Previous REU projects

Observational Stellar Astrophysics (Prof. Bob Mathieu):

As part of the NSF-supported WIYN Open Cluster Study, our group investigates the binary populations of stellar open clusters. Binary stars in clusters are not only the fuel behind cluster evolution, they also provide an intriguing opportunity to explore the interplay between stellar evolution and stellar dynamics.  We use knowledge of binary star populations to study non-standard stellar products for which a coherent picture of formation and evolution is not yet fully understood. Examples of such stellar anomalies include blue stragglers and sub-subgiants.

Another focus of our group is exploring accretion dynamics of young binary systems with circumstellar disks. Remnants from formation, these disks affect the orbits and eventual masses of binary systems. Despite being the most common products of star formation, binary evolution at this early phase remains an open topic of research.

Depending upon the particular interests of students, possible projects could involve measuring precise stellar radial velocities using the multi-object spectrograph of WIYN, developing new techniques to determine parameters for binaries, investigating triple systems using imaging and spectroscopic data, searching for faint stellar companions in anomalous stellar systems, or analyzing new data of pre-main-sequence binaries from the SALT high-resolution spectrograph. An observing run at the WIYN Observatory would be likely.

 

Warm Ionized Medium (Dr. Matt Haffner):

Under the leadership of Prof. Ron Reynolds, Wisconsin has carried out the first survey of the entire galaxy in the H-alpha emission line of ionized hydrogen. These maps show the location and effect of hot ionizing stars, but also indicate the presence of a mysterious, low density ionized gas filling much of interstellar space. The velocity resolution provided by WHAM can allow astronomers to map out the distribution of this gas, while observing other diffuse optical emission lines can characterize the temperature, chemical state, and ionization level of the gas.

 

Th/Ar Spectra for Wavelength Calibration in the Search for Exoplanets (Dr. Elizabeth Den Hartog and Prof. Jim Lawler)

Thorium-Argon (Th/Ar) hollow cathode lamps are commonly used as optical wavelength calibration lamps for high-resolution spectrographs on ground-based astronomical telescopes.  The high atomic weight of thorium and its complex atomic spectrum provide over 20,000 narrow calibration lines, covering wavelengths from 277 nm to 5400 nm. (see the Th/Ar atlas at:  www.nist.gov/pml/spectrum-th-ar-hollow-cathode-lamps) This has made Th/Ar lamps an ideal calibration source for the calibration of optical spectra from high-resolution spectrographs used for exoplanet detection.  Uranium containing lamps are similarly used as calibration sources in the near-infrared. (Redman et al. 2011, ApJS 195:24; Redman et al. 2012, ApJS 199:2)

Recently, however, the quality of commercially available Th/Ar lamps has deteriorated, with molecular bands of ThO that are strong enough to obscure the thorium spectral lines used for calibration. This has become a major concern for the use of these lamps in the future for calibration of astronomical spectrographs. However, if the positions of the ThO lines can be measured, it will be possible to use them in addition to the atomic thorium lines for wavelength calibration.

Previous laboratory measurements of the spectra of Th/Ar hollow cathode lamps have been made using Fourier transform (FT) spectrometry. This technique provides the most accurate wavelength calibration standards. However, this is not a suitable technique for the measurement of weak molecular lines in hollow cathode lamps, as the noise in a spectrum from a FT spectrometer is dominated by the strong lines and is spread out equally throughout the spectrum to obscure the weaker molecular lines. An alternative instrument for measuring the Th/Ar spectrum is the University of Wisconsin high-resolution echelle spectrograph.  This spectrograph has a resolving power of 250,000, and as a dispersive instrument, does not suffer from the noise constraints of an interferometric device like an FT spectrometer.  It is ideal for the measurement and characterization of the weak ThO molecular lines.

This project will involve measuring the spectrum of the Th/Ar hollow cathode lamp with the high-resolution echelle spectrograph.  The spectrum will then be carefully characterized: line wavelengths and relative intensities will be measured; known lines will be identified with their respective energy levels, etc.  Some programming may be required to turn the 2-D CCD spectra into 1-D spectra and extract the wavelength and intensity information.  In collaboration with National Institute of Standards and Technology (NIST) personnel, this data will be added to the Th/Ar atlas cited above.  This NIST atlas will be an important resource for the wavelength calibration of planet-finding spectrographs as well as other high-resolution spectrographs on ground-based telescopes.

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