Herschel Measurements of Molecular Oxygen in Orion

We report observations of three rotational transitions of molecular oxygen (O_2) in emission from the H_2 Peak 1 position of vibrationally excited molecular hydrogen in Orion. We observed the 487 GHz, 774 GHz, and 1121 GHz lines using the Heterodyne Instrument for the Far Infrared on the Herschel Space Observatory, having velocities of 11 km s^(–1) to 12 km s^(–1) and widths of 3 km s^(–1). The beam-averaged column density is N(O_2) = 6.5 × 10^(16) cm^(–2), and assuming that the source has an equal beam-filling factor for all transitions (beam widths 44, 28, and 19"), the relative line intensities imply a kinetic temperature between 65 K and 120 K. The fractional abundance of O_2 relative to H_2 is (0.3-7.3) × 10^(–6). The unusual velocity suggests an association with a ~5" diameter source, denoted Peak A, the Western Clump, or MF4. The mass of this source is ~10 M_⊙ and the dust temperature is ≥150 K. Our preferred explanation of the enhanced O_2 abundance is that dust grains in this region are sufficiently warm (T ≥ 100 K) to desorb water ice and thus keep a significant fraction of elemental oxygen in the gas phase, with a significant fraction as O_2. For this small source, the line ratios require a temperature ≥180 K. The inferred O_2 column density ≃5 × 10^(18) cm^(–2) can be produced in Peak A, having N(H_2) ≃4 × 10^(24) cm^(–2). An alternative mechanism is a low-velocity (10-15 km s^(–1)) C-shock, which can produce N(O_2) up to 10^(17) cm^(–2)

Herschel/HIFI line surveys: Discovery of interstellar chloronium (H_2Cl^+)

Prior to the launch of Herschel, HCl was the only chlorine-containing molecule detected in the interstellar medium (ISM). However, chemical models have identified chloronium, H_2Cl^+, as a relatively abundant species that is potentially detectable. H_2Cl^+ was predicted to be most abundant in the environments where the ultraviolet radiation is strong: in diffuse clouds, or near the surfaces of dense clouds illuminated by nearby O and B stars. The HIFI instrument on Herschel provided the first detection of H_2Cl^+ in the ISM. The 2_(12)-1_(01) lines of ortho- H_2^(35)Cl^+ and ortho- H_2^(37)Cl^+ were detected in absorption toward NGC 6334I, and the 1_(11)-0_(00) transition of para- H_2^(35)Cl^+ was detected in absorption toward NGC 6334I and Sgr B2(S). The derived HCl/H_2Cl^+ column density ratios, ∼1-10, are within the range predicted by models of diffuse and dense Photon Dominated Regions (PDRs). However, the observed H_2Cl^+ column densities, in excess of 10^(13) cm^(−2), are significantly higher than the model predictions. These observations demonstrate the outstanding spectroscopic capabilities of HIFI for detecting new interstellar molecules and providing key constraints for astrochemical models

The Sagittarius B2 molecular cloud : an extreme case of a galactic center giant molecular cloud.

AstronomyDoctor of Philosophy (PhD

Dust emission in the Sagittarius B2 molecular cloud core

A model is presented for the dust emission from the Sagittarius B2 molecular cloud core which reproduces the observed spectrum between 30 and 1300 micron, as well as the distribution of the emission at 1300 micron. The model is based on the assumption that Sgr B2(N) continuum source is located behind the dust cloud associated with Sgr B2(M) continuum source. The fact that Sgr B2(N) is stronger at 1300 micron can be attributed to a local column density maximum at the position of this source. Absence of a 53 micron emission peak at the position of Sgr B2(N) suggests that the luminosity of the north source is lower than that of the middle source

Water: from clouds to planets

Results from recent space missions, in particular Spitzer and Herschel, have lead to significant progress in our understanding of the formation and transport of water from clouds to disks, planetesimals, and planets. In this review, we provide the underpinnings for the basic molecular physics and chemistry of water and outline these advances in the context of water formation in space, its transport to a forming disk, its evolution in the disk, and finally the delivery to forming terrestrial worlds and accretion by gas giants. Throughout, we pay close attention to the disposition of water as vapor or solid and whether it might be subject to processing at any stage. The context of the water in the solar system and the isotopic ratios (D/H) in various bodies are discussed as grounding data point for this evolution. Additional advances include growing knowledge of the composition of atmospheres of extra-solar gas giants, which may be influenced by the variable phases of water in the protoplanetary disk. Further, the architecture of extra-solar systems leaves strong hints of dynamical interactions, which are important for the delivery of water and subsequent evolution of planetary systems. We conclude with an exploration of water on Earth and note that all of the processes and key parameters identified here should also hold for exoplanetary systems.Comment: 24 pages, 13 figures; updated exoplanet observations references. Accepted for publication as a chapter in Protostars and Planets VI, University of Arizona Press (2014), eds. H. Beuther, R. Klessen, C. Dullemond, Th. Hennin

The CARMA-NRO Orion Survey

We present the first results from a new, high-resolution ^(12)CO(1–0), ^(13)CO(1–0), and C^(18)O(1–0) molecular-line survey of the Orion A cloud, hereafter referred to as the CARMA-NRO Orion Survey. CARMA observations have been combined with single-dish data from the Nobeyama 45 m telescope to provide extended images at about 0.01 pc resolution, with a dynamic range of approximately 1200 in spatial scale. Here we describe the practical details of the data combination in uv space, including flux scale matching, the conversion of single-dish data to visibilities, and joint deconvolution of single-dish and interferometric data. A Δ-variance analysis indicates that no artifacts are caused by combining data from the two instruments. Initial analysis of the data cubes, including moment maps, average spectra, channel maps, position–velocity diagrams, excitation temperature, column density, and line ratio maps, provides evidence of complex and interesting structures such as filaments, bipolar outflows, shells, bubbles, and photo-eroded pillars. The implications for star formation processes are profound, and follow-up scientific studies by the CARMA-NRO Orion team are now underway. We plan to make all the data products described here generally accessible; some are already available at https://dataverse.harvard.edu/dataverse/CARMA-NRO-Orion

The CARMA-NRO Orion Survey

We present the first results from a new, high-resolution ^(12)CO(1–0), ^(13)CO(1–0), and C^(18)O(1–0) molecular-line survey of the Orion A cloud, hereafter referred to as the CARMA-NRO Orion Survey. CARMA observations have been combined with single-dish data from the Nobeyama 45 m telescope to provide extended images at about 0.01 pc resolution, with a dynamic range of approximately 1200 in spatial scale. Here we describe the practical details of the data combination in uv space, including flux scale matching, the conversion of single-dish data to visibilities, and joint deconvolution of single-dish and interferometric data. A Δ-variance analysis indicates that no artifacts are caused by combining data from the two instruments. Initial analysis of the data cubes, including moment maps, average spectra, channel maps, position–velocity diagrams, excitation temperature, column density, and line ratio maps, provides evidence of complex and interesting structures such as filaments, bipolar outflows, shells, bubbles, and photo-eroded pillars. The implications for star formation processes are profound, and follow-up scientific studies by the CARMA-NRO Orion team are now underway. We plan to make all the data products described here generally accessible; some are already available at https://dataverse.harvard.edu/dataverse/CARMA-NRO-Orion

Review: far-infrared instrumentation and technological development for the next decade

Far-infrared astronomy has advanced rapidly since its inception in the late 1950s, driven by a maturing technology base and an expanding community of researchers. This advancement has shown that observations at far-infrared wavelengths are important in nearly all areas of astrophysics, from the search for habitable planets and the origin of life to the earliest stages of galaxy assembly in the first few hundred million years of cosmic history. The combination of a still-developing portfolio of technologies, particularly in the field of detectors, and a widening ensemble of platforms within which these technologies can be deployed, means that far-infrared astronomy holds the potential for paradigm-shifting advances over the next decade. We examine the current and future far-infrared observing platforms, including ground-based, suborbital, and space-based facilities, and discuss the technology development pathways that will enable and enhance these platforms to best address the challenges facing far-infrared astronomy in the 21st century

A Comprehensive Survey of Hydrogen Chloride in the Galaxy

We report new observations of the fundamental $J=1-0$ transition of HCl (at 625.918GHz) toward a sample of 25 galactic star-forming regions, molecular clouds, and evolved stars, carried out using the Caltech Submillimeter Observatory. Fourteen sources in the sample are also observed in the corresponding H\tscl\ $J=1-0$ transition (at 624.978GHz). We have obtained clear detections in all but four of the targets, often in emission. Absorptions against bright background continuum sources are also seen in nine cases, usually involving a delicate balance between emission and absorption features. From RADEX modeling, we derive gas densities and HCl column densities for sources with HCl emission. HCl is found in a wide range of environments, with gas densities ranging from $10^5$ to $10^7$~cm$^{-3}$. The HCl abundance relative to H$_2$ is in the range of $(3-30)\times10^{-10}$. Comparing with the chlorine abundance in the solar neighborhood, this corresponds to a chlorine depletion factor of up to $\sim$400, assuming that HCl accounts for one third of the total chlorine in the gas phase. The [\tfcl]/[\tscl] isotopic ratio is rather varied, from unity to $\sim$5, mostly lower than the terrestrial value of 3.1. Such variation is highly localized, and could be generated by the nucleosynthesis in supernovae, which predicts a \tscl\ deficiency in most models. The lower ratios seen in W3IRS4 and W3IRS5 likely confine the progenitors of the supernovae to stars with relatively large mass (\ga25M_\sun) and high metallicity (Z$\sim$0.02).Comment: 11 pages, 5 figures, accepted by Ap

Herschel/HIFI Spectral Mapping of C+^+, CH+^+, and CH in Orion BN/KL: The Prevailing Role of Ultraviolet Irradiation in CH+^+ Formation

The CH$^+$ ion is a key species in the initial steps of interstellar carbon chemistry. Its formation in diverse environments where it is observed is not well understood, however, because the main production pathway is so endothermic (4280 K) that it is unlikely to proceed at the typical temperatures of molecular clouds. We investigation CH$^+$ formation with the first velocity-resolved spectral mapping of the CH$^+$ $J=1-0, 2-1$ rotational transitions, three sets of CH $\Lambda$-doubled triplet lines, $^{12}$C$^+$ and $^{13}$C$^+$, and CH$_3$OH 835~GHz E-symmetry Q branch transitions, obtained with Herschel/HIFI over $\approx$12 arcmin$^2$ centered on the Orion BN/KL source. We present the spatial morphologies and kinematics, cloud boundary conditions, excitation temperatures, column densities, and $^{12}$C$^+$ optical depths. Emission from C$^+$, CH$^+$, and CH is indicated to arise in the diluted gas, outside of the explosive, dense BN/KL outflow. Our models show that UV-irradiation provides favorable conditions for steady-state production of CH$^+$ in this environment. Surprisingly, no spatial or kinematic correspondences of these species are found with H$_2$ S(1) emission tracing shocked gas in the outflow. We propose that C$^+$ is being consumed by rapid production of CO to explain the lack of C$^+$ and CH$^+$ in the outflow, and that fluorescence provides the reservoir of H$_2$ excited to higher ro-vibrational and rotational levels. Hence, in star-forming environments containing sources of shocks and strong UV radiation, a description of CH$^+$ formation and excitation conditions is incomplete without including the important --- possibly dominant --- role of UV irradiation.Comment: Accepted for publication in The Astrophysical Journa