In this artist's conception, a rogue planet drifts through space. Credit: Christine Pulliam (CfA)
A massive rogue planet has been discovered in the Beta Pictoris moving group. The planet, called PSO J318.5338-22.8603 (Sorry, I didn’t name it), is over eight times as massive as Jupiter. Because it’s one of the few directly-imaged exoplanets we know of, and is accessible for study by spectroscopy, this massive planet will be extremely important when piecing together the details of planetary formation and evolution.
Most planets outside our solar system are not directly observable. They are discovered when they transit in front of their host star. That’s how the Kepler mission finds exoplanets. After that, their properties are inferred by their gravitational interactions with their star and with any other planets in their system. We can infer a lot, and get quite detailed, but studying planets with spectroscopy is a whole other ball game.
The team of researchers, led by K. Allers of Bucknell University, used the Gemini North telescope, and its Near-Infrared Spectrograph, to find PSO’s radial and rotational velocities. As reported in a draft study on January 20th, PSO J318.5338-22.8603 (PSO from now on…) was confirmed as a member of the Beta Pictoris moving group, a group of young stars with a known age.
The Beta Pictoris moving group is a group of stars moving through space together. Since they are together, they are understood to be formed at the same time, and to have the same age. Confirming that PSO is a member of this group also confirmed PSO’s age.
Once the age of PSO was known, its identity as a planet was confirmed. Without knowing the age, it’s impossible to rule it out as a brown dwarf, a “failed star” that lacked the mass to ignite fusion.
This new rogue planet is 8.3 + or – 0.5 times the mass of Jupiter, and its temperature is about 1130 K. Spectra from the Gemini scope show that PSO rotates at between 5 to 10.2 hours, and that its radial velocity is within the envelope of values for this group. According to the researchers, determining these properties accurately means that PSO J318.5338-22.8603 is “an important benchmark for studies of young, directly imaged planets.”
PSO is in an intermediate position in terms of other planets in the Beta Pictoris moving group. 51 Eridani-b is another directly imaged planet, only slightly larger than Jupiter, discovered in 2014. The third planet in the group is Beta Pictoris b, which is thought to be almost 11 times as massive as Jupiter.
Beta Pictoris-b in orbit around the debris-disk star Beta Pictoris. Image: ESA/A-M LeGrange et. al.
Rogue, or “free-floating” planets like PSO J318.5338-22.8603 are important because they are not near a star. Light from a star dominates the star’s surroundings, and makes it difficult to discern much detail in the planets that orbit the star. Now that PSO is confirmed as a planet, rather than a brown dwarf, studying it will add to our knowledge of planetary formation.
Just. Wow. The motion of an alien world, reduced to a looping .gif. We truly live in an amazing age. A joint press release out of the Gemini Observatory and the University of Toronto demonstrates a stunning first: a sequence of direct images showing an exoplanet… in motion.
The world imaged is Beta Pictoris b, about 19 parsecs (63 light years) distant in the southern hemisphere constellation Pictor the Painter’s Easel. The Gemini Planet Imager (GPI), working in concert with the Gemini South telescope based in Chile captured the sequence.
The images span an amazing period of a year and a half, starting in November 2013 and running through April of earlier this year. Beta Pictoris b has an estimated 22 year orbital period… hey, in the year 2035 or so, we’ll have a complete animation of its orbit!
Current estimates place Beta Pictoris b in the 7x Jupiter mass range, about plus or minus 4 Jupiter masses… and yes, the high end of that range is flirting with the lower boundary for a sub-stellar brown dwarf. Several exoplanet candidates blur this line, and we suspect that the ‘what is a planet debate?’ that has plagued low mass worlds will one day soon extend into the high end of the mass spectrum as well.
An annotated diagram of the Beta Pictoris system. Image credit: ESO/A.-M Lagrange et al.
Beta Pictoris has long been a target for exoplanetary research, as it is known to host a large and dynamic debris disk spanning 4,000 astronomical units across. The host star Beta Pictoris is 1.8 times as massive as our Sun, and 9 times as luminous. Beta Pic is also a very young star, at an estimated age of only 8-20 million years old. Clearly, we’re seeing a very young solar system in the act of formation.
Orbiting its host star 9 astronomical units distant, Beta Pictoris b has an orbit similar to Saturn’s. Place Beta Pictoris b in our own solar system, and it would easily be the brightest planet in the sky.
The Heavyweight world B Pictoris b vs planets in our solar system… note the rapid rotation rate! Image credit: ESO/I. Snellen (Leiden University)
“The images in the series represent the most accurate measurements of a planet’s position ever made,” says astronomer Maxwell Millar-Blanchaer of the Department of Astronomy and Astrophysics at the University of Toronto in a recent press release. ‘With the GPI, we’re able to see both the disk and the planet at the exact same time. With our combined knowledge of the disk and the planet we’re really able to get a sense of the planetary system’s architecture and how everything interacts.”
A recent paper released in the Astrophysical Journal described observations of Beta Pictoris b made with the Gemini Planet Imager. As with bodies in our own solar system, refinements in the orbit of Beta Pictoris b will enable astronomers to understand the dynamic relationship it has with its local environment. Already, the orbit of Beta Pictoris b appears inclined out of our line of sight in such a way that a transit of the stellar disk is unlikely to occur. This is the case with most exoplanets, which elude the detection hunters such as the Kepler space telescope. As a matter of fact, watching the animation, it looks like Beta Pictoris b will pass behind the occluding disk and out of view of the Gemini Planet Imager in the next few years.
The location of Beta Pictoris in the southern hemisphere sky. Image credit: Stellarium
“It’s remarkable that Gemini is not only able to directly image exoplanets but is also capable of effectively making movies of them orbiting their parent star,” Says National Science Foundation astronomy division program director Chris Davis in Monday’s press release. The NSF is one of five international partners that funds the Gemini telescope program. “Beta Pic is a special target. The disk of gas and dust from which planets are currently forming was one of the first observed and is a famous laboratory for the study of young solar systems.”
The Gemini Planet Imager is part of the GPI Exoplanet Survey (GPIES), which discovered its first exoplanet 51 Eridani b just last month. The survey will target 600 stars over the next three years. The current tally of known exoplanets currently sits at 1,958 and counting, with thousands more in the queue courtesy of Kepler awaiting confirmation.
And as new spacecraft such as the Transiting Exoplanet Survey Satellite (TESS) take to orbit in 2018, we wouldn’t be surprised if the tally of exoplanets hits five digits by the end of this decade.
An amazing view of a brave new world in motion. It’s truly a golden age of exoplanetary science, with more exciting discoveries to come!
A binary star system Credit: Michael Osadciw/University of Rochester
Astronomers have reported the discovery of a star that passed within the outer reaches of our Solar System just 70,000 years ago, when early humans were beginning to take a foothold here on Earth. The stellar flyby was likely close enough to have influenced the orbits of comets in the outer Oort Cloud, but Neandertals and Cro Magnons – our early ancestors – were not in danger. But now astronomers are ready to look for more stars like this one.
A comparison of the Solar System and its Oort Cloud. 70,000 years ago, Scholz’s Star and companion passed along the outer boundaries of our Solar System (Credit: NASA, Michael Osadciw/University of Rochester, Illustration-T.Reyes)
Lead author Eric Mamajek from the University of Rochester and collaborators report in The Closest Known Flyby Of A Star To The Solar System (published in Astrophysical Journal on February 12, 2015) that “the flyby of this system likely caused negligible impact on the flux of long-period comets, the recent discovery of this binary highlights that dynamically important Oort Cloud perturbers may be lurking among nearby stars.”
The star, named Scholz’s star, was just 8/10ths of a light year at closest approach to the Sun. In comparison, the nearest known star to the Sun is Proxima Centauri at 4.2 light years.
While the internet has been rife with threads and accusations of a Nemesis star that is approaching the inner Solar System and is somehow being “hidden” by NASA, this small red dwarf star with a companion represents the real thing.
In 1984, the paleontologists David Raup and Jack Sepkoski postulated that a dim dwarf star, now widely known on the internet as the Nemesis Star, was in a very long period Solar orbit. The elliptical orbit brought the proposed star into the inner Solar System every 26 million years, causing a rain of comets and mass extinctions on that time period. By no coincidence, because of the sheer numbers of red dwarfs throughout the galaxy, Scholz’s star nearly fits such a scenario. Nemesis was proposed to be in a orbit extending 95,000 A.U. compared to Scholz’s nearest flyby distance of 50,000 A.U. Recent studies of impact rates on Earth, the Moon and Mars have discounted the existence of a Nemesis star (see New Impact Rate Count Lays Nemesis Theory to Rest, Universe Today, 8/1/2011)
But Scholz’s star — a real-life Oort Cloud perturber — was a small red dwarf star star with a M9 spectral classification. M-class stars are the most common star in our galaxy and likely the whole Universe, as 75% of all stars are of this type. Scholz’s is just 15% of the mass of our Sun. Furthermore, Scholz’s is a binary star system with the secondary being a brown dwarf of class T5. Brown Dwarfs are believed to be plentiful in the Universe but due to their very low intrinsic brightness, they are very difficult to discover … except, as in this case, as companions to brighter stars.
The astronomers reported that their survey of new astrometric data of nearby stars identified Scholz’s as an object of interest. The star’s transverse velocity was very low, that is, the stars sideways motion. Additionally, they recognized that its radial velocity – motion towards or away from us, was quite high. For Scholz’s, the star was speeding directly away from our Solar System. How close could Scholz’s star have been to our system in the past? They needed more accurate data.
The collaborators turned to two large telescopes in the southern hemisphere. Spectrographs were employed on the Southern African Large Telescope (SALT) in South Africa and the Magellan telescope at Las Campanas Observatory, Chile. With more accurate trangental and radial velocities, the researchers were able to calculate the trajectory, accounting for the Sun’s and Scholz’s motion around the Milky Way galaxy.
Scholz’s star is an active star and the researchers added that while it was nearby, it shined at a dimly of about 11th magnitude but eruptions and flares on its surface could have raised its brightness to visible levels and could have been seen as a “new” star by primitive humans of the time.
The relative sizes of the inner Solar System, Kuiper Belt and the Oort Cloud. (Credit: NASA, William Crochot)
At present, Scholz’s star is 20 light years away, one of the 70 closest stars to our Solar System. However, the astronomers calculated, with a 98% certainty, that Scholz’s passed within 0.5 light years, approximately 50,000 Astronomical Units (A.U.) of the Sun.
An A.U. is the mean distance from the Earth to the Sun and 50,000 is an important mile marker in our Solar System. It is the outer reaches of the Oort Cloud where billions of comets reside in cold storage, in orbits that take hundreds of thousands of years to circle the Sun.
With this first extraordinary close encounter discovered, the collaborators of this paper as well as other researchers are planning new searches for “Nemesis” type stars. The Large Synoptic Survey Telescope (LSST) and other telescopes within the next decade will bring an incredible array of data sets that will uncover many more red dwarf, brown dwarf and possibly orphan planets roaming in nearby space. Some of these could likewise be traced to past or future near misses to the Sun and Earth system.
This artist's conception shows the object named WISE J085510.83-071442.5, the coldest known brown dwarf. Image credit: Penn State University/NASA/JPL-Caltech
Our stellar neighborhood just got a little busier … and a little colder.
A brown dwarf that’s as frosty as the Earth’s North Pole has been discovered lurking incredibly close to our Solar System. Astronomer Keven Luhman from Pennsylvania State University used NASA’s Wide-field Infrared Survey Explorer (WISE) and the Spitzer Space Telescope to pinpoint the object’s temperature and distance. This is the coldest brown dwarf found so far, and it’s a mere 7.2 light-years away, making it the seventh closest star-like object to the Sun.
“It is very exciting to discover a new neighbor of our Solar System that is so close,” said Luhman in a press release.
Brown dwarfs emerge when clouds of gas and dust collapse. But unlike stars, they never grow dense enough or burn hot enough to ignite nuclear fusion in their cores. They live their lives less massive than stars, but more massive than gas giants. So they burn hot at first, then cool over time. And this newly discovered brown dwarf is as cold as ice. Literally.
WISE surveyed the entire sky twice in its short 14-month lifetime, looking at cooler objects, which radiate in infrared light (but often remain invisible in visible light). It saw cold asteroids, dust clouds, proto-planetary disks, distant galaxies and hundreds of brown dwarfs.
But one of these objects — dubbed WISE J085510.83-071442.5 — was moving rapidly, suggesting it was extremely close to the Solar System. All stars orbit around the Milky Way, with apparent motions seen on the timescale of hundreds of years. Stars close to the Sun, however, can be seen to make the slightest of movements on the timescale of just a few years. This object appeared to move in just a few months.
Click on the image above to see an animation of WISE J085510.83-071442.5. It was first seen in two infrared images taken six months apart in 2010 by WISE (see orange triangles). Two additional images of the object were taken with NASA’s Spitzer Space Telescope in 2013 and 2014 (green triangles). Image credit: NASA/JPL-Caltech/Penn State
After first spotting this wacky object in the WISE data, Luhman analyzed additional images taken with the Spitzer Space Telescope and the Gemini South Pole Telescope in Chile. The combined detections taken from different positions around the Sun enabled the measurement of the objects parallax — the apparent position of the object against a background set of stars as seen along multiple lines of sight — allowing Luhman to determine the objects distance.
Spitzer’s additional observations helped pin down the objects chilly temperature, which can be determined based on how much light it gives off in different colors. Like a flame, the hottest part is blue, while the coldest part is red. Luhman found the brown dwarfs temperature to be between –54° and 9° Fahrenheit (–48° to –13° Celsius). Previous record-holders for the coldest brown dwarfs were about room temperature.
“It is remarkable that even after many decades of studying the sky, we still do not have a complete inventory of the Sun’s nearest neighbors,” said Michael Werner from NASA’s Jet Propulsion Laboratory. “This exciting new result demonstrates the power of exploring the universe using new tools, such as the infrared eyes of WISE and Spitzer.”
With a stretch of the imagination and advanced technology, it’s possible that other cooler objects, be them brown dwarfs of even rogue exoplanets, are yet closer to the Sun.
The paper will be published in the Astrophysics Journal and is available for download here.
This artist's conception could resemble a planetary system in front of a background star. Image Credit: NASA Goddard Space Flight Center / Francis Reddy
When astronomers detect new exoplanets they typically do so using one of two techniques. First, there’s the famous transit technique, which looks for slight dips in light as a planet passes in front of its host star, and second is the radial velocity technique, which senses the motion of a star due to the gravitational pull of its planet.
But then there is gravitational microlensing, the chance magnification of the light from a distant star by the mass of a foreground star and its planets due to the distortion in the fabric of spacetime. While this technique sounds almost improbable, it is so accurate that every detection skips nominating planets as candidates and immediately verifies them as bona-fide worlds.
But without follow-up observations, the microlensing technique struggles with characterizing the incredibly faint host star. Now, a team of international astronomers led by PhD candidate Jennifer Yee from Ohio State University has detected the first microlensing signature, lovingly called MOA-2013-BLG-220Lb, that looks like a confirmed planet orbiting a candidate brown dwarf — an object so faint because it isn’t massive enough to kick-off nuclear fusion in its core.
Matter — no matter how great or small — curves the fabric of spacetime. It can ultimately acts like a lens by curving the background light around it and therefore magnifying the background source. In microlensing, the intervening matter is simply a faint star or perhaps a planetary system.
“As the ‘lens system’ passes in front of a distant, background star, the magnification of that background star changes as a function of time,” Yee told Universe Today. “By measuring the changing magnification of the background star, we can learn about the lensing star and perhaps whether or not it has a planet.”
In a planetary system, the light from the background star will be magnified when the foreground star passes in front of it. If there is a cirlcing planet, there will be an additional cusp in brightness (to a lesser extent but still a tell-tale detection nonetheless).
A sketch of a microlensing signature with a planet in the lens system. Image Credit: NASA / ESA / K. Sahu / STScI
At the moment the planetary system transits in front of the background star (and for many years after) we can’t separate the two objects. While the light of the background star may be greatly magnified, its image is distorted because its light merges with the planetary system.
So the microlensing signature cannot tell astronomers anything about the lens system’s star. “It’s out of the ordinary,” Andrew Gould, Yee’s PhD advisor and coauthor on the paper, told Universe Today. “In other techniques people have definitely detected a star and they’re struggling to detect the planet. But microlensing is just the opposite. We detect the planet very clearly, but we can’t detect the host star.”
However, the microlensing signature does give away the lens system’s proper motion — the apparent change in distance over time — as it passes in front of the background star. MOA-2013-BLG-220Lb’s proper motion is extremely high, clocking in at 12.5 milliarcseconds (a distance on the sky that is 2400 times smaller than the size of the full moon) per year. This is roughly three times higher than average.
A high proper motion may be caused by an object that is very close by and is moving slowly or a very distant object moving rapidly. As most stars tend not to move at high speeds, the team assumes the object is relatively close, placing it at a distance of 6,000 light-years.
With a distance fixed, the team is also able to assume a mass for the object. It weighs in below the hydrogen-burning limit and is therefore considered the best brown dwarf candidate microlensing has detected.
“The double-edged sword of microlensing is that no light from the lens star is required,” Yee told Universe Today. “On the one hand, microlensing can find planets around dark or faint objects like brown dwarfs. The flip side is that it’s very difficult to characterize the lens star if its light is not detected.”
Astronomers will have to wait until 2021 to take a second look at the lens system. This time frame is how long we expect it to take before the candidate brown dwarf separates appreciably on the sky from the background star. Once it has done so astronomers will be able to verify whether or not the candidate is truly a brown dwarf.
Two views of the brown dwarf map for Luhman 16B. Image credit: ESO/I. Crossfield
By now, you will probably have heard that astronomers have produced the first global weather map for a brown dwarf. (If you haven’t, you can find the story here.) May be you’ve even built the cube model or the origami balloon model of the surface of the brown dwarf Luhman 16B the researchers provided (here).
Since one of my hats is that of public information officer at the Max Planck Institute for Astronomy, where most of the map-making took place, I was involved in writing a press release about the result. But one aspect that I found particularly interesting didn’t get much coverage there. It’s that this particular bit of research is a good example of how fast-paced astronomy can be these days, and, more generally, it shows how astronomical research works. So here’s a behind-the-scenes look – a making-of, if you will – for the first brown dwarf surface map (see image on the right).
As in other sciences, if you want to be a successful astronomer, you need to do something new, and go beyond what’s been done before. That, after all, is what publishable new results are all about. Sometimes, such progress is driven by larger telescopes and more sensitive instruments becoming available. Sometimes, it’s about effort and patience, such as surveying a large number of objects and drawing conclusion from the data you’ve won.
Ingenuity plays a significant role. Think of the telescopes, instruments and analytical methods developed by astronomers as the tools in a constantly growing tool box. One way of obtaining new results is to combine these tools in new ways, or to apply them to new objects.
That’s why our opening scene is nothing special in astronomy: It shows Ian Crossfield, a post-doctoral researcher at the Max Planck Institute for Astronomy, and a number of colleagues (including institute director Thomas Henning) in early March 2013, discussing the possibility of applying one particular method of mapping stellar surfaces to a class of objects that had never been mapped in this way before.
The method is called Doppler imaging. It makes use of the fact that light from a rotating star is slightly shifted in frequency as the star rotates. As different parts of the stellar surfaces go by, whisked around by the star’s rotation, the frequency shifts vary slightly different depending on where the light-emitting region is located on the star. From these systematic variations, an approximate map of the stellar surface can be reconstructed, showing darker and brighter areas. Stars are much too distant for even the largest current telescopes to discern surface details, but in this way, a surface map can be reconstructed indirectly.
The method itself isn’t new. The basic concept was invented in the late 1950s, and the 1980s saw several applications to bright, slowly rotating stars, with astronomers using Doppler imaging to map those stars’ spots (dark patches on a stellar surface; the stellar analogue to Sun spots).
Crossfield and his colleagues were wondering: Could this method be applied to a brown dwarf – an intermediary between planet and star, more massive than a planet, but with insufficient mass for nuclear fusion to ignite in the object’s core, turning it into a star? Sadly, some quick calculations, taking into account what current telescopes and instruments can and cannot do as well as the properties of known brown dwarfs, showed that it wouldn’t work.
The available targets were too faint, and Doppler imaging needs lots of light: for one because you need to split the available light into the myriad colors of a spectrum, and also because you need to take many different rather short measurements – after all, you need to monitor how the subtle frequency shifts caused by the Doppler effect change over time.
So far, so ordinary. Most discussions of how to make observations of a completely new type probably come to the conclusion that it cannot be done – or cannot be done yet. But in this case, another driver of astronomical progress made an appearance: The discovery of new objects.
Kevin Luhman discovered the brown dwarf pair in data from NASA’s Wide-field Infrared Survey Explorer (WISE; artist’s impression). Image: NASA/JPL-Caltech
On March 11, Kevin Luhman, an astronomer at Penn State University, announced a momentous discovery: Using data from NASA’s Wide-field Infrared Survey Explorer (WISE), he had identified a system of two brown dwarfs orbiting each other. Remarkably, this system was at a distance of a mere 6.5 light-years from Earth. Only the Alpha Centauri star system and Barnard’s star are closer to Earth than that. In fact, Barnard’s star was the last time an object was discovered to be that close to our Solar system – and that discovery was made in 1916.
Modern astronomers are not known for coming up with snappy names, and the new object, which was designated WISE J104915.57-531906.1, was no exception. To be fair, this is not meant to be a real name; it’s a combination of the discovery instrument WISE with the system’s coordinates in the sky. Later, the alternative designation “Luhman 16AB” for the system was proposed, as this was the 16th binary system discovered by Kevin Luhman, with A and B denoting the binary system’s two components.
These days, the Internet gives the astronomical community immediate access to new discoveries as soon as they are announced. Many, probably most astronomers begin their working day by browsing recent submissions to astro-ph, the astrophysical section of the arXiv, an international repository of scientific papers. With a few exceptions – some journals insist on exclusive publication rights for at least a while –, this is where, in most cases, astronomers will get their first glimpse of their colleagues’ latest research papers.
Luhman posted his paper “Discovery of a Binary Brown Dwarf at 2 Parsecs from the Sun” on astro-ph on March 11. For Crossfield and his colleagues at MPIA, this was a game-changer. Suddenly, here was a brown dwarf for which Doppler imaging could conceivably work, and yield the first ever surface map of a brown dwarf.
However, it would still take the light-gathering power of one of the largest telescopes in the world to make this happen, and observation time on such telescopes is in high demand. Crossfield and his colleagues decided they needed to apply one more test before they would apply. Any object suitable for Doppler imaging will flicker ever so slightly, growing slightly brighter and darker in turn as brighter or darker surface areas rotate into view. Did Luhman 16A or 16B flicker – in astronomer-speak: did one of them, or perhaps both, show high variability?
Astronomy comes with its own time scales. Communication via the Internet is fast. But if you have a new idea, then ordinarily, you can’t just wait for night to fall and point your telescope accordingly. You need to get an observation proposal accepted, and this process takes time – typically between half a year and a year between your proposal and the actual observations. Also, applying is anything but a formality. Large facilities, like the European Southern Observatory’s Very Large Telescopes, or space telescopes like the Hubble, typically receive applications for more than 5 times the amount of observing time that is actually available.
But there’s a short-cut – a way for particularly promising or time-critical observing projects to be completed much faster. It’s known as “Director’s Discretionary Time”, as the observatory director – or a deputy – are entitled to distribute this chunk of observing time at their discretion.
To monitor Luhman 16A and B’s brightness flucutations, Beth Biller used the MPG/ESO 2.2. meter telescope at ESO’s La Silla Observatory. Image credit: ESO/José Francisco Salgado (josefrancisco.org)
On April 2, Beth Biller, another MPIA post-doc (she is now at the University of Edinburgh), applied for Director’s Discretionary Time on the MPG/ESO 2.2 m telescope at ESO’s La Silla observatory in Chile. The proposal was approved the same day.
Biller’s proposal was to study Luhman 16A and 16B with an instrument called GROND. The instrument had been developed to study the afterglows of powerful, distant explosions known as gamma ray bursts. With ordinary astronomical objects, astronomers can take their time. These objects will not change much over the few hours an astronomer makes observations, first using one filter to capture one range of wavelengths (think “light of one color”), then another filter for another wavelength range. (Astronomical images usually capture one range of wavelengths – one color – at a time. If you look at a color image, it’s usually the result of a series of observations, one color filter at a time.)
Gamma ray bursts and other transient phenomena are different. Their properties can change on a time scale of minutes, leaving no time for consecutive observations. That is why GROND allows for simultaneous observations of seven different colors.
Biller had proposed to use GROND’s unique capability for recording brightness variations for Luhman 16A and 16B in seven different colors simultaneously – a kind of measurement that had never been done before at this scale. The most simultaneous information researchers had gotten from a brown dwarf had been at two different wavelengths (work by Esther Buenzli, then at the University of Arizona’s Steward Observatory, and colleagues). Biller was going for seven. As slightly different wavelength regimes contain information about gas at slightly different colors, such measurements promised insight into the layer structure of these brown dwarfs – with different temperatures corresponding to different atmospheric layers at different heights.
For Crossfield and his colleagues – Biller among them –, such a measurement of brightness variations should also show whether or not one of the brown dwarfs was a good candidate for Doppler imaging.
The robotic telescope TRAPPIST, also at ESO’s La Silla observatory, was the first to find brightness fluctuations of the brown dwarf Luhman 16B.
As it turned out, they didn’t even have to wait that long. A group of astronomers around Michaël Gillon had pointed the small robotic telescope TRAPPIST, designed for detecting exoplanets by the brightness variations they cause when passing between their host star and an observer on Earth, to Luhman 16AB. The same day that Biller had applied for observing time, and her application been approved, the TRAPPIST group published a paper “Fast-evolving weather for the coolest of our two new substellar neighbours”, charting brightness variations for Luhman 16B.
This news caught Crossfield thousands of miles from home. Some astronomical observations do not require astronomers to leave their cozy offices – the proposal is sent to staff astronomers at one of the large telescopes, who make the observations once the conditions are right and send the data back via Internet. But other types of observations do require astronomers to travel to whatever telescope is being used – to Chile, say, to or to Hawaii.
When the brightness variations for Luhman 16B were announced, Crossfield was observing in Hawaii. He and his colleagues realized right away that, given the new results, Luhman 16B had moved from being a possible candidate for the Doppler imaging technique to being a promising one. On the flight from Hawaii back to Frankfurt, Crossfield quickly wrote an urgent observing proposal for Director’s Discretionary Time on CRIRES, a spectrograph installed on one of the 8 meter Very Large Telescopes (VLT) at ESO’s Paranal observatory in Chile, submitting his application on April 5. Five days later, the proposal was accepted.
Antu, the first of the four 8 meter Unit Telescopes (UTs) of the Very Large Telescope (VLT) shortly after installation in 2000. Image: ESO
On May 5, the giant 8 meter mirror of Antu, one of the four Unit Telescopes of the Very Large Telescope, turned towards the Southern constellation Vela (the “Sail of the Ship”). The light it collected was funneled into CRIRES, a high-resolution infrared spectrograph that is cooled down to about -200 degrees Celsius (-330 Fahrenheit) for better sensitivity.
Three and two weeks earlier, respectively, Biller’s observations had yielded rich data about the variability of both the brown dwarfs in the intended seven different wavelength bands.
At this point, no more than two months had passed between the original idea and the observations. But paraphrasing Edison’s famous quip, observational astronomy is 1% observation and 99% evaluation, as the raw data are analyzed, corrected, compared with models and inferences made about the properties of the observed objects.
For Beth Biller’s multi-wavelength monitoring of brightness variations, this took about five months. In early September, Biller and 17 coauthors, Crossfield and numerous other MPIA colleagues among them, submitted their article to the Astrophysical Journal Letters (ApJL) after some revisions, it was accepted on October 17. From October 18 onward, the results were accessible online at astro-ph, and a month later they were published on the ApJL website.
In late September, Crossfield and his colleagues had finished their Doppler imaging analysis of the CRIRES data. Results of such an analysis are never 100% certain, but the astronomers had found the most probable structure of the surface of Luhman 16B: a pattern of brighter and darker spots; clouds made of iron and other minerals drifting on hydrogen gas.
As is usual in the field, the text they submitted to the journal Nature was sent out to a referee – a scientist, who remains anonymous, and who gives recommendations to the journal’s editors whether or not a particular article should be published. Most of the time, even for an article the referee thinks should be published, he or she has some recommendations for improvement. After some revisions, Nature accepted the Crossfield et al. article in late December 2013.
With Nature, you are only allowed to publish the final, revised version on astro-ph or similar servers no less than 6 month after the publication in the journal. So while a number of colleagues will have heard about the brown dwarf map on January 9 at a session at the 223rd Meeting of the American Astronomical Society, in Washington, D.C., for the wider astronomical community, the online publication, on January 29, 2014, will have been the first glimpse of this new result. And you can bet that, seeing the brown dwarf map, a number of them will have started thinking about what else one could do. Stay tuned for the next generation of results.
And there you have it: 10 months of astronomical research, from idea to publication, resulting in the first surface map of a brown dwarf (Crossfield et al.) and the first seven-wavelength-bands-study of brightness variations of two brown dwarfs (Biller et al.). Taken together, the studies provide fascinating image of complex weather patterns on an object somewhere between a planet and a star the beginning of a new era for brown dwarf study, and an important step towards another goal: detailed surface maps of giant gas planets around other stars.
On a more personal note, this was my first ever press release to be picked up by the Weather Channel.
