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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 1,261 records · Page 70
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DOE OSTI2014

N(H I)/E(B – V)

We explore the relationship between dust-emission derived reddening E(B – V) and atomic hydrogen column density N(H I) derived from 21 cm emission surveys. We consider measurements at galactic latitudes |b| ≳ 20{sup o} and E(B – V) ≲ 0.1 mag where the interstellar gas is predominantly neutral and atomic, and opacity corrections to 21 cm H I profiles are small. Over the Galaxy at large, at lower resolutions in H I, and on smaller scales at higher resolutions, we find that the reddening is always much smaller than would be expected from the usually quoted relation N(H) =5.8 × 10{sup 21} cm{sup –2} E(B – V) based on stellar reddening and UV absorption toward early-type stars. On wide scales we find N(H I) = 8.3 × 10{sup 21} cm{sup –2} E(B – V). We cite various precedents for such a large N(H I)/E(B – V) ratio whenever wide-field 21 cm emission surveys are considered, including when reddening based on galaxy counts and colors is substituted for the dust-emission derived reddening measure.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Andromeda's dust

Spitzer Space Telescope and Herschel Space Observatory imaging of M31 is used, with a physical dust model, to construct maps of dust surface density, dust-to-gas ratio, starlight heating intensity, and polycyclic aromatic hydrocarbon (PAH) abundance, out to R ≈ 25 kpc. The global dust mass is M {sub d} = 5.4 × 10{sup 7} M {sub ☉}, the global dust/H mass ratio is M {sub d}/M {sub H} = 0.0081, and the global PAH abundance is (q {sub PAH}) = 0.039. The dust surface density has an inner ring at R = 5.6 kpc, a maximum at R = 11.2 kpc, and an outer ring at R ≈ 15.1 kpc. The dust/gas ratio varies from M {sub d}/M {sub H} ≈ 0.026 at the center to ∼0.0027 at R ≈ 25 kpc. From the dust/gas ratio, we estimate the interstellar medium metallicity to vary by a factor ∼10, from Z/Z {sub ☉} ≈ 3 at R = 0 to ∼0.3 at R = 25 kpc. The dust heating rate parameter (U) peaks at the center, with (U) ≈ 35, declining to (U) ≈ 0.25 at R = 20 kpc. Within the central kiloparsec, the starlight heating intensity inferred from the dust modeling is close to what is estimated from the stars in the bulge. The PAH abundance reaches a peak q {sub PAH} ≈ 0.045 at R ≈ 11.2 kpc. When allowance is made for the different spectrum of the bulge stars, q {sub PAH} for the dust in the central kiloparsec is similar to the overall value of q {sub PAH} in the disk. The silicate-graphite-PAH dust model used here is generally able to reproduce the observed dust spectral energy distribution across M31, but overpredicts 500 μm emission at R ≈ 2-6 kpc, suggesting that at R = 2-6 kpc, the dust opacity varies more steeply with frequency (with β ≈ 2.3 between 200 and 600 μm) than in the model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

H I-to-H{sub 2} transitions and H I column densities in galaxy star-forming regions

We present new analytic theory and radiative transfer computations for the atomic-to-molecular (H I-to-H{sub 2}) transitions and the buildup of atomic hydrogen (H I) gas columns in optically thick interstellar clouds irradiated by far-UV (FUV) photodissociating radiation fields. We derive analytic expressions for the total H I column densities for (one-dimensional (1D)) planar slabs, for beamed or isotropic radiation fields, from the weak- to strong-field limits, for gradual or sharp atomic-to-molecular transitions, and for arbitrary metallicity. Our expressions may be used to evaluate the H I column densities as functions of the radiation field intensity and the H{sub 2}-dust-limited dissociation flux, the hydrogen gas density, and the metallicity-dependent H{sub 2} formation rate coefficient and FUV dust grain absorption cross section. We make the distinction between 'H I-dust' and 'H{sub 2}-dust' opacity, and we present computations for the 'universal H{sub 2}-dust-limited effective dissociation bandwidth'. We validate our analytic formulae with Meudon PDR code computations for the H I-to-H{sub 2} density profiles and total H I column densities. We show that our general 1D formulae predict H I columns and H{sub 2} mass fractions that are essentially identical to those found in more complicated (and approximate) spherical (shell-core) models. We apply our theory to compute H{sub 2} mass fractions and star-formation thresholds for individual clouds in self-regulated galaxy disks, for a wide range of metallicities. Our formulae for the H I columns and H{sub 2} mass fractions may be incorporated into hydrodynamics simulations for galaxy evolution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

CO-spatial white light and hard X-ray flare footpoints seen above the solar limb

We report analysis of three solar flares that occur within 1° of limb passage, with the goal to investigate the source height of chromospheric footpoints in white light (WL) and hard X-rays (HXR). We find the WL and HXR (≥30 keV) centroids to be largely co-spatial and from similar heights for all events, with altitudes around 800 km above the photosphere or 300–450 km above the limb height. Because of the extreme limb location of the events we study, emissions from such low altitudes are influenced by the opacity of the atmosphere and projection effects. STEREO images reveal that for SOL2012-11-20T12:36 the projection effects are smallest, giving upper limits of the absolute source height above the nominal photosphere for both wavelengths of ∼1000 km. To be compatible with the standard thick target model, these rather low altitudes require very low ambient densities within the flare footpoints, in particular if the HXR-producing electrons are only weakly beamed. That the WL and HXR emissions are co-spatial suggests that the observed WL emission mechanism is directly linked to the energy deposition by flare accelerated electrons. If the WL emission is from low-temperature (⩽10{sup 4} K) plasma as currently thought, the energy deposition by HXR-producing electrons above ∼30 keV seems only to heat chromospheric plasma to such low temperatures. This implies that the energy in flare-accelerated electrons above ∼30 keV is not responsible for chromospheric evaporation of hot (>10{sup 6} K) plasma, but that their energy is lost through radiation in the optical range.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Non-LTE analysis of neutral copper in late-type metal-poor stars

We investigated the copper abundances of 64 late-type stars in the Galactic disk and halo with effective temperatures from 5400 to 6700 K and [Fe/H] from −1.88 to −0.17. For the first time, the copper abundances are derived using both local thermodynamic equilibrium (LTE) and non-local thermodynamic equilibrium (non-LTE) calculations. High-resolution (R>40,000), high signal-to-noise ratio (S/N>100) spectra from the FOCES spectrograph are used. The atmospheric models are calculated based on the MAFAGS opacity sampling code. All the abundances are derived using spectrum synthesis methods. Our results indicate that the non-LTE effects of copper are important for metal-poor stars, showing a departure of ∼0.17 dex at a metallicity of ∼−1.5. We also find that the copper abundances derived from non-LTE calculations are enhanced compared with those from LTE. The enhancements show clear dependence on the metallicity, which gradually increases with decreasing [Fe/H] for our program stars, leading to a flatter distribution of [Cu/Fe] with [Fe/H] than previous work. There is a hint that the thick- and thin-disk stars have different behaviors in [Cu/Fe], and bending of the disk stars may exist.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Assessing molecular outflows and turbulence in the protostellar cluster Serpens South

Molecular outflows driven by protostellar cluster members likely impact their surroundings and contribute to turbulence, affecting subsequent star formation. The very young Serpens South cluster consists of a particularly high density and fraction of protostars, yielding a relevant case study for protostellar outflows and their impact on the cluster environment. We combined CO J=1−0 observations of this region using the Combined Array for Research in Millimeter-wave Astronomy and the Institut de Radioastronomie Millimétrique 30 m single-dish telescope. The combined map allows us to probe CO outflows within the central, most active region at size scales of 0.01–0.8 pc. We account for effects of line opacity and excitation temperature variations by incorporating {sup 12}CO and {sup 13}CO data for the J = 1 − 0 and J = 3 − 2 transitions (using Atacama Pathfinder Experiment and Caltech Submillimeter Observatory observations for the higher CO transitions), and we calculate mass, momentum, and energy of the molecular outflows in this region. The outflow mass-loss rate, force, and luminosity, compared with diagnostics of turbulence and gravity, suggest that outflows drive a sufficient amount of energy to sustain turbulence, but not enough energy to substantially counter the gravitational potential energy and disrupt the clump. Further, we compare Serpens South with the slightly more evolved cluster NGC 1333, and we propose an empirical scenario for outflow-cluster interaction at different evolutionary stages.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

On extreme-ultraviolet helium line intensity enhancement factors on the sun

Helium lines in the solar EUV spectrum provide useful diagnostics of the solar atmosphere plasma. Helium is one of the few elements that exhibits strong emission lines formed in the lower transition region, and it is the second most abundant element in the Sun. However, the analysis of helium lines is complicated by their optical thickness and the unusual behavior of their intensities, with enhancements by a factor of up to 15 reported in the literature. Detailed study requires spatially and spectrally resolved observations in the EUV range, as well as sophisticated atomic modeling. The present work focuses on the application of the differential emission measure distribution to reproduce the observed fluxes of the He i and He ii lines observed by the Solar and Heliospheric Observatory (SOHO)/Coronal Diagnostic Spectrometer and Hinode/EIS spectrometers, using the latest atomic data. It is found that the comparison between observed and reconstructed intensities for He i resonance lines λλ537.03, 522.21, and 515.62 and the intercombination line λ591.41 does not show a real enhancement. By contrast, He i λ584.33, the first line of the 1s{sup 2} {sup 1}S−1s np {sup 1}P resonance series, shows a depletion of a factor ∼2, due to the opacity effect, as supported by non-LTE radiative transfer calculations. For single ionized helium lines 303.78 and 256.32 Å, the enhancement factors obtained are higher and agree with those of previous work. The different behavior of He i and He ii lines suggests a mechanism that affects ionized helium only.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Oister optical and near-infrared observations of type Iax supernova 2012Z

We report observations of the Type Iax supernova (SN Iax) 2012Z at optical and near-infrared (NIR) wavelengths from immediately after the explosion until ∼260 days after the maximum luminosity using the Optical and Infrared Synergetic Telescopes for Education and Research Target-of-Opportunity program and the Subaru Telescope. We found that the NIR light curve evolutions and color evolutions are similar to those of SNe Iax 2005hk and 2008ha. The NIR absolute magnitudes (M{sub J}∼−18.1 mag and M{sub H}∼−18.3 mag) and the rate of decline of the light curve (Δm{sub 15}(B) = 1.6±0.1 mag) are very similar to those of SN 2005hk (M{sub J}∼−17.7 mag, M{sub H}∼−18.0 mag, and Δm{sub 15}(B) ∼ 1.6 mag), yet differ significantly from SNe 2008ha and 2010ae (M{sub J} ∼ −14 to −15 mag and Δm{sub 15}(B) ∼ 2.4–2.7 mag). The estimated rise time is 12.0 ± 3.0 days, which is significantly shorter than that of SN 2005hk or any other SNe Ia. The rapid rise indicates that the {sup 56}Ni distribution may extend into the outer layer or that the effective opacity may be lower than that in normal SNe Ia. The late-phase spectrum exhibits broader emission lines than those of SN 2005hk by a factor of six to eight. Such high velocities of the emission lines indicate that the density profile of the inner ejecta extends more than that of SN 2005hk. We argue that the most favored explosion scenario is a “failed deflagration” model, although the pulsational delayed detonations is not excluded.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The mass–radius relation of young stars. I. USCO 5, an M4.5 eclipsing binary in upper Scorpius observed by K2

We present the discovery that UScoCTIO 5, a known spectroscopic binary in the Upper Scorpius star-forming region (P = 34 days, M{sub tot}sin(i)=0.64 M{sub ⊙}), is an eclipsing system with both primary and secondary eclipses apparent in K2 light curves obtained during Campaign 2. We have simultaneously fit the eclipse profiles from the K2 light curves and the existing RV data to demonstrate that UScoCTIO 5 consists of a pair of nearly identical M4.5 stars with M{sub A}=0.329±0.002 M{sub ⊙}, R{sub A}=0.834±0.006 R{sub ⊙}, M{sub B}=0.317±0.002 M{sub ⊙}, and R{sub B}=0.810±0.006 R{sub ⊙}. The radii are broadly consistent with pre-main-sequence ages predicted by stellar evolutionary models, but none agree to within the uncertainties. All models predict systematically incorrect masses at the 25%–50% level for the HR diagram position of these mid-M dwarfs, suggesting significant modifications to mass-dependent outcomes of star and planet formation. The form of the discrepancy for most model sets is not that they predict luminosities that are too low, but rather that they predict temperatures that are too high, suggesting that the models do not fully encompass the physics of energy transport (via convection and/or missing opacities) and/or a miscalibration of the SpT–T{sub eff} scale. The simplest modification to the models (changing T{sub eff} to match observations) would yield an older age for this system, in line with the recently proposed older age of Upper Scorpius (τ ∼ 11 Myr).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE SNOW LINE IN VISCOUS DISKS AROUND LOW-MASS STARS: IMPLICATIONS FOR WATER DELIVERY TO TERRESTRIAL PLANETS IN THE HABITABLE ZONE

The water-ice or snow line is one of the key properties of protoplanetary disks that determines the water content of terrestrial planets in the habitable zone. Its location is determined by the properties of the star, the mass accretion rate through the disk, and the size distribution of dust suspended in the disk. We calculate the snow-line location from recent observations of mass accretion rates and as a function of stellar mass. By taking the observed dispersion in mass accretion rates as a measure of the dispersion in initial disk mass, we find that stars of a given mass will exhibit a range of snow-line locations. At a given age and stellar mass, the observed dispersion in mass accretion rates of 0.4 dex naturally leads to a dispersion in snow-line locations of ∼0.2 dex. For ISM-like dust sizes, the 1σ snow-line location among solar-mass stars of the same age ranges from ∼2 to ∼5 AU. For more realistic dust opacities that include larger grains, the snow line is located up to two times closer to the star. We use these locations and the outcome of N-body simulations to predict the amount of water delivered to terrestrial planets that formed in situ in the habitable zone. We find that the dispersion in snow-line locations leads to a large range in water content. For ISM-like dust sizes, a significant fraction of habitable-zone terrestrial planets around Sun-like stars remain dry, and no water is delivered to the habitable zones of low-mass M stars (<0.5 M{sub ⊙}) as in previous works. The closer-in snow line in disks with larger grains enables water delivery to the habitable zone for a significant fraction of M stars and all FGK stars. Considering their larger numbers and higher planet occurrence, M stars may host most of the water-rich terrestrial planets in the galaxy if these planets are able to hold on to their water in their subsequent evolution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

New measurements of the radio photosphere of Mira based on data from the JVLA and ALMA

We present new measurements of the millimeter wavelength continuum emission from the long period variable Mira (o Ceti) at frequencies of 46, 96, and 229 GHz (λ≈7, 3, and 1 mm) based on observations obtained with the Jansky Very Large Array (JVLA) and the Atacama Large Millimeter/submillimeter Array (ALMA). The measured millimeter flux densities are consistent with a radio photosphere model derived from previous observations, where flux density S{sub ν}∝ν{sup 1.86}. The stellar disk is resolved, and the measurements indicate a decrease in the size of the radio photosphere at higher frequencies, as expected if the opacity decreases at shorter wavelengths. The shape of the radio photosphere is found to be slightly elongated, with a flattening of ∼10%–20%. The data also reveal evidence for brightness non-uniformities on the surface of Mira at radio wavelengths. Mira’s hot companion, Mira B was detected at all three observed wavelengths, and we measure a radius for its radio-emitting surface of ≈2.0×10{sup 13} cm. The data presented here highlight the power of the JVLA and ALMA for the study of the atmospheres of evolved stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Impact of neutrino flavor oscillations on the neutrino-driven wind nucleosynthesis of an electron-capture supernova

Neutrino oscillations, especially to light sterile states, can affect nucleosynthesis yields because of their possible feedback effect on the electron fraction (Y{sub e}). For the first time, we perform nucleosynthesis calculations for neutrino-driven wind trajectories from the neutrino-cooling phase of an 8.8 M{sub ⊙} electron-capture supernova (SN), whose hydrodynamic evolution was computed in spherical symmetry with sophisticated neutrino transport and whose Y{sub e} evolution was post-processed by including neutrino oscillations between both active and active–sterile flavors. We also take into account the α-effect as well as weak magnetism and recoil corrections in the neutrino absorption and emission processes. We observe effects on the Y{sub e} evolution that depend in a subtle way on the relative radial positions of the sterile Mikheyev–Smirnov–Wolfenstein resonances, on collective flavor transformations, and on the formation of α particles. For the adopted SN progenitor, we find that neutrino oscillations, also to a sterile state with eV mass, do not significantly affect the element formation and in particular cannot make the post-explosion wind outflow neutron-rich enough to activate a strong r-process. Our conclusions become even more robust when, in order to mimic equation-of-state-dependent corrections due to nucleon potential effects in the dense-medium neutrino opacities, six cases with reduced Y{sub e} in the wind are considered. In these cases, despite the conversion of active neutrinos to sterile neutrinos, Y{sub e} increases or is not significantly lowered compared to the values obtained without oscillations and active flavor transformations. This is a consequence of a complicated interplay between sterile-neutrino production, neutrino–neutrino interactions, and α-effect.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Jupiter’s deep cloud structure revealed using Keck observations of spectrally resolved line shapes

Technique: We present a method to determine the pressure at which significant cloud opacity is present between 2 and 6 bars on Jupiter. We use (a) the strength of a Fraunhofer absorption line in a zone to determine the ratio of reflected sunlight to thermal emission, and (b) pressure-broadened line profiles of deuterated methane (CH{sub 3}D) at 4.66 μm to determine the location of clouds. We use radiative transfer models to constrain the altitude region of both the solar and thermal components of Jupiter’s 5 μm spectrum. Results: For nearly all latitudes on Jupiter the thermal component is large enough to constrain the deep cloud structure even when upper clouds are present. We find that hot spots, belts, and high latitudes have broader line profiles than do zones. Radiative transfer models show that hot spots in the North Equatorial Belt and South Equatorial Belt (SEB) typically do not have opaque clouds at pressures greater than 2 bars. The South Tropical Zone (STZ) at 32{sup ∘}S has an opaque cloud top between 4 and 5 bars. From thermochemical models this must be a water cloud. We measured the variation of the equivalent width of CH{sub 3}D with latitude for comparison with Jupiter’s belt-zone structure. We also constrained the vertical profile of H{sub 2}O in an SEB hot spot and in the STZ. The hot spot is very dry for P < 4.5 bars and then follows the H{sub 2}O profile observed by the Galileo Probe. The STZ has a saturated H{sub 2}O profile above its cloud top between 4 and 5 bars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The metagalactic ionizing background: A crisis in UV photon production or incorrect galaxy escape fractions?

Recent suggestions of a “photon underproduction crisis” have generated concern over the intensity and spectrum of ionizing photons in the metagalactic ultraviolet background (UVB). The balance of hydrogen photoionization and recombination determines the opacity of the low-redshift intergalactic medium (IGM). We calibrate the hydrogen photoionization rate (Γ{sub H}) by comparing Hubble Space Telescope spectroscopic surveys of the low-redshift column density distribution of H i absorbers and the observed (z<0.4) mean Lyα flux decrement, D{sub A}=(0.014)(1+z){sup 2.2}, to new cosmological simulations. The distribution, f(N{sub H I},z)≡d{sup 2}N/d(logN{sub H I})dz, is consistent with an increased UVB that includes contributions from both quasars and galaxies. Our recommended fit, Γ{sub H}(z)=(4.6×10{sup −14} s{sup −1})(1+z){sup 4.4} for 0<z<0.47, corresponds to unidirectional LyC photon flux Φ{sub 0}≈5700 cm{sup −2} s{sup −1} at z = 0. This flux agrees with observed IGM metal ionization ratios (C iii/C iv and Si iii/Si iv) and suggests a 25%–30% contribution of Lyα absorbers to the cosmic baryon inventory. The primary uncertainties in the low-redshift UVB are the contribution from massive stars in galaxies and the LyC escape fraction (f{sub esc}), a highly directional quantity that is difficult to constrain statistically. We suggest that both quasars and low-mass starburst galaxies are important contributors to the ionizing UVB at z<2. Their additional ionizing flux would resolve any crisis in photon underproduction.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

To cool is to accrete: Analytic scalings for nebular accretion of planetary atmospheres

Planets acquire atmospheres from their parent circumstellar disks. We derive a general analytic expression for how the atmospheric mass grows with time t as a function of the underlying core mass M{sub core} and nebular conditions, including the gas metallicity Z. Planets accrete as much gas as can cool: an atmosphere's doubling time is given by its Kelvin–Helmholtz time. Dusty atmospheres behave differently from atmospheres made dust-free by grain growth and sedimentation. The gas-to-core mass ratio (GCR) of a dusty atmosphere scales as GCR ∝ t{sup 0.4}M{sub core}{sup 1.7}Z{sup −0.4}μ{sub rcb}{sup 3.4}, where μ{sub rcb}∝1/(1−Z) (for Z not too close to 1) is the mean molecular weight at the innermost radiative–convective boundary. This scaling applies across all orbital distances and nebular conditions for dusty atmospheres; their radiative–convective boundaries, which regulate cooling, are not set by the external environment, but rather by the internal microphysics of dust sublimation, H{sub 2} dissociation, and the formation of H{sup −}. By contrast, dust-free atmospheres have their radiative boundaries at temperatures T{sub rcb} close to nebular temperatures T{sub out}, and grow faster at larger orbital distances where cooler temperatures, and by extension lower opacities, prevail. At 0.1 AU in a gas-poor nebula, GCR ∝ t{sup 0.4}T{sub rcb}{sup −1.9}M{sub core}{sup 1.6}Z{sup −0.4}μ{sub rcb}{sup 3.3}, while beyond 1 AU in a gas-rich nebula, GCR ∝ t{sup 0.4}T{sub rcb}{sup −1.5}M{sub core}{sup 1}Z{sup −0.4}μ{sub rcb}{sup 2.2}. We confirm our analytic scalings against detailed numerical models for objects ranging in mass from Mars (0.1M{sub ⊕}) to the most extreme super-Earths (10–20M{sub ⊕}), and explain why heating from planetesimal accretion cannot prevent the latter from undergoing runaway gas accretion.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The formation of IRIS diagnostics. V. A quintessential model atom of C ii and general formation properties of the C ii lines at 133.5 nm

The C ii 133.5 nm lines are important observables for the NASA/SMEX mission Interface Region Imaging Spectrograph. To make three-dimensional (3D) non-LTE radiative transfer computationally feasible, it is crucial to have a model atom with as few levels as possible while retaining the main physical processes. We here develop such a model atom and we study the general formation properties of the C ii lines. We find that a nine-level model atom of C i–C iii with the transitions treated assuming complete frequency redistribution (CRD) suffices to describe the C ii 133.5 nm lines. 3D scattering effects are important for the intensity in the core of the line. The lines are formed in the optically thick regime. The core intensity is formed in layers where the temperature is about 10 kK at the base of the transition region. The lines are 1.2–4 times wider than the atomic absorption profile due to the formation in the optically thick regime. The smaller opacity broadening happens for single peak intensity profiles where the chromospheric temperature is low with a steep source function increase into the transition region, the larger broadening happens when there is a temperature increase from the photosphere to the low chromosphere leading to a local source function maximum and a double peak intensity profile with a central reversal. Assuming optically thin formation with the standard coronal approximation leads to several errors: neglecting photoionization severly underestimates the amount of C ii at temperatures below 16 kK, erroneously shifts the formation from 10 kK to 25 kK, and leads to too low intensities.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Velocity-resolved [C ii] emission and [C ii]/FIR mapping along Orion with Herschel

We present the first ∼7.′5 × 11.′5 velocity-resolved (∼0.2 km s{sup −1}) map of the [C ii] 158 μm line toward the Orion molecular cloud 1 (OMC 1) taken with the Herschel/HIFI instrument. In combination with far-IR (FIR) photometric images and velocity-resolved maps of the H41α hydrogen recombination and CO J = 2–1 lines, this data set provides an unprecedented view of the intricate small-scale kinematics of the ionized/photodissociation region (PDR)/molecular gas interfaces and of the radiative feedback from massive stars. The main contribution to the [C ii] luminosity (∼85%) is from the extended, FUV-illuminated face of the cloud (G{sub 0} > 500, n{sub H} > 5 × 10{sup 3} cm{sup −3}) and from dense PDRs (G{sub 0} ≳ 10{sup 4}, n{sub H} ≳ 10{sup 5} cm{sup −3}) at the interface between OMC 1 and the H ii region surrounding the Trapezium cluster. Around ∼15% of the [C ii] emission arises from a different gas component without a CO counterpart. The [C ii] excitation, PDR gas turbulence, line opacity (from [{sup 13}C ii]), and role of the geometry of the illuminating stars with respect to the cloud are investigated. We construct maps of the L[C ii]/L{sub FIR} and L{sub FIR}/M{sub Gas} ratios and show that L[C ii]/L{sub FIR} decreases from the extended cloud component (∼10{sup −2}–10{sup −3}) to the more opaque star-forming cores (∼10{sup −3}−10{sup −4}). The lowest values are reminiscent of the “[C ii] deficit” seen in local ultraluminous IR galaxies hosting vigorous star formation. Spatial correlation analysis shows that the decreasing L[C ii]/L{sub FIR} ratio correlates better with the column density of dust through the molecular cloud than with L{sub FIR}/M{sub Gas}. We conclude that the [C ii]-emitting column relative to the total dust column along each line of sight is responsible for the observed L[C ii]/L{sub FIR} variations through the cloud.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Model atmospheres of irradiated exoplanets: The influence of stellar parameters, metallicity, and the C/O ratio

Many parameters constraining the spectral appearance of exoplanets are still poorly understood. We therefore study the properties of irradiated exoplanet atmospheres over a wide parameter range including metallicity, C/O ratio, and host spectral type. We calculate a grid of 1D radiative-convective atmospheres and emission spectra. We perform the calculations with our new Pressure–Temperature Iterator and Spectral Emission Calculator for Planetary Atmospheres (PETIT) code, assuming chemical equilibrium. The atmospheric structures and spectra are made available online. We find that atmospheres of planets with C/O ratios ∼1 and T{sub eff} ≳ 1500 K can exhibit inversions due to heating by the alkalis because the main coolants CH{sub 4}, H{sub 2}O, and HCN are depleted. Therefore, temperature inversions possibly occur without the presence of additional absorbers like TiO and VO. At low temperatures we find that the pressure level of the photosphere strongly influences whether the atmospheric opacity is dominated by either water (for low C/O) or methane (for high C/O), or both (regardless of the C/O). For hot, carbon-rich objects this pressure level governs whether the atmosphere is dominated by methane or HCN. Further we find that host stars of late spectral type lead to planetary atmospheres which have shallower, more isothermal temperature profiles. In agreement with prior work we find that for planets with T{sub eff}<1750 K the transition between water or methane dominated spectra occurs at C/O ∼ 0.7, instead of ∼1, because condensation preferentially removes oxygen.

79 ASTRONOMY AND ASTROPHYSICS↗