The Halos and Environments of Nearby Galaxies (HERON) survey
We have used a dedicated 0.7m telescope to image 123 galaxies in the Local Volume
to ~ 30 mag/sq arcsec. We find a broad correlation between luminosity and halo diameter.
Spiral and lenticular galaxies have similar halo diameters, while the largest halos
(~100 kpc diameter) are found in elliptical galaxies. Extreme interactions are found
throughout the color-magnitude diagram, but most prominently in the blue cloud. It is also
likely that no meaningful constraints on halo mass for face-on disk galaxies can be gleaned
low surface brightness imaging. Related interesting problems, such as tidally disrupting
dwarfs, low level star formation near elliptical galaxies, and interactions in Hickson compact
groups, will be presented.
When: December 11, 2017 @1:30-2:30pm
Where: WRF Data Science Studio, The Seminar Room
Strongly Lensed Supernovae
In 1964, Norwegian astronomer Sjur Refsdal showed that time delays between the multiple images of strongly lensed supernovae (LSNe) could be used to measure the Hubble constant (H0). Today, more than 50 years later, only two LSNe have been found. I will describe novel techniques for discovering LSNe that will increase the expected yields of upcoming surveys by ~10x, leading to O(10-20) events from the Zwicky Transient Facility and O(1000) from the Large Synoptic Survey Telescope. This unprecedented sample will enable sub-percent constraints on H0, the value of which is currently in tension at the 3.4 sigma level. I will also describe H0TDOGS (H0 from Time Delay Observations of Gravitationally-lensed Supernovae), a new collaboration dedicated to observing LSNe. I will discuss the effects of microlensing on time delays from Type Ia LSNe, and present a method for controlling them to ~1% precision. Finally, I will show that with the proper computational and observational infrastructure, LSNe can enable exciting new observations—such as shock breakout in strongly lensed Type IIP supernovae—based on predicting the reappearance of lensed images.
On October 25, 2017, the first discovery of an interstellar object (ISO), 1I/’Oumuamua, was announced to the world after it was detected by the Pan-STARRS telescope in Maui, Hawaii. Initially, the object was thought to be a comet from the far reaches of the solar system in a region known as the Oort Cloud, where objects have extreme orbits that take them careening through the inner solar system at speeds exceeding 60 km/s. Astronomers soon realized that 1I/’Oumuamua could not be an ordinary comet; its speed was too high to be bound to our solar system. As 1I/’Oumuamua reached its closest approach to our Sun, it was moving at 87.7 km/s, about 4.2 km/s too fast for it to be bound to our solar system. Additional observations also showed that it was not cometary, but instead appeared more like an asteroid.
Soon after the Minor Planet Center’s official announcement of 1I, a group of astronomers at the University of Washington — Bryce Bolin (also at B612 Asteroid Institute), Lynne Jones, Daniela Huppenkothen, Joachim Moeyens, Mario Jurić, Željko Ivezić and Andrew Connolly — teamed up with researchers Hal Weaver and Carey Lisse at Johns Hopkins University Applied Physics Laboratory and Yan Fernandez from the University of Central Florida, and rapidly obtained observations at the Apache Point 3.5 m telescope in Sunspot, New Mexico.
The team observed 1I in the New Mexico desert skies, imaging it in three different color filters and obtaining measurements covering a 4-hour lightcurve. Halfway through the observations, the brightness of 1I dramatically increased by 5 times and the object become relatively easy to spot in individual images. After combining the data from APO with observations by other teams, and applying advanced statistical methods, the team found that 1I had a likely rotation period of ~8.1 hours and an unusually high aspect ratio ~6:1. This aspect ratio revealed that the object is shaped like a fingerling potato. In addition, photometric color measurements implied that 1I has surface similar to primitive C and D type asteroids from the asteroid Main Belt and Jupiter Trojan swarms. These results are in agreement with several independent studies of 1I by groups at the University of Hawaii, University of California, Los Angeles and Queen’s University Belfast. The UW results have been accepted to the Astrophysical Journal Letters (Bolin et al., “APO Time Resolved Color Photometry of Highly-Elongated Interstellar Object 1I/’Oumuamua”), with a preprint available at https://arxiv.org/abs/1711.04927.
“Everyone was quite enthusiastic about this so-far unique opportunity to observe an interstellar asteroid. Nothing like this had been seen before except in the realms of science fiction!” said Bolin, the study’s lead author, B612 Asteroid Institute researcher and a DIRAC Postdoctoral Fellow. “It was extremely exciting to be part of this effort to learn more about 1I/’Oumuamua before it faded from view. Having a resource like the Apache Point telescope available on short notice made a huge difference in what we could contribute,” added Lynne Jones, an asteroid expert at UW/DIRAC who analyzed ‘Oumuamua’s colors.
Advanced statistical methods played a role in constraining the period and shape with only a short observational baseline. “It was a great proof of concept how different groups within the new DIRAC Institute can work together in new and unexpected ways! I normally work on black holes, but it turns out many of the statistical methods I think about in that context were really useful here.”, said Huppenkothen. “To get to work on asteroids for a change was a new and exciting challenge for me, and exactly the kind of interdisciplinary work we are hoping to foster at DIRAC.“
In addition to publishing the results, the DIRAC team made all of their raw data and analysis notebooks publicly available. “We are strong believers in making it possible for other researchers to verify, re-use, and build upon our work. Transparency, open data, and open science are one of the core tenets of both DIRAC and the Asteroid Institute.” said Professor Mario Juric, Bolin’s postdoctoral advisor at the University of Washington.
Petar Zečević is a PhD student from University of Zagreb, Croatia. He has been working in the software industry for more than 15 years, as a full-stack developer, consultant, analyst, and team leader. Petar is the author of Spark in Action book (Manning, September 2016). He also gives talks on Apache Spark, organizes monthly Apache Spark Zagreb meetups, and has several Apache Spark projects behind him.
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 email@example.com 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.