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!
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!!
You may have heard of the spectral sequence, OBAFGKM. What may be less well-known is that new brown dwarf spectral classes have been added in the past few decades. Now the full spectral sequence is OBAFGKMLTY, where the O stars are the most luminous, most massive, and hottest stars, while Y dwarfs are the lowest-mass, faintest, and coldest objects.
While the temperature drops through the MLTY spectral sequence, the chemistry occurring in the atmospheres of theses objects changes dramatically. This can be seen most clearly when looking at the spectra of these objects. The figure below shows what happens to the infrared spectra of objects spanning the MLTY spectral classes. On this figure, we have also marked the positions of the WISE filters (W1 and W2). Note that how bright each spectral type is in each filter changes. This is seen most dramatically in the Y dwarf, where almost no flux is emitted in the W1 filter and a relatively large amount of flux is emitted at W2. This is because large amounts of methane are present in the atmospheres of T and Y dwarfs, and methane absorbs light in the wavelength range covered by W1, and there are no absorbing sources at W2.
We can look at how this difference between W1 and W2 changes as a function of spectral type by finding their “color”. In astronomy, “color” refers to the difference in brightness of an object at different wavelengths. So when we look at the W1-W2 color of objects, large values mean that an object is much brighter at W2 than W1. The next figure shows how WISE colors vary with spectral type. The coldest objects, T and Y dwarfs, have very distinct WISE colors.
In fact, the WISE filters were built specifically to exploit this color difference in cold brown dwarfs. Thus, the WISE images of a very cold brown dwarf will show nothing in W1 and a bright point source in W2 (third figure). This is why some objects look orange in our WISE images. The mover example in the field guide is a good example of an orange-looking brown dwarf.
The WISE colors of Planet 9 have been estimated to be very different than the colors of brown dwarfs. This is why the point source in the Planet 9 simulation in the field guide looks blue.
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.
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.
If you’ve found something interesting in a flipbook and you want to know more about it, SIMBAD is the right place to start. Just figure out the object’s coordinates using the numbers on the left and bottom of the images, type them in to SIMBAD’s coordinate query page. And poof, you’ll have all the answers! Right?
Well it’s not always that simple. So let’s talk for a bit about what SIMBAD can tell you–and what it can’t tell you–about your favorite patch of sky. I’m going to try to explain here, from start to finish, how to use SIMBAD to reliably determine if if you have rediscovered a well known object with high proper motion, or if you have possibly found a new high-proper motion object, worth submitting on the Think-You’ve -Got-One form.
First of all, SIMBAD is an acronym. It stands for Set of Identifications, Measurements, and Bibliography for Astronomical Data. SIMBAD began in 1972 as database of stars only (no galaxies, asteroids,planetary nebulae, clusters, novae, supernovae, etc.). But other objects have since been added in. SIMBAD now contains about 4.5 million stars and 3.5 million nonstellar objects.
Note that SIMBAD’s inventory is still heavily biased towards stars. Astronomers have cataloged far more galaxies than stars, for example, and a small fraction of these appear in SIMBAD. The NASA/IPAC Extragalactic Database (NED), for example, contains more than 214 million distinct sources. The VizieR database contains even more. But those extragalactic objects are not the high-proper-motion object we are seeking. And VizieR is much less user friendly than SIMBAD. So you’re better off sticking with SIMBAD to start.
When you do a SIMBAD search, start by typing in the coordindates of your object. No comma needed. SIMBAD offers you chance to select a coordinate system; go with the default, which is FK5. Leave the epoch and the equinox (i.e. for the coordinate system) both set to the year 2000. But where it says “define a radius”, change that number to 1 arc min. Objects further than one arcminute from your search location are probably too far away to be the object you are looking for.
After you hit return or click, “Submit Query,” SIMBAD will take you to one of three places: a page saying “No astronomical object found”,a table of objects it found, or a page that’s all about one specific object. Here’s what the “No astronomical object found” page looks like. If you end up here, be sure to flag your object with the #notinsimbad tag in TALK and submit your object using the Think-You’ve-Got-One form! If not, it’s still possible that your object is not in SIMBAD, and hence an interesting find. So read on!
If SIMBAD finds more than one object within the radius you chose, it will take you to a table listing all the objects, in order of how far away they are in angular separation from the coordinates you typed in. Here’s an example table.
The first place to look on the table is the column that says dist(asec). That’s because your fist task is to make sure the object SIMBAD is showing you corresponds to the object you care about! If the distance in this column is more than about 60 asec (arcseconds), i.e. one arcminute, from the coordinates you entered, it may be too far away on the sky to match the object you care about, unless you were sloppy when you looked up its coordinates. Note that the spacing between the tick marks on the left of the flipbooks is about 3 arcminutes (180 arcseconds). I bet you were much more accurate than that with your measurement.
Next, since Backyard Worlds: Planet 9 is all about finding objects with high proper motions, you’ll probably want to check the Otype column and the Proper motions column. The Otype column lists some codes that indicate what kind of object the object is, according to SIMBAD.
“PM*” means star with high proper motion. If you spot an object with this label, there’s a good chance you’re seeing it as a dipole or mover. But note that objects with high proper motion are also sometimes labeled “BD*”, “WD*”, “Fl*”, “LM*”, “SB*”, or even “*i*” or “Q?”! Here is a guide to all of SIMBAD’s object type codes, and here are a few more, defined.
Keep in mind that one star can sometimes have many known properties that would demand multiple classifications in SIMBAD’s system. For example, you could have a low mass star that is also a flare stare and is in a spectroscopic binary system with a white dwarf. That object should probably be labeled something like “LM*, Fl*,SB*, WD*”. But SIMBAD only gives it one of those labels. Bummer. So check that column for objects called “PM*”. But just because you don’t see “PM*” on the table you get, doesn’t mean SIMBAD hasn’t located the dipole or mover you’re looking at. It might just have given it a different Otype label.
As a next step, you’ll want to look at the column labeled “Proper Motion”. This column is really sort of two columns smushed into one; it lists a pair of numbers. The first number is its motion west to east due to its proper motion. The second number is its motion from south to north) due to its proper motion. That first number is motion in the direction of increasing Right Ascension, so it’s sometimes called the Right Ascension component. The second number is motion in the direction of increasing declination, so it’s sometimes called the declination component. Just note that there are some additional weird subtleties about actually figuring out how the Right Ascension of a star actually varies in time because of the nature of the equatorial coordinate system.
Proper motion, as you may recall, is how an object moves on the sky as a result of having a different orbit around the Galactic center than the Sun does. Objects near the Sun (Planet nine is an extreme example) can also shift around on the sky due to parallax, i.e. the effect of the Earth’s orbit. Parallactic motion alone would make a star move round and round in an ellipse. Proper motion goes in a straight line. Together, parallactic motion and proper motion combine to make stars move in a squiggly path like this (below). Experts in astrometry (the craft of measuring stellar positions) look at plots like this one and disentangle the two kinds of motion from it.
Now, what really matters to us is figuring out if the object might be a dipole or mover that we could spot. And that depends on a different number than what’s listed in SIMBAD: the total proper motion. To get the total proper motion, you need to add together the two proper motion numbers you read in SIMBAD in a kind of funny way: you square them both, sum the squares and take the square root. Anyway, if a object’s total proper motion is bigger than about 100 milliarcseconds per year, it will probably show up as a dipole. If it’s bigger than about 1000 milliarcseconds per year, it will probably show up as a mover. If you don’t see any objects with total proper motion greater than 100 milliarcseconds per year on this table, flag your object as #notinsimbad and submit your object on the Think-You’ve -Got-One form!
A third possibility is that SIMBAD will find only one single object within the search radius you entered. In that case, SIMBAD will jump right to a page on that specific object, like the one below for the star Vega (its proper motion and parallactic motion are shown above). You’ll notice that this page also lists the object’s proper motion, if it is known. I’ve circled it in red on the screen shot below. The units here are milliarcseconds per year again, which is what we want.
Let’s pretend your SIMBAD search pulled up this page. I’m super lazy so I’m just going to do it using Google as a calculator. Type sqrt(200.94^2 +286.23^2) into a Google search bar and you get 349.720597763. That’s clearly higher than 100 but less than 1000. So this star should show up as a dipole. Too bad. It’s already a well known high-proper-motion object. You can flag it with the #known tag on talk. But don’t submit it to the Think-You’ve-Got-One form.
Of course, sometimes, SIMBAD only finds one object, and it takes you directly that object’s page, and the object is clearly not the one you’re seeing in the flipbook! What if SIMBAD sends you directly to a page like the one below, for an active galaxy called M 81? There’s no proper motion listed because object outside the Milky Way don’t have proper motions.
If this happens, it means SIMBAD couldn’t find any high-proper-motion objects near the one you found. So go ahead and flag your object as #notinsimbad and submit your object on the Think-You’ve -Got-One form.
To summarize: SIMBAD can send you to one of three different pages. But–no matter where it sends you–if you can’t find an object on that page with TOTAL proper motion > 100 milliarcseconds per year, then you have an object worth flagging with #notinsimbad and submitting on the Think-You’ve-Got-One form.
One last comment. Good scientists take lots of notes. So I strongly encourage you to write notes in a subject’s TALK page about what you learned from SIMBAD. If you did find a high-proper-motion object in SIMBAD within a 1 arcsec search radius, type in some information about it, like its name, proper motion, otype, and distance to the coordiantes you used. That way people can check your work, and maybe they won’t need to repeat your search. We can also use your notes to develop a better understanding for our ability to recover known objects at Backyard Worlds: Planet 9. That’s an important way to measure the power of our search.
OK I think that’s enough for now. There’s lots more you can learn from SIMBAD of course. But maybe we’ll come back to that another day.
You probably didn’t realize it, but when you started classifying on BackyardWorlds.org you were actually helping us search the nearby solar neighborhood for cold hidden worlds called brown dwarfs. You might be asking yourself “Brown what”? And I’m here to answer that! Lets start from the beginning. Here is a cartoon version of star formation (on the left) and brown dwarf formation (on the right). They form the same way! The ingredients are a cloud of Hydrogen and Helium that collapses, fragments and then ignites. Now the difference is that the star can ignite nuclear fusion. The brown dwarf isn’t massive enough to get the core hot enough for that to happen. So instead of having a nuclear engine that sustains its brightness for millions or billions of years like stars do, brown dwarfs just cool off for their entire lives.
Want to know another kind of object that cools for the entirety of its existence? A planet. So I like to say that brown dwarfs are objects that form like stars but evolve like planets.
Now brown dwarfs have temperatures so low that the majority of their light doesn’t come out in visible light. While we now know that they are ABUNDANT in the Milky Way Galaxy, if you look up in the nighttime sky not a single one of those several thousand points of light you see is a brown dwarf. They are invisible to human perception. In order to find them we must turn to longer wavelength light. Brown dwarfs glow in the infrared. Thats why the NASA data we are using from the Wide-Field Infrared Survey Explorer (or WISE for short) is so critical to brown dwarf science. WISE has scanned the entire sky in the infrared and given us an unprecedented search tool for cold brown dwarfs near the Sun. In fact the WISE telescope was designed in part to be able to find the coldest types of these objects.
Brown dwarfs come in three types of “flavors”. There are L types, T types and Y types. See the image below for some details on the temperatures of these types.The L types are the warmest and the Y types are the coldest. Arguments could be made for which kind of brown dwarf is the most exciting to study but for the sake of this blog post I’ll tell you about two different ones that were stupendous discoveries to come out of mining WISE data the same way that you are doing.
Just a few years ago an Astronomer from Penn State named Kevin Luhman was looking through the WISE data for objects that moved over the full timeline of the spacecraft. In 2013 he discovered a fantastic brown dwarf binary (named Luhman16AB after him) that turned out to be the 3rd closest system to the Sun. Until that time Astronomers figured they had the solar neighborhood solidified. The last time the top 5 closest objects to the Sun had changed was almost a century prior. More than that, Luhman16AB is a dynamic system. One of the objects is an L type and one is a T type. The L type appears to have large violent storms raging in the outer atmosphere. Astronomers have made maps of it and are using it to understand what exoplanet weather might look like. This binary had been missed by numerous professional and very experienced astronomers (myself included) because it moves very fast and is in a particularly crowded part of the sky. By blinking images you might be able to uncover another bright, beautiful system like this one.
The second object I want to tell you about is one of the most exciting discoveries I’ve seen in my career as a brown dwarf scientist. Its an object called WISE0855 and its a Y type brown dwarf with a mass between 3 – 10 times that of Jupiter and a surface temperature equivalent to a balmy day at the North Pole. Dr. Luhman also found this one by blinking images and it turns out to be the coldest compact source ever discovered outside our own solar system. It’s so cold that its outer atmosphere is likely teeming with water ice clouds. In 2014 I wrote a paper on the indications of those water clouds in the object and in 2016 I worked with a team that obtained the very first spectrum of it. We directly compared it to Jupiter and found striking similarities. Best of all, WISE0855 is the 4th closest system to the Sun. Just a bit further than Luhman16AB. In just one year, WISE data completely changed the solar neighborhood. This should make you wonder, what else is out there? With so many eyes working on the WISE dataset I’m hoping we pinpoint a brown dwarf that is closer than proxima centauri (the closest star). One that is covered in strange exotic clouds. Hopefully one of our thousands of volunteers is blinking an image right now and marking a key object in understanding the atmospheres of worlds beyond our solar system.
Since Mike Brown and Konstantin Batygin announced evidence for the existence of a distant ninth planet in the solar system, astronomers have been furiously analyzing and collecting data in hopes of being the first to spot it. A lot of the excitement is driven by the fact that planet nine may already have been detected in existing data sets. Astronomers love the idea of sifting through a huge pile of data to make that one epic discovery, and planet nine is the ultimate “needle in a haystack” adventure.
The standard approach to detecting a faint Trans-Neptunian Object (TNO) such as planet nine is to look for its reflected sunlight using the biggest ground-based visible light telescopes on Earth. There are several planet nine searches of this type currently underway. Mike Brown is using the Subaru 8 meter telescope on the Mauna Kea mountain top in Hawaii. Scott Sheppard is leading a dedicated TNO survey using the Dark Energy Camera (DECam) instrument on the Blanco 4 meter telescope at Cerro Tololo, in Chile. David Gerdes is also using archival DECam data to hunt for planet nine, and recently discovered “DeeDee” a possible dwarf planet over ninety times more distant from the Sun than the Earth. However, none of these surveys has yet or ever will cover the entire sky.
Since April 2016, I have been performing an automated planet nine search using WISE data, with help from my colleagues Benjamin Bromley, Peter Nugent, David Schlegel, Scott Kenyon, Edward Schlafly, and Kyle Dawson. WISE is a bit of an “X factor” when it comes to the search for planet nine, because using it to look for TNOs is very unconventional. WISE is comparatively a tiny telescope (0.4 meter diameter), and observes in the infrared from low-Earth orbit (as opposed to visible light from the ground). With WISE, we are searching for intrinsic emission from planet nine itself, rather than reflected sunlight. The big advantage of WISE is that it has already covered the entire sky more than six times. However, the main disadvantage is that there is an enormous uncertainty in how bright or faint planet nine might appear in the infrared. So planet nine might very well exist, even if it turns out that WISE can’t detect it.
My automated planet nine searches will likely have major problems in certain areas of the sky, particularly in the plane of our Milky Way galaxy, where there are huge numbers of background stars. This is where we really need Backyard Worlds: Planet 9. In the search for rare moving objects, professional astronomers often painstakingly blink through thousands or even millions of images by eye. Having a team of citizen scientists look through the WISE images will help make sure that no brown dwarf or ninth planet in this data set evades discovery.
Backyard Worlds: Planet 9 is my first time being involved in a citizen science project, and it’s been a lot of fun so far, even though I know we’re just getting started. Thanks for joining the search!