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At least 775 records · Page 43
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DOE OSTI2013

THREE-DIMENSIONAL GEOMETRIES AND THE ANALYSIS OF H II REGIONS

We compare emission line intensities from photoionization models of smooth and fractal shell geometries for low density H II regions, with particular focus on the low-ionization diagnostic diagram [N II]/H{alpha} versus H{alpha}. Building on previously published models and observations of Barnard's Loop, we show that the observed range of intensities and variations in the line intensity ratios may be reproduced with a three-dimensional shell geometry. Our models adopt solar abundances throughout the model nebula, in contrast with previous one-dimensional modeling which suggested the variations in line intensity ratios could only be reproduced if the heavy element abundances were increased by a factor of {approx}1.4. For spatially resolved H II regions, the multiple sightlines that pierce and sample different ionization and temperature conditions within smooth and fractal shells produce a range of line intensities that are easily overlooked if only the total integrated intensities from the entire nebula model are computed. Our conclusion is that inference of H II region properties, such as elemental abundances, via photoionization models of one-dimensional geometries must be treated with caution and further tested through three-dimensional modeling.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

RESOLVING THE OPTICAL EMISSION LINES OF Ly{alpha} BLOB ''B1'' AT z = 2.38: ANOTHER HIDDEN QUASAR

We have used the SINFONI near-infrared integral field unit on the Very Large Telescope to resolve the optical emission line structure of one of the brightest (L{sub Ly{alpha}} Almost-Equal-To 10{sup 44} erg s{sup -1}) and nearest (z Almost-Equal-To 2.38) of all Ly{alpha} blobs (LABs). The target, known in the literature as object {sup B}1{sup ,} lies at a redshift where the main optical emission lines are accessible in the observed near-infrared. We detect luminous [O III] {lambda}{lambda}4959, 5007 and H{alpha} emission with a spatial extent of at least 32 Multiplication-Sign 40 kpc (4'' Multiplication-Sign 5''). The dominant optical emission line component shows relatively broad lines (600-800 km s{sup -1}, FWHM) and line ratios consistent with active galactic nucleus (AGN) photoionization. The new evidence for AGN photoionization, combined with previously detected C IV and luminous, warm infrared emission, suggest that B1 is the site of a hidden quasar. This is confirmed by the fact that [O II] is relatively weak compared with [O III] (extinction-corrected [O III]/[O II] of about 3.8), which is indicative of a high, Seyfert-like ionization parameter. From the extinction-corrected [O III] luminosity we infer a bolometric AGN luminosity of {approx}3 Multiplication-Sign 10{sup 46} erg s{sup -1}, and further conclude that the obscured AGN may be Compton-thick given existing X-ray limits. The large line widths observed are consistent with clouds moving within the narrow-line region of a luminous QSO. The AGN scenario is capable of producing sufficient ionizing photons to power the Ly{alpha}, even in the presence of dust. By performing a census of similar objects in the literature, we find that virtually all luminous LABs harbor obscured quasars. Based on simple duty-cycle arguments, we conclude that AGNs are the main drivers of the Ly{alpha} in LABs rather than the gravitational heating and subsequent cooling suggested by cold stream models. We also conclude that the empirical relation between LABs and overdense environments at high redshift must be due to a more fundamental correlation between AGNs (or massive galaxies) and environment.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

CHEMICAL ENRICHMENT OF DAMPED Ly{alpha} SYSTEMS AS A DIRECT CONSTRAINT ON POPULATION III STAR FORMATION

Observations of damped Ly{alpha} absorbers (DLAs) can be used to measure gas-phase metallicities at large cosmological look-back times with high precision. Furthermore, relative abundances can still be measured accurately deep into the reionization epoch (z > 6) using transitions redward of Ly{alpha}, even though Gunn-Peterson absorption precludes measurement of neutral hydrogen. In this paper, we study the chemical evolution of DLAs using a model for the coupled evolution of galaxies and the intergalactic medium (IGM), which is constrained by a variety of observations. Our goal is to explore the influence of Population III stars on the abundance patterns of DLAs to determine the degree to which abundance measurements can discriminate between different Population III stellar initial mass functions (IMFs). We include effects, such as inflows onto galaxies due to cosmological accretion and outflows from galaxies due to supernova feedback. A distinct feature of our model is that it self-consistently calculates the effect of Population III star formation on the reionization of an inhomogeneous IGM, thus allowing us to calculate the thermal evolution of the IGM and implement photoionization feedback on low-mass galaxy formation. We find that if the critical metallicity of Population III to II/I transition is {approx}< 10{sup -4} Z{sub Sun }, then the cosmic Population III star formation rate drops to zero for z < 8. Nevertheless, at high redshift (z {approx} 6), chemical signatures of Population III stars remain in low-mass galaxies (halo mass {approx}< 10{sup 9} M{sub Sun }). This is because photoionization feedback suppresses star formation in these galaxies until relatively low redshift (z {approx} 10), and the chemical record of their initial generation of Population III stars is retained. We model DLAs as these low-mass galaxies, and assign to them a mass-dependent H I absorption cross-section in order to predict the expected distribution of DLA abundance ratios. We find that these distributions are anchored toward abundance ratios set by Population II supernova yields, but they exhibit a tail which depends significantly on the Population III IMF for z > 5. Thus, a sample of DLA metallicity and relative abundance measurements at high redshift holds the promise to constrain Population III enrichment and the Population III IMF. We find that a sample of just 10 DLAs with relative abundances measured to an accuracy of 0.1 dex is sufficient to constrain the Population III IMF at 4{sigma}. These constraints may prove stronger than other probes of Population III enrichment, such as metal-poor stars and individual metal-poor DLAs. Our results provide a global picture of the thermal, ionization, and chemical evolution of the universe, and have the potential to rule out certain Population III scenarios.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

DETECTING THE RAPIDLY EXPANDING OUTER SHELL OF THE CRAB NEBULA: WHERE TO LOOK

We present a range of steady-state photoionization simulations, corresponding to different assumed shell geometries and compositions, of the unseen postulated rapidly expanding outer shell to the Crab Nebula. The properties of the shell are constrained by the mass that must lie within it, and by limits to the intensities of hydrogen recombination lines. In all cases the photoionization models predict very strong emissions from high ionization lines that will not be emitted by the Crab's filaments, alleviating problems with detecting these lines in the presence of light scattered from brighter parts of the Crab. The near-NIR [Ne VI] {lambda}7.652 {mu}m line is a particularly good case; it should be dramatically brighter than the optical lines commonly used in searches. The C IV {lambda}1549 doublet is predicted to be the strongest absorption line from the shell, which is in agreement with Hubble Space Telescope observations. We show that the cooling timescale for the outer shell is much longer than the age of the Crab, due to the low density. This means that the temperature of the shell will actually ''remember'' its initial conditions. However, the recombination time is much shorter than the age of the Crab, so the predicted level of ionization should approximate the real ionization. In any case, it is clear that IR observations present the best opportunity to detect the outer shell and so guide future models that will constrain early events in the original explosion.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Electron-ion recombination of Fe{sup 12+} forming Fe{sup 11+}: Laboratory measurements and theoretical calculations

We have measured dielectronic recombination (DR) for Fe{sup 12+} forming Fe{sup 11+} using the heavy ion storage ring TSR located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Using our results, we have calculated a plasma rate coefficient from these data that can be used for modeling astrophysical and laboratory plasmas. For the low temperatures characteristic of photoionized plasmas, the experimentally derived rate coefficient is orders of magnitude larger than the previously recommended atomic data. The existing atomic data were also about 40% smaller than our measurements at temperatures relevant for collisionally ionized plasmas. Recent state-of-the-art theory has difficulty reproducing the detailed energy dependence of the DR spectrum. However, for the Maxwellian plasma rate coefficient, recent theoretical results agree with our measurements to within about 30% for both photoionized and collisionally ionized plasmas.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The COS-Halos survey: physical conditions and baryonic mass in the low-redshift circumgalactic medium

We analyze the physical conditions of the cool, photoionized (T ∼10{sup 4} K) circumgalactic medium (CGM) using the COS-Halos suite of gas column density measurements for 44 gaseous halos within 160 kpc of L ∼ L* galaxies at z ∼ 0.2. These data are well described by simple photoionization models, with the gas highly ionized (n {sub H} {sub II}/n {sub H} ≳ 99%) by the extragalactic ultraviolet background. Scaling by estimates for the virial radius, R {sub vir}, we show that the ionization state (tracked by the dimensionless ionization parameter, U) increases with distance from the host galaxy. The ionization parameters imply a decreasing volume density profile n {sub H} = (10{sup –4.2±0.25})(R/R {sub vir}){sup –0.8±0.3}. Our derived gas volume densities are several orders of magnitude lower than predictions from standard two-phase models with a cool medium in pressure equilibrium with a hot, coronal medium expected in virialized halos at this mass scale. Applying the ionization corrections to the H I column densities, we estimate a lower limit to the cool gas mass M{sub CGM}{sup cool}>6.5×10{sup 10} M {sub ☉} for the volume within R < R {sub vir}. Allowing for an additional warm-hot, O VI-traced phase, the CGM accounts for at least half of the baryons purported to be missing from dark matter halos at the 10{sup 12} M {sub ☉} scale.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

NuSTAR unveils a Compton-thick type 2 quasar in MrK 34

We present Nuclear Spectroscopic Telescope Array (NuSTAR) 3-40 keV observations of the optically selected Type 2 quasar (QSO2) SDSS J1034+6001 or Mrk 34. The high-quality hard X-ray spectrum and archival XMM-Newton data can be fitted self-consistently with a reflection-dominated continuum and a strong Fe Kα fluorescence line with equivalent width >1 keV. Prior X-ray spectral fitting below 10 keV showed the source to be consistent with being obscured by Compton-thin column densities of gas along the line of sight, despite evidence for much higher columns from multiwavelength data. NuSTAR now enables a direct measurement of this column and shows that N {sub H} lies in the Compton-thick (CT) regime. The new data also show a high intrinsic 2-10 keV luminosity of L {sub 2-10} ∼ 10{sup 44} erg s{sup –1}, in contrast to previous low-energy X-ray measurements where L {sub 2-10} ≲ 10{sup 43} erg s{sup –1} (i.e., X-ray selection below 10 keV does not pick up this source as an intrinsically luminous obscured quasar). Both the obscuring column and the intrinsic power are about an order of magnitude (or more) larger than inferred from pre-NuSTAR X-ray spectral fitting. Mrk 34 is thus a 'gold standard' CT QSO2 and is the nearest non-merging system in this class, in contrast to the other local CT quasar NGC 6240, which is currently undergoing a major merger coupled with strong star formation. For typical X-ray bolometric correction factors, the accretion luminosity of Mrk 34 is high enough to potentially power the total infrared luminosity. X-ray spectral fitting also shows that thermal emission related to star formation is unlikely to drive the observed bright soft component below ∼3 keV, favoring photoionization instead.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Constraining UV continuum slopes of active galactic nuclei with cloudy models of broad-line region extreme-ultraviolet emission lines

Understanding the composition and structure of the broad-line region (BLR) of active galactic nuclei (AGNs) is important for answering many outstanding questions in supermassive black hole evolution, galaxy evolution, and ionization of the intergalactic medium. We used single-epoch UV spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope to measure EUV emission-line fluxes from four individual AGNs with 0.49 ≤ z ≤ 0.64, two AGNs with 0.32 ≤ z ≤ 0.40, and a composite of 159 AGNs. With the CLOUDY photoionization code, we calculated emission-line fluxes from BLR clouds with a range of density, hydrogen ionizing flux, and incident continuum spectral indices. The photoionization grids were fit to the observations using single-component and locally optimally emitting cloud (LOC) models. The LOC models provide good fits to the measured fluxes, while the single-component models do not. The UV spectral indices preferred by our LOC models are consistent with those measured from COS spectra. EUV emission lines such as N IV λ765, O II λ833, and O III λ834 originate primarily from gas with electron temperatures between 37,000 K and 55,000 K. This gas is found in BLR clouds with high hydrogen densities (n {sub H} ≥ 10{sup 12} cm{sup –3}) and hydrogen ionizing photon fluxes (Φ{sub H} ≥ 10{sup 22} cm{sup –2} s{sup –1}).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A DEEP NARROWBAND IMAGING SEARCH FOR C iv AND He ii EMISSION FROM Lyα BLOBS

We conduct a deep narrowband imaging survey of 13 Lyα blobs (LABs) located in the SSA22 proto-cluster at z ∼ 3.1 in the C iv and He ii emission lines in an effort to constrain the physical process powering the Lyα emission in LABs. Our observations probe down to unprecedented surface brightness (SB) limits of (2.1–3.4) × 10{sup −18} erg s{sup −1} cm{sup −2} arcsec{sup −2} per 1 arcsec{sup 2} aperture (5σ) for the He ii λ1640 and C iv λ1549 lines, respectively. We do not detect extended He ii and C iv emission in any of the LABs, placing strong upper limits on the He ii/Lyα and C iv/Lyα line ratios, of 0.11 and 0.16, for the brightest two LABs in the field. We conduct detailed photoionization modeling of the expected line ratios and find that, although our data constitute the deepest ever observations of these lines, they are still not deep enough to rule out a scenario where the Lyα emission is powered by the ionizing radiation from an obscured active galactic nucleus. Our models can accommodate He ii/Lyα and C iv/Lyα ratios as low as ≃0.05 and ≃0.07, respectively, implying that one needs to reach SB as low as (1–1.5) × 10{sup −18} erg s{sup −1} cm{sup −2} arcsec{sup −2} (at 5σ) in order to rule out a photoionization scenario. These depths will be achievable with the new generation of image-slicing integral field units such as the Multi Unit Spectroscopic Explorer (MUSE) on VLT and the Keck Cosmic Web Imager (KCWI). We also model the expected He ii/Lyα and C iv/Lyα in a different scenario, where Lyα emission is powered by shocks generated in a large-scale superwind, but find that our observational constraints can only be met for shock velocities v{sub s} ≳ 250 km s{sup −1}, which appear to be in conflict with recent observations of quiescent kinematics in LABs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE SMARTS MULTI-EPOCH OPTICAL SPECTROSCOPY ATLAS (SaMOSA): AN ANALYSIS OF EMISSION LINE VARIABILITY IN SOUTHERN HEMISPHERE FERMI BLAZARS

We present multi-epoch optical spectroscopy of seven southern Fermi-monitored blazars from 2008 to 2013 using the Small and Medium Aperture Research Telescope System (SMARTS), with supplemental spectroscopy and polarization data from the Steward Observatory. We find that the emission lines are much less variable than the continuum; four of seven blazars had no detectable emission line variability over the 5 yr observation period. This is consistent with photoionization primarily by an accretion disk, allowing us to use the lines as a probe of disk activity. Comparing optical emission line flux with Fermi γ-ray flux and optical polarized flux, we investigate whether relativistic jet variability is related to the accretion flow. In general, we see no such dependence, suggesting that the jet variability is likely caused by internal processes like turbulence or shock acceleration rather than a variable accretion rate. However, three sources showed statistically significant emission line flares in close temporal proximity to very large Fermi γ-ray flares. While we do not have sufficient emission line data to quantitatively assess their correlation with the γ-ray flux, it appears that in some cases the jet might provide additional photoionizing flux to the broad-line region (BLR), which implies that some γ-rays are produced within the BLR, at least for these large flares.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Time-variable non-thermal emission in the planetary nebula IRAS 15103–5754

The beginning of photoionization marks the transition between the post-AGB and planetary nebula (PN) phases of stars with masses ≲8 M {sub ⊙}. This critical phase is difficult to observe, as it lasts only a few decades. The combination of jets and magnetic fields, the key agents of PN shaping, could give rise to synchrotron emission, but this has never been observed before in any PNe, since free–free emission from the ionized gas is expected to dominate its radio spectrum. In this paper we report radio continuum observations taken with the ATCA between 1 and 46 GHz of the young PN IRAS 15103–5754. Our observations in 2010–2011 show non-thermal emission compatible with synchrotron emission from electrons accelerated at a shock with spectral index α≃−0.54. However, in 2012, the spectral index α≃−0.28 is no longer compatible with synchrotron emission in these types of processes. Several hypotheses are discussed to explain this change. The more plausible ones are related to the presence of the newly photoionized region in this young PN: either energy loss of electrons due to Coulomb collisions with the plasma, or selective suppression of synchrotron radiation due to the Razin effect. We postulate that the observed flattening of non-thermal radio spectra could be a hallmark identifying the beginning of the PN phase.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

DEEP HE ii AND C iv SPECTROSCOPY OF A GIANT LYα NEBULA: DENSE COMPACT GAS CLUMPS IN THE CIRCUMGALACTIC MEDIUM OF A z ∼ 2 QUASAR

The recent discovery by Cantalupo et al. of the largest (∼500 kpc) luminous (L ≃ 1.43 × 10{sup 45} erg s{sup −1}) Lyα nebula associated with the quasar UM287 (z = 2.279) poses a great challenge to our current understanding of the astrophysics of the halos hosting massive z ∼ 2 galaxies. Either an enormous reservoir of cool gas is required M ≃ 10{sup 12} M{sub ⊙}, exceeding the expected baryonic mass available, or one must invoke extreme gas clumping factors not present in high-resolution cosmological simulations. However, observations of Lyα emission alone cannot distinguish between these two scenarios. We have obtained the deepest ever spectroscopic integrations in the He ii λ1640 and C iv λ1549 emission lines with the goal of detecting extended line emission, but detect neither line to a 3σ limiting SB ≃ 10{sup −18} erg s{sup −1} cm{sup −2} arcsec{sup −2}. We construct simple models of the expected emission spectrum in the highly probable scenario that the nebula is powered by photoionization from the central hyper-luminous quasar. The non-detection of He ii implies that the nebular emission arises from a mass M{sub c} ≲ 6.4 × 10{sup 10} M{sub ⊙} of cool gas on ∼200 kpc scales, distributed in a population of remarkably dense (n{sub H} ≳ 3 cm{sup −3}) and compact (R ≲ 20 pc) clouds, which would clearly be unresolved by current cosmological simulations. Given the large gas motions suggested by the Lyα line (v ≃ 500 km s{sup −1}), it is unclear how these clouds survive without being disrupted by hydrodynamic instabilities. Our work serves as a benchmark for future deep integrations with current and planned wide-field IFU spectrographs such as MUSE, KCWI, and KMOS. Our observations and models suggest that a ≃10 hr exposure would likely detect ∼10 rest-frame UV/optical emission lines, opening up the possibility of conducting detailed photoionization modeling to infer the physical state of gas in the circumgalactic medium.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

PHOTOCHEMICAL HEATING OF DENSE MOLECULAR GAS

Photochemical heating is analyzed with an emphasis on the heating generated by chemical reactions initiated by the products of photodissociation and photoionization. The immediate products are slowed down by collisions with the ambient gas and then heat the gas. In addition to this direct process, heating is also produced by the subsequent chemical reactions initiated by these products. Some of this chemical heating comes from the kinetic energy of the reaction products and the rest from collisional de-excitation of the product atoms and molecules. In considering dense gas dominated by molecular hydrogen, we find that the chemical heating is sometimes as large, if not much larger than, the direct heating. In very dense gas, the total photochemical heating approaches 10 eV per photodissociation (or photoionization), competitive with other ways of heating molecular gas.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
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

An extreme metallicity, large-scale outflow from a star-forming galaxy at z ∼ 0.4

We present a detailed analysis of a large-scale galactic outflow in the circumgalactic medium of a massive (M{sub h}∼10{sup 12.5} M{sub ⊙}), star-forming (∼6.9 M{sub ⊙} yr{sup −1}), sub-L{sub *} (∼0.5L{sub B}{sup ∗}) galaxy at z = 0.39853 that exhibits a wealth of metal-line absorption in the spectra of the background quasar Q 0122−003 at an impact parameter of 163 kpc. The galaxy inclination angle (i=63{sup ∘}) and the azimuthal angle (Φ=73{sup ∘}) imply that the QSO sightline is passing through the projected minor-axis of the galaxy. The absorption system shows a multiphase, multicomponent structure with ultra-strong, wide velocity spread O VI (logN=15.16±0.04, Δv{sub 90} = 419 km s{sup −1}) and N V (logN=14.69±0.07, Δv{sub 90} = 285 km s{sup −1}) lines that are extremely rare in the literature. The highly ionized absorption components are well explained as arising in a low density (∼10{sup −4.2} cm{sup −3}), diffuse (∼10 kpc), cool (∼10{sup 4} K) photoionized gas with a super-solar metallicity ([X/H]≳0.3). From the observed narrowness of the Lyβ profile, the non-detection of S IV absorption, and the presence of strong C IV absorption in the low-resolution FOS spectrum, we rule out equilibrium/non-equilibrium collisional ionization models. The low-ionization photoionized gas with a density of ∼10{sup −2.5} cm{sup −3} and a metallicity of [X/H]≳−1.4 is possibly tracing recycled halo gas. We estimate an outflow mass of ∼2×10{sup 10} M{sub ⊙}, a mass-flow rate of ∼54 M{sub ⊙} yr{sup −1}, a kinetic luminosity of ∼9×10{sup 41} erg s{sup −1}, and a mass loading factor of ∼8 for the outflowing high-ionization gas. These are consistent with the properties of “down-the-barrel” outflows from infrared-luminous starbursts as studied by Rupke et al. Such powerful, large-scale, metal-rich outflows are the primary means of sufficient mechanical and chemical feedback as invoked in theoretical models of galaxy formation and evolution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

ON THE ELECTRON-TO-NEUTRAL NUMBER DENSITY RATIO IN THE COMA OF COMET 67P/CHURYUMOV–GERASIMENKO: GUIDING EXPRESSION AND SOURCES FOR DEVIATIONS

We compute partial photoionization frequencies of H{sub 2}O, CO{sub 2}, and CO, the major molecules in the coma of comet 67P/Churyumov–Gerasimenko, the target comet of the ongoing ESA Rosetta mission. Values are computed from Thermosphere Ionosphere Mesosphere Energy and Dynamics/Solar EUV Experiment solar EUV spectra for 2014 August 1, 2015 March 1, and for perihelion (2015 August, as based on prediction). From the varying total photoionization frequency of H{sub 2}O, as computed from 2014 August 1 to 2015 May 20, we derive a simple analytical expression for the electron-to-neutral number density ratio as a function of cometocentric and heliocentric distance. The underlying model assumes radial movement of the coma constituents and does not account for chemical loss or the presence of electric fields. We discuss various effects/processes that can cause deviations between values from the analytical expression and actual electron-to-neutral number density ratios. The analytical expression is thus not strictly meant as predicting the actual electron-to-neutral number density ratio, but is useful in comparisons with observations as an indicator of processes at play in the cometary coma.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

CO-SPATIAL LONG-SLIT UV/OPTICAL SPECTRA OF TEN GALACTIC PLANETARY NEBULAE WITH HST/STIS. II. NEBULAR MODELS, CENTRAL STAR PROPERTIES, AND He+CNO SYNTHESIS

The goal of the present study is twofold. First, we employ new HST/STIS spectra and photoionization modeling techniques to determine the progenitor masses of eight planetary nebulae (IC 2165, IC 3568, NGC 2440, NGC 3242, NGC 5315, NGC 5882, NGC 7662, and PB 6). Second, for the first time we are able to compare each object’s observed nebular abundances of helium, carbon, and nitrogen with abundance predictions of these same elements by a stellar model that is consistent with each object’s progenitor mass. Important results include the following: (1) the mass range of our objects’ central stars matches well with the mass distribution of other central stars of planetary nebulae and white dwarfs; (2) He/H is above solar in all of our objects, in most cases likely due to the predicted effects of first dredge-up; (3) most of our objects show negligible C enrichment, probably because their low masses preclude third dredge-up; (4) C/O versus O/H for our objects appears to be inversely correlated, which is perhaps consistent with the conclusion of theorists that the extent of atmospheric carbon enrichment from first dredge-up is sensitive to a parameter whose value increases as metallicity declines; (5) stellar model predictions of nebular C and N enrichment are consistent with observed abundances for progenitor star masses ≤1.5 M{sub ⊙}. Finally, we present the first published photoionization models of NGC 5315 and NGC 5882.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Powerful, rotating disk winds from stellar-mass black holes

We present an analysis of ionized X-ray disk winds found in the Fe K band of four stellar-mass black holes observed with Chandra, including 4U 1630−47, GRO J1655−40, H 1743−322, and GRS 1915+105. High-resolution photoionization grids were generated in order to model the data. Third-order gratings spectra were used to resolve complex absorption profiles into atomic effects and multiple velocity components. The Fe xxv line is found to be shaped by contributions from the intercombination line (in absorption), and the Fe xxvi line is detected as a spin–orbit doublet. The data require 2–3 absorption zones, depending on the source. The fastest components have velocities approaching or exceeding 0.01c, increasing mass outflow rates and wind kinetic power by orders of magnitude over prior single-zone models. The first-order spectra require re-emission from the wind, broadened by a degree that is loosely consistent with Keplerian orbital velocities at the photoionization radius. This suggests that disk winds are rotating with the orbital velocity of the underlying disk, and provides a new means of estimating launching radii—crucial to understanding wind driving mechanisms. Some aspects of the wind velocities and radii correspond well to the broad-line region in active galactic nuclei (AGNs), suggesting a physical connection. We discuss these results in terms of prevalent models for disk wind production and disk accretion itself, and implications for massive black holes in AGNs.

79 ASTRONOMY AND ASTROPHYSICS↗