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Demory B.-O.,Astrophysics Group | Demory B.-O.,Massachusetts Institute of Technology
Astrophysical Journal Letters | Year: 2014

Exoplanet research focusing on the characterization of super-Earths is currently limited to the handful of targets orbiting bright stars that are amenable to detailed study. This Letter proposes to look at alternative avenues to probe the surface and atmospheric properties of this category of planets, known to be ubiquitous in our galaxy. I conduct Markov Chain Monte Carlo light-curves analyses for 97 Kepler close-in RP ≲ 2.0 R ⊕ super-Earth candidates with the aim of detecting their occultations at visible wavelengths. Brightness temperatures and geometric albedos in the Kepler bandpass are constrained for 27 super-Earth candidates. A hierarchical Bayesian modeling approach is then employed to characterize the population-level reflective properties of these close-in super-Earths. I find median geometric albedos Ag in the Kepler bandpass ranging between 0.16 and 0.30, once decontaminated from thermal emission. These super-Earth geometric albedos are statistically larger than for hot Jupiters, which have medians Ag ranging between 0.06 and 0.11. A subset of objects, including Kepler-10b, exhibit significantly larger albedos (Ag ≳ 0.4). I argue that a better understanding of the incidence of stellar irradation on planetary surface and atmospheric processes is key to explain the diversity in albedos observed for close-in super-Earths. © 2014. The American Astronomical Society. All rights reserved.


Feroz F.,Astrophysics Group | Hobson M.P.,Astrophysics Group
Monthly Notices of the Royal Astronomical Society | Year: 2014

GJ667C is the least massive component of a triple star system which lies at a distance of about 6.8 pc (22.1 light-year) from the Earth. GJ667C has received much attention recently due to the claims that it hosts up to seven planets including three super-Earths inside the habitable zone. We present a Bayesian technique for the analysis of radial velocity (RV) data sets in the presence of correlated noise component ('red noise'), with unknown parameters. We also introduce hyper-parameters in our model in order to deal statistically with under- or overestimated error bars on measured RVs as well as inconsistencies between different data sets. By applying this method to the RV data set of GJ667C, we show that this data set contains a significant correlated (red) noise component with correlation time-scale for HARPS data of the order of 9 d. Our analysis shows that the data only provide strong evidence for the presence of two planets: GJ667Cb and c with periods 7.19 and 28.13 d, respectively, with some hints towards the presence of a third signal with period 91 d. The planetary nature of this third signal is not clear and additional RV observations are required for its confirmation. Previous claims of the detection of additional planets in this system are due the erroneous assumption of white noise. Using the standard white noise assumption, our method leads to the detection of up to five signals in this system. We also find that with the red noise model, the measurement uncertainties from HARPS for this system are underestimated at the level of ~50 per cent. ©2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Green D.A.,Astrophysics Group
Bulletin of the Astronomical Society of India | Year: 2014

A revised catalogue of 294 Galactic supernova remnants (SNRs) is presented, along with some simple statistics. This catalogue has twenty more entries than did the previous version (from 2009), as 21 new remnants have been added, and one object has been removed as it has been identified as an Hii region. © 2014, Astronomical Society of India, Indian Institute of Astrophysics. All rights reserved.


Feroz F.,Astrophysics Group | Hobson M.P.,Astrophysics Group
Monthly Notices of the Royal Astronomical Society | Year: 2012

Weak gravitational lensing studies of galaxy clusters often assume a spherical cluster model to simplify the analysis, but some recent studies have suggested this simplifying assumption may result in large biases in estimated cluster masses and concentration values, since clusters are expected to exhibit triaxiality. Several such analyses have, however, quoted expressions for the spatial derivatives of the lensing potential in triaxial models, which are open to misinterpretation. In this paper, we give a clear description of weak lensing by triaxial Navarro-Frenk-White (NFW) galaxy clusters and also present an efficient and robust method to model these clusters and obtain parameter estimates. By considering four highly triaxial NFW galaxy clusters, we re-examine the impact of the simplifying assumption of sphericity and find that while the concentration estimates are largely unbiased, except in one of our triaxial NFW simulated clusters, the masses are significantly biased, by up to 40 per cent, for all the clusters we analysed. Moreover, we find that erroneously assuming spherical symmetry can lead to the mistaken conclusion that some substructure is present in the galaxy clusters or, even worse, that multiple galaxy clusters are present in the field. Our cluster fitting method also allows one to answer the question of whether a given cluster exhibits triaxiality or a simple spherical model is good enough. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


News Article | December 13, 2016
Site: www.cnet.com

Some 1,000 light-years away in the direction of the constellation of Cygnus is a gas giant called HAT-P-7b, discovered by the Kepler Mission in 2008. Coming in at 16 times larger than the Earth (Jupiter is 11 times larger), HAT-P-7b was pretty nondescript -- until now. For the first time, researchers have identified weather in a planet outside the solar system, and that planet is HAT-P-7b. "Using the NASA Kepler satellite we were able to study light reflected from HAT-P-7b's atmosphere, finding that the atmosphere was changing over time. HAT-P-7b is a tidally locked planet, with the same side always facing its star. We expect clouds to form on the cold night side of the planet, but they would evaporate quickly on the hot dayside," said David Armstrong of the University of Warwick's Astrophysics Group. "These results show that strong winds circle the planet, transporting clouds from the night side to the dayside. The winds change speed dramatically, leading to huge cloud formations building up then dying away. This is the first detection of weather on a gas giant planet outside the solar system." According to the research, HAT-P-7b is extremely hot on its dayside, averaging 2,860 Kelvin, and those clouds would be spectacular if we could see them, as they're probably made of corundum, the mineral that makes up rubies and sapphires.


News Article | December 12, 2016
Site: phys.org

Dr David Armstrong in Warwick's Astrophysics Group has discovered that the gas giant HAT-P-7b is affected by large scale changes in the strong winds moving across the planet, likely leading to catastrophic storms. This discovery was made by monitoring the light being reflected from the atmosphere of HAT-P-7b, and identifying changes in this light, showing that the brightest point of the planet shifts its position. This shift is caused by an equatorial jet with dramatically variable wind-speeds - at their fastest, pushing vast amounts of cloud across the planet. The clouds themselves would be visually stunning - likely made of up corundum, the mineral which forms rubies and sapphires. The planet could never be inhabitable, due to its likely violent weather systems, and unaccommodating temperatures. One side of the planet always faces the star, because it is tidally locked, and that side remains much hotter than the other - the day side average temperature on HAT-P-7 being 2860K. Thanks to this pioneering research, astrophysicists can now begin to explore how weather systems on other planets outside our solar system change over time. "Using the NASA Kepler satellite we were able to study light reflected from HAT-P-7b's atmosphere, finding that the atmosphere was changing over time. HAT-P-7b is a tidally locked planet, with the same side always facing its star. We expect clouds to form on the cold night side of the planet, but they would evaporate quickly on the hot dayside. "These results show that strong winds circle the planet, transporting clouds from the night side to the dayside. The winds change speed dramatically, leading to huge cloud formations building up then dying away. This is the first detection of weather on a gas giant planet outside the solar system." First discovered in 2008, HAT-P-7b is 320 parsecs (over 1040 light years) away from us. It is an exoplanet 40% larger than Jupiter and 500 times more massive than the Earth - and orbits a star 50% more massive, and twice as large, as the Sun. The results are published in Nature Astronomy this week.


News Article | December 12, 2016
Site: motherboard.vice.com

Over 1,000 light-years from Earth is a monstrous gas giant of a planet—500 times more massive than our own—where clouds seem to be made from corundum, the same mineral that creates rubies and sapphires here on Earth. This conjures up the image of a glittering disco ball of a planet, but HAT-P-7b, as it's called, isn't anyplace you'd want to visit. It's wracked by catastrophic storms, ferocious winds, and temperatures that reach a scalding 2,500℃ and higher on its day-facing side (the planet is tidally locked with its host sun). This is according to a new study in Nature Astronomy, in which scientists managed to observe weather systems on a gas giant outside our solar system for the first time. "Because it's a gas giant, it has a lot of atmosphere. It's almost all atmosphere," lead author David Armstrong of the University of Warwick's Astrophysics Group told me in an interview. Using NASA's Kepler space telescope, his team was able to track light bouncing off the atmosphere of HAT-P-7b, which is what scientists call a "Hot Jupiter"—a gas giant like our solar system's kingpin, but one that squeezes in close to its star. Read More: Scientists Studied the Atmospheres of Earth-size Exoplanets For the First Time Looking over all four years of Kepler data, they observed dips in the light reflecting off this planet that indicated a shifting bright point, which is thought to be caused by a jetstream driving massive amounts of cloud across its face, and probably causing some mindboggling storms along the way. These clouds, if they contain corundum, wouldn't literally be studded with sapphires and rubies, of course. "Because this planet is so hot, it would have very different materials" than on Earth, Armstrong told me, and corundum—which gives the gemstones their colour—is a likely candidate. So would the clouds be red? "It depends on what else is in the atmosphere," he said. "We don't know the colour, but it would certainly be stunning." Armstrong described a scene of massive cloud banks coursing over towards the day side of the planet, where they'd be lit by the host star and evaporate. While we don't know how fast winds would whip across the planet, they likely travel "kilometers a second," he said. It's not the first time we've heard of a planet described as being jam-packed with gemstones. Years ago, scientists reported that one outside of our solar system called 55 Cancri e might be mostly made of diamond, although they later revised that. Armstrong wants to continue to study HAT-P-7b, and look at weather systems on other exoplanets, too. (Using Kepler to do this isn't possible for more than a handful, though. Planets need to be extremely hot gas giants for the technique to work.) As for whether he'd ever want to visit, well, "it's a hellhole," Armstrong said. So probably not. A sky of gaseous sapphires and rubies is something to observe from afar. Get six of our favorite Motherboard stories every day by signing up for our newsletter.


News Article | November 18, 2015
Site: phys.org

The atmosphere of the planet, Kepler-438b, is thought to have been stripped away as a result of radiation emitted from a superflaring Red Dwarf star, Kepler-438. Regularly occurring every few hundred days, the superflares are approximately ten times more powerful than those ever recorded on the Sun and equivalent to the same energy as 100 billion megatons of TNT. While superflares themselves are unlikely to have a significant impact on Kepler-438b's atmosphere, a dangerous phenomenon associated with powerful flares, known as a coronal mass ejection (CME), has the potential to strip away any atmosphere and render it uninhabitable. The planet Kepler-438b, to date the exoplanet with the highest recorded Earth Similarity Index, is both similar in size and temperature to the Earth but is in closer proximity to the Red Dwarf than the Earth is to the Sun. Lead researcher, Dr David Armstrong of the University of Warwick's Astrophysics Group, explains: "Unlike the Earth's relatively quiet sun, Kepler-438 emits strong flares every few hundred days, each one stronger than the most powerful recorded flare on the Sun. It is likely that these flares are associated with coronal mass ejections, which could have serious damaging effects on the habitability of the planet. "If the planet, Kepler-438b, has a magnetic field like the Earth, it may be shielded from some of the effects. However, if it does not, or the flares are strong enough, it could have lost its atmosphere, be irradiated by extra dangerous radiation and be a much harsher place for life to exist". Discussing the impact of the superflares and radiation on the atmosphere of Kepler-438b, Chloe Pugh, of the University of Warwick's Centre for Fusion, Space and Astrophysics, says: "The presence of an atmosphere is essential for the development of life. While flares themselves are unlikely to have a significant impact on an atmosphere as a whole, there is another more dangerous phenomenon associated with powerful flares, known as a coronal mass ejection. "Coronal mass ejections are where a huge amount of plasma is hurled outwards from the Sun, and there is no reason why they should not occur on other active stars as well. The likelihood of a coronal mass ejection occurring increases with the occurrence of powerful flares, and large coronal mass ejections have the potential to strip away any atmosphere that a close-in planet like Kepler-438b might have, rendering it uninhabitable. With little atmosphere, the planet would also be subject to harsh UV and X-ray radiation from the superflares, along with charged particle radiation, all of which are damaging to life". Explore further: Kepler satellite telescope reveals hundreds of superflares on distant stars More information: The research, The Host Stars of Kepler's Habitable Exoplanets: Superflares, Rotation and Activity, is published by the Monthly Notices of the Royal Astronomical Society.


News Article | December 12, 2016
Site: www.eurekalert.org

Signs of powerful changing winds have been detected on a planet 16 times larger than Earth, over 1,000 light years away -- the first time ever that weather systems have been found on a gas giant outside our solar system Signs of powerful changing winds have been detected on a planet 16 times larger than Earth, over 1000 light years away - the first time ever that weather systems have been found on a gas giant outside our solar system - according to new research by the University of Warwick. Dr David Armstrong in Warwick's Astrophysics Group has discovered that the gas giant HAT-P-7b is affected by large scale changes in the strong winds moving across the planet, likely leading to catastrophic storms. This discovery was made by monitoring the light being reflected from the atmosphere of HAT-P-7b, and identifying changes in this light, showing that the brightest point of the planet shifts its position. This shift is caused by an equatorial jet with dramatically variable wind-speeds - at their fastest, pushing vast amounts of cloud across the planet. The clouds themselves would be visually stunning - likely made of up corundum, the mineral which forms rubies and sapphires. The planet could never be inhabitable, due to its likely violent weather systems, and unaccommodating temperatures. One side of the planet always faces the star, because it is tidally locked, and that side remains much hotter than the other - the day side average temperature on HAT-P-7 being 2860K. Thanks to this pioneering research, astrophysicists can now begin to explore how weather systems on other planets outside our solar system change over time. "Using the NASA Kepler satellite we were able to study light reflected from HAT-P-7b's atmosphere, finding that the atmosphere was changing over time. HAT-P-7b is a tidally locked planet, with the same side always facing its star. We expect clouds to form on the cold night side of the planet, but they would evaporate quickly on the hot dayside. "These results show that strong winds circle the planet, transporting clouds from the night side to the dayside. The winds change speed dramatically, leading to huge cloud formations building up then dying away. This is the first detection of weather on a gas giant planet outside the solar system." First discovered in 2008, HAT-P-7b is 320 parsecs (over 1040 light years) away from us. It is an exoplanet 40% larger than Jupiter and 500 times more massive than the Earth - and orbits a star 50% more massive, and twice as large, as the Sun. The work was led by the University of Warwick, and performed by a team of scientists from Warwick, Queens University Belfast, Dublin City University and University College London. The paper, 'Variability in the Atmosphere of the Hot Jupiter HAT-P-7', is published in the first issue of Nature Astronomy.


News Article | February 15, 2017
Site: spaceref.com

An exotic binary star system 380 light-years away has been identified as an elusive white dwarf pulsar -- the first of its kind ever to be discovered in the universe -- thanks to research by the University of Warwick. Professors Tom Marsh and Boris Gänsicke of the University of Warwick's Astrophysics Group, with Dr. David Buckley from the South African Astronomical Observatory, have identified the star AR Scorpii (AR Sco) as the first white dwarf version of a pulsar -- objects found in the 1960s and associated with very different objects called neutron stars. The white dwarf pulsar has eluded astronomers for over half a century. AR Sco contains a rapidly spinning, burnt-out stellar remnant called a white dwarf, which lashes its neighbour -- a red dwarf -- with powerful beams of electrical particles and radiation, causing the entire system to brighten and fade dramatically twice every two minutes. The latest research establishes that the lash of energy from AR Sco is a focused 'beam,' emitting concentrated radiation in a single direction -- much like a particle accelerator -- something which is totally unique in the known universe. AR Sco lies in the constellation Scorpius, 380 light-years from Earth, a close neighbour in astronomical terms. The white dwarf in AR Sco is the size of Earth but 200,000 times more massive, and is in a 3.6 hour orbit with a cool star one third the mass of the Sun. With an electromagnetic field 100 million times more powerful than Earth, and spinning on a period just shy of two minutes, AR Sco produces lighthouse-like beams of radiation and particles, which lash across the face of the cool star, a red dwarf. As the researchers previously discovered, this powerful light house effect accelerates electrons in the atmosphere of the red dwarf to close to the speed of light, an effect never observed before in similar types of binary stars. The red dwarf is thus powered by the kinetic energy of its spinning neighbour. The distance between the two stars is around 1.4 million kilometres -- which is three times the distance between the Moon and the Earth. Professor Tom Marsh comments: "The new data show that AR Sco's light is highly polarised, showing that the magnetic field controls the emission of the entire system, and a dead ringer for similar behaviour seen from the more traditional neutron star pulsars." Professor Boris Gänsicke comments: "AR Sco is like a gigantic dynamo: a magnet, size of the Earth, with a field that is ~10,000 times stronger than any field we can produce in a laboratory, and it is rotating every two minutes. This generates an enormous electric current in the companion star, which then produces the variations in the light we detect." Reference: "Polarimetric Evidence of a White Dwarf Pulsar in the Binary System AR Scorpii," D. A. H. Buckley et al., 2017 Jan. 23, Nature Astronomy [http://www.nature.com/articles/s41550-016-0029, preprint: https://arxiv.org/abs/1612.03185]. Please follow SpaceRef on Twitter and Like us on Facebook.

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