The Crystal Ball White Dwarf

Today is a big day at Backyard Worlds: Planet 9!  We’re celebrating our 2nd anniversary, our reboot, and announcing our second paper, published in the Astrophysical Journal letters.   (You can read it here for free.) It’s about a unique white dwarf that’s an analog for the solar system three billion years from now; the oldest white dwarf known to host a dusty disk, the likely remains of a planetary system.   Check out this guest blog post by our own Melina Thévenot, who explains how she discovered this record-breaking object, which provides such a chilling glimpse into the future.

Melina Thevenot
Melina Thévenot, the citizen scientist at Backyard Worlds: Planet 9 who discovered the infrared excess from white dwarf LSPM J0207+3331.

Hi everyone. I am Melina Thévenot, a volunteer of the Backyard Worlds: Planet 9 project from Germany. Here I want to tell you a bit about how I discovered an unusual white dwarf and how the researchers uncovered that it is not only unusual, but also cool.

How did I discover the white dwarf LSPM J0207+3331?

As a volunteer of the Backyard Worlds: planet 9 project, I spent a lot of time searching for brown dwarfs. The Gaia Data release 2 was my favorite survey for the search of brown dwarfs. I uncovered probably several hundred new brown dwarf candidates that move in wiseview with the help of three other volunteers: Katharina Doll, Hugo Durantini Luca and Peter Jalowiczor. 

While improving my search I noticed something about brown dwarfs in the Gaia catalog: some good sources don’t have color information in Gaia DR2. This is a problem, because I relied on a color-cut. To check if I missed any good T-dwarf, I decided to use Allwise to find sources with high infrared excess and the high parallax measurement in Gaia DR2. In the resulting list I could find fake sources that did not move in wiseview, T-dwarfs (distance 5 to 10 parsec) and one source that does not belong in this list.

I don’t remember where I saved the original list, but it probably looked like this:

list

The object in the red circle has a distance of 44 parsec. Gaia should not detect a T-dwarf at this distance.

Is it another fake source? I could have ignored it. I am glad I checked the movement.

Wiseview link: http://byw.tools/wiseview#ra=31.891736099354006&dec=33.52476141170008&size=60&band=3&speed=295&trimbright=98.88&linear=0.845&color=gray&mode=percent&coadd_mode=pre-post&zoom=17&border=0

As you can see: Compared to the background objects it is moving and in PanSTARRS you can see a blue source.

This source is LSPM J0207+3331. At this time I still had no clue what it could be. I did need some days to think about it. After checking the position in a HR-diagram I knew that it was a white dwarf with large infrared excess (Allwise w1-w2≃1). I guessed that this excess comes from a circumstellar disk. Time to loop in some other volunteers, who are advanced users of Disk Detective. Katharina Doll told me that the source looks good and she confirmed that it was possible for a white dwarf to have a disk, something I did not know until she told me. We decided to contact Marc Kuchner and soon John Debes joined the discussion.

Observation with Keck

John Debes told us this white dwarf is cold, in fact it was 1000 Kelvin cooler than any known white dwarf with an infrared excess. So the researchers decided to observe it with APO. But the dome was closed because of bad weather. Soon the white dwarf was observed with Keck! The telescope with the largest mirror on this planet!

I watched closely how things developed. I made a timeline:

Date
2018-10-17 Discovery of LSPM J0207+3331 (still no clue what it could be)
2018-10-19 Sending LSPM J0207+3331 to the researchers
2018-10-20 Bad weather at APO
2018-10-27 LSPM J0207+3331 is being observed with Keck (Adam Burgasser observed it for us – THANK YOU!!)
2018-12-01 Paper is submitted to ApJ Letters
2019-02-02 Paper is accepted

 

A 3 Gyr White Dwarf with Warm Dust

Let’s talk about the paper. Des Pudels Kern. (German Saying, “The core of the poodle” meaning the main point)

What is a white dwarf? Our sun will develop into a red giant billion of years in the future. The red giant will lose the outer layers in a Planetary Nebula. The core that is left is a hot white dwarf and it will gradually cool and become fainter.

The process is very violent and “loosing the outer layers” is nothing else than burning the orbiting planets in strong solar winds. But not everything will perish. White dwarfs have a leftover stellar system with asteroids, comets and planets. If an asteroid or comet comes too close to the white dwarf, it can be torn apart by the tidal forces caused by the gravity of the white dwarf and the material settles down in a disk around the white dwarf.

figure 1 of the paper

In figure 1 of the paper you can see a blue line. This is how the Spectral Energy Distribution (SED) of the white dwarf should look like without a disk. The gray lines are the spectra from Keck NIRES and the black squares are the photometry from different surveys. You can see how the spectra and the photometry are somehow taking off to the right side. This blog post from Disk Detective explains what a SED is and how a SED looks like for star+disk. It might help you interpret this figure. 

Models that try to describe disks around white dwarfs predict that young white dwarfs are more likely to develop a disk. It is therefore surprising that a 3 Gigayear (3 Billion years old) white dwarf has a disk. Is LSPM J0207+3331 special or are the models about the formation of disks around white dwarfs not accurate enough? Future searches for similar white dwarfs might shine light on this mystery.

But this is not where the story of this white dwarf ends. The disk around LSPM J0207+3331 is not a simple disk, but it consists of two components: an outer colder ring with a temperature of 480 Kelvin and an inner ring with a temperature between 550-1400 Kelvin. The white dwarf has an temperature of 6120 Kelvin and a mass of 0.69 solar masses. The outer ring might have formed from a small asteroid that was disrupted by the tidal forces in the recent history of the system. This is the first time such a system was observed.

In the future, researchers will observe this white dwarf again and obtain more data, which might tell more about this system. An optical spectrum, for example, might tell us if any material from the disk is falling into the atmosphere of the white dwarf, and what that material is made of.

I am very proud to be part of this discovery and hope you enjoyed reading this blog post.

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The Reboot Is Here!

Team,

As you may know, the WISE mission has continued to scan the sky during the last few years—collecting more images for us to search.   So we’ve started uploading new batches of subjects for you to classify that incorporate new WISE data.

These new subjects are improved in at least four ways:

  1. They include two entire new years of data, so they cover a 50% longer time span. That means movers move farther and dipoles look brighter.
  2. The Poisson noise and the amplifier noise (the stripes) are reduced by at least 41%, sometimes by a factor of up to 10 in regions near the ecliptic poles.
  3. All the images have been realigned, so stationary stars subtract out better.  Some of the artifacts and ghosts have been averaged away in the process too.
  4. Planet 9 and other solar system planets no longer hop and jump.  They are simply ordinary dipoles or movers.  (If they exist.)

We’ve also taken this opportunity to fix some of the broken links in the metadata and add some handy new ones, like links to WiseView  and to WISE images on LegacySurveys. Now, it might not be obvious immediately that you’re looking at a reboot image; they might look at first glance to be just as noisy as the pre-reboot images you’re used to.  That’s because we cranked up the gain to match the noise reduction!  So they images look just as noisy, but now the objects you’re looking for will be at least 41% brighter.  You can always tell you’re looking at a reboot subject if the metadata includes links to WiseView and LegacySurveys and doesn’t say anything about the motion of planet nine.

Now, there’s something important to be aware of when you’re using the reboot data. There are still four frames like you’re used to.  But now the biggest time interval is between the first and second frames.   Previously, dipoles tended to flip sides between frames 2 and 3.  But now, the dipoles will tend to flip between frames 1 and 2.  We’ll be updating the tutorials and field guide to illustrate this change (and if you have any nice examples that you think we ought to show, please bring them to our attention).

RebootExample_animation
Nearby Y dwarf WISE 0855 before and after the reboot. The brown dwarf (moving red dot, upper left) moves farther and faster in the reboot flipbook (right), and the stars dance less.  The biggest time step, when you see the red dot move the farthest, is between frames 1 and 2 in the reboot flipbook, 

Unfortunately, each new subject will have its own new TALK page, even if it covers the same region os sky as an older subject.  But there will often be a link in the metadata to the old TALK page (if it exists).  There will also be links in the metadata to the old TALK pages of the adjacent subtiles, to help you track a dipole or mover that seems to go off the edge of the image.

We will be re-uploading the whole sky bit by bit over the next few months.  This is a big project.  But we’re starting with a sector that we have not yet looked at before so there there should be some nice new things to discover right away.

Thanks for all the hard work you put in so far—you made it through about 2/3 of the sky once already!   Now we’re gonna start fresh and kick it up a notch.  Have fun!

Marc Kuchner

 

 

 

42 Confirmed Brown Dwarfs and Counting

Hey everybody!   Thanks to your efforts, we’re now up to 879 brown dwarf candidates.  Wow.  We’ve been following up your discoveries as fast as we can, getting spectra to determine their spectral types and distances, test for membership in moving groups, and look for unusual features. For the coolest objects, we’ve also been working on taking new images.  Here’s a little update on all this follow-up work.

First of all, we have a big stack of new spectra. Jackie Faherty confirmed 17 of our brown dwarf candidates with the ARCoIRIS spectrograph on the Blanco 4m telescope in Chile, and Jonathan Gagné, Jackie Faherty and Michaela Allen observed another batch of 8 targets with the SpeX spectrograph on NASA’s Infrared Telescope Facility (IRTF).  Of those 8 we observed with IRTF, 6 are brown dwarfs. The other two are late Ms; one has a co-mover (spotted by Tadeas Cernohous) and the other has an unusual J band flux that threw off our initial spectral type estimate.

Picture of Michaela Allen’s desk at NASA Goddard Space Flight Center while she was observing our brown dwarf candidates remotely with the IRTF telescope.

That’s right, Michaela, our TALK moderator, is now participating in observing runs! Michaela is spending her summer as a NASA intern here at Goddard Space Flight Center in exotic Greenbelt, Maryland.  She’s working on our Gemini data, and looking through the long long list of moving objects you have found that did not appear, at first glance, to be brown dwarfs.  You can follow her on Twitter @sasstronaut42 to find out more about how her summer is going, and you’ll hear more about her work later on.

Thanks to Jackie, Jonathan and Michaela’s hard work, I can now say that we have confirmed a total of 42 brown dwarfs.  These confirmed objects include 10 L dwarfs and 32 T dwarfs.  Of these, fourteen are closer than 20 parsecs, and four are closer than 15 parsecs. Congrats to Nikolaj Stevnbak Andersen, Dan Caselden, Guillaume Colin, Sam Goodman,  and Melina Thevenot, whose TYGO form submissions were observed with ARCOIRIS and confirmed to be brown dwarfs!   And congrats to Nikolaj Stevnbak Andersen, Dan Caselden, Tadeas Cernohous and Guillaume Colin, whose TYGO submissions were observed with IRTF and confirmed to brown dwarfs!  I believe those are Nikolaj’s, Tadeas’s and Melina’s first brown dwarf discoveries.

The “seeing” at IRTF was only about 0.8 arcseconds, which is poor for that site, and there were thin cirrus clouds. So we were only able to take decent spectra of objects brighter than about 16th magnitude in J band.  So this run was a bit disappointing.  But just today we learned that we won four more nights on IRTF this fall! 

In fact, here’s a summary of our follow-up program so far—where we’ve been an where we’re going.    The “R” value is the spectral resolution of the spectrograph we’re using. R = the central wavelength of the spectrum divided by the smallest difference in wavelengths the spectrograph can distinguish.   So larger R means finer resolution.  But finer resolution comes at a cost; you need to collect more light to begin with if you’re going to spread it out more by wavelength.

Table 1. Status of our follow-up observing program.
Gemini-North/NIRI Fast Turnaround J/K band imaging 9.2 hours, 16 targets Images of 16 targets obtained
Magellan/FIRE Prism R~450 17 targets Spectra of 17 targets obtained
Apache Point Observatory (APO)/Triplespec R~3500 1 night Bad weather, spectra of 2 targets obtained
Blanco 4 m/ARCoIRIS R~3500 2 nights Spectra of 17 BDs obtained (see above!)
Magellan/FIRE Echelle R~7000 1 target Spectrum of 1 target obtained 2/3/18, RV measured
Infrared Telescope Facility (IRTF)/SpeX R~150 2 nights, 20 targets 1 night weathered out, spectra of 8 targets obtained during second night (see above!)
HST/WFC3 F125W/F105W imaging 5 orbits, 5 targets Awarded 5 orbits
Mont Mégantic/CPAPIR J-band imaging 8.5 hours, 60 targets

 

Awarded time to observe 60 targets. Images of 12 obtained May 2018
Magellan/FIRE Prism

 

R~450 1 night, 20 targets Awarded 1 night in 2018B
Keck/NIRES

 

R~2700

 

1.5 nights, 10 targets Awarded 1.5 nights in 2018B
Spitzer

 

3.6 and 4.5 micron imaging 26.8 hours, 65 targets Awarded 26.8 hours
Infrared Telescope Facility (IRTF)/SpeX R~150 4 nights, 40 targets Awarded 4 nights in 2018B
Gemini-South/Flamingos 2 R~600 13.7 hours, 27 targets Proposal Submitted, Pending
Magellan/FourStar J-band imaging 1 night, 8 targets Proposal Submitted, Pending
Gemini-North/GNIRS R~11,800 9.4 hours, 5 targets Proposal Submitted, Pending

Keep up the amazing work!  And stay tuned for more cool discoveries!!

Marc

 

Guest Blog Post by Peter Jalowiczor

(One of our volunteers, Peter Jalowiczor, gave a talk about Backyard Worlds: Planet 9 at his own astronomy club.  Today’s informative blog post is his report about the experience. Did you know that brown dwarfs get smaller the more massive they are?  Read on. -Marc)

I had the pleasure to give a talk at one of the UK’s leading Astronomical Societies: the MSAS (the Mexborough and Swinton Astronomical Society). The society is situated ~20 km from Sheffield (pop, 570,000) in England and was founded in 1978.  Every Thursday evening is a great social occasion centred on a lecture.  At least once a month, some academic visits the society to present on an aspect of Astronomy. Academics really enjoy visiting and describe this place as an Aladdin’s cave as may be seen by some of the photos!

2018 146 MSAS Presentation
The first slide of Peter’s presentation.

The evening was divided-up into two parts consisting of two completely different presentations. One sent by Marc specially for the occasion and the other prepared weeks in advance by myself. They turned out to complement each other perfectly (thank you Marc!). You’re welcome, Peter! -Marc

  1. The First Presentation

I started with an introduction to the Science team and the important fact that Planet Nine is presumed to exist. It is estimated to be around 10 Earth masses, on an elliptical orbit, averaging a=700 AU because of visible disruption in the orbits of detached Kuiper Belt Objects. Next, the nearest neighbours to the Sun were discussed with examples of these BD systems and the prizes of participating in BYW:P9 included discovering such objects.

The flipbook was introduced followed by examples of what to mark and what not to mark: the submissions procedure. How this would be related to the Astronomical software/ procedures described in the second presentation blended both presentations ideally.

The successes of BYW:P9 include the discovery of a T Dwarf in the first few days of the project!

2018 166 MSAS Presentation
Members of the Mexborough and Swinton Astronomical Society, enjoying Peter’s presentation, and thinking up tough questions (see below).
  1. The Second Presentation

I started with a comprehensive description of brown dwarfs, with the three main categories and their associated spectral classes; this culminated in a review of the mass-radius relationship from solar-type stars to the terrestrial planets (G. Chabrier et. al., 2008). A chart demonstrated the decrease (compression) of BD radii with mass before the critical mass is reached as a BD turns into a star. After this point the radius increases dramatically. The positions of L, T and Y objects and sub-BD objects was discussed down to Jovian mass.

MassRadiusdiagram
Mass-radius diagram for planet, brown dwarfs and low-mass stars, from Fortney, Baraffe and Militzer 2014.  More massive brown dwarfs are slightly smaller than less massive ones.

 

Second, I a gave detailed description of the 2MASS project and the WISE mission, the wavebands in which the detectors operated and the positions of the IR bands on the electromagnetic spectrum. 2MASS: j=1.235um, h=1.662um, k=2.159um. WISE: W1=3.4um, W2=4.6um, W3= 12um, W4=22um. I showed that WISE goes much deeper than 2MASS into the Mid-Infrared.

Third, I gave a complete overview of the astronomical tools used: the Backyard Worlds: Planet 9 flipbook, which is at the heart of the project, SIMBAD, VizieR, IRSA Finderchart and BYE Tools (Wiseview).

Fourth, I showed a home video of how everything comes together.

Fifth, I described the project’s results by showing a presentation of the spreadsheet that has been built-up. I described how the photometry of 2MASS and WISE come into this, i.e., W1-W2, J-W2 and how these differences can be used to constrain the spectral types of objects. I referred to photometric Brown Dwarf classification charts from Skrzypek, N., et al.,

I showed clips from Backyard Worlds: Planet 9 Hangouts to demonstrate the international calibre of this project, which put on a completely different light on everything.

Illustration of the spectral coverage provided by the DustPedia database, showing filter response functions of all bands for which we present data. As can be seen, the data we employ effectively provides complete sampling of over five orders of magnitude in wavelength. Response functions of the bands for which we present both imagery and aperture-matched photometry are traced with solid lines. Bands for which we present supplementary external photometry are traced with dashed lines. Bands for which we present imagery only are traced with dotted lines.
The spectral bands used by 10 different survey telescopes. 2MASS (blue) and WISE (leftmost greeen) are the surveys we use in Backyard Worlds: Planet 9.

And finally!

  • The principle aims of the project are to discover Brown Dwarfs and Planet Nine. Red Dwarfs are a secondary target and are being catalogued.
  • Volunteers are encouraged to distinguish real celestial objects from image artefacts in data from NASA’s WISE mission
  • roughly 5 million classifications of images from NASA’s WISE telescope.
  • 432 objects of interest for the follow up campaign, mostly newly discovered BD candidates. We now have more than 500!  -Marc
  • Planet Nine has remained elusive, as have Planet X and Tyche (instruments are sensitive to gas giants out to about 50,000 astronomical units from the Sun).

Peter Jalowiczor

There was also Question and Answer Session at the end of the lecture.  I’ve attempted to answer some of the questions. –Marc

Q: What causes the ‘ghosts’/artefacts in the images?

A: Though the optics in the WISE telescope are first rate, they are not perfect; some black surfaces are not perfectly black, and some transparent optics are partly reflective.  As a result, the light from particularly bright stars can create secondary images from bouncing around more than, ideally, it should.  Those appear as artifacts and ghosts.  –Marc

Q: The candidates submissions procedure. If it is listed in a Red Dwarf catalog. There seemed to be contradiction in what I said and what seemed to implied by the project. (e.g. I don’t submit a candidate if it is listed in a Red Dwarf catalog in VizieR). Whereas there could be objects listed in Red Dwarf catalogues that are misclassified? Should such objects be submitted or not? It would save time for the user.

A: The rule is: if it’s moving and it’s not in SIMBAD (and not a ghost or star or other artifact), please submit it to the Think-You’ve-Got-One form. Sorry for the confusion!  -Marc

Q: Brown Dwarfs or Brown Dwarves? One member picked-up on this after I used this (I was using Brown Dwarfs). It turns out that Dwarfs is American English and Dwarves is British English. I was ‘instructed’ to write properly!

A:  I’m no expert on British English, but perhaps you could consult with the Extrasolar Planets and Brown Dwarfs group at the University of Hertfordshire

Thank you, Peter, for being such a compelling ambassador for Backyard Worlds: Planet 9, and for composing this delightful blog post. –Marc

BYWP9 Peter Jalowiczor
Pete at his computer working on Backyard Worlds: Planet 9.