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Robert J. Thornton, Jr.

Department of Physics


My primary research is in astronomical instrumentation - designing and building instruments for large telescopes in places like Hawaii and Chile. When time permits (which is rare), I get to use these instruments to do some interesting science. You will also see that I have been guilty of pursuing other research areas when astronomy-related funding has been particularly bleak. Below is a list of current and past projects I have been involved with.

Atacama Cosmology Telescope
The Atacama Cosmology Telescope is a 6-meter telescope whose goals are to improve measurements of cosmological parameters that describe the early universe and to measure distant clusters of galaxies. ACT is located at an altitude of 17,000 ft. in a remote region of northern Chile. I began working on ACT in 2005 as one of the principal designers of its commissioning camera. With this camera ACT was able to make several key findings, including the first evidence of Dark Energy using only CMB data as well as the first detection of the gravitational lensing of the cosmic microwave background. For more information, the official ACT website can be found at http://www.princeton.edu/act/. The PI of the project is Lyman Page.

ACTPol is a new polarization-sensitive receiver for the ACT telescope. In addition to being polarization-sensitive, it is projected to substantially improve upon the temperature sensitivity of the MBAC receiver. One of the primary science goals of the instrument is to measure the intrinsic temperature and polarization CMB anisotropy at high-multipoles to probe the spectral index of inflation, the primordial helium abundance, and neutrino properites. Another important science driver is to measure the gravitational lensing of the CMB both in temperature and polarization to constrain early dark energy and the sum of the neutrino masses. The completed instrument will feature two 150 GHz arrays and one multichroic array with simultaneous 90 GHz and 150 GHz sensitivity. Each array consists of 1000 TES bolometers. The reciever is cooled using a custom-designed dilution refrigerator with a base temperature of approximately 80 milli-Kelvin. The ACTPol receiver was deployed with its first 150 GHz array in early 2013, and is predicted to be fully functional with all three arrays in mid-2014.


MUSTANG-1.5 on the GBT

MUSTANG-1.5 is a 32-feedhorn bolometer camera which will be commissioned on the 100-meter Green Bank telescope in late 2013. It is being developed by a collaboration including the University of Pennsylvania, NIST, NRAO, the University of Michigan, and Cardiff University. Similar to ACTPol, the detectors will be feedhorn coupled, with two linear polarizations per feed. The field of view will be 2.5 arcminutes, much larger than the 40 arcsecond FOV of its predecessor. As shown in the CAD cross-section on the right, the receiver design incorporates a tilted refrigerator and receiver rotator (the latter not shown), resulting in much lower dependence of colling performance on telescope elevation. Due to my heavy time commitment to ACTPol, my involvment with this project is only peripheral, unfortunately. The eventual goal is to expand the instrument to a much larger bolometer camera (MUSTANG -2).

Medical Nuclear Magnetic Resonance

In between my time in Hawaii and the University of Pennsylvania, I worked in medical imaging research with a diverse group of physicists, radiologists, neuroscientists, and oncologists at the Baylor College of Medicine and Texas Children’s Hospital.  The figure at the right shows a region in the frontal/parietal lobe that was selected to perform a technique called two-dimensional chemical-shift imaging, which can be used to quantify important brain metabolites including creatine, glutathione, and N-acetyl aspartate, that affect a vast number of neural processes.  More details on this and related research can be found in Hunter et al. and Thornton et al.

Air Force AEOS Telescope

My dissertation at the University of Hawaii was building a dual visible and near-infrared spectrograph for the U.S. Air Force Advanced Electro-Optical System (AEOS) telescope atop Mt. Haleakala on Maui.  One of the most distinguishing features of the spectrograph was its high spectral resolution (10,000-50,000), which allows the atmospheric OH lines, a hindrance to astronomers doing spectroscopy at these wavelengths, to be sufficiently resolved.  Achieving adequate sensitivity between the OH lines for useful science was made possible with the low read noise and dark current of the large-format HgCdTe detectors in the HAWAII array development program.  The inside of the infrared cryostat is shown on the left.  The instrument is best suited for stellar research, and the first data were obtained with the visible channel to study active M star flares.  After I left Hawaii, the project PI, Jeff Kuhn, and David Harringtown upgraded the visible arm of the spectrograph into a spectropolarimeter. More details can be found in Thornton et al. and Harrington et al.

Active Galactic Nuclei

Although the majority of my time is spent designing new instruments, active galactic nuclei have been of my observational interests in astronomy.  These regions exhibit properties considerably different from those of “normal galaxies,” including strong emission lines (e.g., H-alpha, [OIII]) having large line widths, complex geometries and dynamics, and non-thermal radiation over a broad range of frequencies.  AGNs are thought to have existed at some point in the lives of most, if not all galaxies, and therefore are an important part of understanding galaxy evolution.  Shown are spectra obtained of the luminous radio galaxy Cygnus A (3C405) by Alan Stockton and Susan Ridgway, with whom I worked on the project.  The visible spectrum [left panel] was obtained from the W.M. telescope and the IR spectrum [right panel] from the United Kingdom Infrared Telescope (UKIRT).   More details can be found in Thornton et al.

Gemini Near Infrared Imager  

The first major project I worked on as a graduate student was the the primary near-infrared imaging instruemtn for the Gemini North 8-meter telescope. The Gemini Near-InfraRed Imager (NIRI), featured three different pixel scales to match different operating modes of the Gemini telescope. Polarimetry and spectroscopic observations were also available with the instrument. NIRI featured an on-instrument wave-front sensor, which provided centroid and focus information to the tip-tilt secondary mirror and astigmatism measurements to the primary mirror support system. I worked on this project when I was a new graduate student and still taking classes, so my contributions were only modest. The PI of the instrument, and my future dissertation advisor, was Klaus Hodapp. The picture on the right shows the back side of the telescope, at the bottom of which is the instrument support structure where all Cassegrain instruments (including NIRI) mount.



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