Dino Hsu awarded the Lattimer Award for Graduate Excellence

Cool Star Lab graduate student Chihchun “Dino” Hsu

Graduate student Chihchun “Dino” Hsu has been awarded the 2019-2020 Carol and George Lattimer Award for Graduate Excellence.

The Lattimer Award honors outstanding graduate students in UCSD’s Division of Physical Sciences (Chemistry & Biochemistry, Mathematics & Physics) who seek interdisciplinary approaches to problem solving and have a strong commitment to education, mentorship, and service. The award is named after local philanthropists Carol and George Lattimer, who have supported UCSD through charitable giving and advising. Carol volunteers at The Preuss School as a mentor, and George has served on the UC San Diego Foundation Board of Trustees.

Dino was one of two recipients of the Lattimer Award this year, and both recipients will be honored at a luncheon in the Spring term.

Congratulations Dino!

Ryan Low awarded Dean’s Undergraduate Award for Excellence

Cool Star Lab undergraduate researcher Ryan Low

Ryan Low, an undergraduate researcher in the Cool Star Lab, has been awarded the UCSD Division of Physical Sciences Dean’s Undergraduate Award for Excellence for 2019-2010.

Ryan is a Physics major and has been a member of the Cool Star Lab since Winter 2018. He has been leading the analysis of optical spectral of very low mass stars and brown dwarfs obtained with the Lick Observatory KAST instrument, and his work is uncovering some of our nearest (and previously overlooked) stellar neighbors.

The Dean’s Award recognizes undergraduate students for academic excellence throughout their undergraduate period. Students are nominated by faculty and advisors, and evaluated by selection committees in each department. Ryan is one of 33 students across the Division that were selected for this award this year. Ryan and his fellow recipients will be honored at a reception in May.

Congratulations Ryan!

Jessica Birky awarded NSF Graduate Fellowship

Jessica Birky, a graduating senior at UCSD and student participant in the Cool Star Lab’s SDSS Faculty and Student Team program, has been awarded the 2019 NSF Graduate Research Fellowship. Started in 1952, the NSF Graduate Research Fellowship Program (GRFP) supports outstanding graduate students in NSF-supported science, technology, engineering, and mathematics (STEM) Master’s and doctoral degrees at US institutions. In 2018, 2,000 awards were made among 12,000 applicants (roughly in line with other NSF funding programs), making the NSF GRFP one of the most competitive fellowship programs currently available.

Jessica designed her application around developing data-driven spectroscopic models for M dwarfs to determine detailed chemical abundances (<0.1 dex precision) for these common, low-mass stars. She has already started this work at UCSD and MPIA (collaborating with NYU’s David Hogg and UNC’s Andrew Mann) by analyzing SDSS APOGEE data with The Cannon. Jessica’s proposal aims to extend this work by using the thousands of kinematic pairs identified in Gaia, while separating out binaries and rapid rotators.

Jessica has less than a week to decide which graduate program she will be attending, but the fortunate institution will now have a fully-funded prize-winning scholar for the first 3 years!

Congratulations Jessica!

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

Chris Theissen is Awarded both Sagan and NSF Fellowships

Chris Theissen, former Boston University graduate student and postdoctoral researcher in the Cool Star Lab, has been awarded both the NASA Sagan Postdoctoral Fellowship and the NSF Postdoctoral Fellowship for 2019. The award is based on his proposed program: “Planetary Collisions around Low-Mass Stars: Constraining the Timescale for Collisions and Testing the Origin of the Kepler Dichotomy”, which builds from his graduate research investigating infrared excesses around relatively old M dwarfs. He will conduct this work with one of these fellowships under the mentorship of Prof. Quinn Konopacky here at UCSD.

The NASA Sagan Fellowship is one of the most prestigious postdoctoral awards in Astronomy, with an oversubscription rate of 16:1. Similarly, the NSF Postdoctoral Fellowship (which spans all science fields) is highly coveted. Chris has previously been an NSF Graduate K-12 STEM Fellow and Ford Foundation Fellow.

Congratulations Chris!