Student Research Group


In the summer of 2014, Jackie Pezzato ('17) and Randy Doyle ('16) worked with me on projects involving the interpretation of X-ray spectra of massive stars. I presented some of their preliminary results at a meeting in 2014.

dnp slide 1   dnp slide 2

In November 2015, I gave a presentation about my group's massive star research to inform students about our research and about opportunities to join the research group. I will not be taking new students in the summer of 2016, but I will be taking two new students in the fall of 2017. Starting by doing some reading, talking, and little bit of paid work in the spring of 2016 is possible. Come and talk to me if you think you might be interested.

Summer Research 2013

Zack Li and Kelley Langhans, both rising sophomores, are working on different aspects of the problems of measuring and modeling the plasma temperature distribution in the shock-heated winds of massive stars.

kelley apec fitting   zack NpT

Summer Research 2012

Astrophysics major Jake Neely ('13) has been working on a project to analyze the X-ray line emission in the O stars ζ Ori and ζ Pup, as measured with the Reflection Grating Spectrometer on the XMM X-ray Telescope. Jake is using these data to derive elemental abundances in these massive stars winds, and address questions related to rotational mixing and chemical evolution in O stars.

Summer Research 2011

Sierra Eckert ('14) and Jackson Goodman ('13) have started working on projects involving X-ray emission line profiles in massive stars. Neither of them were on campus this summer, but they're continuing their projects in the fall.

Summer Research 2010

Tzitlaly Barajas (Cal. State Los Angeles, '12) worked with the Peter van de Kamp Observatory here on campus to study Bp and other magnetic massive stars. While James MacArthur ('11) worked on a new project: using the curve of growth technique to measure the column density and ionization balance in X-ray photoionized neon plasma we're studying at the Z-Machine facility at Sandia National Lab.

To get a sense of other student projects that my student-based research group will be working on in the future, you can check out this brief presentation about potential projects I gave in February 2009. The project on the laboratory astrophysics experiments and modeling is described in the poster by my old student, Michael Rosenberg, who did some preliminary work on the project two summers ago.

Summer Research 2009

James MacArthur ('11), a physics major, worked with some new Chandra observations this summer, with his project continuing into the semester. He presented his preliminary research results at the American Astronomical Society meeting in January (see below). We're working - along with Marc Gagné at West Chester and Leisa Townsley at Penn State - on trying to understand the strong X-ray emission from a pair of binary stars in M17.

Jan. 2010: James MacArthur has presented his preliminary research results at the American Astronomical Society meeting in Washington, DC, with a poster entitled, "The Source of Anomalously Hard X-rays in M17's Central O4-O4 Binary".

james macarthur's cen1 poster   james macarthur at aas


Aug. 2011: James helped out on another project, using his expertise with spectroscopy in crowded Chandra fields. He's a coauthor on our group's study of HD 93129A, one of the most massive stars in the Galaxy.



Vernon Chaplin ('07) has published a paper: "Spectroscopic Measurements of Temperature and Plasma Impurity Concentration During Magnetic Reconnection at the Swarthmore Spheromak Experiment," in Physics of Plasmas that was based on his senior thesis at Swarthmore. Congratulations, Vernon!

vernon's paper images


Erin Martell and Emma Wollman presented a poster about their stellar wind research at the Atomic Processes in Plasmas meeting in Monterey, California in March 2009. They won the prize for the best student poster at the meeting.

Erin and Emma


July 2010: Emma's work on the X-ray line profiles of the massive star, zeta Puppis, has been published.

Aug. 2010: Erin's work on the broad-band X-ray spectral trends among massive stars has been published.


2009: Emma Wollman ('09) studied Greek, and modeled the resolved X-ray line profiles in the Chandra spectra of several massive stars. Erin Martell ('09) studied Latin, and analyzed the morphological trends in the Chandra spectra of over a dozen massive stars.

Emma gave a presentation at the 19th Annual Keck Northeast Astronomy Consortium Student Research Symposium, at Wesleyan University in November 2008, titled, "Spectral Modeling of X-rays from Hot Star Winds." You can look at her talk and read her paper.

Upon graduation, both Erin and Emma received High Honors in their external honors examinations. Erin won the Department's Berman Prize. Emma won the Department's Elmore Prize as well as the College's Lang Award. Erin is now attending the University of Chicago's astronomy and astrophysics program (update: Erin has won a Clare Boothe Luce Fellowship), while Emma is in Caltech's physics program (working with Keith Schwab's research group).

2008:Mike Rosenberg ('08) was a physics major, and entered the Physics PhD program at MIT, continuing his study of plasma physics, after graduating. His research project involved modeling the x-ray photoionization of plasma at the Z-Machine, with applications to astrophysics. This was the basis of Mike's senior honors thesis. In September 2007, Mike presented some preliminary results of his thesis research at the Swarthmore student research poster session, sponsored by Sigma Xi [ppt, png, pdf].

Older graduates include Vernon Chaplin ('07), Mike Kuhn ('07), Steve St. Vincent ('07), Victoria Swisher ('06), Micah Walter-Range ('06), Kevin Grizzard (St. John's College '06), Casey Reed ('05), Nate Shupe ('05), Marty Mudd (Williams '04), Mark Janoff ('04), Rachel Sapiro ('04), Eric Levy ('04), Kate Penrose ('04), Dave Conners ('03), Elliot Reed ('03), Carie Cardamone (Wellesley '02), Stephanie Tonnesen ('03), Roban Kramer ('03), and Allison Adelman (Bryn Mawr '03).

After leaving Swarthmore, these people have done things like worked in Vietnam, worked on science policy at the National Academy of Sciences, gone to law school, to graduate school in international relations, linguistics, physics, and astrophysics, and become a science librarian at a small liberal arts college.

Students who wrote honors theses under David's direction include:

  • James MacArthur ('11), "Laboratory Astrophysics: Spectral Analysis of Photoionized Neon" [pdf]
  • Michael Rosenberg ('08), "Spectral and Hydrodynamic Modeling of X-ray Photoionization Experiments" [pdf]
  • Vernon Chaplin ('07), "High Time Resolution Spectroscopic Measurements of Electron Temperature in the SSX Plasma" [jpg poster or pdf thesis]
  • Nate Shupe ('05), "Modeling Studies of Photoionization Experiments Driven by Z-pinch X-rays" [pdf]
  • Genevieve de Messieres ('04), "XMM-Newton X-ray Spectroscopy of the B2 Bright Giant ε Canis Majoris" [pdf]
  • Roban Kramer ('03), "Modelling O-Star X-Ray Emission Line Profiles" [pdf]
  • Stephanie Tonnesen ('03), "X-Ray Emission Line Profiles from the Magnetically Confined Wind Shock Model" [pdf]
  • Joanna Brown ('02), "Modelling Density Enhanced Shells in the Circumstellar Envelope of the Carbon-Rich AGB Star IRC+10216"


Some of our work is supported through Prism Computational Sciences, in Madison, Wisconsin. Prism is a small company that does basic and applied physics research and code development. It is run by Dr. Joe MacFarlane, who is a long-time collaborator of ours.

Mike Rosenberg used the VisRad view-factor code, from Prism Computational Sciences, to make an animation of the imploding Z-pinch wire array at the Z-Machine facility at Sandia, as part of his senior thesis work.

The students also work closely with Stan Owocki at the Bartol Research Institute at the University of Delaware, and Marc Gagné and his group at West Chester University.

You can also access information about older students and their presentations.


Research Information

Astrobetter – lots of useful information about the nitty-gritty of astronomical research and many aspects of being an astronomy student and astronomer

Astrobites – very short summaries of interesting research papers, written for undergraduates by graduate students; an excellent way to browse the literature or find articles on a given topic

Astronomy Image Explorer – images from refereed papers; browsable and searchable; a good (fun) way to browse papers

Practical, for Group Members

Local computing information

Astronomical Catalogs

Chandra X-ray Center
XMM Guest Observer Facility

ATOMDB atomic database

XSPEC manual

Tutorial on thermal radiation processes, by J. Kaastra. A good (but somewhat technical) place to start answering the question Why do these X-ray spectra look the way they do?


Historical graphics
Edward Tufte
Visualizing Astronomy at the CfA
Information Aesthetics

Student Travel and Research Funding

HHMI travel funding
Sigma Xi travel funding
(these two will fund travel to meetings)

Soffen Memorial Fund
(they fund travel to meetings)
Sigma Xi grants in aid of research
National Geographic Young Explorers
(things like travel to an observatory are eligible)

Professional Organizations

Pathways to Science
Useful collection of many opportunities

Society of Physics Students
Students! You should join the SPS, it's cheap and you get a lot of good benefits

American Astronomical Society

Grad School Information

Choosing a graduate program
The physics grad school shopper
Questions to ask when visiting grad schools

Advice from Career Services about letters of recommendation
and many other topics



Return to David's home page


David Cohen: cohen -at- astro -dot- swarthmore -dot- edu
Last modified: November 11, 2015