Research
Dr. Harrison's main research interest is cataclysmic variables (CVs),
concentrating
on their fundamental properties: distances, component masses, luminosities
and abundances. He has led or participated in several astrometric projects to
measure the distances to cataclysmic variables (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 using the IRTF, Keck, and Gemini. These data reveal
that the secondary stars are peculiar with highly unusual abundance patterns.
This suggests that their evolutionary history must be different from the
currently accepted paradigm. Graduate student
Joe Wellhouse is constructing
stellar atmosphere models using MOOG to provide quantitative abundance
measurements for CV secondary stars. Harrison is extending this work to X-ray
binaries that have black hole primaries using high resolution K-band spectra
obtained at Keck.
Another prominent research area is magnetic cataclysmic variables. Graduate
student Ryan Campbell is finishing a PhD thesis that models the cyclotron
spectra of "polars", cataclysmic variables with highly magnetic white
dwarf (B > 10 MG) primaries. As cited below, we have used the Spitzer Observatory
to examine the mid-infrared spectra of Intermediate Polars (systems where
B < 10 MG on the primary white dwarfs), finding that
synchrotron emission is probably an important process in these objects.
He has a current project in collaboration with Michael Rupen of the VLA
to obtain deep radio observations to confirm this. Accepted, but not
scheduled, are Suzaku observations of the Intermediate Polar GK Per to look
for the hard X-ray tail that could be detected if synchrotron emission is
present.
In addition, Dr. Harrison is also part of two large HST projects that are
using the FGSs to measure the masses of explanets, and determine whether
their orbits are co-planar. Other research interests include X-ray, infrared and radio observations of Low
Mass X-ray Binaries (with Jillian Bornak), and the automated
indentification of variable stars (with Doug Hoffman).
Instrumentation
With Professor Holtzman, Harrison has obtained an NSF grant under the PREST
program to help revitalize the NMSU 1m telescope. Included in the upgrades
is a new instrument, the NMSU High Speed Photometer. This instrument employs
Avalanche Photodiode detectors that have greatly improved quantum efficiency
over the older photomultiplier tube-type detectors. This instrument can
obtain high speed photometry simultaneously in UBVRI. One of the goals
is to obtain light curves for transiting exoplanets, along with a variety
of projects on CVs and pulsating stars. The instrument was designed and built
by undergraduate students, and several such students continue to be employed
in the deployment and calibration phase of the project.
Teaching
Dr. Harrison currently oversees the Astronomy 110 laboratories which includes
the development of new labs, as well as maintenance of the campus observing
facilities (two Meade 12" telescopes). He has taught "Introduction to Astronomy"
[ASTR-110],
"Revolutionary Ideas in Science"
[ASTR-301], and
"Into the Final Frontier" [ASTR-308]. He recently supervised the graduate
seminar for Spring 2004 [ASTR-500].
Selected Publications...
Cyclotron Modeling Phase-Resolved Infrared Spectroscopy of Polars. I. EF Eridani
Campbell, R. K., Harrison, T. E., Schwope, A. D., & Howell, Steve B. 2008,
ApJ, 672, 531
Spitzer IRS Spectroscopy of Intermediate Polars: Constraints on Mid-Infrared
Cyclotron Emission
Harrison, T.E., Cambell, R. K., Howell, S. B., Cordova, F.A., & Schwope, A. D. 2007, ApJ, 656, 444
The Nature of the Secondary Star in the Black Hole X-Ray Transient V616 Mon
Harrison, T.E., Howell, S. B., Szkody, P., & Cordova, F.A. 2007, AJ, 133, 162
Why Are the Secondary Stars in Polars So Normal?
Harrison, T.E., Howell, S. B., Szkody, P., & Cordova, F.A. 2005, ApJ, 632, L123
The Detection of Abundance Anomalies in the Infrared Spectra of Cataclysmic Variables: Shorter Period Systems
Harrison, T.E., Osborne, H.L., & Howell, S. B. 2005, AJ, 129, 240
Phase-Resolved Infrared H- and K-Band Spectroscopy of EF Eridani
Harrison, T.E., Howell, S. B., Szkody, P., Homeier, D., Johnson, J.J., & Osborne, H.L.
2004, ApJ, 614, 947
