MUST READ! – Backyard Worlds: Planet 9

A Guide to Classifying on Backyard Worlds: Planet 9 from the Point of View of a Citizen Scientist

Enjoy this guest post by one of our moderators, Michaela Allen, featuring a video by Guillaume Colin!

Hello newcomers to Backyard Worlds: Planet 9! Or maybe you are a returning citizen scientist to this project… whatever the case, welcome! My goal for this post is to give you a basic beginner’s guide to classifying objects on BW (Backyard Worlds: Planet 9). I am in NO way an expert, but I’d like to share what I have learned so far so that maybe you can learn something too!

A little about me first… My name is Michaela Allen, (@mallen33 on Zooniverse) and I am a current college undergrad student studying physics and astronomy. I’ve been helping classify objects on BW since the project launched, and I’ve learned so much since then! Going into this project I had no idea what it entailed—I was just excited at the prospect of potentially finding something that hadn’t been discovered before!

The first thing I want to share with everyone is a YouTube video made by fellow citizen scientist Guillaume Colin (@karmeliet on Zooniverse) all about his method of analyzing flipbooks on BW. This is a great video where he talks about the basics of BW, SIMBAD, and IRSA. He also goes through the steps of filling out the Think-You’ve-Got-One Form, which can be tricky to find all of the information needed for the form. Seriously, go check it out, and thanks to Guillaume for making this video!

Now, for the rest of this post, we going to look at some of my favorite subjects on BW. So let’s get started!

When you first go on BW, you get to go through a tutorial that shows you all kinds of examples of dipoles, movers, artifacts, etc. You also have a handy field guide on the right of the screen that shows examples of these as well. The tutorial and the field guide are great references to go back and look at– do not forget to use them! I still reference back to them all the time. While those are great examples to get started with, classifying your first subject can still be kind of overwhelming! I’d like to give y’all a few more examples of types of objects and subjects you may encounter while classifying.

In terms of fast movers, I haven’t come across any (yet!). The example in the field guide of Y Dwarf WISE 0855-0714 is what I still go off of. And remember, a true fast mover will appear in all four frames of a subject.

This subject contains a type of artifact called a ghost—it only appears in two frames. These ghosts are not movers and do not need to be submitted to the Think-You’ve-Got-One form.

Other mover “imposters” to look out for is extra noise surrounding the area of declination of the South Atlantic Anomaly. This is in the -25 degrees region of declination, give or take a few arcminutes. This anomaly, which Marc talks more about in his Fast Movers post, tends to cause more noise in the subjects—and the noise can often look a lot like fast movers. For example, take a look at this subject.

There are a few orange dots visible throughout the frames that do look deceivingly like fast movers, but they are just noise. The area of declination and the often sporadic movement of these dots give away that these are not movers.

In terms of dipoles or slow movers, I have seen many! Some are definitely easier to spot than others. A dipole is an object that is moving but in a different way to all of the other objects in the subject. This subject is one of the first subjects I classified on BW, and it has a dipole! See if you can find it.

There it is at RA 151.99, dec 25.51 . I think this one is a great example of a lot of the dipoles I have seen. It isn’t super bright, but it’s not too faint either. It immediately stuck out to me, so I commented on the TALK page and asked for other opinions– don’t forget to comment on the talk pages too! If you’re ever unsure about anything, TALK about it (pun intended)! Sure enough, some people commented back, and I had found my first dipole!

Now, they aren’t all as easy to spot as this one. Faint dipoles take a little more effort. And remember, the fainter a dipole, the better of a chance it has of not being discovered! See if you can find the faint dipole in this subject.

This one is at RA 161.21, dec 13.79— to the right of that artifact. In terms of bigger and brighter dipoles, most of them I have seen have been in SIMBAD and are high proper motion stars. But just because it is bigger and brighter doesn’t mean it is going to be in SIMBAD! Always check to make sure!

Now sometimes you may find multiple objects of interest in a subject, which is great! You have to be careful of misalignment errors sometimes, though. These errors, caused by slight movements of the telescope, make the subjects seem like there are multiple dipoles. We talked about this subject, mentioned by another citizen scientist, @Chrismkemp, in one of the BW hangouts. She had seen seven or eight dipoles in this one subject and was wondering if that was even possible. I’ve come across subjects like these a few times, and they can be pretty tricky to classify. Do you see how the “dipoles” seem to kind of elongate? Marc calls them petals. Unfortunately, they can’t actually be classified as dipoles. If you ever have a subject that seems as if it has multiple dipoles, look for this “petal effect”. There was one real dipole in this subject, though. See if you can spot it!

That real dipole is at RA 349.77 dec -53.63 . This object one doesn’t seem to grow petals like all of the other imposter “dipoles” do in this subject.

The last thing I have to share with y’all is bad frames in some of the subjects. These can range anywhere from stripes across the frame, completely black frames, to half of the frame being cut off like in frame 3 of this subject. While these frames may sometimes look interesting, they do not need to be reported. If you ever come across them, you can always add the #badimage hashtag on the talk page.

Well, I hope that my limited experience has helped some of y’all on classifying objects at Backyard Worlds: Planet 9. Thanks to Marc for letting me share with everyone here! I’ve loved getting to participate in this project, and I’m excited to continue working on it!

See you on TALK, and happy hunting!

-Michaela Allen

Getting Started with SIMBAD

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!

simbadnoobject — This is what you’ll see if your SIMBAD search comes up empty. If you end up here, head for the Think-You’ve-Got One form.

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.

* = star

BD* = brown dwarf

WD* = white dwarf

Fl* = flare star

LM* = low mass star (i.e. less mass than the Sun)

SB*=spectroscopic binary

*i* = star in double system

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.

Motion of the star Vega, as measured by the Hipparcos satellite. The squiggle results from a combination of parallactic motion and proper motion.

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.

simbadvegaannotated — SIMBAD page for the nearby star, Vega. The two components of this star’s proper motion are circled.

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.

See you on TALK!

Best,

Marc

Fast Movers: Are They Planet 9?

This post was updated on 1/20/19 to go with the reboot images.

There! In frame one: a red dot. And there it is in frame two, halfway across the image!

Fast movers. They are tantalizing. A nearby star or brown dwarf can only crawl so far in the four year time span of our data. The star that currently holds the record for the highest proper motion is Barnard’s Star, which plods along at a leisurely 10.36 arcseconds per year (3.8 pixels per year). If you see an object that moves more than about 0.01 degrees (16 pixels) between the first and last frames, it may be moving too fast to be a star or brown dwarf; you’d have to consider the possibility that it might be in our own solar system.

But are those flying red dots Planet Nine?? Well, it’s not that simple.

Let’s start by take a closer look at how planets move on the sky. Here’s a spectacular multi-exposure image of the planet Mars from Astronomy Picture of the Day. As you can see, Mars takes a complicated, looping path through the sky. So do all planets in the solar system. As you may know, that’s why they are called “planets”; the word stems from a Greek word meaning “wanderer”.

retrogrademars_tezel_big — The looping path of Mars through the sky.

Planets in the solar system move in these loops because their motion on the sky is the sum of two components: the planet’s orbital motion around the Sun, and the motion of the Earth around the sun, which changes our point of view. The component of the planet’s motion that is caused by the Earth’s orbiting around the sun is called “parallactic” motion.

So what does this mean for us here at Backyard Worlds: Planet 9? We can’t see the planet’s whole looping path because we have only four exposures. But we still know a fair bit about what the motion will look like. It will be the sum of two components: the planet’s slow orbital motion and the relatively speedy parallactic motion. We know that the parallactic motion will be the faster, dominant component, simply because the Earth is much closer to the Sun than Planet Nine is, so it orbits faster. And we know what the Earth’s orbit is, so we know a lot about that dominant parallactic component of the motion.

Here is a simulation, from the field guide, of how Planet Nine might appear in a Backyard Worlds flipbook. First of all, notice that Planet Nine’s motion is more or less right to left (West-East) because it’s roughly in the plane of the solar system. If you see a fast mover moving vertically in the flipbook, be very suspicious. We can not really see asteroids or comets in our images. So a fast vertical mover is probably just noise.

Second of all, notice that there are two copies of planet nine! The second copy is created by the motion of the Earth around the sun: the “parallactic” motion. If the planet is closer than 700 AU, the parallactic motion will be bigger, and the two images will be farther apart. They might not even fit in one image. The size of the images we show is a compromise; if we made them too big they might be better suited for finding some nearby versions of Planet Nine, but then they would each take forever to scan. For that reason, we’ve provided links in the metadata (click the “i” button under the flipbook to see the metadata) that allow you to visit adjacent (pre-reboot) images to trace your favorite mover from one subframe to the next.

Image result for south atlantic anomaly — The South Atlantic Anomaly causes lots of fake fast “movers” to appear near declinations -25 degrees.

So what are those bright spots you’re seeing flying across that flipbook? Some of them are random noise, caused by the non-zero temperature of the detectors (you might call that “heat”). Some of them are probably caused by cosmic rays, those vagrant high energy protons and atomic nuclei that traipse in from beyond the solar system, sometimes bearing fascinating news of distant explosions, sometimes just being nuisances. If the images you are looking at are from a declination of roughly -25 degrees, the cosmic rays can be especially pesky. At this declination, a droopy bit of the Earth’s magnetic field called the South Atlantic Anomaly allows cosmic rays to get a little bit closer to the WISE satellite than we might prefer. Here are some examples of what cosmic ray hits do to WISE images. Cosmic ray hits are another reason why we need human eyes to examine these images.

Hey, nobody said finding Planet Nine would be easy. But, hey, in the reboot images, we’ve been able to made those cosmic rays much fainter, and Planet Nine easier to recognize. Thanks to @RonArzi for requesting this post, and thanks to you for reading it!

Best,

Marc