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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

A Census of the Taurus Star-forming Region and Neighboring Associations with Gaia*

I have used high-precision photometry and astrometry from the third data release of Gaia to perform a survey for members of the Taurus star-forming region and young associations in its vicinity. This work has produced a new catalog of 532 adopted members of Taurus, which has only minor changes relative to the previous catalog from Esplin & Luhman. I have used the Gaia astrometry to divide the Taurus members into 13 groups that have distinct kinematics. Meanwhile, I have identified 1378 candidate members of seven associations near Taurus. All of these associations have histograms of spectral types that peak near M5 (~0.15 M ⊙ ), resembling other young populations in the solar neighborhood. For the Taurus groups and neighboring associations, I have estimated ages from their sequences of low-mass stars in Hertzsprung–Russell diagrams. Most of the Taurus groups have median ages of ~1–3 Myr, while the associations have ages ranging from 13 to 56 Myr. I have used mid-infrared photometry from the Wide-field Infrared Survey Explorer to search for excess emission from circumstellar disks among the candidate members of the associations. Disks are detected for 51 stars, 20 of which are reported for the first time in this work. Some recent studies have proposed that samples of older stars (≳10 Myr) found in the vicinity of Taurus represent a distributed population that is associated with the Taurus cloud complex. However, I find that most of those stars have kinematics that are inconsistent with any relationship with Taurus.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Gaia EDR3 Reveals the Substructure and Complicated Star Formation History of the Greater Taurus-Auriga Star-forming Complex

The Taurus-Auriga complex is the prototypical low-mass star-forming region, and provides a unique testbed of the star formation process, which left observable imprints on the spatial, kinematic, and temporal structure of its stellar population. Taurus’s rich observational history has uncovered peculiarities that suggest a complicated star-forming event, such as members at large distances from the molecular clouds and evidence of an age spread. With Gaia, an in-depth study of the Taurus census is possible, to confirm membership, identify substructure, and reconstruct its star formation history. We have compiled an expansive census of the greater Taurus region, identifying spatial subgroups and confirming that Taurus is substructured across stellar density. There are two populations of subgroups: clustered groups near the clouds and sparse groups spread throughout the region. The sparse groups comprise Taurus’s distributed population, which is on average older than the population near the clouds, and hosts subpopulations up to 15 Myr old. The ages of the clustered groups increase with distance, suggesting that the current star formation was triggered from behind. Still, the region is kinematically coherent, and its velocity structure reflects an initial turbulent spectrum similar to Larson’s Law that has been modified by dynamical relaxation. Overall, Taurus has a complicated star formation history, with at least two epochs of star formation featuring both clustered and distributed modes. Given the correlations between age and spatial distribution, Taurus might be part of a galaxy-scale star-forming event that can only begin to be understood in the Gaia era.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Modeling optical systematics for the Taurus CMB experiment

We simulate a variety of optical systematics for Taurus, a balloon-borne cosmic microwave background (CMB) polarisation experiment, to assess their impact on large-scale E-mode polarisation measurements and constraints of the optical depth to reionisation τ. We model a one-month flight of Taurus from Wanaka, New Zealand aboard a super-pressure balloon (SPB). We simulate night-time scans of both the CMB and dust foregrounds in the 150 GHz band, one of Taurus's four observing bands. We consider a variety of possible systematics that may affect Taurus's observations, including non-gaussian beams, pointing reconstruction error, and half-wave plate (HWP) non-idealities. For each of these, we evaluate the residual power in the difference between maps simulated with and without the systematic, and compare this to the expected signal level corresponding to Taurus's science goals. Our results indicate that most of the HWP-related systematics can be mitigated to be smaller than sample variance by calibrating with Planck's TT spectrum and using an achromatic HWP model, with a preference for five layers of sapphire to ensure good systematic control. However, additional beam characterization will be required to mitigate far-sidelobe pickup from dust on larger scales.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Formation of 1 H -Phenalene (C 13 H 10 ) in the Taurus Molecular Cloud via Methylidyne Addition-Cyclization-Aromatization (MACA)

The formation of 1H-phenalene (C 13 H 10 ) in cold molecular clouds, such as the Taurus Molecular Cloud-1 (TMC-1), presents a significant challenge to traditional astrochemical models, which predominantly suggest high-temperature pathways for polycyclic aromatic hydrocarbon (PAH) formation. In this study, we explore computationally the Methylidyne Addition-Cyclization-Aromatization (MACA) mechanism as a viable, barrierless pathway for phenalene synthesis under low-temperature conditions. Through electronic structure calculations and Rice–Ramsperger–Kassel–Marcus (RRKM) statistical methods, we demonstrate that the reaction of 1-vinylnaphthalene (C 10 H 7 C 2 H 3 ) with the methylidyne radical (CH) leads to the formation of 1H-phenalene via a bimolecular reaction, a process that is exoergic and without entrance barrier. The MACA mechanism facilitates the growth of the aromatic carbon backbone via a [5 + 1] ring annulation, providing a new insight into PAH formation in cold molecular clouds. Notably, the MACA mechanism has previously been shown to form indene (C9H8), which was detected in TMC-1 as well, via a [4 + 1] annulation, demonstrating its potential to produce a variety of complex PAHs by addition of a five- and six-membered ring to a benzene moiety via [4 + 1] and [5 + 1] annulation, respectively. As a result, this work highlights the importance of barrierless, exoergic reactions involving MACA in the synthesis of complex aromatic molecules in space, expanding our physicochemical understanding of carbon-rich chemistry in cold molecular clouds.

Aromatic compounds↗
DOE OSTI2025

Revealing the Moon's Taurus‐Littrow Landslide via Integrated Analysis of Pristine Apollo 17 Soil Core 73001/2

The “light mantle” deposit at the base of South Massif in the Moon's Taurus‐Littrow Valley was a primary science target for the Apollo 17 exploration. The possibility that it was a landslide triggered by ejecta from Tycho Crater is critical for establishing the age of Tycho and constraining recent lunar impact chronology; however, the mechanism of emplacement of the deposit has recently been questioned. The newly opened 73001/73002 double drive tube from Station 3 sampled 70.6 cm deep into the regolith and represents the first stratigraphic section of an extraterrestrial landslide deposit returned to Earth. Here we provide an overview of the stratigraphy of the 73001/73002 core based on top to bottom variations revealed by coordinated laboratory analyses and explore constraints on the emplacement of the light mantle deposit. Briefly, the upper ∼10 cm of 73002 contains a disturbed zone from space weathering and emplacement of ejecta from a nearby crater that excavated and ejected basaltic material. Below 10 cm is a nearly uniform unit of immature regolith. These data support a single event for the emplacement of the deposit at this location, followed by weathering and mixing of materials from nearby crater ejecta in the upper 10 cm. Slight variations in chemistry and clast components may reflect the relative stratigraphy of the South Massif slope, with material toward the bottom of 73001 originating from lower slopes and material from higher up in the core representing regolith from higher up the South Massif slopes.

58 GEOSCIENCES↗
DOE OSTI2023

Elucidating the Formation of Ethynylbutatrienylidene (HCCCHCCC; X 1 A′) in the Taurus Molecular Cloud (TMC-1) via the Gas-phase Reaction of Tricarbon (C 3 ) with the Propargyl Radical (C 3 H 3 )

Abstract The recent astronomical detection of ethynylbutatrienylidene (HCCCHCCC)—a high-energy isomer of triacetylene (HCCCCCCH) and hexapentaenylidene (H 2 CCCCCC)—in TMC-1 puzzled the laboratory astrophysics community since proposed reaction pathways could not synthesize the ethynylbutatrienylidene (HCCCHCCC) under cold molecular cloud conditions. Exploiting a retrosynthesis coupled with electronic structure calculations and astrochemical modeling, we reveal that observed fractional abundance of ethynylbutatrienylidene (HCCCHCCC) of 1.3 ± 0.2 × 10 −11 can be quantitatively replicated though the barrierless and exoergic reaction of tricarbon (C 3 ) with the resonantly stabilized propargyl radical (C 3 H 3 ) after a few 10 5 yr—typical ages of cold molecular clouds. Our study provides persuasive evidence that previously assumed “dead” reactants such as tricarbon (C 3 ) and the propargyl radical (C 3 H 3 ) provide fundamental molecular building blocks in molecular mass growth processes leading to exotic, high-energy isomers of hydrocarbons: ethynylbutatrienylidene (HCCCHCCC).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Using online tools at the Bovine Genome Database to manually annotate genes in the new reference genome

With the availability of a new highly contiguous Bos taurus reference genome assembly (ARS-UCD1.2), it is the opportune time to upgrade the bovine gene set by seeking input from researchers. Furthermore, advances in graphical genome annotation tools now make it possible for researchers to leverage sequence data generated with the latest technologies to collaboratively curate genes. For many years the Bovine Genome Database (BGD) has provided tools such as the APOLLO genome annotation editor to support manual bovine gene curation. The goal of this paper is to explain the reasoning behind the decisions made in the manual gene curation process while providing examples using the existing BGD tools. We will describe the sources of gene annotation evidence provided at the BGD, including RNAseq and Iso-Seq data. We will also explain how to interpret various data visualizations when curating gene models, and will demonstrate the value of manual gene annotation. The process described here can be applied to manual gene curation for other species with similar tools. With a better understanding of manual gene annotation, researchers will be encouraged to edit gene models and contribute to the enhancement of livestock gene sets.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Sarcocystis cruzi (Hasselmann, 1923) Wenyon, 1926: redescription, molecular characterization and deposition of life cycle stages specimens in the Smithsonian Museum

Currently, 7 named Sarcocystis species infect cattle: Sarcocystis hirsuta, S. cruzi, S. hominis, S. bovifelis, S. heydorni, S. bovini and S. rommeli; other, unnamed species also infect cattle. Of these parasites of cattle, a complete life cycle description is known only for S. cruzi, the most pathogenic species in cattle. The life cycle of S. cruzi was completed experimentally in 1982, before related parasite species were structurally characterized, and before the advent of molecular diagnostics; to our knowledge, no archived frozen tissues from the cattle employed in the original descriptions remain for DNA characterization. Here, we isolated DNA from a paraffin-embedded kidney of a calf experimentally infected with S. cruzi in 1980; we then sequenced portions of 18S rRNA, 28S rRNA, COX1 and Acetyl CoA genes and verified that each shares 99–100% similarity to other available isolates attributed to S. cruzi from naturally infected cattle. We also reevaluated histological sections of tissues of calves experimentally infected with S. cruzi in the original description, exploiting improvements in photographic technology to render clearer morphological detail. Finally, we reviewed all available studies of the life cycle of S. cruzi, noting that S. cruzi was transmitted between bison (Bison bison) and cattle (Bos taurus) and that the strain of parasite derived from bison appeared more pathogenic than the cattle strain. Based on these newfound molecular, morphological and physiological data, we thereby redescribed S. cruzi and deposited reference material in the Smithsonian Museum for posterity.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Directed Gas-Phase Formation of the 1-Cyanovinyl Radical (H 2 CCCN, X 2 A′) in the Interstellar Medium

The formation pathways to nitrogen-containing molecules and radicals are crucial to the understanding of the carbon–nitrogen chemistry in interstellar and atmospheric environments. While over 65 nitrogen-containing neutral species have been observed in deep space to date, their formation mechanisms─in particular, those of radical species─remain largely speculative. The crossed molecular beam technique in conjunction with electronic structure and statistical calculations was utilized to offer a detailed overview of the fundamental pathways in the gas-phase bimolecular reaction of ground-state atomic carbon (C, 3 P) with acetonitrile-d 3 (CD 3 CN, X 1 A 1 ) under single-collision conditions leading to the formation of the 1-cyanovinyl radical (D 2 CCCN, X 2 A′) coupled with deuterium atom loss. Here, the indirect reaction was initiated by barrierless carbon-atom addition, with the most probable route involving carbon addition across the carbon–nitrogen nitrile triple bond of acetonitrile, forming a three-membered ring intermediate followed by ring-opening and unimolecular decomposition via atomic deuterium loss from the C3 carbon atom. The reaction was overall exoergic, and intermediates and transition states lie lower in energy than the separated reactants, unlocking the reaction of carbon with acetonitrile in low-temperature environments such as cold molecular clouds, e.g., Taurus Molecular Cloud (TMC-1), and planetary atmospheres, e.g., Saturn’s moon Titan. In these environments, the 1-cyanovinyl radical may act as a building block for cyano-substituted polycyclic aromatic hydrocarbons and N-heterocycles, thus furthering our understanding of the complex carbon–nitrogen chemistry in deep space.

Chemical reactions↗
DOE OSTI2025

Binding the Power of Cycloaddition and Cross-Coupling in a Single Mechanism: An Unexpected Bending Journey to Radical Chemistry of Butadiynyl with Conjugated Dienes

What if an experiment could combine the power of cycloaddition and cross-coupling with the in situ formation of an aromatic molecule in a single collision? Crossed molecular beam experiments augmented with electronic structure and statistical calculations provided compelling evidence on a novel radical route involving 1,3-butadiynyl (HCCCC; X 2 Σ + ) radicals synthesizing (substituted) arylacetylenes in the gas phase upon reactions with 1,3-butadiene (CH 2 CHCHCH 2 ; X 1 Ag) and 2-methyl-1,3-butadiene (isoprene; CH 2 C(CH 3 )CHCH 2 ; X 1 A'). Furthermore, this elegant mechanism de facto merges two previously disconnected concepts of cross-coupling and cycloaddition–aromatization in a single collision event via the formation of two new C(sp 2 )–C(sp 2 ) bonds and bending the 180° moiety of the linear 1,3-butadiynyl radical out of the ordinary by 60° to 120°. In addition to its importance to fundamental organic chemistry, this unconventional mechanism links two previously separated routes of gas-phase molecular mass growth processes of polyacetylenes and polycyclic aromatic hydrocarbons (PAHs), respectively, in low-temperature environments such as in cold molecular clouds like the Taurus Molecular Cloud (TMC-1) and in hydrocarbon-rich atmospheres of planets and their moons such as Titan, what revises the established understanding of low-temperature molecular mass growth processes in the Universe.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Directed Gas-Phase Formation of Azulene (C 10 H 8 ): Unraveling the Bottom-Up Chemistry of Saddle-Shaped Aromatics

The azulene (C 10 H 8 ) molecule, the simplest polycyclic aromatic hydrocarbon (PAH) carrying a fused seven- and five-membered ring, is regarded as a fundamental molecular building block of saddle-shaped carbonaceous nanostructures such as curved nanographenes in the interstellar medium. However, an understanding of the underlying gas-phase formation mechanisms of this nonbenzenoid 10π-Hückel aromatic molecule under low-temperature conditions is in its infancy. Here, by merging crossed molecular beam experiments with electronic structure calculations and molecular dynamics simulations, our investigations unravel an unconventional low-temperature, barrierless route to azulene via the reaction of the simplest organic radical, methylidyne (CH), with indene (C 9 H 8 ) through ring expansion. This reaction might represent the initial step toward to the formation of saddle-shaped PAHs with seven-membered ring moieties in hydrocarbon-rich cold molecular clouds such as the Taurus Molecular Cloud-1 (TMC-1). These findings challenge conventional wisdom that molecular mass growth processes to nonplanar PAHs, especially those containing seven-membered rings, operate only at elevated pressure and high-temperature conditions, thus affording a versatile low-temperature route to contorted aromatics in our galaxy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Low-temperature formation of pyridine and (iso)quinoline via neutral–neutral reactions

Aromatic molecules represent fundamental building blocks in prebiotic chemistry and are contemplated as vital precursors to DNA and RNA nitrogen bases. However, despite the identification of some 300 molecules in extraterrestrial environments, the pathways to pyridine (C 5 H 5 N), pyridinyl (C 5 H 4 N•), and (iso)quinoline (C 9 H 7 N) – the simplest represen-tative of mono and bicyclic aromatic molecule carrying nitrogen – are elusive. Here, we afford compelling evidence on the gas-phase formation of methylene amidogen (H 2 CN•) and cyanomethyl (H 2 CCN•) radicals via molecular beam studies and electronic structure calcula-tions. The modeling of the chemistries of Taurus Molecular Cloud (TMC-1) and Titan’s atmosphere contemplates a complex chain of reactions synthesizing pyridine, pyridinyl, and (iso)quinoline from H 2 CN• and H 2 CCN• at levels of up to 75%. Furthermore, this study affords unique entry points to precursors of DNA and RNA nitrogen bases in hydrocarbon-rich extraterrestrial environments thus changing the way we think about the origin of prebiotic molecules in our Galaxy.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Gas phase formation of cyclopentanaphthalene (benzindene) isomers via reactions of 5- and 6-indenyl radicals with vinylacetylene

The tricyclic polycyclic aromatic hydrocarbons (PAHs) 3H-cyclopenta[a]naphthalene (C 13 H 10 ), 1H-cyclopenta[b]naphthalene (C 13 H 10 ) and 1H-cyclopenta[a]naphthalene (C 13 H 10 ) along with their indene-based bicyclic isomers (E)-5-(but-1-en-3-yn-1-yl)-1H-indene, (E)-6-(but-1-en-3-yn-1-yl)-1H-indene, 5-(but-3-ene-1-yn-1-yl)-1H-in-dene, and 6-(but-3-ene-1-yn-1-yl)-1H-indene were formed via a “directed synthesis” in a high-temperature chemical micro reactor at the temperature of 1300 ± 10 K through the reactions of the 5- and 6-indenyl radicals (C 9 H 7 ˙) with vinylacetylene (C 4 H 4 ). The isomer distributions were probed utilizing tunable vacuum ultraviolet light by recording the photoionization efficiency curves at mass-to-charge of m/z = 166 (C 13 H 10 ) and 167 ( 13 CC 12 H 10 ) of the products in a supersonic molecular beam. Here, the underlying reaction mechanisms involve the initial formation of van-der-Waals complexes followed by addition of the 5- and 6-indenyl radicals to vinylacetylene via submerged barriers, followed by isomerization (hydrogen shifts, ring closures), and termination via atomic hydrogen elimination accompanied by aromatization. All the barriers involved in the formation of 3H-cyclopenta[a]naphthalene, 1H-cyclopenta[b]naphthalene and 1H-cyclopenta[a]naphthalene are submerged with respect to the reactants indicating that the mechanisms are in fact barrierless, potentially forming PAHs via the hydrogen abstraction – vinylacetylene addition (HAVA) pathway in the cold molecular clouds such as Taurus Molecular Cloud-1 (TMC-1) at temperatures as low as 10 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Mapping the magnetic field in the Taurus/B211 filamentary cloud with SOFIA HAWC + and comparing with simulation

ABSTRACT Optical and infrared polarization mapping and recent Planck observations of the filametary cloud L1495 in Taurus show that the large-scale magnetic field is approximately perpendicular to the long axis of the cloud. We use the HAWC + polarimeter on SOFIA to probe the complex magnetic field in the B211 part of the cloud. Our results reveal a dispersion of polarization angles of 36°, about five times that measured on a larger scale by Planck. Applying the Davis–Chandrasekhar–Fermi (DCF) method with velocity information obtained from Institut de Radioastronomie Millimétrique 30 m C18O(1-0) observations, we find two distinct sub-regions with magnetic field strengths differing by more than a factor 3. The quieter sub-region is magnetically critical and sub-Alfv$\acute{\rm e}$nic; the field is comparable to the average field measured in molecular clumps based on Zeeman observations. The more chaotic, super-Alfv$\acute{\rm e}$nic sub-region shows at least three velocity components, indicating interaction among multiple substructures. Its field is much less than the average Zeeman field in molecular clumps, suggesting that the DCF value of the field there may be an underestimate. Numerical simulation of filamentary cloud formation shows that filamentary substructures can strongly perturb the magnetic field. DCF and true field values in the simulation are compared. Pre-stellar cores are observed in B211 and are seen in our simulation. The appendices give a derivation of the standard DCF method that allows for a dispersion in polarization angles that is not small, present an alternate derivation of the structure function version of the DCF method, and treat fragmentation of filaments.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Determination of fluorine distribution in shark teeth by laser-induced breakdown spectroscopy

Quantifying the chemical composition of fast-growing hard tissues in the environment can shed valuable information in terms of understanding ecosystems both prehistoric and current. Changes in chemical composition can be correlated with environmental conditions and can provide information about the organism's life. Sharks can lose 0.1 to 1.1 teeth/day, depending on species, which offers a unique opportunity to record environmental changes over a short duration of time. Shark teeth contain a biomineral phase that is made up of fluorapatite [Ca 5 (PO 4 ) 3 F], and the F distribution within the tooth can be correlated to tooth hardness. Typically, this is determined by bulk acid digestion, energy-dispersive X-ray spectroscopy (EDS), or wavelength-dispersive spectroscopy. Here we present laser-induced breakdown spectroscopy (LIBS) as an alternative and faster approach for determining F distribution within shark teeth. Using a two-volume laser ablation chamber (TwoVol3) with innovative embedded collection optics for LIBS, shark teeth were investigated from sand tiger (Carcharias Taurus), tiger (Galeocerdo Cuvier), and hammerhead sharks (Sphyrnidae). Fluorine distribution was mapped using the CaF 603 nm band (CaF, Β 2 Σ + → X 2 Σ + ) and quantified using apatite reference materials. In addition, F measurements were cross referenced with EDS analyses to validate the findings. Distributions of F (603 nm), Na (589 nm), and H (656 nm) within the tooth correlate well with the expected biomineral composition and expected tooth hardness. This rapid methodology could transform the current means of determining F distribution, particularly when large sample specimens (350 mm 2 , presented here) and large quantities of specimens are of interest.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Experimental Senecavirus A Infection of Bovine Cell Lines and Colostrum-Deprived Calves

Senecavirus A (SVA) is a causative agent for vesicular disease in swine, which is clinically indistinguishable from other vesicular diseases of swine including foot-and-mouth disease (FMD). Recently, it was reported that buffalo in Guangdong, China were experiencing clinical symptoms similar to FMD including mouth ulcers and lameness tested positive for SVA. The objective of this study was to determine the susceptibility of cattle (Bos taurus) to SVA infection. Initial in vitro work using the PrimeFlow assay demonstrated that bovine cell lines and peripheral blood mononuclear cells from cattle were susceptible to SVA infection. Subsequently, six colostrum-deprived Holstein calves were challenged with SVA intranasally. No vesicular lesions were observed after challenge. Serum, oral, nasal, and rectal swabs tested for SVA nucleic acid did not support significant viral replication and there was no evidence of seroconversion. Therefore, demonstrating cattle from this study were not susceptible to experimental SVA infection.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Probing UV-sensitive Pathways for CN and HCN Formation in Protoplanetary Disks with the Hubble Space Telescope

The UV radiation field is a critical regulator of gas-phase chemistry in surface layers of disks around young stars. In an effort to understand the relationship between photocatalyzing UV radiation fields and gas emission observed at infrared and submillimeter wavelengths, we present an analysis of new and archival Hubble Space Telescope (HST), Spitzer, ALMA, IRAM, and SMA data for five targets in the Lupus cloud complex and 14 systems in Taurus-Auriga. The HST spectra were used to measure Lyα and far-UV (FUV) continuum fluxes reaching the disk surface, which are responsible for dissociating relevant molecular species (e.g., HCN, N{sub 2}). Semi-forbidden C ii] λ2325 and UV-fluorescent H{sub 2} emission were also measured to constrain inner disk populations of C{sup +} and vibrationally excited H{sub 2}. We find a significant positive correlation between 14 μm HCN emission and fluxes from the FUV continuum and C ii] λ2325, consistent with model predictions requiring N{sub 2} photodissociation and carbon ionization to trigger the main CN/HCN formation pathways. We also report significant negative correlations between submillimeter CN emission and both C ii] and FUV continuum fluxes, implying that CN is also more readily dissociated in disks with stronger FUV irradiation. No clear relationships are detected between either CN or HCN and Lyα or UV-H{sub 2} emission. This is attributed to the spatial stratification of the various molecular species, which span several vertical layers and radii across the inner and outer disk. We expect that future observations with the James Webb Space Telescope will build on this work by enabling more sensitive IR surveys than were possible with Spitzer.

79 ASTRONOMY AND ASTROPHYSICS↗