I study planet-forming disks around nearby young stars using submillimeter interferometers, principally ALMA in Chile, and the SMA and JCMT on Maunakea. I also use optical and infrared telescopes to characterize the host stars. My previous work included large scale molecular cloud structure and clustered star formation. These subjects link to my current focus on disks through the broad goal of placing our solar system in context, and reconciling astronomical observations with meteoritic constraints on our origin.
Understanding the origins of our Solar System and the tremendous diversity of exoplanetary systems are key questions in modern astronomy. Primarily using (sub-)millimeter wavelength telescopes, we have been measuring the dust and gas content of protoplanetary disks in different regions to learn about the initial conditions and timescale for forming exoplanets. The Atacama Large Millimeter Array has revolutionized many of the issues discussed in our pre-ALMA review.
We can readily measure the solid content (aka dust) in protoplanetary disks from millimeter continuum observations. Measuring the gas mass is much harder but we think we have a way and we are currently working on expanding our parametric modeling to infer gas surface densities. This is now being applied to new large ALMA surveys.
During my ~30 years as an astronomer, I have followed the advances in radio instrumention to go from studying molecular clouds to individual star formation in dense cores and now to planet formation in disks. Some of this work is summarized in a Protostars and Planets IV review, or at this old research page.
The most long-lasting impact of my PhD work is an algorithm, CLUMPFIND, that I developed to analyze the structure in 3-d datasets from spectral line mapping and which, to my amazement, continues to be used today!
- The textbook "Introduction to the Interstellar Medium" was published by Cambridge University Press in 2021 (details available in the teaching tab). A list of peer-reviewed research papers is at the ADS link below
The gas and dust between the stars emit across the electromagnetic spectrum and are found in a range of physical conditions from diffuse plasmas to cold, dense molecules. Through their study we see how quantum processes shape the structure of our Galaxy and fluid mechanics sets the stellar mass scale. The interstellar medium is a very broad subject with layers of complexity, a long history, and a steady flow of new results. This comprehensive yet accessible textbook provides a self-contained one-semester course for advanced undergraduate or beginning graduate students. It is written in a style that students can follow by themselves and allows instructors to use class time to go deeper into the details or show applications to current research. Most figures were created using publicly available data with accompanying Python scripts available online, so that students can learn to analyze real data and create figures for their own research.(published 2021)
A two credit seminar series for graduate students and senior undergraduate astrophysics majors who wish to learn about the science and methodology of observations at radio wavelengths. The course will include lectures and reading from an assigned free online textbook but the majority of the students’ work (and grade) will be the construction and operation of a basic telescope to map the HI line in the Galaxy using a software defined receiver.
A research seminar consisting of online and asynchronous lectures with individual mentoring for each registered participant. The time is split approximately 50/50 between the formation of stars from dense cores in the ISM and the planetary systems in the disks found around these young stars. I cover the basic theory and key observations and highlight current areas of active research.
This is the one core course that is required of all graduate students in the Astronomy program. It introduces fundamental conccepts that you will find yourself using throughout your PhD research. By the end of this class, you should know how the optics and detectors on telescopes (especially those on Maunakea) work, how to acquire data, and how to analyze it.
(taught 2017, 2018, 2019)
The Interstellar Medium (ISM) is the gas and dust between the stars. Stars form from it, their winds and supernova enrich and replenish it. Temperatures in the ISM range from the very hot, ~106 K, to the very cold, ~10 K. Densities span an even wider dynamic range, from less than 10-3 to greater than 106particles per cubic centimeter. Even the highest densities, however, are far more rarefied than the best vacuums currently attainable on Earth and thus the ISM allows us to explore physical processes in unique environments. This course will discuss observations and theories of a wide range of ISM environments from pervasive diffuse, ionized gas to dense, molecular clouds and star forming regions. In the last part of the course, we will transition from interstellar to circumstellar material (i.e. disks) as this is an active area of research at the IfA.
(taught 2004, 2006, 2008, 2009, 2012, 2014, 2016)
Estimation is an essential skill for astronomy and life in general. This course will introduce students to the utility of order of magnitude calculations and practicing the ability to “think on your feet”. I will give short overviews of basic physical concepts but the majority of the class time will be spent interactively, with students tackling pre-assigned problems at the whiteboard. If time permits, I will challenge the class by extending the problem or asking a new, unseen question.
(taught Spring 2015)
This series of seminars will introduce students to radio astronomy and inteferometry. The course will be split roughly evenly between lectures on the techniques and applications of observing at submillimeter wavelengths and practical work using real data. For the latter, we will use ALMA science verification datasets and work through the associated tutorials on data reduction and analysis. Students will need a laptop computer running (Mac OS) unix or linux. The goal is for students to learn the skills of submillimeter astronomy and interferometry so as to be able to propose for SMA, ALMA, or JVLA observations in their chosen science area.
(taught Spring 2003, Spring 2013)
How did the Earth and other planets form? How common are planets around other stars, and what are their properties? These questions are at the forefront of the earth and space sciences and are the modern manifestations of questions about our origin and uniqueness that are probably as old as human consciousness itself. Observations and measurements have almost always preceded theory in this field of inquiry, and hence this course is structured according to the three windows through which almost everything has been learned in this field: (1) astronomical observations of the process of star and planet formation; (2) measurements of early events recorded in Solar System materials, and detection and (3) characterization of planets around other stars.
(co-taught with Sasha Krot and Eric Gaidos, Spring 2006)
This is a non-mathematical, introductory class for undergraduate non-science majors. I give a broad overview of astronomy from planets to quasars. Click on the link above for the course web page.
(taught Spring 2005, Fall 2010)
AURA Member Representative, 2014 – present
ALMA Science Advisory Committee, 2007 – 2008, 2010 – 2012
ALMA North American Science Advisory Committee, 2005 – 2008 (Chair, 2006-2007), 2010 – 2012
JCMT Board member, 2003 – 2006, 2008 – 2014
SMA Advisory Committee, 2003 – 2006
CSO Time Allocation Committee, 2002 – 2006
AAS Committee for the Status of Minorities in Astronomy, 2002-2007
Editor of the Test Bank for The Cosmic Perspective. 2000-2006
Participant in AAS Congressional Visits Day, 2001
Panelist for NSF, NASA, ERC grant review committees 2002+
Panelist for ALMA, HST, NRAO, and NOAO time allocation committees 2000+ (HST panel chair 2014)
Referee for Nature, Science, ApJ, AJ, A&A, MNRAS, PASJ, Ap&SS
SOC for >10 meetings from 2005+
Graduate Chair, 2015 – 2016
Faculty Chair, 2012 – 2014
Astronomy Personnel Subcommittee, 2011 (Chair)
Graduate Research Oversight Group, 2011 – 2015
Director Search Committee, 2011
University Research Council, 2008 – 2011
Faculty Advisory Committee, 2006 – 2009
Faculty Review Committee, 2006 – 2009
Scientific Staff Screening Committee, 2009 – 2012
Graduate Admissions Committee, 2004 – 2006 (Chair, 2006), 2010-11, 2015-2018
Qualifying Exam Committee, 2005 – 2006, 2009 – 2011, 2016-2018
Telescope Time Allocation Committee, 2003 – 2005, 2011, 2018++
- PI of NSF, NASA, and NRAO grants
- NSF CAREER awardee
- NRAO Jansky fellow
- The Berkeley Fellowship for Graduate study
- Scholarship, Queens' College, Cambridge University
- Megan Ansdell (Phd 2017)
- Chris Beaumont (PhD 2013)
- Geoff Mathews (PhD 2012)
- Rita Mann (PhD 2010)
- Sean Andrews (PhD 2007)
- Sandrine Bottinelli (PhD 2006)
- Catherine Garland (PhD 2004)
- Greta Guidi (visiting PhD student from Arcetri 2016-2017)
- Christian Flores (699-1 MS 2016)
- Conor McPartland (699-2 MS 2015)
- Ehsan Kourkchi (699-1 MS 2013)
- Will Best (699-2 MS 2012)
- Nicholas Lee (699-2 MS 2010)
- Chian Chou-Chen (699-1 MS 2009)
- Nienke van der Marel (2015-2017)
- Lucas Cieza (2010-2014)
- Jagadheep Pandian (2008-2011)
- Jon Swift (2005-2008)
- Thomas Stanke (2003-2005)