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Project Progress

During this reporting period, Mr. Avi Mandell was a graduate student at the Pennsylvania State University, pursuing his Ph. D. under the joint mentorship of Prof. Steinn Sigurdsson (of the Penn State Astrobiology Team) and Michael Mumma (GCA P. I.). His thesis topic is a two part study: the re-formation of water-rich worlds after migration of a Jovian-mass planet through the terrestrial-planets region of exoplanetary systems, and 2. the investigation of chemistry and physics of proto-planetary disks through a new molecular marker. Part 2 was performed while Mr. Mandell was in residence at Goddard, and formed part of an ongoing collaboration with GCA co-I Prof. Geoffrey A. Blake (Calif. Inst. Tech.). This work establishes OH as only the second infrared molecular probe (after CO) of these disks.

Mandell detected OH ro-vibrational emission from proto-planetary disks near two Herbig Be stars, AB Aurigae and MWC 758. The targeted emissions fall at wavelengths within the range 2.9 – 3.6 μm, and are formerly known as the P-branch of the OH 1-0 fundamental vibrational band. GCA-member Boncho Bonev characterized these spectral emissions as part of his Ph. D. dissertation, forming the background for Mandell’s work, and NPP Geronimo Villanueva guided the spectral reductions.

Mandell used the NIRSPEC cross-dispersed echelle grating spectrometer at the Keck-2 telescope (Mauna Kea, HI). He developed a double-differencing approach that permitted removal of the stellar continuum overlying the much-weaker OH emission lines. He measured the spectral line shapes (velocity profiles) for the detected OH lines, and compared them with CO lines observed near 4.7 μm. He showed that the two molecular systems have consistent velocity profiles and likely are formed in the same physical region of the circumstellar disks. He then extracted rotational temperatures by applying a standard Boltzmann analysis to six OH doublets, showing that the rotational temperature of OH was intermediate to that of CO in each stellar system.

Mandell next won time for follow-up observations with the CRIRES spectrometer at ESO’s Very large Telescope (Paranal, Chile). CRIRES covers the same wavelength range as NIRSPEC but with improved velocity resolution (3 km/s) and better spatial resolution (0.1 arc-seconds). These data were acquired but have not yet been received from the observatory. They will be analyzed in the next reporting period.

Leadership:

Mandell organized AbGradCon 2007 (San Juan, PR 14-15 June 2007), co-sponsored by NAI. AbGradCon is a Conference for graduate students and 1st-Term Postdoctoral Fellows, and was held in conjunction with BioAstronomy 2007.

Conference Presentations:

Mandell, A. M., S. Sigurdsson, M. J. Mumma, G. A. Blake, et al. 2007, “First Detection of Warm OH in the Planet-Forming Regions of Gas-Rich Circumstellar Disks”, Oral presentation at BioAstronomy 2007, June 2007 (San Juan, Puerto Rico, 16-20 July).