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Juan Mateu P.,University of Carabobo | Mateu C.,National Autonomous University of Mexico | Gustavo Bruzual A.,National Autonomous University of Mexico | Gladis Magris C.,Astrophysics Research Institute
Publications of the Astronomical Society of the Pacific | Year: 2015

We explore the ability of four different inverse population synthesis codes to recover the physical properties of galaxies from their spectra by SED fitting. Three codes, DynBaS, TGASPEX, and GASPEX, have been implemented by the authors and are described in detail in the paper. STARLIGHT, the fourth code, is publicly available. DynBaS selects dynamically a different spectral basis to expand the spectrum of each target galaxy, and TGASPEX uses an unconstrained age basis, whereas GASPEX and STARLIGHT use for all fits a fixed spectral basis selected a priori by the code developers. Variable and unconstrained basis reflect the peculiarities of the fitted spectrum and allow for simple and robust solutions to the problem of extracting galaxy parameters from spectral fits. We assemble a Synthetic Spectral Atlas of Galaxies (SSAG),3 comprising 100,000 galaxy spectra corresponding to an equal number of star formation histories based on the recipe of Chen et al.We select a subset of 120 galaxies from SSAG with a color distribution similar to that of local galaxies in the seventh data release (DR7) of the Sloan Digital Sky Survey (SDSS), and produce 30 random noise realizations for each of these spectra. For each spectrum, we recover the mass, mean age, metallicity, internal dust extinction, and velocity dispersion characterizing the dominant stellar population in the problem galaxy. All methods produce almost-perfect fits to the target spectrum, but the recovered physical parameters can differ significantly. Our tests provide a quantitative measure of the accuracy and precision with which these parameters are recovered by each method. From a statistical point of view, all methods yield similar precisions, whereas DynBaS produces solutions with minimal systematic biases in the distributions of residuals for all of these parameters.We caution the reader that the results obtained in our consistency tests represent lower limits to the uncertainties in parameter determination. Our tests compare theoretical galaxy spectra built from the same synthesis models used in the fits. Using different synthesis models and the lack of particular stellar types in the synthesis models but present in real galaxies will increase these errors considerably. Additional sources of error expected to be present in real galaxy spectra are not easy to emulate, and again will result in larger errors © 2015. The Astronomical Society of the Pacific. All rights reserved.


News Article | October 26, 2016
Site: cerncourier.com

Siegmund Brandt was born on 17 July 1936 in Berlin and studied physics at Bonn University in Germany. In his diploma work, which was carried out under the supervision of Wolfgang Paul, he constructed a small bubble chamber for experiments at the Bonn 500 MeV electron synchrotron. As early as 1961, Brandt worked at CERN on bubble-chamber physics studying pion–proton interactions, which became the topic of his PhD thesis. After his habilitation in 1966, he became associate professor at Heidelberg University, and in 1972 he became professor, founding senator of physics and vice rector at the newly founded University of Siegen. At Siegen, Brandt’s interest turned to electronic detectors and he worked at DESY on the PLUTO experiment at DORIS and PETRA. He contributed to the three-jet analysis with the “triplicity” method, which led to the discovery of gluons in 1979. After PLUTO, Brandt continued with the PETRA experiments by joining TASSO. During this time, Brandt was also member of the Scientific Council of DESY, which he chaired from 1990 to 1993, and he was later elected to the Polish Academy of Arts and Sciences. Brandt left DESY for CERN in the late 1980s, where he joined the ALEPH experiment at LEP and contributed to the ALEPH forward detectors and the analysis of Bhabha scattering and jet production. Brandt was an extremely creative author – his books include Data Analysis: Statistical and Computational Methods for Scientists and Engineers (1975) and The Harvest of a Century: Discoveries of Modern Physics (2013). He is also well known by many students as one of the authors of the general-physics textbook series he wrote with his theory colleague Hans Dieter Dahmen. Brandt was a versatile physicist. His work spanned the operation of now-historic detectors such as bubble chambers and the construction and analysis of modern electronic high-resolution instruments, and his successes will live on in his books on basic science. Brandt passed away peacefully in Munich on 28 August after a long period of illness, leaving behind his son and his grandchildren. He will be dearly missed by his friends and colleagues. Jim Cronin, who shared the 1980 Nobel Prize in Physics with Val Fitch for the discovery of CP violation, died on 25 August 2016. He was a brilliant experimentalist and data analyst who had remarkable careers in both particle and cosmic-ray physics. Jim was a man of extraordinary drive. Born in Chicago, he was raised in Dallas where his father was a classics professor. In 1953 he moved to Brookhaven and then Princeton, where he honed the spark-chamber technique before returning to the University of Chicago in 1971. He was appointed to head the colliding-beams division at Fermilab in 1977, but he soon resigned: a largely administrative role was not for him. In 1982, while on leave at CERN, he led a small team to make the best direct measurement of the lifetime of the π0. In 1986, to the surprise of many, Jim turned to cosmic rays and started to discuss his design for an air-shower array that could search for PeV gamma rays from the binary source Cygnus X-3. His visit to Leeds, UK, in November 1986 led to a lasting friendship, and in 1991 we embarked on an effort to build a collaboration and raise money to construct an instrument of unprecedented size to study cosmic rays with energies up to 1020 eV. Thirteen years later, the Pierre Auger Observatory, which covers 3000 km2 of Western Argentina, began data-taking, and continues to do so with a team of more than 400 scientists from 16 countries. The route to this achievement was strewn with difficulties, which were largely overcome through Jim’s formidable drive and his discrete and modest use of his status. He obtained $100,000 from UNESCO to bring scientists from developing countries to Fermilab for a six-month-long design study, won support for us to tour the Far East to raise interest, and prised $1 million from the University of Chicago to build a new centre at the site. Evaluation of our plans by an international body proved impossible, so Jim invited a panel of experts, including CERN’s Jack Steinberger, to assess us. Their report helped to raise $50 million, although one agency commented “Of course it is a favourable report: you chose the committee.” The success of the Auger project has greatly enhanced the profile of fundamental physics in Argentina, Brazil, Mexico and Vietnam, while the host town of Malargüe is home to the James Cronin School. Despite the large size of the collaboration, Jim stimulated young people while carrying out key analyses alone using FORTRAN 77 and “TopDrawer” – an ancient graphics package hosted on a dedicated Chicago computer. Jim will be sorely missed by all who knew him. Without his strong sense of direction and his persuasive skills, the Pierre Auger Observatory and many other projects would never have succeeded. He is survived by his second wife, Carol, and by a daughter, a son and six grandchildren. His first wife, Annette, and an older daughter pre-deceased him. Erwin Gabathuler, a highly respected experimental physicist and former CERN research director, passed away on 29 August 2016. Gabathuler was born in 1933 in Maghera, Northern Ireland, the son of the manager of an embroidery factory. He graduated in physics from Queen’s University Belfast in 1956 and was awarded his PhD from the University of Glasgow in 1961. After a postdoc at Cornell University he returned to the UK in 1964 to work on the NINA electron synchrotron at the Daresbury Laboratory, where, among a number of experiments, he made a pivotal measurement of “ρ–ω interference” in wide-angle electron–positron pair production. In 1974, Gabathuler moved to CERN and led the European Muon collaboration, which was aimed at understanding the quark structure of nucleons and nuclei. He became head of the CERN experimental division in 1978 and CERN research director in 1981, guiding CERN’s programme in the years leading to the discovery of the W and Z bosons. In 1983, Gabathuler was appointed to a chair at the University of Liverpool and to the position of head of the particle-physics group, taking charge of the leadership of the group’s programme as it entered the collider era. He initiated major Liverpool involvement in the H1 and HERMES experiments at the HERA electron–proton collider at DESY, while also nurturing Liverpool’s contribution to the DELPHI experiment at LEP. At the same time, his interest in the role of fundamental symmetries in physics led him to also conceive and establish CERN’s unique CPLEAR experiment to study kaon decay. While continuing his interest in deeply inelastic lepton–hadron physics with colleagues on H1, and following the completion of CPLEAR, Gabathuler took Liverpool into the BaBar experiment at SLAC, California. His appointment to Liverpool led Gabathuler to have a substantial influence on the development of high-energy physics in the UK, at a time when the then UK government was considering possible withdrawal from CERN. His commitment contributed greatly to the success of his colleagues in physics and in other fields. He helped to secure funding for the Liverpool Surface Science Centre, and initiated new undergraduate courses with the Astrophysics Research Institute at Liverpool John Moores University. In 1990, Gabathuler was elected to the fellowship of the Royal Society. He was also a fellow of the UK Institute of Physics, received the institute’s Rutherford Medal and Prize in 1992, and was awarded the Order of the British Empire in 2001 for services to physics. He received two honorary doctorates in science, and during his emeritus years continued to contribute as a member of national and international scientific advisory committees. As a colleague in Liverpool, he was widely admired and respected. He was a friend and mentor who exhibited unswerving support and concern for his colleagues’ individual well-being and career advancement, while demanding in return delivery of physics of the very highest standard. Experimental particle-physicist Werner Kienzle was born in Wiernsheim, a small town in Baden-Württemberg close to Stuttgart. His childhood was profoundly marked by the war and the death of his father on the German eastern front. Despite life after the war being difficult for his family, he was very successful in his academic studies and earned a fellowship at the University of Göttingen, where he did his PhD in solid-state physics. Werner joined CERN in 1964 as a postdoc fellow and he remained at the Organization for his entire career. Concerned and eager for peace in the tense context of the Cold War, he was deeply involved in collaboration with Russian colleagues and participated in experiments in Serpukhov from 1968 to 1972. Back at CERN, his work concentrated on searching for evidence of the presence of quarks in hadrons. He was among the main initiators of the NA3 experiment at the Super Proton Synchrotron (SPS), which allowed measurements of the structure functions of pions. The results indicated a cross-section about twice as high as anticipated, corresponding to QCD high-order corrections, and this enhancement was named the “K” factor by the collaboration, as recognition of Werner’s contribution. Werner was appointed SPS co-ordinator at the beginning of the 1980s and participated in the discovery of the W and Z bosons. In parallel, he became involved in new outreach programmes: in particular, he was promoter of the Microcosm in 1988 and editor of the Hadrons for Health reference booklet in 1996. While reaching his retirement age, Werner participated in the development of the total cross-section measurement set-ups that initiated the TOTEM experiment at the LHC. Werner was a fantastic and enthusiastic storyteller, an adventurer and an innovator. His wife, Maria, and his sons, Francesco and Marco, can be proud of everything he did for CERN. The great theoretician Stanley Mandelstam passed away in June, aged 87. He was born in Johannesburg, South Africa, from a Jewish family originating in Latvia, and studied in the UK under doctoral adviser Richard Dalitz. He became a professor at the University of Birmingham in 1960, then at the University of California at Berkeley in 1963. His initial reputation came from his 1958 proposal of what is called the Mandelstam representation, which implies that the scattering amplitude is the boundary value of an analytic function in a 2D domain in which the only singularities are cuts. Some people could say, now that we have the Standard Model of particle physics, that all this was useless. This is not the case historically, however, since it supported the idea that interesting results could be obtained from the combination of analyticity and unitarity. The main example is the “Froissart Bound” obtained in 1961, which says that the cross-section cannot increase faster than the square of the logarithm of the energy. In 1966, a proof of the Froissart bound was obtained without the Mandelstam representation. Around that time, V N Gribov also used the Mandelstam representation to predict that the scattering amplitude does not behave as was expected at high energies. It is also clear that the Veneziano amplitude, which was proposed in 1968 and led to dual models in which particles interact via “strings”, was inspired by the Mandelstam representation. The surprise was that theoreticians proposed that particles themselves be strings or superstrings. It is precisely in this domain that Mandelstam made further fundamental contributions. It’s not possible to list all of his papers here, but let me single out his proof that N = 4 supersymmetry is finite, an important result for which he sought absolutely no publicity. Mandelstam was a fellow of the Royal Society and of the American Academy of Arts and Sciences. He received the Dirac Medal in1991 and the Dannie Heineman Prize in 1992. Testimonies from students say that he was an excellent lecturer, including in undergraduate courses. Stanley Mandelstam was an affable person and incredibly modest. We shall miss him.


News Article | February 22, 2017
Site: www.csmonitor.com

An artist's conception of what the TRAPPIST-1 planetary system may look like, based on available data about their diameters, masses, and distances from the host star. Color and other details about appearance are completely speculative. —“The universe is a pretty big place. If it's just us, seems like an awful waste of space,” Carl Sagan once said. We still don’t know if we’re alone or not, but a new discovery suggests that at least one nearby solar system makes good use of its space indeed. Seven Earth-sized planets densely populate the area around a nearby dwarf star, circling it in tight, fast ellipses, announced an international team of scientists on Wednesday. An unprecedented three of those seven planets could support oceans, making them prime candidates in the search for life, and upcoming space telescopes promise to reveal more about the fascinating system in the near future – including how much potentially deadly radiation the star TRAPPIST-1 could be unleashing on its planets. “This is an amazing planetary system – not only because we have found so many planets, but because they are all surprisingly similar in size to the Earth!” lead author Michaël Gillon, of the STAR Institute at the University of Liège in Belgium, said in a press release. Sitting at a Millennium Falcon-friendly 12 parsecs (39 light years) away, ultracool dwarf star TRAPPIST-1 is relatively close to Earth, but don’t bother trying to find it in the sky tonight. It's just a little larger than Jupiter and burns about 2,000 times more dimly than our sun. Despite its unassuming stature, this mini-star is home to seven planets, all about the same mass as Earth, give or take a third. They zoom around their host at dizzying speeds, with orbits ranging from about two days to two weeks. If dropped into our solar system, the whole bunch would fit comfortably inside the orbit of Mercury. An observer on any one planet’s surface would be treated to a view of several planets hanging in the sky, each looking larger than our moon appears to us, say scientists. Inter-planetary trips would take days, rather than months or years. But what’s really turning heads is where the planets orbit relative to their host. Astronomers are especially interested in the area around a star where surface temperatures are not too hot and not too cold for liquid water to exist. Nicknamed “the Goldilocks zone,” this habitable band is just right for liquid water to support life as we know it. The TRAPPIST-1 system is much more compact than our solar system, but because dwarf stars emit so much less energy than our sun, that turns out to be just right for three of the seven planets. "What is significant about this system is the number of rocky, Earth-sized planets, and the number of planets in the habitable zone, both of which are unprecedented," Chris Copperwheat, one of the paper's co-authors and the head astronomer at the Astrophysics Research Institute of Liverpool, tells The Christian Science Monitor in an email. In this respect, the newly discovered system may be even more habitable than our own. "TRAPPIST-1 now holds the record for the most rocky planets in the habitable zone," says Lisa Kaltenegger, the director of the Carl Sagan Institute at Cornell University, who was not part of the study. "Our solar system only has two (Earth and Mars)," she writes in an email to the Monitor. "We have other systems with up to seven planets, but we don't have a system with seven rocky ones." Even the outliers could support at least some water, depending on the amount of heat produced internally by the gravitational stretching of the worlds, a process known as tidal heating. A cosmic accident of geometry made the discovery possible. The solar system spins in such a way that, as viewed from Earth, the seven observed planets pass directly between TRAPPIST-1 and our telescopes. When these transits take place, the star dims just a little, its brightness dropping about 1 percent. Gillon’s team had already known that TRAPPIST-1 was home to exoplanets, observing three crossing simultaneously in 2015. But uncovering the rest of the family was a team effort involving data from telescopes in Chile, Morocco, Hawaii, the Canary Islands, South Africa, and NASA’s Spitzer Space Telescope, which observed the system continuously for 20 days straight. Now the question on everyone’s lips is, what about life? Scientists are a long way from answering the question conclusively, but excitement is high. "Looking for life elsewhere, this system is probably our best bet as of today," co-author Brice-Olivier Demory, a professor at the University of Bern’s Center for Space and Habitability, said in a press release. Dr. Copperwheat agrees that initial signs are promising, if scant. "I think this is a very significant discovery – certainly one of the most exciting I have been involved with in my career," he says. "This is a very interesting and complex system which will be a key future target for the search for Earth-like conditions and life." The most tantalizing targets are the three middle planets. In their paper, published in Nature on Wednesday, the researchers speculate that they might be home to a familiar feature: liquid-water oceans. "Using a one-dimensional cloud-free climate model that accounts for the low-temperature spectrum of the host star, we deduce that planets e, f and g could harbor water oceans on their surfaces, assuming Earth-like atmospheres," they wrote. In addition to their Goldilocks real estate, the planets are all less dense than the Earth, says Copperwheat, which implies dynamic compositions potentially featuring liquid water, plentiful ice, or extended atmospheres. But everything hinges on that assumption of Earth-like atmospheres, which are far from a sure bet. Remember that Mars falls in the sun’s habitable zone, too, but surface water doesn’t hang around too long, even on a nice day, before the ultra-thin atmosphere lets it boil off into space. Just how life-friendly this kind of dwarf star might be is a hot topic, since the long-lived, slow-burning stars are paradoxically much more active than our sun, constantly shooting off solar flares that may bathe these super-close planets in high levels of harsh ultraviolet and X-ray radiation. A recent paper from NASA considered just this effect, concluding that our neighboring dwarf star Proxima Centauri would likely erode any atmosphere that may exist around orbiting planet Proxima b over the course of about a hundred million years. The same process could spell trouble for anything orbiting around TRAPPIST-1. The dwarf star's X-ray emission is roughly the same as our sun's, says Copperwheat, but "these planets are a lot closer so will suffer a greater degree of irradiation." That's not necessarily a deal-breaker for life, he cautions. "The short answer is that we don't know what the long-term consequences of high-energy radiation are to the habitability of Earth-type planets," he writes. "It may strip off the atmospheres, rendering the planets inhospitable to life, but on the other hand it could actually help by just stripping off the hydrogen and helium," he explains: atmospheric ingredients that, some scientists have argued, are not conducive to life. Dr. Kaltenegger, currently in the process of publishing papers modeling atmospheric erosion of both Proxima b and the TRAPPIST-1 planets, sees plenty of potential even for environments bathed in UV radiation. She points out that planets in either system could keep their atmospheres if they have Earth-like features like a magnetic field or an ozone layer. "I would not worry too much about a complete erosion of the atmosphere, but a thinner atmosphere is definitely possible, although that would still be able to shelter an ocean," she explains. "Life is a definite possibility on these worlds... but it might look different." Kaltenegger published a paper last summer outlining one UV survival strategy, based on Earth's bioluminescent corals. Organisms on planets around a dwarf star could protect themselves from the damaging rays by absorbing the UV radiation, and then releasing it at a longer, safer wavelength, she theorized. Such an ecosystem could react to solar flares by literally lighting up the planet, a sign she proposes could be observed from Earth. With so many theories flying around, astronomers’ next task is clear: Observe the TRAPPIST-1 system and gather as much data as possible to answer some of these questions. “At the moment, theoretical work on these questions is I think somewhat inconclusive, so it's up to observers like myself to actually try and detect the atmospheres to better inform the models,” Copperwheat explains. Fortunately, they might not have to wait long. A number of next-gen planet finders will come online next year, including the Transiting Exoplanet Survey Satellite and the James Webb Space Telescope. Scientists have high hopes in particular for the James Webb Space Telescope, which should be able to take direct measurements of the planets as they cross in front of TRAPPIST-1, revealing tell-tale signs of composition, atmosphere, and potential biosignatures like ozone. “The James Webb Space Telescope, Hubble’s successor, will have the possibility to detect the signature of ozone if this molecule is present in the atmosphere of one of these planets,” explained Dr. Demory in a press release. “This could be an indicator for biological activity on the planet.” And the signal shouldn’t be hard to pick up. Unlike our planet, which transits the sun only once every 365 days, the near-daily frequency with which these seven planets transit TRAPPIST-1 basically guarantees good chances for observation. Kaltenegger says that finding biosignatures requires a clear view of the planet and “roughly 70 to 100 hours (of observation) as a rule of thumb.” Copperwheat is also looking forward to the data collection bonanza to come, saying the system “is going to be intensively studied for many years to come” to help determine its habitability. Even if all seven worlds turn out to be solar flare-roasted wastelands, Copperwheat suggests we’ve still learned an important lesson about our place in the cosmos: "It seems Earth-sized planets may be very common in the Universe!"


News Article | February 22, 2017
Site: www.csmonitor.com

An artist's conception of what the TRAPPIST-1 planetary system may look like, based on available data about their diameters, masses, and distances from the host star. Color and other details about appearance are completely speculative. —“The universe is a pretty big place. If it's just us, seems like an awful waste of space,” Carl Sagan once said. We still don’t know if we’re alone or not, but a new discovery suggests that at least one nearby solar system makes good use of its space indeed. Seven Earth-sized planets densely populate the area around a nearby dwarf star, circling it in tight, fast ellipses, announced an international team of scientists on Wednesday. An unprecedented three of those seven planets could support oceans, making them prime candidates in the search for life, and upcoming space telescopes promise to reveal more about the fascinating system in the near future – including how much potentially deadly radiation the star TRAPPIST-1 could be unleashing on its planets. “This is an amazing planetary system – not only because we have found so many planets, but because they are all surprisingly similar in size to the Earth!” lead author Michaël Gillon, of the STAR Institute at the University of Liège in Belgium, said in a press release. Sitting at a Millennium Falcon-friendly 12 parsecs (39 light years) away, ultracool dwarf star TRAPPIST-1 is relatively close to Earth, but don’t bother trying to find it in the sky tonight. It's just a little larger than Jupiter and burns about 2,000 times more dimly than our sun. Despite its unassuming stature, this mini-star is home to seven planets, all about the same mass as Earth, give or take a third. They zoom around their host at dizzying speeds, with orbits ranging from about two days to two weeks. If dropped into our solar system, the whole bunch would fit comfortably inside the orbit of Mercury. An observer on any one planet’s surface would be treated to a view of several planets hanging in the sky, each looking larger than our moon appears to us, say scientists. Inter-planetary trips would take days, rather than months or years. But what’s really turning heads is where the planets orbit relative to their host. Astronomers are especially interested in the area around a star where surface temperatures are not too hot and not too cold for liquid water to exist. Nicknamed “the Goldilocks zone,” this habitable band is just right for liquid water to support life as we know it. The TRAPPIST-1 system is much more compact than our solar system, but because dwarf stars emit so much less energy than our sun, that turns out to be just right for three of the seven planets. "What is significant about this system is the number of rocky, Earth-sized planets, and the number of planets in the habitable zone, both of which are unprecedented," Chris Copperwheat, one of the paper's co-authors and the head astronomer at the Astrophysics Research Institute of Liverpool, tells The Christian Science Monitor in an email. In this respect, the newly discovered system may be even more habitable than our own. "TRAPPIST-1 now holds the record for the most rocky planets in the habitable zone," says Lisa Kaltenegger, the director of the Carl Sagan Institute at Cornell University, who was not part of the study. "Our solar system only has two (Earth and Mars)," she writes in an email to the Monitor. "We have other systems with up to seven planets, but we don't have a system with seven rocky ones." Even the outliers could support at least some water, depending on the amount of heat produced internally by the gravitational stretching of the worlds, a process known as tidal heating. A cosmic accident of geometry made the discovery possible. The solar system spins in such a way that, as viewed from Earth, the seven observed planets pass directly between TRAPPIST-1 and our telescopes. When these transits take place, the star dims just a little, its brightness dropping about 1 percent. Gillon’s team had already known that TRAPPIST-1 was home to exoplanets, observing three crossing simultaneously in 2015. But uncovering the rest of the family was a team effort involving data from telescopes in Chile, Morocco, Hawaii, the Canary Islands, South Africa, and NASA’s Spitzer Space Telescope, which observed the system continuously for 20 days straight. Now the question on everyone’s lips is, what about life? Scientists are a long way from answering the question conclusively, but excitement is high. "Looking for life elsewhere, this system is probably our best bet as of today," co-author Brice-Olivier Demory, a professor at the University of Bern’s Center for Space and Habitability, said in a press release. Dr. Copperwheat agrees that initial signs are promising, if scant. "I think this is a very significant discovery – certainly one of the most exciting I have been involved with in my career," he says. "This is a very interesting and complex system which will be a key future target for the search for Earth-like conditions and life." The most tantalizing targets are the three middle planets. In their paper, published in Nature on Wednesday, the researchers speculate that they might be home to a familiar feature: liquid-water oceans. "Using a one-dimensional cloud-free climate model that accounts for the low-temperature spectrum of the host star, we deduce that planets e, f and g could harbor water oceans on their surfaces, assuming Earth-like atmospheres," they wrote. In addition to their Goldilocks real estate, the planets are all less dense than the Earth, says Copperwheat, which implies dynamic compositions potentially featuring liquid water, plentiful ice, or extended atmospheres. But everything hinges on that assumption of Earth-like atmospheres, which are far from a sure bet. Remember that Mars falls in the sun’s habitable zone, too, but surface water doesn’t hang around too long, even on a nice day, before the ultra-thin atmosphere lets it boil off into space. Just how life-friendly this kind of dwarf star might be is a hot topic, since the long-lived, slow-burning stars are paradoxically much more active than our sun, constantly shooting off solar flares that may bathe these super-close planets in high levels of harsh ultraviolet and X-ray radiation. A recent paper from NASA considered just this effect, concluding that our neighboring dwarf star Proxima Centauri would likely erode any atmosphere that may exist around orbiting planet Proxima b over the course of about a hundred million years. The same process could spell trouble for anything orbiting around TRAPPIST-1. The dwarf star's X-ray emission is roughly the same as our sun's, says Copperwheat, but "these planets are a lot closer so will suffer a greater degree of irradiation." That's not necessarily a deal-breaker for life, he cautions. "The short answer is that we don't know what the long-term consequences of high-energy radiation are to the habitability of Earth-type planets," he writes. "It may strip off the atmospheres, rendering the planets inhospitable to life, but on the other hand it could actually help by just stripping off the hydrogen and helium," he explains: atmospheric ingredients that, some scientists have argued, are not conducive to life. Dr. Kaltenegger, currently in the process of publishing papers modeling atmospheric erosion of both Proxima b and the TRAPPIST-1 planets, sees plenty of potential even for environments bathed in UV radiation. She points out that planets in either system could keep their atmospheres if they have Earth-like features like a magnetic field or an ozone layer. "I would not worry too much about a complete erosion of the atmosphere, but a thinner atmosphere is definitely possible, although that would still be able to shelter an ocean," she explains. "Life is a definite possibility on these worlds... but it might look different." Kaltenegger published a paper last summer outlining one UV survival strategy, based on Earth's bioluminescent corals. Organisms on planets around a dwarf star could protect themselves from the damaging rays by absorbing the UV radiation, and then releasing it at a longer, safer wavelength, she theorized. Such an ecosystem could react to solar flares by literally lighting up the planet, a sign she proposes could be observed from Earth. With so many theories flying around, astronomers’ next task is clear: Observe the TRAPPIST-1 system and gather as much data as possible to answer some of these questions. “At the moment, theoretical work on these questions is I think somewhat inconclusive, so it's up to observers like myself to actually try and detect the atmospheres to better inform the models,” Copperwheat explains. Fortunately, they might not have to wait long. A number of next-gen planet finders will come online next year, including the Transiting Exoplanet Survey Satellite and the James Webb Space Telescope. Scientists have high hopes in particular for the James Webb Space Telescope, which should be able to take direct measurements of the planets as they cross in front of TRAPPIST-1, revealing tell-tale signs of composition, atmosphere, and potential biosignatures like ozone. “The James Webb Space Telescope, Hubble’s successor, will have the possibility to detect the signature of ozone if this molecule is present in the atmosphere of one of these planets,” explained Dr. Demory in a press release. “This could be an indicator for biological activity on the planet.” And the signal shouldn’t be hard to pick up. Unlike our planet, which transits the sun only once every 365 days, the near-daily frequency with which these seven planets transit TRAPPIST-1 basically guarantees good chances for observation. Kaltenegger says that finding biosignatures requires a clear view of the planet and “roughly 70 to 100 hours (of observation) as a rule of thumb.” Copperwheat is also looking forward to the data collection bonanza to come, saying the system “is going to be intensively studied for many years to come” to help determine its habitability. Even if all seven worlds turn out to be solar flare-roasted wastelands, Copperwheat suggests we’ve still learned an important lesson about our place in the cosmos: "It seems Earth-sized planets may be very common in the Universe!"


News Article | February 22, 2017
Site: www.csmonitor.com

An artist's conception of what the TRAPPIST-1 planetary system may look like, based on available data about their diameters, masses, and distances from the host star. Color and other details about appearance are completely speculative. —“The universe is a pretty big place. If it's just us, seems like an awful waste of space,” Carl Sagan once said. We still don’t know if we’re alone or not, but a new discovery suggests that at least one nearby solar system makes good use of its space indeed. Seven Earth-sized planets densely populate the area around a nearby dwarf star, circling it in tight, fast ellipses, announced an international team of scientists on Wednesday. An unprecedented three of those seven planets could support oceans, making them prime candidates in the search for life, and upcoming space telescopes promise to reveal more about the fascinating system in the near future – including how much potentially deadly radiation the star TRAPPIST-1 could be unleashing on its planets. “This is an amazing planetary system – not only because we have found so many planets, but because they are all surprisingly similar in size to the Earth!” lead author Michaël Gillon, of the STAR Institute at the University of Liège in Belgium, said in a press release. Sitting at a Millennium Falcon-friendly 12 parsecs (39 light years) away, ultracool dwarf star TRAPPIST-1 is relatively close to Earth, but don’t bother trying to find it in the sky tonight. It's just a little larger than Jupiter and burns about 2,000 times more dimly than our sun. Despite its unassuming stature, this mini-star is home to seven planets, all about the same mass as Earth, give or take a third. They zoom around their host at dizzying speeds, with orbits ranging from about two days to two weeks. If dropped into our solar system, the whole bunch would fit comfortably inside the orbit of Mercury. An observer on any one planet’s surface would be treated to a view of several planets hanging in the sky, each looking larger than our moon appears to us, say scientists. Inter-planetary trips would take days, rather than months or years. But what’s really turning heads is where the planets orbit relative to their host. Astronomers are especially interested in the area around a star where surface temperatures are not too hot and not too cold for liquid water to exist. Nicknamed “the Goldilocks zone,” this habitable band is just right for liquid water to support life as we know it. The TRAPPIST-1 system is much more compact than our solar system, but because dwarf stars emit so much less energy than our sun, that turns out to be just right for three of the seven planets. "What is significant about this system is the number of rocky, Earth-sized planets, and the number of planets in the habitable zone, both of which are unprecedented," Chris Copperwheat, one of the paper's co-authors and the head astronomer at the Astrophysics Research Institute of Liverpool, tells The Christian Science Monitor in an email. In this respect, the newly discovered system may be even more habitable than our own. "TRAPPIST-1 now holds the record for the most rocky planets in the habitable zone," says Lisa Kaltenegger, the director of the Carl Sagan Institute at Cornell University, who was not part of the study. "Our solar system only has two (Earth and Mars)," she writes in an email to the Monitor. "We have other systems with up to seven planets, but we don't have a system with seven rocky ones." Even the outliers could support at least some water, depending on the amount of heat produced internally by the gravitational stretching of the worlds, a process known as tidal heating. A cosmic accident of geometry made the discovery possible. The solar system spins in such a way that, as viewed from Earth, the seven observed planets pass directly between TRAPPIST-1 and our telescopes. When these transits take place, the star dims just a little, its brightness dropping about 1 percent. Gillon’s team had already known that TRAPPIST-1 was home to exoplanets, observing three crossing simultaneously in 2015. But uncovering the rest of the family was a team effort involving data from telescopes in Chile, Morocco, Hawaii, the Canary Islands, South Africa, and NASA’s Spitzer Space Telescope, which observed the system continuously for 20 days straight. Now the question on everyone’s lips is, what about life? Scientists are a long way from answering the question conclusively, but excitement is high. "Looking for life elsewhere, this system is probably our best bet as of today," co-author Brice-Olivier Demory, a professor at the University of Bern’s Center for Space and Habitability, said in a press release. Dr. Copperwheat agrees that initial signs are promising, if scant. "I think this is a very significant discovery – certainly one of the most exciting I have been involved with in my career," he says. "This is a very interesting and complex system which will be a key future target for the search for Earth-like conditions and life." The most tantalizing targets are the three middle planets. In their paper, published in Nature on Wednesday, the researchers speculate that they might be home to a familiar feature: liquid-water oceans. "Using a one-dimensional cloud-free climate model that accounts for the low-temperature spectrum of the host star, we deduce that planets e, f and g could harbor water oceans on their surfaces, assuming Earth-like atmospheres," they wrote. In addition to their Goldilocks real estate, the planets are all less dense than the Earth, says Copperwheat, which implies dynamic compositions potentially featuring liquid water, plentiful ice, or extended atmospheres. But everything hinges on that assumption of Earth-like atmospheres, which are far from a sure bet. Remember that Mars falls in the sun’s habitable zone, too, but surface water doesn’t hang around too long, even on a nice day, before the ultra-thin atmosphere lets it boil off into space. Just how life-friendly this kind of dwarf star might be is a hot topic, since the long-lived, slow-burning stars are paradoxically much more active than our sun, constantly shooting off solar flares that may bathe these super-close planets in high levels of harsh ultraviolet and X-ray radiation. A recent paper from NASA considered just this effect, concluding that our neighboring dwarf star Proxima Centauri would likely erode any atmosphere that may exist around orbiting planet Proxima b over the course of about a hundred million years. The same process could spell trouble for anything orbiting around TRAPPIST-1. The dwarf star's X-ray emission is roughly the same as our sun's, says Copperwheat, but "these planets are a lot closer so will suffer a greater degree of irradiation." That's not necessarily a deal-breaker for life, he cautions. "The short answer is that we don't know what the long-term consequences of high-energy radiation are to the habitability of Earth-type planets," he writes. "It may strip off the atmospheres, rendering the planets inhospitable to life, but on the other hand it could actually help by just stripping off the hydrogen and helium," he explains: atmospheric ingredients that, some scientists have argued, are not conducive to life. Dr. Kaltenegger, currently in the process of publishing papers modeling atmospheric erosion of both Proxima b and the TRAPPIST-1 planets, sees plenty of potential even for environments bathed in UV radiation. She points out that planets in either system could keep their atmospheres if they have Earth-like features like a magnetic field or an ozone layer. "I would not worry too much about a complete erosion of the atmosphere, but a thinner atmosphere is definitely possible, although that would still be able to shelter an ocean," she explains. "Life is a definite possibility on these worlds... but it might look different." Kaltenegger published a paper last summer outlining one UV survival strategy, based on Earth's bioluminescent corals. Organisms on planets around a dwarf star could protect themselves from the damaging rays by absorbing the UV radiation, and then releasing it at a longer, safer wavelength, she theorized. Such an ecosystem could react to solar flares by literally lighting up the planet, a sign she proposes could be observed from Earth. With so many theories flying around, astronomers’ next task is clear: Observe the TRAPPIST-1 system and gather as much data as possible to answer some of these questions. “At the moment, theoretical work on these questions is I think somewhat inconclusive, so it's up to observers like myself to actually try and detect the atmospheres to better inform the models,” Copperwheat explains. Fortunately, they might not have to wait long. A number of next-gen planet finders will come online next year, including the Transiting Exoplanet Survey Satellite and the James Webb Space Telescope. Scientists have high hopes in particular for the James Webb Space Telescope, which should be able to take direct measurements of the planets as they cross in front of TRAPPIST-1, revealing tell-tale signs of composition, atmosphere, and potential biosignatures like ozone. “The James Webb Space Telescope, Hubble’s successor, will have the possibility to detect the signature of ozone if this molecule is present in the atmosphere of one of these planets,” explained Dr. Demory in a press release. “This could be an indicator for biological activity on the planet.” And the signal shouldn’t be hard to pick up. Unlike our planet, which transits the sun only once every 365 days, the near-daily frequency with which these seven planets transit TRAPPIST-1 basically guarantees good chances for observation. Kaltenegger says that finding biosignatures requires a clear view of the planet and “roughly 70 to 100 hours (of observation) as a rule of thumb.” Copperwheat is also looking forward to the data collection bonanza to come, saying the system “is going to be intensively studied for many years to come” to help determine its habitability. Even if all seven worlds turn out to be solar flare-roasted wastelands, Copperwheat suggests we’ve still learned an important lesson about our place in the cosmos: "It seems Earth-sized planets may be very common in the Universe!"


News Article | February 22, 2017
Site: www.csmonitor.com

An artist's conception of what the TRAPPIST-1 planetary system may look like, based on available data about their diameters, masses, and distances from the host star. Color and other details about appearance are completely speculative. —“The universe is a pretty big place. If it's just us, seems like an awful waste of space,” Carl Sagan once said. We still don’t know if we’re alone or not, but a new discovery suggests that at least one nearby solar system makes good use of its space indeed. Seven Earth-sized planets densely populate the area around a nearby dwarf star, circling it in tight, fast ellipses, announced an international team of scientists on Wednesday. An unprecedented three of those seven planets could support oceans, making them prime candidates in the search for life, and upcoming space telescopes promise to reveal more about the fascinating system in the near future – including how much potentially deadly radiation the star TRAPPIST-1 could be unleashing on its planets. “This is an amazing planetary system – not only because we have found so many planets, but because they are all surprisingly similar in size to the Earth!” lead author Michaël Gillon, of the STAR Institute at the University of Liège in Belgium, said in a press release. Sitting at a Millennium Falcon-friendly 12 parsecs (39 light years) away, ultracool dwarf star TRAPPIST-1 is relatively close to Earth, but don’t bother trying to find it in the sky tonight. It's just a little larger than Jupiter and burns about 2,000 times more dimly than our sun. Despite its unassuming stature, this mini-star is home to seven planets, all about the same mass as Earth, give or take a third. They zoom around their host at dizzying speeds, with orbits ranging from about two days to two weeks. If dropped into our solar system, the whole bunch would fit comfortably inside the orbit of Mercury. An observer on any one planet’s surface would be treated to a view of several planets hanging in the sky, each looking larger than our moon appears to us, say scientists. Inter-planetary trips would take days, rather than months or years. But what’s really turning heads is where the planets orbit relative to their host. Astronomers are especially interested in the area around a star where surface temperatures are not too hot and not too cold for liquid water to exist. Nicknamed “the Goldilocks zone,” this habitable band is just right for liquid water to support life as we know it. The TRAPPIST-1 system is much more compact than our solar system, but because dwarf stars emit so much less energy than our sun, that turns out to be just right for three of the seven planets. "What is significant about this system is the number of rocky, Earth-sized planets, and the number of planets in the habitable zone, both of which are unprecedented," Chris Copperwheat, one of the paper's co-authors and the head astronomer at the Astrophysics Research Institute of Liverpool, tells The Christian Science Monitor in an email. In this respect, the newly discovered system may be even more habitable than our own. "TRAPPIST-1 now holds the record for the most rocky planets in the habitable zone," says Lisa Kaltenegger, the director of the Carl Sagan Institute at Cornell University, who was not part of the study. "Our solar system only has two (Earth and Mars)," she writes in an email to the Monitor. "We have other systems with up to seven planets, but we don't have a system with seven rocky ones." Even the outliers could support at least some water, depending on the amount of heat produced internally by the gravitational stretching of the worlds, a process known as tidal heating. A cosmic accident of geometry made the discovery possible. The solar system spins in such a way that, as viewed from Earth, the seven observed planets pass directly between TRAPPIST-1 and our telescopes. When these transits take place, the star dims just a little, its brightness dropping about 1 percent. Gillon’s team had already known that TRAPPIST-1 was home to exoplanets, observing three crossing simultaneously in 2015. But uncovering the rest of the family was a team effort involving data from telescopes in Chile, Morocco, Hawaii, the Canary Islands, South Africa, and NASA’s Spitzer Space Telescope, which observed the system continuously for 20 days straight. Now the question on everyone’s lips is, what about life? Scientists are a long way from answering the question conclusively, but excitement is high. "Looking for life elsewhere, this system is probably our best bet as of today," co-author Brice-Olivier Demory, a professor at the University of Bern’s Center for Space and Habitability, said in a press release. Dr. Copperwheat agrees that initial signs are promising, if scant. "I think this is a very significant discovery – certainly one of the most exciting I have been involved with in my career," he says. "This is a very interesting and complex system which will be a key future target for the search for Earth-like conditions and life." The most tantalizing targets are the three middle planets. In their paper, published in Nature on Wednesday, the researchers speculate that they might be home to a familiar feature: liquid-water oceans. "Using a one-dimensional cloud-free climate model that accounts for the low-temperature spectrum of the host star, we deduce that planets e, f and g could harbor water oceans on their surfaces, assuming Earth-like atmospheres," they wrote. In addition to their Goldilocks real estate, the planets are all less dense than the Earth, says Copperwheat, which implies dynamic compositions potentially featuring liquid water, plentiful ice, or extended atmospheres. But everything hinges on that assumption of Earth-like atmospheres, which are far from a sure bet. Remember that Mars falls in the sun’s habitable zone, too, but surface water doesn’t hang around too long, even on a nice day, before the ultra-thin atmosphere lets it boil off into space. Just how life-friendly this kind of dwarf star might be is a hot topic, since the long-lived, slow-burning stars are paradoxically much more active than our sun, constantly shooting off solar flares that may bathe these super-close planets in high levels of harsh ultraviolet and X-ray radiation. A recent paper from NASA considered just this effect, concluding that our neighboring dwarf star Proxima Centauri would likely erode any atmosphere that may exist around orbiting planet Proxima b over the course of about a hundred million years. The same process could spell trouble for anything orbiting around TRAPPIST-1. The dwarf star's X-ray emission is roughly the same as our sun's, says Copperwheat, but "these planets are a lot closer so will suffer a greater degree of irradiation." That's not necessarily a deal-breaker for life, he cautions. "The short answer is that we don't know what the long-term consequences of high-energy radiation are to the habitability of Earth-type planets," he writes. "It may strip off the atmospheres, rendering the planets inhospitable to life, but on the other hand it could actually help by just stripping off the hydrogen and helium," he explains: atmospheric ingredients that, some scientists have argued, are not conducive to life. Dr. Kaltenegger, currently in the process of publishing papers modeling atmospheric erosion of both Proxima b and the TRAPPIST-1 planets, sees plenty of potential even for environments bathed in UV radiation. She points out that planets in either system could keep their atmospheres if they have Earth-like features like a magnetic field or an ozone layer. "I would not worry too much about a complete erosion of the atmosphere, but a thinner atmosphere is definitely possible, although that would still be able to shelter an ocean," she explains. "Life is a definite possibility on these worlds... but it might look different." Kaltenegger published a paper last summer outlining one UV survival strategy, based on Earth's bioluminescent corals. Organisms on planets around a dwarf star could protect themselves from the damaging rays by absorbing the UV radiation, and then releasing it at a longer, safer wavelength, she theorized. Such an ecosystem could react to solar flares by literally lighting up the planet, a sign she proposes could be observed from Earth. With so many theories flying around, astronomers’ next task is clear: Observe the TRAPPIST-1 system and gather as much data as possible to answer some of these questions. “At the moment, theoretical work on these questions is I think somewhat inconclusive, so it's up to observers like myself to actually try and detect the atmospheres to better inform the models,” Copperwheat explains. Fortunately, they might not have to wait long. A number of next-gen planet finders will come online next year, including the Transiting Exoplanet Survey Satellite and the James Webb Space Telescope. Scientists have high hopes in particular for the James Webb Space Telescope, which should be able to take direct measurements of the planets as they cross in front of TRAPPIST-1, revealing tell-tale signs of composition, atmosphere, and potential biosignatures like ozone. “The James Webb Space Telescope, Hubble’s successor, will have the possibility to detect the signature of ozone if this molecule is present in the atmosphere of one of these planets,” explained Dr. Demory in a press release. “This could be an indicator for biological activity on the planet.” And the signal shouldn’t be hard to pick up. Unlike our planet, which transits the sun only once every 365 days, the near-daily frequency with which these seven planets transit TRAPPIST-1 basically guarantees good chances for observation. Kaltenegger says that finding biosignatures requires a clear view of the planet and “roughly 70 to 100 hours (of observation) as a rule of thumb.” Copperwheat is also looking forward to the data collection bonanza to come, saying the system “is going to be intensively studied for many years to come” to help determine its habitability. Even if all seven worlds turn out to be solar flare-roasted wastelands, Copperwheat suggests we’ve still learned an important lesson about our place in the cosmos: "It seems Earth-sized planets may be very common in the Universe!"


Smith G.P.,University of Birmingham | Smith G.P.,California Institute of Technology | Khosroshahi H.G.,Institute for Research in Fundamental Sciences | Khosroshahi H.G.,Astrophysics Research Institute | And 8 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We study the luminosity gap, Δm12, between the first- and second-ranked galaxies in a sample of 59 massive ( 1015 M) galaxy clusters, using data from the Hale Telescope, the Hubble Space Telescope, Chandra and Spitzer. We find that the Δm12 distribution, p(Δm12), is a declining function of Δm12 to which we fitted a straight line: p(Δm12) -(0.13 ± 0.02)Δm12. The fraction of clusters with 'large' luminosity gaps is p(Δm12≥ 1) = 0.37 ± 0.08, which represents a 3σ excess over that obtained from Monte Carlo simulations of a Schechter function that matches the mean cluster galaxy luminosity function. We also identify four clusters with 'extreme' luminosity gaps, Δm12≥ 2, giving a fraction of More generally, large luminosity gap clusters are relatively homogeneous, with elliptical/discy brightest cluster galaxies (BCGs), cuspy gas density profiles (i.e. strong cool cores), high concentrations and low substructure fractions. In contrast, small luminosity gap clusters are heterogeneous, spanning the full range of boxy/elliptical/discy BCG morphologies, the full range of cool core strengths and dark matter concentrations, and have large substructure fractions. Taken together, these results imply that the amplitude of the luminosity gap is a function of both the formation epoch and the recent infall history of the cluster. 'BCG dominance' is therefore a phase that a cluster may evolve through and is not an evolutionary 'cul-de-sac'. We also compare our results with semi-analytic model predictions based on the Millennium Simulation. None of the models is able to reproduce all of the observational results on Δm12, underlining the inability of the current generation of models to match the empirical properties of BCGs. We identify the strength of active galactic nucleus feedback and the efficiency with which cluster galaxies are replenished after they merge with the BCG in each model as possible causes of these discrepancies. © 2010 The Authors. Journal compilation © 2010 RAS.


Steele I.A.,Astrophysics Research Institute | Bates S.D.,Astrophysics Research Institute | Guidorzi C.,University of Ferrara | Mottram C.J.,Astrophysics Research Institute | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

We describe the design and construction of a new novel optical polarimeter (RINGO2) for the Liverpool Telescope. The instrument is designed for rapid (< 3 minute) followup observations of Gamma Ray Bursts in order to measure the early time polarization and time evolution on timescales of ∼ 1 - 10000 seconds. By using a fast rotating Polaroid whose rotation is synchronized to control the readout of an electron multiplying CCD eight times per revolution, we can rebin our data in the time domain after acquisition with little noise penalty, thereby allowing us to explore the polarization evolution of these rapidly variable objects for the first time. © 2010 Copyright SPIE - The International Society for Optical Engineering.


Arnold D.M.,Astrophysics Research Institute | Steele I.A.,Astrophysics Research Institute | Bates S.D.,Astrophysics Research Institute | Mottram C.J.,Astrophysics Research Institute | Smith R.J.,Astrophysics Research Institute
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

GRB jets contain rapidly moving electrons which will spiral around magnetic field lines. This causes them to emit polarized synchrotron emission. We have built a series of polarimeters (RINGO and RINGO2) to investigate this by measuring the polarization of optical light from GRBs at a certain single wavelength. The instruments are mounted on the Liverpool Telescope, which is a fully robotic (i.e. unmanned) telescope on La Palma which reacts to triggers from satellites such as the NASA SWIFT mission. This has had great success, with the first ever detections of early time optical polarization being made. In addition, the first measurements of the change in optical polarization from a GRB as the jet expands have recently been obtained. In this paper we describe the design and construction of RINGO3. This will be a multi-colour instrument that can observe simultaneously at three wavelengths. By doing so we will be able to unambiguously identify where in the burst the polarized emission is coming from. This will allow us to distinguish between three possibilities: (1) Magnetic instabilities generated in the shock front, (2) Line of sight effects and (3) Large-scale magnetic fields present throughout the relativistic outflow. The instrument design combines a rapidly rotating polaroid, specially designed polarization insensitive dichroic mirrors and three electron multiplying CCD cameras to provide simultaneous wavelength coverage with a time resolution of 1 second. © 2012 SPIE.


An astronomer from LJMU's Astrophysics Research Institute has discovered a new family of stars in the core of the Milky Way Galaxy which provides new insights into the early stages of the Galaxy's formation.

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