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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Communication: Methane dissociation on Ni(111) surface: Importance of azimuth and surface impact site

Understanding the role of reactant ro-vibrational degrees of freedom (DOFs) in reaction dynamics of polyatomic molecular dissociation on metal surfaces is of great importance to explore the complex chemical reaction mechanism. Here, we present an expensive quantum dynamics study of the dissociative chemisorption of CH{sub 4} on a rigid Ni(111) surface by developing an accurate nine-dimensional quantum dynamical model including the DOF of azimuth. Based on a highly accurate fifteen-dimensional potential energy surface built from first principles, our simulations elucidate that the dissociation probability of CH{sub 4} has the strong dependence on azimuth and surface impact site. Some improvements are suggested to obtain the accurate dissociation probability from quantum dynamics simulations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Interaction of solitons with a string of coupled quantum dots

In this paper, we develop a theory for discrete solitons interaction with a string of coupled quantum dots in view of the local field effects. Discrete nonlinear Schrodinger (DNLS) equations are used to describe the dynamics of the string. Numerical calculations are carried out and results are analyzed with the help of matlab software. With the help of numerical solutions we demonstrate that in the quantum dots string, Rabi oscillations (RO) are self trapped into stable bright Rabi solitons. The Rabi oscillations in different types of nanostructures have potential applications to the elements of quantum logic and quantum memory.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Benchmarking all-atom simulations using hydrogen exchange

Molecular dynamics simulations have recently become capable of observing multiple protein unfolding and refolding events in a single-millisecond–long trajectory. This major advance produces atomic-level information with nanosecond resolution, a feat unmatched by experimental methods. Such simulations are being extensively analyzed to assess their description of protein folding, yet the results remain difficult to validate experimentally. We apply a combination of hydrogen exchange, NMR, and other techniques to test the simulations with a resolution of single H-bonds. Several significant discrepancies between the simulations and experimental data were uncovered for regions of the energy surface outside of the native basin. This comparison yields suggestions for improving the force fields and provides a general method for experimentally validating folding simulations.

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

Review and Modeling of Integrated Energy Systems with Nuclear Reactor Coupled Desalination and District Heating

Detailed reviews of a past advanced nuclear reactor based integrated energy system, as well as other nuclear reactor and fossil fuel based integrated energy systems have been performed for this work. Review of the utilization of heat from nuclear reactors for various applications and cogeneration has been done. The heat can be utilized by extraction of the steam from the turbine while the steam is still at a desired temperature. While use of nuclear process heat for district heating in countries like Finland, France, China, Poland, and elsewhere is discussed, more focus of the review has been given on nuclear desalination processes. Integrated energy systems (IES) where distinct types of reactors like PWR, BWR, sodium cooled fast reactor, heavy water reactor and other advanced reactors are coupled with various nuclear desalination processes like multi-effect distillation (MED), multi-stage flashing (MSF) and reverse osmosis (RO) methods have been discussed. The nuclear desalination plant at Aktau has been discussed in more detail due to its decades of successful operation. The IES of the Aktau plant coupled with 5-effect MED desalination plant has been taken as a reference for modeling the Open Modelica (OM) based IES of this work. Here, the OM IES model shows good agreement with the MED plant output of Aktau and can be extended for future applications of IES.

42 ENGINEERING↗
DOE OSTI2013

CATALOG AND STATISTICAL STUDY OF X-RAY SELECTED BL LACERTAE OBJECTS

This paper presents a catalog of 312 X-ray selected BL Lacerate objects (XBLs), optically identified through the end of 2011. It contains the names from different surveys, equatorial coordinates, redshifts, multifrequency flux values, and luminosities for each source. In addition, the different characteristics of XBLs are statistically investigated (redshift, radio/optical/X-ray luminosities, central black hole (BH) mass, synchrotron peak frequency, broadband spectral indices, optical flux variability). Their values are collected through an extensive bibliographic and database search or calculated by us. The redshifts range from 0.031 to 0.702 with a maximum of the distribution at z = 0.223. The 1.4 GHz luminosities of XBLs log {nu}L{sub {nu}} {approx} 39-42 erg s{sup -1} while optical V and X-ray 0.1-2.4 keV bands show log {nu}L{sub {nu}} {approx} 43-46 erg s{sup -1}. The XBL hosts are elliptical galaxies with effective radii r{sub eff} = 3.2625.40 kpc and ellipticities, in = 0.040.52. Their R-band absolute magnitudes M{sub R} range from -21.11 mag to -24.86 mag with a mean value of -22.83 mag. The V - R indices of the hosts span from 0.61 to 1.52 and reveal a fourth-degree polynomial relationship with z that enables us to evaluate the redshifts of five sources whose V - R indices were determined from the observations but whose irredshifts values are either not found or not confirmed. The XBL nuclei show a wider range of 7.31 mag for M{sub R} with the highest luminosity corresponding to M{sub R} = -27.24 mag. The masses of central BHs are found in the interval log M{sub BH} = 7.39-9.30 solar masses (with distribution maximum at log M{sub BH}/M{sub Sun} = 8.30). The synchrotron peak frequencies are spread over the range log {nu}{sub peak} = 14.56-19.18 Hz with a peak of the distribution at log {nu}{sub peak} = 16.60 Hz. The broadband radio-to-optical ({alpha}{sub ro}), optical-to-X-ray ({alpha}{sub ox}), and radio-to-X-ray ({alpha}{sub rx}) spectral indices are distributed in the intervals (0.17,0.59), (0.56,1.48), and (0.41,0.75), respectively. In the optical energy range, the overall flux variability increases, on average, towards shorter wavelengths: ({Delta}m) = 1.22, 1.50, and 1.82 mag through the R, V, B bands of Johnson-Cousins system, respectively. XBLs seem be optically less variable at the intranight timescales compared to the radio-selected BL Lacs (RBLs).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Prompt emission by OH in comet Hyakutake

Laboratory studies predict that the photo-dissociation of H{sub 2}O by solar Ly{sub α} photons in the comae of comets should lead to a small percentage of OH in high rotational states of the A {sup 2}Σ{sup +} electronic state. These states should promptly emit a near-ultraviolet (near-UV) photon in a transition to the X {sup 2}Π state. From there, the radicals decay to the lowest rotational states by direct rotational transitions and via ro-vibrational cascade in the 1-0 vibrational band, all within the X {sup 2}Π state. Normally in Earth-based observations the lines are extremely weak compared to the fluorescence of OH in sunlight. Since the prompt emission rate is directly proportional to the column density of water, whereas the fluorescent emission of OH is proportional to the column density of OH, the lines due to prompt emission are relatively strongest very close to the nucleus, a region not often accessible from Earth. We report here the first spectrally resolved detection of near-UV prompt emission by cometary OH, as seen in the bright comet Hyakutake (C/1996 B2), on the day of its closest approach to Earth. All the expected doublets are seen, in both the P and Q branches, up to rotational quantum number N′ = 22 with relative strengths in good agreement with the laboratory results. The fluxes of the lines are in agreement with what one expects from the various measurements of the water production rate of the comet, including that deduced from the OH fluorescent lines in these spectra.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

A SIMPLE NONLINEAR MODEL FOR THE ROTATION OF MAIN-SEQUENCE COOL STARS. I. INTRODUCTION, IMPLICATIONS FOR GYROCHRONOLOGY, AND COLOR-PERIOD DIAGRAMS

We here introduce a simple nonlinear model to describe the rotational evolution of cool stars on the main sequence. It is formulated only in terms of the Rossby number (Ro = P/{tau}), its inverse, and two dimensionless constants which we specify using solar and open-cluster data. The model has two limiting cases of stellar rotation, previously called C and I, that correspond to two observed sequences of fast and slowly rotating stars in young open clusters. The model describes the evolution of stars from C-type, with particular mass and age dependencies, to I-type, with different mass and age dependencies, through the rotational gap, g, separating them. The proposed model explains various aspects of stellar rotation, and provides an exact expression for the age of a rotating cool star in terms of P and {tau}, thereby generalizing gyrochronology. Using it, we calculate the time interval required for stars to reach the rotational gap-a monotonically increasing, mildly nonlinear function of {tau}. Beginning with the range of initial periods indicated by observations, we show that the (mass-dependent) dispersion in rotation period initially increases, and then decreases rapidly with the passage of time. The initial dispersion in period contributes up to 128 Myr to the gyro-age errors of solar-mass field stars. Finally, we transform to color-period space, calculate appropriate isochrones, and show that this model explains some detailed features in the observed color-period diagrams of open clusters, including the positions and shapes of the sequences, and the observed density of stars across these diagrams.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

A MOLECULAR HYDROGEN NEBULA IN THE CENTRAL cD GALAXY OF THE PERSEUS CLUSTER

We report narrowband imaging of the 1-0 S(1) ro-vibrational transition of molecular hydrogen (H{sub 2}) from NGC 1275, the central cD galaxy of the Perseus Cluster. We find that the H{sub 2} gas has a spatial morphology identical to the optical emission-line nebula associated with this galaxy, a total luminosity in H{sub 2} 1-0 S(1) only an order of magnitude less than in H{alpha}, and if the line-emitting gas is thermalized a mass (at {approx}2000 K) that is over two orders of magnitude smaller than that of the optical emission-line nebula (at {approx}10,000 K). The ratio in H{sub 2} 1-0 S(1) to H{alpha}+[N II] line intensities spans a characteristic range of {approx}0.02-0.08 throughout the nebula; the brighter inner nebula exhibits patches with (nearly) constant line ratios unrelated to individual filaments. Recent models proposed to explain the peculiar nebular spectrum from the optical to infrared invoke thermalized along with non-thermalized injection of energy from ionizing particles. The energy density of highly relativistic electrons inferred to cause inverse-Compton scattering of hard X-ray emission from the core of the Perseus Cluster decreases steeply beyond a central radius of {approx}20 kpc, yet we do not find any changes in the average or range spanned by the H{sub 2} 1-0 S(1) to H{alpha}+[N II] line ratio between the inner ({approx}<20 kpc) and outer ({approx}20-50 kpc) nebulae. On the other hand, saturated conduction from the surrounding X-ray gas produces, in the absence of magnetic fields, a heat flux that is approximately constant throughout the nebula: the change in the line ratio with position would then reflect the ability of the X-ray gas to penetrate presumably magnetically threaded filaments at different locations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

CHARACTERIZING CO FOURTH POSITIVE EMISSION IN YOUNG CIRCUMSTELLAR DISKS

Carbon monoxide is a commonly used IR/submillimeter tracer of gas in protoplanetary disks. We present an analysis of ultraviolet CO emission in Hubble Space Telescope Cosmic Origins Spectrograph spectra for 12 Classical T Tauri stars (CTTSs). Several ro-vibrational bands of the CO A{sup 1}{Pi}-X{sup 1}{Sigma}{sup +} (Fourth Positive) electronic transition system are spectrally resolved from emission of other atoms and H{sub 2}. The CO A{sup 1}{Pi} v' = 14 state is populated by absorption of Ly{alpha} photons, created at the accretion column on the stellar surface. For targets with strong CO emission, we model the Ly{alpha} radiation field as an input for a simple fluorescence model to estimate CO rotational excitation temperatures and column densities. Typical column densities range from N{sub CO} = 10{sup 18} to 10{sup 19} cm{sup -2}. Our measured excitation temperatures are mostly below T{sub CO} = 600 K, cooler than typical M-band CO emission. These temperatures and the emission line widths imply that the UV emission originates in a different population of CO than that which is IR-emitting. We also find a significant correlation between CO emission and the disk accretion rate M-dot and age. Our analysis shows that ultraviolet CO emission can be a useful diagnostic of CTTS disk gas.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

THE ANATOMY OF THE YOUNG PROTOSTELLAR OUTFLOW HH 211

We present Spitzer Space Telescope 5-36 {mu}m mapping observations toward the southeastern lobe of the young protostellar outflow HH 211. The southeastern terminal shock of the outflow shows a rich mid-infrared spectrum including molecular emission lines from OH, H{sub 2}O, HCO{sup +}, CO{sub 2}, H{sub 2}, and HD. The spectrum also shows a rising infrared continuum toward 5 {mu}m, which we interpret as unresolved emission lines from highly excited rotational levels of the CO v = 1-0 fundamental band. This interpretation is supported by a strong excess flux observed in the Spitzer/IRAC 4-5 {mu}m channel 2 image compared to the other IRAC channels. The extremely high critical densities of the CO v = 1-0 ro-vibrational lines and a comparison to H{sub 2} and CO excitation models suggest jet densities larger than 10{sup 6} cm{sup -3} in the terminal shock. We also observed the southeastern terminal outflow shock with the Submillimeter Array and detected pure rotational emission from CO 2-1, HCO{sup +} 3-2, and HCN 3-2. The rotationally excited CO traces the collimated outflow backbone as well as the terminal shock. HCN traces individual dense knots along the outflow and in the terminal shock, whereas HCO{sup +} solely appears in the terminal shock. The unique combination of our mid-infrared and submillimeter observations with previously published near-infrared observations allow us to study the interaction of one of the youngest known protostellar outflows with its surrounding molecular cloud. Our results help us to understand the nature of some of the so-called green fuzzies (Extended Green Objects), and elucidate the physical conditions that cause high OH excitation and affect the chemical OH/H{sub 2}O balance in protostellar outflows and young stellar objects. In an appendix to this paper, we summarize our Spitzer follow-up survey of protostellar outflow shocks to find further examples of highly excited OH occurring together with H{sub 2}O and H{sub 2}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

DIRECT DETERMINATION OF THE HF/H{sub 2} ABUNDANCE RATIO IN INTERSTELLAR GAS

We report the first detection of the v = 1-0, R(0) ro-vibrational transition of HF at 2.499385 {mu}m arising from interstellar gas. The line is seen in absorption toward three background sources-HD 154368, Elias 29, and AFGL 2136 IRS 1-all of which have reported H{sub 2} column densities determined from observations of H{sub 2}. This allows for the first direct determination of the HF/H{sub 2} abundance ratio. We find values of N(HF)/N(H{sub 2}) = 1.15 Multiplication-Sign 10{sup -8} and 0.69 Multiplication-Sign 10{sup -8} for HD 154368 and Elias 29, respectively. The sight line toward AFGL 2136 IRS 1 also shows absorption from the v = 1-0, R(1) transition of HF, indicating warm, dense (n {sub H} {approx}> 10{sup 9} cm{sup -3}) gas, likely very close to the central protostar. Ascribing portions of the HF absorption to warm and cold gas, we find N(HF)/N(H{sub 2}) = (1.7-2.9) Multiplication-Sign 10{sup -8} and (0.33-0.58) Multiplication-Sign 10{sup -8} for the two components, respectively. Except for the warm component toward AFGL 2136 IRS 1, all observed HF/H{sub 2} ratios are well below N(HF)/N(H{sub 2}) = 3.6 Multiplication-Sign 10{sup -8}, the value predicted if nearly all gas phase fluorine is in the form of HF. Models of fluorine chemistry that account for depletion onto grains are able to reproduce the results toward HD 154368, but not in the cold, dense gas toward AFGL 2136 IRS 1 and Elias 29. Most likely, some combinations of simplifying assumptions made in the chemical models are responsible for these discrepancies.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2013

WATER ABSORPTION FROM GAS VERY NEAR THE MASSIVE PROTOSTAR AFGL 2136 IRS 1

We present ground-based observations of the ν{sub 1} and ν{sub 3} fundamental bands of H{sub 2}O toward the massive protostar AFGL 2136 IRS 1, identifying absorption features due to 47 different ro-vibrational transitions between 2.468 μm and 2.561 μm. Analysis of these features indicates the absorption arises in warm (T = 506 ± 25 K), very dense (n(H{sub 2}) > 5 × 10{sup 9} cm{sup –3}) gas, suggesting an origin close to the central protostar. The total column density of warm water is estimated to be N(H{sub 2}O) = (1.02 ± 0.02) × 10{sup 19} cm{sup –2}, giving a relative abundance of N(H{sub 2}O)/N(H{sub 2}) ≈ 10{sup –4}. Our study represents the first extensive use of water vapor absorption lines in the near infrared, and demonstrates the utility of such observations in deriving physical parameters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Infrared H{sub 3}{sup +} and CO studies of the galactic core: GCIRS 3 and GCIRS 1W

We have obtained improved spectra of key fundamental band lines of H{sub 3}{sup +}, R(1, 1) {sup l}, R(3, 3) {sup l}, and R(2, 2) {sup l}, and ro-vibrational transitions of CO on sightlines toward the luminous infrared sources GCIRS 3 and GCIRS 1W, each located in the Central Cluster of the Galactic center within several arcseconds of Sgr A*. The spectra reveal absorption occurring in three kinds of gaseous environments: (1) cold dense and diffuse gas associated with foreground spiral/lateral arms; (2) warm and diffuse gas absorbing over a wide and mostly negative velocity range, which appears to fill a significant fraction of the Galaxy's Central Molecular Zone (CMZ); and (3) warm, dense and compact clouds with velocities near +50 km s{sup –1} probably within 1-2 pc of the center. The absorptions by the first two cloud types are nearly identical for all the sources in the Central Cluster, and are similar to those previously observed on sightlines from Sgr A* to 30 pc east of it. Cloud type (3), which has only been observed toward the Central Cluster, shows distinct differences between the sightlines to GCIRS 3 and GCIRS 1W, which are separated on the sky by only 0.33 pc in projection. We identify this material as part of an inward extension of the circumnuclear disk previously known from HCN mapping. Lower limits on the products of the hydrogen ionization rate ζ and the path length L are 2.3 × 10{sup 5} cm s{sup –1} and 1.5 × 10{sup 3} cm s{sup –1} for the warm and diffuse CMZ gas and for the warm and dense clouds in the core, respectively. The limits indicate that the ionization rates in these regions are well above 10{sup –15} s{sup –1}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Effects of the seasonal cycle on superrotation in planetary atmospheres

The dynamics of dry atmospheric general circulation model simulations forced by seasonally varying Newtonian relaxation are explored over a wide range of two control parameters and are compared with the large-scale circulation of Earth, Mars, and Titan in their relevant parameter regimes. Of the parameters that govern the behavior of the system, the thermal Rossby number (Ro) has previously been found to be important in governing the spontaneous transition from an Earth-like climatology of winds to a superrotating one with prograde equatorial winds, in the absence of a seasonal cycle. This case is somewhat unrealistic as it applies only if the planet has zero obliquity or if surface thermal inertia is very large. While Venus has nearly vanishing obliquity, Earth, Mars, and Titan (Saturn) all have obliquities of ∼25° and varying degrees of seasonality due to their differing thermal inertias and orbital periods. Motivated by this, we introduce a time-dependent Newtonian cooling to drive a seasonal cycle using idealized model forcing, and we define a second control parameter that mimics non-dimensional thermal inertia of planetary surfaces. We then perform and analyze simulations across the parameter range bracketed by Earth-like and Titan-like regimes, assess the impact on the spontaneous transition to superrotation, and compare Earth, Mars, and Titan to the model simulations in the relevant parameter regime. We find that a large seasonal cycle (small thermal inertia) prevents model atmospheres with large thermal Rossby numbers from developing superrotation by the influences of (1) cross-equatorial momentum advection by the Hadley circulation and (2) hemispherically asymmetric zonal-mean zonal winds that suppress instabilities leading to equatorial momentum convergence. We also demonstrate that baroclinic instabilities must be sufficiently weak to allow superrotation to develop. In the relevant parameter regimes, our seasonal model simulations compare favorably to large-scale, seasonal phenomena observed on Earth and Mars. In the Titan-like regime the seasonal cycle in our model acts to prevent superrotation from developing, and it is necessary to increase the value of a third parameter—the atmospheric Newtonian cooling time—to achieve a superrotating climatology.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

EMPIRICAL DETERMINATION OF EINSTEIN A-COEFFICIENT RATIOS OF BRIGHT [Fe II] LINES

The Einstein spontaneous rates (A-coefficients) of Fe{sup +} lines have been computed by several authors with results that differ from each other by up to 40%. Consequently, models for line emissivities suffer from uncertainties that in turn affect the determination of the physical conditions at the base of line excitation. We provide an empirical determination of the A-coefficient ratios of bright [Fe II] lines that would represent both a valid benchmark for theoretical computations and a reference for the physical interpretation of the observed lines. With the ESO-Very Large Telescope X-shooter instrument between 3000 Å and 24700 Å, we obtained a spectrum of the bright Herbig-Haro object HH 1. We detect around 100 [Fe II] lines, some of which with a signal-to-noise ratios ≥100. Among these latter lines, we selected those emitted by the same level, whose dereddened intensity ratios are direct functions of the Einstein A-coefficient ratios. From the same X-shooter spectrum, we got an accurate estimate of the extinction toward HH 1 through intensity ratios of atomic species, H I recombination lines and H{sub 2} ro-vibrational transitions. We provide seven reliable A-coefficient ratios between bright [Fe II] lines, which are compared with the literature determinations. In particular, the A-coefficient ratios involving the brightest near-infrared lines (λ12570/λ16440 and λ13209/λ16440) are in better agreement with the predictions by the Quinet et al. relativistic Hartree-Fock model. However, none of the theoretical models predict A-coefficient ratios in agreement with all of our determinations. We also show that literature data of near-infrared intensity ratios better agree with our determinations than with theoretical expectations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

LOW-TEMPERATURE SPECTROSCOPY OF THE {sup 12}C{sub 2}H{sub 2} (υ{sub 1} + υ{sub 3}) BAND IN A HELIUM BUFFER GAS

Buffer gas cooling with a {sup 4}He gas is used to perform laser-absorption spectroscopy of the {sup 12}C{sub 2}H{sub 2} (υ{sub 1} + υ{sub 3}) band at cryogenic temperatures. Doppler thermometry is first carried out to extract translational temperatures from the recorded spectra. Then, rotational temperatures down to 20 K are retrieved by fitting the Boltzmann distribution to the relative intensities of several ro-vibrational lines. The potential of our setup to tune the thermal equilibrium between translational and rotational degrees of freedom is also demonstrated. This can be used to reproduce in a controlled way the regime of non-local thermal equilibrium typically encountered in the interstellar medium. The underlying helium-acetylene collisional physics, relevant for modeling planetary atmospheres, is also addressed. In particular, the diffusion time of {sup 12}C{sub 2}H{sub 2} in the buffer cell is measured against the {sup 4}He flux at two separate translational temperatures; the observed behavior is then compared with that predicted by a Monte Carlo simulation, thus providing an estimate for the respective total elastic cross sections: σ{sub el}(100 K) = (4 ± 1) × 10{sup –20} m{sup 2} and σ{sub el}(25 K) = (7 ± 2) × 10{sup –20} m{sup 2}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

RARE ISOTOPIC SPECIES OF SULFUR MONOXIDE: THE ROTATIONAL SPECTRUM IN THE THz REGION

Many sulfur-bearing species have been detected in different astronomical environments and have allowed us to derive important information about the chemical and physical composition of interstellar regions. In particular, these species have also been shown to trace and probe hot-core environment time evolution. Among the most prominent sulfur-bearing molecules is SO, the sulfur monoxide radical, one of the more ubiquitous and abundant, which is also observed in its isotopic substituted species such as {sup 34}SO and S{sup 18}O. Due to the importance of this simple diatomic system, and in order to face the challenge of modern radioastronomical facilities, an extension to the THz range of the rare isotopologues of sulfur monoxide has been performed. High-resolution rotational molecular spectroscopy has been employed to extend the available data set of four isotopic species, SO, {sup 34}SO, S{sup 17}O, and S{sup 18}O, up to the 1.5 THz region. The frequency coverage and spectral resolution of our measurements allowed a better constraint of the molecular constants of the four species considered, specifically focusing on the two oxygen-substituted isotopologues. Our measurements were also employed in an isotopically invariant fit including all of the available pure rotational and ro-vibrational transitions for all of the SO isotopologues, thus enabling accurate predictions of the rotational transitions at higher frequencies. We also provide comparisons with recent works performed on the same system, demonstrating the quality of our experiment and the improvement of the data sets for all of the species considered. Transition frequencies for this system can now be used with confidence by the astronomical community well into the THz spectral region.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Solving the excitation and chemical abundances in shocks: The case of HH 1

We present deep spectroscopic (3600–24700 Å ) X-shooter observations of the bright Herbig–Haro object HH 1, one of the best laboratories to study the chemical and physical modifications caused by protostellar shocks on the natal cloud. We observe atomic fine structure lines, H i and He i recombination lines and H{sub 2} ro-vibrational lines (more than 500 detections in total). Line emission was analyzed by means of Non-local Thermal Equilibiurm codes to derive the electron temperature and density, and for the first time we are able to accurately probe different physical regimes behind a dissociative shock. We find a temperature stratification in the range 4000 K ÷ 80,000 K, and a significant correlation between temperature and ionization energy. Two density regimes are identified for the ionized gas, a more tenuous, spatially broad component (density ∼10{sup 3} cm{sup −3}), and a more compact component (density ⩾ 10{sup 5} cm{sup −3}) likely associated with the hottest gas. A further neutral component is also evidenced, having a temperature ≲10,000 K and a density >10{sup 4} cm{sup −3}. The gas fractional ionization was estimated by solving the ionization equilibrium equations of atoms detected in different ionization stages. We find that neutral and fully ionized regions co-exist inside the shock. Also, indications in favor of at least partially dissociative shock as the main mechanism for molecular excitation are derived. Chemical abundances are estimated for the majority of the detected species. On average, abundances of non-refractory/refractory elements are lower than solar of about 0.15/0.5 dex. This indicates the presence of dust inside the medium, with a depletion factor of iron of ∼40%.

79 ASTRONOMY AND ASTROPHYSICS↗