Our second paper just got published! Steven Silverberg, the lead author on the paper, tells up more:
More kudos to us! Our second paper was published by The Astrophysical Journal Letters over the weekend. It will be going up on astro-ph later today. In it, we discuss a potential new kind of disk we’ve found, around an M dwarf.
M dwarfs are really valuable targets to look for. They’re smaller and less massive than the Sun, which makes it easy to find planets around them with the most common detection methods used, radial velocity and transit searches. There are more of these stars in the solar neighborhood than any other kind of star, too. Our nearest neighbor star, Proxima Centauri, is an M dwarf; you may recognize the name from the recent discovery that it has a planet orbiting it <with link to story on it from somewhere>. Since we expect disks to appear about as often as planets appear, we would expect to see lots of M dwarf disks, too, but we haven’t observed that many. The largest survey of M dwarf debris disks to date only found ~175 new disks, and most of those were quite old, over 1 billion years old. Young disks are in some ways more interesting, since any planets around the star would be young enough and therefore warm enough to observe via direct imaging (like the planets around Beta Pictoris).
One method we have of determining the age of a star is seeing if it is a member of a Young Moving Group (YMG). These are groups of stars whose position and motions through the galaxy, along with age indicators in their spectra, suggest that they were born in about the same place at about the same time. Using the online tool BANYAN II by Jonathan Gagne, we can test the likelihood that a star is a member of a moving group, based solely on its observable astrometics (its coordinates, its parallax, its proper motion, and its velocity directly toward or away from us). And you all have found…
…the oldest M dwarf in a YMG! You first met this object at AWI0005x3s, and flagged it as good. We ran its astrometry data through BANYAN II, and found that it has a 93.9% chance of being a member of the ~45 Myr-old Carina association. Very cool, right?
Well, that’s not all. Because it’s a very unusual disk, too.
As stars form, their circumstellar material is mostly gas and dust that settles into a YSO disk. As time goes on, the gas usually accretes onto the star, forms gas giants, or is blown out of the system, leaving the dust behind as a debris disk. Since there’s more material, the gas disk is usually hotter and more massive than the dusty debris disk. This usually occurs in the first 20 Myr or so of the system’s existence.
This star, however, shows a large infrared excess in both the W3 and W4 bands, which suggests that it’s warm (~263 K) and massive. That implies that there’s still a lot of gas in the system, but there’s not enough data yet to tell us *why* that is. It could be an unusually old YSO disk, or it could be something we’ve never seen before.
To help us get a sense of what the system might look like from an artist’s perspective, we enlisted the help of one of our Disk Detectives, Jonathan Holden. Jonathan put together this rather stunning depiction of what this system might look like, that we’ll be using in press releases about this discovery.
You’ll also notice that there are eight citizen scientists listed as co-authors on the paper: Joseph R. Biggs, Milton Bosch, Katharina Doll, Hugo A. Durantini-Luca, Alexandru Enachioaie, Phillip Griffith, Sr., Michiharu Hyogo, and Fernanda Piniero. These fellow Disk Detectives on the Advanced User team helped collect the kinematic data from online astronomical catalogs that we used to test each object with BANYAN II. If you’ve done more than 300 classifications and you would like to join the group, email us at email@example.com.
Great work, everyone! Two papers accepted in the space of four months is excellent progress for the project, and there’s more on the way. Stay tuned, and keep classifying!
Congratulations, us! Our first paper was accepted for publication in the Astrophysical Journal. The journal will copy-edit it and typeset it nicely. But in the meantime, you can read a draft online here at the astro-ph archive. If you spot any errors, please let us know. The paper describes how the project works (you’re probably familiar with that) and announces 37 new disk candidates, including what looks like…
the first debris disk around a star with a companion white dwarf! You met this star, HD 74389, as subject AWI00000wz and several of you (including Artman40 and Dolorous_Edd) immediately recognized it as a good candidate, roughly two years ago. Well, amazingly, this critter is the first of its kind. Stars with white dwarf companions are common; some of the brightest stars in the sky have white dwarf companions, like Sirius and Procyon. And this star is an “early A” type star, meaning its about twice as hot as the Sun. Debris disks around “A” stars are fairly common; maybe 15-20% of A stars host debris disks. But for some reason, nobody had ever found a star with BOTH a debris disk and a white dwarf companion.
One possible reason for why these objects are rare is that the birth of a white dwarf is somewhat violent. In astronomy, we generally assume that the all the stars in a binary or triple system formed at the same time. More massive stars live shorter lives; they turn into white dwarfs (or neutron stars or black holes) sooner. So that means the white dwarf in this system probably came from a star slightly more massive than the A star that has the debris disk, maybe a B type star. This B star lost most of its mass–more than the mass of the sun–into a wind that shines for a while as a planetary nebula. This wind can blow away the small dust grains that are the part of debris disks that we actually see with our telescopes.
However, there are three stars known that have extrasolar planets orbiting them that have white dwarf companions. So maybe this wind isn’t all that harsh on planetary systems. Alternatively, some theorists have suggested that the wind from an evolved star can form a new disk around the star’s companion. So maybe this disk we saw is a kind of second-generation debris disk.
To make things even weirder, HD 74389 also has an M dwarf companion; it’s what’s sometimes called a hierarchical triple, meaning that the M dwarf and the A dwarf look like a somewhat close binary, and the white dwarf orbits much farther out. The distance to this triple system is about 111 parsecs (360 light years), based on observations from the Hipparcos telescope. Based on that distance and the separation between the images of the A star, the M dwarf and the white dwarf, we can estimate that the white dwarf orbits roughly 2200 astronomical units (AU) away from the A star with the disk. The M star orbits much closer in, at about 400 AU. For comparison, Pluto’s orbit around the Sun is about 39 AU.
Besides this exotic object HD 74389, our paper reports thirty two other new debris disk candidates that we found and it describes a new detection of 22 micron excess from a previously known debris disk host: the star HD 22128. About half of the new debris disks are close enough to the Sun that they are potential targets for imaging with coronagraphs to search for extrasolar planets that could be lurking within them.
The paper reports four more interesting objects that we discovered, classical Be stars HD 6612, HD 7406, HD 164137, and HD 218546. A classical Be star is a funny kind of beast: a rapidly rotating star surrounded by a disk made of gas. Nobody knows quite how these objects form, but it seems most likely that the gas disks are ejected from the stars themselves. These objects are not the kind of disks that are thought to host planetary systems, but they are fun to think about nonetheless. Here’s a handy review paper about Be stars you might like.
The paper lists the user names of everyone who helped classify one of the new disks–and you may have noticed the eight of the authors of this paper are citizen scientists: Joseph Biggs, Milton Bosch, Tadeas Cernohous, Hugo A. Durantini Luca, Michiharu Hyogo, Lily Lau Wan Wah, Art Piipuu, Fernanda Pineiro. They are members of the Disk Detective Advanced Users Group who helped do some of the more in depth background research on the stars discussed in the paper. If you’ve done more than 300 classifications and you’d like to join this group, just send an email to firstname.lastname@example.org.
Nice work, everybody! And we’re just getting started. Stay tuned for more papers later this year.
Disk Detective Milton Bosch stopped by NASA Goddard Space Flight Center this month to meet with some of the science team and see the James Webb Space Telescope being built. What ended up happening that day we never could have guessed! Here’s the story, in his words.
My Day at NASA Goddard Space Flight Center
by Milton Bosch Nov.20, 2015
Greenbelt, Maryland has always held a special place in my heart and mind. I met and courted my wife there and lived three wonderful years in a unique New Deal era city in suburban Maryland outside Washington, DC. It has a lake and even camping at Greenbelt Park, part of the National Park system. Best of all, NASA in its wisdom had chosen Greenbelt as the site
for its first Space Flight Center. NASA Goddard opened on May 01, 1959. We had it all.
I’d always look at the guarded entrance across from our shopping center, and wonder, What is going on inside those gates? Really cool stuff, no doubt. That was in 1981; I was in medical school and there was almost zero chance I’d ever be invited there. Even after moving to California for residency training and my career in internal medicine, my NASA Goddard
memories were kept alive whenever I had a faint recollection. When a good friend named Willy got a job at Goddard as a machinist in 2010, the connection deepened a wee bit. I could picture myself inside if Willy could get permission to bring a visitor. That snippet of hope left when Willy left NASA Goddard after a couple years.
Fast forward: It’s now November 04, 2015 and I’m on a Google hangout call with the science team of Disk Detective, a citizen science project run by NASA. Months earlier, a NASA email arrived announcing a new citizen science project on January 30, 2014 , with a grant from The Zooniverse. Disk Detective’s goal was to locate protoplanetary disks – very early solar
systems – around young stars, and debris disks around more mature ones. I thought, “Discover new solar systems and planets and help learn how they form? I’m in!” I thought “in” was just doing classifications of objects, using the Disk Detective flip-book to triage them into two basic categories: a good candidate, or flawed (and reasons why). After doing many classifications came the invitation to become a superuser from principal investigator Marc Kuchner. As such, I learned how to navigate the astronomy catalogs, and choose promising objects for the main spreadsheet and hone my classifying skills. Step by step, with lots of mentoring and greater responsibilities, I was eventually asked to join the science team and here I was, sitting at my computer on November 5th for our weekly Google hangout with the science team.
I mentioned to Marc that I had won two free concert tickets to Madison Square Gardens for Nov. 7th, and would be staying near Greenbelt in Crofton, MD. Then Marc asked if I’d like to drop by on Nov. 6th for a tour of NASA Goddard Space Flight Center. Two days later I fulfilled my dream. What came later was a big surprise for everyone.
We started out with meeting everyone on the Disk Detective team at NASA Goddard. It was great finally meeting Marc Kuchner, PI, and graduate students Steven Silverberg and Shambo Bhattacharjee. We did a quick tour of the ground level, and then visited the offices of each. Then, upstairs to see the world’s largest clean room, where the James Webb Space Telescope (JWST) is under construction. We exited the elevator to discover a VIP tour in progress, and it slowly dawned on me that I was looking at North Dakota senator Heidi Heitkamp. She was not just any US Senator; she was a senator I liked and had supported her campaign. I whispered to Marc that I knew a bit about Senator Heitkamp, so he asked me to ask her a question about citizen science. I said, OK, and waited for my opportunity.
Just when it seemed like the right moment would never appear, I saw a raised hand asking if we could talk about citizen science. Senator Heitkamp walked over and introduced herself to each one of us, asking our names, where we lived, what our jobs were, and what we did before coming to NASA Goddard. She was pleased to meet a supporter from Napa, California. She wanted to know my journey from organic chemist, to medical doctor, to having to go on full disability, to finding and joining Disk Detective. So I told her my story of today being the fulfillment of a 34 year-old dream, all made possible by joining Disk Detective almost two years earlier, and a 1:20,000 chance of winning 2 free concert tickets to Madison Square Gardens.
While we talked, the cameras were snapping away and all-in-all, I think we got to spend 15 minutes on Disk Detective and citizen science. It was an unlooked-for opportunity to get the word out about Disk Detective and citizen science with one of our U.S. Senators and it could not have gone better. We were glowing for the rest of the day from the encounter.
Then the room cleared, and we got to see what we had come upstairs for: the James Webb Space Telescope under construction. (One of the goals of Disk Detective is to find targets to propose to observe with this telescope.) We could see the frame, the folded wings, and folded arm for the secondary mirror. On catwalks 80 feet above the crew sat a row of flat dewar flasks, each containing one hexagonal mirror. Launch date is less than 3 years away – October, 2018. Giant rolls of shrink wrap were placed all about for final sealing before JWST’s journey to the launch vehicle. I looked at everything in the room visible from our vantage point and then went downstairs and peeked through an entrance door window. No photos are allowed through that window, nor inside either.
Next stop was one of the “testing rooms”; though I’m sure it has a formal name. It had an 8 story high egg-shaped metal container, filled with liquid nitrogen for starters. Inside that was another cryogenic container filled with liquid helium. Every single piece, every instrument, every device must survive that environment before it can be trusted for launch. After all, they must function at extremely low temperatures. But more terrors awaited the equipment and instruments that go into space.
Nearby was a huge room with a centrifuge that dwarfed a blue whale. It was like the room where the centrifuge scene from The Right Stuff movie was filmed, but this centrifuge has a different purpose. In order to test equipment properly (not people), the centrifuge reaches up to 15 G’s of acceleration, helping insure against failure in the most stressful environments imaginable. Steven said it would tear a human to pieces.
Next door to that was a huge acoustic testing room with a 7 or 8 foot “tweeter” and a 12 foot “woofer” with a maximum combined sound intensity of 150 decibels. No humans are allowed inside that lethal chamber. An adjacent room held the machinery that powered the 150 decibel monster. A six inch hose for pressurized nitrogen powered the tweeter, and emitted so much of the simple asphyxiant that there is no admittance during testing. We paused our tour for a relaxing lunch in the cafeteria, and then filled time while Marc had teaching duties. Those duties now completed, we all met in Marc’s office, where all the Google hangouts take place (with other scientists joining from Adler Planetarium, The Space Telescope Science Institute, University of Oklahoma, and more).
We spent an hour discussing ways to improve our sound recordings and other technical issues, as well as more important problems, like finding a replacement llama doll for Marc’s very young son, should he lose his beloved cozy-coze. Then I was presented with a highly coveted Disk Detective coffee mug, and we took photos of a poster where my name appeared as co-author, alongside the names of five other citizen volunteers like myself. Then it was time to go.
It was a truly great day, full of the unexpected, and a real pleasure meeting some of the science team in person. Never give up on your dreams! Disk Detective will take you as far as you want go and has all types of support while you navigate the learning curve…all the way up to co-authorship of scientific papers.
Bernard Lyot was a French astronomer who invented a tool called a “coronagraph” that’s useful for making images of disks and exoplanets. A few weeks ago, I went to a conference in Montreal, called “In the Spirit of Lyot 2015” named in his honor, and I learned lots of cool new stuff about images of disks and planetary systems. Here are some of the highlights.
First of all, Disk Detective superuser Manon Gingras came to the conference and I got to meet her! Manon was spending her last few days in Montreal before she moved to Australia, and she drove downtown to the conference hotel to spend the afternoon with us. While she was at the conference, she did an interview with a reporter from the French language magazine Le Devoir about Disk Detective. Manon described her experience at the conference in this blog post. (Don’t worry, when Manon says “gunning down” she is not talking about anything violent–it’s just an expression.)
Disk Detective science team member Dr. Thayne Currie described a debris disk around the star HD 115600 that he imaged for the first time. It’s a beauty, an eccentric ring of debris about 15 million years old around a star just about 50% more massive than the sun, essentially a younger version of the Kuiper Belt in our solar system. And–arrgh!–this star is in the Disk Detective catalog, just nobody had gotten around to looking at it yet. So we might have been able to claim this as one of our Disk Detective discoveries too. Oh well. Next time.
Dr. Erika Nesvold gave a talk about her new dynamical models of the Beta Pictoris debris disk. They show what happens when a planet, embedded in a debris disk, orbits very slightly out of the plane of the disk. Here’s the press release about her results and the YouTube video. You might remember Erika if you were around during the first week after Disk Detective’s launch; she pitched in to help answer questions on Talk.
And last but not least, the Gemini Planet Imager (GPI) team announced a new directly-imaged extrasolar planet, 51 Eridani b, located inside a debris disk. You have probably heard of the many hundreds of planets discovered by NASA’s Kepler space telescope; those planets have been inferred from the way they sometimes block part of the light from the stars they orbit. Directly imaged planets–planets whose light we can collect like 51 Eridani b–are much rarer. And most of these directly-imaged planets orbit within debris disks, one kind of disk that we’re searching for at Disk Detective. So when we search for disks, in a way, we’re searching for planets too!
Everyone I spoke to at the meeting was interested in learning about Disk Detective, and eager to hear what we have found. I showed off some of the work we did following up our Disk Detective Objects of Interest (DDOIs) with RoboAO, and several colleagues asked to collaborate with us as a result. Hugo, Michi, Ted, Joe, Lily, Katharina, and Milton hustled to get this data analysis work done in time for me to show off. So the science of disks and exoplanets marches on…and we’re right in the thick of it. Keep up the good work, everybody!
A list of 102 interesting objects that you helped pick for follow up (let us call them Disk Detective Objects of Interest, or DDOIs) shows that many of the stars with disks we locate will be A dwarfs or K giant stars. We don’t yet know all the spectral types of the DDOI stars precisely, but you can see the distribution of the types we do know in the figure below. The peaks correspond to A dwarfs and K giants.
So what are A dwarfs and K giants? “A” dwarfs are very hot, fast spinning and blue stars that are younger and brighter than “G” stars such as our Sun. The bright stars Sirius and Vega are some well known A dwarfs. Many of the best studied debris disks are around A dwarfs.
What are these “K giants”? K giants and A dwarfs are two sides of the same coin. Let’s talk a bit about the life cycle of a typical star.
Most ordinary stars like our Sun burn hydrogen fuel for many millions of years. Once all the hydrogen is used up however, the star balloons in size and becomes a red giant. In the far future when our own Sun becomes a red giant, it will become so big that it will swallow up Mercury, Venus and possibly the Earth. Giants also tend to steadily lose a lot of their own mass all the time. This is because hot winds are blowing off the gas that is part of the star. (This hot gas is tricky because it might be mistaken for a dusty disk)
K giants are former A stars that have evolved for hundreds of millions of years. Like the sun, they have burned through their hydrogen, and ballooned up in size. Both A and K stars are about twice as massive as our Sun.
K giants are also really interesting because Jupiter-sized exoplanets orbiting these old, giant stars have been found to be more common than Jupiter-sized exoplanets orbiting less massive stars that are still on the main sequence. These exoplanets around K giants have been found by the popular radial velocity (Doppler shift) method.
Also, some of these K giants have debris disks, sometimes even dustier than their younger counterparts. This is surprising, because giants are very bright and light from the star exerts radiation pressure on small dust particles that ought to blow the dust away, or cause them to slow down and spiral into the star and be swallowed up.
So where is the dust around these K giants coming from? Nobody really knows yet, but there are several hypotheses. One is that dust is coming from the star itself. Another is that the dust is in fact interstellar dust in our galaxy. A third is that giants are breaking up more comets. Whatever the cause, we have a lot of K giants in our list of DDOIs that potentially have dusty disks–so once we can follow these up with telescopes we will be able to help solve this mystery.
Dawoon Jung (@dirkpitt2050) is a graduate student at the International Space University currently at NASA Goddard Space Flight Center doing a summer internship with the Disk Detective team. He was born in Korea, and is interested in exoplanets and space flight.
We’re excited to announce that Disk Detective has been translated into Mandarin Chinese–both simplified and traditional character fonts! Many thanks to Ruobing Dong at the University of California, Berkeley Astronomy Department and Mei-Yin Chou at Academia Sinica’s Institute of Astronomy & Astrophysics (ASIAA) for the translation work and to Chris Snyder at Zooniverse for the technical work.
Here is a brief description of Disk Detective in traditional character Chinese and then followed in English:
為了找到這些盤，我們結合了數十萬張來自美國太空總署（NASA）的廣域紅外線巡天探測（WISE）任務的影像。已經有很多科學家搜尋來自 WISE的資料並試著用電腦找出這些盤。然而這些盤容易跟星系、小行星、星際物質團塊和其他天體搞混，科學團隊檢視後發現必須用人眼來辨識這 些資料才行。
在尋盤偵探（DiskDetective.org） 中，有了你的協助，這些被辨識出來的盤將能用來建立一個最大的盤資料目錄。NASA的James Webb太空望遠鏡和其他望遠鏡將用這個目錄為主要目標來尋找系外行星。我們找到的這些盤將有助於了解太陽系的過去跟未來。
Planets like the Earth form within disks of gas, dust, rock and ice grains that surround young stars. We need your help to find more examples of these planet-forming disks so we can locate extrasolar planets and better understand how they grow and mature.
To find these disks, we’re combing through a catalog of hundreds of thousands of sources from NASA’s Wide-field Infrared Survey Explorer (WISE) mission. Many scientists have been searching through the data from the WISE space telescope to find disks using computers. But the disks are mixed in among galaxies, asteroids, clumps of interstellar matter, and other contaminants. And each team that has looked through the data has found that every source has to be verified by eye.
With your help, at Disk Detective.org we will produce a catalog of verified sources many times bigger than any other catalog. This catalog will yield key targets for NASA’s James Webb Space Telescope and other telescopes to search for exoplanets. The disks we find will help us understand the history and future of our solar system.
A few folks have asked us: what’s the relationship between Disk Detective and Planet Hunters? Planet Hunters, of course, is the Zooniverse citizen science website that invites users to examine data from NASA’s Kepler mission to search for extrasolar planets.
The success of Planet Hunters helped inspire us to launch Disk Detective! But beyond that, there are several scientific connections between the two projects. Both are about extrasolar planets. As you probably know, in Planet Hunters, users look at measurements of a star’s brightness, checking for sudden dips that could indicate a planet crossing in front of the star (called “transits”). In Disk Detective, we search for the homes of planets: stars surrounded by disks where planets form and often dwell.
Let’s talk more specifically–about what stars the two projects have in common. First of all, the data from the WISE mission that we’re examining at Disk Detective covers the whole sky. So it overlaps with everything, including the part of the sky that Kepler/Planet Hunters has already studied and whatever parts of the sky Kepler will image in the future. Indeed, the part of the sky Kepler has already examined has already been searched for disks at least once; Samantha Lawler and Brett Gladman claimed to find eight debris disks around stars with Kepler planets in 2012, using data from the WISE mission. However, further studies of the Kepler field were unable to replicate this result. The map above illustrates the current Kepler field, mostly located within the constellation of Cygnus.
But there will be more such Kepler/WISE disks for us to find via Disk Detective and Planet Hunters. For one, both the Kepler and WISE databases have improved substantially since that work was done. Kepler has found more transiting planets, and WISE scanned the sky again, leading to the new ALLWISE data release this fall.
Moreover, plans are afoot to extend the Kepler mission. The extended mission, called “K2” will search for planets in a different region of sky, near the plane of the Earth’s orbit. Here at Disk Detectives, we will already be searching that region for disks. And I’m pretty sure the new K2 data will be searchable at Planet Hunters as well.
So stay tuned–and keep digging for new disks! You might find one around a star that Kepler has already found planets around, or that it will find planets around soon. And even if there is not a direct match, we still learn by combining the statistical information from both surveys about how and where planets form.
“It has long been an axiom of mine that the little things are infinitely the most important”
It was the curly-haired Dr. David Leisawitz who first told me about the WISE mission. I remember sitting in his office in front of a giant black-green-magenta sky map while he described how the WISE mission would find amazing kinds of disks: disks hosting young planetary systems, disks in old planetary systems, all kinds of exotic phenomena.
He told me how the science team was combing through the data right now by computer to find these disks. But every source had to be verified by eye.
I started wondering: is it possible that folks are going about this backwards? What if we could check through the whole WISE catalog by eye, right off the bat? What would we find then?
I made some quick estimates of how many disks could be find in the database that others had not already found by computer. The WISE mission observed more than 747 million sources all around the sky. My calculations told me that if we went through the catalog using the amazing power of human vision right off the bat, we could find almost 400 debris disks among this sample that nobody else could find. That’s not to mention all the other kinds of disks whose numbers I couldn’t calculate: protoplanetary disks, transitional disks, disks around white dwarfs and other evolved stars. And there could be other kinds of fascinating objects to find lurking in the data: Kardashev Type III civilizations, metal poor stars, planetary nebulae—
But I still wasn’t confident in the idea. So I called up Drs. Debbie Padgett and Luisa Rebull, who were also leading large efforts to find disks with WISE. Debbie discovered a spectacular example of a debris disk that in Hubble images resembled a giant skinny V, probably sculpted by a hidden planet. Luisa had been scouring star-forming regions, finding protoplanetary disks. And once again, in both Luisa’s and Debbie’s WISE searches, every source had to be verified by eye.
The next step was obvious; we wrote the Zooniverse folks and began working on a site. Fast forward through a few years of planning. Now David, John, Debbie and Luisa and I have joined with Dr. Mike McElwain and other experts to become the Disk Detective science team. A few more months of site development and here we are on launch day, ready to work with you, ready to find some disks that nobody else will spot–thanks to your eyes.
So let me take this chance to say that we can’t wait to meet you. I hope you are patient and determined, because it won’t be easy. But I think the chance to discover a new disk—a whole nascent planetary system—in one shot like this is worth the effort. And who knows what else we will find lurking in the spectacular WISE database, the deepest all-sky infrared survey every undertaken?
Thank you for joining us at Disk Detective. Good luck, and remember that the world is full of obvious things that no one ever observes.