Citizen Scientist Discovers Dusty Debris Disk Around White Dwarf

Citizen scientist Melina Thévenot of Germany helped the Backyard Worlds/Planet 9 program discover a unique white dwarf with a dusty debris disk, and observations made by Cool Star Lab members with the Keck/NIRES instrument were critical its confirmation. The work, led by STScI astronomer John Debes, was reported in Astrophysical Journal Letters today.

Since 2017, the Backyard Worlds project has been engaging citizen scientists to search through data from NASA’s WISE mission to identify overlooked stars in the vicinity of the Sun. These have mostly been cold brown dwarfs, of which the project has found more than 1,000 too date – more than one a day! But it also picks up other dim, red things, in this case the white dwarf LSPM J0207+3331.

White dwarfs are normally “blue” due to their high surface temperatures (they are after all the cores of spent stars), but this white dwarf is surrounded by a complex disk of dusty debris, likely the result of the tidal disruption of an orbiting planet or asteroid (the same process is likely responsible for the rings around Saturn and other giant planets). This disk, heated by the white dwarf, glows in the infrared, allowing it to show up in WISE. While tidal debris disks aren’t new around white dwarfs (Cool Star Lab’s Carl Melis is specialist in this area), both the structure of this disk—which appears to be made of several distinct ring-like components—and that age of the white dwarf are surprising.

Very little was known about J0207+3331 prior to its identification by Melina in the Backyard Worlds program; only one prior paper had identified it as a high proper motion star. After an initial attempt to measure its spectrum was foiled by bad weather, it was therefore up to Cool Star Lab members Adam Burgasser & Jon Rees to get the necessary spectral data. Using the newly-commissioned NIRES instrument on Keck (during admittedly more not so great weather), Adam & Jon managed to measure the near-infrared spectrum of the source, which was largely consistent with a hot blackbody with slight uptick at the red end. This tiny bit of near-infrared excess, and the much greater mid-infrared excess in WISE photometry, could arise from several things, including an unseen brown dwarf companion (much like the first L dwarf ever discovered, GD 165B). However, we were able to show that the combined NIRES spectrum and WISE photometry were inconsistent with any white dwarf-brown dwarf combination, leaving a debris disk as the best model. (For once, Adam was happy not to find a brown dwarf!)

(Left) Analysis of our NIRES spectrum shows that any brown dwarf companion to J0207+0331 would be too small (blue dots) compared to model predictions to reproduce the observed excess, which rules out the binary model. (Right) instead, a model that includes a single white dwarf (orange line) and a debris ring system (red dashed line) can fit both spectral and photometric data (from Debes et al. 2019)

The NIRES spectrum, which contains several weak Hydrogen lines, allowed our team to determine the temperature and surface gravity of the white dwarf, and in turn its mass (0.69±0.02 solar masses) and age (3.0±0.2 billion years). By combining all of the data together, our team was also able to generate a model for the disk, which requires more than one “ring” of material with a total mass greater than a typical asteroid or comet. Both of these features are surprising: structure in the ring suggests there may be another body clearing a gap in the disk, or perhaps there have been two tidal disruption events that happened sequentially. This dust should also be cleared our “relatively” quickly (“relatively” = few 100 million years), requiring a “relatively” recent disruption.

Overall, the properties of J0207+3331 suggest that planetary systems may be continuously dismantled for billions of years after a star dies, which gives us a lot more time to study the innards of planets after tidal dissection (yech!). Moreover, the discovery of such an interesting, and relatively nearby system (only 45 parsecs, or 150 light-years, away), means that there may be many more such systems out there. Plenty of opportunity for future citizen scientists like Melina Thévenot!

Here are some links to press reports on this result:

NASA: https://www.nasa.gov/feature/goddard/2019/citizen-scientist-finds-ancient-white-dwarf-star-encircled-by-puzzling-rings

NOAO: https://www.noao.edu/news/2019/pr1904.php

UCSD: https://ucsdnews.ucsd.edu/pressrelease/astronomers_invite_citizens_to_crowd_source_new_worlds

ASU: https://asunow.asu.edu/20190219-discoveries-citizen-science-finds-ancient-white-dwarf-star

CNN: https://www.cnn.com/2019/02/19/world/white-dwarf-rings-discovery/index.html

Backyard Worlds Blog, where Melina Thévenot describes her discovery: https://blog.backyardworlds.org/2019/02/19/the-crystal-ball-white-dwarf/

Want to find your own new world? Give Backyard Worlds/Planet 9 a try! https://www.zooniverse.org/projects/marckuchner/backyard-worlds-planet-9

Cool Stars Lab shines in 2016 Summer Research Conference

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The Cool Star Lab had a strong showing at this year’s 2016 UCSD Summer Research Conference, held August 11th around campus.  Ten students from the Lab presented results during the full day event, including six in Session #1 alone!

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Cool Star Lab Presents Work at 2016 Physics Education Research Conference

Mike Lopez, Isabela Rodrigues and Adam Burgasser presented their early analysis of an experimental Physics course at the 2016 Physics Education Research Conference in Sacramento, CA. This was the first PERC for all three researchers. In addition, former Cool Star Lab member Dianna Cowern was on hand for the overlapping American Association of Physics Teachers (AAPT) meeting presenting her work on the Physics Girl video series.

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Past and present Cool Star Lab members at the 2016 PERC; from left to right: Isabela Rodrigues, Dianna Cowern, Adam Burgasser and Mike Lopez.

The primary research presentations focused on analysis of an experiment conducted in Fall 2015 to implement Cooperative Problem Solving (CPS) in the large Physics 1A Introductory Mechanics course. The current course format, which is lecture-based, does not specifically build up students’ problem solving skills, skills that students often struggle with and which may benefit them more in their other majors and in their future careers. Inspired by work being done by Thomas Gredig at CSU Long Beach, I implemented a form of CPS as described in Heller & Heller (2010) as a flipped-format course, with online video lectures providing the primary instruction and class time primarily devoted to problem-solving skills and techniques.  To validate the model, Adam taught 9 sections of the CPS course with 1 (large) section of interactive lecture. The work presented at the PERC was a preliminary analysis of student outcomes.

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Work by Cool Star Lab Alumna Aishwarya Iyer Featured in NASA Press Release

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Cool Star Lab alumna Aishwarya Iyer, currently a Master’s student at CSU Northridge and intern at Jet Propulsion Laboratory, has recently published work on exoplanet atmospheres that has been featured in a NASA Press Release. Her paper, “A Characteristic Transmission Spectrum Dominated by H2O Applies to the Majority of HST/WFC3 Exoplanet Observations“, published in the Astrophysical Journal, concludes that most hot Jupiter atmospheres likely contain water vapor, even those that show weak water features. This is due to the role of hazes and clouds, which can obscure molecular gas features. Aisha and her team performed a comprehensive analysis of 19 Hot Jupiter transmission spectra taken by HST/WFC3, and modeling analysis indicates that the bulk of water vapor lies below the cloud layers. This work is a major advance in understanding the role of clouds and haze in exoplanetary atmospheres, which are also important constituents in brown dwarf atmospheres.

The paper can be accessed at http://adsabs.harvard.edu/abs/2016ApJ…823..109I and the press release can be found at http://www.jpl.nasa.gov/news/news.php?feature=6527

Cool Star Lab Contributes to the Discovery of 3 Potentially Habitable Earth-Sized Worlds

 

Adam Burgasser and Daniella Bardalez Gagliuffi were part of an international team headed by Michael Gillon at the University of Liege that discovered three Earth-sized planets orbiting around the habitable zone of a nearby ultracool dwarf, TRAPPIST-1. The results were reported in the May 2, 2016 issue of Nature.

This artist’s impression shows an imagined view of the three planets orbiting an ultracool dwarf star just 40 light-years from Earth that were discovered using the TRAPPIST telescope at ESO’s La Silla Observatory. These worlds have sizes and temperatures similar to those of Venus and Earth and may be the best targets found so far for the search for life outside the Solar System. They are the first planets ever discovered around such a tiny and dim star. In this view one of the inner planets is seen in transit across the disc of its tiny and dim parent star.

This artist’s impression shows an imagined view of the three planets orbiting an ultracool dwarf star just 40 light-years from Earth that were discovered using the TRAPPIST telescope at ESO’s La Silla Observatory. These worlds have sizes and temperatures similar to those of Venus and Earth and may be the best targets found so far for the search for life outside the Solar System. They are the first planets ever discovered around such a tiny and dim star. In this view one of the inner planets is seen in transit across the disc of its tiny and dim parent star (ESO/M. Kornmesser, CC BY)

Below is a reproduction of a The Conversation article I wrote for this discovery, with images from the official ESO press release.

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