Fluorescent H2 Research Articles

A new method to measure aquaporin-facilitated membrane diffusion of hydrogen peroxide and cations in plant suspension cells.

Plant aquaporins (AQPs) facilitate the membrane diffusion of water and small solutes, including hydrogen peroxide (H2 O2 ) and, possibly, cations, essential signalling molecules in many physiological processes. While the determination of the channel activity generally depends on heterologous expression of AQPs in Xenopus oocytes or yeast cells, we established a genetic tool to determine whether they facilitate the diffusion of H2 O2 through the plasma membrane in living plant cells. We designed genetic constructs to co-express the fluorescent H2 O2 sensor HyPer and AQPs, with expression controlled by a heat shock-inducible promoter in Nicotiana tabacum BY-2 suspension cells. After induction of ZmPIP2;5 AQP expression, a HyPer signal was recorded when the cells were incubated with H2 O2 , suggesting that ZmPIP2;5 facilitates H2 O2 transmembrane diffusion; in contrast, the ZmPIP2;5W85A mutated protein was inactive as a water or H2 O2 channel. ZmPIP2;1, ZmPIP2;4and AtPIP2;1 also facilitated H2 O2 diffusion. Incubation with abscisic acid and the elicitor flg22 peptide induced the intracellular H2 O2 accumulation in BY-2 cells expressing ZmPIP2;5. We also monitored cation channel activity of ZmPIP2;5 using a novel fluorescent photo-switchable Li+ sensor in BY-2 cells. BY-2 suspension cells engineered for inducible expression of AQPs as well as HyPer expression and the use of Li+ sensors constitute a powerful toolkit for evaluating the transport activity and the molecular determinants of PIPs in living plant cells.

Behaviour of molecular hydrogen emission in three solar flares

ABSTRACT We have systematically investigated ultraviolet (UV) emission from molecular hydrogen (H2) using the Interface Region Imaging Spectrograph (IRIS), during three X-ray flares of C5.1, C9.7, and X1.0 classes on 2014 October 25. Significant emission from five H2 spectral lines appeared in the flare ribbons, interpreted as photoexcitation (fluorescence) due to the absorption of UV radiation from two Si iv spectral lines. The H2 profiles were broad and consisted of two non-stationary components in red and in the blue wings of the line in addition to the stationary component. The red-wing (blue-wing) components showed small redshifts (blueshifts) of ∼5–15 km s−1 (∼5–10 km s−1). The non-thermal velocities were found to be ∼5–15 km s−1. The interrelation between intensities of H2 lines and their branching ratios confirmed that H2 emission formed under optically thin plasma conditions. There is a strong spatial and temporal correlation between Si iv and H2 emissions, but the H2 emission is more extended and diffuse, further suggesting H2 fluorescence, and – by analogy with flare ‘back-warming’ – providing a means to estimate the depth from which the H2 emission originates. We find that this is 1871 ± 157 and 1207 ± 112 km below the source of the Si iv emission, in two different ribbon locations.

The Radial Distribution and Excitation of H2 around Young Stars in the HST-ULLYSES Survey

The spatial distribution and evolution of gas in the inner 10 au of protoplanetary disks form the basis for estimating the initial conditions of planet formation. Among the most important constraints derived from spectroscopic observations of the inner disk are the radial distributions of the major gas phase constituents, how the properties of the gas change with inner disk dust evolution, and how the chemical abundances and excitation conditions are influenced by the high-energy radiation from the central star. We present a survey of the radial distribution, excitation, and evolution of inner disk molecular hydrogen (H2) obtained as part of the Hubble Space Telescope-ULLYSES program. We analyze far-UV spectroscopy of 71 (63 accreting) pre-main-sequence systems in ULLYSES DR5 to characterize the H2 emission lines, H2 dissociation continuum emission, and major photochemical/disk evolution driving the UV emissions (Lyα, UV continuum, and C iv). We use the widths of the H2 emission lines to show that most fluorescent H2 arises between 0.1 and 1.4 au from the parent star, and show positive correlations of the average emitting radius with the accretion luminosity and with the dust disk mass. We find a strong correlation between H2 dissociation emission and both the accretion-dominated Lyα luminosity and the inner disk dust clearing, painting a picture where water molecules in the inner 3 au are exposed to and dissociated by strong Lyα emission as the opacity of the inner disk declines with time.

A simple quinolimide-based fluorescent sensor for formaldehyde and its applications in test strips and living cells

A simple fluorescent sensor H2 containing quinolimide as a fluorophore and hydrazine as a reaction site was designed and synthesized for the detection of formaldehyde (FA). H2 had the high selectivity and sensitivity to FA through the pseudo-first-order reaction (k = 0.048 min−1), exhibiting the significantly enhanced fluorescence signal. The quantitative determination range of H2 for FA was 0–180 μM, and the LOD of FA is 1.7 μM. Moreover, H2-loaded test strips were demonstrated in the visualization of sensing FA. And H2 was successfully applied for imaging FA in living cells.

HST UV Spectroscopy of the Planet-hosting T Tauri Star PDS 70

We summarize Hubble Space Telescope (HST) UV observations of the weak-lined T Tauri star (wTTS) PDS 70 obtained with the Space Telescope Imaging Spectrograph. These observations provide the first far-UV (FUV) and near-UV (NUV) spectra of PDS 70. Ground-based observations have so far revealed two formative giant planets orbiting in a wide gap in its circumstellar disk. Both the star and young planets are thought to still be accreting. The HST spectra provide new insight into physical conditions in the star’s outer atmosphere and circumstellar environment. The spectra are dominated by chromospheric and transition-region emission lines with maximum formation temperatures log T = 4.5–5.2 K. Stellar continuum emission is present in the NUV but we find no significant FUV continuum, as could arise from accretion shocks. Several fluorescent FUV H2 emission lines are present, a surprising result since H2 lines are usually undetected in wTTS. The H2 lines likely originate in irradiated circumstellar gas that could serve as a reservoir for the star’s waning accretion. A previously established correlation between C iv line luminosity and accretion rate yields , consistent with previous estimates. Atacama Large Millimeter/submillimeter Array disk gas models imply strong absorption of stellar X-ray and UV (XUV) radiation near the star, effectively shielding the planets. Inner disk gas is exposed to ongoing photoevaporation by XUV radiation and the disk is nearing the end of its expected lifetime, making PDS 70 an important example of a young planet-hosting star in the late stage of accretion.

A Cell Trappable Methyl Rhodol-Based Fluorescent Probe for Hydrogen Sulfide Detection.

Hydrogen sulfide is a biologically important molecule and developing chemical tools that enable further investigations into the functions of H2 S is essential. Fluorescent turn-on H2 S probes have been developed for use in cellulo and in vivo, but the membrane permeability of these probes can lead to probe leakage and signal attenuation over time. Here we report a cell trappable fluorescent probe for H2 S, CT-MeRhoAz, which is based on a methylrhodolazide scaffold derivatized with an acetoxymethyl ester group. Prior to ester cleavage, the CT-MeRhoAz probe generates a 2500-fold turn-on response to H2 S, which is enhanced to a 3000-fold response for the carboxylic acid form of the probe. Additionally, the probe is highly selective for H2 S over other biologically relevant sulfur, oxygen, and nitrogen-based analytes. Live cell imaging experiments confirmed the biocompatibility of CT-MeRhoAz and also that it is cell trappable, unlike the parent MeRhoAz scaffold.

Sensitivity and Selectivity Analysis of Fluorescent Probes for Hydrogen Sulfide Detection.

Hydrogen sulfide (H2S) is a gasotransmitter known to regulate physiological and pathological processes. Abnormal H2S levels have been associated with a range of conditions, including Parkinson's and Alzheimer's diseases, cardiovascular and renal diseases, bacterial and viral infections, as well as cancer. Therefore, fast and sensitive H2S detection is of significant clinical importance. Fluorescent H2S probes hold great potential among the currently developed detection methods because of their high sensitivity, selectivity, and biocompatibility. However, many proposed probes do not provide a gold standard for proper use and selection. Consequently, issues arise when applying the probes in different conditions. Therefore, we systematically evaluated four commercially available probes (WSP‐1, WSP‐5, CAY, and P3), considering their detection range, sensitivity, selectivity, and performance in different environments. Furthermore, their capacity for endogenous H2S imaging in live cells was demonstrated.

Role of ferroptosis iron-dependent cell death in neurodegenerative processes.

Accumulation or overload of bioavailable redox active metals causes protein overexpression-aggregation, mitochondrial dysfunction, nucleus alterations, inflammation-immune responses and high oxidative stress that directly disrupt normal neuronal cell functions. Significantly, a novel form of iron-dependent regulated cell death process termed ferroptosis was recently identified. Misregulated ferroptosis pathways have been speculated to trigger neurodegeneration through programmed cell death that is distinct from classical mechanisms, although the underlying mechanisms remain only partially understood. We induced ferroptosis (erastin, buthioninesulfoximine and sulfasalazine, ammonium iron(III) citrate) on in vitro cultured neurons. Neuronal responses were characterized by bioassays (ROS, GSH, Iron, DPPP), RNA-seq and confocal microscopy. We induced ferroptosis using compounds that target the main ferroptotic pathways and analyzed the biochemical responses. We selected buthionine-sulfoximine targeting GPX4, erastin targeting system Xc - , and iron (III) citrate targeting iron transporters/trafficking . We dosed neurons with 0-200μM to determine IC50, dose- and time-dependent responses. Notably, the ferroptosis inducers caused a time-dependent increase in cytosolic and lipid ROS, as assessed by microplate assay and fluorescent microscopy using fluorescent probes H2 DCFDA and DPPP, respectively. After 24 h, the increase in ROS was accompanied by cell detachment, cell death and change in morphology. Intracellular glutathione pool suffered depletion, whereas labile iron accumulated over the course of the treatment. ROS accumulation and cell death were suppressed by cotreatment with the iron chelator deferoxamine (100 μM). Furthermore, we performed RNA-seq to determine pathways altered by ferroptosis, and morphological characterization by confocal and electron microscopy. Our data show marked alteration in metabolism of iron, glutathione depletion, ROS overproduction, and marked lipid peroxidation in neurons dosed with ferroptosis inducers, confirming susceptibility of neurons to iron-dependent ferroptosis cell death.

High-resolution Near-infrared Spectroscopy of Diffuse Sources around MWC 1080

Abstract To reveal the origins of diffuse Hα emissions observed around the Herbig star MWC 1080, we have performed a high-resolution near-infrared (NIR) spectroscopic observation using the Immersion Grating Infrared Spectrograph. In the NIR H and K bands, we detected various emission lines (six hydrogen Brackett lines, seven H2 lines, and an [Fe ii] line) and compared their spatial locations with the optical (Hα and [S ii]) and radio (13CO and CS) line maps. The shock-induced H2 and [Fe ii] lines indicate the presence of multiple outflows, consisting of at least three associated young stars in this region. The kinematics of H2 and [Fe ii] near the northeast (NE) cavity edge supports the idea that the NE main outflow from MWC 1080A is the blueshifted one with a low inclination angle. The H2 and [Fe ii] lines near the southeast molecular region newly reveal that additional highly blueshifted outflows originate from other young stars. The fluorescent H2 lines were found to trace photodissociation regions formed on the cylindrical surfaces of the main outflow cavity, which are expanding outward with a velocity of about 10–15 km s−1. For the Hα emission, we identify its components associated with two stellar outflows and two young stars in addition to the dominant component of MWC 1080A scattered by dust. We also report a few faint Hα features located ∼0.4 pc away in the southwest direction from MWC 1080A, which lie near the axes of the NE main outflow and one of the newly identified outflows.

Fluorescent H2 Receptor Squaramide-Type Antagonists: Synthesis, Characterization, and Applications.

Fluorescence labeled ligands have been gaining importance as molecular tools, enabling receptor-ligand-binding studies by various fluorescence-based techniques. Aiming at red-emitting fluorescent ligands for the hH2R, a series of squaramides labeled with pyridinium or cyanine fluorophores (19-27) was synthesized and characterized. The highest hH2R affinities in radioligand competition binding assays were obtained in the case of pyridinium labeled antagonists 19-21 (pK i: 7.71-7.76) and cyanine labeled antagonists 23 and 25 (pK i: 7.67, 7.11). These fluorescent ligands proved to be useful tools for binding studies (saturation and competition binding as well as kinetic experiments), using confocal microscopy, flow cytometry, and high content imaging. Saturation binding experiments revealed pK d values comparable to the pK i values. The fluorescent probes 21, 23, and 25 could be used to localize H2 receptors in HEK cells and to determine the binding affinities of unlabeled compounds.

HST spectra reveal accretion in MY Lupi

The mass accretion rate is a crucial parameter for the study of the evolution of accretion discs around young low-mass stellar and substellar objects (YSOs). We revisit the case of MY Lup, an object where VLT/X-shooter data suggested a negligible mass accretion rate, and show it to be accreting on a level similar to other Class II YSOs in Lupus based on Hubble Space Telescope (HST) observations. In our HST-Cosmic Origins Spectrograph (HST-COS) and -Space Telescope Imaging Spectrograph (HST-STIS) spectra, we find many emission lines, as well as substantial far-ultraviolet (FUV) continuum excess emission, which can be ascribed to active accretion. The total luminosity of the C IV λ1549 Å doublet is 4.1 × 10−4 L⊙. Using scalings between accretion luminosity, Lacc, and C IV luminosity from the literature, we derive Lacc ~2 × 10−1 L⊙, which is more than an order of magnitude higher than the upper limit estimated from the X-shooter observations. We discuss possible reasons for the X-shooter-HST discrepancy, the most plausible being that the low contrast between the continuum excess emission and the photospheric+chromospheric emission at optical wavelengths in MY Lup hampered detection of excess emission. The luminosity of the FUV continuum and C IV lines, strong H2 fluorescence, and a “1600 A Bump” place MY Lup in the class of accreting objects with gas-rich discs. So far, MY Lup is the only peculiar case in which a significant difference between the HST and X-shooter Ṁacc estimates exists that is not ascribable to variability. The mass accretion rate inferred from the revisited Lacc estimate is Ṁacc ~ 1(−0.5+1.5) × 10−8 M⊙ yr−1. This value is consistent with the typical value derived for accreting YSOs of similar mass in Lupus and points to less clearing of the inner disc than indicated by near- and mid-infrared observations. This is confirmed by Atacama Large Millimeter Array (ALMA) data, which show that the gaps and rings seen in the sub-millimetre are relatively shallow.

Optical and UV surface brightness of translucent dark nebulae

Context. Dark nebulae display a surface brightness because dust grains scatter light of the general interstellar radiation field (ISRF). High-galactic-latitudes dark nebulae are seen as bright nebulae when surrounded by transparent areas which have less scattered light from the general galactic dust layer. Aims. Photometry of the bright dark nebulae LDN 1780, LDN 1642, and LBN 406 shall be used to derive scattering properties of dust and to investigate the presence of UV fluorescence emission by molecular hydrogen and the extended red emission (ERE). Methods. We used multi-wavelength optical photometry and imaging at ground-based telescopes and archival imaging and spectroscopic UV data from the spaceborn GALEX and SPEAR/FIMS instruments. In the analysis we used Monte Carlo RT and both observational data and synthetic models for the ISRF in the solar neighbourhood. The line-of-sight extinctions through the clouds have been determined using near infrared excesses of background stars and the 200/250 μm far infrared emission by dust as measured using the ISO and Herschel space observatories. Results. The optical surface brightness of the three target clouds can be explained in terms of scattered light. The dust albedo ranges from ~0.58 at 3500 Å to ~0.72 at 7500 Å. The spectral energy distribution of LDN 1780 is explained in terms of optical depth and background scattered light effects instead of the original published suggestion in terms of ERE. The far-ultraviolet surface brightness of LDN 1780 cannot be explained by scattered light only. In LDN 1780, H2 fluorescent emission in the wavelength range 1400–1700 Å has been detected and analysed. Conclusions. Our albedo values are in good agreement with the predictions of the dust model of Weingartner and Draine and with the THEMIS CMM model for evolved core-mantle grains. The distribution of H2 fluorescent emission in LDN 1780 shows a pronounced dichotomy with a strong preference for its southern side where enhanced illumination is impinging from the Sco OB2 association and the O star ζ Oph. A good correlation is found between the H2 fluorescence and a previously mapped 21-cm excess emission. The H2 fluorescence emission in LDN 1780 has been modelled using a PDR code; the resulting values for H2 column density and the total gas density are consistent with the estimates derived from CO observations and optical extinction along the line of sight.

Sustainable synthesis of CeO2/CdS-diethylenetriamine composites for enhanced photocatalytic hydrogen evolution under visible light

Cadmium sulfide (CdS) is a promising semiconductor material for photocatalytic hydrogen (H2) evolution. However, the serious photocorrosion and low visible-light utilization limit its practical application. In this work, cerium oxide (CeO2) modified inorganic-organic CdS-diethylenetriamine (CeO2/CdS-DETA) composite material with different mass ratios was fabricated by hydrothermal method. Crystal structure, light absorption properties, microstructure, photocatalytic H2 production activity, photocurrent and fluorescence spectra of the composites were investigated. The results exhibited that photocatalytic performance of CeO2/CdS-DETA materials was improved and 7%CeO2/CdS-DETA exhibited excellent catalytic activity (14.84 mmol g-1 h-1) under visible light irradiation (λ ≥ 420 nm), which is twice more than that of CdS-DETA. Moreover, the photocatalytic mechanism was preliminarily discussed. This work not only promotes the development of novel inorganic-organic CdS-DETA-based photocatalytic materials for solar energy utilization but provides sustainable photocatalysts by taking both photocatalytic H2 production and repeated utilization into consideration.

The Orion Fingers: H2 Temperatures and Excitation in an Explosive Outflow

Abstract We measure H2 temperatures and column densities across the Orion Becklin-Neugebauer/Kleinmann-Low (BN/KL) explosive outflow from a set of 13 near-infrared (IR) H2 rovibrational emission lines observed with the TripleSpec spectrograph on Apache Point Observatory’s 3.5 m telescope. We find that most of the region is well characterized by a single temperature (∼2000–2500 K), which may be influenced by the limited range of upper-energy levels (6000–20,000 K) probed by our data set. The H2 column density maps indicate that warm H2 comprises 10−5–10−3 of the total H2 column density near the center of the outflow. Combining column density measurements for co-spatial H2 and CO at T = 2500 K, we measure a CO/H2 fractional abundance of 2 × 10−3 and discuss possible reasons why this value is in excess of the canonical 10−4 value, including dust attenuation, incorrect assumptions on co-spatiality of the H2 and CO emission, and chemical processing in an extreme environment. We model the radiative transfer of H2 in this region with ultraviolet (UV) pumping models to look for signatures of H2 fluorescence from H i Lyα pumping. Dissociative (J-type) shocks and nebular emission from the foreground Orion H ii region are considered as possible Lyα sources. From our radiative transfer models, we predict that signatures of Lyα pumping should be detectable in near-IR line ratios given a sufficiently strong source, but such a source is not present in the BN/KL outflow. The data are consistent with shocks as the H2 heating source.

Signatures of Hot Molecular Hydrogen Absorption from Protoplanetary Disks. I. Non-thermal Populations

Abstract The environment around protoplanetary disks (PPDs) regulates processes that drive the chemical and structural evolution of circumstellar material. We perform a detailed empirical survey of warm molecular hydrogen (H2) absorption observed against H i-Lyα (Lyα: λ1215.67) emission profiles for 22 PPDs, using archival Hubble Space Telescope ultraviolet (UV) spectra to identify H2 absorption signatures and quantify the column densities of H2 ground states in each sightline. We compare thermal equilibrium models of H2 to the observed H2 rovibrational level distributions. We find that, for the majority of targets, there is a clear deviation in high-energy states (T exc ≳ 20,000 K) away from thermal equilibrium populations (T(H2) ≳ 3500 K). We create a metric to estimate the total column density of non-thermal H2 (N(H2)nLTE) and find that the total column densities of thermal (N(H2)) and N(H2)nLTE correlate for transition disks and targets with detectable C iv-pumped H2 fluorescence. We compare N(H2) and N(H2)nLTE to circumstellar observables and find that N(H2)nLTE correlates with X-ray and far-UV luminosities, but no correlations are observed with the luminosities of discrete emission features (e.g., Lyα, C iv). Additionally, N(H2) and N(H2)nLTE are too low to account for the H2 fluorescence observed in PPDs, so we speculate that this H2 may instead be associated with a diffuse, hot, atomic halo surrounding the planet-forming disk. We create a simple photon-pumping model for each target to test this hypothesis and find that Lyα efficiently pumps H2 levels with T exc ≥ 10,000 K out of thermal equilibrium.

H2 Fluorescence in M Dwarf Systems: A Stellar Origin

Abstract Observations of molecular hydrogen (H2) fluorescence are a potentially useful tool for measuring the H2 abundance in exoplanet atmospheres. This emission was previously observed in dwarfs with planetary systems. However, low signal-to-noise prevented a conclusive determination of its origin. Possible sources include exoplanetary atmospheres, circumstellar gas disks, and the stellar surface. We use observations from the “Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanet Host Stars” Treasury Survey to study H2 fluorescence in dwarfs. We detect fluorescence in Hubble Space Telescope spectra of 8/9 planet-hosting and 5/6 non-planet-hosting dwarfs. The detection statistics, velocity centroids, and line widths of the emission suggest a stellar origin. We calculate H2-to-stellar-ion flux ratios to compare flux levels between stars. For stars with planets, we find an average ratio of , using the fluxes of the brightest H2 feature and two stellar C iv lines. This is compared to for stars without planets, showing that the planet-hosting dwarfs do not have significant excess H2 emission. This claim is supported by the direct FUV imaging of GJ 832, where no fluorescence is observed at the expected star–planet separation. Additionally, the 3σ upper limit of 4.9 × 10−17 erg cm−2 s−1 from these observations is two orders of magnitude below the spectroscopically observed H2 flux. We constrain the location of the fluorescing H2 using 1D radiative transfer models, and find that it could reside in starspots or a ∼2500–3000 region in the lower chromosphere. The presence of this emission could complicate efforts to quantify the atmospheric abundance of H2 in exoplanets orbiting dwarfs.

A Far-ultraviolet Fluorescent Molecular Hydrogen Emission Map of the Milky Way Galaxy

Abstract We present the far-ultraviolet (FUV) fluorescent molecular hydrogen (H2) emission map of the Milky Way Galaxy obtained with FIMS/SPEAR covering ∼76% of the sky. The extinction-corrected intensity of the fluorescent H2 emission has a strong linear correlation with the well-known tracers of the cold interstellar medium (ISM), including color excess E(B–V), neutral hydrogen column density N(H i), and Hα emission. The all-sky H2 column density map was also obtained using a simple photodissociation region model and interstellar radiation fields derived from UV star catalogs. We estimated the fraction of H2 (f H2) and the gas-to-dust ratio (GDR) of the diffuse ISM. The f H2 gradually increases from <1% at optically thin regions where E(B–V) < 0.1 to ∼50% for E(B–V) = 3. The estimated GDR is ∼5.1 × 1021 atoms cm−2 mag−1, in agreement with the standard value of 5.8 × 1021 atoms cm−2 mag−1.

The 1600 Å Emission Bump in Protoplanetary Disks: A Spectral Signature of H2O Dissociation∗

Abstract The FUV continuum spectrum of many accreting pre-main sequence stars, Classical T Tauri Stars (CTTSs), does not continue smoothly from the well-studied Balmer continuum emission in the NUV, suggesting that additional processes contribute to the short-wavelength emission in these objects. The most notable spectral feature in the FUV continuum of some CTTSs is a broad emission approximately centered at 1600 Å, which has been referred to as the “1600 Å Bump.” The origin of this feature remains unclear. In an effort to better understand the molecular properties of planet-forming disks and the UV spectral properties of accreting protostars, we have assembled archival FUV spectra of 37 disk-hosting systems observed by the Hubble Space Telescope-Cosmic Origins Spectrograph. Clear 1600 Å Bump emission is observed above the smooth, underlying 1100–1800 Å continuum spectrum in 19/37 Classical T Tauri disks in the HST-COS sample, with the detection rate in transition disks (8/8) being much higher than that in primordial or non-transition sources (11/29). We describe a spectral deconvolution analysis to separate the Bump (spanning 1490–1690 Å) from the underlying FUV continuum, finding an average Bump luminosity L(Bump) ≈ 7 × 1029 erg s−1. Parameterizing the Bump with a combination of Gaussian and polynomial components, we find that the 1600 Å Bump is characterized by a peak wavelength λ o = 1598.6 ± 3.3 Å, with FWHM = 35.8 ± 19.1 Å. Contrary to previous studies, we find that this feature is inconsistent with models of H2 excited by electron -impact. We show that this Bump makes up between 5%–50% of the total FUV continuum emission in the 1490–1690 Å band and emits roughly 10%–80% of the total fluorescent H2 luminosity for stars with well-defined Bump features. Energetically, this suggests that the carrier of the 1600 Å Bump emission is powered by Lyα photons. We argue that the most likely mechanism is Lyα-driven dissociation of H2O in the inner disk, r ≲ 2 au. We demonstrate that non-thermally populated H2O fragments can qualitatively account for the observed emission (discrete and continuum) and find that the average Lyα-driven H2O dissociation rate is 1.7 × 1042 water molecules s−1.

Hyperpolarized 129 Xe Magnetic Resonance Imaging Sensor for H2 S.

A new magnetic resonance imaging (MRI) molecular sensor for hydrogen sulfide detection and imaging using the nuclear spin resonance of hyperpolarized 129 Xe is developed. The designed MRI sensor employs cryptophane for NMR sensing, together with an azide group serving as a reaction site. It demonstrates a "proof-of-concept" that a fluorescent H2 S probe can be linked to a xenon-binding cryptophane and thereby converted into an MRI probe, which could provide a very generalizable template.

EMPIRICALLY ESTIMATED FAR-UV EXTINCTION CURVES FOR CLASSICAL T TAURI STARS

ABSTRACT Measurements of extinction curves toward young stars are essential for calculating the intrinsic stellar spectrophotometric radiation. This flux determines the chemical properties and evolution of the circumstellar region, including the environment in which planets form. We develop a new technique using H2 emission lines pumped by stellar Lyα photons to characterize the extinction curve by comparing the measured far-ultraviolet H2 line fluxes with model H2 line fluxes. The difference between model and observed fluxes can be attributed to the dust attenuation along the line of sight through both the interstellar and circumstellar material. The extinction curves are fit by a Cardelli et al. (1989) model and the A V (H2) for the 10 targets studied with good extinction fits range from 0.5 to 1.5 mag, with R V values ranging from 2.0 to 4.7. A V and R V are found to be highly degenerate, suggesting that one or the other needs to be calculated independently. Column densities and temperatures for the fluorescent H2 populations are also determined, with averages of log10(N(H2)) = 19.0 and T = 1500 K. This paper explores the strengths and limitations of the newly developed extinction curve technique in order to assess the reliability of the results and improve the method in the future.