Thomas HarrisonResearch Faculty, Observatory Research Specialist NMSUAstronomy
Dr. Harrison’s main research interest is cataclysmic variables (CVs) and other interacting binaries observed across the electromagentic spectraum, concentrating on their fundamental properties: distances, component masses, luminosities, abundances, and emission processes. He has led or participated in several astrometric projects to measure the distances to cataclysmic variables and classical novae (and other astrophysically important stars, such as Cepheid and RR Lyr variables, very low metallicity stars, and planetary nebulae) using the Fine Guidance Sensors (FGS) on the Hubble Space Telescope.
Dr. Harrison specializes in infrared observations, and has obtained infrared spectra of cataclysmic variable stars and X-ray binaries using APO, the IRTF, the VLT, Keck, and Gemini. These data reveal that the secondary stars in these systems are peculiar with highly unusual abundance patterns. This suggests that their evolutionary history must be different from the currently accepted paradigm. Starting as a graduate student project (with Ryan Hamilton), he has developed the ability to create synthetic spectra that span the range from 0.8 microns to 2.5 microns to measure the abundances of the late type secondary stars of CVs. He finds that there are two main abundance anomalies: deficits of both carbon and magnesium. In addition, however, there are several objects that show enhancements of sodium. Two such objects appeared to be best explained as having deficits of hydrogen. He recently used Kurucz’s ATLAS12 program to generate hydrogen-deficient atmospheres to determine if any CV donor stars have such deficits. He found four cases. While there are completely normal main sequence-like secondary stars in CVs, there are others that appear to be the stripped cores of red giants. There are multiple paths for creating a cataclysmic variable.
Another prominent research area is magnetic cataclysmic variables. We have used the Spitzer Observatory and data from the WISE mission to examine the mid-infrared spectra of Intermediate Polars (systems where B < 10 MG on the primary white dwarfs), and non-magnetic CVs finding that synchrotron emission is probably an important process in most CVs. He has also obtained X-ray observations of V1500 Cyg using XMM. These latter data show that the spin rate of the white dwarf is rapidly synchronizing with the orbital period (V1500 Cyg is a highly magnetic system that was knocked out of synchronous rotation by a classical nova eruption in 1975), much faster than had been predicted (200 years). Observations at APO have shown that this object has discrete cyclotron harmonic emission, confirming the apparent synchronization of the white dwarf.
- Nicholas M. Ule, PhD, 2015. “Quantifying Differential Rotation Across the Main Sequence”
- Ryan T. Hamilton, PhD, 2013. “Constraining Photospheric Abundances of Donor Stars in Cataclysmic Variables”
- Jeffrey L. Couglin, PhD, 2012. “Fundamental Parameters of Exoplanets and Their Host Stars”
- Jillian Bornak, PhD, 2012. “A New Approach to Modeling Dust Emission in Classical Novae”
Dr. Harrison currently oversees the Astronomy 105 and 110 laboratories which includes the development of new labs, as well as maintenance of the campus observing facilities (Celestron 11″ and Meade 12″ telescopes). He has taught “The Planets [ASTR-105], “Introduction to Astronomy” [ASTR-110], “Revolutionary Ideas in Science” [ASTR-301], and “Into the Final Frontier” [ASTR-308]. He also supervised the graduate seminar for Spring 2015 [ASTR-500], and taught the now defunct “Observational Techniques II” [ASTR-536].
Selected recent publications (student authors denoted by *):
The Detection of Discrete Cyclotron Emission Features in Phase-Resolved Optical Spectroscopy of V1500 Cygni, Harrison, T. E., & Campbell, R. K. 2018, MNRAS, 474, 1572
A Refined Radial Velocity Curve for the L Dwarf Donor of WZ Sagittae, Harrison, T. E. 2017, PASP, 129, 1242
Determinations of the 12C/13C Ratio for the Secondary Stars of AE Aquarii, SS Cygni, and RU Pegasi, Harrison, T. E., & *Marra, R. E. 2017, ApJ, 843, 152
HD 202206: A Circumbinary Brown Dwarf System, Benedict, G. F. & Harrison, T. E. 2017, AJ, 153, 258
Testing Metal-Poor Stellar Models and Isochrones with HST Parallaxes of Metal-Poor Stars, Chaboyer, B., et al. 2017, ApJ, 835, 152
Abundance Derivations for the Secondary Stars in Cataclysmic Variables from Near-Infrared Spectroscopy, Harrison, T. E. 2016, ApJ, 833, 14
The Apparent Synchronization of V1500 Cygni, Harrison, T. E., & Campbell, R. K. 2016, MNRAS, 459, 4161
Quantifying the Carbon Abundances in the Secondary Stars of SS Cygni, RU Pegasi, and GK Persei,, Harrison, T. E., & *Hamilton, R. T. 2015, AJ, 150, 12
The WISE Light Curves of Polars, Harrison, T. E., & Campbell, R. K., 2015, ApJS, 219, 32
The WISE Light Curves of Z Camelopardalis During Outburst: Evidence for Synchrotron Emission?, Harrison, T. E. 2014, ApJ, 791, L18