One Hundred Thirty-One Brown Dwarfs

Hi Everyone!

We’ve been so busy following up your discoveries that we have fallen behind in our blogging.  Here’s a long overdue update on the project.

First some numbers.  You have now performed more than 6 million classifications!  That’s right; please ignore the “Backyard Worlds: Planet 9 Statistics” link on the Backyard Worlds main page.  That only shows you a few months’ worth of classifications. The total number of classifications since we launched is much bigger.

You have submitted 32,810 sources via the Think-You’ve-Got-One form(s).  Adam Schneider has done one pass through this list to confirm these sources, check for objects that have not been previously published, and check for duplicates.  We also have a group of superusers separately working their way through this list to look for new solar system planets (e.g. planet nine). We haven’t discovered a planet yet, but we are getting familiar with the variety of false positives that we need to understand, and there is still at least 2/3 of the sky left to search in this mode.

These submissions boil down to 1305 objects that are on our follow-up list: mostly brown dwarf candidates.  These objects feed what has become a vast follow-up program with telescopes in the north (Keck, Apache Point Observatory, IRTF, Mont Megantic), the south (Magellan, Gemini, SOAR) and in space (Hubble and Spitzer). Of these candidates, we have confirmed and classified 70 T dwarfs and 61 L dwarfs by taking their spectra and comparing them against spectra of known brown dwarfs, for a total of 131 spectroscopically confirmed brown dwarf discoveries.   And that doesn’t include our most recent Magellan run, which took place over July 4 weekend.

The T dwarfs and L dwarfs teach us about brown dwarf demographics and formation processes when they are nearby, and indeed 55 of our brown dwarfs and brown dwarf candidates are within a distance of 20 parsecs from the Sun.  This group also contains exotic objects such as co-movers, and color outliers, which tell us about brown dwarf ages—and thereby brown dwarf masses.  We are working on writing a paper about a very rare co-mover submitted by Sam Goodman: a pair of brown dwarfs that appear to orbit one another.

We’ve also been focusing lately on the reddest and coldest, the Y dwarfs.   These are the objects that overlap with exoplanets in terms of temperature and mass; only 27 examples are currently in the published literature. We can spot many of our Y dwarf candidates using the WISE images; we consider those with W1–W2 colors (or color limits) greater than 2.7 magnitudes to be Y candidates. So far, roughly 100 of our objects meet this criterion to be considered Y dwarf candidates. 

YDwarfCandidates
How do you tell if you have a Y dwarf on your hands?  Well, Y dwarfs are at least 10 times brighter in the WISE W2 band than in the W1 band. This plot shows the ratio of the flux in the WISE 1 band to that in the WISE 2 band. If you think in magnitudes like an astronomer, this  ratio works out to be a difference, since magnitudes are logarithms. That’s the y axis of this diagram.  The yellow dots show known Y dwarfs; the grey dots show our candidates, which all sit above a W1-W2 “color” of about 2.5.

These Y dwarf candidates generally need more photometry (measurements of their brightness) at various wavelengths to constrain their temperatures and solidify our interpretation of them as Y dwarfs.  In our first round of Spitzer photometry, we observed 65 Y candidates and we easily confirmed 3 of these as Y dwarfs.  An additional 15-20 are either Y0 or late T based on the Spitzer data; we’ll need to take spectra to sort it out.  We’ve since won a second round of time—13 hours—on the Spitzer space telescope to observe 33 more of these sources, and we’ve also been observing them at shorter wavelengths with the CPAPIR camera on Mont Mégantic.  These discoveries will all be part of a paper probably within the next year.

We’ve started a new astrometry project!   “Astrometry” just means measuring the positions of targets on the sky, i.e. their Right Ascension and declination and how they change over time. Astrometry of nearby objects like brown dwarfs is important because a series of accurate position measurements reveals the object’s distance (though “parallax”) and its dynamical relationship to other objects in the Galaxy (via “proper motion”).   To do this project, we’ve teamed up with Davy Kirkpatrick and the “CATWISE” team, who have also been scouring the WISE images for brown dwarfs.  We’ll be using the Spitzer Space Telescope, and prioritizing the coldest objects.

And (surprise!) it turns out that BackyardWorlds.org is good for finding interesting white dwarfs.  You probably saw our paper on the coldest and oldest white dwarf with a debris disk.  We have since taken a spectrum of a second white dwarf, also discovered by Melina Thévenot, using the Apache Point Observatory. The spectrum implies that this white dwarf probably also has an infrared excess.  Stay tuned for more details!

Keep up the good work!!    You’ve already taken this project in directions we never anticipated and made more discoveries than we imagined.  And did I mention that the WISE mission that provides all the images we look at is STILL TAKING DATA?

Congratulations to Vinod Thakur, Peter Jalowiczor, Tadeas Cernohous, Hugo Durantini Luca, Giovanni Colombo, Sam Deen, Andres Stenner, Melina Thévenot, Les Hamlet, Nikolaj Stevnbak Andersen, Sam Goodman, Dan Caselden, Jörg Schümann, Guillaume Colin, Paul Beaulieu, Karl Selg-Mann, Tamara Stajic, Austin Rothermich, Billy Pendrill, Ken Hinckley, Christopher Tanner, Rosa Castro and Bob Fletcher for finding confirmed L and T dwarfs! Congrats to Guillaume Colin, Sam Goodman, Dan Caselden, Billy Pendrill, Nikolaj Stevnbak Andersen, Les Hamlet, Jörg Schümann, Ken Hinckley, Melina Thevenot, Austin Rothermich, Karl Selg-Mann, and Christopher Tanner for finding Y dwarf candidates…stay tuned!

Thank you for all your hard work so far…and good luck!  And if you are a Facebook person, there’s a new Facebook Group for NASA citizen science that might interest you.  Come join the Sciencing with NASA group and help teach new people about Backyard Worlds: Planet 9!

Best,

Marc Kuchner and the Backyard Worlds: Planet 9 Science Team.

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The Crystal Ball White Dwarf

Today is a big day at Backyard Worlds: Planet 9!  We’re celebrating our 2nd anniversary, our reboot, and announcing our second paper, published in the Astrophysical Journal letters.   (You can read it here for free.) It’s about a unique white dwarf that’s an analog for the solar system three billion years from now; the oldest white dwarf known to host a dusty disk, the likely remains of a planetary system.   Check out this guest blog post by our own Melina Thévenot, who explains how she discovered this record-breaking object, which provides such a chilling glimpse into the future.

Melina Thevenot
Melina Thévenot, the citizen scientist at Backyard Worlds: Planet 9 who discovered the infrared excess from white dwarf LSPM J0207+3331.

Hi everyone. I am Melina Thévenot, a volunteer of the Backyard Worlds: Planet 9 project from Germany. Here I want to tell you a bit about how I discovered an unusual white dwarf and how the researchers uncovered that it is not only unusual, but also cool.

How did I discover the white dwarf LSPM J0207+3331?

As a volunteer of the Backyard Worlds: planet 9 project, I spent a lot of time searching for brown dwarfs. The Gaia Data release 2 was my favorite survey for the search of brown dwarfs. I uncovered probably several hundred new brown dwarf candidates that move in wiseview with the help of three other volunteers: Katharina Doll, Hugo Durantini Luca and Peter Jalowiczor. 

While improving my search I noticed something about brown dwarfs in the Gaia catalog: some good sources don’t have color information in Gaia DR2. This is a problem, because I relied on a color-cut. To check if I missed any good T-dwarf, I decided to use Allwise to find sources with high infrared excess and the high parallax measurement in Gaia DR2. In the resulting list I could find fake sources that did not move in wiseview, T-dwarfs (distance 5 to 10 parsec) and one source that does not belong in this list.

I don’t remember where I saved the original list, but it probably looked like this:

list

The object in the red circle has a distance of 44 parsec. Gaia should not detect a T-dwarf at this distance.

Is it another fake source? I could have ignored it. I am glad I checked the movement.

Wiseview link: http://byw.tools/wiseview#ra=31.891736099354006&dec=33.52476141170008&size=60&band=3&speed=295&trimbright=98.88&linear=0.845&color=gray&mode=percent&coadd_mode=pre-post&zoom=17&border=0

As you can see: Compared to the background objects it is moving and in PanSTARRS you can see a blue source.

This source is LSPM J0207+3331. At this time I still had no clue what it could be. I did need some days to think about it. After checking the position in a HR-diagram I knew that it was a white dwarf with large infrared excess (Allwise w1-w2≃1). I guessed that this excess comes from a circumstellar disk. Time to loop in some other volunteers, who are advanced users of Disk Detective. Katharina Doll told me that the source looks good and she confirmed that it was possible for a white dwarf to have a disk, something I did not know until she told me. We decided to contact Marc Kuchner and soon John Debes joined the discussion.

Observation with Keck

John Debes told us this white dwarf is cold, in fact it was 1000 Kelvin cooler than any known white dwarf with an infrared excess. So the researchers decided to observe it with APO. But the dome was closed because of bad weather. Soon the white dwarf was observed with Keck! The telescope with the largest mirror on this planet!

I watched closely how things developed. I made a timeline:

Date
2018-10-17 Discovery of LSPM J0207+3331 (still no clue what it could be)
2018-10-19 Sending LSPM J0207+3331 to the researchers
2018-10-20 Bad weather at APO
2018-10-27 LSPM J0207+3331 is being observed with Keck (Adam Burgasser observed it for us – THANK YOU!!)
2018-12-01 Paper is submitted to ApJ Letters
2019-02-02 Paper is accepted

 

A 3 Gyr White Dwarf with Warm Dust

Let’s talk about the paper. Des Pudels Kern. (German Saying, “The core of the poodle” meaning the main point)

What is a white dwarf? Our sun will develop into a red giant billion of years in the future. The red giant will lose the outer layers in a Planetary Nebula. The core that is left is a hot white dwarf and it will gradually cool and become fainter.

The process is very violent and “loosing the outer layers” is nothing else than burning the orbiting planets in strong solar winds. But not everything will perish. White dwarfs have a leftover stellar system with asteroids, comets and planets. If an asteroid or comet comes too close to the white dwarf, it can be torn apart by the tidal forces caused by the gravity of the white dwarf and the material settles down in a disk around the white dwarf.

figure 1 of the paper

In figure 1 of the paper you can see a blue line. This is how the Spectral Energy Distribution (SED) of the white dwarf should look like without a disk. The gray lines are the spectra from Keck NIRES and the black squares are the photometry from different surveys. You can see how the spectra and the photometry are somehow taking off to the right side. This blog post from Disk Detective explains what a SED is and how a SED looks like for star+disk. It might help you interpret this figure. 

Models that try to describe disks around white dwarfs predict that young white dwarfs are more likely to develop a disk. It is therefore surprising that a 3 Gigayear (3 Billion years old) white dwarf has a disk. Is LSPM J0207+3331 special or are the models about the formation of disks around white dwarfs not accurate enough? Future searches for similar white dwarfs might shine light on this mystery.

But this is not where the story of this white dwarf ends. The disk around LSPM J0207+3331 is not a simple disk, but it consists of two components: an outer colder ring with a temperature of 480 Kelvin and an inner ring with a temperature between 550-1400 Kelvin. The white dwarf has an temperature of 6120 Kelvin and a mass of 0.69 solar masses. The outer ring might have formed from a small asteroid that was disrupted by the tidal forces in the recent history of the system. This is the first time such a system was observed.

In the future, researchers will observe this white dwarf again and obtain more data, which might tell more about this system. An optical spectrum, for example, might tell us if any material from the disk is falling into the atmosphere of the white dwarf, and what that material is made of.

I am very proud to be part of this discovery and hope you enjoyed reading this blog post.

42 Confirmed Brown Dwarfs and Counting

Hey everybody!   Thanks to your efforts, we’re now up to 879 brown dwarf candidates.  Wow.  We’ve been following up your discoveries as fast as we can, getting spectra to determine their spectral types and distances, test for membership in moving groups, and look for unusual features. For the coolest objects, we’ve also been working on taking new images.  Here’s a little update on all this follow-up work.

First of all, we have a big stack of new spectra. Jackie Faherty confirmed 17 of our brown dwarf candidates with the ARCoIRIS spectrograph on the Blanco 4m telescope in Chile, and Jonathan Gagné, Jackie Faherty and Michaela Allen observed another batch of 8 targets with the SpeX spectrograph on NASA’s Infrared Telescope Facility (IRTF).  Of those 8 we observed with IRTF, 6 are brown dwarfs. The other two are late Ms; one has a co-mover (spotted by Tadeas Cernohous) and the other has an unusual J band flux that threw off our initial spectral type estimate.

Picture of Michaela Allen’s desk at NASA Goddard Space Flight Center while she was observing our brown dwarf candidates remotely with the IRTF telescope.

That’s right, Michaela, our TALK moderator, is now participating in observing runs! Michaela is spending her summer as a NASA intern here at Goddard Space Flight Center in exotic Greenbelt, Maryland.  She’s working on our Gemini data, and looking through the long long list of moving objects you have found that did not appear, at first glance, to be brown dwarfs.  You can follow her on Twitter @sasstronaut42 to find out more about how her summer is going, and you’ll hear more about her work later on.

Thanks to Jackie, Jonathan and Michaela’s hard work, I can now say that we have confirmed a total of 42 brown dwarfs.  These confirmed objects include 10 L dwarfs and 32 T dwarfs.  Of these, fourteen are closer than 20 parsecs, and four are closer than 15 parsecs. Congrats to Nikolaj Stevnbak Andersen, Dan Caselden, Guillaume Colin, Sam Goodman,  and Melina Thevenot, whose TYGO form submissions were observed with ARCOIRIS and confirmed to be brown dwarfs!   And congrats to Nikolaj Stevnbak Andersen, Dan Caselden, Tadeas Cernohous and Guillaume Colin, whose TYGO submissions were observed with IRTF and confirmed to brown dwarfs!  I believe those are Nikolaj’s, Tadeas’s and Melina’s first brown dwarf discoveries.

The “seeing” at IRTF was only about 0.8 arcseconds, which is poor for that site, and there were thin cirrus clouds. So we were only able to take decent spectra of objects brighter than about 16th magnitude in J band.  So this run was a bit disappointing.  But just today we learned that we won four more nights on IRTF this fall! 

In fact, here’s a summary of our follow-up program so far—where we’ve been an where we’re going.    The “R” value is the spectral resolution of the spectrograph we’re using. R = the central wavelength of the spectrum divided by the smallest difference in wavelengths the spectrograph can distinguish.   So larger R means finer resolution.  But finer resolution comes at a cost; you need to collect more light to begin with if you’re going to spread it out more by wavelength.

Table 1. Status of our follow-up observing program.
Gemini-North/NIRI Fast Turnaround J/K band imaging 9.2 hours, 16 targets Images of 16 targets obtained
Magellan/FIRE Prism R~450 17 targets Spectra of 17 targets obtained
Apache Point Observatory (APO)/Triplespec R~3500 1 night Bad weather, spectra of 2 targets obtained
Blanco 4 m/ARCoIRIS R~3500 2 nights Spectra of 17 BDs obtained (see above!)
Magellan/FIRE Echelle R~7000 1 target Spectrum of 1 target obtained 2/3/18, RV measured
Infrared Telescope Facility (IRTF)/SpeX R~150 2 nights, 20 targets 1 night weathered out, spectra of 8 targets obtained during second night (see above!)
HST/WFC3 F125W/F105W imaging 5 orbits, 5 targets Awarded 5 orbits
Mont Mégantic/CPAPIR J-band imaging 8.5 hours, 60 targets

 

Awarded time to observe 60 targets. Images of 12 obtained May 2018
Magellan/FIRE Prism

 

R~450 1 night, 20 targets Awarded 1 night in 2018B
Keck/NIRES

 

R~2700

 

1.5 nights, 10 targets Awarded 1.5 nights in 2018B
Spitzer

 

3.6 and 4.5 micron imaging 26.8 hours, 65 targets Awarded 26.8 hours
Infrared Telescope Facility (IRTF)/SpeX R~150 4 nights, 40 targets Awarded 4 nights in 2018B
Gemini-South/Flamingos 2 R~600 13.7 hours, 27 targets Proposal Submitted, Pending
Magellan/FourStar J-band imaging 1 night, 8 targets Proposal Submitted, Pending
Gemini-North/GNIRS R~11,800 9.4 hours, 5 targets Proposal Submitted, Pending

Keep up the amazing work!  And stay tuned for more cool discoveries!!

Marc

 

We Love You! And Happy Anniversary!

Team,

This Thursday, February 15, marks the one year anniversary of the launch of Backyard Worlds: Planet 9.  What a year it has been!  Let me attempt to sum up where we are, scientifically. It’s hard not to stop and gasp in awe at all you’ve accomplished.

AnniversaryImageBYP9For starters, you have performed 4.775 million classifications of images from NASA’s WISE telescope. (The backyardworlds.org site only shows classification numbers for the current batch of subjects–you have done about 322,000 classifications of those.) You have also submitted more than 20,000 objects on the Think-You’ve-Got-One form.  All this hard work has yielded 432 objects of interest for our follow up campaign, mostly newly discovered brown dwarf candidates.

Because of these objects–and your interest in this work–seem so promising, this fall we were awarded a grant from NASA ‘s Astrophysics Data Analysis Program that will keep us working on the project with you into the year 2020.

Mauna Kea Observatory
In two weeks, we’re headed to NASA’s Infrared Telescope Facility to follow up more brown dwarf candidates.

Soon afterward, we were awarded five nights of telescope time on NASA’s Infrared Telescope Facility, Apache Point Observatory, and the Blanco 4-meter.  That should be enough to follow up about 100 of your discoveries.  We have only had a chance to use one of these nights so far–and it was cloudy!  Yet, thanks to donations of observing time from other projects, we have managed to collect spectra for 20 brown dwarf candidates (Thank you, Jonathan Gagne and Katelyn Allers!).  These spectra show that we have discovered 17 new brown dwarfs.  Their spectral types and distances, in units of parsecs (pc) are all listed at the bottom of this post.
Only three of the objects we have followed up so far turned out not to be brown dwarfs.  Two of these objects (first reported by Sam Goodman, Dan Caselden, and Guillaume Colin) are newly discovered cool subdwarfs, a rare class of metal-poor stars. The one other is an unknown object that’s not really moving, though it might be time variable. So I’d say our batting average is 95%  (I supposed that would be .950 if it were an actual batting average).Congratulations to the citizen scientists who spotted these 17 brown dwarfs!  They are: Dan Caselden, Rosa Castro, Guillaume Colin, Sam Deen, Sam Goodman, Bob Fletcher, Les Hamlet, Jörg Schümann, Khasan Mokaev, and Tamara Stajic.

As you can see from the list, we’re getting close to our dream of finding Y dwarfs. The newest batch of follow-up spectra contained a T9, our coldest brown dwarf find yet, just one subclass warmer than Y0. And we have 38 Y dwarf candidates that we have yet to get spectra of!  These take some extra work to follow-up because they are so faint, but we will be working our way down that list over the next year. Note that there are only about 25 known Y dwarfs so far, found by other surveys.  So even if only half of our candidates pan out, we will have made a big difference to the field.

We haven’t yet found any brown dwarfs closer than Proxima Centauri (1.3) parsecs or Luhman 16 (2.0 parsecs).  But they might well be out there, waiting for us.  Three of our brown dwarf discoveries are closer than 20 parsecs, so they will have an impact on statistical studies of brown dwarf populations.  Our list of candidates contains 25 more that are closer than 20 parsecs, including five closer than 15 parsecs.

GUPscb GMOSiz WIRCamJ noinset.jpg
GU Psc b, a brown dwarf/rogue planet with the mass of roughly 11 Jupiter masses (credit: NASA, Marie-Eve Naud et al, Gemini Observatory)

We may have already found some young moving group members–brown dwarfs that are young, with relatively well-constrained ages, that could potentially be rogue planets.  We have taken spectra now of two objects that seemed likely to be moving group members.  No luck yet, but one object was a very near miss.  Our initial estimates showed a > 90% probability for membership in the AB Doradus moving group. Then, when Jonathan Gagne observed it with the FIRE spectrograph on Magellan, he saw a spectrum that closely resembles that of GU Psc b, a planetary-mass T dwarf in that AB Doradus.  So the next night, Jonathan took an might higher resolution spectrum of this object to measure its radial velocity, i.e., how fast it is moving in the direction along our line of sight.  Alas, it turned out that the radial velocity was is not consistent with the AB Doradus moving group.  But among our candidates are 20 more possible moving group members we haven’t yet been able to check.

Most stars in the galaxy come in multiple systems–and brown dwarfs often have companions as well.  So we’ve been searching the literature, with help from our citizen scientists, to check for companions to our brown dwarf candidates.  We spotted five such likely pairs so far (though one of the companions orbits around a candidate subdwarf, not a brown dwarf).  Finding a companion like this around a brown often allows you to constrain the brown dwarf’s age and mass.  So we’ve prioritized these for our follow-up campaign. Congratulations to Tadeáš Cernohous, Jörg Schümann and Andy Fischer for finding the comovers.

When a brown dwarf has a near infrared “color” that is unusual for its type, it can inform us.  Brown dwarfs that are redder than average are often younger; blue brown dwarfs may be metal poor.  About 19 of our brown dwarf candidates have stood out to us as having unusual colors.  Plus, the spectra we have taken turned up two unusually red objects, and three more that seem notably blue.

Planet nine artistic plain.png
Artist’s concept of Planet Nine.

Planet Nine has so far remained elusive, as have Planet X and Tyche (we are sensitive to gas giants out to about 50,000 astronomical units from the Sun).  But we’ve acquired some useful search experience that we’re going to put to use when we reboot the site this spring (see below).  Also…nobody else has found any new planets beyond Neptune yet either.

So what’s next?  Well, we think there are probably roughly 800 more brown dwarfs to find in the data that’s online so far.   And clearly our follow-up campaign is just beginning.

But that’s not all.  As we’ve mentioned, WISE has continued to take new data since the project launched, and already 2 more years of images have been recorded, beyond what’s online at backyardworlds.org!  We’re working on adding those to the flipbooks, to help you disentangle dipoles from stars and movers from cosmic rays.  They should make our search for new planets in the solar system much easier too, allowing us to process the data in a way that avoids the mess of different hopping and jumping patterns.  In the meantime, we’re working on more telescope proposals to follow-up the objects you discovered already.  So keep searching, and stay tuned for a reboot of the whole site in the next few months!  And thank you for a thrilling, inspiring first year.

Happy Valentine’s Day!

With love from Marc Kuchner and the Backyard Worlds: Planet 9 Science Team

T3 16.8 pc
T9 17.1 pc
T3.5 17.6 pc
T8 19.0 pc
T7 21.6 pc
T6.5 21.7 pc
T8 22.5 pc
T5 25.0 pc
T4 29.1 pc
T6 30.2 pc
T5.5 33.7 pc
L9 34.0 pc
L9.5 37.0 pc
T0 40.6 pc
T5 45.7 pc
L2 48.4 pc
L5 64.1 pc

This table lists our brown dwarf discoveries so far.

Snow White and the Seven New Confirmed Brown Dwarfs

It is now winter here in the northern hemisphere, and we’re expecting snow on Friday in Washington, DC.  But fear of snow doesn’t stop us from going observing…and observing we have been!   Jonathan Gagne returned from his last trip to the telescope with spectra of nine of our brown dwarf candidates—and seven of them are now bonafide brown dwarfs.  That brings the total number of brown dwarfs discovered by the project to eight, when you add in our first confirmed brown dwarf from earlier this year.  Thanks to Ellie and Eileen for helping with the observations, which they performed using the Folded-port InfraRed Echellette spectrometer prism on the Magellan telescope!  And a big congratulations to Sam Goodman, Les Hamlet, Guillaume Colin and Dan Caselden for submitting these candidates that are now confirmed!

The spectral types of the new brown dwarfs are: T0,T2.8, T5, T6, T6.5, and two T8s.  (WISEA 1101+5400, which we discovered earlier, is a T5.5).  Curious how we tell the spectral type from the spectrum?  We make plots like this one, below.  The black curve is one of the new spectra from Magellan, and the colored lines are other brown dwarfs with known spectral types, ranging from  T4 to T8.  Which one do you think matches best?

BYW_J004143.14-401924.3_tc_1 cropped

Yes, it’s a T8, and it’s currently the coolest brown dwarf we have found with Backyard Worlds: Planet 9, with a temperature of around 750 Kelvin (about 890 degrees Farenheit). The other two objects turned out to be cool subdwarfs, a kind of star that is poor in iron and other metals, suggesting it formed before the most recent generations of stars enriched the galaxy with these metals.  Those are poorly understood and interesting in their own right.

This new batch of confirmed brown dwarfs contained a few surprises for use. Three of them are strangely bright in the K band; we’re not sure how to interpret that yet.  Also, one of the brown dwarfs initially seemed like it might be a member of the AB Doradus moving group, based on its proper motion.  Its spectrum looks very similar to that of GU Psc b, a planetary-mass T dwarf in that AB moving group.  But Jonathan took a higher resolution spectrum of it, and the new spectrum showed that our brown dwarf wasn’t in the moving group after all.  Close call!

This new batch is still just the beginning for our follow-up program. First, we have  half a night on the TripleSpec instrument on the ARC 3.5 meter at the Apache Point Observatory on January 6, thanks to a proposal led by Katelyn Allers.  Then, we have two nights using the ARCoIRIS spectrograph on the Victor Blanco 4 meter telescope coming up on March 1+2 thanks to a proposal by Jackie Faherty. By the way, our sister citizen science project, Disk Detective, also won observing time on ARCoIRIS, for April 1+2 to follow up debris disk candidates, so we might do some trading between the two projects. And we have two more proposals for observing time still pending—and a list of now 337 brown dwarf candidates to follow up this winter and beyond.

So stay tuned—and have a super holiday, wherever your backyard may be!  (And yes indeed, “brown dwarfs” is not spelled like “dwarves”.)

–Marc

 

 

Our First Paper: the Discovery of Brown Dwarf WISEA 1101+5400

Our first paper was published in the Astrophysical Journal Letters, Volume 841, Number 2 on May 24.   Hooray!!   (It may be easier to read here.)

The paper announces the discovery of our first brown dwarf, shows a spectrum we took of the brown dwarf, and describes the Backyard Worlds: Planet 9 project. There’s a press release from the American Museum of Natural History, a nice NPR story about it featuring Rosa Castro, and several other news stories.

Of course, this paper is already out-of-date.  In the time it took to write the paper, you’ve discovered at least twelve more good brown dwarf candidates.  And we used those discoveries to make an even better estimate of the sensitivity of our search than the one that appears in the paper. But let’s talk more about the paper and our first discovery, a source called WISEA 1101+5400 which we now know is a real brown dwarf, spectral type T5.5.   Here is WISEA 1101+5400’s flipbook.

You may recall that shortly after launch, we were all excited about a faint dipole/mover, which Bob Fletcher had flagged on talk and Tamara Stajic reported on the Think-You’ve-Got-One form.  That’s WISEA 1101+5400.  A few weeks later, science team member Jackie Faherty nabbed a spectrum of it using NASA’s Infrared Telescope Facility.  Here’s a nice plot of the spectrum, created by science team member Joe Filippazzo comparing the our object’s spectrum (black) to the spectrum of another T5.5 brown dwarf (red).  It’s a great match! The extra wiggles in our spectrum are simply noise.

Figure3.cropped

The quality of the match demonstrates that WISEA 1101+5400 is indeed a brown dwarf, and tells us that its temperature is in the range 900-1500 Kelvin (1200 – 2200 degrees Fahrenheit).  We can tell the temperature range by looking at what molecules show up in the spectrum.  The spectrum shows features associated with water, methane, iron hydride, potassium, and molecular hydrogen, labelled above.  If the brown dwarf were hotter or cooler, the relative sizes of the dips in the spectrum from each molecule would be different.

Knowing the brown dwarf’s spectral type also teaches us roughly how bright it is, intrinsically.  And since we know that the brightness of an astronomical object falls off as the inverse distance to it, squared, we can compare our images of WISEA 1101+5400 to those of other brown dwarfs to estimate its distance:  roughly 34 parsecs or about 111 light years.  For comparison, the closest known brown dwarf is the binary Luhman 16AB at 6.59 light years.

So what does this discovery mean for our understanding of brown dwarfs?  Well, there are already a few hundred T dwarfs known–and this new one turns out to be somewhat run-of-the mill.  It’s not super cool, and it’s not in a moving group, for example.  Its infrared colors are close to the average colors for brown dwarfs with this spectral type.  So we haven’t shattered any paradigms or broken any records with this object just yet.

But the discovery is a dramatic proof-of-concept.  Just the fact that we found it, only six days after launch, shows that we’re on the right track toward lots more discoveries.  Also, Zooniverse founder Chris Lintott tells me that our paper now holds the record for fastest publication from a Zooniverse project.   How cool is that?

This is a moment to celebrate.  Congratulations to us!!   Let’s make some more discoveries and write some more papers together.

Marc

We’re up to twelve brown dwarf candidates now, plus one real verified brown dwarf!

Hey everyone!  It’s proposal season here at NASA.  Every spring, NASA offers astronomers opportunities to apply for grant funding to do their research, and we’ve been busy taking advantage of that, writing proposals.

In the meantime, you’ve been hard at work, discovering stuff.  We’re up to twelve brown dwarf candidates now plus one real verified brown dwarf.  Holy smoke!  We can estimate their spectral types based on their relative flux in the WISE 1 and WISE 2 bands (3.5 and 4.6 microns), and it looks like we have 7 new candidate L dwarfs and five new candidate T dwarfs. We’re going to try to get spectra for as many of these as we can.

In the meantime, did I mention we’ve been writing proposals? Well in a proposal, you try to make predictions about what you’re going to be able to learn or discover. You also try to show how your work compares to other work in the field. So we started by taking all thirteen objects and putting them on a plot, showing their proper motions and magnitudes in the WISE 2  (W2) band. Those are the red stars on the plot below, which was made by science team member Jonathan Gagne.

PM_relW2_BYW

Then, as you can see, we plotted lots of other interesting stuff on here.   For starters, we did our best to add all the brown dwarfs that were previously known.  The little blue dots show every other brown dwarf in this database, which is every brown dwarf we could find in the literature.  You can see right away that our discoveries, the red stars, fall towards the bottom of the cloud of blue dots made by the other discoveries.  So our discoveries are fainter than average.

Next, we plotted some lines indicating the detection limits of some other recent surveys, by Adam Schneider et al and by Davy Kirkpatrick et al. (That’s Adam Schneider from our science team.) Those are the two biggest brown dwarfs searches made using WISE before we began ours. The survey done by Schneider et al. only detected brown dwarfs that fall above the orange dashed line. The survey done by Kirkpatrick et al only detected brown dwarfs that fall above the black dash-dot line.  Those lines slant upward to the right because the WISE images they used were not divided into as fine time slices as ours, so some faster moving objects got blurred out.

Finally, we added some green lines showing what we think are the limits of Backyard Worlds: Planet 9.  Now this part is harder since our survey, of course, isn’t complete yet. But we do know more or less what the shapes of the curves should be.  We know that they slant up on the left side of the plot because that’s where the motion is too slow and the images of a moving object start self-subtracting.  And we know that the objects we have already detected, the red stars, must lie above the lines.  So we draw the curves and shift them around till they hug the bottom of the cluster of red stars—and that’s our best guess at our detection limits.

Note that there are two green lines.  That’s because WISE spent more time making images at higher latitudes (here the symbol, beta, means latitude), so our survey is a bit more sensitive there.  There’s only one brown dwarf candidate that’s up at a high latitude where this effect comes into play, though—it’s the one sitting on the lower green line.

So there we have it: a prediction for the sensitivity of our search.  We will spot any brown dwarfs that fall above the green lines (pick the right one based on latitude).  And we are the first to make an all-sky survey of the region above the green lines and below the orange and black lines.  (A few brown dwarfs are already known in this region, but they came from surveys that only covered relatively small portions of the sky).

Now, remember that this plot uses logarithmic scales!  Each of the big ticks on the x axis is a factor of 10. Each magnitude  (the y axis) represents a factor of about 2.512. So that space on the plot could contain lots of brown dwarfs and other interesting objects, especially at high proper motions.  Good luck!

Marc Kuchner