List of publications

ADS link features recently published papers by DIRAC researchers.

DIRAC Postdoctoral Positions

The DIRAC Institute in the Department of Astronomy at the University of Washington is seeking applicants with a strong research record in the development of statistical techniques or algorithms for analyzing large astrophysical data sets for two postdoctoral positions.

AstroML: The first position is to help in the development of the second edition of astroML (http://astroml.org) a popular Python-based machine learning package for astrophysics. New components we are incorporating within astroML include methodologies from deep learning and hierarchical bayesian statistics. Special emphasis will be placed on building a broader community and making astroML a sustainable open-source project. The successful candidate will lead these activities, including the application of the new codes to dataset available to UW researchers.

Time Series Data: The second position is to develop new approaches for analyzing astronomical time series data using modern computational frameworks. The goal of this framework will be to enable science with the ZTF and LSST data sets. Promising applicants should possess an interest in time domain science and experience or interest in the use of databases and large scale compute platforms such as Spark, Dask, or similar. Good Python skills, and experience with machine learning libraries, image processing of astronomical images, or astronomical databases are desirable.

The DIRAC Institute is a newly formed center for data intensive astrophysics at the University of Washington. The Institute consists of six faculty and senior fellows, and over 20 postdoctoral researchers and research scientists. It has active research programs in Cosmology, Solar System science, Milky-Way structure, the Variable and Transient universe, andAstronomical Software.

The University of Washington is a partner in the Zwicky Transient Facility (ZTF) project, a new time-domain survey which will begin operations in early 2018. The UW is a founding partner of the LSST project, and leads the construction of its time domain and solar system processing pipelines. Other research activities at UW/DIRAC include topics in extragalactic science, as well as the understanding the structure, formation, and evolution of the Milky Way using large surveys (SDSS, WISE, PanSTARRS PS1, and others).

A Ph.D. degree in astronomy, physics, computer science, or a related subject is required. The initial appointment is for two years, renewable up to three years, and offers competitive salary and benefits. The appointments are available immediately and are expected to start no later than September 2018.

Applicants should submit a curriculum vitae, description of research interests (with links to Github if relevant) and arrange for three letters of reference to be submitted to Nikolina Horvat at horvat@uw.edu with subject line “DIRAC postdoc application (your name)”. Applications will be accepted until the positions are filled, to assure full consideration, please send your application by Dec 31st 2017

For detailed information about the benefits available through the University of Washington, including dental, medical and disability insurance, retirement, and childcare centers, see the University of Washington benefits page: https://www.washington.edu/admin/hr/benefits/.

The DIRAC Institute is a community of people with diverse interests and areas of expertise, engaged in the understanding of our universe through the analysis of large and complex data sets. We are an open, ethical, highly engaged and collaborative community based on trust, transparency and mutual respect. We believe in providing a welcoming and inclusive environment, in the importance of quality of life, in embracing diversity, in making a difference and having fun.

Google Summer of Code With DiRAC

By Biswarup Banerjee

I am a Computer Science Engineering student who is very much passionate about building web apps and creating products for people and communities.

I have previously worked/interned at multiple VC funded tech startups and this summer I started working remotely with the Data Engineering team from UW DiRAC institute under Google Summer of Code 2020!

Project Summary

My project revolved around building a Jupyter Notebook/Lab Extension. The extension can be used by the astronomy community to create and configure apache pyspark clusters just on the click of a few buttons. It can be done from within the Jupyter Environment without the need to write multiple lines of cumbersome codes. 

Fig 1: The “SparkManager” Extension.

Fig 2: The options to configure an apache pyspark cluster using SparkManager

Fig 3: “spark” variable is injected into the jupyter notebook using SparkManager

UW DiRAC Data Engineering Team

The best part of my summer project was definitely getting to meet the entire team of UW DiRAC and getting to know about the astronomy projects that DiRAC is working on, like the LSST! 

I feel lucky to have worked  with a very experienced, passionate and welcoming team of engineers and astronomers.

Also it is so fascinating when I realize that we were thousands of miles apart and yet we were working in a very collaborative manner. 

It was a great learning experience for me as I learnt a lot about the Jupyter Ecosystem and remote collaborative work. 

External Links for further reading

  1. The github repository link: https://github.com/astronomy-commons/sparkmanager
  2. How “SparkManager” works: https://github.com/astronomy-commons/sparkmanager/blob/master/docs/how_it_works.md
  3. My blog post about how my interests grew for space science: https://medium.com/@biswarupbanerjee/tryst-with-astronomy-and-space-science-b8df974cb159?source=friends_link&sk=802662559d1d0dbfa206e58b05efac86
  4. My Linkedin account: https://www.linkedin.com/in/techguybiswa/

Photometric Redshifts with the LSST II: The Impact of Near-Infrared and Near-Ultraviolet Photometry

A photograph and rendering mix of the exterior of the Vera C. Rubin Observatory building on Cerro Pachón in Chile. Image credit: LSST/NSF/AURA

The groundbreaking advances in cosmological astrophysics to be made by the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) all rely, at least in part, on accurate photometric redshift estimates for billions galaxies in our Universe. These photometric redshifts measure how much the light from a far off galaxy is shifted to lower frequencies by the accelerated expansion of the Universe, as the photons travel from their galaxy to ours. Astronomers use the photometric redshifts as a proxy for distance when they map out the locations of galaxies over the vast expanse of space, and backwards in time. These cosmological maps are essential to further our understanding the origin, evolution and future of the Universe.

The six filters in the Rubin Observatory LSST science camera will collect light at optical frequencies. Although it will be the most sensitive wide-field astronomical surveys to date, and will provide photometric redshifts for an unprecedented number of distant galaxies (approximately four billion!) — observations made in the optical frequencies alone impose a constraint on how well the photometric redshift can be measured. This recent paper by UW researchers, lead by staff scientist Melissa Graham, explores the benefits of incorporating measurements at ultraviolet and near-infrared frequencies. In particular, this team simulated ultraviolet data for the future Cosmological Advanced Survey Telescope for Optical and uv Research (CASTOR) mission and near-infrared data for the future Euclid Space Telescope and Nancy Grace Roman Space Telescope, and combined it with simulated optical data for the LSST. 

This research shows that including the ultraviolet and near-infrared data is the only way to significantly lower the fraction of galaxies for which the photometric redshift estimate is catastrophically incorrect — instances where faint red galaxies that are nearby are mistaken for bright blue galaxies that are at such great distances that they appear faint and red. In fact, these researchers found that incorporating data from multiple observatories can reduce such instances from 10% to less than 2%, which will allow astronomers to make much more precise cosmological maps. This research demonstrates why astronomers need many different types of telescopes operating at different frequencies  — and is a good example of how we all get by with a little help from our friends.

CASTOR: https://www.castormission.org/

Cosmological Advanced Survey Telescope for Optical and uv Research (CASTOR)

Euclid Space Telescope: https://sci.esa.int/web/euclid

Nancy Grace Roman Space Telescope: https://roman.gsfc.nasa.gov/

Formally the Wide Field Infrared Survey Telescope (WFIRST)

Photometric Redshift: https://en.wikipedia.org/wiki/Photometric_redshift

Ultraviolet, Optical, and Near-Infrared: https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html

Letter From the Director

Welcome to the DiRAC Institute newsletter, and to the new academic year!

Allow me to begin by introducing myself: I’m Mario Juric, Associate Professor of Astronomy at UW and the new Director of DiRAC. My interests span science and technology: from asteroids of the Solar System, the origins of planetary systems, or the structure of our Milky Way, to imagining and building computing systems that allow us to do such studies — whether it’s data systems for the upcoming Bn$1 Rubin Observatory or new cloud-based data analysis platforms. I am joined by Prof. James Davenport, our new Associate Director, whose diverse research includes everything from variable stars to searches for extraterrestrial intelligence.

We take over from Prof. Andy Connolly, our founding Director who stepped down to lead the University’s eScience Institute, and Dr. Daniela Huppenkothen, our founding Associate Director who is departing for a faculty appointment in the Netherlands. And what a remarkable Institute they created! Since its inception in 2017, under Andy and Daniela’s leadership DiRAC pioneered a groundbreaking collaborative research and mentoring program that combines astronomy, data science, and software engineering. The initial research themes — the Solar System, the Milky Way, transients, cosmology, inference, and software systems — generated over 80 publications and software products. In that time, the Institute has doubled in size, hosted 13 postdocs (including 6 DIRAC Fellows, two NSF Fellows, and two B612 Asteroid Institute Fellows) plus numerous research scientists, students, and visitors. DiRAC spawned numerous cross-cutting collaborations: from a PNAS-published study on Hack Weeks, the introduction of X-ray astronomy techniques to asteroid light curve analyses, the search for peculiar stars in 1Bn+ ZTF light-curves using big data analytics tools, to our continued work on building the LSST (now known as the Rubin Observatory). As Jim and I take over, we do so with great humility and a profound sense of responsibility: to build on the great work Andy and Daniela began will be no easy task!

I hope you will enjoy reading about the research that is ongoing at DiRAC. Even through these difficult times, we continue to think about the wonders of the universe and work to build a more fair and inclusive community at DiRAC and beyond. We hope this newsletter brings you a few snapshots of the new and exciting work happening in DiRAC, and entices you to stop by some of the public (now virtual) events we have planned for the coming year.

Mario Jurić

Professor, Department of Astronomy
Director, DiRAC Institute

Meet DiRAC’s Research Team: Dr. James Davenport

DiRAC is pleased to introduce the new Associate Director of our Institute, Professor James (Jim) Davenport. Davenport received his PhD from the University of Washington in 2015, working on exploring magnetic activity from low-mass stars using NASA’s Kepler mission. He was then awarded a NSF postdoctoral fellowship at Western Washington University, and returned to UW in the inaugural class of DiRAC postdoctoral fellows in 2017.

Prof. Davenport’s research focuses on stars within our own Milky Way, using “time domain” astronomy techniques with large surveys such as NASA’s Kepler and TESS missions, and the ZTF survey. He is best known for exploring the evolution of “magnetic activity” as stars age, particularly in studying the declining rate of powerful stellar flares over time. 

In his most recent paper, Prof. Davenport and collaborators from UW used new data from the TESS mission to revisit one of the most prominent flare stars from the original Kepler mission, a small red dwarf named GJ 1243. These datasets give two precise point-in-time estimates of the flare rate for GJ 1243, over a span of 10 years, and found that unlike our Sun, GJ 1243 does not appear to show any variation in its flaring behavior. This has opened new lines of exploration for Prof. Davenport and his group, searching for changes in stellar flare rates over decades of observations.

Davenport currently leads a group of graduate and undergraduate researchers in a range of data-intensive studies of the active lives of nearby stars, including projects on eclipsing binary stars, variability from massive stars, detecting rotating stars, and studying stellar flares. He is currently working on a review of variable star astronomy for the public with TESS. Davenport is also interested in developing methods to search for signs of life in the universe – particularly for intelligent life – using tools developed for “traditional” data intensive astronomy. 

For the coming year he will be leading the DiRAC Time Domain research group in their collaborative search for mysterious “dipper” stars from the ZTF survey.

After three years of careful and thoughtful guidance by the outgoing Associate Director, Dr. Daniela Huppenkothen, DiRAC has developed a wonderfully collaborative and productive atmosphere for researchers studying a wide range of topics. Prof. Davenport is excited to take on the role of Associate Director for DiRAC. He hopes to build on this foundation, encouraging new and novel collaboration from researchers and students, and most importantly to foster an inclusive institute that places the value of people above all else.

Prof. Davenport lives north of Seattle with his family, and in the mornings can often be found drinking coffee and writing at Cafe Solstice on the Ave. He also produces a YouTube series called “Astro Vlog” that showcases the work and life of an astronomer, and can be found on Twitter @jradavenport.

DiRAC & Astronomy on Tap Seattle Present: Astronomy at Home

Once per month, we invite you to join us for an evening with a UW astronomer and participate in talks and live conversations about topics that vary from searching for the most mysterious stars in our Galaxy to the Starlink satellites changing our view to the night sky!

All talks are streaming from DiRAC YouTube channel dirac.us/yt.

List of upcoming talks http://dirac.us/talks

Astronomy at Home talks are for everyone: astronomy enthusiasts, students, and all who are curious and interested in astronomy and data science in astronomy.

Photometric Biases in Modern Surveys

Precise brightness measurements, or photometry, are essential for many areas of astronomy. DiRAC Postdoctoral Fellow Stephen Portillo, together with collaborators Joshua Speagle and Douglas Finkbeiner, published the  paper “Photometric Biases in Modern Surveys” which illustrates a measurement bias that is common in astronomical surveys.

Surveys often use maximum likelihood methods to fit a model of the noise-free sky to observed images. Fitting the model gives measurements of the positions and brightnesses of astronomical objects like stars and galaxies. However, when the position of an object is not known beforehand but is part of the fit, Portillo and collaborators show that the brightness of that object will be systematically overestimated. This bias is strongest for the faintest objects, which are often the most interesting objects. Resolved objects like galaxies are more drastically affected by this bias. The authors also show that forced photometry, a common method to combine images taken with different telescope filters, can bias the measured color of sources.

Portillo and collaborators derive a formula that can be used to correct the bias and confirm that formula on simulated images. They then show that the bias exists in observations from the Sloan Digital Sky Survey and show that their formula predicts the bias consistently. Portillo & Speagle were recently interviewed about this paper by Frank Timmes, a Senior Lead Editor of the American Astronomical Society Journals: https://www.youtube.com/watch?v=Sl8RA1cU_rk

Studying the first-known asteroid to orbit the Sun closer than Venus

DiRAC research scientist Sarah Greenstreet recently published a paper on the orbital stability of the first-known asteroid discovered on an orbit entirely interior to the orbit of Venus. Greenstreet and colleagues were the first to predict that such asteroids should exist back in 2012.

Near-Earth objects (NEOs) on orbits that always remain closer to the Sun than the planet Venus are called Vatira-class asteroids. The “Vatira” name was first coined by Greenstreet et al. (2012) as a play on the name of the Atira-class asteroids, which follow orbits that always keep them closer to the Sun than the Earth and are named after the first-known asteroid of its type, (163693) Atira. Vatira-class asteroids are rare among the NEOs. They are predicted to be approximately 0.2% of the NEO population, with only a couple Vatiras larger than about 0.5 miles in diameter expected to exist at any given time. Vatiras reach such small orbits around the Sun by interacting with the planets through gravity as the asteroids migrate from the main asteroid belt between the orbits of Mars and Jupiter down closer to the Sun and eventually to the very small Vatira orbits, which is a process that takes millions of years. Vatiras can then stay on such orbits for tens of millions of years before they most likely collide with a planet (most often with Venus itself).

On 4 January 2020, the Zwicky Transient Facility discovered the first Vatira-class asteroid, provisionally named 2020 AV2. 2020 AV2 is roughly 1 mile in diameter and is likely one of two Vatiras of this size currently in existence. In a paper published earlier this year by Dr. Greenstreet, she studied the stability of 2020 AV2’s orbit in the Vatira region. She found that 2020 AV2 will likely remain a Vatira for the next couple hundred thousand years before it will migrate onto a larger, Earth-crossing orbit and will most likely eventually collide with Venus (the most common scenario for Vatiras).

In addition to studying the best-fit orbit for 2020 AV2 available shortly after its discovery, Dr. Greenstreet also studied thousands of similar orbits for 2020 AV2 that were all consistent with the uncertainty of 2020 AV2’s orbit given its limited number of observations at the time. She found that it is possible that 2020 AV2 has been a Vatira for millions of years instead of a couple hundred thousand years. This is possible because 2020 AV2’s current location in the Solar System is fairly sheltered from gravitational interactions with the planets, which would otherwise cause it to leave the Vatira region much more quickly. This finding is significant, because it means the orbital location of 2020 AV2 could be where more Vatiras are lurking and provides a good hunting ground for discovering more of this rare type of asteroid.

Dr. Greenstreet is an Asteroid Institute senior researcher and a research scientist with the DiRAC Institute. She joined DiRAC in January 2018 after completing a two-year postdoctoral fellowship at Las Cumbres Observatory in Santa Barbara, CA. She received her Masters in Astronomy in 2011 and her PhD in Astronomy in 2015 from the University of British Columbia in Vancouver, Canada. She also has a Bachelors in Physics with a double minor in Astronomy and Mathematics from Western Washington University in Bellingham, WA, which she earned in 2007. 

Dr. Greenstreet’s research interests involve populations of small bodies in the Solar System that undergo unique dynamical phenomena. This includes studying the long-term evolution of asteroids in the inner and outer Solar System as their orbits change over time due to gravitational interactions with the planets and determining the potential for asteroids to impact the planets. She discovered that asteroids can orbit the Sun backwards, and she has studied asteroids that can become trapped in orbits around the Sun very near the orbit of a planet where the asteroid and planet appear to “co-orbit” the Sun. Dr. Greenstreet has also used telescopic observations to help refine the orbits of newly-discovered near-Earth asteroids, determine physical properties of asteroids of interest to NASA and upcoming targets of the Goldstone and Arecibo radar telescopes, and confirm that predicted asteroids undergo the Yarkovsky effect. She has also studied the rate at which small bodies in the Solar System impact planets, creating impact craters on their surfaces, such as those observed by the New Horizons mission to the Pluto system. Dr. Greenstreet has worked with researchers at the Asteroid Institute as well as with Associate Professor and DiRAC Institute Director Dr. Mario Juric (DIRAC, Department of Astronomy) to study the threat to Earth due to asteroid impacts and by how much we would need to “nudge” an asteroid out of Earth’s way to avoid an impact.

Dr. Greenstreet’s paper on the orbital stability of the first-known Vatira-class asteroid, 2020 AV2, was featured in an article in Physics Today earlier this year.

The full research paper can be found here.

Learn more about Dr. Greenstreet’s work at http://www.sarahgreenstreet.com

Greenstreet, S., Gladman, B., & Ngo, H., The orbital distribution of near-Earth objects inside Earth’s orbit, 2012, Icarus, 217, 355.

Greenstreet, S., Orbital dynamics of 2020 AV2: the first Vatira Asteroid, 2020, MNRAS, 493, L129.

Watch DiRAC Scientists on the Asteroid Day TV

Last year, Asteroid Day celebrated their Fifth anniversary, with events in 192 countries. In the next few days, Asteroid Day TV is broadcasting asteroid related programming from Discovery Science, TED, IMAX, BBC, CNN, The European Space Agency (ESA), the European Southern Observatory (ESO) and other top content producers.

Tune in here and watch Asteroid Day TV!

DiRAC & Vera C. Rubin Observatory LSST videos are broadcasted under the names:

LSST | Making Census of the Solar System,

LSST | New Era of Cosmic Discovery

“Asteroids” Trailer from Nikolina Horvat on Vimeo.

New Era of Cosmic Discovery from Nikolina Horvat on Vimeo.

DiRAC & Astronomy on Tap Seattle Present: ASTRONOMY AT HOME

Join us for an evening with an astronomer and participate in talks and live conversations about topics that vary from searching for the most mysterious stars in our Galaxy to the Starlink satellites changing our view to the night sky!

UW astronomers will talk about their work and latest discoveries. Astronomy at Home talks are for everyone: astronomy enthusiasts, students, and all who are curious and interested in astronomy and data science in astronomy. The talks will be 20 minutes in length with plenty of time for Q&A. All talks are streamed on YouTube and you can join for live discussion via Zoom.

Tune in on October 8th at 7:00pm! 

Streaming from DiRAC YouTube channel https://dirac.us/yt

Join us via Zoom

https://dirac.us/zoom

October 8 | Keaton Bell | Sounding the Depths of Stars

The dazzling starlight that we enjoy on a dark night originates from only the very outer surfaces of stars. Locked beneath these layers, in the deep stellar interiors, are much more extreme physical environments. In this talk, I will describe how, for some especially revealing stars, we are able to sound these distant interiors by measuring how they experience vibrations. With the tools of “asteroseismology,” we can turn seemingly ordinary stars into remote cosmic laboratories for studying extreme physics that are beyond the grasp of human-made laboratories here on Earth.

Keaton Bell grew up in Kent and is now an NSF Astronomy and Astrophysics Postdoctoral Fellow at the University of Washington. He studies all the ways that white dwarf stars change in brightness and is working to discover the first planet that orbits one.

Past Live Stream:

Stephen Portillo | Computer, Enhance! | Sep 10, 2020

Emily Levesque | The Last Stargazers | Aug 6, 2020

Meredith Rawls | It’s a Star, it’s a Galaxy, it’s… Starlink? | July 23, 2020

Željko Ivezić | The Greatest Movie of All Time | June 9, 2020

James Davenport | Searching for the Most Mysterious Stars in Our Galaxy | May 28, 2020