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A Dwarfs and K Giants

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.

Distribution of DDOIs according to spectral type. The two peaks at AV and K show that most stars hosting disks in our list are stars of type A and K that are about twice as massive as our Sun.

Distribution of DDOIs according to spectral type. The two peaks at AV and K show that most stars hosting disks in our list are stars of type A and K that are about twice as massive as our Sun.

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.


Left: Artist’s impression of Sirius, and A dwarf. Credit: NASA, ESA, G. Bacon

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.

​Herschel image of κ Coronae Borealis 31.1 parsecs away. This K giant is about twice as massive as our Sun. The red regions correspond to dust orbiting the star. Interestingly, this star also hosts at least one exoplanet with a mass of about 2 Jupiters. Credit: Bonsor et al. 2013.

​Herschel image of κ Coronae Borealis 31.1 parsecs away. This K giant is about twice as massive as our Sun. The red regions correspond to dust orbiting the star. Interestingly, this star also hosts at least one exoplanet with a mass of about 2 Jupiters. Credit: Bonsor et al. 2013.


Disk Detective–in Chinese!

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:

類似地球的行星是在圍繞著年輕恆星的氣體、塵埃、岩石和冰塊所構成的盤中形成。我們需要你的幫忙來找出更多這種孕育行星的盤,這樣我們才能找 到系外行星且更加了解它們如何成長。

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( 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 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.

Marc Kuchner  and Meg Schwamb



Disk Detective and Planet Hunters

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 extrasolaKepler Field of View Star Chartr 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”

Marc Kuchner

Seven Hundred Million Sources. Four Hundred Disks.

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 left David’s office inspired, and eager to find new ways to use the vast database from the WISE mission. So I called on Dr. John Debes, an expert in white dwarfs, a kind of old, dead star. He started digging through the WISE data, finding disks around these white dwarfs—ghosts of dead planetary systems. It was a different kind of search. But again, every source had to be verified by eye.The Vela Molecular Cloud, Imaged with WISE

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.

Marc Kuchner