Pulsar Web Could Detect Low-Frequency Gravitational Waves

The recent detection of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (LIGO) came from two black holes, each about 30 times the mass of our sun, merging into one. Gravitational waves span a wide range of frequencies that require different technologies to detect. A new study from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has shown that low-frequency gravitational waves could soon be detectable by existing radio telescopes.


“Detecting this signal is possible if we are able to monitor a sufficiently large number of pulsars spread across the sky,” said Stephen Taylor, lead author of the paper published this week in The Astrophysical Journal Letters. He is a postdoctoral researcher at NASA’s Jet Propulsion Laboratory, Pasadena, California. “The smoking gun will be seeing the same pattern of deviations in all of them.” Taylor and colleagues at JPL and the California Institute of Technology in Pasadena have been studying the best way to use pulsars to detect signals from low-frequency gravitational waves. Pulsars are highly magnetized neutron stars, the rapidly rotating cores of stars left behind when a massive star explodes as a supernova.

Einstein’s general theory of relativity predicts that gravitational waves — ripples in spacetime — emanate from accelerating massive objects. Nanohertz gravitational waves are emitted from pairs of supermassive black holes orbiting each other, each of which contain millions or a billion times more mass than those detected by LIGO. These black holes each originated at the center of separate galaxies that collided. They are slowly drawing closer together and will eventually merge to create a single super-sized black hole.

As they orbit each other, the black holes pull on the fabric of space and create a faint signal that travels outward in all directions, like a vibration in a spider’s web. When this vibration passes Earth, it jostles our planet slightly, causing it to shift with respect to distant pulsars. Gravitational waves formed by binary supermassive black holes take months or years to pass Earth and require many years of observations to detect.

“Galaxy mergers are common, and we think there are many galaxies harboring binary supermassive black holes that we should be able to detect,” said Joseph Lazio, one of Taylor’s co-authors, also based at JPL. “Pulsars will allow us to see these massive objects as they slowly spiral closer together.”

Once these gigantic black holes get very close to each other, the gravitational waves are too short to detect using pulsars. Space-based laser interferometers like eLISA, a mission being developed by the European Space Agency with NASA participation, would operate in the frequency band that can detect the signature of supermassive black holes merging. The LISA Pathfinder mission, which includes a stabilizing thruster system managed by JPL, is currently testing technologies necessary for the future eLISA mission.

Finding evidence for supermassive black hole binaries has been a challenge for astronomers. The centers of galaxies contain many stars, and even monstrous black holes are quite small — comparable to the size of our solar system. Seeing visible signatures of these binaries amid the glare of the surrounding galaxy has been difficult for astronomers.

Radio astronomers search instead for the gravitational signals from these binaries. In 2007, NANOGrav began observing a set of the fastest-rotating pulsars to try to detect tiny shifts caused by gravitational waves.

Pulsars emit beams of radio waves, some of which sweep across Earth once every rotation. Astronomers detect this as a rapid pulse of radio emission. Most pulsars rotate several times a second. But some, called millisecond pulsars, rotate hundreds of times faster.

“Millisecond pulsars have extremely predictable arrival times, and our instruments are able to measure them to within a ten-millionth of a second,” said Maura McLaughlin, a radio astronomer at West Virginia University in Morgantown and member of the NANOGrav team. “Because of that, we can use them to detect incredibly small shifts in Earth’s position.”

But astrophysicists at JPL and Caltech caution that detecting faint gravitational waves would likely require more than a few pulsars. “We’re like a spider at the center of a web,” said Michele Vallisneri, another member of the JPL/Caltech research group. “The more strands we have in our web of pulsars, the more likely we are to sense when a gravitational wave passes by.”

Vallisneri said accomplishing this feat will require international collaboration. “NANOGrav is currently monitoring 54 pulsars, but we can only see some of the southern hemisphere. We will need to work closely with our colleagues in Europe and Australia in order to get the all-sky coverage this search requires.”

The feasibility of this approach was recently called into question when a group of Australian pulsar researchers reported that they were unable to detect such signals when analyzing a set of pulsars with the most precise timing measurements. After studying this result, the NANOGrav team determined that the reported non-detection was not a surprise, and resulted from the combination of optimistic gravitational wave models and analysis of too few pulsars. Their one-page response was released recently via the arXiv electronic print service.

Despite the technical challenges, Taylor is confident their team is on the right track. “Gravitational waves are washing over Earth all the time,” Taylor said. “Given the number of pulsars being observed by NANOGrav and other international teams, we expect to have clear and convincing evidence of low-frequency gravitational waves within the next decade.”

NANOGrav is a collaboration of over 60 scientists at more than a dozen institutions in the United States and Canada. The group uses radio pulsar timing observations acquired at NRAO’s Green Bank Telescope in West Virginia and at Arecibo Radio Observatory in Puerto Rico to search for ripples in the fabric of spacetime. In 2015, NANOGrav was awarded $14.5 million by the National Science Foundation to create and operate a Physics Frontiers Center.

“With the recent detection of gravitational waves by LIGO, the outstanding work of the NANOGrav collaboration is particularly relevant and timely,” said Pedro Marronetti, National Science Foundation program director for gravitational wave research. “This NSF-funded Physics Frontier Center is poised to complement LIGO observations, extending the window of gravitational wave detection to very low frequencies.”.”

ATLASGAL Survey Of Milky Way Completed

APEX, the Atacama Pathfinder EXperiment telescope, is located at 5100 metres above sea level on the Chajnantor Plateau in Chile’s Atacama region. The ATLASGAL survey took advantage of the unique characteristics of the telescope to provide a detailed view of the distribution of cold dense gas along the plane of the Milky Way galaxy. The new image includes most of the regions of star formation in the southern Milky Way.

milky way

The new ATLASGAL maps cover an area of sky 140 degrees long and 3 degrees wide, more than four times larger than the first ATLASGAL release [3]. The new maps are also of higher quality, as some areas were re-observed to obtain a more uniform data quality over the whole survey area.

The ATLASGAL survey is the single most successful APEX large programme with nearly 70 associated science papers already published, and its legacy will expand much further with all the reduced data products now available to the full astronomical community .

At the heart of APEX are its sensitive instruments. One of these, LABOCA (the LArge BOlometer Camera) was used for the ATLASGAL survey. LABOCA measures incoming radiation by registering the tiny rise in temperature it causes on its detectors and can detect emission from the cold dark dust bands obscuring the stellar light.

The new release of ATLASGAL complements observations from ESA’s Planck satellite. The combination of the Planck and APEX data allowed astronomers to detect emission spread over a larger area of sky and to estimate from it the fraction of dense gas in the inner Galaxy. The ATLASGAL data were also used to create a complete census of cold and massive clouds where new generations of stars are forming.

“ATLASGAL provides exciting insights into where the next generationof high-mass stars and clusters form. By combining these with observations from Planck, we can now obtain a link to the large-scale structures of giant molecular clouds,” remarks Timea Csengeri from the Max Planck Institute for Radio Astronomy (MPIfR), Bonn, Germany, who led the work of combining the APEX and Planck data.

The APEX telescope recently celebrated ten years of successful research on the cold Universe. It plays an important role not only as pathfinder, but also as a complementary facility to ALMA, the Atacama Large Millimeter/submillimeter Array, which is also located on the Chajnantor Plateau. APEX is based on a prototype antenna constructed for the ALMA project, and it has found many targets that ALMA can study in great detail.

Leonardo Testi from ESO, who is a member of the ATLASGAL team and the European Project Scientist for the ALMA project, concludes: “ATLASGAL has allowed us to have a new and transformational look at the dense interstellar medium of our own galaxy, the Milky Way. The new release of the full survey opens up the possibility to mine this marvellous dataset for new discoveries. Many teams of scientists are already using the ATLASGAL data to plan for detailed ALMA follow-up

Discovery Of A Fast Radio Burst Reveals ‘Missing Matter’ In The Universe

An international research team including scientists from the Max Planck Institute for Radio Astronomy in Bonn, Germany used a combination of radio and optical telescopes to identify the precise location of a fast radio burst (FRB) in a distant galaxy, allowing them to conduct a unique census of the Universe’s matter content.


Their result, published in today’s edition of Nature, confirms current cosmological models of the distribution of matter in the Universe.

On April 18, 2015, a fast radio burst or FRB was detected by the 64-m Parkes radio telescope of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia within the framework of the SUrvey for Pulsars and Extragalactic Radio Bursts (SUPERB) project. An international alert was triggered to follow it up with other telescopes and within a few hours, a number of telescopes around the world were looking for the signal, including CSIRO’s Australia Telescope Compact Array (ATCA) and the Effelsberg Radio Telescope in Germany.

FRBs are mysterious bright radio flashes generally lasting only a few milliseconds. Their origin is still unknown, with a long list of potential phenomena associated with them. FRBs are very difficult to detect; before this discovery only 16 had been detected.

“In the past FRBs have been found by sifting through data months or even years later. By that time it is too late to do follow up observations.” says Evan Keane, Project Scientist at the Square Kilometre Array Organisation and the lead scientist behind the study. To remedy this, the team developed their own observing system (SUPERB) to detect FRBs within seconds, and to immediately alert other telescopes, when there is still time to search for more evidence in the aftermath of the initial flash.

Thanks to the ATCA’s six 22-m dishes and their combined resolution, the team was able to pinpoint the location of the signal with much greater accuracy than has been possible in the past and detected a radio afterglow that lasted for around 6 days before fading away. This afterglow enabled them to pinpoint the location of the FRB about 1000 times more precisely than for previous events.

The puzzle still required another piece to be put in place. The team used the National Astronomical Observatory of Japan (NAOJ)’s 8.2-m Subaru optical telescope in Hawaii to look at where the signal came from, and identified an elliptical galaxy some 6 billion light years away. “It’s the first time we’ve been able to identify the host galaxy of an FRB” adds Evan Keane. The optical observation also gave them the redshift measurement (the speed at which the galaxy is moving away from us due to the accelerated expansion of the Universe), the first time a distance has been determined for an FRB.

For understanding the physics of such events it is important to know basic properties like the exact position, the distance of the source and whether it will be repeated. “Our analysis leads us to conclude that this new radio burst is not a repeater, but resulting from a cataclysmic event in that distant galaxy,” states Michael Kramer from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany who analysed the radio profile’s structure of the event. MPIfR’s Effelsberg Radio Telescope was also used for radio follow up observations after the alert.

FRBs show a frequency-dependent dispersion , a delay in the radio signal caused by how much material it has gone through. “Until now, the dispersion measure is all we had. By also having a distance we can now measure how dense the material is between the point of origin and Earth, and compare that with the current model of the distribution of matter in the Universe” explains Simon Johnston, co-author of the study, from CSIRO’s Astronomy and Space Science division. “Essentially this lets us weigh the Universe, or at least the normal matter it contains.”

In the current model, the Universe is believed to be made of 70% dark energy, 25% dark matter and 5% ‘ordinary’ matter, the matter that makes everything we see. However, through observations of stars, galaxies and hydrogen, astronomers have only been able to account for about half of the ordinary matter, the rest could not be seen directly and so has been referred to as ‘missing’.

“The good news is our observations and the model match, we have found the missing matter” explains Evan Keane. “It’s the first time a fast radio burst has been used to conduct a cosmological measurement.”

“This shows the potential for FRBs as new tools for cosmology,” concludes Michael Kramer who also worked on the calculation to weigh the missing matter. “Just think what we can do when we have discovered hundreds of these.”

Looking forward, the Square Kilometre Array, with its extreme sensitivity, resolution and wide field of view is expected to be able to detect many more FRBs and to pinpoint their host galaxies. A much larger sample will enable precision measurements of cosmological parameters such as the distribution of matter in the Universe, and provide a refined understanding of dark energy.

The SUrvey for Pulsars and Extragalactic Radio Bursts (SUPERB) is a large-scale astrophysics project using several telescopes, high-speed GPU analysis codes, a large supercomputer and artificial neural networks to identify new astrophysical discoveries. In particular it deals with pulsars, and explosions in space known as Fast Radio Bursts (FRBs).

Bulusan Volcano Spews Ash

Bulusan Volcano spewed a grayish steam and an ash column reaching 500 meters on Monday afternoon, February 22, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) said.


In the latest bulletin issued by PHIVOLCS at 6:00 pm, Bulusan Volcano’s ash fall occurred at 5:01 pm, which also reflected as an explosion type earthquake that lasted for four minutes and twenty-one seconds.

PHIVOLCS detected a total of 12 volcanic earthquakes prior to the ash fall.

The agency raised Alert Level 1 over Bulusan Volcano and the public is reminded not to go inside the 4-kilometer radius Permanent Danger Zone (PDZ) due to risks of sudden steam and ash explosions.

PHIVOLCS said it is closely monitoring the volcano’s activity and advised residents located in the northwest and southwest sectors of the volcano to take precautions against ash falls.

PHIVOLCS also reminded residents near valleys and river channels to be watchful against lahar.

Bulusan Volcano is the southernmost volcano on Luzon Island. It is located in the province of Sorsogon in the Bicol region, 70 km southeast of Mayon Volcano and approximately 250 km southeast of Manila.

It is considered as the Philippines’ 4th most active volcano after Mayon, Taal, and Kanlaon. Its last eruption was in June 2015.

Five-Dimensional Black Hole Could ‘Break’ General Relativity

Researchers have shown how a bizarrely shaped black hole could cause Einstein’s general theory of relativity, a foundation of modern physics, to break down. However, such an object could only exist in a universe with five or more dimensions.

black hole

The researchers, from the University of Cambridge and Queen Mary University of London, have successfully simulated a black hole shaped like a very thin ring, which gives rise to a series of ‘bulges’ connected by strings that become thinner over time. These strings eventually become so thin that they pinch off into a series of miniature black holes, similar to how a thin stream of water from a tap breaks up into droplets.

Ring-shaped black holes were ‘discovered’ by theoretical physicists in 2002, but this is the first time that their dynamics have been successfully simulated using supercomputers. Should this type of black hole form, it would lead to the appearance of a ‘naked singularity’, which would cause the equations behind general relativity to break down. The results are published in the journal Physical Review Letters.

General relativity underpins our current understanding of gravity: everything from the estimation of the age of the stars in the universe, to the GPS signals we rely on to help us navigate, is based on Einstein’s equations. In part, the theory tells us that matter warps its surrounding spacetime, and what we call gravity is the effect of that warp. In the 100 years since it was published, general relativity has passed every test that has been thrown at it, but one of its limitations is the existence of singularities.

A singularity is a point where gravity is so intense that space, time, and the laws of physics, break down. General relativity predicts that singularities exist at the centre of black holes, and that they are surrounded by an event horizon — the ‘point of no return’, where the gravitational pull becomes so strong that escape is impossible, meaning that they cannot be observed from the outside.

“As long as singularities stay hidden behind an event horizon, they do not cause trouble and general relativity holds — the ‘cosmic censorship conjecture’ says that this is always the case,” said study co-author Markus Kunesch, a PhD student at Cambridge’s Department of Applied Mathematics and Theoretical Physics (DAMTP). “As long as the cosmic censorship conjecture is valid, we can safely predict the future outside of black holes. Because ultimately, what we’re trying to do in physics is to predict the future given knowledge about the state of the universe now.”

But what if a singularity existed outside of an event horizon? If it did, not only would it be visible from the outside, but it would represent an object that has collapsed to an infinite density, a state which causes the laws of physics to break down. Theoretical physicists have hypothesised that such a thing, called a naked singularity, might exist in higher dimensions.

“If naked singularities exist, general relativity breaks down,” said co-author Saran Tunyasuvunakool, also a PhD student from DAMTP. “And if general relativity breaks down, it would throw everything upside down, because it would no longer have any predictive power — it could no longer be considered as a standalone theory to explain the universe.”

We think of the universe as existing in three dimensions, plus the fourth dimension of time, which together are referred to as spacetime. But, in branches of theoretical physics such as string theory, the universe could be made up of as many as 11 dimensions. Additional dimensions could be large and expansive, or they could be curled up, tiny, and hard to detect. Since humans can only directly perceive three dimensions, the existence of extra dimensions can only be inferred through very high energy experiments, such as those conducted at the Large Hadron Collider.

Einstein’s theory itself does not state how many dimensions there are in the universe, so theoretical physicists have been studying general relativity in higher dimensions to see if cosmic censorship still holds. The discovery of ring-shaped black holes in five dimensions led researchers to hypothesise that they could break up and give rise to a naked singularity.

What the Cambridge researchers, along with their co-author Pau Figueras from Queen Mary University of London, have found is that if the ring is thin enough, it can lead to the formation of naked singularities.

Using the COSMOS supercomputer, the researchers were able to perform a full simulation of Einstein’s complete theory in higher dimensions, allowing them to not only confirm that these ‘black rings’ are unstable, but to also identify their eventual fate. Most of the time, a black ring collapses back into a sphere, so that the singularity would stay contained within the event horizon. Only a very thin black ring becomes sufficiently unstable as to form bulges connected by thinner and thinner strings, eventually breaking off and forming a naked singularity. New simulation techniques and computer code were required to handle these extreme shapes.

“The better we get at simulating Einstein’s theory of gravity in higher dimensions, the easier it will be for us to help with advancing new computational techniques — we’re pushing the limits of what you can do on a computer when it comes to Einstein’s theory,” said Tunyasuvunakool. “But if cosmic censorship doesn’t hold in higher dimensions, then maybe we need to look at what’s so special about a four-dimensional universe that means it does hold.”

The cosmic censorship conjecture is widely expected to be true in our four-dimensional universe, but should it be disproved, an alternative way of explaining the universe would then need to be identified. One possibility is quantum gravity, which approximates Einstein’s equations far away from a singularity, but also provides a description of new physics close to the singularity.

The COSMOS supercomputer at the University of Cambridge is part of the Science and Technology Facilities Council (STFC) DiRAC HPC Facility.

Pluto’s ‘Hulk-like’ Moon Charon: A Possible Ancient Ocean?

Images from NASA’s New Horizons mission suggest that Pluto’s moon Charon once had a subsurface ocean that has long since frozen and expanded, pushing outward and causing the moon’s surface to stretch and fracture on a massive scale.


The side of Pluto’s largest moon viewed by NASA’s passing New Horizons spacecraft in July 2015 is characterized by a system of “pull apart” tectonic faults, which are expressed as ridges, scarps and valleys — the latter sometimes reaching more than 4 miles (6.5 kilometers) deep. Charon’s tectonic landscape shows that, somehow, the moon expanded in its past, and — like Bruce Banner tearing his shirt as he becomes the Incredible Hulk — Charon’s surface fractured as it stretched.

The outer layer of Charon is primarily water ice. This layer was kept warm when Charon was young by heat provided by the decay of radioactive elements, as well as Charon’s own internal heat of formation. Scientists say Charon could have been warm enough to cause the water ice to melt deep down, creating a subsurface ocean. But as Charon cooled over time, this ocean would have frozen and expanded (as happens when water freezes), lifting the outermost layers of the moon and producing the massive chasms we see today.

The top portion of this image shows part of the feature informally named Serenity Chasma, part of a vast equatorial belt of chasms on Charon. In fact, this system of chasms is one of the longest seen anywhere in the solar system, running at least 1,100 miles (about 1,800 kilometers) long and reaching 4.5 miles (7.5 kilometers) deep. By comparison, the Grand Canyon is 277 miles (446 kilometers) long and just over a mile (1.6 kilometers) deep.

The lower portion of the image shows color-coded topography of the same scene. Measurements of the shape of this feature tell scientists that Charon’s water ice layer may have been at least partially liquid in its early history, and has since refrozen.

This image was obtained by the Long-Range Reconnaissance Imager (LORRI) on New Horizons. North is up; illumination is from the top-left of the image. The image resolution is about 1,290 feet (394 meters) per pixel. The image measures 240 miles (386 kilometers) long and 110 miles (175 kilometers) wide. It was obtained at a range of approximately 48,900 miles (78,700 kilometers) from Charon, about an hour and 40 minutes before New Horizons’ closest approach to Charon on July 14, 2015.

Longest-Lasting Stellar Eclipse: Three-And-A-Half Year Eclipses In Binary System

Imagine living on a world where, every 69 years, the sun disappears in a near-total eclipse that lasts for three and a half years.

That is just what happens in an unnamed binary star system nearly 10,000 light years from Earth. The newly discovered system, known only by its astronomical catalog number TYC 2505-672-1, sets a new record for both the longest duration stellar eclipse and the longest period between eclipses in a binary system.


Discovery of the system’s extraordinary properties was made by a team of astronomers from Vanderbilt and Harvard with the assistance of colleagues at Lehigh, Ohio State and Pennsylvania State universities, Las Cumbres Observatory Global Telescope Network and the American Association of Variable Star Observers and is described in a paper accepted for publication in the Astronomical Journal.

“It’s the longest duration stellar eclipse and the longest orbit for an eclipsing binary ever found…by far,” said the paper’s first author Vanderbilt doctoral student Joey Rodriguez.

The previous record holder is Epsilon Aurigae, a giant star that is eclipsed by its companion every 27 years for periods ranging from 640 to 730 days.

“Epsilon Aurigae is much closer — about 2,200 light years from Earth — and brighter, which has allowed astronomers to study it extensively,” said Rodriguez. The leading explanation is that Epsilon Aurigae consists of a yellow giant star orbited by a normal star slightly bigger than the sun embedded in a thick disk of dust and gas oriented nearly edge on when viewed from Earth.

“One of the great challenges in astronomy is that some of the most important phenomena occur on astronomical timescales, yet astronomers are generally limited to much shorter human timescales,” said co-author Keivan Stassun, professor of physics and astronomy at Vanderbilt. “Here we have a rare opportunity to study a phenomenon that plays out over many decades and provides a window into the types of environments around stars that could represent planetary building blocks at the very end of a star system’s life.”

Two unique astronomical resources made the discovery possible: observations by the American Association of Variable Star Observers (AAVSO) network and the Digital Access to a Sky Century @ Harvard (DASCH) program.

AAVSO is a non-profit organization of professional and amateur astronomers dedicated to understanding variable stars. It provided a few hundred observations of TYC 2505-672-1’s most recent eclipse.

The DASCH survey is based on thousands of photographic plates taken by Harvard astronomers between 1890 and 1989 as part of a regular survey of the northern sky. In recent years the university has begun digitizing these plates. In the process TYC 2505-672-1 caught the eye of Sumin Tang at the Harvard-Smithsonian Center for Astrophysics.

Rodriguez attended a conference where Tang presented her results on TYC 2505-672-1 and the system piqued his interest as well. He is a member of the survey team for the low-cost Kilodegree Extremely Little Telescope (KELT) system that consists of a pair of robotic telescopes designed to find exoplanets around bright stars operated by astronomers at Ohio State University, Vanderbilt University, Lehigh University and the South African Astronomical Observatory. KELT has an extremely wide field of view (26 degrees by 26 degrees) and he thought it was likely that the KELT database contained a number of recent images of the distant binary system.

After the lecture Rodriguez contacted Tang and they agreed to collaborate. When he searched the KELT database, Rodriguez found about 9,000 images of the obscure system taken in the last eight years that they could combine with the 1,432 images taken over the last century at Harvard. Rodriquez also contacted the AAVSO network and obtained several hundred more observations of the system’s most recent eclipse to help fill in the picture. When she became busy with some other projects, Tang agreed to let Rodriguez take the lead.

The resulting analysis revealed a system similar to the one at Epsilon Aurigae, with some important differences. It appears to consist of a pair of red giant stars, one of which has been stripped down to a relatively small core and surrounded by an extremely large disk of material that produces the extended eclipse.

“About the only way to get these really long eclipse times is with an extended disk of opaque material. Nothing else is big enough to block out a star for months at a time,” Rodriguez said.

TYC-2505-672-1 is so distant that the amount of data the astronomers could extract from the images was limited. However, they were able to estimate the surface temperature of the companion star and found that it is about 2,000 degrees Celsius hotter than the surface of the sun. Combined with the observation that it appears to be less than half the diameter of the sun has led them to propose that it is a red giant that has had its outer layers stripped away and that this stripped material may account for the obscuring disk. However, they don’t know that for certain.

In order to produce the 69-year interval between eclipses, the astronomers calculate that they must be orbiting at an extremely large distance, about 20 astronomical units, which is approximately the distance between the Sun and Uranus.

“Right now even our most powerful telescopes can’t independently resolve the two objects,” said Rodriguez. “Hopefully, technological advances will make that possible by 2080 when the next eclipse occurs.”

Michael B. Lund and Kyle Conroy at Vanderbilt University; Joshua Pepper at Lehigh University; Robert Siverd at Las Cumbres Observatory Global Telescope Network; Stella Kafka at the American Association of Variable Star Observers; Scott Gaudi and Daniel Stevens at Ohio State University; and Thomas Beatty at Pennsylvania State University also contributed to the study.

The research was funded by National Science Foundation grants NNG040G070G, AST-1056524, AST-1358862, AST-0407380, AST-0909073, AST-1313370, AST-0909182 and AST-1313422 and National Aeronautics and Space Administration grant NNG05GF22G.