2008 Annual Science Report
University of Arizona Reporting | JUL 2007 – JUN 2008
LAPLACE Annual Report Executive Summary
This year has been a substantial one for benefiting from the resources and activities of the previous years. The astrochemistry module, module 1 has been focused on the study of circumstellar material ejected from cool stars because this constitutes about 80% of the material that becomes available for formation of new stars and planetary systems. Four themes have come to the fore:
1) Where is the carbon? Most models have assumed that carbon is mainly present in the form of CO. However observations of oxygen rich stars, especially Supergiants show that to be incorrect. The form of the majority of the carbon is at present unknown.
2) Why are carbon isotopic ratios so widely ranging? Here the analysis of observations shows that in M giant stages (presumably mostly before helium ignition, there must be huge mass loss an mixing to generate the observed C12/C13 ratios. For later stages, in which carbon stars are found for low and intermediate mass, small amounts of injection of helium burning processed materials explain both the carbon/oxygen ratio, and the rise to high values of C12/C13.
3) Phosphorus exists in a variety of gas phase molecules in the stellar ejecta.
PO, PN, HCP, PH3, and CCP have been observed. Particularly intriguing is the detection of the CCP radical, which has phosphorus attached to a C-C bond. Discovery of this molecule was made possible by spectroscopic measurements conducted in collaboration with Dennis Clouthier (University of Kentucky). A new phosphorus source has been developed for one of the spectrometer systems that has not only enabled the measurements for CCP, but several other possible new interstellar phosphorus-bearing compounds, including PCN, HPS, and CH3PH2. Phosphorus is thus taking on forms other than the mineral schreibersite, [Fe,Ni]3P. Astronomical searches are currently being conducted for possible new gas-phase phosphorus molecules.
4) The chemistry and ionization of stellar envelopes is far more complex than had been thought. Oxygen bearing molecules have been found in carbon rich stars and carbon bearing molecules found in oxygen rich stars. There is even indication of appreciable ionization shown by the detection of HCO+ in several of these objects.
Our study of planetary system disks and young stars is module 2 of our work. Data from the Spitzer Space Telescope has been used to study the formation and evolution of planetary systems. Recent observations of warm were used dust to constrain theories of planet formation. Results suggest that the processes thought to have lead to the formation of terrestrial planets in our solar system could be very common around sun-like stars. Follow-up studies include: a) analysis of the disk chemistry using mid-infrared spectra from Spitzer, b) deep sub-millimeter surveys for gas and dust; and c) thermal IR search for planets thought to be the outcome of such processes. We have investigated whether forming planets could be detected as hot proto-planet collision afterglows.
We have reported the detection of organic molecules and water in typical T Tauri disks using high resolution Spitzer spectroscopy in the journal Science. We have explored disk chemistry models to understand the disk physical and chemical conditions that are needed to produce such emission. We have also used high resolution IR spectroscopy of CO fundamental emission to study the gas content and distribution in T Tauri disks. In one transition object CO emission is radially truncated and the possible interpretations include the presence of an orbiting planetary companion. In a complementary study we have used IR molecular absorption spectroscopy to probe the properties of organic molecules in the disk atmosphere of an edge on disk. We have also used high resolution IR spectroscopy to explore the origin of the hot compact excess in MWC 480 detected with interferometry. We found no evidence that the emission is due to hot water emission, in contrast with an earlier study, and explore the alternative explanations.
We are studying how extrasolar planetary host stars are chemically distinct from the general stellar population, displaying significant variations in key planet-building elements such as Fe, C, O, Mg, and Si. These enrichments are primordial in origin, established in the giant molecular cloud from which these systems formed. As a result, the chemistry of planet-building materials in many of these systems is distinctly different from that in our Solar System. Using combined chemical and dynamical modeling of planet formation in known extrasolar planetary systems, they have predicted that terrestrial planets are ubiquitous. Furthermore, the mass and chemistry of these model planets is highly variable. For example, terrestrial planets similar to Earth are believed to exist in the majority of extrasolar planetary systems while on the other hand systems that are enriched in C, regardless of the actual C abundance, produce terrestrial planets that are dominated by carbide phases. In the context of planet formation models within realistic circumstellar disks, they plan to investigate how these compositional variations influencw the interior structure and processes, surface compositions and features, atmospheric chemistry, and the possibility of life.
The analysis of the light curves from their first year of Pleiades observations shows that the solar type cluster members clearly show greater variability in both amplitude and frequency than field stars of similar brightness. G-type Pleiades members have variability amplitudes that are twice as large as those of non-member stars with similar brightness. Indications suggest the need for more frequent sampling of the data because of the rapid rotation of young stars. The first year of observations of solar analogs in the 4 Gyr old cluster M67 are complete and ready for analysis. The chromospheric Ca II H & K survey of a more limited sample of solar-type Pleiades members reveal that the Pleiades sun-like stars exhibit levels of chromospheric activity that are one-half to one order of magnitude greater than the average Sun.
Additional Outreach Activities
We have continued the two series of public lectures, the College of Science series, which was this time about the “Edges of Life”, and the fourth year of our Templeton lectures on Astrobiology and the Sacred. Lecturers for this latter included Ursula Goodenough, Jonathan Lunine, Lisa Kaltenegger, Gregory Benford, Roger Angel, Jennifer Hecht, Lynda Williams and Nick Woolf. Edges of Life speakers were Roy Parker, Jonathan Lunine, Michael Rosenzweig, Anna Dornhaus, Michael Gill and Ray Kurzweil. The audience for these lectures exceeded 1000 per talk. In each of these lecture series the LAPLACE team has been involved in the giving of lectures, the organization of the series and in a display associated with the series at the University Science Library. For each of the events in both series we have also organized teacher-training workshops. Preparations are now underway for the next College of Science series.
Two astrobiology workshops have been conducted at Biosphere 2, supported by the University College of Science. The first was on the theme “Evolutionary Watersheds, Genome or Biome” and the second was on the topic “Astrobiology: enhancing our view of society and ourselves”. The next workshop, planned for 2009 will be “From Stardust to Stardust: Evolution of Organic Chemistry from Interstellar Space to Returned Comet Samples”.
Other activities that have fallen outside the three modules of our organization include studies related to the issue of the future of humanity. Angel is currently following up this work with non-NAI resources, to study reducing the cost of solar electricity production. He is exploring the development of solar electricity from multiple junction solar cells fed by 2-D concentrators. He is using both Steward Observatory Mirror Lab experience in glass technology, and in the design of minimum mass support structures.