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Recent Work
Visit my personal homepage to see the poster I am presenting at the AAS in Austin in January 2012.
Highlights of Academic Career
I double-majored in Physics and Astronomy at Wesleyan University in Connecticut. While I was an undergrad, my summers consisted of working in the Research Department at Cartoon Network - Asia Pacific in Hong Kong, working as a Research Assistant for the Wesleyan University Physics Department, and working as a Research Assistant for the Wesleyan University Astronomy Department. My summer project with the Astronomy Department led to my senior thesis, simulating the formation of a proto-planetary disk. I modeled observations that (at that time) were thought to potentially be the first exo-planet detection to come from observations of flat-bottomed eclipses due to the exo-planet forming a gap in the planetary disk.
While I was at Wesleyan, I was also a member of their ZeroG team. We designed and built an experiment to be conducted in zero gravity. We were accepted into NASA's Reduced Gravity Student Flight Opportunities Program and flew aboard their astronaut-training aircraft. Floating in zero gravity was one of the highlights of my undergraduate career.
Since starting graduate school at NMSU, I have worked on projects involving Mars, OH/IR stars, quiescent novae, and galaxy halos. Two of those projects were summer internships at Arecibo Observatory in Puerto Rico and at the Indian Institute of Astrophysics in Bangalore, India.
Teaching
I was a Teaching Assistant for ASTR 105G, The Planets, from Fall 2005 to Spring 2009. During those eight semesers, I taught 10 lab sections that complemented the lecture portion of the class. This is an introductory Astronomy course that focuses on our Solar System and the techniques and physics that make studying it possible.
Research -- Current Project
I am pleased to acknowledge support from a Consortium for Higher Education (HED) grant for women in the sciences and from a New Mexico Space Grant Consortium Graduate Research Fellowship.
Halo Gas Velocities of Nearby, Edge-on Galaxies: Galaxy halos generally show a decrease in rotational velocity with increasing height above the miplane. This can be explained by the Galactic Fountain model, in which gas is ejected from the disk by supernovae. As the gas rises, its rotational velocity decreases, and it moves radially outward. This results in what is called a lagging halo -- rotational velocities are lower for halo gas than for disk gas. This was originally accepted as the entire reason for a lagging halo. However, simulations of halos show that the galactic fountain alone cannot account for the magnitude of the lag observed in several galaxies. An external source of low angular momentum gas, such as accretion, is needed. Computer models in which ~10% of halo gas is from accretion and ~90% of halo gas is from outflow best match observed velocity gradients.
Recent observations have shown that evidence of accretion (eg, from the IGM, molecular clouds, or companion galaxies) is more common than previously thought. This supports the notion that infalling gas plays a non-trivial role in galaxy halo formation and evolution. Additionally, current star formation rates indicate that most galaxies should have used up all of their gas by now if there were no source to replenish the gas. Since galaxies are still forming stars, there must be an accretion mechanism that is providing new material to form stars.
My PhD project involves measuring velocities of H-alpha-emitting halo gas as a function of height above the midplane in edge-on galaxies in order to measure the magnitude of the lagging halo. I aided in the implementation of a multi-slit spectroscopic setup for this project at the 3.5m telescope at Apache Point Observatory in New Mexico. A slit-mask with a series of uniform, parallel slits allows for simultaneous observations of H-alpha emission at several different radii in a target galaxy. A narrow band filter prevents overlapping of spectra from neighboring slits. This is an ongoing project, and optical observations will be augmented by radio and UV data to characterize galaxy halos. The goal of this project is to determine to what extent halo rotation is coupled to disk rotation by measuring rotatational velocity gradients for a sample of nearby, edge-on galaxies. This has implications for the contributions of infalling gas and outflowing gas to the origin and evolution of galaxy halos. I am collaborating with the HALOGAS team (PI: G. Heald, ASTRON), which is studying cold gas accretion in the local universe. The lags that I measure will be incorporated into their galaxy models, which will further constrain the kinematic characteristics of those galaxies. (Advisor: R. Walterbos, New Mexico State University, 2007-present)
I maintain a site dedicated to the current 'challenges' I am dealing with while working on this project. Click here to see it.
Research -- Previous Projects
Spectroscopic and Photometric Observations of IV Cep 1971: Reduced spectroscopic data and performed photometric observations with the 2.0m Himalayan Chandra Telescope at the Indian Astronomical Observatory, India, of IV Cep 1971, a quiescent nova. Determined a possible period of ~5.1 hours for the system from our observations. This is an ongoing project. Analysis of the spectroscopic data and comparison to previous photometric observations are still being performed. The goal of this project is to determine the spectral types of the primary and secondary stars in this system and to determine a period of the system that is consistent with observations dating back 20 years. Presented my project in a talk at the Indian Institute of Astrophysics, India, August 2008. (Advisor: U.S. Kamath, Indian Institute of Astrophysics, Bangalore, India, 2008)
Mass Loss in High Latitude OH/IR Stars: Simulated detached, expanding dust shells around an AGB star using the public domain radiative transfer code DUSTY. Experimented with mass loss rates and durations in an effort to reproduce the MIR color range observed in OH/IR stars with galactice latitudes greater than 10 degrees. Determined that a mass loss rate of ~3.5E-5 solar masses per year for durations between ~20 and ~200 years best matches observations. Presented my results in a poster at AAS, January 2008. (Advisor: B.M. Lewis, Arecibo Observatory, Puerto Rico, 2007)
Martian Wind Speeds: Analyzed temperature data from the Mars Pathfinder mission. Calibrated temperature measurements to determine surficial wind speeds from lack of heating in temperature sensor wires (stronger winds cause less heating). Calculated preliminary wind speeds. (Advisor: J. Murphy, New Mexico State University, New Mexico, 2005-2007)
Opposition Effect on Saturn's Moons: Wrote an IRAF script to reduce (subtract the overscan, dark subtract, and flatfield) images obtained from the Apache Point Observatory 1.0-meter telescope, display each image and prompt the user to identify an alignment star (if the image is good) or discard the image (if the image is bad), and shift and add all good images from the same night and same field. Images are ready for photometry, with a final goal of extracting a light curve for several of Saturn's moons. (Advisor: J. Holtzman, New Mexico State University, New Mexico, 2006)
Simulation of a Protoplanetary Disk: Using Fortran, simulated the evolution of a planet-containing dust disk around a solar-like T Tauri Star. Wrote IDL programs to create morphological models of and extract light curves from the computer-generated system. Experimented with various initial conditions and tested realistic constraints on the models in a fairly successful attempt to match the data with actual observations of KH 15D, a (then) recently discovered star system that exhibited unprecedented flat-bottomed eclipses hypothesized to arise from the presence of a circumstellar disk. Presented the research process and results in an honors senior thesis project. (Advisor: K. Johnston, Wesleyan University, Connecticut, 2002-2003)
T Tauri Star Rotation Rates: Analyzed data from the most current observing season using Fortran, IDL, and IRAF. Produced light curves and determined plausible rotation periods for variable T Tauri stars, most of which had never been studied or had not yet been found to be periodic. Organized the results in a short paper and compared the findings to data from the previous (and first) observing season. (Advisor: W. Herbst, Wesleyan University, Connecticut, 2002)
ZeroG Test of the Space Station Fire Extinguisher: Designed and built an experiment, as part of Wesleyan University's Zero Gravity team, that tested the safety of fire extinguishers on the International Space Station. The experiment was performed by the team in micro gravity aboard NASA's astronaut-training aircraft at Johnson Space Center as part of NASA's Reduced Gravity Student Flight Opportunities Program. Flew as an alternate with Arizona State University. Spoke about the program and Wesleyan's experiment at three grade schools, two Wesleyan University colloquiums, and a science seminar for high school students. Organized an exhibit and talked to visitors at the Science Center of Connecticut museum. Edited a video with footage provided by NASA for the talks and exhibit. (Advisor: F. Ellis, Wesleyan University, Connecticut, 1999-2001)
Meetings
219th AAS. Austin, TX. January 2012.
HALOGAS Research Meeting. Bochum, Germany. September 2011.
The Role of Disk-Halo Interaction in Galaxy Evolution: Outflow vs Infall. Espinho, Portugal. August 2008.
211th AAS. Austin, TX. January 2008.
Short Talks
- Kinematics of Ionized Gas from Multi-Slit Spectroscopy, New Mexico State University, Las Cruces, NM (January 2010)
Poster: Ionized Gas Velocities for Edge-on HALOGAS Galaxies.
Cat Wu, Rene Walterbos, Rich Rand, George Heald, and the HALOGAS team
27th Annual New Mexico Symposium. Socorro, NM. October 2011.
Poster: Multi-slit Spectroscopy and H-alpha Modeling of Edge-on HALOGAS Galaxies.
Cat Wu, Rene Walterbos, Rich Rand, and the HALOGAS Team
Talk: Update of APO Observations of Edge-on HALOGAS Targets.
Cat Wu, Rene Walterbos, Rich Rand
HALOGAS Research Meeting. Albuquerque, NM. March 2011.
Talk: Modeling of Multi-Slit Spectroscopic Observations.
Cat Wu, Rene Walterbos, Rich Rand
217th AAS. Seattle, WA. January 2011.
Poster: Kinematics of Ionized Gas in Edge-on HALOGAS Galaxies.
Cat Wu, Rene Walterbos, Rich Rand, George Heald, and the HALOGAS team
HALOGAS Research Meeting. ASTRON, the Netherlands. August 2010.
Talk: Kinematics of Ionized Gas from Multi-Slit Spectroscopy.
Cat Wu, Rene Walterbos, Rich Rand
215th AAS. Washington, DC. January 2010.
Talk: Halo Gas Velocities of NGC 4631 from Multi-Long-Slit Spectroscopy.
Cat Wu, Rene Walterbos, Rich Rand
24th Annual New Mexico Symposium. Socorro, NM. October 2008.
Poster: Halo Gas Velocities of NGC 4244 and NGC 891 Using Multi-Long-Slit Spectroscopy.
Cat Wu, Rene Walterbos, Jiehae Choi, Rich Rand
Poster: Halo Gas Velocities of NGC 4244 and NGC 891 Using Multi-Long-Slit Spectroscopy.
Cat Wu, Rene Walterbos, Jiehae Choi, Rich Rand
Poster: Duration of Mass Loss and Mass Loss Rates in High Latitude OH/IR Stars.
Cat Wu, B. Murray Lewis
Poster: Multi-Long-Slit Spectroscopy for Kinematic Studies. II. Initial Results for Edge-on Galaxies NGC 891 and NGC 4244.
Jiehae Choi, Sophia Cisneros, Cat Wu, Maria Patterson, Rene Walterbos
Poster: Multi-Long-Slit Spectroscopy for Kinematic Studies. I. Implementation and Demonstration.
Rene Walterbos, Jiehae Choi, Sophia Cisneros, Maria Patterson, Cat Wu
- Halo Gas Velocities from Multi-Slit Spectroscopy, New Mexico Space Grant Consortium, Las Cruces, NM (October 2008)
- Spectroscopic and Photometric Observations of the Quiescent Nova IV Cep 1971, Indian Institute of Astrophysics, Bangalore, India (June and August 2008)
- Mass Loss Rates in High Altitude OH/IR Stars, Arecibo Observatory, Puerto Rico (August 2007)