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.
For 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.
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.
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 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
This table lists our brown dwarf discoveries so far.