Dana E. Anderson

HERSCHEL OBSERVATIONS OF EXTRAORDINARY SOURCES: ANALYSIS OF THE FULL HERSCHEL/HIFI MOLECULAR LINE SURVEY OF SAGITTARIUS B2(N) ∗

A sensitive broadband molecular line survey of the Sagittarius B2(N) star-forming region has been obtained with the Heterodyne Instrument for the Far-Infrared (HIFI) instrument on the Herschel Space Observatory, offering the first high spectral resolution look at this well-studied source in a wavelength region largely inaccessible from the ground (625–157 μm). From the roughly 8000 spectral features in the survey, a total of 72 isotopologues arising from 44 different molecules have been identified, ranging from light hydrides to complex organics, and arising from a variety of environments from cold and diffuse to hot and dense gas. We present a local thermodynamic equilibrium (LTE) model to the spectral signatures of each molecule, constraining the source sizes for hot core species with complementary Submillimeter Array interferometric observations and assuming that molecules with related functional group composition are cospatial. For each molecule, a single model is given to fit all of the emission and absorption features of that species across the entire 480–1910 GHz spectral range, accounting for multiple temperature and velocity components when needed to describe the spectrum. As with other HIFI surveys toward massive star-forming regions, methanol is found to contribute more integrated line intensity to the spectrum than any other species. We discuss the molecular abundances derived for the hot core where the LTE approximation is generally found to describe the spectrum well, in comparison to abundances derived for the same molecules in the Orion KL region from a similar HIFI survey. Notably, we find significantly higher abundances of amine- and amide-bearing molecules (CH_3NH_2, CH_2NH, and NH_2CHO) toward Sgr B2(N) than Orion KL and lower abundances of some complex oxygen-bearing molecules (CH_3OCHO in particular). In addition to information on the chemical composition of the hot core, the strong far-infrared dust continuum allows a number of molecules to be detected in absorption in the Sgr B2(N) envelope for the first time at high spectral resolution, and we discuss the possible physical origin of the kinematic components observed in absorption. Additionally, from the detection of new HOCO^+ transitions in absorption compared to published HCO^+ isotopic observations, we discuss constraints on the gas-phase CO_2 abundance and compare this to observations of the ice composition in the Galactic center region, and to CO_2 abundance estimates toward other high-mass star-forming regions. The reduced HIFI spectral scan and LTE model are made available to the public as a resource for future investigations of star-forming regions in the submillimeter and far-infrared.

Characterization of LIBS emission lines for the identification of chlorides, carbonates, and sulfates in salt/basalt mixtures for the application to MSL ChemCam data: LIBS OF CL, C, S IN SALT-BASALT MIXTURES

Ancient environmental conditions on Mars can be probed through the identification of minerals on its surface, including water-deposited salts and cements dispersed in the pore space of sedimentary rocks. Laser-induced breakdown spectroscopy (LIBS) analyses by the Martian rover Curiositys ChemCam instrument can indicate salts, and ChemCam surveys aid in identifying and selecting sites for further, detailed in situ analyses. We performed laboratory LIBS experiments under simulated Mars conditions with a ChemCam-like instrument on a series of mixtures containing increasing concentrations of salt in a basaltic background to investigate the potential for identifying and quantifying chloride, carbonate, and sulfate salts found only in small amounts, dispersed in bulk rock with ChemCam, rather than concentrated in veins. Data indicate that the presence of emission lines from the basalt matrix limited the number of Cl, C, and S emission lines found to be useful for quantitative analysis; nevertheless, several lines with intensities sensitive to salt concentration were identified. Detection limits for the elements based on individual emission lines ranged from ~20 wt % carbonate (2 wt % C), ~5–30 wt % sulfate (1–8 wt % S), and ~5–10 wt % chloride (3–6 wt % Cl) depending on the basaltic matrix and/or salt cation. Absolute quantification of Cl, C, and S in the samples via univariate analysis depends on the cation-anion pairing in the salt but appears relatively independent of matrices tested, following normalization. These results are promising for tracking relative changes in the salt content of bulk rock on the Martian surface with ChemCam.

HERSCHEL OBSERVATIONS of EXTRAORDINARY SOURCES: ANALYSIS of the HIFI 1.2 THz WIDE SPECTRAL SURVEY TOWARD ORION KL II. CHEMICAL IMPLICATIONS

We present chemical implications arising from spectral models fit to the Herschel/HIFI spectral survey toward the Orion Kleinmann-Low nebula (Orion KL). We focus our discussion on the eight complex organics detected within the HIFI survey utilizing a novel technique to identify those molecules emitting in the hottest gas. In particular, we find the complex nitrogen bearing species CH_3CN, C_2H_3CN, C_2H_5CN, and NH_2CHO systematically trace hotter gas than the oxygen bearing organics CH_3OH, C_2H_5OH, CH_3OCH_3, and CH_3OCHO, which do not contain nitrogen. If these complex species form predominantly on grain surfaces, this may indicate N-bearing organics are more difficult to remove from grain surfaces than O-bearing species. Another possibility is that hot (T_(kin) ~ 300 K) gas phase chemistry naturally produces higher complex cyanide abundances while suppressing the formation of O-bearing complex organics. We compare our derived rotation temperatures and molecular abundances to chemical models, which include gas-phase and grain surface pathways. Abundances for a majority of the detected complex organics can be reproduced over timescales ≳10^5 years, with several species being underpredicted by less than 3σ. Derived rotation temperatures for most organics, furthermore, agree reasonably well with the predicted temperatures at peak abundance. We also find that sulfur bearing molecules that also contain oxygen (i.e., SO, SO_2, and OCS) tend to probe the hottest gas toward Orion KL, indicating the formation pathways for these species are most efficient at high temperatures.

Destruction of Refractory Carbon in Protoplanetary Disks

The Earth and other rocky bodies in the inner solar system contain significantly less carbon than the primordial materials that seeded their formation. These carbon-poor objects include the parent bodies of primitive meteorites, suggesting that at least one process responsible for solid-phase carbon depletion was active prior to the early stages of planet formation. Potential mechanisms include the erosion of carbonaceous materials by photons or atomic oxygen in the surface layers of the protoplanetary disk. Under photochemically generated favorable conditions, these reactions can deplete the near-surface abundance of carbon grains and polycyclic aromatic hydrocarbons by several orders of magnitude on short timescales relative to the lifetime of the disk out to radii of ~20–100+ au from the central star depending on the form of refractory carbon present. Due to the reliance of destruction mechanisms on a high influx of photons, the extent of refractory carbon depletion is quite sensitive to the disks internal radiation field. Dust transport within the disk is required to affect the composition of the midplane. In our current model of a passive, constant-α disk, where α = 0.01, carbon grains can be turbulently lofted into the destructive surface layers and depleted out to radii of ~3–10 au for 0.1–1 μm grains. Smaller grains can be cleared out of the planet-forming region completely. Destruction may be more effective in an actively accreting disk or when considering individual grain trajectories in non-idealized disks.

Unlocking CO Depletion in Protoplanetary Disks. I. the Warm Molecular Layer

CO is commonly used as a tracer of the total gas mass in both the interstellar medium and in protoplanetary disks. Recently there has been much debate about the utility of CO as a mass tracer in disks. Observations of CO in protoplanetary disks reveal a range of CO abundances, with measurements of low CO to dust mass ratios in numerous systems. One possibility is that carbon is removed from CO via chemistry. However, the full range of physical conditions conducive to this chemical reprocessing is not well understood. We perform a systematic survey of the time dependent chemistry in protoplanetary disks for 198 models with a range of physical conditions. We varying dust grain size distribution, temperature, comic ray and X-ray ionization rate, disk mass, and initial water abundance, detailing what physical conditions are necessary to activate the various CO depletion mechanisms in the warm molecular layer. We focus our analysis on the warm molecular layer in two regions: the outer disk (100 au) well outside the CO snowline and the inner disk (19 au) just inside the midplane CO snow line. After 1 Myr, we find that the majority of models have a CO abundance relative to H

Characterization of Hydrogen in Basaltic Materials With Laser‐Induced Breakdown Spectroscopy (LIBS) for Application to MSL ChemCam Data

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New constraints on the sulfur reservoir in the dense interstellar medium provided by Spitzer observations of S I in shocked gas

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Characterization of Laser-Induced Breakdown Spectroscopy (LIBS) emission lines for the identification of chlorides, carbonates, and sulfates in salt/basalt mixtures for the application to MSL ChemCam data

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CHARACTERIZATION OF HYDROGEN IN BASALTIC MATERIALS WITH LASER-INDUCED BREAKDOWN SPECTROSCOPY (LIBS)

in the outer disk, while an abundance less than

CHEMCAM SURVEY OFVOLATILE ELEMENTS IN THE MURRAY FORMATION, GALE CRATER, MARS

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