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Award-Winning Graduate Student Research at the IfA:

From Brown Dwarfs to Gamma-Ray Bursts

Three students present their research work that won
the Friends of the IfA masters-level research awards

Monday 28 January 2008 at 7:30 p.m.
IfA Manoa Auditorium

binary stars with brown drarfs
Credit: D. Looper & M. Liu

Brown Dwarfs: Filling the Mass Range between Planets and Stars
speaker by Dagny Looper
Brown dwarfs are substellar objects with masses between that of normal stars and planets. They are too small (less than about 75 times the mass of Jupiter) to fuse hydrogen in their cores, and because they do not have a sustainable source of energy like stars do, over time they cool and contract to a size slightly smaller than Jupiter. While the existence of brown dwarfs was first proposed in 1965, the first bona-fide brown dwarf was not identified until 30 years later despite many intensive searches by the astronomical community. The coolest known brown dwarf has a surface temperature of only about 920° C (about 1,700° F), nearly 100° C cooler than the surface of Venus and more than 5,000° C cooler than our Sun's surface. Since they are so difficult to detect, the solar neighborhood could be filled with these cool objects, but we are unable to see most of them. I will give an overview of brown dwarfs, summarize my research in expanding the local census, and discuss what we can learn about the cooling sequence of these objects based on studying them in binary systems.

more on Dagny

gamma-ray bursts
Credit: NASA / SkyWorks Digital

speakerGamma-ray Bursts by Emily Levesque
Gamma-ray bursts are the signatures of extraordinarily high-energy events occurring throughout our universe. Some of them are the signature of the death throes of very massive and rapidly rotating stars. The final moments in a star's life are thought to be determined mostly by properties they acquired at birth, such as their mass and rotation rate, but can also be affected by the surrounding environments as the stars evolve. The particular properties and environments that must be present for gamma-ray bursts to occur are still a mystery. By observing galaxies where gamma-ray bursts have occurred, we can begin to understand the formation, evolution, and details of these enigmatic objects.

more on Emily

starbursts and AGN 
NASA/JPL-Caltech/C. Lonsdale (Caltech/IPAC) and the SWIRE Team
Bridging Starbursts and AGN
in the Ultra-Luminous Infrared Galaxies

speakerby Tiantian Yuan
If you had an eye that could see light at all wavelengths, and you looked at all the galaxies in the sky, you'd find that the most luminous ones are those whose energy peaks in the far-infrared part of the spectrum.  These galaxies are known as ultra-luminous infrared galaxies (ULIRGs). Their high infrared luminosity is caused by the merger of  gas-rich galaxies. ULIRGs have been thought to be a transition stage between starburst galaxies, which emit most of their light from stars, and active galactic nuclei (AGNs), whose light is created by gas being sucked into black holes. Using a new classification scheme from the Sloan Digital Sky Survey, we have found a class of starburst-AGN composite galaxies within the ULIRG population.

more on Tiantian

Dagny Looper went to college at Caltech and University College London, receiving her BSc in Astrophysics in 2004. As an undergraduate, she studied transiting extrasolar planets with David Charbonneau and brown dwarfs with Davy Kirkpatrick. She worked as an assistant researcher at Caltech's Infrared Processing and Analysis Center for a year before coming to the Institute for Astronomy as a graduate student in 2005. Dagny is a Caltech Presidential Scholar, Mellon Mays Fellow, and Research Science Institute alumna. She and her teammates won the English Women's College Football (soccer) Cup in 2004. She is also interested in kayaking and hiking.

Emily Levesque grew up in southeastern Massachusetts and received her bachelor's degree in physics from MIT. She is currently in her second year of graduate school at the IfA and will begin work on her Ph.D. thesis this semester. Her past research and publications have covered topics such as active galactic nuclei, galaxy environments, light element abundances in stars, radio-astronomy-based searches for deuterium (heavy hydrogen), the physical properties of massive stars, and the environments of gamma-ray burst host galaxies.In her spare time she enjoys any activities that get her outdoors, particularly backpacking, skiing, rock climbing, hiking, and biking. She also enjoys writing and is currently trying to get some of her work published.

Tiantian Yuan was born in Chongqing, a city in southwest China. She received her BS from the Department of Astronomy of Beijing Normal University in 2006 and is now a second-year graduate student at IfA. When she is not studying astronomy, Tiantian enjoys jogging and hiking. She says, "I'm fascinated by our physical universe, and want to share what I've learned with you."

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