Good news, everyone: our latest paper from Disk Detective has just been accepted for publication in the Astrophysical Journal! You can read it on the arXiv now. In it, we estimate the number of disks we expect to find in Disk Detective, and present over two hundred new disk candidates that have received high-resolution follow-up imaging.
Disk Detective is designed to identify new disk candidates in the AllWISE catalog by eliminating false positives. Because we have such a large catalog and so many classifications that have been made so far (keep them coming!), we can get some statistics on how many objects are false positives, and use that to estimate the number of disks we expect to find. We can also break this down by what kind of false positive we find, and where in the galaxy we find it.
In general, “multiples,” objects for which a majority of classifiers clicked “Multiple objects in the Red Circle,” are the most common type of object–more than 70% of the objects in the catalog! Only about 8% of objects are classified as “None of the Above/Good candidate” by a majority of classifiers. These occur most often in the Galactic plane, as you’d expect–if there’s more stars in the Galactic plane, you’d expect to get more disk candidates there. However, multiples become much more common in the Galactic plane, as well–the multiple fraction in the Galactic plane is over 70%!
We looked to see the multiple fraction (the fraction of objects in a given range that were multiples) as a function of Galactic latitude. We expected that these would be most common in the Galactic plane, and fall off as you got further away from it. We found instead that while for the most part this is the case, there’s an additional peak between -30 and -35 degrees Galactic latitude.
So we looked at the multiple fraction as a function of both Galactic latitude and longitude, as shown on this heatmap (brighter = higher multiple fraction), and found that most of those multiples outside the Galactic plane occurred at the same Galactic latitude as the Large Magellanic Cloud–we have multiples caused by stars in nearby dwarf galaxies, too.
In addition to the website classifications, we also review our objects in the literature to ensure that we’re not identifying things that are known to be non-disk sources (like background galaxies). This eliminates an additional 14% of our objects, the remainder of which becomes DDOIs.
We took high-resolution images of 261 of our DDOIs to see if we could identify faint background objects, fainter than would be detectable in our survey data but bright enough to produce a false positive at W4, using the Robo-AO instrument while it was at Palomar, and RetroCam on the Irenee R. Dupont telescope at Las Campanas Observatory in Chile. (I wrote about my observing experience at LCO here.) We included some volunteers from our advanced user team in the analysis of this data–they’ll have a blog post up on the details of what they did soon. Overall, we found that 244 of the 261 objects were good disk candidates once faint background objects were taken into account.
Combining all of these, we estimate that only 7.9% of all infrared excess candidates in AllWISE are or will be good disk candidates. That means that we expect to find 21,600 disks in AllWISE, almost double our original estimate!
We were able to use our false positive rates to estimate how many false positives appear in published disk searches. Many surveys do a good job, but have some false positives due to objects only detectable in high-resolution imaging. Some larger searches, however, seems to be riddled with false positives, including the McDonald et al. (2014) and (2017) searches, and the Marton et al. (2016) search. These searches don’t include a visual inspection of the images, and thus are likely to have high rates of false positives due to multiples at the minimum.
We were also able to leverage the knowledge base of our Disk Detectives to analyze the M dwarf disk candidates of Theissen & West (2014). M dwarf disks are key targets, because very few have been found, despite the abundance of M dwarfs nearby. The advanced user team got together and found a way to analyze the targets as if they were Disk Detective objects (more on this in their blog post coming soon). We found that only 13 of the candidates from Theissen & West (2014) had high enough signal-to-noise for the Disk Detective methodology to apply. Advanced users found flaws with all thirteen, making all of them false positives.
Finally, we presented a list of 244 disk candidates with follow-up high-resolution imaging, 213 of which are new discoveries by Disk Detective. These seem to be split evenly among debris and YSO disks, though some of those YSO disks could potentially be “extreme” debris disks, which are thought to result from collisions of terrestrial planets. We made some further interesting discoveries among these:
- We found that twelve of our new disks were in comoving pairs (that is, another star nearby to them has similar motion), providing further support to the hypothesis that warm circumstellar dust is associated with binary systems.
- We made the first identification of 22-micron excess around two stars that are known to be in the Scorpius-Centaurus young association, and identified known disk host WISEA J164540.79-310226.6 as a likely member of Sco-Cen, based on its motion through the sky. By identifying these targets as members of Sco-Cen, we give them likely ages, letting us put these on timelines of disk evolution.
- We found thirty-one disk candidates within 125 pc, including 27 debris disks. These are good targets for both direct imaging exoplanet searches, and spatially resolving the disk itself in scattered light–making these targets optimal for observation with the James Webb Space Telescope.
And there’s still more work to be done! We recently hit 76% complete (that is, 76% of all our targets have enough classifications to be retired from the website), but that leaves more than 60,000 excesses to evaluate with your help. We now know how many objects we’re going to find–now it’s our job to finish finding them.
This spring we did a big classification push to prepare for the second data release from the Gaia mission, which arrived on April 25, providing distances to more than a billion stars. This data instantly converted a substantial fraction of our Disk Detective catalog from mystery objects into stars with known distances and spectral types. Thank you for all your help getting ready for this event! We’ve been hard at work since then on (at least) two projects involving Gaia Data Release 2 (DR 2) and Disk Detective data. And here to tell you about one of them is Susan Higashio, a masters student at International Space University who has been spending her summer as an internal at Goddard Space Flight Center, working on Disk Detective data in Goddard’s new Augmented Reality/Virtual Reality lab.
Greetings, Disk Detectives!
It’s Susan here and I’m thrilled to be a summer intern with Dr. Marc Kuchner on Disk Detective this summer! When I found out that I would be working at NASA Goddard, I was SUPER stoked; not only because it was NASA, but being from the West Coast of Canada, I was really looking forward to visiting the East Coast of America for the first time! Truth be told, I felt a little (A LOT!) intimidated being in the Astrophysics department here at NASA—especially because my background is NOT Astrophysics—but I quickly learned that one of the great things about citizen science is that with a little hard work and dedication, anyone can be a citizen scientist!
Thanks to all you Disk Detectives for classifying all those stars with debris disks and accretion disks! Now, I’m working on a Virtual Reality (VR) project with these Disk Detective objects. They are loaded into VR with the Gaia DR2 Release, and the Disk Detective objects that you’ve classified light up in the VR system.
In addition to being great fun, VR is a really great way to see stars from different perspectives. When we evolve their positions backwards and forwards in time, the Disk Detective objects help reveal groups of stars that move together, or “young moving groups”! Stars within a moving group formed from the same event so they are about the same age, originate from the same area in space and move in the same direction at about the same speed. Many of the Disk Detective objects I am looking at are young, relatively speaking, (we’re talking tens of millions of years old, compared to our sun, which is about 4.56 billion years old) and so moving groups can be studied to learn about how our solar system may have formed and evolved over time. There are many known moving groups (e.g., a list of young moving groups can be found here) and stars found in Gaia DR2 that we can see in VR might belong to a known group, or maybe even be part of a new one. Wouldn’t it be exciting if some Disk Detective stars made up a new moving group?
In the 6 weeks that I have been here, I have learned so many new things. I’ve learned how to make calculations to plot H-R diagrams with stellar isochrones, which are helpful to estimate the approximate age of objects, as well as position/proper motion vector diagrams which illustrate the movement of objects over time. These diagrams can be used to plot any interesting Disk Detective objects to see if they move together over time and possibly see if they might form a moving group. I have also been spending time in the VR lab to search for additional stars that move with together with some interesting Disk Detective objects that I have had my eye on. This is not as easy as it sounds!
It’s not all work here though! I’ve had the pleasure of meeting Disk Detective citizen scientists, Josh Hamilton and his wife, Sarah, when they came to visit NASA Goddard. Marc took us all, including Steven Silverberg and another citizen science intern Michaela Allen, on a tour of the integration and test facility. It was really cool that the James Webb Space Telescope had been in the clean room just months earlier and information about the telescope is still on display.
I have long dreamed of working at NASA, and because of Disk Detective and citizen science, this has been an unforgettable experience and a dream come true! Many thanks to Marc, without whose support and guidance I would not be here on this internship; to Professor Hugh Hill at ISU, who was formerly at NASA Goddard and who still has many friends here; as well as many other people who I have learned so much from during my stay here so far: Steven Silverberg and the Disk Detective team, Sarah Logsdon, Michaela Allen, and Peter Pokorny; along with the VR team: Matt Brandt, Tom Grubb, and interns Stewart Slocum, Tyler Cahill, and Hayden Hotham, to name a few. I am really looking forward to spending the rest of the summer here and continuing my work with Disk Detective and all of you citizen scientists. Thank you for your hard work and keep on classifying those objects!
Today we have a guest post from Disk Detective citizen scientist Hugo Durantini Luca., from Cordoba, Argentina, who just returned from another trip to the Complejo Astronómico El Leoncito (CASLEO) observatory to make follow-up observations of our disk candidates. I think Hugo is going to end up a professional astronomer if he keeps this up! –Marc
My Year in Astronomy
First of all, and to avoid repetitions, if you have not read my other post in this blog, you can take a look here: This post is a continuation of that experience, my love for Astronomy has only get bigger since back them.
2016 and 2017 have been a without a doubt a couple of interesting years for me regarding astronomy, but 2017 takes the prize in my opinion. Even if not in the way that I originally planned or imagined, a lot of the things that I thought back in 2015 started to take form.
While the work in Disk Detective was progressing, 2016 was dedicated to expanding my practical knowledge in Astronomy thanks to the different workshops of the Grupo de Astrometría y Fotometría / Astrometry and Photometry Group (GAF) at the Observatorio Astronómico Córdoba (OAC). I learned some basics about astronomical instruments and more advanced concepts about image processing to be able to make scientifically valuable reports of astrometry and photometry.
In 2017 the travel opportunities started to appear again and, of course, I tried to make the most of them, with two travels to CASLEO in the San Juan province for Disk Detective observations, one to the Observatorio Astronómico Tolar (OAT) in the Salta province, and a couple of good experiences in La Estación Astrofísica de Bosque Alegre (EABA) in my own province. Except for CASLEO, the rest were related to my participation in the GAF and IATE.
CASLEO feels after three trips like a very familiar places, so much that even after observing 100 stars this year alone for Disk Detective, I never get tired and always looks forward to return again. Plus, working along Luciano Garcia from the OAC is always a pleasure and a great learning experience. Without a doubt, working with spectrographs never ceases to be interesting.
This year I enjoyed the opportunity of exploring the landscapes of CASLEO in two different seasons of the year, and along the trip of 2015, now I have almost a complete picture almost complete of how they change throughout the year. What never changes is the enjoyable environment which welcomes our arrival—another reason to return.
My trip to Salta and the OAT was the longest distance I have traveled and my longest stay away from home in a very long time, but a wonderful experience for multiple reasons. Not only I never visited before the north of my country, with a visit to the National University of Salta included, I was traveling to collaborate in the project of a new astronomical observatory that is starting to work at the same time that I keep my formation as Telescope Operator and advancing in my Astronomy career with help of exceptional people.
The trip to the OAT, located in the small town of Tolar Grande is, let’s say… a bit longer compared with the trip to CASLEO (1200 vs 750 kilometers), but the landscape alone makes the trip worthwhile. Even with the OAT in a stage of construction, we already were able to capture CCD images with enough quality to make a few first contributions: exoplanet transit reports and others events. The potential of the site is huge.
Tolar Grande is a town with a bit more than 200 inhabitants, but the calm that possesses you along with an incomparable night sky that surpassed the experience of seeing for the first time the Milky Way at CASLEO.
Bosque Alegre (EABA) in Cordoba was another great experience this year, was able to interact with both telescopes while we were doing observations for the June transit of transneptunian object MU69. The 1.54 meter telescope is the same one that participated of the kilonova discovery that traveled the world with the news of the first gravitational wave event with a confirmed optical counterpart (is worth to mention that the OAT also tried to contributed there), but in this case I worked with the Perrine Telescope (76 cm).
I could keep writing pages upon pages describing in detail all the experiences, but that is not the idea of this post. The idea was to present a small summary of my experiences and current activities, whose initial seeds started in Disk Detective and then started to branch off in ways that I was unable to imagine. Citizen science is without a doubt an invaluable tool for common people to get involved with subjects what they love, maybe at first only like a hobby, maybe later like the start of a career in the scientific world.
Never stop chasing your dreams, and in the case of Astronomy, looking to the skies!
With thanks to Marc Kuchner, Steven Silverberg, Alissa Bans and Milton Bosch from Disk Detective, to the people of the Space Telescope Science Institute–Bernie Shiao, John Debes and Geoff Wallace–and the people of the OAC / GAF / IATE–Diego García Lambas, Carlos Colazo, Matías Schneiter, Cecilia Quiñones, Rodolfo Artola, Carla Girardini, Raul Melia and others. Without them I would not be writing these words, with so many projects in my mind that I hope to get done.
Howdy Disk Detectives,
Just thought I’d give you an update on some goings on since our last blog post.
First of all—the project is now 59% complete! That’s fantastic. Keep up the good work, everybody! The James Webb Space Telescope is set to launch next fall, and start taking science data in the spring of 2019. Let’s try to finish up all the classification work by then! I bet we can.
Second of all, Goddard Space Flight Center held a “Citizen Science/Crowdsourcing Week” this summer, and Disk Detective’s own Dr. Milton Bosch came out to participate. Milton also spent a day visiting NASA headquarters, talking to scientists and managers about how citizen science can help NASA. The goal of the week was to encourage more scientists at Goddard and the rest of NASA to launch citizen projects and use crowdsourcing in their research. It was a huge success! There were nine talks on citizen science and crowdsourcing, and Milton met with 16 different scientists from all our scientific divisions at Goddard. We are planning to do it again next year; let us know if you might want to come down to Greenbelt, MD and participate!
Third of all, I can report that our ALMA proposal did not get selected. But it was a near miss–and we are going to try again! We submitted a proposal called “Sub-millimeter Observations of Long-lived Accretion Disks'”asking to measure submillimeter radiation from dust around WISE J080822.18-644357.3, the record-breaking disk we discovered plus a few other similar object. The review panel ranked the proposal in the second quartile and gave us a few tips on how to improve it for next round.
In other news, a handy new catalog of disks has appeared online: CircumstellarDisks.org. This catalog shows what we dream of at Disk Detective: disks that have been “resolved” by telescopes. “Resolved” means that an image of the disk shows more than a dot of light; it actually has the shape of a disk, maybe even a disk with some structure. Anyway, if you want to see some of the awesome images that keep us disk researchers motivated, take a peek at CircumstellarDisks.org.
Behind the scenes, the science team is busy working on papers about our follow-up observations from the FAST spectrograph, Robo AO, and the duPont telescope. The advanced users group is vetting objects of interest for future proposals and looking for new moving groups. And we’re finding lots of interesting disks!
Stay tuned for more news—and keep up the good searching!
Hi, all. Steven Silverberg from the science team here. Rather than my blog posts appearing under Marc’s name, I’ll be writing on this name from now on. It should make the blog a bit easier and less confusing to read.
Two weeks ago, I was lucky enough to observe on the Stratospheric Observatory For Infrared Astronomy (SOFIA). Here’s a summary of what we did, and what it was like.
SOFIA is a 747 with a custom hatch in the back and a telescope mounted inside, allowing us to observe from 40,000 feet. That altitude is above the primary part of the atmosphere that blocks infrared light, which means the telescope can observe at wavelengths longer than the ones we see in our Disk Detective WISE data, but shorter than the submillimeter wavelengths we’ve observed at with the James Clerk Maxwell Telescope. This neatly fills in a gap in our SEDs, giving us a clearer picture of how dust is distributed in these systems.
Last SOFIA proposal cycle, we submitted two proposals, and one was accepted for “do if time” status. This proposal was to get 53 micron data on a set of our main sequence A stars, as well as those identified by other projects (such as Patel et al. 2014). Our first set of observations was scheduled for May 9-11, so John Debes from the science team (and Space Telescope Science Institute) and I flew to California to ride along.
The plane itself is pretty impressive. 747s are big.
SOFIA is a working plane, so everyone onboard is piped in to the comms system. Wearing a flight comms headset makes you look important.
Because they had space, I was given permission to ride along in the cockpit for takeoff. Unfortunately, our first flight had to be scrubbed before takeoff, due to issues with some of the engine gauges.
I did, however, get to ride in the cockpit for takeoff on the second night. Sunset is really pretty when looking through the windshield of a 747.
The main cabin of SOFIA feels a little bit like mission control; lots of people looking at lots of monitors, all in rows. On these flights, we had SOFIA flight safety crew, the mission directors, telescope operators, and the team that built the HAWC+ instrument we were using.
We proposed to look at objects with an instrument called HAWC+ (High-resolution Airborne Wideband Camera-plus). This is a far-infrared camera, designed to probe long wavelengths. If the detector is sensitive enough and our target bright enough, we would be able to see light from our star+disk systems to add another point to our SED for that DDOI, but at worst we can get upper limits on what flux there is, letting us at least constrain the system.
HAWC+ has to come into the cabin through the main doors of the airplane. It’s engineered to fit through with 1/8 of an inch of clearance on either side.
SOFIA helpfully has lots of posters along the bulkhead about how it works…
…and some of the science it does
It also has one about how NASA came to acquire the plane.
Sunsets were impressive through the regular windows, too.
So was the Moon on our second flight.
Our last flight lasted long enough that the Sun was rising as we went into our descent.
The hangar the program is based out of is (unsurprisingly) huge.
All in all, it was a very educational, very informative, very fun trip on SOFIA. Thanks to you all for contributing to this project to make things like getting data from it feasible.
Good news, everyone: the Disk Detective team won an award from NASA!
Disk Detective received a 2016 Robert H. Goddard Honor Award for Exceptional Achievement in Outreach by a team.
We won this award for “providing an outstanding example of how NASA can serve the public by including them in the process of astronomical discovery.” If that’s not a perfect description of Disk Detective, I don’t know what is.
Marc accepted the award on behalf of the team. However, he wasn’t the only one there; also in attendance were Steven Silverberg (i.e., me, from the science team), and Katie Lowe, a member of the advanced user group who lives in Baltimore and came down to Goddard Space Flight Center for the day.
It’s thanks to the contributions of everyone–especially our citizen scientists–that we were able to win this award. Thanks to all of you for your contributions to the project, and keep up the good work! (The project is about 55% complete.)
Steven Silverberg from our science team recently traveled to Chile again, as he did in October 2015. Here’s his story on our most recent observing run.
Last December, Disk Detective applied for and was granted time at Cerro Tololo Inter-American Observatory, the Southern Hemisphere counterpart to Kitt Peak National Observatory in Arizona. I traveled to Chile last month to conduct the observations.
Due to an issue with flights, I unfortunately missed our planned first night on the telescope. However, I was able to get up to the mountain for nine nights of observations with the 0.9-m telescope, as well as half a night with the 4m Victor Blanco Telescope.
There are quite a few telescopes on the mountain. In addition to the 5 telescopes that belong to CTIO (the 4m Victor Blanco, and the 1.5m, 1.3m, 1.0m, and 0.9m telescopes run by the SMARTS consortium), there are a slew of other projects hosted on the mountain. The collection of domes makes for a rather impressive site–especially when viewed from the lodge at dawn.
Sunrises were a thing of absolute beauty coming over the mountains, from anywhere in the complex. This was from the lodge.
My first nine nights on the mountain were spent with this telescope, the 0.9-m. While not the biggest telescope, it proved quite capable for our mission: monitoring AWI0005x3s (from Paper 2) for flares and other stellar activity. The activity we detect in these observed light curves could give us more information as to its age, and could provide information on how the star and its disk might interact.
The next mountain over (or what seems like it) is Cerro Pachon, home to the SOAR telescope, another telescope run by CTIO. This mountain is also where the Large Synodic Space Telescope (LSST) is currently under construction. Seeing our “neighbors” from the summit of Cerro Tololo was quite nice.
The most notable result from our initial analysis is the light curve from night 4, where we observed this flare. It is rather impressive, both for its duration (~1.8 hours) and its brightness (3 times the non-flare brightness at peak). This flare, any others we find in the light curve, and any other interesting features we find in the light curve will be the subject of a future Disk Detective paper.
Sunrise on the morning of night 5 was particularly beautiful from on top of the mountain.
The view from the dining hall at the lodge was rather spectacular, as well. You can see what appears to be an ancient riverbed in the valley.
Sunsets could be particularly delightful, too. This one’s beauty comes from some rather annoying clouds, but these fortunately never came into play for our target of interest. We had fairly good observing weather throughout the run.
In addition to our time with the 0.9m telescope, we also had time on the 4.1m Victor Blanco Telescope, using the COSMOS instrument. We used this spectrograph to get what we believe is the first optical spectrum recorded of AWI0005x3s. That would give us more accurate information on its spectral type (and temperature), age (to confirm membership in Carina), and potentially radial velocity (also to confirm Carina membership).
All in all, traveling to CTIO was a fantastic experience. I gained some valuable practical experience for future observing runs, and we got what should be some quite good science out of the observations. Keep checking back here, and you should see more on what we learned from our observations soon.
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 firstname.lastname@example.org.
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 email@example.com.
Nice work, everybody! And we’re just getting started. Stay tuned for more papers later this year.
When you find a good candidate at Disk Detective, it goes into our queue to be researched and often to be re-observed. Many of those good candidates that are in the Southern Hemisphere get re-observed from the CASLEO observatory in Argentina, where we split up their light with a spectrograph to find out what kinds of stars they are.
Disk Detective Hugo Durantini Luca lives in the city of Cordoba, Argentina, much closer to the CASLEO observatory than most of us on the Disk Detective science team, but still a long journey away from it. He traveled for more than eighteen hours across the country of Argentina to join a Disk Deective observing run. Hugo spent five days on the mountain with Luciano García (astronomer from Observatorio Astronomico de Cordoba) helping observe good candidates. He wrote down some memories from the trip to share with us. I think you’ll find them as inspiring and poetic as I did!
You can read about his experiences below, and even watch some short videos he took at the observatory:
Dentro de la Cúpula de CASLEO / Inside the CASLEO Dome
Afuera del Observatorio de CASLEO / Outside the CASLEO Observatory
Centro de Control de CASLEO / CASLEO Control Room
My Travel to CASLEO
by Hugo Durantini Luca
Reaching CASLEO requires a little patience. Even if you were to reach the city of San Juan by plane, you still have to endure traveling approximately 5 and half hours more to reach the observatory. The landscape is very interesting, especially if it’s your first time in the region, with the mountains presenting multiple colors and the sight of the Andes while you gradually approach to its foot.
After getting off the bus to San Juan, I was greeted almost immediately by Luciano García and we started our travel to the observatory after picking up some staff that also was going to the complex to start their work shifts. I don’t know if was because I just had made a 8 and a half hour trip, or if it was because of the landscape and the excitement, but the travel of almost 5 hours from the city to the complex felt pretty quick and we reached the place just in time for lunch.
After that, we checked in to our rooms and I was able to do a small tour to see with my own eyes the telescope along with the instrument what we were about to use: the REOSC Spectrograph. The sensation of seeing all the instruments and the control room in person was almost like going back to my childhood, even though I had previously checked all available information on the internet.
I must say that the first night was a bit hard, not only because at first we lost the first hour or so thanks to the clouds, but also because after we started the work and learned the basics of what we were about to do, fighting the urge to sleep and our biologic clocks was something that required a little technique.
To input the coordinates of the star that we wanted to observe and then to give the order to REOSC to initiate the exposure was a great privilege. I was assigned this task for the whole run. But even repeating this process over and over didn’t diminish the excitement of directly generating new data for our research.
Another amazing experience was to go outside of the telescope and be able to contemplate the Milky Way in a clean and clear sky. I saw details that are impossible to see from the city due to light pollution, treasures that the people that have never left the city or studied astronomy don’t know they are losing.
It was really fun and illuminating for me to participate in all the nights, to watch how the instrument behaved according to the magnitude of the stars. I learned how to add more or less time to obtain a good reading and how in some cases, there is no trick aside from perseverance. All this experience brought me closer to a better understanding of the work of an astronomer beyond all the commons fantasies that one can hold.
The second day was much easier than the first, at least in the sleep management department. Even if your body is still complaining about some things; one can feel how it adapts to the day to night change. The second night was when we ended doing most of our brightest stars because even if they can be a little difficult, there is less exposure time required. I also had the chance, thanks Luciano, to explore and visit a few sites close to the complex. The landscape and autumn colors, views almost like paintings, and the lonely roads added to the unforgettableness of the trip.
All the CASLEO staff that we had the opportunity to interact with were extremely kind and it was like being at home almost all the time. Even though we were just there four days, by the end, I felt like I had been there for a long time. The return trip was somewhat bittersweet. You miss home, but at the same time this experience has reinforced to the max my love for science and especially astronomy.
To pass days far away and entire nights collecting information can look like something disconnected from reality, but it’s actually the opposite. To gain consciousness of the scale of our Galaxy and our place in the universe is an experience that makes you humble, and being able to participate in building our knowledge and understanding of the universe fills me with a sense of obligation to others here in our own world.