arcetri Astrophysical Observatory in Firenze, Italy: they realised that quasars can be used as probes of the expansion history of the universe. The results of their study are presented in a paper, published today in the Astrophysical Journal. "The history of cosmic expansion holds a wealth of information about the universe, including its age and the relative abundance of its components, and to pin it down we need to observe astronomical sources at a wide range of distances from us," explains Guido Risaliti, one of the scientists who led the study. "But determining distances in the universe is not at all trivial and can be best performed only with a few classes of sources. In this study, we show how it can be done with quasars," he adds. The main obstacle to measuring distances to astronomical objects lies in our ignorance of their true brightness, which makes it virtually impossible to assess whether a source is intrinsically bright or whether it just appears so because it is very close to us. For relatively nearby stars in our Galaxy, astronomers can get a very precise handle on distances using parallax – the tiny apparent shift of a star's position in the sky when viewed from different locations in the Earth's orbit. However, the greater the distance the smaller the parallax, which restricts the reach of this method to our local cosmic neighbourhood. Farther away, astronomers have to rely on 'standard candles' – astronomical objects whose intrinsic luminosity can be calculated from another of their observable properties. Amongst the most widely used standard candles are supernovae of type Ia – exploding white dwarf stars in a binary system. These explosions release roughly the same amount of energy every time, so their observed luminosity is a good indicator of the actual luminosity and, in turn, of their distance. In the 1990s, teams of scientists collected many observations of these supernovae to map distances to faraway galaxies and to study how these are affected by the overall cosmic expansion. This led to the surprising discovery that the universe's expansion is currently accelerating under the repulsive effect of a mysterious dark energy. In the standard cosmological model, dark energy dominates the present universe, making up about three quarters of its total energy budget, with the invisible dark matter accounting for about one fifth of the total, and ordinary matter amounting to a mere few percent. But it has not always been so, and delving deep into the history of our cosmos is crucial to figure out the nature and evolution of these 'dark' components. "Type Ia supernovae are a powerful tool for cosmology, but they cannot be observed at very large distances from us, so they are mostly used to probe the relatively recent universe," says co-author Elisabeta Lusso. Few supernovae of type Ia have been observed in earlier cosmic phases, when our almost 14 billion-year-old universe was younger than 5 billion years. "This is why we suggest to complement type Ia supernovae with quasars, which can be observed in large quantities out to much greater distances, probing cosmic history up to the epoch when the universe was only one billion years of age," she adds. To determine how far quasars are from us, Risaliti and Lusso used an interesting property of these sources: a link between the amount of light they emit at ultraviolet and X-ray wavelengths, which has been known since the late 1970s. Both types of emission derive from the black hole's activity, although they are caused by different processes. As the accreted material flows towards the black hole through a disc, it is heated by friction and shines brightly at visible and ultraviolet wavelengths. Then, part of the light emitted by the disc interacts with nearby electrons, receiving an extra energy boost and turning into X-rays. The key point underlying the application of this relation to cosmology is that the link between the luminosities at the two different wavelengths is not linear. This means that the ratio between a quasar's measured X-ray and ultraviolet emission is not fixed, but varies – in a known way – depending on the ultraviolet luminosity itself. So by measuring a quasar's X-ray and ultraviolet emission the scientists can estimate the absolute luminosity at ultraviolet wavelengths; in turn, this can be used to gauge the quasar's distance. While the physical mechanism underlying this relation is unclear, Risaliti and Lusso could still use it to treat quasars as standard candles and employ them as distance indicators for cosmological studies. To do so, they compiled a pilot sample of quasars with both ultraviolet and X-ray measurements, collecting 1138 sources from several data sets that were published in the scientific literature over the past decade. Most of the X-ray data came from surveys performed with ESA's XMM-Newton, including the COSMOS survey. "First, we verified that the relation between ultraviolet and X-ray luminosity holds for quasars observed at any cosmic epoch: this is an essential condition if we want to treat them as cosmological probes," explains Risaliti. Then, the scientists determined distances to the quasars in their sample and used these to study how the expansion of the universe changed in the span of cosmic history covered by these sources. From this, they evaluated the relative abundance of dark matter and dark energy in the universe, obtaining results that agree with current estimates obtained from supernovae and other observations, albeit with larger errors. "Quasars are a less precise tool to measure distances than supernovae of type Ia, but they yield complementary information about the distant universe that is inaccessible to supernova observations," says Lusso. The power of this new approach is best unleashed through the combination of quasars and supernovae of type Ia, spanning over 13 billion years of cosmic evolution to investigate how the universe changed across most of its history. In fact, combining data from current surveys of both types of sources yields constraints on the relative abundance of dark matter and dark energy that are tighter and more precise than those obtained from supernovae alone. The method developed by Risaliti and Lusso appears especially promising in light of future surveys, since a larger quasar sample means smaller errors on the cosmological parameters. On the X-ray front, the German-led eROSITA instrument on-board the Russian Spektr-RG satellite, planned for launch in 2017, is expected to observe millions of quasars, and ESA's Advanced Telescope for High-ENergy Astrophysics (ATHENA), planned for launch in 2028, could survey up to 10 million quasars. Meanwhile, ESA's Euclid mission, planned for launch in 2020, will observe a few million quasars at visible and near-infrared wavelengths – the portion of the spectrum where the ultraviolet light emitted by distant quasars is redshifted due to cosmic expansion. "It is very gratifying to see that the data collected by XMM-Newton over many years are being used as the basis for a creative and promising method to investigate the darkest secrets of our universe," comments Norbert Schartel, ESA XMM-Newton Project Scientist. The study is based on a sample of 1138 quasars that was obtained by compiling many different data sets published previously in scientific papers. The sample contains an estimate of the X-ray and ultraviolet luminosity for each quasar. The X-ray data come mainly from ESA's XMM-Newton X-ray observatory, as well as from NASA's Chandra X-ray Observatory and the German Aerospace Center-led ROSAT satellite. The ultraviolet luminosity was estimated using data from the Sloan Digital Sky Survey, NASA's Galaxy Evolution Explorer (GALEX) and Spitzer Space Telescope, NOAJ's Subaru Telescope, the Canada France Hawaii Telescope (CFHT), the Two Micron All Sky Survey (2MASS) and the UKIRT Infrared Deep Sky Survey (UKIDSS). The European Space Agency's X-ray Multi-Mirror Mission, XMM-Newton, was launched in December 1999. The largest scientific satellite to have been built in Europe, it is also one of the most sensitive X-ray observatories ever flown. More than 170 wafer-thin, cylindrical mirrors direct incoming radiation into three high-throughput X-ray telescopes. XMM-Newton's orbit takes it almost a third of the way to the Moon, allowing for long, uninterrupted views of celestial objects. Explore further: Astronomers discover new way to measure Universe
Hinz P.,University of Arizona |
Bailey V.P.,University of Arizona |
Defrere D.,University of Arizona |
Downey E.,University of Arizona |
And 11 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014
The Large Binocular Telescope Interferometer (LBTI) is a strategically important instrument for exploiting the use of the LBT as a 22.7 m telescope. The LBTI has two science cameras (covering the 1.5-5 μm and 8-13 μm atmospheric windows), and a number of observing modes that allow it to carry out a wide range of high-spatial resolution observations. Some simple modes, such as AO imaging, are in routine use. We report here on testing and commissioning of the system for its more ambitious goals as a nulling interferometer and coherent imager. The LBTI will carry out key surveys to Hunt for Observable Signatures of Terrestrial planetary Systems (HOSTS) and an LBTI Exozodi-Exoplanet Common Hunt (LEECH). The current nulling and coherent imaging performance is described. © 2014 SPIE.
Hinz P.,University of Arizona |
Arbo P.,University of Arizona |
Bailey V.,University of Arizona |
Connors T.,University of Arizona |
And 14 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012
We report the first phased images using adaptive optics correction from the Large Binocular Telescope Interferometer. LBTI achieved first fringes in late 2010, with seeing-limited operation. Initial tests verified the feasibility of the setup and allowed us tócharacterize the phase variations from both the atmosphere and mechanical vibrations. Integration of the secondary-base AO systems was carried out in spring 2011 and spring 2012 for the right and left side respectively. Single aperture, diffraction-limited, operation has been commissioned and is used as a productive mode of the LBTI with the LMIRCam subsystem. We describe the initial observation for dual aperture observations and coherent imaging results. © 2012 SPIE.
Bouchez A.H.,GMTO Corporation |
Acton D.S.,Ball Corporation |
Agapito G.,Arcetri Astrophysical Observatory |
Arcidiacono C.,Arcetri Astrophysical Observatory |
And 41 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012
The Giant Magellan Telescope adaptive optics system will be an integral part of the telescope, providing laser guide star generation, wavefront sensing, and wavefront correction to most of the currently envisioned instruments. The system will provide three observing modes: Natural Guidestar AO (NGSAO), Laser Tomography AO (LTAO), and Ground Layer AO (GLAO). Every AO observing mode will use the telescope's segmented adaptive secondary mirror to deliver a corrected beam directly to the instruments. High-order wavefront sensing for the NGSAO and LTAO modes is provided by a set of wavefront sensors replicated for each instrument and fed by visible light reflected off the cryostat window. An infrared natural guidestar wavefront sensor with open-loop AO correction is also required to sense tip-tilt, focus, segment piston, and dynamic calibration errors in the LTAO mode. GLAO mode wavefront sensing is provided by laser guidestars over a ∼5 arcminute field of view, and natural guidestars over wider fields. A laser guidestar facility will project 120 W of 589 nm laser light in 6 beacons from the periphery of the primary mirror. An off-axis phasing camera and primary and secondary mirror metrology systems will ensure that the telescope optics remain phased. We describe the system requirements, overall architecture, and innovative solutions found to the challenges presented by high-order AO on a segmented extremely large telescope. Further details may be found in specific papers on each of the observing modes and major subsystems. © 2012 SPIE.