More Discoveries: New Candidate L Dwarfs!

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!

Ldwarf.x2.y1

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!

Ldwarf.x7.y6

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

Ldwarf.x4.y1

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

Ldwarf.x6.y4

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!!

LdwarfFinder

Marc Kuchner

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Our First Discoveries

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.

TdwarfCandidate_animation

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.