Ronald G. Probst

CTIO Scientific Staff

Areas of Interest

Star Forming Regions, Low Mass Stars, Infrared Imaging Instrumentation

Recent Research Results

Infrared astronomy has been largely technology driven. Over the past decade, NOAO's deployment of sensitive, large format infrared detector arrays in robust and flexible imaging systems has brought an immense increase in scientific capability to the astronomical community. A part of Probst's research has been to apply this capability to the study of photodissociation regions: the boundary layers between hot, thin, ionized gas and cold, dense, molecular material. These layers are associated with stellar birth, as hot young stars carve holes in their natal dust clouds; and stellar death, when radiation from newly exposed inner portions of a star interacts with material ejected earlier from its outer layers. One of the best techniques for tracing these regions is imaging in the 2.12 mm line of molecular hydrogen. The morphology itself offers insight into the processes at work, and quantitative measurement of radiation at this wavelength is a guide to the energy exchange. While on sabbatical at CTIO, Probst has assembled a special purpose small telescope and coupled it to a facility IR camera equipped with custom filters. This permits imaging of H2 emission over an area the size of the full Moon in a single picture, a unique and powerful capability for mapping extended faint structure. Probst has applied this technique to the molecular cloud in which the Orion Nebula is imbedded in order to trace the complex H2 morphology of this nearby region of massive star formation. He has also extended this work to H2 imaging of star forming regions in the Large Magellanic Cloud with the CTIO 1.5-m telescope. Use of a large telescope on a more distant object enables comparisons at the same linear scales. A surprising result is the complex and extensive H2 morphology of the 30 Dor region, a more energetic region of star formation than Orion which serves as a stepping stone to the starburst phenomenon seen in more distant galaxies.

Future Research Plans

Probst plans to follow up this work with additional infrared imaging and spectroscopy of star forming regions in the Large Magellanic Cloud. Higher spatial resolution provided by larger telescopes, together with IR adaptive optics soon to be implemented at CTIO, will improve the morphological understanding of the 30 Dor H2 complex. Imaging in other infrared lines, made possible in part by the deployment of new detectors, will enable determination of dust extinction. This helps to disentangle the actual three-dimensional structure of this star forming region. H2 emission can be induced by the impact of a shock front on neutral material, or as fluorescence caused by radiation of the appropriate wavelength. Infrared spectroscopy will allow discrimination between these much different physical mechanisms by measurement of H2 line strengths. It may also be possible to infer the neutral hydrogen content of the LMC directly, a fundamental and poorly understood parameter for study of the star formation process in an environment much different from our own surroundings in the Galaxy. Together with Monica Rubio (U. of Chile) as principal investigator, Probst will use the SEST telescope at ESO for high resolution millimeter wave maps to trace the spatial and density structure of cold molecular gas around 30 Dor.


Probst's staff position as a Support Scientist requires him to spend the bulk of his time in service activities. As a member of the KPNO Infrared Group, he has been centrally involved in the development and deployment of infrared imaging systems over the past ten years. This involves close interaction with engineering staff during design and construction, in order to deliver a scientifically capable, technically maintainable, astronomer friendly instrument; and with scientific users at the telescope, so that they may get the most out of an instrument's capabilities. His most recent, multiyear endeavor has been as Project Scientist for the Cryogenic Optical Bench (COB), an advanced imager with multiple spatial and spectral filtering capabilities. After bringing this instrument from conceptual design through construction to deployment at the focal plane as a facility instrument, Probst was Project Scientist for its upgrade to high spatial resolution capability in the Diffraction Limited IR Imager (DLIRIM) project. As part of a rebalancing of instrumental resources between CTIO and KPNO, COB will be upgraded to a larger detector and redeployed permanently at CTIO, where it will serve as the science sensor in a tip-tilt adaptive optics system on the 4-m telescope. Probst will accompany the instrument to Chile, transferring to the CTIO staff for a three year period. He will be responsible for bringing this combination on-line as a user facility. As a part of his continuing support of facility IR instruments, Probst provides assistance to potential observers in the preparation of technically competent proposals and does feasibility review on all IR imaging proposals received in our biannual cycle. In addition to his service in the Infrared Group, Probst recognized the benefits to be gained from a systematic, mountain-wide program of collimation and related optical work on facility telescopes. He therefore created the position of Optics Scientist and served in this role for two years, coordinating engineering and mountain technical staff in the improvement of delivered image quality at all KPNO focal planes. This initial effort led to the creation of a new scientific staff position with enlarged responsibilities, subsequently filled by C. Claver. Finally, while on sabbatical at CTIO, Probst has been working with operations staff to prepare the infrastructure necessary for receipt, maintenance, and operation of COB and other large infrared instruments which will be deployed there.

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NOAO is operated by the Association of U niversities for Research in Astronomy (AURA), Inc. under cooperative agreement with the National Science Foundation
Posted: 06Dec1996