Infrared Investigations of the Composition and Structure of Nearby Protoplanetary Disks

Near- to far-infrared imaging and spectroscopy of nearby (pc), low mass pre-main sequence stars that are orbited by gaseous and dusty circumstellar disks allow astronomers to probe the chemical composition and structure of protoplanetary disks, and further understand disk evolution and planet formation processes. In this dissertation, I present an infrared imaging and spectral analysis of the young star-disk systems V4046 Sgr, T Cha and MP Mus. V4046 Sgr is a nearby (D~73 pc), ~20 Myr-old spectroscopic binary surrounded by a large (R~350 AU) circumbinary disk. T Cha and MP Mus are similarly nearby (Dpc) and young (old) single-star systems orbited by relatively gas-rich circumstellar disks. Both V4046 Sgr and T Cha display evidence for recent or ongoing planet formation in the form of large inner disk holes detected via submm imaging. Spitzer and Herschel spectroscopy of V4046 Sgr reveals emission from atomic and molecular species (e.g., [Ne II], [O I], OH) suggesting that high-energy photons from the central stars are driving the disk chemistry. Modeling of the Spitzer spectra reveals the presence of large (um-sized) dust grains and a high crystallinity fraction, signifying that grain growth and planet formation may be occurring within the inner disk hole. Analysis of the Spitzer and Herschel spectra of T Cha and MP Mus reveal that MP Mus shows emission from [O I] and has a high mass fraction of crystalline dust, whereas T Cha shows emission from [Ne II] and has a low crystallinity fraction. Polarimetric/coronagraphic imaging of V4046 Sgr at near-infrared wavelengths with the new Gemini Planet Imager (GPI) traces starlight scattered off small

A Combined Spitzer and Herschel Infrared Study of Gas and Dust in the Circumbinary Disk Orbiting V4046 Sgr

We present results from a spectroscopic Spitzer and Herschel mid-to-far-infrared study of the circumbinary disk orbiting the evolved (age ~12-23 Myr) close binary T Tauri system V4046 Sgr. Spitzer IRS spectra show emission lines of [Ne II], H_2 S(1), CO_2 and HCN, while Herschel PACS and SPIRE spectra reveal emission from [O I], OH, and tentative detections of H_2O and high-J transitions of CO. We measure [Ne III]/[Ne II] < 0.13, which is comparable to other X-ray/EUV luminous T Tauri stars that lack jets. We use the H_2 S(1) line luminosity to estimate the gas mass in the relatively warm surface layers of the inner disk. The presence of [O I] emission suggests that CO, H_2O, and/or OH is being photodissociated, and the lack of [C I] emission suggests any excess C may be locked up in HCN, CN and other organic molecules. Modeling of silicate dust grain emission features in the mid-infrared indicates that the inner disk is composed mainly of large (r~5 um) amorphous pyroxene and olivine grains (~86% by mass) with a relatively large proportion of crystalline silicates. These results are consistent with other lines of evidence indicating that planet building is ongoing in regions of the disk within ~30 AU of the central, close binary.Comment: 33 pages, 9 figures, 3 tables. Accepted for publication in Ap

The Birthplace of Tatooine: Infrared Observations of a Planet-forming Disk Around Twin Young Suns in Sagittarius

V4046 Sagittarius is a young binary star system that is located a mere 200 light years from Earth and is orbited by a gaseous circumstellar disk. Most young stars dissipate their disks after only 3 million years or so, but V4046 Sgr is believed to be roughly 12 million years old and still accreting disk material onto its twin young suns. We present a preliminary analysis of the composition of this circumbinary disk via infrared spectroscopy from both the Spitzer and Herschel Space Telescopes. We find numerous emission lines of atomic gas and volatile molecules, including water, in the disk. Other observations suggest that the disk around V4046 Sgr has an inner gap that may have been caused by planet formation. Our spectroscopic results concerning the composition and processes occurring within this disk will help us determine why the disk is still present, the composition of any planets forming in the inner gap, and the overall structure and evolution of this system