Category: 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. 

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.

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?

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

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.

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

Good work, everybody!  You’ve submitted at least five good newly discovered candidate L dwarfs on the Think-You’ve-Got-One form.

Let’s talk about L dwarfs.  The L spectral type contains object with temperatures in the range of about 1400-2200 Kelvin.  It was first established in 1999 by Kirkpatrick et al.. They chose the letter “L” because it is next to “M” in the alphabet; M was the coolest spectral type in the literature at the time, and “N” was already taken to describe a class of evolved stars.  Amazingly, L dwarfs are about twice as common as main sequence stars. They are just harder to spot because they are so much more faint and red.

The first L dwarf discovered was GD 165B, found by Becklin & Zuckerman in 1988.  Curiously, 165B orbits another special kind of astronomical object: a white dwarf.  Nowadays, about 1300 L dwarfs are known.  So discovering one new one doesn’t usually merit a paper on its own.  But when we collect a batch of 50 or so we will definitely want to announce them with a publication, especially if one or more turn out to be in moving groups of young stars.   For example, here’s a recent paper by our own Adam Schneider announcing the discovery of 47 new L dwarfs, including seven that are in young moving groups.  Membership in a moving group is important because it establishes the objects age.

A good clue that you might have an L dwarf is if it doesn’t appear in the DSS images, only in 2MASS and WISE.   That’s because the DSS images were taken in visible wavelengths, and L dwarfs are too cool to shine in visible light, so they only show up in 2MASS and WISE bands, which are infrared.   (T and Y dwarfs may not even show up in the 2MASS images). Just remember, the rule of thumb is that if it’s not in SIMBAD, we want to see it on the Think-You-ve-Got-One form.  There are still interesting objects to find that are in DSS images.

Here’s one of the ones you found.  It’s a great test for the eyes!

It’s a faint bluish dipole. Can you spot it in this flipbook?  If not, scroll down to the answer key at the end of this article.

Here’s another one.  Remember, each one of these is a real new discovery–not a recovery of an object that was known before!

Can you see it there?  Here’s a third on to challenge yourself with.

OK here’s one more for you to test your skill on…

Ignore that giant blinking blue ghost in the middle!  They are tough to spot.  If you need help, here are the answers, below.  Congratulations to @Andy_Arg,  @karmeliet,  @graham_d,  @stevnbak, and @NibiruX for their exceptional eyesight And keep up the good work, everybody!!

Marc Kuchner

It’s only 23 days since launch.  And you’ve already discovered stuff!

We are still working on interpreting your classification clicks, and we probably will be for many months to come.  But people have already submitted more than 1100 interesting subjects using the Think-You’ve-Got-One form, which is a bit easier for us on the science team to use right away.  Among these objects, science team member Adam Schneider quickly spotted at least three interesting ones that we’ll want to include in an upcoming paper.  Let me tell you about them.

This one has got the science team all abuzz.

It’s either a fast dipole or a slow mover.  It mover about 1.25 pixels between the first and last epochs.  And it’s faint.  Faint is good!  That means it’s less likely to already have been discovered.

It’s a little red (maybe pink)  in color, meaning it’s significantly brighter in the WISE 2 band than in the WISE 1 band.  In  fact, if you look at how bright it is in the WISE 1 and WISE 2 bands, and the fact that it doesn’t appear in the 2MASS catalog at all,  you would infer that it is likely to be a kind of brown dwarf called a “T dwarf”.  If it is a T dwarf, it is about 30 parsecs (98 light years) away.   PLEASE FIND MORE OF THESE!!

We are trying right now to find someone who is at the right telescope at the right time to take a spectrum of it, which would confirm that it really is a T dwarf.  A colleague offered to observe it for us this week using NASA’s Infrared Telescope Facility. Alas, the weather was bad, and they didn’t even open the observatory dome. There are some opportunities coming up for us to get a spectrum from other telescopes in Hawaii.  We will keep you posted.

The next two new discoveries appear to be nearby M dwarfs, based on their WISE and 2MASS colors.  Nearby M dwarfs like these should make good targets for future exoplanet searches with the Transiting Exoplanet Survey Satellite (TESS)  and near infrared spectrographs like SPIREou, iLocator, and the Habitable Zone Planet Finder.

Take a peek at this subject.  At R.A. 11.8858634 degrees, declination -34.5458256 degrees (halfway up, near the left edge) is a blue-white dipole that appears to be a previously undiscovered M dwarf.  This flipbook is a bit tricky, since if you only looked at frame 1, for example, you might think it were covered with dipoles!  But when you play the animation, it becomes clear that most of those sources are ordinary artifacts.  Thanks to @raychieng for submitting it.

Finally, check out this subject.  Near the top, slightly left of center, at R.A. 217.8208564 degrees, declination 86.2991835 degrees (it’s almost at the north pole), is a moderately bright white dipole, which also appears to be a previously unreported M dwarf.   A VizieR search turns up a high-proper motion source at those coordinates in the PPMXL catalog and the URAT1 catalog, but without a spectral type. However, the photometry (i.e. how bright the star is, in magnitudes) across the suggests that this star is probably an M dwarf. Thanks to @stevnbak for submitting it.

How can you tell the spectral type of an object from its photometry? How can you recognize if your dipole/mover is an earth shattering new Y dwarf, a dazzling new T dwarf, a cool new M dwarf, or just a boring old early-type star? Stay tuned–we’ll talk about that in the next blog post.

Great work, everybody!   These discoveries are the proof of concept that we were hoping for.  And I’m sure there will be more to come.