Sean Brittain

We present spectral data from a small sample of FU Ori stars. High-resolution spectra spanning 2-5 microns were taken with the NIRSPEC spectrograph on the Keck II telescope. These data were examined for near-IR spectral features, targeting H2, H, CO and H2O lines which are characteristic of this class of objects. Even within such a small sample, different spectral properties

We present a comparison of CO infrared emission from the inner circumstellar disks around the Herbig AeBe stars AB Aurigae and HD 141569. The CO emission from the disk of the 2-4 Myr star AB Aurigae shows at least two temperature components, the inner rim (1500K) and the outer flared disk (160K). For both components, the excitation of CO is

We present Brackett-gamma and Balmer Discontinuity observations of a large sample of Herbig Ae/Be candidate stars. Herbig Ae/Be stars are the higher mass analogues of T Tauri stars, and both are young stellar objects accreting material from a circumstellar disk. We determine the mass accretion rates of the stars in our sample by measuring the veiling of the Balmer Discontinuity

As part of an ongoing effort to monitor and classify the small group of known young eruptive variables, we present High Resolution Near-Infrared ( 2-5 micron) spectra of 4 FUor, EXor and FUor-like sources which show emission and absorption features not necessarily indicative of their presumed classification. This work makes clear that the natures of these objects are not well described by singular classic FUor or EXor accretion models and begins to define a continuum of source types. Specifically, ZCMa, an FUor-like system, as well as PV Cep, an EXor system, show CO absorption at 5 microns but exhibit CO emission at 2 microns, while Brackett gamma is also in emission for both. XZ Tau, a purported EXor, shows Brackett gamma is in emission while the CO at both 2 and 5 microns is in absorption. L1551 IRS 5 shows absorption for CO at 2 microns, but shows emission at 5 microns. Weak Brackett gamma absorption is detected for this source. Hence, we discuss the implications of using the ove...

We present the first direct observational verification and theoretical modeling of the stratification of gas and dust in disks around young stellar objects (YSOs). The physical structure of extended flared disks around YSOs depends on a variety of parameters including the extent of gas and dust mixing (i.e. turbulence), the rate of dust settling and the process of grain coagulation. In this work, we present line of sight measurements of the column density of gas and dust for four YSOs having different inclinations and extinctions but similar ages. Because dust particles are expected to settle to the midplane around YSOs, The line of sight gas/dust ratios for each inclination provides a direct measure of the dust settling and indirectly provides a constraint on the midplane turbulence. The measurements provide the first observational evidence and initial quantification of the stratification of gas and dust in the extended disks around very young stellar objects that are probably in t...

We used high-resolution infrared spectra of the heavily embedded T Tauri star HL Tau to search for evidence of absorption due to the R0, R1, and R2 gas-phase CH 4 ν 3 lines near 3.3 μm. From this, we report a 3 σ upper limit of 1.3× 10 15 cm-2 for the CH 4 gas column ...

In this study, we will report a new upper limit on the luminosity of H3+ emission from the exoplanet host Tau Boo. Using high-resolution NIR spectra data collected with cshell on the IRTF over the course of two nights, our limit of 9.0 x 1017 W pushes down the limit presented by Shkolnik et. Al. (2006) by a factor of approximately 2.5 and rules out the prediction made by Miller et Al. (2000). We do not have the sensitivity to test Yelle's (2004) prediction. This upper limit brings to discussion the feasibility of using ground based high-resolution spectroscopy to study the atmosphere of large Jupiter-like giant exoplanets around neighboring stars.

We present initial results of a search for H3+ in the extended atmosphere towards the giant exoplanet orbiting HD 209458. The observations were taken during 3 transits on June 8, June 15, and July 31, 2004 using NIRSPEC at the Keck II Observatory atop Mauna Kea, Hawaii. NIRSPEC provides high sensitivity and spectral resolution (R ˜ 2.5 × 104). Unfortunately, the instrument filter wheel was stuck in the K-prime position during our June observations, necessitating a search for the 2 nu 22 -> 0 Q(1,0) and Q(3,0) transitions of H3+ lines at 2.04 mu m rather than the stronger nu 2 -> 0 R(1,1)u and R(1,0) transitions near 3.68 mu m. In addition, we also made simultaneous observations of HD 209458 with CSHELL on June 15, which also provides high resolution (R ˜ 2 × 104). Data analysis is complicated by the fact that the Doppler shift of the planet as it orbits the star changes dramatically over the course of the transit, requiring very careful stacking of each data frame. We discuss ...

High contrast and high angular resolution imagery has opened new viewpoints on the formation and early evolution of planetary systems, revealing features of protoplanetary and young planetary systems which would go undetected in the integrated measures of the systems. Much of the power of such studies has resulted from pan-chromatic data, but the majority of studies to date have been limited to optical and longer wavelengths, despite the wealth of atomic, ionic, and molecular tracers of circumstellar material in the FUV. As with high-contrast imaging at longer wavelengths, realizing the full potential of FUV imagery of young stars requires subtraction of PSF template data, which are now available for 3 of the HST ACS/SBC bandpasses. Such imagery has resulted in the first imagery of the circumstellar disk around the Herbig Ae star PDS 144S and can trace the geometry of the molecular gas disk for T Tauri stars. FUV imaging data also provide exquisite detail for molecular outflows for systems like T Tauri, complementing studies in the FIR with Herschel. Such data can also reveal the presence of previously unsuspected disk winds, as seen in GM Aur. Since FUV imagery is sensitive to extinction, FUV data preferentially detect circumstellar material on the near side of disks and the approaching components of outflows, removing ambiguities in disk viewing geometry, and can map, at the highest angular resolution achievable with HST, where disks are shadowed. This is a capability which future UV/Optical telescopes optimized for studies of planetary system formation should not be without. This study is based on data obtained with the Hubble Space Telescope under GO programs 10864, 11336, and 12016.

Circumstellar disks are not only a byproduct of star formation, but are also the place where planets form and migrate. The dominant gas-phase constituent of disks early in their evolution is H2, and its lifetime in the disk limits the time available for gas giant planet formation and migration. A number of mechanisms have been proposed to remove gas, including