We present an analysis of Spitzer-IRS observations of H 2 O, OH, HCN, C 2 H 2 and CO 2 emission, and Keck-NIRSPEC observations of CO emission, from a diverse sample of T Tauri and Herbig Ae/Be circumstellar disks. We find that detections and strengths of most mid-IR molecular emission features are correlated with each other, suggesting a common origin and similar excitation conditions for this mid-infrared line forest. Aside from the remarkable differences in molecular line strengths between T Tauri, Herbig Ae/Be and transitional disks discussed in Pontoppidan et al. (2010b), we note that the line detection efficiency is anti-correlated with the 13/30 µm SED spectral slope, which is a measure of the degree of grain settling in the disk atmosphere. We also note a correlation between detection efficiency and Hα equivalent width, and tentatively with accretion rate, suggesting that accretional heating contributes to line excitation. If detected, H 2 O line fluxes are correlated with the mid-IR continuum flux, and other co-varying system parameters, such as L ⋆ . However, significant sample variation, especially in molecular line ratios, remains, and its origin has yet to be explained. LTE models of the H 2 O emission show that line strength is primarily related to the best-fit emitting area, and this accounts for most source-to-source variation in H 2 O emitted flux. Best-fit temperatures and column densities cover only a small range of parameter space, near ∼ 10 18 cm −2 and 450 K for all sources, suggesting a high abundance of H 2 O in many planet-forming regions. Other molecules have a range of excitation temperatures from ∼ 500 − 1500 K, also consistent with an origin in planet-forming regions. We find molecular ratios relative to water of ∼ 10 −3 for all molecules, with the exception of CO, for which n(CO)/n(H 2 O)∼1. However, LTE fitting caveats and differences in the way thermochemical modeling results are reported make comparisons with such models difficult, and highlight the need for additional observations coupled with the use of line-generating radiative transfer codes.

The chemical composition of protoplanetary disks is expected to hold clues to the physical and chemical processes that influence the formation of planetary systems. However, characterizing the gas composition in the planet formation region of disks has been a challenge to date. We report here that the protoplanetary disk within 3 astronomical units of AA Tauri possesses a rich molecular emission spectrum in the mid-infrared, indicating a high abundance of simple organic molecules (HCN, C2H2, and CO2), water vapor, and OH. These results suggest that water is abundant throughout the inner disk and that the disk supports an active organic chemistry.

We report the results of a high-resolution spectroscopic survey for CO fundamental emission from T Tauri stars. CO fundamental emission is frequently detected, with the likely origin of the emission in the circumstellar disk. An initial assessment of the line profiles indicates that the emission region includes the equivalent of the terrestrial planet region of our solar system, a result that suggests the utility of CO fundamental emission as a probe of disks at planet formation distances. Since fundamental emission is detected frequently from both close binary and apparently single stars, it appears that both low column density regions, such as disk gaps, and temperature inversion regions in disk atmospheres can produce significant emission. The estimated excitation temperature of the emitting gas is unexpectedly warm for the disk radii that they appear to probe. Thus, the surface gaseous component of inner disks may be significantly warmer than the surface dust component. We also detect CO emission from a transitional T Tauri star. Because fundamental emission from CO and its isotopes is sensitive to a wide range of gas masses, including masses5M È , CO fundamental emission may prove useful in measuring the residual gas content of dissipating disks. This may be an effective way to explore the gas dissipation timescale in inner disks and to thereby place constraints on the timescale for giant planet formation.

We present a Spitzer InfraRed Spectrometer (IRS) search for 10-36 µm molecular emission from a large sample of protoplanetary disks, including lines from H 2 O, OH, C 2 H 2 , HCN and CO 2 . This paper describes the sample and data processing and derives the detection rate of mid-infrared molecular emission as a function of stellar mass. The sample covers a range of spectral type from early M to A, and is supplemented by archival spectra of disks around A and B stars. It is drawn from a variety of nearby star forming regions, including Ophiuchus, Lupus and Chamaeleon. Spectra showing strong emission lines are used to identify which lines are the best tracers of various physical and chemical conditions within the disks. In total, we identify 22 T Tauri stars with strong mid-infrared H 2 O emission. Integrated water line luminosities, where water vapor is detected, range from 5 × 10 −4 to 9 × 10 −3 L ⊙ , likely making water the dominant line coolant of inner disk surfaces in classical T Tauri stars. None of the 5 transitional disks in the sample show detectable gaseous molecular emission with Spitzer upper limits at the 1% level in terms of line-to-continuum ratios (apart from H 2 ), but the sample is too small to conclude whether this is a general property of transitional disks. We find a strong dependence on detection rate with spectral type; no disks around our sample of 25 A and B stars were found to exhibit water emission, down to 1-2% line-to-continuum ratios, in the mid-infrared, while almost 2/3 of the disks around K stars show sufficiently intense water emission to be detected by Spitzer. Some Herbig Ae/Be stars show tentative H 2 O/OH emission features beyond 20 µm at the 1-2% level, however, and one of them shows CO 2 in emission. We argue that the observed differences between T Tauri disks and Herbig Ae/Be disks is due to a difference in excitation and/or chemistry depending on spectral type and suggest that photochemistry may be playing an important role in the observable characteristics of mid-infrared molecular line emission from protoplanetary disks.

The first measurement of the photospheric abundances in a star at the Galactic Center are presented. A detailed abundance analysis of the Galactic Center M2 supergiant IRS 7 was carried out using high-resolution near-infrared echelle spectra. The Fe abundance for IRS 7 was found to be close to solar, [Fe/H] = -0.02 ± 0.13, and nearly identical to the Fe abundances we obtained for the nearby M supergiants α Ori and VV Cep. Analysis of the first and second overtone lines of CO was used to derive an effective temperature of 3600 ± 230 K, a microturbulent velocity of 3.0 ± 0.3 km s -1 , and a carbon abundance log ε(C) = 7.78 ± 0.13, or [C/H] = -0.77. In addition, we find a high depletion of 0.74 ± 0.32 dex in O and an enhancement of 0.92 ± 0.18 dex in N. These abundances are consistent with the dredge-up of CNO-cycle products but require deep mixing in excess of that predicted by standard models for red supergiants. In light of our measured solar Fe abundance for IRS 7, we discuss other indicators of metallicity at the Galactic Center, the interpretation of low-resolution near-infrared spectra of late-type giants and supergiants, including the need for caution in using such spectra as measures of metallicity, and the evolution of massive young stars at the Galactic Center. We suggest the possibility that rapid stellar rotation is common for stars formed under conditions in the Galactic Center, and that extra internal mixing induced by high rotation rates, rather than evolution at high metallicity, is the explanation for many of the unusual properties of the hot emission-line stars in the Galactic Center.