SDSS-IV MaNGA - the spatially resolved transition from star formation to quiescence

NASA Astrophysics Data System (ADS)

Belfiore, Francesco; Maiolino, Roberto; Maraston, Claudia; Emsellem, Eric; Bershady, Matthew A.; Masters, Karen L.; Bizyaev, Dmitry; Boquien, Médéric; Brownstein, Joel R.; Bundy, Kevin; Diamond-Stanic, Aleksandar M.; Drory, Niv; Heckman, Timothy M.; Law, David R.; Malanushenko, Olena; Oravetz, Audrey; Pan, Kaike; Roman-Lopes, Alexandre; Thomas, Daniel; Weijmans, Anne-Marie; Westfall, Kyle B.; Yan, Renbin

2017-04-01

Using spatially resolved spectroscopy from SDSS-IV MaNGA we have demonstrated that low ionization emission-line regions (LIERs) in local galaxies result from photoionization by hot evolved stars, not active galactic nuclei, hence tracing galactic region hosting old stellar population where, despite the presence of ionized gas, star formation is no longer occurring. LIERs are ubiquitous in both quiescent galaxies and in the central regions of galaxies where star formation takes place at larger radii. We refer to these two classes of galaxies as extended LIER (eLIER) and central LIER (cLIER) galaxies, respectively. cLIERs are late-type galaxies primarily spread across the green valley, in the transition region between the star formation main sequence and quiescent galaxies. These galaxies display regular disc rotation in both stars and gas, although featuring a higher central stellar velocity dispersion than star-forming galaxies of the same mass. cLIERs are consistent with being slowly quenched inside-out; the transformation is associated with massive bulges, pointing towards the importance of bulge growth via secular evolution. eLIERs are morphologically early types and are indistinguishable from passive galaxies devoid of line emission in terms of their stellar populations, morphology and central stellar velocity dispersion. Ionized gas in eLIERs shows both disturbed and disc-like kinematics. When a large-scale flow/rotation is observed in the gas, it is often misaligned relative to the stellar component. These features indicate that eLIERs are passive galaxies harbouring a residual cold gas component, acquired mostly via external accretion. Importantly, quiescent galaxies devoid of line emission reside in denser environments and have significantly higher satellite fraction than eLIERs. Environmental effects thus represent the likely cause for the existence of line-less galaxies on the red sequence.

Ionization in MHD-Gas interactions

NASA Astrophysics Data System (ADS)

Wilson, A.; Diver, D. A.

2013-09-01

The study of partially ionized plasmas is important in a number of astrophysical situations and is vital for the study of laboratory plasmas. The interactions between a neutral gas and a plasma define a hybrid medium that has aspects of each, but does not only sustain the pure modes of the individual species. Previously we have shown that momentum coupling between the gas and the magnetized plasma alters the behaviour of both; as an extension of that simulation, we present results for the extension to the coupling in which the relative motion between the species provides enough kinetic energy in the flow to allow a measure of species exchange Alfvén ionization (AI) (also known as critical velocity ionization), allowing the ionization fraction to evolve as the dynamics evolve.

Application of modern online instrumentation for chemical analysis of gas and particulate phases of exhaust at the European Commission heavy-duty vehicle emission laboratory.

PubMed

Adam, T W; Chirico, R; Clairotte, M; Elsasser, M; Manfredi, U; Martini, G; Sklorz, M; Streibel, T; Heringa, M F; Decarlo, P F; Baltensperger, U; De Santi, G; Krasenbrink, A; Zimmermann, R; Prevot, A S H; Astorga, C

2011-01-01

The European Commission recently established a novel test facility for heavy-duty vehicles to enhance more sustainable transport. The facility enables the study of energy efficiency of various fuels/scenarios as well as the chemical composition of evolved exhaust emissions. Sophisticated instrumentation for real-time analysis of the gas and particulate phases of exhaust has been implemented. Thereby, gas-phase characterization was carried out by a Fourier transform infrared spectrometer (FT-IR; carbonyls, nitrogen-containing species, small hydrocarbons) and a resonance-enhanced multiphoton ionization time-of-flight mass spectrometer (REMPI-TOFMS; monocyclic and polycyclic aromatic hydrocarbons). For analysis of the particulate phase, a high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS; organic matter, chloride, nitrate), a condensation particle counter (CPC; particle number), and a multiangle absorption photometer (MAAP; black carbon) were applied. In this paper, the first application of the new facility in combination with the described instruments is presented, whereby a medium-size truck was investigated by applying different driving cycles. The goal was simultaneous chemical characterization of a great variety of gaseous compounds and particulate matter in exhaust on a real-time basis. The time-resolved data allowed new approaches to view the results; for example, emission factors were normalized to time-resolved consumption of fuel and were related to emission factors evolved during high speeds. Compounds could be identified that followed the fuel consumption, others showed very different behavior. In particular, engine cold start, engine ignition (unburned fuel), and high-speed events resulted in unique emission patterns.

Modeling Line Emission from Structures Seen at High Resolution in the Nebulae m1 and M16

NASA Astrophysics Data System (ADS)

Sankrit, Ravi

1998-12-01

Narrow band images of the Crab Nebula supernova remnant and of the Eagle Nebula H II region taken with the Hubble Space Telescope (HST) show the ionization structure of the emitting gas in unprecedented detail because of the high spatial resolution. The physics of the emission processes-shock excited emission and photoionized emission-is well understood. Sophisticated numerical codes are used to model the ionization structure and emission observed in these images. It is found that the thin skin of material around the Crab synchrotron nebula visible in (O III) λ5007 emission is best explained as the cooling region behind a shock driven by the synchrotron nebula into a surrounding remnant of freely expanding ejecta. Shock models, with parameters derived from independently known properties of the Crab, explain the observed spectrum of the skin while photoionization models fail to explain the observed strength of high ionization lines such as C IV λ1549. This result is clear evidence that the synchrotron nebula is interacting with an extended remnant of ejecta, which in turn has significant implications for the structure and evolution of the Crab. At HST resolution, it is seen that low ionization emission, from lines such as (O I) λ6300, is concentrated in sharp structures while high ionization emission (from (O III) λ5007) is much more diffuse. Individual filaments are found to lie along a sequence of ionization structure ranging from features in which all lines are concentrated in the same compact volume through features with low ionization cores surrounded by high ionization envelopes. Photoionization models of cylindrically symmetrical filaments with varying 'core-halo' density profiles can match the observed variation in the filament structure in the Crab. A photoionization model of a uniform low density medium matches the extended diffuse component which dominates the high ionization emission. It is found that detailed knowledge of the filament structures present in an aperture is needed to correctly interpret ground-based spectra of the Crab. The images also show that many filament cores coincide with dust extinction features, which suggest that the dust to gas mass ratio may be up to an order of magnitude higher than is typical in the interstellar medium. Nebula show the interface between the ionized gas and the molecular cloud in tangency against the background of the ionized cavity which constitutes the H II region. A photoionization model using a density profile for the photoevaporative flow that is expected at such an interface is successful at explaining the observed emission profiles of Hα λ6563, (S II) λλ6716,6731, and (O III) λ5007. The ionizing flux is well constrained by the Hα emission and the sulphur abundance is constrained by the peak of the (S II) emission. A grid of models using the same density profiles shows how various emission properties depend on the ionizing continuum shape, ionizing flux and elemental abundances.

The Impact of Nonequilibrium Ionization on SDO/AIA and Hinode/EIS Observations of Impulsively Heated Plasmas

NASA Technical Reports Server (NTRS)

Klimchuk, James A.; Bradshaw, Stephen J.

2011-01-01

Most plasma diagnostics assume the emitting material is in a state of ionization equilibrium. For example, the AIA temperature response functions have been derived on this basis. The assumption is reasonable whenever the plasma is evolving slowly or is very dense, but these are not the conditions that apply during impulsive heating events. It is now widely believed that many coronal loops are bundles of unresolved strands that are heated quasi-randomly by nanoflares. Full blown flares are thought to have similar sub-structure. We have studied the importance of nonequilibrium effects in these circumstances by modeling nanoflare-heated loops and simulating their observation by AIA and the EIS spectrometer on Hinode. We find that the intensities of hot emission lines can be highly suppressed and that the net emission from the loop tends to be dominated by strands that have entered a slow cooling phase, well after the impulsive energy release has ended. The hottest strands are relatively invisible, both because they are tenuous and because they cool rapidly by thermal conduction. Thus, AIA channels that are normally thought of as being sensitive to hot plasma, such 131 and 94, are in fact frequently not able to detect the hot plasma that is present. The magnitude of the effect is case dependent. Great care must be exercised when using the standard temperature response functions in situations where nonequilibrium ionization is likely to be important.

The different origins of high- and low-ionization broad emission lines revealed by gravitational microlensing in the Einstein cross

NASA Astrophysics Data System (ADS)

Braibant, L.; Hutsemékers, D.; Sluse, D.; Anguita, T.

2016-07-01

We investigate the kinematics and ionization structure of the broad emission line region of the gravitationally lensed quasar QSO2237+0305 (the Einstein cross) using differential microlensing in the high- and low-ionization broad emission lines. We combine visible and near-infrared spectra of the four images of the lensed quasar and detect a large-amplitude microlensing effect distorting the high-ionization CIV and low-ionization Hα line profiles in image A. While microlensing only magnifies the red wing of the Balmer line, it symmetrically magnifies the wings of the CIV emission line. Given that the same microlensing pattern magnifies both the high- and low-ionization broad emission line regions, these dissimilar distortions of the line profiles suggest that the high- and low-ionization regions are governed by different kinematics. Since this quasar is likely viewed at intermediate inclination, we argue that the differential magnification of the blue and red wings of Hα favors a flattened, virialized, low-ionization region whereas the symmetric microlensing effect measured in CIV can be reproduced by an emission line formed in a polar wind, without the need of fine-tuned caustic configurations. Based on observations made with the ESO-VLT, Paranal, Chile; Proposals 076.B-0197 and 076.B-0607 (PI: Courbin).

Classical vs. evolved quenching parameters and procedures in scintillation measurements: The importance of ionization quenching

NASA Astrophysics Data System (ADS)

Bagán, H.; Tarancón, A.; Rauret, G.; García, J. F.

2008-07-01

The quenching parameters used to model detection efficiency variations in scintillation measurements have not evolved since the decade of 1970s. Meanwhile, computer capabilities have increased enormously and ionization quenching has appeared in practical measurements using plastic scintillation. This study compares the results obtained in activity quantification by plastic scintillation of 14C samples that contain colour and ionization quenchers, using classical (SIS, SCR-limited, SCR-non-limited, SIS(ext), SQP(E)) and evolved (MWA-SCR and WDW) parameters and following three calibration approaches: single step, which does not take into account the quenching mechanism; two steps, which takes into account the quenching phenomena; and multivariate calibration. Two-step calibration (ionization followed by colour) yielded the lowest relative errors, which means that each quenching phenomenon must be specifically modelled. In addition, the sample activity was quantified more accurately when the evolved parameters were used. Multivariate calibration-PLS also yielded better results than those obtained using classical parameters, which confirms that the quenching phenomena must be taken into account. The detection limits for each calibration method and each parameter were close to those obtained theoretically using the Currie approach.

Non-relativistic Free–Free Emission due to the n -distribution of Electrons—Radiative Cooling and Thermally Averaged and Total Gaunt Factors

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Avillez, Miguel A.; Breitschwerdt, Dieter, E-mail: mavillez@galaxy.lca.uevora.pt

Tracking the thermal evolution of plasmas, characterized by an n -distribution, using numerical simulations, requires the determination of the emission spectra and of the radiative losses due to free–free emission from the corresponding temperature-averaged and total Gaunt factors. Detailed calculations of the latter are presented and associated with n -distributed electrons with the parameter n ranging from 1 (corresponding to the Maxwell–Boltzmann distribution) to 100. The temperature-averaged and total Gaunt factors with decreasing n tend toward those obtained with the Maxwell–Boltzmann distribution. Radiative losses due to free–free emission in a plasma evolving under collisional ionization equilibrium conditions and composed bymore » H, He, C, N, O, Ne, Mg, Si, S, and Fe ions, are presented. These losses decrease with a decrease in the parameter n , reaching a minimum when n  = 1, and thus converge with the loss of thermal plasma. Tables of the thermal-averaged and total Gaunt factors calculated for n -distributions, and a wide range of electron and photon energies, are presented.« less

SDSS-IV MaNGA: evidence of the importance of AGN feedback in low-mass galaxies

NASA Astrophysics Data System (ADS)

Penny, Samantha J.; Masters, Karen L.; Smethurst, Rebecca; Nichol, Robert C.; Krawczyk, Coleman M.; Bizyaev, Dmitry; Greene, Olivia; Liu, Charles; Marinelli, Mariarosa; Rembold, Sandro B.; Riffel, Rogemar A.; Ilha, Gabriele da Silva; Wylezalek, Dominika; Andrews, Brett H.; Bundy, Kevin; Drory, Niv; Oravetz, Daniel; Pan, Kaike

2018-05-01

We present new evidence for AGN feedback in a subset of 69 quenched low-mass galaxies (M⋆ ≲ 5 × 109 M⊙, Mr > -19) selected from the first 2 yr of the Sloan Digital Sky Survey-IV Mapping Nearby Galaxies at APO (SDSS-IV MaNGA) survey. The majority (85 per cent) of these quenched galaxies appear to reside in a group environment. We find six galaxies in our sample that appear to have an active AGN that is preventing on-going star formation; this is the first time such a feedback mechanism has been observed in this mass range. Interestingly, five of these six galaxies have an ionized gas component that is kinematically offset from their stellar component, suggesting the gas is either recently accreted or outflowing. We hypothesize these six galaxies are low-mass equivalents to the `red geysers' observed in more massive galaxies. Of the other 63 galaxies in the sample, we find 8 do appear for have some low level, residual star formation, or emission from hot, evolved stars. The remaining galaxies in our sample have no detectable ionized gas emission throughout their structures, consistent with them being quenched. This work shows the potential for understanding the detailed physical properties of dwarf galaxies through spatially resolved spectroscopy.

A Suzaku Study of Ejecta Structure and Origin of Hard X-ray Emission in the Supernova Remnant G156.2+5.7

NASA Technical Reports Server (NTRS)

Uchida, Hiroyuki; Tsunemi, Hiroshi; Katsuda, Satoru; Mori, Koji; Petre, Robert; Yamaguchi, Hiroya

2012-01-01

We report an X-ray study of the evolved Galactic supernova remnant (SNR) G1S6.2+S.7 based on six pointing observations with Suzaku. The remnant's large extent (100' in diameter) allows us to investigate its radial structure in the northwestern and eastern directions from the apparent center. The X-ray spectra. were well fit with a two-component non-equilibrium ionization model representing the swept-up interstellar medium (ISM) and the metal-rich ejecta. We found prominent central concentrations of Si, S and Fe from the ejecta component; the lighter elements of O, Ne and Mg were distributed more uniformly. The temperature of the ISM component suggests a slow shock (610-960 km/s), hence the remnant's age is estimated to be 7,000-15,000 yr, assuming its distance to be approx. 1.1 kpc. G1S6.2+5.7 has also been thought to emit hard, non-thermal X-rays, despite being considerably older than any other such remnant. In response to a recent discovery of a background cluster of galaxies (2XMM J045637.2+522411), we carefully excluded its contribution, and reexamined the origin of the hard X-ray emission. We found that the residual hard X-ray emission is consistent with the expected level of the cosmic X-ray background. Thus, no robust evidence for the non-thermal emission was obtained from G156.2+5.7. These results are consistent with the picture of an evolved SNR.

Observation of increased space-charge limited thermionic electron emission current by neutral gas ionization in a weakly-ionized deuterium plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hollmann, E. M.; Yu, J. H.; Doerner, R. P.

2015-09-14

The thermionic electron emission current emitted from a laser-produced hot spot on a tungsten target in weakly-ionized deuterium plasma is measured. It is found to be one to two orders of magnitude larger than expected for bipolar space charge limited thermionic emission current assuming an unperturbed background plasma. This difference is attributed to the plasma being modified by ionization of background neutrals by the emitted electrons. This result indicates that the allowable level of emitted thermionic electron current can be significantly enhanced in weakly-ionized plasmas due to the presence of large neutral densities.

Characteristics of plasma plume in ultrafast laser ablation with a weakly ionized air channel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hou, Huaming; Yang, Bo; Mao, Xianglei

We report the influence of femtosecond (fs) laser weakly ionized air channel on characteristics of plasma induced from fs-laser ablation of solid Zr metal target. A novel method to create high temperature, low electron density plasma with intense elemental emission and weak bremsstrahlung emission was demonstrated. Weakly ionized air channel was generated as a result of a non-linear phenomenon. Two-dimensional time-resolved optical-emission images of plasma plumes were taken for plume dynamics analysis. Dynamic physical properties of filament channels were simulated. In particular, we investigated the influence of weakly ionized air channel on the evolution of solid plasma plume. Plasma plumemore » splitting was observed whilst longer weakly ionized air channel formed above the ablation spot. The domination mechanism for splitting is attributed to the long-lived underdense channel created by fs-laser induced weakly ionization of air. The evolutions of atomic/molecular emission intensity, peak broadening, and plasma temperature were analyzed, and the results show that the part of plasma entering weakly ionized air channel features higher initial temperature, lower electron density and faster decay.« less

Characteristics of plasma plume in ultrafast laser ablation with a weakly ionized air channel

DOE PAGES

Hou, Huaming; Yang, Bo; Mao, Xianglei; ...

2018-05-10

We report the influence of femtosecond (fs) laser weakly ionized air channel on characteristics of plasma induced from fs-laser ablation of solid Zr metal target. A novel method to create high temperature, low electron density plasma with intense elemental emission and weak bremsstrahlung emission was demonstrated. Weakly ionized air channel was generated as a result of a non-linear phenomenon. Two-dimensional time-resolved optical-emission images of plasma plumes were taken for plume dynamics analysis. Dynamic physical properties of filament channels were simulated. In particular, we investigated the influence of weakly ionized air channel on the evolution of solid plasma plume. Plasma plumemore » splitting was observed whilst longer weakly ionized air channel formed above the ablation spot. The domination mechanism for splitting is attributed to the long-lived underdense channel created by fs-laser induced weakly ionization of air. The evolutions of atomic/molecular emission intensity, peak broadening, and plasma temperature were analyzed, and the results show that the part of plasma entering weakly ionized air channel features higher initial temperature, lower electron density and faster decay.« less

The ionized gas in the CALIFA early-type galaxies. I. Mapping two representative cases: NGC 6762 and NGC 5966

NASA Astrophysics Data System (ADS)

Kehrig, C.; Monreal-Ibero, A.; Papaderos, P.; Vílchez, J. M.; Gomes, J. M.; Masegosa, J.; Sánchez, S. F.; Lehnert, M. D.; Cid Fernandes, R.; Bland-Hawthorn, J.; Bomans, D. J.; Marquez, I.; Mast, D.; Aguerri, J. A. L.; López-Sánchez, Á. R.; Marino, R. A.; Pasquali, A.; Perez, I.; Roth, M. M.; Sánchez-Blázquez, P.; Ziegler, B.

2012-04-01

As part of the ongoing CALIFA survey, we have conducted a thorough bidimensional analysis of the ionized gas in two E/S0 galaxies, NGC 6762 and NGC 5966, aiming to shed light on the nature of their warm ionized ISM. Specifically, we present optical (3745-7300 Å) integral field spectroscopy obtained with the PMAS/PPAK integral field spectrophotometer. Its wide field-of-view (1' × 1') covers the entire optical extent of each galaxy down to faint continuum surface brightnesses. To recover the nebular lines, we modeled and subtracted the underlying stellar continuum from the observed spectra using the STARLIGHT spectral synthesis code. The pure emission-line spectra were used to investigate the gas properties and determine the possible sources of ionization. We show the advantages of IFU data in interpreting the complex nature of the ionized gas in NGC 6762 and NGC 5966. In NGC 6762, the ionized gas and stellar emission display similar morphologies, while the emission line morphology is elongated in NGC 5966, spanning ~6 kpc, and is oriented roughly orthogonal to the major axis of the stellar continuum ellipsoid. Whereas gas and stars are kinematically aligned in NGC 6762, the gas is kinematically decoupled from the stars in NGC 5966. A decoupled rotating disk or an "ionization cone" are two possible interpretations of the elongated ionized gas structure in NGC 5966. The latter would be the first "ionization cone" of such a dimension detected within a weak emission-line galaxy. Both galaxies have weak emission-lines relative to the continuum[EW(Hα) ≲ 3 Å] and have very low excitation, log([Oiii]λ5007/Hβ) ≲ 0.5. Based on optical diagnostic ratios ([Oiii]λ5007/Hβ, [Nii]λ6584/Hα, [Sii]λ6717, 6731/Hα, [Oi]λ6300/Hα), both objects contain a LINER nucleus and an extended LINER-like gas emission. The emission line ratios do not vary significantly with radius or aperture, which indicates that the nebular properties are spatially homogeneous. The gas emission in NGC 6762 can be best explained by photoionization by pAGB stars without the need of invoking any other excitation mechanism. In the case of NGC 5966, the presence of a nuclear ionizing source seems to be required to shape the elongated gas emission feature in the "ionization cone" scenario, although ionization by pAGB stars cannot be ruled out. Further study of this object is needed to clarify the nature of its elongated gas structure. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck-Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).

Revealing the Ionization Properties of the Magellanic Stream Using Optical Emission

NASA Astrophysics Data System (ADS)

Barger, K. A.; Madsen, G. J.; Fox, A. J.; Wakker, B. P.; Bland-Hawthorn, J.; Nidever, D.; Haffner, L. M.; Antwi-Danso, Jacqueline; Hernandez, Michael; Lehner, N.; Hill, A. S.; Curzons, A.; Tepper-García, T.

2017-12-01

The Magellanic Stream, a gaseous tail that trails behind the Magellanic Clouds, could replenish the Milky Way (MW) with a tremendous amount of gas if it reaches the Galactic disk before it evaporates into the halo. To determine how the Magellanic Stream’s properties change along its length, we have conducted an observational study of the Hα emission, along with other optical warm ionized gas tracers, toward 39 sight lines. Using the Wisconsin Hα Mapper telescope, we detect Hα emission brighter than 30–50 mR in 26 of our 39 sight lines. This Hα emission extends over 2^\\circ away from the H I emission. By comparing {I}{{H}α } and {I}[{{O}{{I}}]}, we find that regions with {log}{N}{{H}{{I}}}/{{cm}}-2≈ 19.5{--}20.0 are 16%–67% ionized. Most of the {I}{{H}α } along the Magellanic Stream are much higher than expected if the primary ionization source is photoionization from Magellanic Clouds, the MW, and the extragalactic background. We find that the additional contribution from self ionization through a “shock cascade” that results as the Stream plows through the halo might be sufficient to reproduce the underlying level of Hα emission along the Stream. In the sparsely sampled region below the South Galactic Pole, there exists a subset of sight lines with uncharacteristically bright emission, which suggest that gas is being ionized further by an additional source that could be a linked to energetic processes associated with the Galactic center.

AN IONIZED OUTFLOW FROM AB AUR, A HERBIG AE STAR WITH A TRANSITIONAL DISK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodríguez, Luis F.; Zapata, Luis A.; Ortiz-León, Gisela N.

AB Aur is a Herbig Ae star with a transitional disk. Transitional disks present substantial dust clearing in their inner regions, most probably because of the formation of one or more planets, although other explanations are still viable. In transitional objects, accretion is found to be about an order of magnitude smaller than in classical full disks. Since accretion is believed to be correlated with outflow activity, centimeter free-free jets are expected to be present in association with these systems, at weaker levels than in classical protoplanetary (full) systems. We present new observations of the centimeter radio emission associated withmore » the inner regions of AB Aur and conclude that the morphology, orientation, spectral index, and lack of temporal variability of the centimeter source imply the presence of a collimated, ionized outflow. The radio luminosity of this radio jet is, however, about 20 times smaller than that expected for a classical system of similar bolometric luminosity. We conclude that centimeter continuum emission is present in association with stars with transitional disks, but at levels than are becoming detectable only with the upgraded radio arrays. On the other hand, assuming that the jet velocity is 300 km s{sup –1}, we find that the ratio of mass loss rate to accretion rate in AB Aur is ∼0.1, similar to that found for less evolved systems.« less

Measurements of the structure of an ionizing shock wave in a hydrogen-helium mixture

NASA Technical Reports Server (NTRS)

Leibowitz, L. P.

1972-01-01

Shock structure during ionization of a hydrogen-helium mixture was studied using hydrogen line and continuum emission measurements. A reaction scheme is proposed which includes hydrogen dissociation and a two-step excitation-ionization mechanism for hydrogen ionization by atom-atom and atom-electron collisions. Agreement was achieved between numerical calculations and measurements of emission intensity as a function of time for shock velocities from 13 to 20 km/sec in a 0.208 H2 - 0.792 He mixture. The electron temperature was found to be significantly different from the heavy particle temperature during much of the ionization process. Similar time histories for H beta and continuum emission indicate upper level populations of hydrogen in equilibrium with the electron concentration during the relaxation process.

Measurements of the structure of an ionizing shock wave in a hydrogen-helium mixture.

NASA Technical Reports Server (NTRS)

Leibowitz, L. P.

1973-01-01

Shock structure during ionization of a hydrogen-helium mixture has been followed using hydrogen line and continuum emission measurements. A reaction scheme is proposed which includes hydrogen dissociation and a two-step excitation-ionization mechanism for hydrogen ionization by atom-atom and atom-electron collisions. Agreement has been achieved between numerical calculations and measurements of emission intensity as a function of time for shock velocities from 13 to 20 km/sec in a 0.208 H2-0.792 He mixture. The electron temperature was found to be significantly different from the heavy particle temperature during much of the ionization process. Similar time histories for H beta and continuum emission indicate upper level populations of hydrogen in equilibrium with the electron concentration during the relaxation process.

Planetary nebulae: 20 years of Hubble inquiry

NASA Astrophysics Data System (ADS)

Balick, Bruce

2012-08-01

The Hubble Space Telescope has served the critical roles of microscope and movie camera in the past 20 years of research on planetary nebulae (``PNe''). We have glimpsed the details of the evolving structures of neutral and ionized post-AGB objects, built ingenious heuristic models that mimic these structures, and constrained most of the relevant physical processes with careful observations and interpretation. We have searched for close physical binary stars with spatial resolution ~50 AU at 1 AU, located jets emerging from the nucleus at speeds up to 2000 km s-1 and matched newly discovered molecular and X-ray emission regions to physical substructures in order to better understand how stellar winds and ionizing radiation interact to form the lovely symmetries that are observed. Ultraviolet spectra of CNO in PNe help to uncover how stars process deep inside AGB stars with unstable nuclear burning zones. HST broadband imaging has been at the forefront of uncovering surprisingly complex wind morphologies produced at the tip of the AGB, and has led to an increasing realization of the potentially vital roles of close binary stars and emerging magnetic fields in shaping stellar winds.

He 2-104 - A link between symbiotic stars and planetary nebulae?

NASA Technical Reports Server (NTRS)

Lutz, Julie H.; Kaler, James B.; Shaw, Richard A.; Schwarz, Hugo E.; Aspin, Colin

1989-01-01

Ultraviolet, optical and infrared observations of He 2-104 are presented, and estimates for some of the physical properties of the nebular shell are made. It is argued that He 2-104 is in transition between the D-type symbiotic star and bipolar planetary nebula phases and, as such, represents a link between subclasses of these two types of objects. The model includes a binary system with a Mira variable and a hot, evolved star. Previous mass loss has resulted in the formation of a disk of gas and dust around the whole system, while the hot star has an accretion disk which produces the observed highly ionized emission line spectrum. Emission lines from cooler, lower density gas is also observed to come from the nebula. In addition, matter is flowing out of the system in a direction perpendicular to the disk with a high velocity and is impacting upon the previously-ejected red giant wind and/or the ambient interstellar medium.

He 2-104: A link between symbiotic stars and planetary nebulae

NASA Technical Reports Server (NTRS)

Lutz, Julie H.; Kaler, James B.; Shaw, Richard A.; Schwarz, Hugo E.; Aspin, Colin

1989-01-01

Ultraviolet, optical and infrared observations of He 2-104 are presented, and estimates for some of the physical properties of the nebular shell are made. It is argued that He 2-104 is in transition between the D-type symbiotic star and bipolar planetary nebula phases and, as such, represents a link between subclasses of these two types of objects. The model includes a binary system with a Mira variable and a hot, evolved star. Previous mass loss has resulted in the formation of a disk of gas and dust around the whole system, while the hot star has an accretion disk which produces the observed highly ionized emission line spectrum. Emission lines from cooler, lower density gas is also observed to come from the nebula. In addition, matter is flowing out of the system in a direction perpendicular to the disk with a high velocity and is impacting upon the previously-ejected red giant wind and/or the ambient interstellar medium.

A Pan-Carina Young Stellar Object Catalog: Intermediate-mass Young Stellar Objects in the Carina Nebula Identified Via Mid-infrared Excess Emission

NASA Astrophysics Data System (ADS)

Povich, Matthew S.; Smith, Nathan; Majewski, Steven R.; Getman, Konstantin V.; Townsley, Leisa K.; Babler, Brian L.; Broos, Patrick S.; Indebetouw, Rémy; Meade, Marilyn R.; Robitaille, Thomas P.; Stassun, Keivan G.; Whitney, Barbara A.; Yonekura, Yoshinori; Fukui, Yasuo

2011-05-01

We present a catalog of 1439 young stellar objects (YSOs) spanning the 1.42 deg2 field surveyed by the Chandra Carina Complex Project (CCCP), which includes the major ionizing clusters and the most active sites of ongoing star formation within the Great Nebula in Carina. Candidate YSOs were identified via infrared (IR) excess emission from dusty circumstellar disks and envelopes, using data from the Spitzer Space Telescope (the Vela-Carina survey) and the Two-Micron All Sky Survey. We model the 1-24 μm IR spectral energy distributions of the YSOs to constrain physical properties. Our Pan-Carina YSO Catalog (PCYC) is dominated by intermediate-mass (2 M sun < m <~ 10 M sun) objects with disks, including Herbig Ae/Be stars and their less evolved progenitors. The PCYC provides a valuable complementary data set to the CCCP X-ray source catalogs, identifying 1029 YSOs in Carina with no X-ray detection. We also catalog 410 YSOs with X-ray counterparts, including 62 candidate protostars. Candidate protostars with X-ray detections tend to be more evolved than those without. In most cases, X-ray emission apparently originating from intermediate-mass, disk-dominated YSOs is consistent with the presence of low-mass companions, but we also find that X-ray emission correlates with cooler stellar photospheres and higher disk masses. We suggest that intermediate-mass YSOs produce X-rays during their early pre-main-sequence evolution, perhaps driven by magnetic dynamo activity during the convective atmosphere phase, but this emission dies off as the stars approach the main sequence. Extrapolating over the stellar initial mass function scaled to the PCYC population, we predict a total population of >2 × 104 YSOs and a present-day star formation rate (SFR) of >0.008 M sun yr-1. The global SFR in the Carina Nebula, averaged over the past ~5 Myr, has been approximately constant.

Electron gyroharmonic effects in ionization and electron acceleration during high-frequency pumping in the ionosphere.

PubMed

Gustavsson, B; Leyser, T B; Kosch, M; Rietveld, M T; Steen, A; Brändström, B U E; Aso, T

2006-11-10

Optical emissions and incoherent scatter radar data obtained during high-frequency electromagnetic pumping of the ionospheric plasma from the ground give data on electron energization in an energy range from 2 to 100 eV. Optical emissions at 4278 A from N2+ that require electrons with energies above the 18 eV ionization energy give the first images ever of pump-induced ionization of the thermosphere. The intensity at 4278 A is asymmetric around the ionospheric electron gyroharmonic, being stronger above the gyroresonance. This contrasts with emissions at 6300 A from O(1D) and of electron temperature enhancements, which have minima at the gyroharmonic but have no apparent asymmetry. This direct evidence of pump-induced ionization contradicts previous indirect evidence, which indicated that ionization is most efficiently produced when the pump frequency was below the gyroharmonic.

A Deep Chandra ACIS Study of NGC 4151. III. The Line Emission and Spectral Analysis of the Ionization Cone

NASA Astrophysics Data System (ADS)

Wang, Junfeng; Fabbiano, Giuseppina; Elvis, Martin; Risaliti, Guido; Karovska, Margarita; Zezas, Andreas; Mundell, Carole G.; Dumas, Gaelle; Schinnerer, Eva

2011-11-01

This paper is the third in a series in which we present deep Chandra ACIS-S imaging spectroscopy of the Seyfert 1 galaxy NGC 4151, devoted to study its complex circumnuclear X-ray emission. Emission features in the soft X-ray spectrum of the bright extended emission (L 0.3-2 keV ~ 1040 erg s-1) at r > 130 pc (2'') are consistent with blended brighter O VII, O VIII, and Ne IX lines seen in the Chandra HETGS and XMM-Newton RGS spectra below 2 keV. We construct emission line images of these features and find good morphological correlations with the narrow-line region clouds mapped in [O III] λ5007. Self-consistent photoionization models provide good descriptions of the spectra of the large-scale emission, as well as resolved structures, supporting the dominant role of nuclear photoionization, although displacement of optical and X-ray features implies a more complex medium. Collisionally ionized emission is estimated to be lsim12% of the extended emission. Presence of both low- and high-ionization spectral components and extended emission in the X-ray image perpendicular to the bicone indicates leakage of nuclear ionization, likely filtered through warm absorbers, instead of being blocked by a continuous obscuring torus. The ratios of [O III]/soft X-ray flux are approximately constant (~15) for the 1.5 kpc radius spanned by these measurements, indicating similar relative contributions from the low- and high-ionization gas phases at different radial distances from the nucleus. If the [O III] and X-ray emission arise from a single photoionized medium, this further implies an outflow with a wind-like density profile. Using spatially resolved X-ray features, we estimate that the mass outflow rate in NGC 4151 is ~2 M ⊙ yr-1 at 130 pc and the kinematic power of the ionized outflow is 1.7 × 1041 erg s-1, approximately 0.3% of the bolometric luminosity of the active nucleus in NGC 4151.

Directed Field Ionization: A Genetic Algorithm for Evolving Electric Field Pulses

NASA Astrophysics Data System (ADS)

Kang, Xinyue; Rowley, Zoe A.; Carroll, Thomas J.; Noel, Michael W.

2017-04-01

When an ionizing electric field pulse is applied to a Rydberg atom, the electron's amplitude traverses many avoided crossings among the Stark levels as the field increases. The resulting superposition determines the shape of the time resolved field ionization spectrum at a detector. An engineered electric field pulse that sweeps back and forth through avoided crossings can control the phase evolution so as to determine the electron's path through the Stark map. In the region of n = 35 in rubidium there are hundreds of potential avoided crossings; this yields a large space of possible pulses. We use a genetic algorithm to search this space and evolve electric field pulses to direct the ionization of the Rydberg electron in rubidium. We present the algorithm along with a comparison of simulated and experimental results. This work was supported by the National Science Foundation under Grants No. 1607335 and No. 1607377 and used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation Grant Number OCI-1053575.

Global X-ray Spectral Variation of Eta Carinae through the 2003 X-ray Minimum

NASA Technical Reports Server (NTRS)

Hamaguchi, K.; Corcoran, M. F.; White, N. E.; Gull, T.; Damineli, A.; Davidson, K.

2006-01-01

We report on the results of the X-ray observing campaign of the massive, evolved star Eta Carinae in 2003 around its recent X-ray Minimum, mainly using data from the XMM-Newton observatory. These imaging observations show that the hard X-ray source associated with the Eta Carinae system does not completely disappear in any of the observations during the Minimum. The variation of the spectral shape revealed two emission components. One newly discovered component did not exhibit any variation on kilo-second to year-long timescales, in a combined analysis with earlier ASCA and ROSAT data, and might represent the collision of a high speed outflow from Eta Carinae with ambient gas clouds. The other emission component was strongly variable in flux but the temperature of the hottest plasma did not vary significantly at any orbital phase. Absorption to the hard emission, was about a factor of three larger than the absorption determined from the cutoff of the soft emission, and reached a maximum of approx.4 x 10(exp 23)/sq cm before the Minimum. The thermal Fe\\rm XXV emission line showed significant excesses on both the red and blue sides of the line outside the Minimum and exhibited a large redward excess during the Minimum. This variation in the line profile probably requires an abrupt change in ionization balance in the shocked gas.

MICROLENSING OF QUASAR BROAD EMISSION LINES: CONSTRAINTS ON BROAD LINE REGION SIZE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guerras, E.; Mediavilla, E.; Jimenez-Vicente, J.

2013-02-20

We measure the differential microlensing of the broad emission lines between 18 quasar image pairs in 16 gravitational lenses. We find that the broad emission lines are in general weakly microlensed. The results show, at a modest level of confidence (1.8{sigma}), that high ionization lines such as C IV are more strongly microlensed than low ionization lines such as H{beta}, indicating that the high ionization line emission regions are more compact. If we statistically model the distribution of microlensing magnifications, we obtain estimates for the broad line region size of r{sub s} = 24{sup +22} {sub -15} and r{sub s}more » = 55{sup +150} {sub -35} lt-day (90% confidence) for the high and low ionization lines, respectively. When the samples are divided into higher and lower luminosity quasars, we find that the line emission regions of more luminous quasars are larger, with a slope consistent with the expected scaling from photoionization models. Our estimates also agree well with the results from local reveberation mapping studies.« less

The many sides of RCW 86: a Type Ia supernova remnant evolving in its progenitor's wind bubble

NASA Astrophysics Data System (ADS)

Broersen, Sjors; Chiotellis, Alexandros; Vink, Jacco; Bamba, Aya

2014-07-01

We present the results of a detailed investigation of the Galactic supernova remnant RCW 86 using the XMM-Newton X-ray telescope. RCW 86 is the probable remnant of SN 185 A.D., a supernova that likely exploded inside a wind-blown cavity. We use the XMM-Newton Reflection Grating Spectrometer to derive precise temperatures and ionization ages of the plasma, which are an indication of the interaction history of the remnant with the presumed cavity. We find that the spectra are well fitted by two non-equilibrium ionization models, which enables us to constrain the properties of the ejecta and interstellar matter plasma. Furthermore, we performed a principal component analysis on EPIC MOS and pn data to find regions with particular spectral properties. We present evidence that the shocked ejecta, emitting Fe K and Si line emission, are confined to a shell of approximately 2 pc width with an oblate spheroidal morphology. Using detailed hydrodynamical simulations, we show that general dynamical and emission properties at different portions of the remnant can be well reproduced by a Type Ia supernova that exploded in a non-spherically symmetric wind-blown cavity. We also show that this cavity can be created using general wind properties for a single degenerate system. Our data and simulations provide further evidence that RCW 86 is indeed the remnant of SN 185, and is the likely result of a Type Ia explosion of single degenerate origin.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Plotkin, Richard M.; Gallo, Elena; Shemmer, Ohad

Over the past 15 yr, examples of exotic radio-quiet quasars with intrinsically weak or absent broad emission line regions (BELRs) have emerged from large-scale spectroscopic sky surveys. Here, we present spectroscopy of seven such weak emission line quasars (WLQs) at moderate redshifts (z = 1.4–1.7) using the X-shooter spectrograph, which provides simultaneous optical and near-infrared spectroscopy covering the rest-frame ultraviolet (UV) through optical. These new observations effectively double the number of WLQs with spectroscopy in the optical rest-frame, and they allow us to compare the strengths of (weak) high-ionization emission lines (e.g., C iv) to low-ionization lines (e.g., Mg ii,more » Hβ, Hα) in individual objects. We detect broad Hβ and Hα emission in all objects, and these lines are generally toward the weaker end of the distribution expected for typical quasars (e.g., Hβ has rest-frame equivalent widths ranging from 15–40 Å). However, these low-ionization lines are not exceptionally weak, as is the case for high-ionization lines in WLQs. The X-shooter spectra also display relatively strong optical Fe ii emission, Hβ FWHM ≲ 4000 km s{sup −1}, and significant C iv blueshifts (≈1000–5500 km s{sup −1}) relative to the systemic redshift; two spectra also show elevated UV Fe ii emission, and an outflowing component to their (weak) Mg ii emission lines. These properties suggest that WLQs are exotic versions of “wind-dominated” quasars. Their BELRs either have unusual high-ionization components, or their BELRs are in an atypical photoionization state because of an unusually soft continuum.« less

No evidence for a significant AGN contribution to cosmic hydrogen reionization

NASA Astrophysics Data System (ADS)

Parsa, Shaghayegh; Dunlop, James S.; McLure, Ross J.

2018-03-01

We reinvestigate a claimed sample of 22 X-ray detected active galactic nuclei (AGN) at redshifts z > 4, which has reignited the debate as to whether young galaxies or AGN reionized the Universe. These sources lie within the Great Observatories Origins Deep Survey-South (GOODS-S)/Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) field, and we examine both the robustness of the claimed X-ray detections (within the Chandra 4Ms imaging) and perform an independent analysis of the photometric redshifts of the optical/infrared counterparts. We confirm the reality of only 15 of the 22 reported X-ray detections, and moreover find that only 12 of the 22 optical/infrared counterpart galaxies actually lie robustly at z > 4. Combining these results we find convincing evidence for only seven X-ray AGN at z > 4 in the GOODS-S field, of which only one lies at z > 5. We recalculate the evolving far-ultraviolet (1500 Å) luminosity density produced by AGN at high redshift, and find that it declines rapidly from z ≃ 4 to z ≃ 6, in agreement with several other recent studies of the evolving AGN luminosity function. The associated rapid decline in inferred hydrogen ionizing emissivity contributed by AGN falls an order-of-magnitude short of the level required to maintain hydrogen ionization at z ≃ 6. We conclude that all available evidence continues to favour a scenario in which young galaxies reionized the Universe, with AGN making, at most, a very minor contribution to cosmic hydrogen reionization.

Peas in a Pod: Environment and Ionization in Green Pea Galaxies

NASA Astrophysics Data System (ADS)

Kurtz, Heather; Jaskot, Anne; Drew, Patrick; Pare, Dylan; Griffin, Jon; Petersen, Michael

2016-01-01

The Green Peas are extreme, highly ionized, starburst galaxies with strong [OIII] 5007 emission. Using the Sloan Digital Sky Survey, we present statistics on the environment of Green Peas and investigate its effects on their ionized gas properties. Although most dwarf starburst galaxies are in low-density environments, we identify a sample of Green Peas in dense environments. Emission line observations with the WIYN 0.9-meter telescope at Kitt Peak reveal that one cluster Green Pea is more highly ionized in the direction of the cluster center. Ram pressure stripping likely generates this ionization gradient. We explore the role of the environment in enhancing star formation rates and ionization, and we compare the nebular properties of Green Peas in high-density environments to those in low-density environments.

Mapping Seyfert and LINER Excitation Modes in the Inner kpc of NGC 3393

NASA Astrophysics Data System (ADS)

Maksym, W. Peter; Fabbiano, Giuseppina; Elvis, Martin; Karovska, Margarita; Paggi, Alessandro; Raymond, John; Wang, Junfeng; Storchi-Bergmann, Thaisa

2016-09-01

We mapped the extended narrowline region (ENLR) of NGC 3393 on scales of r≲ 4\\prime\\prime (˜ 1 kpc) from the nucleus using emission line images of Hα λ6563, [O III]λ 5007, and [S II]λ λ 6717,6731, taken with the Hubble Space Telescope as part of the CHandra survey of Extended Emission line Regions in nearby Seyfert galaxies (CHEERS). By mapping these lines onto a spatially resolved Baldwin-Phillips-Terlevich diagram, we investigate the impact of feedback from a Compton-thick active galactic nucleus on its circumnuclear ISM. We find that the expected Seyfert-like emission within the ionization bicone (≲ 3\\prime\\prime ; 770 pc). We also find a new, figure-8-shaped low ionization emission line region (LINER) cocoon enveloping the bicone and defining a sharp (≲ 100 pc) transition between higher and lower-ionization zones. These data illustrate the morphological dependence of ionization states of the ENLR relative to bicone and host gas geometries.

Flash ionization signature in coherent cyclotron emission from brown dwarfs

NASA Astrophysics Data System (ADS)

Vorgul, I.; Helling, Ch.

2016-05-01

Brown dwarfs (BDs) form mineral clouds in their atmospheres, where charged particles can produce large-scale discharges in the form of lightning resulting in substantial sudden increase of local ionization. BDs are observed to emit cyclotron radio emission. We show that signatures of strong transient atmospheric ionization events (flash ionization) can be imprinted on a pre-existing radiation. Detection of such flash ionization events will open investigations into the ionization state and atmospheric dynamics. Such events can also result from explosion shock waves, material outbursts or (volcanic) eruptions. We present an analytical model that describes the modulation of a pre-existing electromagnetic radiation by a time-dependent (flash) conductivity that is characteristic for flash ionization events like lightning. Our conductivity model reproduces the conductivity function derived from observations of terrestrial gamma-ray flashes, and is applicable to astrophysical objects with strong temporal variations in the local ionization, as in planetary atmospheres and protoplanetary discs. We show that the field responds with a characteristic flash-shaped pulse to a conductivity flash of intermediate intensity. More powerful ionization events result in smaller variations of the initial radiation, or in its damping. We show that the characteristic damping of the response field for high-power initial radiation carries information about the ionization flash magnitude and duration. The duration of the pulse amplification or the damping is consistently shorter for larger conductivity variations and can be used to evaluate the intensity of the flash ionization. Our work suggests that cyclotron emission could be probe signals for electrification processes inside BD atmosphere.

A Herschel study of NGC 650

NASA Astrophysics Data System (ADS)

van Hoof, P. A. M.; Van de Steene, G. C.; Exter, K. M.; Barlow, M. J.; Ueta, T.; Groenewegen, M. A. T.; Gear, W. K.; Gomez, H. L.; Hargrave, P. C.; Ivison, R. J.; Leeks, S. J.; Lim, T. L.; Olofsson, G.; Polehampton, E. T.; Swinyard, B. M.; Van Winckel, H.; Waelkens, C.; Wesson, R.

2013-12-01

As part of the Herschel guaranteed time key project Mass loss of Evolved StarS (MESS) we have imaged a sample of planetary nebulae. In this paper we present the Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging Receiver (SPIRE) images of the classical bipolar planetary nebula NGC 650. We used these images to derive a temperature map of the dust. We also constructed a photoionization and dust radiative transfer model using the spectral synthesis code Cloudy. To constrain this model, we used the PACS and SPIRE fluxes and combined them with hitherto unpublished International Ultraviolet Explorer (IUE) and Spitzer InfraRed Spectrograph (IRS) spectra as well as various other data from the literature. A temperature map combined with a photoionization model were used to study various aspects of the central star, the nebula, and in particular the dust grains in the nebula. The central star parameters are determined to be Teff = 208 kK and L = 261 L⊙ assuming a distance of 1200 pc. The stellar temperature is much higher than previously published values. We confirm that the nebula is carbon-rich with a C/O ratio of 2.1. The nebular abundances are typical for a type IIa planetary nebula. With the photoionization model we determined that the grains in the ionized nebula are large (assuming single-sized grains, they would have a radius of 0.15 μm). Most likely these large grains were inherited from the asymptotic giant branch phase. The PACS 70/160 μm temperature map shows evidence of two radiation components heating the grains. The first component is direct emission from the central star, while the second component is diffuse emission from the ionized gas (mainly Lyα). We show that previous suggestions of a photo-dissociation region surrounding the ionized region are incorrect. The neutral material resides in dense clumps inside the ionized region. These may also harbor stochastically heated very small grains in addition to the large grains. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Tables 2-5 are available in electronic form at http://www.aanda.org

Supernova Remnant Evolving in Wind-Blown Bubbles: A Case Study of Kes 27

NASA Astrophysics Data System (ADS)

Li, Jiangtao

2013-10-01

Mixed-morphology (MM) SNRs represent SN explosion in wind-blown bubbles. They are thus good places to study the interaction between massive stellar winds, SNRs, and the surrounding ISM. We propose a 50ks XMM-Newton observation of a peculiar MM SNR, Kes 27. We will map out the spectral parameters in tessellated meshes and construct EW maps of some emission lines with our newly developed spatially-resolved spectroscopy method. These analyses will help us to understand the unusual properties of this MM SNR, such as the X-ray bright outer shell, shell-like interior, and strong NE-SW asymmetry in morphology. We will also search for evidence of over-ionization state plasma and coherent X-ray features associated with the shell of the HI cavity.

Spectral Evidence for Ionization in Air-Filled Glow Discharge Tubes: Application to Sprites

NASA Astrophysics Data System (ADS)

Armstrong, R. A.; Williams, E. R.; Golka, R. K.; Williams, D. R.

2001-12-01

The question of ionization in sprites and the evidence for VLF backscatter from sprites has motivated a quantitative spectral analysis of the various (classical) regions of the glow discharge tube under DC excitation and at air densities appropriate for sprites in the mesosphere. A PR-650 colorimeter (Photo Research, Inc.) has enabled calibrated irradiance measurements for localized zones along the axis of the discharge tube--in the dominantly blue negative glow, in the Faraday dark space and in the red/pink positive column. Consistent with historical nomenclature, nitrogen first and second positive emission is dominant in the positive column (associated with neutral N2), and nitrogen first negative emission, with a prominent peak at 4278 A, is dominant in the blue negative glow (associated with ionized N2+). Whereas nitrogen first and second positive emission are also detected in the negative glow, no spectral evidence for ionization (no 4279, no 3914, no Meinel) is found in the red/pink positive column. This negative result is attributed not to an absence of ionization in the positive column, but rather to a sparse population of N2+ relative to neutral nitrogen in this region, and to the prominent emission in the blue part of the spectrum due to nitrogen second positive. A similar interpretation may be appropriate for the time-integrated spectra from the red body of sprites, also lacking direct evidence for ionization.

The difficulty of ultraviolet emssion from supernovae

NASA Technical Reports Server (NTRS)

Colgate, S. A.

1971-01-01

There are certain conceptual difficulties in the theory of the generation of ultraviolet radiation which is presumed for the creation of the optical fluorescence mechanism of supernova light emission and ionization of a nebula as large as the Gum nebula. Requirements concerning the energy distribution of the ultraviolet photons are: 1) The energy of the greater part of the photons must be sufficient to cause both helium fluorescence and hydrogen ionization. 2) If the photons are emitted in an approximate black body spectrum, the fraction of energy emitted in the optical must be no more than what is already observed. Ultraviolet black body emission depends primarily on the energy source. The probability that the wide mixture of elements present in the interstellar medium and supernova ejecta results in an emission localized in a limited region with less than 0.001 emission in the visible, for either ionization or fluorescence ultraviolet, is remote. Therefore transparent emission must be excluded as unlikely, and black body or at least quasi-black-body emission is more probable.

Broad Absorption Lines in Qsos: Observations and Implications for Models.

NASA Astrophysics Data System (ADS)

Turnshek, David Alvin

Spectroscopic observations of fourteen broad absorption line (BAL) QSOs are presented and analyzed. Other observations are summarized. The following major conclusions are reached. Broad absorption lines (BALs) are probably present in 3 to 10 percent of the spectra of moderate to high redshift QSOs. The BALs exhibit a variety of velocity structures, from seemingly smooth, continuous absorption to complexes of individual absorption lines. Outflow velocities up to 40,000 km s(' -1) are observed. The level of ionization is high. The minimum total absorption column densities are 10('20) to 10('22) cm('-2). The emission line properties of BAL QSOs appear to be different from those of non-BAL QSOs. For example, N V emission is generally stronger in BAL QSOs and the emission near C III} (lamda)1909 is generally broader in BAL QSOs. The distribution of multiplicities for isolated absorption troughs suggests that the large -scale spatial distribution of BAL clouds is non-random, possibly described by a disk geometry. The BAL clouds are incapable of accounting for all of the observed broad emission lines, particularly C III} (lamda)1909 and Mg II (lamda)2798. Therefore, if the BAL clouds give rise to observable emission, the generally adopted (optically thick, single component) model for the emission line region must be incorrect. Also, photoionization models, which utilize solar abundances and take the ionizing continuum to be a simple power law, are incapable of explaining the level of ionization in the BAL clouds. By considering the observed percentage of QSOs with BALs and resonance line scattering models, it is found that the absorption covering factor in BAL QSOs is between 3 and 20 percent. This suggests that possibly all, but not less than 15 percent, of the QSOs have BAL clouds associated with them. The amount of observable emission and polarization expected to be produced by the BAL clouds from resonance line scattering and collisional excitation is considered in detail. It seems likely that the BAL clouds contribute to the observed high ionization emission. A model worth exploring is one in which an inner, optically thick component gives rise to the low ionization emission, whereas an outer BAL cloud region gives rise to much of the high ionization emission.

Detection of Broad Hα Emission Lines in the Late-time Spectra of a Hydrogen-poor Superluminous Supernova

NASA Astrophysics Data System (ADS)

Yan, Lin; Quimby, R.; Ofek, E.; Gal-Yam, A.; Mazzali, P.; Perley, D.; Vreeswijk, P. M.; Leloudas, G.; De Cia, A.; Masci, F.; Cenko, S. B.; Cao, Y.; Kulkarni, S. R.; Nugent, P. E.; Rebbapragada, Umaa D.; Woźniak, P. R.; Yaron, O.

2015-12-01

iPTF13ehe is a hydrogen-poor superluminous supernova (SLSN) at z = 0.3434, with a slow-evolving light curve and spectral features similar to SN2007bi. It rises in 83-148 days to reach a peak bolometric luminosity of ˜1.3 × 1044 erg s-1, then decays slowly at 0.015 mag day-1. The measured ejecta velocity is ˜ 13,000 km s-1. The inferred explosion characteristics, such as the ejecta mass (70-220 M⊙), and the total radiative and kinetic energy (Erad ˜ 1051 erg, Ekin ˜ 2 × 1053 erg), are typical of slow-evolving H-poor SLSN events. However, the late-time spectrum taken at +251 days (rest, post-peak) reveals a Balmer Hα emission feature with broad and narrow components, which has never been detected before among other H-poor SLSNe. The broad component has a velocity width of ˜4500 km s-1 and a ˜300 km s-1 blueward shift relative to the narrow component. We interpret this broad Hα emission with a luminosity of ˜2 × 1041 erg s-1 as resulting from the interaction between the supernova ejecta and a discrete H-rich shell, located at a distance of ˜4 × 1016 cm from the explosion site. This interaction causes the rest-frame r-band LC to brighten at late times. The fact that the late-time spectra are not completely absorbed by the shock-ionized H-shell implies that its Thomson scattering optical depth is likely ≤1, thus setting upper limits on the shell mass ≤30 M⊙. Of the existing models, a Pulsational Pair Instability supernova model can naturally explain the observed 30 M⊙ H-shell, ejected from a progenitor star with an initial mass of (95-150) M⊙ about 40 years ago. We estimate that at least ˜15% of all SLSNe-I may have late-time Balmer emission lines.

LINKING Lyα AND LOW-IONIZATION TRANSITIONS AT LOW OPTICAL DEPTH

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jaskot, A. E.; Oey, M. S.

2014-08-20

We suggest that low optical depth in the Lyman continuum (LyC) may relate the Lyα emission, C II and Si II absorption, and C II* and Si II* emission seen in high-redshift galaxies. We base this analysis on Hubble Space Telescope Cosmic Origins Spectrograph spectra of four Green Pea (GP) galaxies, which may be analogs of z > 2 Lyα emitters (LAEs). In the two GPs with the strongest Lyα emission, the Lyα line profiles show reduced signs of resonant scattering. Instead, the Lyα profiles resemble the Hα line profiles of evolved star ejecta, suggesting that the Lyα emission originatesmore » from a low column density and similar outflow geometry. The weak C II absorption and presence of non-resonant C II* emission in these GPs support this interpretation and imply a low LyC optical depth along the line of sight. In two additional GPs, weak Lyα emission and strong C II absorption suggest a higher optical depth. These two GPs differ in their Lyα profile shapes and C II* emission strengths, however, indicating different inclinations of the outflows to our line of sight. With these four GPs as examples, we explain the observed trends linking Lyα, C II, and C II* in stacked LAE spectra, in the context of optical depth and geometric effects. Specifically, in some galaxies with strong Lyα emission, a low LyC optical depth may allow Lyα to escape with reduced scattering. Furthermore, C II absorption, C II* emission, and Lyα profile shape can reveal the optical depth, constrain the orientation of neutral outflows in LAEs, and identify candidate LyC emitters.« less

Tracking Energetics of a CME Core in the Low Solar Corona

NASA Astrophysics Data System (ADS)

Kocher, M.; Landi, E.; Lepri, S. T.

2017-12-01

In order to understand the processes that generate CMEs, and develop the ability to predict their evolution and geoeffectiveness, it is very important to determine how the plasma properties within coronal mass ejections (CME) evolve through their journey from the low corona through the solar environment. This study uses a combination of remote-sensing and in-situ observations of a filament eruption (that later formed the core of the CME) that left the Sun on August 4th, 2011 - shortly after an M-class flare. Separate absorption and emission diagnostic techniques are utilized to compute time-evolution estimates of the density and temperature of multiple plasma parcels within the filament using SDO/AIA EUV images. Twin STEREO spacecraft observations are used to estimate the height, speed, and acceleration of the CME at corresponding times. These observation-based densities, temperatures, and speeds allowed us to use the Michigan Ionization Code to compute the ionization history of this CME in the low solar corona. Along with the thermal and kinetic properties of this CME, we present a comparison with existing CME evolution models and draw inferences on its heating and acceleration.

The First Detection of (O IV) from an Ultraluminous X-Ray Source with Spitzer. 2. Evidence for High Luminosity in Holmberg II ULX

DTIC Science & Technology

2010-01-01

from the accretion disk of the binary system and inconsistent with narrow beaming. We show that the emission nebula is matter- bounded both in the line...making them very dif- ficult to characterize. The ionization nebulae surrounding some ULXs have become critical for understanding the properties of...Abolmasov et al. 2007). It is located inside an ionized nebula (the “Foot nebula ”), and shows high- ionization optical emission lines coincident with

The generation of a tunable laser emission in the vacuum ultraviolet and its application to supersonic jet/multiphoton ionization mass spectrometry

NASA Astrophysics Data System (ADS)

Uchimura, Tomohiro; Onoda, Takayuki; Lin, Cheng-Huang; Imasaka, Totaro

1999-08-01

An optical parametric oscillator and a Ti:sapphire laser are used as a pump source for the generation of high-order vibrational stimulated Raman emission in the vacuum ultraviolet region. This tunable laser is employed as an excitation/ionization source in a supersonic jet/multiphoton ionization/time-of-flight mass spectrometric study of benzene. The merits and potential advantages of this approach are discussed in this study.

DIFFERENTIATION OF AEROMONAS ISOLATES OBTAINED FROM DRINKING WATER DISTRIBUTION SYSTEM USING MATRIX-ASSISTED LASER DESCRIPTION/IONIZATION-MASS SPECTROMETRY (MALDI-MS)

EPA Science Inventory

The genus Aeromonas is one of several medically significant genera that have gained prominence due to their evolving taxonomy and controversial role in human diseases. In this study, matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) was used to analyze the...

Irradiated interfaces in the Ara OB1, Carina, Eagle Nebula, and Cyg OB2 massive star formation regions

DOE PAGES

Hartigan, P.; Palmer, J.; Cleeves, L. I.

2012-09-05

Regions of massive star formation offer some of the best and most easily-observed examples of radiation hydrodynamics. Boundaries where fully-ionized H II regions transition to neutral/molecular photodissociation regions (PDRs) are of particular interest because marked temperature and density contrasts across the boundaries lead to evaporative flows and fluid dynamical instabilities that can evolve into spectacular pillar-like structures. Furthermore, when detached from their parent clouds, pillars become ionized globules that often harbor one or more young stars. H2 molecules at the interface between a PDR and an H II region absorb ultraviolet light from massive stars, and the resulting fluoresced infraredmore » emission lines are an ideal way to trace this boundary independent of obscuring dust. This paper presents H2 images of four regions of massive star formation that illustrate different types of PDR boundaries. The Ara OB1 star formation region contains a striking long wall that has several wavy structures which are present in H2, but the emission is not particularly bright because the ambient UV fluxes are relatively low. In contrast, the Carina star formation region shows strong H2 fluorescence both along curved walls and at the edges of spectacular pillars that in some cases have become detached from their parent clouds. The less-spectacular but more well-known Eagle Nebula has two regions that have strong fluorescence in addition to its pillars. And while somewhat older than the other regions, Cyg OB2 has the highest number of massive stars of the regions surveyed and contains many isolated, fluoresced globules that have head–tail morphologies which point towards the sources of ionizing radiation. Our images provide a collection of potential astrophysical analogs that may relate to ablated interfaces observed in laser experiments of radiation hydrodynamics.« less

The Neutral Islands during the Late Epoch of Reionization

NASA Astrophysics Data System (ADS)

Xu, Yidong; Yue, Bin; Chen, Xuelei

2018-05-01

The large-scale structure of the ionization field during the epoch of reionization (EoR) can be modeled by the excursion set theory. While the growth of ionized regions during the early stage are described by the ``bubble model'', the shrinking process of neutral regions after the percolation of the ionized region calls for an ``island model''. An excursion set based analytical model and a semi-numerical code (islandFAST) have been developed. The ionizing background and the bubbles inside the islands are also included in the treatment. With two kinds of absorbers of ionizing photons, i.e. the large-scale under-dense neutral islands and the small-scale over-dense clumps, the ionizing background are self-consistently evolved in the model.

A new X-ray spectral observation of NGC 1068

NASA Technical Reports Server (NTRS)

Marshall, F. E.; Netzer, H.; Arnaud, K. A.; Boldt, E. A.; Holt, S. S.; Jahoda, K. M.; Kelley, R.; Mushotzky, R. F.; Petre, R.; Serlemitsos, P. J.

1993-01-01

A new X-ray observation of NGC 1068, in which improved spectral resolution (R is approximately equal to 40) and broad energy range provide important new constraints on models for this galaxy, is reported. The observed X-ray continuum of NGC 1068 from 0.3 to 10 keV is well fitted as the sum of two power-law spectra with no evidence for absorption intrinsic to the source. Strong Fe K emission lines with a total equivalent width of 2700 eV were detected due to iron less ionized than Fe XX and to iron more ionized than Fe XXIII. No evidence was seen for lines due to the recombination of highly ionized oxygen with an upper limit for the O Ly-alpha emission line of 40 eV. The discovery of multiple Fe K and Fe L emission lines indicates a broad range of ionization states for this gas. The X-ray emission from the two components is modeled for various geometries using a photoionization code that calculates the temperature and ionization state of the gas. Typical model parameters are a total Compton depth of a few percent, an inner boundary of the hot component of about 1 pc, and an inner boundary of the warm component of about 20 pc.

Influence of field emission on the propagation of cylindrical fast ionization wave in atmospheric-pressure nitrogen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levko, Dmitry; Raja, Laxminarayan L.

2016-04-21

The influence of field emission of electrons from surfaces on the fast ionization wave (FIW) propagation in high-voltage nanosecond pulse discharge in the atmospheric-pressure nitrogen is studied by a one-dimensional Particle-in-Cell Monte Carlo Collisions model. A strong influence of field emission on the FIW dynamics and plasma parameters is obtained. Namely, the accounting for the field emission makes possible the bridging of the cathode–anode gap by rather dense plasma (∼10{sup 13 }cm{sup −3}) in less than 1 ns. This is explained by the generation of runaway electrons from the field emitted electrons. These electrons are able to cross the entire gap pre-ionizingmore » it and promoting the ionization wave propagation. We have found that the propagation of runaway electrons through the gap cannot be accompanied by the streamer propagation, because the runaway electrons align the plasma density gradients. In addition, we have obtained that the field enhancement factor allows controlling the speed of ionization wave propagation.« less

Air ionization as a control technology for off-gas emissions of volatile organic compounds.

PubMed

Kim, Ki-Hyun; Szulejko, Jan E; Kumar, Pawan; Kwon, Eilhann E; Adelodun, Adedeji A; Reddy, Police Anil Kumar

2017-06-01

High energy electron-impact ionizers have found applications mainly in industry to reduce off-gas emissions from waste gas streams at low cost and high efficiency because of their ability to oxidize many airborne organic pollutants (e.g., volatile organic compounds (VOCs)) to CO 2 and H 2 O. Applications of air ionizers in indoor air quality management are limited due to poor removal efficiency and production of noxious side products, e.g., ozone (O 3 ). In this paper, we provide a critical evaluation of the pollutant removal performance of air ionizing system through comprehensive review of the literature. In particular, we focus on removal of VOCs and odorants. We also discuss the generation of unwanted air ionization byproducts such as O 3 , NOx, and VOC oxidation intermediates that limit the use of air-ionizers in indoor air quality management. Copyright © 2017. Published by Elsevier Ltd.

Ultraviolet spectra of extreme nearby star-forming regions - approaching a local reference sample for JWST

NASA Astrophysics Data System (ADS)

Senchyna, Peter; Stark, Daniel P.; Vidal-García, Alba; Chevallard, Jacopo; Charlot, Stéphane; Mainali, Ramesh; Jones, Tucker; Wofford, Aida; Feltre, Anna; Gutkin, Julia

2017-12-01

Nearby dwarf galaxies provide a unique laboratory in which to test stellar population models below Z⊙/2. Such tests are particularly important for interpreting the surprising high-ionization ultraviolet (UV) line emission detected at z > 6 in recent years. We present HST/COS UV spectra of 10 nearby metal-poor star-forming galaxies selected to show He II emission in SDSS optical spectra. The targets span nearly a dex in gas-phase oxygen abundance (7.8 < 12 + log O/H < 8.5) and present uniformly large specific star formation rates (sSFR ∼102 Gyr-1). The UV spectra confirm that metal-poor stellar populations can power extreme nebular emission in high-ionization UV lines, reaching C III] equivalent widths comparable to those seen in systems at z ∼ 6-7. Our data reveal a marked transition in UV spectral properties with decreasing metallicity, with systems below 12 + log O/H ≲ 8.0 (Z/Z⊙ ≲ 1/5) presenting minimal stellar wind features and prominent nebular emission in He II and C IV. This is consistent with nearly an order of magnitude increase in ionizing photon production beyond the He+-ionizing edge relative to H-ionizing flux as metallicity decreases below a fifth solar, well in excess of standard stellar population synthesis predictions. Our results suggest that often-neglected sources of energetic radiation such as stripped binary products and very massive O-stars produce a sharper change in the ionizing spectrum with decreasing metallicity than expected. Consequently, nebular emission in C IV and He II powered by these stars may provide useful metallicity constraints in the reionization era.

Theory of void formation in dusty plasmas

NASA Astrophysics Data System (ADS)

Hu, Zuquan; Chen, Yinhua; Zheng, Xiang; Huang, Feng; Shi, Gei-fen; Yu, M. Y.

2009-06-01

A fluid theory of void formation in dusty plasmas taking into account ionization is proposed. It is shown that if the ionization rate is larger than a threshold, an initial steady-state dust-density distribution can evolve into a stable distribution containing a void. As the ionization rate is further increased, the time required for void formation decreases. The void size first increases, but then decreases. However, for still larger ionization rates, the dusty region of the plasma becomes ringlike, including the convection term in dust momentum equation. The results are in agreement with existing experiments and theories.

Spectrophotometry of six broad absorption line QSOs

NASA Technical Reports Server (NTRS)

Junkkarinen, Vesa T.; Burbidge, E. Margaret; Smith, Harding E.

1987-01-01

Spectrophotometric observations of six broad absorption-line QSOs (BALQSOs) are presented. The continua and emission lines are compared with those in the spectra of QSOs without BALs. A statistically significant difference is found in the emission-line intensity ratio for (N V 1240-A)/(C IV 1549-A). The median value of (N V)/(C IV) for the BALQSOs is two to three times the median for QSOs without BALs. The absorption features of the BALQSOs are described, and the column densities and limits on the ionization structure of the BAL region are discussed. If the dominant ionization mechanism is photoionization, then it is likely that either the ionizing spectrum is steep or the abundances are considerably different from solar. Collisional ionization may be a significant factor, but it cannot totally dominate the ionization rate.

Interstellar PAH Emission in the 11-14 micron Region: New Insights and a Tracer of Ionized PAHs

NASA Technical Reports Server (NTRS)

Hudgins, Douglas M.; Allamandola, Louis J.; Mead, Susan (Technical Monitor)

1999-01-01

The Ames infrared spectral database of isolated, neutral and ionized polycyclic aromatic hydrocarbons (PAHs) shows that aromatic CH out-of-plane bending frequencies are significantly shifted upon ionization. For non-adjacent and doubly-adjacent CH groups, the shift is pronounced and consistently toward higher frequencies. The non-adjacent modes are blueshifted by an average of 27 per cm and the doubly-adjacent modes by an average of 17 per cm. For triply- and quadruply-adjacent CH out-of-plane modes the ionization shifts are more erratic and typically more modest. As a result of these ionization shifts, both the non-adjacent and doubly-adjacent CH out-of-plane modes move out of the regions classically associated with their respective vibrations in neutral PAHs. The doubly-adjacent modes of ionized PAHs tend to fall into the frequency range traditionally associated with the non-adjacent modes, while the non-adjacent modes are shifted to frequencies above those normally attributed to out-of-plane bending vibrations. Consequently, the origin of the interstellar infrared emission feature near 11.2 microns, traditionally attributed to the out-of-plane bending of non-adjacent CH groups on PAHs is rendered ambiguous. Instead, this feature likely reflects contributions from both non-adjacent CH units in neutral PAHs and doubly-adjacent CH units in PAH cations, the dominant charge state in the most energetic emission regions. This greatly relieves the structural constraints placed on the interstellar PAH population by the dominance of the 11.2 micron band in this region and eliminates the necessity to invoke extensive dehydrogenation of the emitting species. Furthermore, these results indicate that the emission between 926 and 904 per cm (10.8 and 11.1 microns) observed in many sources can be unambiguously attributed to the non-adjacent CH out-of-plane bending modes of moderately-sized (fewer than 50 carbon atom) PAH cations making this emission an unequivocal tracer of ionized interstellar PAHs.

Evidence for a Hard Ionizing Spectrum from a z = 6.11 Stellar Population

NASA Astrophysics Data System (ADS)

Mainali, Ramesh; Kollmeier, Juna A.; Stark, Daniel P.; Simcoe, Robert A.; Walth, Gregory; Newman, Andrew B.; Miller, Daniel R.

2017-02-01

We present the Magellan/FIRE detection of highly ionized C IV λ1550 and O III]λ1666 in a deep infrared spectrum of the z = 6.11 gravitationally lensed low-mass galaxy RXC J2248.7-4431-ID3, which has previously known Lyα. No corresponding emission is detected at the expected location of He II λ1640. The upper limit on He II, paired with detection of O III] and C IV, constrains possible ionization scenarios. Production of C IV and O III] requires ionizing photons of 2.5-3.5 Ryd, but once in that state their multiplet emission is powered by collisional excitation at lower energies (˜0.5 Ryd). As a pure recombination line, He II emission is powered by 4 Ryd ionizing photons. The data therefore require a spectrum with significant power at 3.5 Ryd but a rapid drop toward 4.0 Ryd. This hard spectrum with a steep drop is characteristic of low-metallicity stellar populations, and less consistent with soft AGN excitation, which features more 4 Ryd photons and hence higher He II flux. The conclusions based on ratios of metal line detections to helium non-detection are strengthened if the gas metallicity is low. RXJ2248-ID3 adds to the growing handful of reionization-era galaxies with UV emission line ratios distinct from the general z=2{--}3 population in a way that suggests hard ionizing spectra that do not necessarily originate in AGNs.

Lyα emitters in the GOODS-S field. A powerful pure nebular SED with N IV] emission at z = 5.563

NASA Astrophysics Data System (ADS)

Raiter, A.; Fosbury, R. A. E.; Teimoorinia, H.

2010-02-01

Context. The Great Observatories Origins Deep Survey (GOODS) has provided us with one of the deepest multi-wavelength views of the distant universe. The combination of multi-band photometry and optical spectroscopy has resulted in the identification of sources whose redshifts extend to values in excess of six. Amongst these distant sources are Lyα emitters whose nature must be deduced by clearly identifying the different components that contribute to the measured SED. Aims: From a sample of Lyα emitters in the GOODS-S field with uncontaminated photometry and optical (red) spectroscopy, we select a spatially compact object at a redshift of 5.563 (Lyα) that shows a second emission line, identified as N IV] 1486 Å. The SED is modelled in a way that accounts for both the N IV] line emission and the photometry in a self-consistent way. Methods: The photoionization code CLOUDY is used to calculate a range of nebular models as a function of stellar ionizing source temperature, ionization parameter, density and nebular metallicity. We compare the theoretical and observed magnitudes and search for the model parameters that also reproduce the observed N IV] luminosity and equivalent width. Results: A nebular model with a hot blackbody ionizing source of around 100 kK and a nebular metallicity of ~5% of solar is able to fit the observed SED and, in particular, explain the large apparent Balmer break which is inferred from the pure stellar population model fitting conventionally applied to multi-band photometric observations. In our model, an apparent spectral break is produced by strong [O III] 4959, 5007 Å emission falling in one of the IR bands (IRAC1 in this case). A lower limit on the total baryonic mass of a model of this type is 3.2 ×10^8~M⊙. Conclusions: It is argued that objects with Lyα emission at high redshift that show an apparent Balmer break may have their SED dominated by nebular emission and so could possibly be identified with very young starbursting galaxies rather than massive evolved stellar populations. Detailed studies of these emission nebulæ with large telescopes will provide a unique insight into very early chemical evolution. Based on observations made at the European Southern Observatory, Paranal, Chile (ESO programme 170.A-0788) The Great Observatories Origins Deep Survey: ESO Public Observations of the SIRTF Legacy/HST Treasury/Chandra Deep Field South.); on observations obtained with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc.; and on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.

The nebular spectra of the transitional Type Ia Supernovae 2007on and 2011iv: broad, multiple components indicate aspherical explosion cores

NASA Astrophysics Data System (ADS)

Mazzali, P. A.; Ashall, C.; Pian, E.; Stritzinger, M. D.; Gall, C.; Phillips, M. M.; Höflich, P.; Hsiao, E.

2018-05-01

The nebular-epoch spectrum of the rapidly declining, `transitional' Type Ia supernova (SN) 2007on showed double emission peaks, which have been interpreted as indicating that the SN was the result of the direct collision of two white dwarfs. The spectrum can be reproduced using two distinct emission components, one redshifted and one blueshifted. These components are similar in mass but have slightly different degrees of ionization. They recede from one another at a line-of-sight speed larger than the sum of the combined expansion velocities of their emitting cores, thereby acting as two independent nebulae. While this configuration appears to be consistent with the scenario of two white dwarfs colliding, it may also indicate an off-centre delayed detonation explosion of a near-Chandrasekhar-mass white dwarf. In either case, broad emission line widths and a rapidly evolving light curve can be expected for the bolometric luminosity of the SN. This is the case for both SNe 2007on and 2011iv, also a transitional SN Ia that exploded in the same elliptical galaxy, NGC 1404. Although SN 2011iv does not show double-peaked emission line profiles, the width of its emission lines is such that a two-component model yields somewhat better results than a single-component model. Most of the mass ejected is in one component, however, which suggests that SN 2011iv was the result of the off-centre ignition of a Chandrasekhar-mass white dwarf.

Electron ionization of metastable nitrogen and oxygen atoms in relation to the auroral emissions

NASA Astrophysics Data System (ADS)

Pandya, Siddharth; Joshipura, K. N.

Atomic and molecular excited metastable states (EMS) are exotic systems due to their special properties like long radiative life-time, large size (average radius) and large polarizability along with relatively smaller first ionization energy compared to their respective ground states (GS). The present work includes our theoretical calculations on electron impact ionization of metastable atomic states N( (2) P), N( (2) D) of nitrogen and O( (1) S), O( (1) D) of oxygen. The targets of our present interest, are found to be present in our Earth's ionosphere and they play an important role in auroral emissions observed in Earth’s auroral regions [1] as also in the emissions observed from cometary coma [2, 3] and airglow emissions. In particular, atomic oxygen in EMS can radiate, the visible O( (1) D -> (3) P) doublet 6300 - 6364 Å red doublet, the O( (1) S -> (1) D) 5577 Å green line, and the ultraviolet O( (1) S -> (3) P) 2972 Å line. For metastable atomic nitrogen one observes the similar emissions, in different wavelengths, from (2) D and (2) P states. At the Earth's auroral altitudes, from where these emissions take place in the ionosphere, energetic electrons are also present. In particular, if the metastable N as well as O atoms are ionized by the impact of electrons then these species are no longer available for emissions. This is a possible loss mechanism, and hence it is necessary to analyze the importance of electron ionization of the EMS of atomic O and N, by calculating the relevant cross sections. In the present paper we investigate electron ionization of the said metastable species by calculating relevant total cross sections. Our quantum mechanical calculations are based on projected approximate ionization contribution in the total inelastic cross sections [4]. Detailed results and discussion along with the significance of these calculations will be presented during the COSPAR-2014. References [1] A.Bhardwaj, and G. R. Gladstone, Rev. Geophys., 38(3), 295-353 (2000) [2] A.Bhardwaj, and S. A. Haider, Adv. Space Res., 29(5), 745-750 (2002) [3] A. Bhardwaj and S. Raghuram, ApJ, 748:13 (2012) [4] S. H. Pandya et al.,Int. J. Mass Spectrom. 323-324, 28-33 (2012)

3D Radiative Transfer in Eta Carinae: Application of the SimpleX Algorithm to 3D SPH Simulations of Binary Colliding Winds

NASA Technical Reports Server (NTRS)

Clementel, N.; Madura, T. I.; Kruip, C. J. H.; Icke, V.; Gull, T. R.

2014-01-01

Eta Carinae is an ideal astrophysical laboratory for studying massive binary interactions and evolution, and stellar wind-wind collisions. Recent three-dimensional (3D) simulations set the stage for understanding the highly complex 3D flows in Eta Car. Observations of different broad high- and low-ionization forbidden emission lines provide an excellent tool to constrain the orientation of the system, the primary's mass-loss rate, and the ionizing flux of the hot secondary. In this work we present the first steps towards generating synthetic observations to compare with available and future HST/STIS data. We present initial results from full 3D radiative transfer simulations of the interacting winds in Eta Car. We use the SimpleX algorithm to post-process the output from 3D SPH simulations and obtain the ionization fractions of hydrogen and helium assuming three different mass-loss rates for the primary star. The resultant ionization maps of both species constrain the regions where the observed forbidden emission lines can form. Including collisional ionization is necessary to achieve a better description of the ionization states, especially in the areas shielded from the secondary's radiation. We find that reducing the primary's mass-loss rate increases the volume of ionized gas, creating larger areas where the forbidden emission lines can form. We conclude that post processing 3D SPH data with SimpleX is a viable tool to create ionization maps for Eta Car.

3D Radiative Transfer in Eta Carinae: Application of the SimpleX Algorithm to 3D SPH Simulations of Binary Colliding Winds

NASA Technical Reports Server (NTRS)

Clementel, N.; Madura, T. I.; Kruip, C.J.H.; Icke, V.; Gull, T. R.

2014-01-01

Eta Carinae is an ideal astrophysical laboratory for studying massive binary interactions and evolution, and stellar wind-wind collisions. Recent three-dimensional (3D) simulations set the stage for understanding the highly complex 3D flows in eta Car. Observations of different broad high- and low-ionization forbidden emission lines provide an excellent tool to constrain the orientation of the system, the primary's mass-loss rate, and the ionizing flux of the hot secondary. In this work we present the first steps towards generating synthetic observations to compare with available and future HST/STIS data. We present initial results from full 3D radiative transfer simulations of the interacting winds in eta Car.We use the SimpleX algorithm to post-process the output from 3D SPH simulations and obtain the ionization fractions of hydrogen and helium assuming three different mass-loss rates for the primary star. The resultant ionization maps of both species constrain the regions where the observed forbidden emission lines can form. Including collisional ionization is necessary to achieve a better description of the ionization states, especially in the areas shielded from the secondary's radiation. We find that reducing the primary's mass-loss rate increases the volume of ionized gas, creating larger areas where the forbidden emission lines can form.We conclude that post processing 3D SPH data with SimpleX is a viable tool to create ionization maps for eta Car.

Improved field emission properties of carbon nanotubes grown on stainless steel substrate and its application in ionization gauge

NASA Astrophysics Data System (ADS)

Li, Detian; Cheng, Yongjun; Wang, Yongjun; Zhang, Huzhong; Dong, Changkun; Li, Da

2016-03-01

Vertically aligned carbon nanotube (CNT) arrays were fabricated by chemical vapor deposition (CVD) technique on different substrates. Microstructures and field emission characteristics of the as-grown CNT arrays were investigated systematically, and its application in ionization gauge was also evaluated preliminarily. The results indicate that the as-grown CNT arrays are vertically well-aligned relating to the substrate surfaces, but the CNTs grown on stainless steel substrate are longer and more crystalline than the ones grown on silicon wafer substrate. The field emission behaviors of the as-grown CNT arrays are strongly dependent upon substrate properties. Namely, the CNT array grown on stainless steel substrate has better field emission properties, including lower turn on and threshold fields, better emission stability and repeatability, compared with the one grown on silicon wafer substrate. The superior field emission properties of the CNT array grown on stainless steel substrate are mainly attributed to low contact resistance, high thermal conductivity, good adhesion strength, etc. In addition, the metrological behaviors of ionization gauge with the CNT array grown on stainless steel substrate as an electron source were investigated, and this novel cathode ionization gauge extends the lower limit of linear pressure measurement to 10-8 Pa, which is one order of magnitude lower than the result reported for the same of gauge with CNT cathode.

Quantum control via a genetic algorithm of the field ionization pathway of a Rydberg electron

NASA Astrophysics Data System (ADS)

Gregoric, Vincent C.; Kang, Xinyue; Liu, Zhimin Cheryl; Rowley, Zoe A.; Carroll, Thomas J.; Noel, Michael W.

2017-08-01

Quantum control of the pathway along which a Rydberg electron field ionizes is experimentally and computationally demonstrated. Selective field ionization is typically done with a slowly rising electric field pulse. The (1/n*)4 scaling of the classical ionization threshold leads to a rough mapping between arrival time of the electron signal and principal quantum number of the Rydberg electron. This is complicated by the many avoided level crossings that the electron must traverse on the way to ionization, which in general leads to broadening of the time-resolved field ionization signal. In order to control the ionization pathway, thus directing the signal to the desired arrival time, a perturbing electric field produced by an arbitrary wave-form generator is added to a slowly rising electric field. A genetic algorithm evolves the perturbing field in an effort to achieve the target time-resolved field ionization signal.

Herschel Galactic plane survey of ionized gas traced by [NII

NASA Astrophysics Data System (ADS)

Yildiz, Umut; Goldsmith, Paul; Pineda, Jorge; Langer, William

2015-01-01

Far infrared and sub-/millimeter atomic & ionic fine structure and molecular rotational lines are powerful tracers of star formation on both Galactic and extragalactic scales. Although CO lines trace cool to moderately warm molecular gas, ionized carbon [CII] produces the strongest lines, which arise from almost all reasonably warm (T>50 K) parts of the ISM. However, [CII] alone cannot distinguish highly ionized gas from weakly ionized gas. [NII] plays a significant role in star formation as it is produced only in ionized regions; in [HII] regions as well as diffuse ionized gas. The ionization potential of nitrogen (14.5 eV) is greater than that of hydrogen (13.6 eV), therefore the ionized nitrogen [NII] lines reflect the effects of massive stars, with possible enhancement from X-ray and shock heating from the surroundings. Two far-infrared 122 um and 205 um [NII] fine structure spectral lines are targeted via Photodetector Array Camera and Spectrometer (PACS) onboard Herschel Space Observatory. The sample consists of 149 line-of-sight (LOS) positions in the Galactic plane. These positions overlap with the [CII] 158 um observations obtained with the GOT C+ survey. With a reasonable assumption that the emission from both 122 um and 205 um lines originate in the same gas; [NII] 122/205 um line ratio indicates the a good measure of the electron density of each of the LOS positions. [NII] detections are mainly toward the Galactic center direction and the [NII] electron densities are found between 7-50 cm^-3, which is enhanced WIM (Warm Ionized Medium). WIM densities are expected to be much lower (~1 cm-3), therefore non-detections toward the opposite side of the Galactic Center shows abundant of this gas. The pixel to pixel variation of the emission within a single Herschel pointing is relatively small, which is interpreted as the [NII] emission comes from an extended gas. It is important to quantify what fraction of [CII] emission arises in the ionized gas. Thus, with the present work of [NII] observations, it will be possible to resolve the different parts of the ISM leading to determine the total mass of the ISM.

A hydrodynamic approach to cosmology - Methodology

NASA Technical Reports Server (NTRS)

Cen, Renyue

1992-01-01

The present study describes an accurate and efficient hydrodynamic code for evolving self-gravitating cosmological systems. The hydrodynamic code is a flux-based mesh code originally designed for engineering hydrodynamical applications. A variety of checks were performed which indicate that the resolution of the code is a few cells, providing accuracy for integral energy quantities in the present simulations of 1-3 percent over the whole runs. Six species (H I, H II, He I, He II, He III) are tracked separately, and relevant ionization and recombination processes, as well as line and continuum heating and cooling, are computed. The background radiation field is simultaneously determined in the range 1 eV to 100 keV, allowing for absorption, emission, and cosmological effects. It is shown how the inevitable numerical inaccuracies can be estimated and to some extent overcome.

Determining the Nature of [CII] 158 Micron Emission: an Improved Star Formation Rate Indicator

NASA Astrophysics Data System (ADS)

Sutter, Jessica; Dale, Daniel A.; KINGFISH Team

2018-06-01

The brightest observed emission line from most normal star-forming galaxies is the 158 micron line arising from singly-ionized carbon (also known as C+ or CII). In fact, astronomers have recently begun using the bright emission line to detect and characterize galaxies in the furthermost reaches of the universe. It is thus imperative that we have the tools to fully understand how this emission line could be utilized as an indicator of star formation rate, a primary parameter by which galaxies and their constituent star-forming regions are characterized. There are two main challenges to utilizing the [CII] 158 micron line as a star formation rate indicator. First, advances in long-wavelength astronomical instrumentation have only recently enabled its detection in statistically-significant samples of galaxies. Second, it is both a blessing and a curse that singly-ionized carbon can be created in both star-forming regions (ionized HII regions) and in non-star forming regions (neutral photo-dissociation regions). In order to better understand and quantify the [CII] emission as an indicator of star-formation rate, the relationship between the [NII] 205 micron emission, which can only arise from the ionized interstellar medium (ISM), and the [CII] 158 micron emission has been employed to determine the fraction of [CII] emission that originates from each phase of the ISM. Sub-kiloparsec measurements of the [NII] 205 micron line in nearby galaxies have recently become available as part of the KINGFISH program. We use these two far-infrared lines along with the full suite of KINGFISH panchromatic data to present an improved calibration of the [CII] emission line as a star formation rate indicator.

Herschel Galactic Plane Survey of [NII] Fine Structure Emission

NASA Astrophysics Data System (ADS)

Goldsmith, Paul F.; Yıldız, Umut A.; Langer, William D.; Pineda, Jorge L.

2015-12-01

We present the first large-scale high angular resolution survey of ionized nitrogen in the Galactic Plane through emission of its two fine structure transitions ([N ii]) at 122 and 205 μm. The observations were largely obtained with the PACS instrument onboard the Herschel Space Observatory. The lines of sight were in the Galactic plane, following those of the Herschel OTKP project GOT C+. Both lines are reliably detected at the 10-8-10-7 Wm-2 sr-1 level over the range -60° ≤ l ≤ 60°. The rms of the intensity among the 25 PACS spaxels of a given pointing is typically less than one third of the mean intensity, showing that the emission is extended. [N ii] is produced in gas in which hydrogen is ionized, and collisional excitation is by electrons. The ratio of the two fine structure transitions provides a direct measurement of the electron density, yielding n(e) largely in the range 10-50 cm-3 with an average value of 29 cm-3 and N+ column densities 1016-1017 cm-2. [N ii] emission is highly correlated with that of [C ii], and we calculate that between 1/3 and 1/2 of the [C ii] emission is associated with the ionized gas. The relatively high electron densities indicate that the source of the [N ii] emission is not the warm ionized medium (WIM), which has electron densities more than 100 times smaller. Possible origins of the observed [N ii] include the ionized surfaces of dense atomic and molecular clouds, the extended low-density envelopes of H ii regions, and low-filling factor high-density fluctuations of the WIM.

THE NATURE OF ACTIVE GALACTIC NUCLEI WITH VELOCITY OFFSET EMISSION LINES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Müller-Sánchez, F.; Comerford, J.; Stern, D.

We obtained Keck/OSIRIS near-IR adaptive optics-assisted integral-field spectroscopy to probe the morphology and kinematics of the ionized gas in four velocity-offset active galactic nuclei (AGNs) from the Sloan Digital Sky Survey. These objects possess optical emission lines that are offset in velocity from systemic as measured from stellar absorption features. At a resolution of ∼0.″18, OSIRIS allows us to distinguish which velocity offset emission lines are produced by the motion of an AGN in a dual supermassive black hole system, and which are produced by outflows or other kinematic structures. In three galaxies, J1018+2941, J1055+1520, and J1346+5228, the spectral offsetmore » of the emission lines is caused by AGN-driven outflows. In the remaining galaxy, J1117+6140, a counterrotating nuclear disk is observed that contains the peak of Pa α emission 0.″2 from the center of the galaxy. The most plausible explanation for the origin of this spatially and kinematically offset peak is that it is a region of enhanced Pa α emission located at the intersection zone between the nuclear disk and the bar of the galaxy. In all four objects, the peak of ionized gas emission is not spatially coincident with the center of the galaxy as traced by the peak of the near-IR continuum emission. The peaks of ionized gas emission are spatially offset from the galaxy centers by 0.″1–0.″4 (0.1–0.7 kpc). We find that the velocity offset originates at the location of this peak of emission, and the value of the offset can be directly measured in the velocity maps. The emission-line ratios of these four velocity-offset AGNs can be reproduced only with a mixture of shocks and AGN photoionization. Shocks provide a natural explanation for the origin of the spatially and spectrally offset peaks of ionized gas emission in these galaxies.« less

Is the Ejecta of ETA Carinae Overabundant or Overexcited

NASA Technical Reports Server (NTRS)

Gull, Theodore; Davidson, Kris; Johansson, Sveneric; Damineli, Augusto; Ishibashi, Kaxunori; Corcoran, Michael; Hartman, Henrick; Viera, Gladys; Nielsen, Krister

2003-01-01

The ejecta of Eta Carinae, revealed by HST/STIS, are in a large range of physical conditions. As Eta Carinae undergoes a 5.52 period, changes occur in nebular emission and nebular absorption. "Warm" neutral regions, partially ionized regions, and fully ionized regions undergo significant changes. Over 2000 emission lines, most of Fe-like elements, have been indentified in the Weigelt blobs B and D. Over 500 emission lines have been indentified in the Strontium Filament. An ionized Little Homunculus is nestled within the neutral-shelled Homunculus. In line of sight, over 500 nebular absorption lines have been identified with up to twenty velocity components. STIS is following changes in many nebular emission and absorption lines as Eta Carinae approaches the minimum, predicted to be in June/July 2003, during the General Assembly. Coordinated observations with HST, CHANDRA, RXTE, FUSE, UVES/VLT, Gemini and other observatories are following this minimum.

A mechanism for large divertor plasma energy loss via lithium radiation in tokamaks

NASA Astrophysics Data System (ADS)

Rognlien, T. D.; Meier, E. T.; Soukhanovskii, V. A.

2012-10-01

Lithium has been used as a wall-conditioning element in a number of tokamaks over the years, including TFTR, FTU, and NSTX, where core plasma energy confinement and particle control are often found to improve following such conditioning. Here the possible role of Li in providing substantial energy loss for divertor plasmas via line radiation is reported. A multi-charge-state 2D UEDGE fluid model is used where the hydrogenic and Li ions and neutrals are each evolved as separate species and separate equations are solved for the electron and ion temperatures. It is shown that a sufficient level of Li neutrals evolving from the divertor surface via sputtering or evaporation can induce energy detachment of the divertor plasma, yielding a strongly radiating zone near the divertor where ionization and recombination from/to neutral Li can radiate most of the power flowing into the scrape-off layer while maintaining low core contamination. A local peaking of Li emissivity for electron temperatures near 1 eV appears to play an important role in the detachment of the mixed deuterium/Li plasma. Evidence of such behavior from NSTX discharges will be discussed.

Understanding the Early Evolution of M dwarf Extreme Ultraviolet Radiation

NASA Astrophysics Data System (ADS)

Peacock, Sarah; Barman, Travis; Shkolnik, Evgenya

2015-11-01

The chemistry and evolution of planetary atmospheres depends on the evolution of high-energy radiation emitted by its host star. High levels of extreme ultraviolet (EUV) radiation can drastically alter the atmospheres of terrestrial planets through ionizing, heating, expanding, chemically modifying and eroding them during the first few billion years of a planetary lifetime. While there is evidence that stars emit their highest levels of far and near ultraviolet (FUV; NUV) radiation in the earliest stages of their evolution, we are currently unable to directly measure the EUV radiation. Most previous stellar atmosphere models under-predict FUV and EUV emission from M dwarfs; here we present new models for M stars that include prescriptions for the hot, lowest density atmospheric layers (chromosphere, transition region and corona), from which this radiation is emitted. By comparing our model spectra to GALEX near and far ultraviolet fluxes, we are able to predict the evolution of EUV radiation for M dwarfs from 10 Myr to a few Gyr. This research is the next major step in the HAZMAT (HAbitable Zones and M dwarf Activity across Time) project to analyze how the habitable zone evolves with the evolving properties of stellar and planetary atmospheres.

Radiation of partially ionized atomic hydrogen

NASA Technical Reports Server (NTRS)

Soon, W. H.; Kunc, J. A.

1990-01-01

A nonlinear collisional-radiative model for determination of production of electrons, positive and negative ions, excited atoms, and spectral and continuum line intensities in stationary partially ionized atomic hydrogen is presented. Transport of radiation is included by coupling the rate equations for production of the electrons, ions, and excited atoms with the radiation escape factors, which are not constant but depend on plasma conditions. It is found that the contribution of the negative ion emission to the total continuum emission can be important. Comparison of the calculated total continuum emission coefficient, including the negative ion emission, is in good agreement with experimental results.

Energy Balance for a Sonoluminescence Bubble Yields a Measure of Ionization Potential Lowering

NASA Astrophysics Data System (ADS)

Kappus, B.; Bataller, A.; Putterman, S. J.

2013-12-01

Application of energy conservation between input sound and the microplasma which forms at the moment of sonoluminescence places bounds on the process, whereby the gas is ionized. Detailed pulsed Mie scattering measurements of the radius versus time for a xenon bubble in sulfuric acid provide a complete characterization of the hydrodynamics and minimum radius. For a range of emission intensities, the blackbody spectrum emitted during collapse matches the minimum bubble radius, implying opaque conditions are attained. This requires a degree of ionization >36%. Analysis reveals only 2.1±0.6eV/atom of energy available during light emission. In order to unbind enough charge, collective processes must therefore reduce the ionization potential by at least 75%. We interpret this as evidence that a phase transition to a highly ionized plasma is occurring during sonoluminescence.

Energy balance for a sonoluminescence bubble yields a measure of ionization potential lowering.

PubMed

Kappus, B; Bataller, A; Putterman, S J

2013-12-06

Application of energy conservation between input sound and the microplasma which forms at the moment of sonoluminescence places bounds on the process, whereby the gas is ionized. Detailed pulsed Mie scattering measurements of the radius versus time for a xenon bubble in sulfuric acid provide a complete characterization of the hydrodynamics and minimum radius. For a range of emission intensities, the blackbody spectrum emitted during collapse matches the minimum bubble radius, implying opaque conditions are attained. This requires a degree of ionization >36%. Analysis reveals only 2.1±0.6  eV/atom of energy available during light emission. In order to unbind enough charge, collective processes must therefore reduce the ionization potential by at least 75%. We interpret this as evidence that a phase transition to a highly ionized plasma is occurring during sonoluminescence.

Interaction with the Lower Ionosphere of Electromagnetic Pulses from Lightning: Heating, Attachment, Ionization, and Optical Emissions

DTIC Science & Technology

1993-09-25

using Opal et al. [1971] data on the secondary electron spectra and the ionization potential approximation used by Richards and Torr [1990]. The...N£ most easily detectable in the natural aurora [ Vallance Jones, 1974]. 4? 44 OPTICAL EMISSIONS To study optical emissions from the D region...here) are considered to be weak based on observed auroral spectra [ Vallance Jones, 1974; p. 90]. The intensity of t’-th line is given by [Chamberlain

Observation of radio-wave-induced red hydroxyl emission at low altitude in the ionosphere.

PubMed

Kagan, L M; Nicolls, M J; Kelley, M C; Carlson, H C; Belikovich, V V; Bakhmet'eva, N V; Komrakov, G P; Trondsen, T S; Donovan, E

2005-03-11

We report the discovery of radio-wave-induced red emission of OH Meinel rotation-vibrational bands at 629.79 nm. These are the first measurements of artificial aurora below 100 km. We believe that the 629.79-nm OH emission was due to radio-wave focusing by sporadic ionization clouds near 80-85 km altitude, thus giving a technique to visualize the low-altitude sporadic ionization and providing insight into ionospheric interactions at these low altitudes.

A bright lensed galaxy at z = 5.4 with strong Lyα emission

NASA Astrophysics Data System (ADS)

McGreer, Ian D.; Clément, Benjamin; Mainali, Ramesh; Stark, Daniel P.; Gronke, Max; Dijkstra, Mark; Fan, Xiaohui; Bian, Fuyan; Frye, Brenda; Jiang, Linhua; Kneib, Jean-Paul; Limousin, Marceau; Walth, Gregory

2018-05-01

We present a detailed study of a unusually bright, lensed galaxy at z = 5.424 discovered within the CFHTLS imaging survey. With an observed flux of iAB = 23.0, J141446.82+544631.9 is one of the brightest galaxies known at z > 5. It is characterized by strong Lyα emission, reaching a peak in (observed) flux density of >10-16 erg s-1 cm-2 Å-1. A deep optical spectrum from the LBT places strong constraints on N V and C IV emission, disfavouring an AGN source for the emission. However, a detection of the N IV] λ1486 emission line indicates a hard ionizing continuum, possibly from hot, massive stars. Resolved imaging from HST deblends the galaxy from a foreground interloper; these observations include narrowband imaging of the Lyα emission, which is marginally resolved on ˜few kpc scales and has EW0 ˜ 260Å. The Lyα emission extends over ˜2000 km s-1 and is broadly consistent with expanding shell models. SED fitting that includes Spitzer/IRAC photometry suggests a complex star formation history that include both a recent burst and an evolved population. J1414+5446 lies 30″ from the centre of a known lensing cluster in the CFHTLS; combined with the foreground contribution this leads to a highly uncertain estimate for the lensing magnification in the range 5 ≲ μ ≲ 25. Because of its unusual brightness J1414+5446 affords unique opportunities for detailed study of an individual galaxy near the epoch of reionization and a preview of what can be expected from upcoming wide-area surveys that will yield hundreds of similar objects.

Hard X-Ray Emission and the Ionizing Source in LINERs

NASA Technical Reports Server (NTRS)

Terashima, Yuichi; Ho, Luis C.; Ptak, Andrew F.

2000-01-01

We report X-ray fluxes in the 2-10 keV band from LINERs (low-ionization nuclear emission-line regions) and low-luminosity Seyfert galaxies obtained with the ASCA satellite. Observed X-ray luminosities are in the range between 4 x 10(exp 39) and 5 x 10(exp 41) ergs/s, which are significantly smaller than that of the "classical" low-luminosity Seyfert 1 galaxy NGC 4051. We found that X-ray luminosities in 2-10 keV of LINERs with broad H.alpha emission in their optical spectra (LINER 1s) are proportional to their Ha luminosities. This correlation strongly supports the hypothesis that the dominant ionizing source in LINER 1s is photoionization by hard photons from low-luminosity AGNs. On the other hand, the X-ray luminosities of most LINERs without broad H.alpha emission (LINER 2s) in our sample are lower than LINER 1s at a given H.alpha luminosity. The observed X-ray luminosities in these objects are insufficient to power their H.alpha luminosities, suggesting that their primary ionizing source is other than an AGN, or that an AGN, if present, is obscured even at energies above 2 keV.

Alfvén ionization in an MHD-gas interactions code

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilson, A. D.; Diver, D. A.

A numerical model of partially ionized plasmas is developed in order to capture their evolving ionization fractions as a result of Alfvén ionization (AI). The mechanism of, and the parameter regime necessary for, AI is discussed and an expression for the AI rate based on fluid parameters, from a gas-MHD model, is derived. This AI term is added to an existing MHD-gas interactions' code, and the result is a linear, 2D, two-fluid model that includes momentum transfer between charged and neutral species as well as an ionization rate that depends on the velocity fields of both fluids. The dynamics ofmore » waves propagating through such a partially ionized plasma are investigated, and it is found that AI has a significant influence on the fluid dynamics as well as both the local and global ionization fraction.« less

Contribution of Solar Hydrogen Lyα Line Emission in Total Ionization Rate in Ionospheric D-region During the Maximum of Solar X-flare

NASA Astrophysics Data System (ADS)

Nina, A.; Čadež, V. M.; Bajčetić, J.

2015-12-01

The solar Lyα line emission can be considered as the dominant source of ionization processes in the ionospheric D-region at altitudes above 70 km during unperturbed conditions. However, large sudden impacts of radiation in some other energy domains can also significantly influence the ionization rate and, in this paper, we present a study on the contribution of Lyα radiation to the ionization rate when the ionosphere is disturbed by solar X-flares. We give relevant analytical expressions and make calculations and numerical simulations for the low ionosphere using data collected by the VLF receiver located in Serbia for the VLF radio signal emitted by the DHO transmitter in Germany.

Optical spectrophotometry of Wolf-Rayet galaxies

NASA Technical Reports Server (NTRS)

Vacca, William D.; Conti, Peter S.

1992-01-01

We have obtained long-slit optical spectra of 10 Wolf-Rayet galaxies and four other starburst galaxies. Using the nebular emission lines we have determined the electron temperatures, electron densities, extinctions, oxygen abundances, mass of ionized hydrogen, and numbers of ionizing photons due to hot stars in these galaxies. The various forbidden line ratios clearly indicate a stellar origin for the emission-line spectrum. From the flux of the broad He II 4686 A emission feature we have estimated the number of Wolf-Rayet stars present. We have accounted for the contribution of these stars to the total ionizing flux and have calculated the ratio of the number of these stars to the number of O stars. Wolf-Rayet galaxies are among the youngest examples of the starburst phenomenon, which we observed at a propitious moment.

grid-model: Semi-numerical reionization code

NASA Astrophysics Data System (ADS)

Hutter, Anne

2018-05-01

grid-model computes the time and spatially dependent ionization of neutral hydrogen (HI), neutral (HeI) and singly ionized helium (HeII) in the intergalactic medium (IGM). It accounts for recombinations and provides different descriptions for the photoionization rate that are used to calculate the residual HI fraction in ionized regions. The ionizing emissivity is directly derived from the RT simulation spectra.

Fine-scale structure in the -185 kilometers per second absorption by HCO(+) in the Galactic center

NASA Technical Reports Server (NTRS)

Marr, Jonathan M.; Rudolph, Alexander L.; Pauls, Thomas A.; Wright, Melvyn C. H.; Backer, Donald C.

1992-01-01

We present a high-resolution study of the HCO(+) (J = 1-0) absorption by the 'high-velocity gas' at velocities between -170 and -200 km/s in Sgr A West. The absorption against the continuum radiation from the ionized gas features in Sgr A West (in particular the 'bar') is stronger than it is against Sgr A which is separated from the ionized gas by a few arcseconds. The positions of peak HCO(+) opacity coincide with the positions of Ne II emission at these velocities. These observations suggest that, even though emission is detected from gas at these high velocities over several arcminutes, some of the absorbing molecular gas may be mixed in with the ionized gas close to Sgr A. Simple calculations show that sufficient shielding can exist in the ionized features to allow molecules to survive very close to the ionizing source.

An Atlas of Computed Equivalent Widths of Quasar Broad Emission Lines

NASA Astrophysics Data System (ADS)

Korista, Kirk; Baldwin, Jack; Ferland, Gary; Verner, Dima

We present graphically the results of several thousand photoionization calculations of broad emission-line clouds in quasars, spanning 7 orders of magnitude in hydrogen ionizing flux and particle density. The equivalent widths of 42 quasar emission lines are presented as contours in the particle density-ionizing flux plane for a typical incident continuum shape, solar chemical abundances, and cloud column density of N(H) = 1023 cm-2. Results are similarly given for a small subset of emission lines for two other column densities (1022 and 1024 cm-2), five other incident continuum shapes, and a gas metallicity of 5 Z⊙. These graphs should prove useful in the analysis of quasar emission-line data and in the detailed modeling of quasar broad emission-line regions. The digital results of these emission-line grids and many more are available over the Internet.

Recombination emissions and spectral blueshift of pump radiation from ultrafast laser induced plasma in a planar water microjet

NASA Astrophysics Data System (ADS)

Anija, M.; Philip, Reji

2009-09-01

We report spectroscopic investigations of an ultrafast laser induced plasma generated in a planar water microjet. Plasma recombination emissions along with the spectral blueshift and broadening of the pump laser pulse contribute to the total emission. The laser pulses are of 100 fs duration, and the incident intensity is around 10 15 W/cm 2. The dominant mechanisms leading to plasma formation are optical tunnel ionization and collisional ionization. Spectrally resolved polarization measurements show that the high frequency region of the emission is unpolarized whereas the low frequency region is polarized. Results indicate that at lower input intensities the emission arises mainly from plasma recombinations, which is accompanied by a weak blueshift of the incident laser pulse. At higher input intensities strong recombination emissions are seen, along with a broadening and asymmetric spectral blueshift of the pump laser pulse. From the nature of the blueshifted laser pulse it is possible to deduce whether the rate of change of free electron density is a constant or variable within the pulse lifetime. Two input laser intensity regimes, in which collisional and tunnel ionizations are dominant respectively, have been thus identified.

Interstellar PAH emission in the 11-14 micron region: new insights from laboratory data and a tracer of ionized PAHs

NASA Technical Reports Server (NTRS)

Hudgins, D. M.; Allamandola, L. J.

1999-01-01

The Ames infrared spectral database of isolated, neutral and ionized polycyclic aromatic hydrocarbons (PAHS) shows that aromatic CH out-of-plane bending frequencies are significantly shifted upon ionization. For solo- and duet-CH groups, the shift is pronounced and consistently toward higher frequencies. The solo-CH modes are blueshifted by an average of 27 cm-1 and the duet-CH modes by an average of 17 cm-1. For trio- and quartet-CH groups, the ionization shifts of the out-of-plane modes are more erratic and typically more modest. As a result of these ionization shifts, the solo-CH out-of-plane modes move out of the region classically associated with these vibrations in neutral PAHS, falling instead at frequencies well above those normally attributed to out-of-plane bending, vibrations of any type. In addition, for the compact PAHs studied, the duet-CH out-of-plane modes are shifted into the frequency range traditionally associated with the solo-CH modes. These results refine our understanding of the origin of the dominant interstellar infrared emission feature near 11.2 microns, whose envelope has traditionally been attributed only to the out-of-plane bending of solo-CH groups on PAHS, and provide a natural explanation for the puzzling emission feature near 11.0 microns within the framework of the PAH model. Specifically, the prevalent but variable long-wavelength wing or shoulder that is often observed near 11.4 microns likely reflects the contributions of duet-CH units in PAH cations. Also, these results indicate that the emission between 926 and 904 cm-1 (10.8 and 11.1 microns) observed in many sources can be unambiguously attributed to the out-of-plane wagging, of solo-CH units in moderately sized (fewer than 50 carbon atom) PAH cations, making this emission an unequivocal tracer of ionized interstellar PAHS.

THE ORIGIN AND OPTICAL DEPTH OF IONIZING RADIATION IN THE 'GREEN PEA' GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jaskot, A. E.; Oey, M. S.

2013-04-01

Although Lyman-continuum (LyC) radiation from star-forming galaxies likely drove the reionization of the universe, observations of star-forming galaxies at low redshift generally indicate low LyC escape fractions. However, the extreme [O III]/[O II] ratios of the z = 0.1-0.3 Green Pea galaxies may be due to high escape fractions of ionizing radiation. To analyze the LyC optical depths and ionizing sources of these rare, compact starbursts, we compare nebular photoionization and stellar population models with observed emission lines in the Peas' Sloan Digital Sky Survey (SDSS) spectra. We focus on the six most extreme Green Peas, the galaxies with themore » highest [O III]/[O II] ratios and the best candidates for escaping ionizing radiation. The Balmer line equivalent widths and He I {lambda}3819 emission in the extreme Peas support young ages of 3-5 Myr, and He II {lambda}4686 emission in five extreme Peas signals the presence of hard ionizing sources. Ionization by active galactic nuclei or high-mass X-ray binaries is inconsistent with the Peas' line ratios and ages. Although stacked spectra reveal no Wolf-Rayet (WR) features, we tentatively detect WR features in the SDSS spectra of three extreme Peas. Based on the Peas' ages and line ratios, we find that WR stars, chemically homogeneous O stars, or shocks could produce the observed He II emission. If hot stars are responsible, then the Peas' optical depths are ambiguous. However, accounting for emission from shocks lowers the inferred optical depth and suggests that the Peas may be optically thin. The Peas' ages likely optimize the escape of LyC radiation; they are old enough for supernovae and stellar winds to reshape the interstellar medium, but young enough to possess large numbers of UV-luminous O or WR stars.« less

Luminous phenomena and electromagnetic VHF wave emission originated from earthquake-related radon exhalation

NASA Astrophysics Data System (ADS)

Seki, A.; Tobo, I.; Omori, Y.; Muto, J.; Nagahama, H.

2013-12-01

Anomalous luminous phenomena and electromagnetic wave emission before or during earthquakes have been reported (e.g., the 1965 Matsushiro earthquake swarm). However, their mechanism is still unsolved, in spite of many models for these phenomena. Here, we propose a new model about luminous phenomena and electromagnetic wave emission during earthquake by focusing on atmospheric radon (Rn-222) and its daughter nuclides (Po-218 and Po-214). Rn-222, Po-218 and Po-214 are alpha emitters, and these alpha particles ionize atmospheric molecules. A light emission phenomenon, called 'the air luminescence', is caused by de-excitation of the ionized molecules of atmospheric nitrogen due to electron impact ionization from alpha particles. The de-excitation is from the second positive system of neutral nitrogen molecules and the first negative system of nitrogen molecule ion. Wavelengths of lights by these transitions include the visible light wavelength. So based on this mechanism, we proposed a new luminous phenomenon model before or during earthquake: 1. The concentration of atmospheric radon and its daughter nuclides increase anomalously before or during earthquakes, 2. Nitrogen molecules and their ions are excited by alpha particles emitted from Rn-222, Po-218 and Po-214, and air luminescence is generated by their de-excitation. Similarly, electromagnetic VHF wave emission can be explained by ionizing effect of radon and its daughter nuclides. Boyarchuk et al. (2005) proposed a model that electromagnetic VHF wave emission is originated when excited state of neutral clusters changes. Radon gas ionizes atmosphere and forms positively and negatively charged heavy particles. The process of ion hydration in ordinary air can be determined by the formation of complex chemically active structures of the various types of ion radicals. As a result of the association of such hydration radical ions, a neutral cluster, which is dipole quasi-molecules, is formed. A neutral cluster's rotation-rotation transition causes electromagnetic VHF wave emission. We also discuss a possibility of electromagnetic VHF wave emission from excitation of polyatomic molecules by alpha particles from Rn-222 and its daughter nuclides, similar to air luminescence by excitation of nitrogen molecule in the viewpoint of electromagnetic radiation in quantum theory.

Importance of biologically active aurora-like ultraviolet emission: stochastic irradiation of Earth and Mars by flares and explosions.

PubMed

Smith, David S; Scalo, John; Wheeler, J Craig

2004-10-01

Habitable planets will be subject to intense sources of ionizing radiation and fast particles from a variety of sources--from the host star to distant explosions--on a variety of timescales. Monte Carlo calculations of high-energy irradiation suggest that the surfaces of terrestrial-like planets with thick atmospheres (column densities greater than about 100 g cm(-2)) are well protected from directly incident X-rays and gamma-rays, but we find that sizeable fractions of incident ionizing radiation from astrophysical sources can be redistributed to biologically and chemically important ultraviolet wavelengths, a significant fraction of which can reach the surface. This redistribution is mediated by secondary electrons, resulting from Compton scattering and X-ray photoabsorption, the energies of which are low enough to excite and ionize atmospheric molecules and atoms, resulting in a rich aurora-like spectrum. We calculate the fraction of energy redistributed into biologically and chemically important wavelength regions for spectra characteristic of stellar flares and supernovae using a Monte-Carlo transport code and then estimate the fraction of this energy that is transmitted from the atmospheric altitudes of redistribution to the surface for a few illustrative cases. For atmospheric models corresponding to the Archean Earth, we assume no significant ultraviolet absorbers, only Rayleigh scattering, and find that the fraction of incident ionizing radiation that is received at the surface in the form of redistributed ultraviolet in the biologically relevant 200-320 nm region (UV-C and UV-B bands) can be up to 4%. On the present-day Earth with its ultraviolet ozone shield, this fraction is found to be 0.2%. Both values are many orders of magnitude higher than the fraction of direct ionizing radiation reaching the surface. This result implies that planetary organisms will be subject to mutationally significant, if intermittent, fluences of UV-B and harder radiation even in the presence of a narrow-band ultraviolet shield like ozone. We also calculate the surficial transmitted fraction of ionizing radiation and redistributed ultraviolet radiation for two illustrative evolving Mars atmospheres whose initial surface pressures were 1 bar. We discuss the frequency with which redistributed ultraviolet flux from parent star flares exceeds the parent star ultraviolet flux at the planetary surface. We find that the redistributed ultraviolet from parent star flares is probably a fairly rare intermittent event for habitable zone planets orbiting solar-type stars except when they are young, but should completely dominate the direct steady ultraviolet radiation from the parent star for planets orbiting all stars less massive than about 0.5 solar masses. Our results suggest that coding organisms on such planets (and on the early Earth) may evolve very differently than on contemporary Earth, with diversity and evolutionary rate controlled by a stochastically varying mutation rate and frequent hypermutation episodes.

Dynamics of photoionization from molecular electronic wavepacket states in intense pulse laser fields: A nonadiabatic electron wavepacket study.

PubMed

Matsuoka, Takahide; Takatsuka, Kazuo

2017-04-07

A theory for dynamics of molecular photoionization from nonadiabatic electron wavepackets driven by intense pulse lasers is proposed. Time evolution of photoelectron distribution is evaluated in terms of out-going electron flux (current of the probability density of electrons) that has kinetic energy high enough to recede from the molecular system. The relevant electron flux is in turn evaluated with the complex-valued electronic wavefunctions that are time evolved in nonadiabatic electron wavepacket dynamics in laser fields. To uniquely rebuild such wavefunctions with its electronic population being lost by ionization, we adopt the complex-valued natural orbitals emerging from the electron density as building blocks of the total wavefunction. The method has been implemented into a quantum chemistry code, which is based on configuration state mixing for polyatomic molecules. Some of the practical aspects needed for its application will be presented. As a first illustrative example, we show the results of hydrogen molecule and its isotope substitutes (HD and DD), which are photoionized by a two-cycle pulse laser. Photon emission spectrum associated with above threshold ionization is also shown. Another example is taken from photoionization dynamics from an excited state of a water molecule. Qualitatively significant effects of nonadiabatic interaction on the photoelectron spectrum are demonstrated.

The WHAM Hα Magellanic Stream Survey: Progress and Early Results

NASA Astrophysics Data System (ADS)

Smart, Brianna; Haffner, L. Matthew; Barger, Kat; Krishnarao, Dhanesh

2017-01-01

We present early analysis of the Hα survey of the Magellanic Stream using the Wisconsin H-Alpha Mapper (WHAM). The neutral component of the Stream extends some 200° across the sky (Nidever et al. 2010). However, the full extent of the ionized gas has not been mapped in detail. Previous studies (e.g., Putman et al. 2003; Weiner & Williams 1996) suggest that ionized gas is likely to be found all along the length of the Stream, and may extend beyond the current neutral boundaries as traced by 21 cm. Barger et al. (2013) used WHAM to map ionized gas throughout the Magellanic Bridge between the Magellanic Clouds. Although ionized emission tracks the neutral emission for the most part, it often spans a few degrees away from the H I at slightly offset velocities. Additionally, Fox et al. (2014) find evidence in an absorption line study that the tidal debris in the Magellanic System contains twice as much ionized gas as neutral material and may extend 30° away from 21-cm sensitivity boundaries. We are now compiling the first comprehensive picture of the ionized component of the Magellanic Stream using WHAM's unprecedented sensitivity to trace diffuse emission (~tens of mR), its velocity resolution (12 km/s) to separate the Stream from the Milky Way, and its multiwavelength capabilities (e.g., [S II] and [N II]) to examine the physical conditions of the gas. Much of the data along the primary axis of the Stream has been collected for the first phase of this extensive study, a complete kinematic Hα survey of the Stream. We present survey progress, challenges in extracting Stream emission, and first-look kinematic maps at select positions along the Stream.

ALMA Reveals Weak [N II] Emission in "Typical" Galaxies and Intense Starbursts at z = 5-6

NASA Astrophysics Data System (ADS)

Pavesi, Riccardo; Riechers, Dominik A.; Capak, Peter L.; Carilli, Christopher L.; Sharon, Chelsea E.; Stacey, Gordon J.; Karim, Alexander; Scoville, Nicholas Z.; Smolčić, Vernesa

2016-12-01

We report interferometric measurements of [N II] 205 μm fine-structure line emission from a representative sample of three galaxies at z = 5-6 using the Atacama Large (sub)Millimeter Array (ALMA). These galaxies were previously detected in [C II] and far-infrared continuum emission and span almost two orders of magnitude in star formation rate (SFR). Our results show at least two different regimes of ionized interstellar medium properties for galaxies in the first billion years of cosmic time, separated by their {L}[{{C}{{II}}]}/{L}[{{N}{{II}}]} ratio. We find extremely low [N II] emission compared to [C II] ({L}[{{C}{{II}}]}/{L}[{{N}{{II}}]}={68}-28+200) from a “typical” ˜ {L}{UV}* star-forming galaxy, likely directly or indirectly (by its effect on the radiation field) related to low dust abundance and low metallicity. The infrared-luminous modestly star-forming Lyman-break galaxy (LBG) in our sample is characterized by an ionized-gas fraction ({L}[{{C}{{II}}]}/{L}[{{N}{{II}}]}≲ 20) typical of local star-forming galaxies and shows evidence for spatial variations in its ionized-gas fraction across an extended gas reservoir. The extreme SFR, warm and compact dusty starburst AzTEC-3 shows an ionized fraction higher than expected given its SFR surface density ({L}[{{C}{{II}}]}/{L}[{{N}{{II}}]}=22+/- 8) suggesting that [N II] dominantly traces a diffuse ionized medium rather than star-forming H II regions in this type of galaxy. This highest redshift sample of [N II] detections provides some of the first constraints on ionized and neutral gas modeling attempts and on the structure of the interstellar medium at z = 5-6 in “normal” galaxies and starbursts.

Time-dependent Ionization in a Steady Flow in an MHD Model of the Solar Corona and Wind

NASA Astrophysics Data System (ADS)

Shen, Chengcai; Raymond, John C.; Mikić, Zoran; Linker, Jon A.; Reeves, Katharine K.; Murphy, Nicholas A.

2017-11-01

Time-dependent ionization is important for diagnostics of coronal streamers and pseudostreamers. We describe time-dependent ionization calculations for a three-dimensional magnetohydrodynamic (MHD) model of the solar corona and inner heliosphere. We analyze how non-equilibrium ionization (NEI) influences emission from a pseudostreamer during the Whole Sun Month interval (Carrington rotation CR1913, 1996 August 22 to September 18). We use a time-dependent code to calculate NEI states, based on the plasma temperature, density, velocity, and magnetic field in the MHD model, to obtain the synthetic emissivities and predict the intensities of the Lyα, O VI, Mg x, and Si xii emission lines observed by the SOHO/Ultraviolet Coronagraph Spectrometer (UVCS). At low coronal heights, the predicted intensity profiles of both Lyα and O VI lines match UVCS observations well, but the Mg x and Si xii emission are predicted to be too bright. At larger heights, the O VI and Mg x lines are predicted to be brighter for NEI than equilibrium ionization around this pseudostreamer, and Si xii is predicted to be fainter for NEI cases. The differences of predicted UVCS intensities between NEI and equilibrium ionization are around a factor of 2, but neither matches the observed intensity distributions along the full length of the UVCS slit. Variations in elemental abundances in closed field regions due to the gravitational settling and the FIP effect may significantly contribute to the predicted uncertainty. The assumption of Maxwellian electron distributions and errors in the magnetic field on the solar surface may also have notable effects on the mismatch between observations and model predictions.

Deep Fabry-Perot Hα observations of two Sculptor group galaxies, NGC 247 and 300

NASA Astrophysics Data System (ADS)

Hlavacek-Larrondo, J.; Marcelin, M.; Epinat, B.; Carignan, C.; de Denus-Baillargeon, M.-M.; Daigle, O.; Hernandez, O.

2011-09-01

It has been suggested that diffuse ionized gas can extend all the way to the end of the H I disc, and even beyond, such as in the case of the warped galaxyNGC 253 (Bland-Hawthorn et al.). Detecting ionized gas at these radii could carry significant implications as to the distribution of dark matter in galaxies. With the aim of detecting this gas, we carried out a deep Hα kinematical analysis of two Sculptor group galaxies, NGC 247 and 300. The Fabry-Perot data were taken at the 36-cm Marseille Telescope in La Silla, Chile, offering a large field of view. With almost 20 hours of observations for each galaxy, very faint diffuse emission is detected. Typical emission measures of 0.1 cm-6 pc are reached. For NGC 247, emission extending up to a radius comparable with that of the H I disc (r˜ 13 arcmin) is found, but no emission is seen beyond the H I disc. For NGC 300, we detect ionized gas on the entirety of our field of view (rmax˜ 14 arcmin), and find that the bright H II regions are embedded in a diffuse background. Using the deep data, extended optical rotation curves are obtained, as well as mass models. These are the most extended optical rotation curves thus far for these galaxies. We find no evidence suggesting that NGC 247 has a warped disc, and to account for our non-detection of Hα emission beyond its H I disc, as opposed to the warped galaxy NGC 253, our results favour the model in which, only through a warp, ionization by hot young stars in the central region of a galaxy can let photons escape and ionize the interstellar medium in the outer parts.

Ultra-bright pulsed electron beam with low longitudinal emittance

DOEpatents

Zolotorev, Max

2010-07-13

A high-brightness pulsed electron source, which has the potential for many useful applications in electron microscopy, inverse photo-emission, low energy electron scattering experiments, and electron holography has been described. The source makes use of Cs atoms in an atomic beam. The source is cycled beginning with a laser pulse that excites a single Cs atom on average to a band of high-lying Rydberg nP states. The resulting valence electron Rydberg wave packet evolves in a nearly classical Kepler orbit. When the electron reaches apogee, an electric field pulse is applied that ionizes the atom and accelerates the electron away from its parent ion. The collection of electron wave packets thus generated in a series of cycles can occupy a phase volume near the quantum limit and it can possess very high brightness. Each wave packet can exhibit a considerable degree of coherence.

Inconstant sun: how solar evolution has affected cosmic and ultraviolet radiation exposure over the history of life on Earth.

PubMed

Karam, P Andrew

2003-03-01

Four billion years ago, sea-level UV exposure was more than 400 times as intense as today, the dose from solar cosmic rays was five times present levels, and galactic cosmic rays accounted for only about 10% their current contribution to sea-level radiation doses. Exposure to cosmic radiation accounts for about 10% of natural background radiation exposure today and includes dose from galactic cosmic rays and solar charged particles. There is little exposure to ionizing wavelengths of UV due to absorption by ozone. The sun has evolved significantly over its life; in the past there were higher levels of particulate radiation and lower UV emissions from the sun, and a stronger solar wind reduced radiation dose in the inner solar system from galactic cosmic rays. Finally, since the early atmosphere contained little to no oxygen, surface levels of UV radiation were far higher in the past.

HF-enhanced 4278-Å airglow: evidence of accelerated ionosphere electrons?

NASA Astrophysics Data System (ADS)

Fallen, C. T.; Watkins, B. J.

2013-12-01

We report calculations from a one-dimensional physics-based self-consistent ionosphere model (SCIM) demonstrating that HF-heating of F-region electrons can produce 4278-Å airglow enhancements comparable in magnitude to those reported during ionosphere HF modification experiments at the High-frequency Active Auroral Research Program (HAARP) observatory in Alaska. These artificial 'blue-line' emissions, also observed at the EISCAT ionosphere heating facility in Norway, have been attributed to arise solely from additional production of N2+ ions through impact ionization of N2 molecules by HF-accelerated electrons. Each N2+ ion produced by impact ionization or photoionization has a probability of being created in the N2+(1N) excited state, resulting in a blue-line emission from the allowed transition to its ground state. The ionization potential of N2 exceeds 18 eV, so enhanced impact ionization of N2 implies that significant electron acceleration processes occur in the HF-modified ionosphere. Further, because of the fast N2+ emission time, measurements of 4278-Å intensity during ionosphere HF modification experiments at HAARP have also been used to estimate artificial ionization rates. To the best of our knowledge, all observations of HF-enhanced blue-line emissions have been made during twilight conditions when resonant scattering of sunlight by N2+ ions is a significant source of 4278-Å airglow. Our model calculations show that F-region electron heating by powerful O-mode HF waves transmitted from HAARP is sufficient to increase N2+ ion densities above the shadow height through temperature-enhanced ambipolar diffusion and temperature-suppressed ion recombination. Resonant scattering from the modified sunlit region can cause a 10-20 R increase in 4278-Å airglow intensity, comparable in magnitude to artificial emissions measured during ionosphere HF-modification experiments. This thermally-induced artificial 4278-Å aurora occurs independently of any artificial aurora maintained by HF-accelerated (non-thermal) electrons. The numerical results presented here do not necessarily rule out the presence of HF-accelerated electrons with energies exceeding 18 eV. However, vertical or field-aligned airglow intensity measurements made during twilight conditions do not provide definitive evidence of energetic HF-accelerated electrons. Consequently, artificial blue-line airglow measurements should not be used to estimate N2+ ionization rates without also accounting for temperature-dependent chemistry and diffusion. Future experiments that make simultaneous measurements of N2+ ion airglow emissions from both the first negative bands and the Meinel bands can potentially resolve the relative contributions of accelerated electron and resonant scattering mechanisms. Airglow emission rates from these bands are expected to be in strict proportion when the emissions result from electron impact ionization of N2 molecules. Side-view altitude-resolved 4278-Å airglow measurements may also indicate the presence of energetic HF-accelerated electrons if the blue-line emissions are determined to occur below the shadow height.

A Gemini view of the galaxy cluster RXC J1504-0248: insights on the nature of the central gaseous filaments

NASA Astrophysics Data System (ADS)

Soja, A. C.; Sodré, L.; Monteiro-Oliveira, R.; Cypriano, E. S.; Lima Neto, G. B.

2018-07-01

We revisit the galaxy cluster RXC J1504-0248, a remarkable example of a structure with a strong cool core in a near redshift (z = 0.216). We performed a combined analysis using photometric and spectroscopic data obtained at Gemini South Telescope. We estimated the cluster mass through gravitational lensing, obtaining M200 = 5.3 ± 0.4 × 1014 h_{70}^{-1} M⊙ within R200 = 1.56 ± 0.04 h^{-1}_{70} Mpc, in agreement with a virial mass estimate. This cluster presents a prominent filamentary structure associated with its brightest cluster galaxy, located mainly along its major axis and aligned with the X-ray emission. A combined study of three emission line diagnostic diagrams has shown that the filament emission falls in the so-called transition region of these diagrams. Consequently, several ionizing sources should be playing a meaningful role. We have argued that old stars, often invoked to explain low-ionization nuclear emission-line region emission, should not be the major source of ionization. We have noticed that most of the filamentary emission has line ratios consistent with the shock excitation limits obtained from shock models. We also found that line fluxes are related to gas velocities (here estimated from line widths) by power laws with slopes in the range expected from shock models. These models also show, however, that only ˜10 per cent of H α luminosity can be explained by shocks. We conclude that shocks probably associated with the cooling of the intracluster gas in a filamentary structure may indeed be contributing to the filament nebular emission, but cannot be the major source of ionizing photons.

The great galactic centre mystery

NASA Technical Reports Server (NTRS)

Riegler, G. R.

1982-01-01

Gamma-ray observations of the center of the Galaxy show a varying positron-electron annihilation radiation emission, while at radio wavelengths a non-thermal compact source surrounded by ionized gas moving at high velocities can be seen. Line emission maps for atomic and ionized hydrogen and molecular gas suggest gas expulsion and a massive collapsed object. IR observations show that ionized gas in the central few parsecs of the Galactic center is concentrated in at least 14 small clouds. Charge-coupled device images show a pair of faint, very red sources within a few arc seconds of IRS 16 and the compact non-thermal radio source. The positron-electron annihilation line emission implies an annihilation rate of 10 to the 43rd per sec, compared with an observed luminosity at IR wavelengths of 10 to the 40 erg per sec. Some models are briefly discussed.

HERSCHEL GALACTIC PLANE SURVEY OF [N ii] FINE STRUCTURE EMISSION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldsmith, Paul F.; Yıldız, Umut A.; Langer, William D.

2015-12-01

We present the first large-scale high angular resolution survey of ionized nitrogen in the Galactic Plane through emission of its two fine structure transitions ([N ii]) at 122 and 205 μm. The observations were largely obtained with the PACS instrument onboard the Herschel Space Observatory. The lines of sight were in the Galactic plane, following those of the Herschel OTKP project GOT C+. Both lines are reliably detected at the 10{sup −8}–10{sup −7} Wm{sup −2} sr{sup −1} level over the range –60° ≤ l ≤ 60°. The rms of the intensity among the 25 PACS spaxels of a given pointingmore » is typically less than one third of the mean intensity, showing that the emission is extended. [N ii] is produced in gas in which hydrogen is ionized, and collisional excitation is by electrons. The ratio of the two fine structure transitions provides a direct measurement of the electron density, yielding n(e) largely in the range 10–50 cm{sup −3} with an average value of 29 cm{sup −3} and N{sup +} column densities 10{sup 16}–10{sup 17} cm{sup −2}. [N ii] emission is highly correlated with that of [C ii], and we calculate that between 1/3 and 1/2 of the [C ii] emission is associated with the ionized gas. The relatively high electron densities indicate that the source of the [N ii] emission is not the warm ionized medium (WIM), which has electron densities more than 100 times smaller. Possible origins of the observed [N ii] include the ionized surfaces of dense atomic and molecular clouds, the extended low-density envelopes of H ii regions, and low-filling factor high-density fluctuations of the WIM.« less

Modeling 13.3nm Fe XXIII Flare Emissions Using the GOES-R EXIS Instrument

NASA Astrophysics Data System (ADS)

Rook, H.; Thiemann, E.

2017-12-01

The solar EUV spectrum is dominated by atomic transitions in ionized atoms in the solar atmosphere. As solar flares evolve, plasma temperatures and densities change, influencing abundances of various ions, changing intensities of different EUV wavelengths observed from the sun. Quantifying solar flare spectral irradiance is important for constraining models of Earth's atmosphere, improving communications quality, and controlling satellite navigation. However, high time cadence measurements of flare irradiance across the entire EUV spectrum were not available prior to the launch of SDO. The EVE MEGS-A instrument aboard SDO collected 0.1nm EUV spectrum data from 2010 until 2014, when the instrument failed. No current or future instrument is capable of similar high resolution and time cadence EUV observation. This necessitates a full EUV spectrum model to study EUV phenomena at Earth. It has been recently demonstrated that one hot flare EUV line, such as the 13.3nm Fe XXIII line, can be used to model cooler flare EUV line emissions, filling the role of MEGS-A. Since unblended measurements of Fe XXIII are typically unavailable, a proxy for the Fe XXIII line must be found. In this study, we construct two models of this line, first using the GOES 0.1-0.8nm soft x-ray (SXR) channel as the Fe XXIII proxy, and second using a physics-based model dependent on GOES emission measure and temperature data. We determine that the more sophisticated physics-based model shows better agreement with Fe XXIII measurements, although the simple proxy model also performs well. We also conclude that the high correlation between Fe XXIII emissions and the GOES 0.1-0.8nm band is because both emissions tend to peak near the GOES emission measure peak despite large differences in their contribution functions.

The Cygnus OB2 Star Forming Complex

NASA Astrophysics Data System (ADS)

Rybarczyk, Daniel R.; Bania, Thomas

2018-01-01

Almost all astrophysical systems—from planets to stars to supernovae to entire galaxies—are impacted by the process of star formation. The brightest, most massive stars (OB stars) form in hot young clusters called OB associations. Cygnus OB2 is an OB association containing over 160 OB stars, making it one of the largest in the Milky Way Galaxy. At a distance of less than 1.5 kpc, its proximity to the Sun makes it optimal for assessing the process of Galactic star formation and its implications for stellar evolution, Galactic structure, and Galactic chemical evolution. Using existing data sets, we derive comprehensive maps of the distribution of thermal continuum, atomic, and molecular emission from the interstellar gas in Cyg OB2. The thermal continuum emission stems from the plasma ionized by OB stars. The atomic gas is probed by emission from atomic hydrogen, HI, at 21 cm wavelength. The molecular gas is traced by emission from the CO molecule which is a proxy for molecular hydrogen, H2. We combine these atomic and molecular data to derive a map of the total proton column density distribution in Cyg OB2. We also analyze the velocity fields of the OB stars, the atomic and molecular hydrogen gas, and the HII regions' radio recombination emission. As expected, we find HII regions to be spatially coincident with zones of higher cloud density. Surrounding the greatest concentration of OB stars is a cavity in the radio continuum and CO emission. This results from shock waves produced by the combined action of the high HII region pressure and winds from the OB stars. Such a distribution implies that Cyg OB2 is old enough to have evolved to this state.

A Flexible Cosmic Ultraviolet Background Model

NASA Astrophysics Data System (ADS)

McQuinn, Matthew

2016-10-01

HST studies of the IGM, of the CGM, and of reionization-era galaxies are all aided by ionizing background models, which are a critical input in modeling the ionization state of diffuse, 10^4 K gas. The ionization state in turn enables the determination of densities and sizes of absorbing clouds and, when applied to the Ly-a forest, the global ionizing emissivity of sources. Unfortunately, studies that use these background models have no way of gauging the amount of uncertainty in the adopted model other than to recompute their results using previous background models with outdated observational inputs. As of yet there has been no systematic study of uncertainties in the background model and there unfortunately is no publicly available ultraviolet background code. A public code would enable users to update the calculation with the latest observational constraints, and it would allow users to experiment with varying the background model's assumptions regarding emissions and absorptions. We propose to develop a publicly available ionizing background code and, as an initial application, quantify the level of uncertainty in the ionizing background spectrum across cosmic time. As the background model improves, so does our understanding of (1) the sources that dominate ionizing emissions across cosmic time and (2) the properties of diffuse gas in the circumgalactic medium, the WHIM, and the Ly-a forest. HST is the primary telescope for studying both the highest redshift galaxies and low-redshift diffuse gas. The proposed program would benefit HST studies of the Universe at z 0 all the way up to z = 10, including of high-z galaxies observed in the HST Frontier Fields.

Tracing the Baryon Cycle within Nearby Galaxies with a next-generation VLA

NASA Astrophysics Data System (ADS)

Kepley, Amanda A.; Leroy, Adam; Murphy, Eric J.; ngVLA Baryon Cycle Science Working Group

2017-01-01

The evolution of galaxies over cosmic time is shaped by the cycling of baryons through these systems, namely the inflow of atomic gas, the formation of molecular structures, the birth of stars, and the expulsion of gas due to associated feedback processes. The best way to study this cycle in detail are observations of nearby galaxies. These systems provide a complete picture of baryon cycling over a wide range of astrophysical conditions. In the next decade, higher resolution/sensitivity observations of such galaxies will fundamentally improve our knowledge of galaxy formation and evolution, allowing us to better interpret higher redshift observations of sources that were rapidly evolving at epochs soon after the Big Bang. In particular, the centimeter-to-millimeter part of the spectrum provides critical diagnostics for each of the key baryon cycling processes and access to almost all phases of gas in galaxies: cool and cold gas (via emission and absorption lines), ionized gas (via free-free continuum and recombination lines), cosmic rays and hot gas (via synchrotron emission and the Sunyaev-Zeldovich effect). This poster highlights a number of key science problems in this area whose solutions require a next-generation radio-mm interferometer such as the next-generation VLA.

Compton Thick AGN in the XMM-COSMOS field

NASA Astrophysics Data System (ADS)

Lanzuisi, G.; Perna, M.; Delvecchio, I.; Berta, S.; Brusa, M.; Gruppioni, C.; Comastri, A.

2016-06-01

I will present results we published in two recent papers (Lanzuisi et al. 2015, A&A 573A 137, Lanzuisi et al. 2015, A≈A 578A 120) on the properties of X-ray selected Compton Thick (CT, NH>10^{24} cm^{-2}) AGN, in the XMM-COSMOS survey. We exploited the rich multi-wavelength dataset available in this field, to show that CT AGN tend to harbor smaller, rapidly growing SMBH with respect to unobscured AGN, and have a higher chance of being hosted by star-forming, merging and post-merger systems. We also demonstrated the detectability of even more heavily obscured AGN (NH>10^{25} cm^{-2}), thanks to a truly multi-wavelength approach in the same field, and to the unrivaled XMM sensitivity. The extreme source detected in this way shows strong evidences of ongoing powerful AGN feedback, detected as blue-shifted wings of high ionization optical emission lines such as [NeV] and [FeVII], as well as of the [OIII] emission line. The results obtained from these works point toward a scenario in which highly obscured AGN occupy a peculiar place in the galaxy-AGN co-evolution process, in which both the host and the SMBH rapidly evolve toward the local relations.

Specific cationic emission of cisplatin following ionization by swift protons

NASA Astrophysics Data System (ADS)

Moretto-Capelle, Patrick; Champeaux, Jean-Philippe; Deville, Charlotte; Sence, Martine; Cafarelli, Pierre

2016-05-01

We have investigated collision-induced ionization and fragmentation by 100 keV protons of the radio sensitizing molecule cisplatin, which is used in cancer treatments. A large emission of HCl+ and NH2+ is observed, but surprisingly, no cationic fragments containing platinum are detected, in contrast to ionization-dissociation induced by electronic collision. Theoretical investigations show that the ionization processes take place on platinum and on chlorine atoms. We propose new ionization potentials for cisplatin. Dissociation limits corresponding to the measured fragmentation mass spectrum have been evaluated and the theoretical results show that the non-observed cationic fragments containing platinum are mostly associated with low dissociation energies. We have also investigated the reaction path for the hydrogen transfer from the NH3 group to the Cl atom, as well as the corresponding dissociation limits from this tautomeric form. Here again the cations containing platinum correspond to lower dissociation limits. Thus, the experimental results suggest that excited states, probably formed via inner-shell ionization of the platinum atom of the molecule, correlated to higher dissociation limits are favored.

Detection of Broad Hα Emission Lines in the Late-Time Spectra of a Hydrogen-Poor Superluminous Supernova

DOE PAGES

Yan, Lin; Quimby, R.; Ofek, E.; ...

2015-11-23

iPTF13ehe is a hydrogen-poor superluminous supernova (SLSN) at z = 0.3434, with a slow-evolving light curve and spectral features similar to SN2007bi. It rises in 83–148 days to reach a peak bolometric luminosity of ~1.3 × 10 44 erg s -1, then decays slowly at 0.015 mag day -1. The measured ejecta velocity is ~ 13,000 km s -1. The inferred explosion characteristics, such as the ejecta mass (70–220 M ⊙), and the total radiative and kinetic energy (E rad ~ 10 51 erg, E kin ~ 2 × 10 53 erg), are typical of slow-evolving H-poor SLSN events. However,more » the late-time spectrum taken at +251 days (rest, post-peak) reveals a Balmer Hα emission feature with broad and narrow components, which has never been detected before among other H-poor SLSNe. The broad component has a velocity width of ~4500 km s -1 and a ~300 km s -1 blueward shift relative to the narrow component. In this paper, we interpret this broad Hα emission with a luminosity of ~2 × 10 41 erg s -1 as resulting from the interaction between the supernova ejecta and a discrete H-rich shell, located at a distance of ~4 × 10 16 cm from the explosion site. This interaction causes the rest-frame r-band LC to brighten at late times. The fact that the late-time spectra are not completely absorbed by the shock-ionized H-shell implies that its Thomson scattering optical depth is likely ≤1, thus setting upper limits on the shell mass ≤30 M ⊙. Of the existing models, a Pulsational Pair Instability supernova model can naturally explain the observed 30 M ⊙ H-shell, ejected from a progenitor star with an initial mass of (95–150) M ⊙ about 40 years ago. Finally, we estimate that at least ~15% of all SLSNe-I may have late-time Balmer emission lines.« less

Broad NE 8 lambda 774 emission from quasars in the HST-FOS snapshot survey (ABSNAP)

NASA Technical Reports Server (NTRS)

Hamann, Fred; Zuo, Lin; Tytler, David

1995-01-01

We discuss the strength and frequency of broad Ne VIII lambda 774 emission from quasars measured in the Hubble Space Telescope Faint Object Spectrograph (HST-FOS) snapshot survey (Absnap). Five sources in the survey have suitable redshifts (0.86 less than or equal to Z(sub em) less than or equal to 1.31), signal-to-noise ratios and no Lyman limit absorptions. Three of the five sources have a strong broad emission line near 774 A (rest), and the remaining two sources have a less securely measured line near this wavelength. We identify these lines with Ne VIII lambda 774 based on the measured wavelengths and theoretical estimates of various line fluxes (Hamann et al. 1995a). Secure Ne VIII detections occur in both radio-loud and radio-quiet sources. We tentatively conclude that broad Ne VIII lambda 774 emission is common in quasars, with typical strengths between approximately 25% and approximately 200% of O VI lambda 1034. These Ne VIII lambda 774 measurements imply that the broad emission line regions have a much hotter and more highly ionized component than previously recognized. They also suggest that quasar continua have substantial ionizing flux out to energies greater than 207 eV (greater than 15.2 ryd, lambda less than 60 A). Photoionization calculations using standard incident spectra indicate that the Ne VIII emission requires ionization parameters U greater than or = 5, total column densities N(sub H) greater than or = 10(sub 22)/sq cm and covering factors greater than or = 25%. The temperatures could be as high as approximately 10(exp 5) K. If the gas is instead collisionally ionized, strong Ne VIII would imply equilibrium temperatures in the range approximately 400,000 less than or approximately = T(sub e) less than or approximately = 10(exp 6) K. In either case, the highly ionized Ne VIII emission regions would appear as X-ray 'warm absorbers' if they lie along our line of sight to the X-ray continuum source.

Directed Field Ionization

NASA Astrophysics Data System (ADS)

Gregoric, Vincent C.; Kang, Xinyue; Liu, Zhimin Cheryl; Rowley, Zoe A.; Carroll, Thomas J.; Noel, Michael W.

2017-04-01

Selective field ionization is an important experimental technique used to study the state distribution of Rydberg atoms. This is achieved by applying a steadily increasing electric field, which successively ionizes more tightly bound states. An atom prepared in an energy eigenstate encounters many avoided Stark level crossings on the way to ionization. As it traverses these avoided crossings, its amplitude is split among multiple different states, spreading out the time resolved electron ionization signal. By perturbing the electric field ramp, we can change how the atoms traverse the avoided crossings, and thus alter the shape of the ionization signal. We have used a genetic algorithm to evolve these perturbations in real time in order to arrive at a target ionization signal shape. This process is robust to large fluctuations in experimental conditions. This work was supported by the National Science Foundation under Grants No. 1607335 and No. 1607377 and used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation Grant Number OCI-1053575.

Effects of target heating on experiments using Kα and Kβ diagnostics.

PubMed

Palmeri, P; Boutoux, G; Batani, D; Quinet, P

2015-09-01

We describe the impact of heating and ionization on emission from the target of Kα and Kβ radiation induced by the propagation of hot electrons generated by laser-matter interaction. We consider copper as a test case and, starting from basic principles, we calculate the changes in emission wavelength, ionization cross section, and fluorescence yield as Cu is progressively ionized. We have finally considered the more realistic case when hot electrons have a distribution of energies with average energies of 50 and 500 keV (representative respectively of "shock ignition" and of "fast ignition" experiments) and in which the ions are distributed according to ionization equilibrium. In addition, by confronting our theoretical calculations with existing data, we demonstrate that this study offers a generic theoretical background for temperature diagnostics in laser-plasma interactions.

Electron Acceleration and Ionization Production in High-Power Heating Experiments at HAARP

NASA Astrophysics Data System (ADS)

Mishin, E. V.; Pedersen, T.

2012-12-01

Recent ionospheric modification experiments with the 3.6 MW transmitter at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska led to discovery of artificial ionization descending from the nominal interaction altitude in the background F-region ionosphere by ~60-80 km. Artificial ionization production is indicated by significant 427.8 nm emissions from the 1st negative band of N2+ and the appearance of transmitter-induced bottomside traces in ionosonde data during the periods of most intense optical emissions. However, the exact mechanisms producing the artificial plasmas remain to be determined. Yet the only existing theoretical models explain the development of artificial plasma as an ionizing wavefront moving downward due to ionization by electrons accelerated by HF-excited strong Langmuir turbulence (SLT) generated near the plasma resonance, where the pump frequency matches the plasma frequency. However, the observations suggest also the significance of interactions with upper hybrid and electron Bernstein waves near multiples of the electron gyrofrequency. We describe recent observations and discuss suitable acceleration mechanisms.

The accuracy of seminumerical reionization models in comparison with radiative transfer simulations

NASA Astrophysics Data System (ADS)

Hutter, Anne

2018-06-01

We have developed a modular seminumerical code that computes the time and spatially dependent ionization of neutral hydrogen (H I), neutral (He I), and single-ionized helium (He II) in the intergalactic medium (IGM). The model accounts for recombinations and provides different descriptions for the photoionization rate that are used to calculate the residual H I fraction in ionized regions. We compare different seminumerical reionization schemes to a radiative transfer (RT) simulation. We use the RT simulation as a benchmark, and find that the seminumerical approaches produce similar H II and He II morphologies and power spectra of the H I 21 cm signal throughout reionization. As we do not track partial ionization of He II, the extent of the double-ionized helium (He III) regions is consistently smaller. In contrast to previous comparison projects, the ionizing emissivity in our seminumerical scheme is not adjusted to reproduce the redshift evolution of the RT simulation, but directly derived from the RT simulation spectra. Among schemes that identify the ionized regions by the ratio of the number of ionization and absorption events on different spatial smoothing scales, we find those that mark the entire sphere as ionized when the ionization criterion is fulfilled to result in significantly accelerated reionization compared to the RT simulation. Conversely, those that flag only the central cell as ionized yield very similar but slightly delayed redshift evolution of reionization, with up to 20 per cent ionizing photons lost. Despite the overall agreement with the RT simulation, our results suggest that constraining ionizing emissivity-sensitive parameters from seminumerical galaxy formation-reionization models are subject to photon nonconservation.

The accuracy of semi-numerical reionization models in comparison with radiative transfer simulations

NASA Astrophysics Data System (ADS)

Hutter, Anne

2018-03-01

We have developed a modular semi-numerical code that computes the time and spatially dependent ionization of neutral hydrogen (H I), neutral (He I) and singly ionized helium (He II) in the intergalactic medium (IGM). The model accounts for recombinations and provides different descriptions for the photoionization rate that are used to calculate the residual H I fraction in ionized regions. We compare different semi-numerical reionization schemes to a radiative transfer (RT) simulation. We use the RT simulation as a benchmark, and find that the semi-numerical approaches produce similar H II and He II morphologies and power spectra of the H I 21cm signal throughout reionization. As we do not track partial ionization of He II, the extent of the double ionized helium (He III) regions is consistently smaller. In contrast to previous comparison projects, the ionizing emissivity in our semi-numerical scheme is not adjusted to reproduce the redshift evolution of the RT simulation, but directly derived from the RT simulation spectra. Among schemes that identify the ionized regions by the ratio of the number of ionization and absorption events on different spatial smoothing scales, we find those that mark the entire sphere as ionized when the ionization criterion is fulfilled to result in significantly accelerated reionization compared to the RT simulation. Conversely, those that flag only the central cell as ionized yield very similar but slightly delayed redshift evolution of reionization, with up to 20% ionizing photons lost. Despite the overall agreement with the RT simulation, our results suggests that constraining ionizing emissivity sensitive parameters from semi-numerical galaxy formation-reionization models are subject to photon nonconservation.

Simulating 3D Stellar Winds and Diffuse X-ray Emissions from Gases in Non-equilibrium Ionization State

NASA Astrophysics Data System (ADS)

Long, Min; Sun, Wei; Niu, Shu; Zhou, Xin; Ji, Li

2017-08-01

We investigate the physical properties of stellar winds launched in super stellar clusters (SSCs). Chandra observations have detected the presence of diffuse X-ray emission caused by hot gas from such winds in SSCs, and provide the best probe for understanding interactions between the stellar winds and the complex nursery regions. However, the details of the origin of cluster winds, the mass and energy ejection, the formation of diffuse X-ray emission, the fraction of winds contribution to the distribution of diffuse X-ray emission still remain unclear. We developed a multiphysics hydrodynamic model including self-gravity, head conduction and performed 3D simulations with an unprecedented grid resolution due to adaptive mesh refinement (AMR) capability in a case study of NGC 3603, as a supplement to the analysis of the archived 500 ks Chandra observations. The synthetic emission will be computed by assuming the gas in a non-equilibrium ionization (NEI) state indicated by Chandra observation, not coronal ionization equilibrium (CIE) that most works assumed, by using a customized NEI calculation module based on AtomDB. The results will be compared to the Chandra observations.

Stars and reionization: the cross-correlation of the 21 cm line and the near-infrared background

NASA Astrophysics Data System (ADS)

Fernandez, Elizabeth R.; Zaroubi, Saleem; Iliev, Ilian T.; Mellema, Garrelt; Jelić, Vibor

2014-05-01

With improving telescopes, it may now be possible to observe the Epoch of Reionization in multiple ways. We examine two of these observables - the excess light in the near-infrared background that may be due to high-redshift stars and ionized HII bubbles, and the 21 cm emission from neutral hydrogen. Because these two forms of emission should result from different, mutually exclusive regions, an anticorrelation should exist between them. We discuss the strengths of using cross-correlations between these observations to learn more about high-redshift star formation and reionization history. In particular, we create simulated maps of emission from both the near-infrared background and 21 cm emission. We find that these observations are anticorrelated, with the strongest anticorrelation originating from times when the universe is half ionized. This result is robust and does not depend on the properties of the stars themselves. Rather, it depends on the ionization history. Cross-correlations can provide redshift information, which the near-infrared background cannot provide alone. In addition, cross-correlations can help separate foreground emission from the true high-redshift component, making it possible to say with greater certainty that we are indeed witnessing the Epoch of Reionization.

Weak and Compact Radio Emission in Early High-Mass Star Forming Regions

NASA Astrophysics Data System (ADS)

Rosero, Viviana; P. Hofner, M. Claussen, S. Kurtz, R. Cesaroni, E. D. Araya, C. Carrasco-González, L. F. Rodríguez, K. M. Menten, F. Wyrowski, L. Loinard, S. P. Ellingsen

2018-01-01

High-mass protostars are difficult to detect: they have short evolutionary timescales, they tend to be located at large distances, and they are usually embedded within complicated cluster environments. In this work, we aimed to identify and analyze candidates at the earliest stages of high-mass star formation, where only low-level (< 1 mJy) radio emission is expected. We used the Karl G. Jansky Very Large Array to achieve one of the most sensitive (image RMS < 3 -- 10 μJy/beam) centimeter continuum surveys towards high-mass star forming regions to date, with observations at 1.3 and 6 cm and an angular resolution < 0.5". The sample is composed of cold molecular clumps with and without infrared sources (CMC--IRs and CMCs, respectively) and hot molecular cores (HMCs), covering a wide range of parameters such as bolometric luminosity and distance. We detected 70 radio continuum sources that are associated with dust clumps, most of which are weak and compact. We detected centimeter wavelength sources in 100% of our HMCs, which is a higher fraction than previously expected and suggests that radio continuum may be detectable at weak levels in all HMCs. The lack of radio detections for some objects in the sample (including most CMCs) contributes strong evidence that these are prestellar clumps, providing interesting constraints and ideal follow up candidates for studies of the earliest stages of high-mass stars. Our results show further evidence for an evolutionary sequence in the formation of high-mass stars, from starless cores (i.e., CMCs) to relatively more evolved ones (i.e., HMCs). Many of our detections have morphologies and other observational parameters that resemble collimated ionized jets, which is highly relevant for recent theoretical models based on core accretion that predict that the first stages of ionization from high-mass stars are in the form of jets. Additionally, we found that properties of ionized jets from low and high-mass stars are extremely well correlated; our data improves upon previous studies of this nature and provides further evidence of a common origin for jets of any luminosity.

OT2_pgolds01_6: Herschel [NII] Observations to Define the Source of [CII] Emission

NASA Astrophysics Data System (ADS)

Goldsmith, P.

2011-09-01

The 158 micron line of ionized carbon is the strongest single long-wavelength emission feature from the interstellar medium and is the most important coolant of gas in which hydrogen is in atomic form. It is a key determinant of the evolution of these largely atomic regions into denser, cooler molecular clouds in which new stars are formed, and is widely used as a tracer of star formation in the Milky Way and other galaxies. There is, however, an ongoing, serious controversy about the origin of the [CII] emission, which has been asserted to come from the extended low-density warm interstellar medium, but has more generally been associated with the primarily molecular photon dominated regions (PDRs) intimately associated with massive, young stars. We propose a combined HIFI and PACS study of the two far-infrared [NII] fine structure lines in order to resolve the important question of the fraction of CII emission that arises in ionized gas. Specifically, we will (1) utilize the fact that due to its ionization potential NII is found only in HII regions, and with PACS 122 and 205 micron observations, determine electron densities in a sample of such regions in the Galactic plane; (2) utilize available data on radio free-free and H-alpha emission to determine the NII column densities and from this the CII column densities in the HII regions; (3) use the electron densities to determine the fraction of CII emission arising in the ionized interstellar medium. These observations will be carried out at 150 of the positions in the Galactic plane observed in [CII] by the GOT-C+ project. We will also carry out HIFI observations of 10 selected positions in the 205 micron line to determine spectral characteristics of the NII emission line, which with CII, CI, and CO profiles already in hand will serve as a further discriminant among the proposed sources of CII emission.

The Impact of Diffuse Ionized Gas on Emission-line Ratios and Gas Metallicity Measurements

NASA Astrophysics Data System (ADS)

Zhang, Kai; Yan, Renbin; MaNGA Team

2016-01-01

Diffuse Ionized Gas (DIG) is prevalent in star-forming galaxies. Using a sample of galaxies observed by MaNGA, we demonstrate how DIG in star-forming galaxies impact the measurements of emission line ratios, hence the gas-phase metallicity measurements and the interpretation of diagnostic diagrams. We demonstrate that emission line surface brightness (SB) is a reasonably good proxy to separate HII regions from regions dominated by diffuse ionized gas. For spatially-adjacent regions or regions at the same radius, many line ratios change systematically with emission line surface brightness, reflecting a gradual increase of dominance by DIG towards low SB. DIG could significantly bias the measurement of gas metallicity and metallicity gradient. Because DIG tend to have a higher temperature than HII regions, at fixed metallicity DIG displays lower [NII]/[OII] ratios. DIG also show lower [OIII]/[OII] ratios than HII regions, due to extended partially-ionized regions that enhance all low-ionization lines ([NII], [SII], [OII], [OI]). The contamination by DIG is responsible for a substantial portion of the scatter in metallicity measurements. At different surface brightness, line ratios and line ratio gradients can differ systematically. As DIG fraction could change with radius, it can affect the metallicity gradient measurements in systematic ways. The three commonly used strong-line metallicity indicators, R23, [NII]/[OII], O3N2, are all affected in different ways. To make robust metallicity gradient measurements, one has to properly isolate HII regions and correct for DIG contamination. In line ratio diagnostic diagrams, contamination by DIG moves HII regions towards composite or LINER-like regions.

Atmospheric NLTE models for the spectroscopic analysis of blue stars with winds. III. X-ray emission from wind-embedded shocks

NASA Astrophysics Data System (ADS)

Carneiro, L. P.; Puls, J.; Sundqvist, J. O.; Hoffmann, T. L.

2016-05-01

Context. Extreme ultraviolet (EUV) and X-ray radiation emitted from wind-embedded shocks in hot, massive stars can affect the ionization balance in their outer atmospheres and can be the mechanism responsible for producing highly ionized atomic species detected in stellar wind UV spectra. Aims: To allow for these processes in the context of spectral analysis, we have implemented the emission from wind-embedded shocks and related physics into our unified, NLTE model atmosphere/spectrum synthesis code FASTWIND. Methods: The shock structure and corresponding emission is calculated as a function of user-supplied parameters (volume filling factor, radial stratification of shock strength, and radial onset of emission). We account for a temperature and density stratification inside the postshock cooling zones, calculated for radiative and adiabatic cooling in the inner and outer wind, respectively. The high-energy absorption of the cool wind is considered by adding important K-shell opacities, and corresponding Auger ionization rates have been included in the NLTE network. To test our implementation and to check the resulting effects, we calculated a comprehensive model grid with a variety of X-ray emission parameters. Results: We tested and verified our implementation carefully against corresponding results from various alternative model atmosphere codes, and studied the effects from shock emission for important ions from He, C, N, O, Si, and P. Surprisingly, dielectronic recombination turned out to play an essential role for the ionization balance of O iv/O v (particularly in dwarfs with Teff~ 45 000 K). Finally, we investigated the frequency dependence and radial behavior of the mass absorption coefficient, κν(r), which is important in the context of X-ray line formation in massive star winds. Conclusions: In almost all of the cases considered, direct ionization is of major influence because of the enhanced EUV radiation field, and Auger ionization only affects N vi and O vi significantly. The approximation of a radially constant κν is justified for r ≳ 1.2 R∗ and λ ≲ 18 Å and also for many models at longer wavelengths. To estimate the actual value of this quantity, however, the He II opacities need to be calculated from detailed NLTE modeling, at least for wavelengths longer than 18 to 20 Å, and information on the individual CNO abundances has to be present.

Attosecond Electron Correlation Dynamics in Double Ionization of Benzene Probed with Two-Electron Angular Streaking

NASA Astrophysics Data System (ADS)

Winney, Alexander H.; Lee, Suk Kyoung; Lin, Yun Fei; Liao, Qing; Adhikari, Pradip; Basnayake, Gihan; Schlegel, H. Bernhard; Li, Wen

2017-09-01

With a novel three-dimensional electron-electron coincidence imaging technique and two-electron angular streaking method, we show that the emission time delay between two electrons can be measured from tens of attoseconds to more than 1 fs. Surprisingly, in benzene, the double ionization rate decays as the time delay between the first and second electron emission increases during the first 500 as. This is further supported by the decay of the Coulomb repulsion in the direction perpendicular to the laser polarization. This result reveals that laser-induced electron correlation plays a major role in strong field double ionization of benzene driven by a nearly circularly polarized field.

A Herschel [C ii] Galactic plane survey. I. The global distribution of ISM gas components

NASA Astrophysics Data System (ADS)

Pineda, J. L.; Langer, W. D.; Velusamy, T.; Goldsmith, P. F.

2013-06-01

Context. The [C ii] 158 μm line is an important tool for understanding the life cycle of interstellar matter. Ionized carbon is present in a variety of phases of the interstellar medium (ISM), including the diffuse ionized medium, warm and cold atomic clouds, clouds in transition from atomic to molecular, and dense and warm photon dominated regions. Aims: Velocity-resolved observations of [C ii] are the most powerful technique available to disentangle the emission produced by these components. These observations can also be used to trace CO-dark H2 gas and determine the total mass of the ISM. Methods: The Galactic Observations of Terahertz C+ (GOT C+) project surveys the [C ii] 158 μm line over the entire Galactic disk with velocity-resolved observations using the Herschel/HIFI instrument. We present the first longitude-velocity maps of the [C ii] emission for Galactic latitudes b = 0°, ±0.5°, and ±1.0°. We combine these maps with those of H i, 12CO, and 13CO to separate the different phases of the ISM and study their properties and distribution in the Galactic plane. Results: [C ii] emission is mostly associated with spiral arms, mainly emerging from Galactocentric distances between 4 and 10 kpc. It traces the envelopes of evolved clouds as well as clouds that are in the transition between atomic and molecular. We estimate that most of the observed [C ii] emission is produced by dense photon dominated regions (~47%), with smaller contributions from CO-dark H2 gas (~28%), cold atomic gas (~21%), and ionized gas (~4%). Atomic gas inside the Solar radius is mostly in the form of cold neutral medium (CNM), while the warm neutral medium gas dominates the outer galaxy. The average fraction of CNM relative to total atomic gas is ~43%. We find that the warm and diffuse CO-dark H2 is distributed over a larger range of Galactocentric distances (4-11 kpc) than the cold and dense H2 gas traced by 12CO and 13CO (4-8 kpc). The fraction of CO-dark H2 to total H2 increases with Galactocentric distance, ranging from ~20% at 4 kpc to ~80% at 10 kpc. On average, CO-dark H2 accounts for ~30% of the molecular mass of the Milky Way. When the CO-dark H2 component is included, the radial distribution of the CO-to-H2 conversion factor is steeper than that when only molecular gas traced by CO is considered. Most of the observed [C ii] emission emerging from dense photon dominated regions is associated with modest far-ultraviolet fields in the range χ0 ≃ 1 - 30. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices are available in electronic form at http://www.aanda.org

Distribution and Kinematics of Ionized Gas in the central 500pc of Seyfert Galaxies

NASA Astrophysics Data System (ADS)

Hyland, Ella; Hicks, Erin K. S.; Kade, Kiana

2018-06-01

We have characterized the spatial distribution and kinematics of the ionized hydrogen gas in a sample of 40 Seyfert galaxies as part of the KONA (Keck OSIRIS Nearby AGN) survey. An analysis of the narrow Brackett Gamma emission (2.16 microns) in the central 500 pc of these local AGN will be presented. Measurements include the azimuthal averages of the flux distribution, velocity dispersion, and emission line equivalent width. In addition, the excitation of the Brackett Gamma emission is considered using the ratio of its flux with that of molecular hydrogen (2.12 microns) as a diagnostic. A comparison of the circumnuclear narrow Brackett Gamma emission characteristics in the Seyfert type 1 and type 2 subsamples will also be presented.

Infrared Abundances and the Chemical Enrichment of the Universe

NASA Astrophysics Data System (ADS)

Smith, J. D.

Elements heavier than helium make up only a small fraction of the mass of the present day Universe, yet they heavily impact how galaxies and stars form and evolve. The chemical enrichment history of the Universe therefore forms an essential part of any complete understanding of galaxy evolution, and with the advent of incredibly sensitive IR/sub-mm/radio facilities, we are poised to begin unraveling it. Nonetheless, significant, decades-old problems plague even the most data-rich local methods of measuring gas phase metal abundance, with large (up to 10x) disagreements stemming principally from unknown and unseen temperature structure in ionized gas. The farinfared fine structure lines of oxygen offer a path out of this deadlock. Oxygen is the most important coolant of ionized gas, and the dominant metal abundance indicator. Its ground state fine structure lines, in particular [OIII] 88¼m, arise from such low-lying energy levels that they are insensitive to temperature. And unlike the faint "auroral" lines used by the gold-standard direct abundance method, they are bright, and readily observable at all metallicities. Indeed this crucial line has already been observed with ALMA in a number of galaxies directly in the era of reionization at z=7-9. Herschel has mapped and archived more than 150 nearby (d<25Mpc) galaxies on scales of 1 kiloparsec and below in the important [OIII] 88¼m line. We propose a comprehensive program to develop the far-infrared fine structure lines of oxygen into direct, empirical gas phase metal abundance measures. We will validate directly against the largest, deepest survey of direct spectroscopic optical metal abundances ever undertaken - the LBT/MODS program CHAOS. We will leverage spatially matched nebular emission lines ([NeII], [NeIII], [SIII], [SIV]) from Spitzer/IRS for ionization balance. We will employ our extensive optical IFU data (PPAK, MUSE, and VENGA) for strong line abundance comparisons, and to bridge the physical scales between Herschel/Spitzer and CHAOS. In addition, we will combine and validate decomposed radio free-free continuum as an extinction-free substitute for recombination emission for hydrogen normalization. This is the first time this unique combination of ionized gas tracers from optical through radio - spanning a factor of 200,000 in wavelength - will have been brought together on the same physical scales in a large and widely varied sample of nearby galaxies. The suite of hybrid abundance indicators we produce will enable empirical, intercomparable, temperature-insensitive, extinction-free measurements of gas phase metal abundance both locally and at high-redshift, even in dusty systems like ULIRGs where inferring abundance has traditionally been impossible. The results will impact, if not resolve, a decades long debate on the true oxygen abundance scale for galaxies. As natural byproducts of this study, we will also (1) construct a system of best practices for determining abundances of high redshift galaxies from fine structure emission lines and related measurements, and (2) produce and deliver a large line atlas of many thousands of independent spatially resolved regions within galaxies in their principal optical, mid- and far-infrared emission lines, enabling many additional studies.

High Resolution IRS Mapping of the Star-Forming Region NGC 6334 A

NASA Astrophysics Data System (ADS)

Sarma, Anuj; Abel, Nicholas; Ferland, Gary; Mayo, Elizabeth; Troland, Thomas

2005-06-01

Star formation involves the interplay of thermal, gravitational and magnetic forces. These processes lead to a dynamically evolving region in which O stars ionize the surrounding medium, and the ionized gas expands into the molecular cloud. Of these forces, magnetic effects are the least understood. A detailed analysis of the conditions in star-forming environments requires that one combine magnetic field observations with observations of the ionized, atomic, and molecular gas along with dust. We propose to carry out high-resolution IRS spectroscopy between 9.9-37.2 microns of the nearby (1.7 kpc) star-forming region NGC 6334 A. Maps of the magnetic field strength in the molecular gas exist for NGC 6334 A, yet the conditions in the H II region, the surrounding photodissociated region (PDR), and the dynamical interaction between the two regions are poorly understood. In the H II region, our proposed observation will allow us to use well-known infrared diagnostic ratios to determine the electron density, temperature, and the hardness of the continuum source. Spitzer observations of rotational transitions of molecular hydrogen and PAH emission, combined with previous observations, will allow us to determine the hydrogen density, UV radiation flux, and temperature in the PDR. We will combine our observations with theoretical calculations, using the spectral synthesis code Cloudy. Recent improvements to Cloudy include a ~1000 reaction molecular network, the ability to treat the dynamical flow of ionized gas into a molecular cloud, and the effects of magnetic pressure. Matching the observed spectra with theoretical calculations will tell us the physical conditions in the H II region and PDR, the role of magnetic fields in NGC 6334 A, and the importance of dynamics in the region. Overall, IRS observations of NGC 6334 A offers a unique opportunity to study, at high spatial resolution, many of the physical processes in star-forming regions.

The Nature of Active Galactic Nuclei with Velocity Offset Emission Lines

NASA Astrophysics Data System (ADS)

Müller-Sánchez, F.; Comerford, J.; Stern, D.; Harrison, F. A.

2016-10-01

We obtained Keck/OSIRIS near-IR adaptive optics-assisted integral-field spectroscopy to probe the morphology and kinematics of the ionized gas in four velocity-offset active galactic nuclei (AGNs) from the Sloan Digital Sky Survey. These objects possess optical emission lines that are offset in velocity from systemic as measured from stellar absorption features. At a resolution of ˜0.″18, OSIRIS allows us to distinguish which velocity offset emission lines are produced by the motion of an AGN in a dual supermassive black hole system, and which are produced by outflows or other kinematic structures. In three galaxies, J1018+2941, J1055+1520, and J1346+5228, the spectral offset of the emission lines is caused by AGN-driven outflows. In the remaining galaxy, J1117+6140, a counterrotating nuclear disk is observed that contains the peak of Paα emission 0.″2 from the center of the galaxy. The most plausible explanation for the origin of this spatially and kinematically offset peak is that it is a region of enhanced Paα emission located at the intersection zone between the nuclear disk and the bar of the galaxy. In all four objects, the peak of ionized gas emission is not spatially coincident with the center of the galaxy as traced by the peak of the near-IR continuum emission. The peaks of ionized gas emission are spatially offset from the galaxy centers by 0.″1-0.″4 (0.1-0.7 kpc). We find that the velocity offset originates at the location of this peak of emission, and the value of the offset can be directly measured in the velocity maps. The emission-line ratios of these four velocity-offset AGNs can be reproduced only with a mixture of shocks and AGN photoionization. Shocks provide a natural explanation for the origin of the spatially and spectrally offset peaks of ionized gas emission in these galaxies. Based on observations at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Breakdown voltage reduction by field emission in multi-walled carbon nanotubes based ionization gas sensor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saheed, M. Shuaib M.; Muti Mohamed, Norani; Arif Burhanudin, Zainal, E-mail: zainabh@petronas.com.my

2014-03-24

Ionization gas sensors using vertically aligned multi-wall carbon nanotubes (MWCNT) are demonstrated. The sharp tips of the nanotubes generate large non-uniform electric fields at relatively low applied voltage. The enhancement of the electric field results in field emission of electrons that dominates the breakdown mechanism in gas sensor with gap spacing below 14 μm. More than 90% reduction in breakdown voltage is observed for sensors with MWCNT and 7 μm gap spacing. Transition of breakdown mechanism, dominated by avalanche electrons to field emission electrons, as decreasing gap spacing is also observed and discussed.

Eta Carinae's Thermal X-Ray Tail Measured with XMM-Newton and NuStar

NASA Technical Reports Server (NTRS)

Hamaguchi, Kenji; Corcoran, Michael F.; Gull, Theodore R.; Takahashi, Hiromitsu; Grefenstette, Brian; Yuasa, Takayuki; Stuhlinger, Martin; Russell, Christopher; Moffat, Anthony F. J.; Madura, Thomas

2016-01-01

The evolved, massive highly eccentric binary system, Car, underwent a periastron passage in the summer of 2014. We obtained two coordinated X-ray observations with XMM-Newton and NuSTAR during the elevated X-ray flux state and just before the X-ray minimum flux state around this passage. These NuSTAR observations clearly detected X-ray emission associated with eta Car extending up to approx. 50 keV for the first time. The NuSTAR spectrum above 10 keV can be fit with the bremsstrahlung tail from a kT approx. 6 keV plasma. This temperature is delta kT 2 keV higher than those measured from the iron K emission line complex, if the shocked gas is in collisional ionization equilibrium. This result may suggest that the companion star's pre-shock wind velocity is underestimated. The NuSTAR observation near the X-ray minimum state showed a gradual decline in the X-ray emission by 40% at energies above 5 keV in a day, the largest rate of change of the X-ray flux yet observed in individual eta Car observations. The column density to the hardest emission component, N(sub H) approx. 10(exp24) H cm(exp-2), marked one of the highest values ever observed for eta Car, strongly suggesting the increased obscuration of the wind-wind colliding X-ray emission by the thick primary stellar wind prior to superior conjunction. Neither observation detected the power-law component in the extremely hard band that INTEGRAL and Suzaku observed prior to 2011. The power-law source might have faded before these observations.

Feeding and Feedback in the Powerful Radio Galaxy 3C 120

NASA Technical Reports Server (NTRS)

Tombesi, F.; Mushotzky, R. F.; Reynolds, C. S.; Kallman, T.; Reeves, J. N.; Braito, V.; Ueda, Y.; Leutenegger, M. A.; Williams, B. J.; Stawarz, L.;

Stellar physics. Observing the onset of outflow collimation in a massive protostar.

PubMed

Carrasco-González, C; Torrelles, J M; Cantó, J; Curiel, S; Surcis, G; Vlemmings, W H T; van Langevelde, H J; Goddi, C; Anglada, G; Kim, S-W; Kim, J-S; Gómez, J F

2015-04-03

The current paradigm of star formation through accretion disks, and magnetohydrodynamically driven gas ejections, predicts the development of collimated outflows, rather than expansion without any preferential direction. We present radio continuum observations of the massive protostar W75N(B)-VLA 2, showing that it is a thermal, collimated ionized wind and that it has evolved in 18 years from a compact source into an elongated one. This is consistent with the evolution of the associated expanding water-vapor maser shell, which changed from a nearly circular morphology, tracing an almost isotropic outflow, to an elliptical one outlining collimated motions. We model this behavior in terms of an episodic, short-lived, originally isotropic ionized wind whose morphology evolves as it moves within a toroidal density stratification. Copyright © 2015, American Association for the Advancement of Science.

High resolution spectroscopy of the disk chromosphere. II - Time sequence observations of Ca II H and K emissions.

NASA Technical Reports Server (NTRS)

Wilson, P. R.; Rees, D. E.; Beckers, J. M.; Brown, D. R.

1972-01-01

Two independent sets of high resolution time series spectra of the Ca II H and K emission obtained at the Solar Tower and at the Big Dome of the Sacramento Peak Observatory on September 11th, 1971 are reported. The evolutionary behavior of the emission first reported by Wilson and Evans is confirmed, but the detail of the evolution is found to be more complex. In one case, a doubly peaked feature showing some K3 emission evolves into a single K2 (red) peak with no K3 emission. Coincidentally, a neighboring doubly peaked feature evolves to a very strong blue peak. In an entirely independent sequence a doubly peaked feature evolves into a single red peak. The K2 emission then fades completely although the continuum threads are still strong. Finally a strong K2 blue peak appears. It is concluded that the observed evolution of the K2 emission is due to temporal variations in the physical conditions which give rise to them.

Photoionization Models of the H_2 Emission of the Narrow Line Region of AGNs

NASA Astrophysics Data System (ADS)

Aleman, I.; Gruenwald, R.

2011-05-01

The excitation mechanism of the narrow line region (NLR) of AGNs is still an open question. Excitation by UV radiation from O and B stars, x-rays from the central black hole, shock from supernovae or jets, or a combination of these mechanisms have been suggested. In the present work, we use photoionization models to study the excitation mechanisms of the H_2 infrared emission lines in the NLR. In the literature, analyzes of the H_2 emission have been done assuming that the molecules is present only in neutral regions (photodissociation regions, x-ray-dominated regions, or shocks; Veilleux et al. 1997, Krabbe et al. 2000, Rigopoulou et al. 2002, Rodriguez-Ardila et al. 2004, 2005, and Davies et al. 2005). However, they are not conclusive. In previous work (Aleman & Gruenwald 2004, 2011), we show that the H_2 emission from the ionized region of PNe can be significant for planetary nebulae (PNe) with hot central stars (T⋆ > 150000 K). Such stars produce copious amounts of high energy photons, which create an extended partially ionized region that favors the H_2 survival. The conditions in the NLR are similar to those in PNe with hot central stars, so we can expect that the H_2 emission might also be important. We obtain and analyze a grid of photoionization models for different NRL parameters. We study the resulting H_2 density and emission, as well as, the formation, destruction, excitation, and de-excitation mechanisms. The higher values observed for the H_2 1-0 S(1)/Brγ ratio cannot be reproduced by our models. The calculated ratios are between 10^-8 and 10^-1, while the observational ration can be as high as 10. The calculated ratio is strongly anti-correlated with the ionization parameter (U) and only models with U<10-3 result in ratios inside the observational range. We show that the NLR is an environment more hostile to the H_2 molecule than the ionized region of PNe. Another interesting result of our calculations is that the H_2 formation on grain surfaces is more important in the NLR than in the ionized region of PNe.

The Origins of [C ii] Emission in Local Star-forming Galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Croxall, K. V.; Smith, J. D.; Pellegrini, E.

The [C ii] 158 μ m fine-structure line is the brightest emission line observed in local star-forming galaxies. As a major coolant of the gas-phase interstellar medium, [C ii] balances the heating, including that due to far-ultraviolet photons, which heat the gas via the photoelectric effect. However, the origin of [C ii] emission remains unclear because C{sup +} can be found in multiple phases of the interstellar medium. Here we measure the fractions of [C ii] emission originating in the ionized and neutral gas phases of a sample of nearby galaxies. We use the [N ii] 205 μ m fine-structuremore » line to trace the ionized medium, thereby eliminating the strong density dependence that exists in the ratio of [C ii]/[N ii] 122 μ m. Using the FIR [C ii] and [N ii] emission detected by the KINGFISH (Key Insights on Nearby Galaxies: a Far- Infrared Survey with Herschel ) and Beyond the Peak Herschel programs, we show that 60%–80% of [C ii] emission originates from neutral gas. We find that the fraction of [C ii] originating in the neutral medium has a weak dependence on dust temperature and the surface density of star formation, and has a stronger dependence on the gas-phase metallicity. In metal-rich environments, the relatively cooler ionized gas makes substantially larger contributions to total [C ii] emission than at low abundance, contrary to prior expectations. Approximate calibrations of this metallicity trend are provided.« less

VizieR Online Data Catalog: Diffuse ionized gas in the Antennae galaxy (Weilbacher+, 2018)

NASA Astrophysics Data System (ADS)

Weilbacher, P. M.; Monreal-Ibero, A.; Verhamme, A.; Sandin, C.; Steinmetz, M.; Kollatschny, W.; Krajnovic, D.; Kamann, S.; Roth, M. M.; Erroz-Ferrer, S.; Marino, R. A.; Maseda, M. V.; Wendt, M.; Bacon, R.; Dreizler, S.; Richard, J.; Wisotzki, L.

2017-11-01

We provide two-dimensional maps of two different ways to measure the diffuse ionized gas as traced by the Halpha emission line in the Antennae Galaxy, both for the central field and the field at the end of the southern tidal tail. We provide a velocity map derived from the Halpha emission line, binned to a S/N~30. Finally, we provide line measurements and derived properties for all HII regions discussed in the paper. (4 data files).

Donor ionization in size controlled silicon nanocrystals: The transition from defect passivation to free electron generation

NASA Astrophysics Data System (ADS)

Crowe, I. F.; Papachristodoulou, N.; Halsall, M. P.; Hylton, N. P.; Hulko, O.; Knights, A. P.; Yang, P.; Gwilliam, R. M.; Shah, M.; Kenyon, A. J.

2013-01-01

We studied the photoluminescence spectra of silicon and phosphorus co-implanted silica thin films on (100) silicon substrates as a function of isothermal annealing time. The rapid phase segregation, formation, and growth dynamics of intrinsic silicon nanocrystals are observed, in the first 600 s of rapid thermal processing, using dark field mode X-TEM. For short annealing times, when the nanocrystal size distribution exhibits a relatively small mean diameter, formation in the presence of phosphorus yields an increase in the luminescence intensity and a blue shift in the emission peak compared with intrinsic nanocrystals. As the mean size increases with annealing time, this enhancement rapidly diminishes and the peak energy shifts further to the red than the intrinsic nanocrystals. These results indicate the existence of competing pathways for the donor electron, which depends strongly on the nanocrystal size. In samples containing a large density of relatively small nanocrystals, the tendency of phosphorus to accumulate at the nanocrystal-oxide interface means that ionization results in a passivation of dangling bond (Pb-centre) type defects, through a charge compensation mechanism. As the size distribution evolves with isothermal annealing, the density of large nanocrystals increases at the expense of smaller nanocrystals, through an Ostwald ripening mechanism, and the majority of phosphorus atoms occupy substitutional lattice sites within the nanocrystals. As a consequence of the smaller band-gap, ionization of phosphorus donors at these sites increases the free carrier concentration and opens up an efficient, non-radiative de-excitation route for photo-generated electrons via Auger recombination. This effect is exacerbated by an enhanced diffusion in phosphorus doped glasses, which accelerates silicon nanocrystal growth.

Investigation of Plasmas Having Complex, Dynamic Evolving Morphology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bellan, Paul M.

2017-01-03

Three different types of plasmas have been investigated using both experimental and theoretical methods. The first type of plasma is dense, highly ionized, governed by magnetohydrodynamics, and highly dynamic. This plasma is relevant to solar coronal loops, astrophysical jets, and other situations where strong magnetic forces act on the plasma. A well-diagnosed laboratory experiment creates a magnetohydrodynamically driven highly collimated plasma jet. This jet undergoes a kink instability such that it rapidly develops a corkscrew shape. The kink causes lateral acceleration of the jet, and this lateral acceleration drives a Rayleigh-Taylor instability that in turn chokes the current flowing inmore » the jet and causes a magnetic reconnection. The magnetic reconnection causes electron and ion heating as well as emission of whistler waves. This entire sequence of events has been observed, measured in detail, and related to theoretical models. The second type of plasma is a transient rf-produced plasma used as a seed plasma for the magnetohydrodynamic experiments described above. Detailed atomic physics ionization processes have been investigated and modeled. The third type of plasma that has been studied is a dusty plasma where the dust particles are spontaneously growing ice grains. The rapid growth of the ice grains to large size and their highly ordered alignment has been investigated as well as collective motion of the ice grains, including well-defined flows on the surface of nested toroids. In addition to the experimental work described above, several related theoretical models have been developed, most notably a model showing how a complex interaction between gravity and magnetic fields on extremely weakly ionized plasma in an accretion disk provides an electric power source that can drive astrophysical jets associated with the accretion disk. Eighteen papers reporting this work have been published in a wide variety of journals.« less

MOLECULAR AND IONIZED HYDROGEN IN 30 DORADUS. I. IMAGING OBSERVATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yeh, Sherry C. C.; Seaquist, Ernest R.; Matzner, Christopher D.

2015-07-10

We present the first fully calibrated H{sub 2} 1–0 S(1) image of the entire 30 Doradus nebula. The observations were conducted using the NOAO Extremely Wide-field Infrared Imager (NEWFIRM) on the CTIO 4 m Blanco Telescope. Together with a NEWFIRM Brγ image of 30 Doradus, our data reveal the morphologies of the warm molecular gas and ionized gas in 30 Doradus. The brightest H{sub 2}-emitting area, which extends from the northeast to the southwest of R136, is a photodissociation region (PDR) viewed face-on, while many clumps and pillar features located at the outer shells of 30 Doradus are PDRs viewedmore » edge-on. Based on the morphologies of H{sub 2}, Brγ, CO, and 8 μm emission, the H{sub 2} to Brγ line ratio, and Cloudy models, we find that the H{sub 2} emission is formed inside the PDRs of 30 Doradus, 2–3 pc to the ionization front of the H ii region, in a relatively low-density environment <10{sup 4} cm{sup −3}. Comparisons with Brγ, 8 μm, and CO emission indicate that H{sub 2} emission is due to fluorescence, and provide no evidence for shock excited emission of this line.« less

Ionized and Molecular Gas in IC 860: Evidence for an Outflow

NASA Astrophysics Data System (ADS)

Adams, Carson; Alatalo, Katherine; Medling, Anne M.

2018-01-01

Galaxies at present-day fall predominantly in two distinct populations, as either blue, star-forming spirals or red, quiescent early-type galaxies. Blue galaxies appear to evolve onto the red sequence as star formation is quenched. The absence of a significant population falling in the intermediate ‘green valley’ implies that these transitions must occur rapidly. Identifying the initial properties of and pathways taken by these ‘dying galaxies’ is essential to building a complete understanding of galactic evolution. In this work, we investigate these phenomena in action within IC860 — a nearby, early-type spiral in the initial stages of undergoing a rapid transition in the presence of a powerful AGN-driven molecular outflow. As a shocked, post-starburst galaxy with an intermediate-age stellar population which lies on the blue end of the green valley, IC860 provides a window into the early stages of galaxy transition and AGN feedback. We present Hubble Space Telescope imaging of IC860 showing a violent, dusty outflow originating from a compact core. We find that the mean velocity map of the CO(1-0) from CARMA suggests a dynamically excited bar funneling molecular gas into the galactic center. Finally, we present kinematic maps of ionized gas emission lines as well as sodium D absorption tracing neutral winds obtained by the Wide-Field Spectrograph.

First detection of winds in red giants by microwave continuum techniques

NASA Technical Reports Server (NTRS)

Drake, S. A.; Linsky, J. L.

1983-01-01

Eight red giants and supergiants have been observed at 4885 MHz (6 cm) with the Very Large Array in an attempt to detect continuum emission. The bright giant Alpha-1 Her (M5 II) was detected at an average flux density of 0.9 + or - 0.13 mJy. Since the likely source of this emission is an ionized, optically thick component of a stellar wind, this detection implies a mass loss rate of 2 x 10 to the -9th solar masses per yr for the ionized gas. The fraction of the outflow in Alpha-1 Her that is ionized (0.002-0.02) seems to be similar to that previously found for Alpha Ori and Alpha Sco A. Alpha Boo (K2 IIIp) and Beta Gem (K0 III) are probable and definite detections, respectively. The derived ionized mass loss rates for these two stars are about 1 x 10 to the -10th solar masses per yr, implying in the case of Alpha Boo that the wind is largely ionized.

Photoionization and heating of a supernova-driven turbulent interstellar medium

NASA Astrophysics Data System (ADS)

Barnes, J. E.; Wood, Kenneth; Hill, Alex S.; Haffner, L. M.

2014-06-01

The diffuse ionized gas (DIG) in galaxies traces photoionization feedback from massive stars. Through three-dimensional photoionization simulations, we study the propagation of ionizing photons, photoionization heating and the resulting distribution of ionized and neutral gas within snapshots of magnetohydrodynamic simulations of a supernova-driven turbulent interstellar medium. We also investigate the impact of non-photoionization heating on observed optical emission line ratios. Inclusion of a heating term which scales less steeply with electron density than photoionization is required to produce diagnostic emission line ratios similar to those observed with the Wisconsin Hα Mapper. Once such heating terms have been included, we are also able to produce temperatures similar to those inferred from observations of the DIG, with temperatures increasing to above 15 000 K at heights |z| ≳ 1 kpc. We find that ionizing photons travel through low-density regions close to the mid-plane of the simulations, while travelling through diffuse low-density regions at large heights. The majority of photons travel small distances (≲100 pc); however some travel kiloparsecs and ionize the DIG.

Multistep Ionization of Argon Clusters in Intense Femtosecond Extreme Ultraviolet Pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bostedt, C.; Thomas, H.; Hoener, M.

The interaction of intense extreme ultraviolet femtosecond laser pulses ({lambda}=32.8 nm) from the FLASH free electron laser (FEL) with clusters has been investigated by means of photoelectron spectroscopy and modeled by Monte Carlo simulations. For laser intensities up to 5x10{sup 13} W/cm{sup 2}, we find that the cluster ionization process is a sequence of direct electron emission events in a developing Coulomb field. A nanoplasma is formed only at the highest investigated power densities where ionization is frustrated due to the deep cluster potential. In contrast with earlier studies in the IR and vacuum ultraviolet spectral regime, we find nomore » evidence for electron emission from plasma heating processes.« less

A singly charged ion source for radioactive {sup 11}C ion acceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katagiri, K.; Noda, A.; Nagatsu, K.

2016-02-15

A new singly charged ion source using electron impact ionization has been developed to realize an isotope separation on-line system for simultaneous positron emission tomography imaging and heavy-ion cancer therapy using radioactive {sup 11}C ion beams. Low-energy electron beams are used in the electron impact ion source to produce singly charged ions. Ionization efficiency was calculated in order to decide the geometric parameters of the ion source and to determine the required electron emission current for obtaining high ionization efficiency. Based on these considerations, the singly charged ion source was designed and fabricated. In testing, the fabricated ion source wasmore » found to have favorable performance as a singly charged ion source.« less

Detection of blueshifted emission and absorption and a relativistic iron line in the X-ray spectrum of ESO323-G077

NASA Astrophysics Data System (ADS)

Jiménez-Bailón, E.; Krongold, Y.; Bianchi, S.; Matt, G.; Santos-Lleó, M.; Piconcelli, E.; Schartel, N.

2008-12-01

We report on the X-ray observation of the Seyfert 1 galaxy ESO323-G077 performed with XMM-Newton. The EPIC spectra show a complex spectrum with conspicuous absorption and emission features. The continuum emission can be modelled with a power law with an index of 1.99 +/- 0.02 in the whole XMM-Newton energy band, marginally consistent with typical values of type I objects. An absorption component with an uncommonly high equivalent hydrogen column (nH = 5.82+0.12-0.11 × 1022cm-2) is affecting the soft part of the spectrum. Additionally, two warm absorption components are also present in the spectrum. The lower ionized one, mainly imprinting the soft band of the spectrum, has an ionization parameter of logU = 2.14+0.06-0.07 and an outflowing velocity of v = 3200+600-200kms-1. Two absorption lines located at ~6.7 and ~7.0keV can be modelled with the highly ionized absorber. The ionization parameter and outflowing velocity of the gas measured are logU = 3.26+0.19-0.15 and v = 1700+600-400kms-1, respectively. Four emission lines were also detected in the soft energy band. The most likely explanation for these emission lines is that they are associated with an outflowing gas with a velocity of ~2000kms-1. The data suggest that the same gas which is causing the absorption could also being responsible of these emission features. Finally, the XMM-Newton spectrum shows the presence of a relativistic iron emission line likely originated in the accretion disc of a Kerr black hole with an inclination of ~25°. We propose a model to explain the observed X-ray properties which invokes the presence of a two-phase outflow with cone-like structure and a velocity of the order of 2000- 4000kms-1. The inner layer of the cone would be less ionized, or even neutral, than the outer layer. The inclination angle of the source would be lower than the opening angle of the outflowing cone. Partially based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. E-mail: elena@astroscu.unam.mx

Weakly ionized cosmic gas: Ionization and characterization

NASA Technical Reports Server (NTRS)

Rosenberg, M.; Mendis, D. A.; Chow, V. W.

1994-01-01

Since collective plasma behavior may determine important transport processes (e.g., plasma diffusion across a magnetic field) in certain cosmic environments, it is important to delineate the parameter space in which weakly ionized cosmic gases may be characterized as plasmas. In this short note, we do so. First, we use values for the ionization fraction given in the literature, wherein the ionization is generally assumed to be due primarily to ionization by cosmic rays. We also discuss an additional mechanism for ionization in such environments, namely, the photoelectric emission of electrons from cosmic dust grains in an interstellar Far Ultra Violet (FUV) radiation field. Simple estimates suggest that under certain conditions this mechanism may dominate cosmic ray ionization, and possibly also the photoionization of metal atoms by the interstellar FUV field, and thereby lead to an enhanced ionization level.

Early evolution of the extraordinary Nova Delphini 2013 (V339 Del)

NASA Astrophysics Data System (ADS)

Skopal, A.; Drechsel, H.; Tarasova, T.; Kato, T.; Fujii, M.; Teyssier, F.; Garde, O.; Guarro, J.; Edlin, J.; Buil, C.; Antao, D.; Terry, J.-N.; Lemoult, T.; Charbonnel, S.; Bohlsen, T.; Favaro, A.; Graham, K.

2014-09-01

Aims: We determine the temporal evolution of the luminosity (LWD), radius (RWD) and effective temperature (Teff) of the white dwarf (WD) pseudophotosphere of V339 Del from its discovery to around day 40. Another main objective was studying the ionization structure of the ejecta. Methods: These aims were achieved by modelling the optical/near-IR spectral energy distribution (SED) using low-resolution spectroscopy (3500-9200 Å), UBVRCIC and JHKLM photometry. Important insights in the physical conditions of the ejecta were gained from an analysis of the evolution of the Hα and Raman-scattered 6825 Å O vi line using medium-resolution spectroscopy (R ~ 10 000). Results: During the fireball stage (Aug. 14.8-19.9, 2013), Teff was in the range of 6000-12 000 K, RWD was expanding non-uniformly in time from ~66 to ~300 (d/ 3 kpc) R⊙, and LWD was super-Eddington, but not constant. Its maximum of ~9 × 1038 (d/ 3 kpc)2 erg s-1 occurred around Aug. 16.0, at the maximum of Teff, half a day before the visual maximum. After the fireball stage, a large emission measure of 1.0-2.0 × 1062 (d/ 3 kpc)2 cm-3 constrained the lower limit of LWD to be well above the super-Eddington value. The mass of the ionized region was a few × 10-4 M⊙, and the mass-loss rate was decreasing from ~5.7 (Aug. 22) to ~0.71 × 10-4 M⊙ yr-1 (Sept. 20). The evolution of the Hα line and mainly the transient emergence of the Raman-scattered O vi 1032 Å line suggested a biconical ionization structure of the ejecta with a disk-like H i region persisting around the WD until its total ionization, around day 40. On Sept. 20 (day 35), the model SED indicated a dust emission component in the spectrum. The dust was located beyond the H i zone, where it was shielded from the hard, ≳105 K, radiation of the burning WD at that time. Conclusions: Our extensive spectroscopic observations of the classical nova V339 Del allowed us to map its evolution from the very early phase after its explosion. It is evident that the nova was not evolving according to the current theoretical prediction. The unusual non-spherically symmetric ejecta of nova V339 Del and its extreme physical conditions and evolution during and after the fireball stage represent interesting new challenges for the theoretical modelling of the nova phenomenon. Based on data collected by amateur astronomers.

Carbon-, sulfur-, and phosphorus-based charge transfer reactions in inductively coupled plasma-atomic emission spectrometry

NASA Astrophysics Data System (ADS)

Grindlay, Guillermo; Gras, Luis; Mora, Juan; de Loos-Vollebregt, Margaretha T. C.

2016-01-01

In this work, the influence of carbon-, sulfur-, and phosphorus-based charge transfer reactions on the emission signal of 34 elements (Ag, Al, As, Au, B, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, Ga, Hg, I, In, Ir, K, Li, Mg, Mn, Na, Ni, P, Pb, Pd, Pt, S, Sb, Se, Sr, Te, and Zn) in axially viewed inductively coupled plasma-atomic emission spectrometry has been investigated. To this end, atomic and ionic emission signals for diluted glycerol, sulfuric acid, and phosphoric acid solutions were registered and results were compared to those obtained for a 1% w w- 1 nitric acid solution. Experimental results show that the emission intensities of As, Se, and Te atomic lines are enhanced by charge transfer from carbon, sulfur, and phosphorus ions. Iodine and P atomic emission is enhanced by carbon- and sulfur-based charge transfer whereas the Hg atomic emission signal is enhanced only by carbon. Though signal enhancement due to charge transfer reactions is also expected for ionic emission lines of the above-mentioned elements, no experimental evidence has been found with the exception of Hg ionic lines operating carbon solutions. The effect of carbon, sulfur, and phosphorus charge transfer reactions on atomic emission depends on (i) wavelength characteristics. In general, signal enhancement is more pronounced for electronic transitions involving the highest upper energy levels; (ii) plasma experimental conditions. The use of robust conditions (i.e. high r.f. power and lower nebulizer gas flow rates) improves carbon, sulfur, and phosphorus ionization in the plasma and, hence, signal enhancement; and (iii) the presence of other concomitants (e.g. K or Ca). Easily ionizable elements reduce ionization in the plasma and consequently reduce signal enhancement due to charge transfer reactions.

The VLA Nascent Disk And Multiplicity Survey of Perseus Protostars (VANDAM). III. Extended Radio Emission from Protostars in Perseus

NASA Astrophysics Data System (ADS)

Tychoniec, Łukasz; Tobin, John J.; Karska, Agata; Chandler, Claire; Dunham, Michael M.; Li, Zhi-Yun; Looney, Leslie W.; Segura-Cox, Dominique; Harris, Robert J.; Melis, Carl; Sadavoy, Sarah I.

2018-01-01

Centimeter continuum emission from protostars offers insight into the innermost part of the outflows, as shock-ionized gas produces free–free emission. We observed a complete population of Class 0 and I protostars in the Perseus molecular cloud at 4.1 and 6.4 cm with resolution and sensitivity superior to previous surveys. From a total of 71 detections, eight sources exhibit resolved emission at 4.1 cm and/or 6.4 cm. In this paper, we focus on this subsample, analyzing their spectral indices along the jet and their alignment with respect to the large-scale molecular outflow. Spectral indices for fluxes integrated toward the position of the protostar are consistent with free–free thermal emission. The value of the spectral index along a radio jet decreases with distance from the protostar. For six sources, emission is well aligned with the outflow central axis, showing that we observe the ionized base of the jet. This is not the case for two sources, where we note misalignment of the emission with respect to the large-scale outflow. This might indicate that the emission does not originate in the radio jet, but rather in an ionized outflow cavity wall or disk surface. For five of the sources, the spectral indices along the jet decrease well below the thermal free–free limit of ‑0.1 with > 2σ significance. This is indicative of synchrotron emission, meaning that high-energy electrons are being produced in the outflows close to the disk. This result can have far-reaching implications for the chemical composition of the embedded disks.

Photon underproduction crisis and the redshift evolution of escape fraction of hydrogen ionizing photons from galaxies

NASA Astrophysics Data System (ADS)

Khaire, Vikram; Srianand, Raghunathan

2016-01-01

In the standard picture, the only sources of cosmic UV background are the quasars and the star forming galaxies. The hydrogen ionizing emissivity from galaxies depends on a parameter known as escape fraction (fesc). It is the ratio of the escaping hydrogen ionizing photons from galaxies to the total produced by their stellar population. Using available multi-wavelength and multi-epoch galaxy luminosity function measurements, we update the galaxy emissivity by estimating a self-consistent combination of the star formation rate density and dust attenuation. Using the recent quasar luminosity function measurements, we present an updated hydrogen ionizing emissivity from quasars which shows a factor of ~2 increase as compared to the previous estimates at z<2. We use these in a cosmological radiative transfer code developed by us to generate the UV background and show that the recently inferred high values of hydrogen photoionization rates at low redshifts can be easily obtained with reasonable values of fesc. This resolves the problem of 'photon underproduction crisis' and shows that there is no need to invoke non-standard sources of the UV background such as decaying dark matter particles. We will present the implications of this updated quasar and galaxy emissivity on the values of fesc at high redshifts and on the cosmic reionization. We will also present the effect of the updated UV background on the inferred properties of the intergalactic medium, especially on the Lyman alpha forest and the metal line absorption systems.

Shocked POststarbust Galaxy Survey. I. Candidate Post-starbust Galaxies with Emission Line Ratios Consistent with Shocks

NASA Astrophysics Data System (ADS)

Alatalo, Katherine; Cales, Sabrina L.; Rich, Jeffrey A.; Appleton, Philip N.; Kewley, Lisa J.; Lacy, Mark; Lanz, Lauranne; Medling, Anne M.; Nyland, Kristina

2016-06-01

There are many mechanisms by which galaxies can transform from blue, star-forming spirals, to red, quiescent early-type galaxies, but our current census of them does not form a complete picture. Recent observations of nearby case studies have identified a population of galaxies that quench “quietly.” Traditional poststarburst searches seem to catch galaxies only after they have quenched and transformed, and thus miss any objects with additional ionization mechanisms exciting the remaining gas. The Shocked POststarburst Galaxy Survey (SPOGS) aims to identify transforming galaxies, in which the nebular lines are excited via shocks instead of through star formation processes. Utilizing the Oh-Sarzi-Schawinski-Yi (OSSY) measurements on the Sloan Digital Sky Survey Data Release 7 catalog, we applied Balmer absorption and shock boundary criteria to identify 1067 SPOG candidates (SPOGs*) within z = 0.2. SPOGs* represent 0.2% of the OSSY sample galaxies that exceed the continuum signal-to-noise cut (and 0.7% of the emission line galaxy sample). SPOGs* colors suggest that they are in an earlier phase of transition than OSSY galaxies that meet an “E+A” selection. SPOGs* have a 13% 1.4 GHz detection rate from the Faint Images of the Radio Sky at Twenty Centimeters Survey, higher than most other subsamples, and comparable only to low-ionization nuclear emission line region hosts, suggestive of the presence of active galactic nuclei (AGNs). SPOGs* also have stronger Na I D absorption than predicted from the stellar population, suggestive of cool gas being driven out in galactic winds. It appears that SPOGs* represent an earlier phase in galaxy transformation than traditionally selected poststarburst galaxies, and that a large proportion of SPOGs* also have properties consistent with disruption of their interstellar media, a key component to galaxy transformation. It is likely that many of the known pathways to transformation undergo a SPOG phase. Studying this sample of SPOGs* further, including their morphologies, AGN properties, and environments, has the potential for us to build a more complete picture of the initial conditions that can lead to a galaxy evolving.

INDIRECT EVIDENCE FOR ESCAPING IONIZING PHOTONS IN LOCAL LYMAN BREAK GALAXY ANALOGS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alexandroff, Rachael M.; Heckman, Timothy M.; Borthakur, Sanchayeeta

2015-09-10

A population of early star-forming galaxies is the leading candidate for the re-ionization of the universe. It is still unclear, however, what conditions and physical processes would enable a significant fraction of the ionizing (Lyman continuum) photons to escape from these gas-rich galaxies. In this paper we present the results of the analysis of Hubble Space Telescope Cosmic Origins Spectrograph far-UV (FUV) spectroscopy plus ancillary multi-waveband data of a sample of 22 low-redshift galaxies that are good analogs to typical star-forming galaxies at high redshift. We measure three parameters that provide indirect evidence of the escape of ionizing radiation (leakiness):more » (1) the residual intensity in the cores of saturated interstellar low-ionization absorption lines, which indicates incomplete covering by that gas in the galaxy; (2) the relative amount of blueshifted Lyα line emission, which can indicate the existence of holes in the neutral hydrogen on the front-side of the galaxy outflow, and (3) the relative weakness of the [S ii] optical emission lines that trace matter-bounded H ii regions. We show that our residual intensity measures are only negligibly affected by infilling from resonance emission lines. We find all three diagnostics agree well with one another. We use these diagnostics to rank-order our sample in terms of likely leakiness, noting that a direct measure of escaping Lyman continuum has recently been made for one of the leakiest members of our sample. We then examine the correlations between our ranking and other proposed diagnostics of leakiness. We find a good correlation with the equivalent width of the Lyα emission line, but no significant correlations with either the flux ratio of the [O iii]/[O ii] emission lines or the ratio of star-formation rates derived from the (dust-corrected) FUV and Hα luminosities. Turning to galaxy properties, we find the strongest correlations with leakiness are with the compactness of the star-forming region (Star formation rate/area) and the speed of the galactic outflow. This suggests that extreme feedback—a high intensity of ionizing radiation and strong pressure from both radiation and a hot galactic wind—combines to create significant holes in the neutral gas. These results not only shed new light on the physical mechanisms that can allow ionizing radiation to escape from intensely star-forming galaxies, they also provide indirect observational indicators that can be used at high redshift where direct measurements of escaping Lyman continuum radiation are impossible.« less

Kinematics of the Diffuse Ionized Gas Disk of Andromeda

NASA Astrophysics Data System (ADS)

Thelen, Alexander; Howley, K.; Guhathakurta, P.; Dorman, C.; SPLASH Collaboration

2012-01-01

This research focuses on the flattened rotating diffuse ionized gas (DIG) disk of the Andromeda Galaxy (M31). For this we use spectra from 25 multislit masks obtained by the SPLASH collaboration using the DEIMOS spectrograph on the Keck-II 10-meter telescope. Each mask contains 200 slits covering the region around M32 (S of the center of M31), the major axis of M31, and the SE minor axis. DIG emission was serendipitously detected in the background sky of these slits. By creating a normalized "sky spectrum” to remove various other sources of emission (such as night sky lines) in the background of these slits, we have examined the rotation of the DIG disk using individual line-of-sight velocity measurements of Hα, [NII] and [SII] emission. his emission is probably the result of newly formed stars ionizing the gas in the disk. The measured IG rotation will be compared to the rotation of M31's stellar disk and HI gas disk, as well as models of an infinitely thin rotating disk, to better understand the relationship between the components of the galactic disk and its differential rotation. We wish to acknowledge the NSF for funding on this project.

Extreme Ultraviolet Spectra of Few-Times Ionized Tungsten for Divertor Plasma Diagnostics

DOE PAGES

Clementson, Joel; Lennartsson, Thomas; Beiersdorfer, Peter

2015-09-09

The extreme ultraviolet (EUV) emission from few-times ionized tungsten atoms has been experimentally studied at the Livermore electron beam ion trap facility. The ions were produced and confined during low-energy operations of the EBIT-I electron beam ion trap. By varying the electron-beam energy from around 30–300 eV, tungsten ions in charge states expected to be abundant in tokamak divertor plasmas were excited, and the resulting EUV emission was studied using a survey spectrometer covering 120–320 Å. It is found that the emission strongly depends on the excitation energy; below 150 eV, it is relatively simple, consisting of strong isolated linesmore » from a few charge states, whereas at higher energies, it becomes very complex. For divertor plasmas with tungsten impurity ions, this emission should prove useful for diagnostics of tungsten flux rates and charge balance, as well as for radiative cooling of the divertor volume. Several lines in the 194–223 Å interval belonging to the spectra of five- and seven-times ionized tungsten (Tm-like W VI and Ho-like W VIII) were also measured using a high-resolution spectrometer.« less

[Morphology determination of ionization region in multi-needle-to-plate negative corona discharge].

PubMed

Su, Peng-Hao; Zhu, Yi-Min; Chen, Hai-Feng

2007-11-01

Based on the former work on the current-voltage characteristics of a multi-needle-to-plate negative corona discharge at atmospheric pressure, the present work uses the method of OES (optical emission spectrum) for measuring N2 emission spectrum, and the morphology determination of the ionization region has been investigated. According to the distribution of N2 second positive band's intensity I(SPB), the highest of all bands, the outline of the ionization region was drawn fairly accurately. The relationship between I(SPB) and discharge current I can be obtained through the volume integral of the I(SPB). The experimental results show that the size of the ionization region enhances with the rise of the applied voltage U, and the electron avalanche begins at about 1 mm off the tips of needle electrode and multiplies only in the range of several millimeters, indicating that, the range of the ionization region is at the magnitude of mm. The electron avalanche along the axis of the needle develops farther than that along the radial direction of needle, and the shape of the ionization region looks like a bullet. The integral of I(SPB) is second-order linear to I, with a very second order coefficient, meaning that the main excited substance is N2. Energetic electrons mainly exist in ionization region while ions are the main charged particles to form discharge current in the transfer region.

A Window on the Earliest Star Formation: Extreme Photoionization Conditions of a High-ionization, Low-metallicity Lensed Galaxy at z ∼ 2*

NASA Astrophysics Data System (ADS)

Berg, Danielle A.; Erb, Dawn K.; Auger, Matthew W.; Pettini, Max; Brammer, Gabriel B.

2018-06-01

We report new observations of SL2S J021737–051329, a lens system consisting of a bright arc at z = 1.84435, magnified ∼17× by a massive galaxy at z = 0.65. SL2S0217 is a low-mass (M < 109 M ⊙), low-metallicity (Z ∼ 1/20 Z ⊙) galaxy, with extreme star-forming conditions that produce strong nebular UV emission lines in the absence of any apparent outflows. Here we present several notable features from rest-frame UV Keck/LRIS spectroscopy: (1) Very strong narrow emission lines are measured for C IV λλ1548, 1550, He II λ1640, O III] λλ1661, 1666, Si III] λλ1883, 1892, and C III] λλ1907, 1909. (2) Double-peaked Lyα emission is observed with a dominant blue peak and centered near the systemic velocity. (3) The low- and high-ionization absorption features indicate very little or no outflowing gas along the sight line to the lensed galaxy. The relative emission-line strengths can be reproduced with a very high ionization, low-metallicity starburst with binaries, with the exception of He II, which indicates that an additional ionization source is needed. We rule out large contributions from active galactic nuclei and shocks to the photoionization budget, suggesting that the emission features requiring the hardest radiation field likely result from extreme stellar populations that are beyond the capabilities of current models. Therefore, SL2S0217 serves as a template for the extreme conditions that are important for reionization and thought to be more common in the early universe.

DETECTION OF THE INTERMEDIATE-WIDTH EMISSION LINE REGION IN QUASAR OI 287 WITH THE BROAD EMISSION LINE REGION OBSCURED BY THE DUSTY TORUS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zhenzhen; Zhou, Hongyan; Wang, Huiyuan

2015-10-20

The existence of intermediate-width emission line regions (IELRs) in active galactic nuclei has been discussed for over two decades. A consensus, however, is yet to be arrived at due to the lack of convincing evidence for their detection. We present a detailed analysis of the broadband spectrophotometry of the partially obscured quasar OI 287. The ultraviolet intermediate-width emission lines (IELs) are very prominent, in high contrast to the corresponding broad emission lines (BELs) which are heavily suppressed by dust reddening. Assuming that the IELR is virialized, we estimated its distance to the central black hole to be ∼2.9 pc, similarmore » to the dust sublimation radius of ∼1.3 pc. Photo-ionization calculations suggest that the IELR has a hydrogen density of ∼10{sup 8.8}–10{sup 9.4} cm{sup −3}, within the range of values quoted for the dusty torus near the sublimation radius. Both its inferred location and physical conditions suggest that the IELR originates from the inner surface of the dusty torus. In the spectrum of this quasar, we identified only one narrow absorption-line system associated with the dusty material. With the aid of photo-ionization model calculations, we found that the obscuring material might originate from an outer region of the dusty torus. We speculate that the dusty torus, which is exposed to the central ionizing source, may produce IELs through photo-ionization processes, as well as obscure BELs as a natural “coronagraph.” Such a “coronagraph” could be found in a large number of partially obscured quasars and may be a useful tool to study IELRs.« less

First Detections of the [NII] 122 Micrometer Line at High Redshift: Demonstrating the Utility of the Line for Studying Galaxies in the Early Universe

NASA Technical Reports Server (NTRS)

Ferkinhoff, Carl; Brisbin, Drew; Nikola, Thomas; Parshley, Stephen C.; Stacey, Gordon J.; Phillips, Thomas G.; Falgarone, Edith; Benford, Dominic J.; Staguhn, Johannes G.; Tucker, Carol E.

2011-01-01

We report the first detections of the [NIl] 122 {\\mu} m line from a high redshift galaxy. The line was strongly (> 6{\\sigma}) detected from SMMJ02399-0136, and HI413+ 117 (the Cloverleaf QSO) using the Redshift(z) and Early Universe Spectrometer (ZEUS) on the CSO. The lines from both sources are quite bright with line-to-FIR continuum luminosity ratios that are approx.7.0x10(exp -4) (Cloverleaf) and 2.1x10(exp -3) (SMMJ02399). With ratios 2-10 times larger than the average value for nearby galaxies, neither source exhibits the line-to-continuum deficits seen in nearby sources. The line strengths also indicate large ionized gas fractions, approx.8 to 17% of the molecular gas mass. The [OIII]/[NII] line ratio is very sensitive to the effective temperature of ionizing stars and the ionization parameter for emission arising in the narrow-line region (NLR) of an AGN. Using our previous detection of the [01II] 88 {\\mu}m line, the [OIII]/ [NIl] line ratio for SMMJ02399-0136 indicates the dominant source of the line emission is either stellar HII regions ionized by 09.5 stars, or the NLR of the AGN with ionization parameter 10g(U) = -3.3 to -4.0. A composite system, where 30 to 50% of the FIR lines arise in the NLR also matches the data. The Cloverleaf is best modeled by a superposition of approx.200 M82like starbursts accounting for all of the FIR emission and 43% of the [NIl] line. The remainder may come from the NLR. This work demonstrates the utility of the [NIl] and [OIII] lines in constraining properties of the ionized medium.

The Charge State of Polycyclic Aromatic Hydrocarbons Across Reflection Nebulae: PAH Charge Balance and Calibration

NASA Astrophysics Data System (ADS)

Boersma, C.; Bregman, J.; Allamandola, L. J.

2016-11-01

Low-resolution Spitzer spectral map data (>1700 spectra) of ten reflection nebulae (RNe) fields are analyzed using the data and tools available through the NASA Ames PAH IR Spectroscopic Database. The PAH emission is broken down into PAH charge state using a database fitting approach. Here, the physics of the PAH emission process is taken into account and uses target appropriate parameters, e.g., a stellar radiation model for the exciting star. The breakdown results are combined with results derived using the traditional PAH band strength approach, which interprets particular PAH band strength ratios as proxies for the PAH charge state, e.g., the 6.2/11.2 μm PAH band strength ratio. These are successfully calibrated against their database equivalent; the PAH ionized fraction (f I ). The PAH ionized fraction is converted into the PAH ionization parameter, which relates the PAH ionized fraction to the strength of the radiation field, gas temperature and electron density. The behavior of the 12.7 μm PAH band is evaluated as a tracer for PAH ionization and erosion. The plot of the 8.6 versus 11.2 μm PAH band strength for the northwest photo-dominated region (PDR) in NGC 7023 is shown to be a robust diagnostic template for the PAH ionized fraction. Remarkably, most of the other RNe fall within the limits set by NGC 7023. Finally, PAH spectroscopic templates are constructed and verified as principal components. Template spectra derived from NGC 7023 and NGC 2023 compare extremely well with each other, with those derived for NGC 7023 successfully reproducing the PAH emission observed from NGC 2023.

THE CHARGE STATE OF POLYCYCLIC AROMATIC HYDROCARBONS ACROSS REFLECTION NEBULAE: PAH CHARGE BALANCE AND CALIBRATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boersma, C.; Bregman, J.; Allamandola, L. J., E-mail: Christiaan.Boersma@nasa.gov

Low-resolution Spitzer spectral map data (>1700 spectra) of ten reflection nebulae (RNe) fields are analyzed using the data and tools available through the NASA Ames PAH IR Spectroscopic Database. The PAH emission is broken down into PAH charge state using a database fitting approach. Here, the physics of the PAH emission process is taken into account and uses target appropriate parameters, e.g., a stellar radiation model for the exciting star. The breakdown results are combined with results derived using the traditional PAH band strength approach, which interprets particular PAH band strength ratios as proxies for the PAH charge state, e.g.,more » the 6.2/11.2 μ m PAH band strength ratio. These are successfully calibrated against their database equivalent; the PAH ionized fraction ( f {sub i} ). The PAH ionized fraction is converted into the PAH ionization parameter, which relates the PAH ionized fraction to the strength of the radiation field, gas temperature and electron density. The behavior of the 12.7 μ m PAH band is evaluated as a tracer for PAH ionization and erosion. The plot of the 8.6 versus 11.2 μ m PAH band strength for the northwest photo-dominated region (PDR) in NGC 7023 is shown to be a robust diagnostic template for the PAH ionized fraction. Remarkably, most of the other RNe fall within the limits set by NGC 7023. Finally, PAH spectroscopic templates are constructed and verified as principal components. Template spectra derived from NGC 7023 and NGC 2023 compare extremely well with each other, with those derived for NGC 7023 successfully reproducing the PAH emission observed from NGC 2023.« less

The study of the effects of ionizing and non-ionizing radiations on birth weight of newborns to exposed mothers.

PubMed

Mortazavi, S M J; Shirazi, K R; Mortazavi, G

2013-01-01

Life evolved in an environment filled with a wide variety of ionizing and non-ionizing radiation. It was previously reported that medical exposures to pregnant women increases the risk of low birth weight. This study intends to investigate the relationship between exposure to ionizing and non-ionizing radiation and the risk of low birth weight. One thousand two hundred mothers with their first-term labor (vaginal or cesarean) whose newborns' history had been registered in neonates' screening program in Shiraz were interviewed and surveyed. Data collection was performed by the assessment of mother's history of radiography before and during pregnancy, physical examination of the mother for height and weight and weighing and examining the newborn for any diagnosis of disease and anomalies. There were no statistical significant differences between the mean weight of newborns whose mothers had been exposed to some common sources of ionizing and non-ionizing radiations such as dental or non dental radiographies, mobile phone, cordless phone and cathode ray tube (CRT) and those of non-exposed mothers. The findings of this study cast doubt on previous reports, which indicated that exposure to ionizing radiation during pregnancy increased the risk of low birth weight.

The study of the effects of ionizing and non-ionizing radiations on birth weight of newborns to exposed mothers

PubMed Central

Mortazavi, S. M. J.; Shirazi, K. R.; Mortazavi, G.

2013-01-01

Objectives: Life evolved in an environment filled with a wide variety of ionizing and non-ionizing radiation. It was previously reported that medical exposures to pregnant women increases the risk of low birth weight. This study intends to investigate the relationship between exposure to ionizing and non-ionizing radiation and the risk of low birth weight. Materials and Methods: One thousand two hundred mothers with their first-term labor (vaginal or cesarean) whose newborns’ history had been registered in neonates’ screening program in Shiraz were interviewed and surveyed. Data collection was performed by the assessment of mother's history of radiography before and during pregnancy, physical examination of the mother for height and weight and weighing and examining the newborn for any diagnosis of disease and anomalies. Results: There were no statistical significant differences between the mean weight of newborns whose mothers had been exposed to some common sources of ionizing and non-ionizing radiations such as dental or non dental radiographies, mobile phone, cordless phone and cathode ray tube (CRT) and those of non-exposed mothers. Conclusions: The findings of this study cast doubt on previous reports, which indicated that exposure to ionizing radiation during pregnancy increased the risk of low birth weight. PMID:23633865

Calculation of H2-He Flow with Nonequilibrium Ionization and Radiation: an Interim Report

NASA Technical Reports Server (NTRS)

Furudate, Michiko; Chang, Keun-Shik

2005-01-01

The nonequilibrium ionization process in hydrogen-helium mixture behind a strong shock wave is studied numerically using the detailed ionization rate model developed recently by Park which accounts for emission and absorption of Lyman lines. The study finds that, once the avalanche ionization is started, the Lyman line is self-absorbed. The intensity variation of the radiation at 5145 Angstroms found by Leibowitz in a shock tube experiment can be numerically reproduced by assuming that ionization behind the shock wave prior to the onset of avalanche ionization is 1.3%. Because 1.3% initial ionization is highly unlikely, Leibowitz s experimental data is deemed questionable. By varying the initial electron density value in the calculation, the calculated ionization equilibration time is shown to increase approximately as inverse square-root of the initial electron density value. The true ionization equilibration time is most likely much longer than the value found by Leibowitz.

Comparison of the Detection Characteristics of Trace Species Using Laser-Induced Breakdown Spectroscopy and Laser Breakdown Time-of-Flight Mass Spectrometry

PubMed Central

Wang, Zhenzhen; Deguchi, Yoshihiro; Yan, Junjie; Liu, Jiping

2015-01-01

The rapid and precise element measurement of trace species, such as mercury, iodine, strontium, cesium, etc. is imperative for various applications, especially for industrial needs. The elements mercury and iodine were measured by two detection methods for comparison of the corresponding detection features. A laser beam was focused to induce plasma. Emission and ion signals were detected using laser-induced breakdown spectroscopy (LIBS) and laser breakdown time-of-flight mass spectrometry (LB-TOFMS). Multi-photon ionization and electron impact ionization in the plasma generation process can be controlled by the pressure and pulse width. The effect of electron impact ionization on continuum emission, coexisting molecular and atomic emissions became weakened in low pressure condition. When the pressure was less than 1 Pa, the plasma was induced by laser dissociation and multi-photon ionization in LB-TOFMS. According to the experimental results, the detection limits of mercury and iodine in N2 were 3.5 ppb and 60 ppb using low pressure LIBS. The mercury and iodine detection limits using LB-TOFMS were 1.2 ppb and 9.0 ppb, which were enhanced due to different detection features. The detection systems of LIBS and LB-TOFMS can be selected depending on the condition of each application. PMID:25769051

Ionized absorbers, ionized emitters, and the X-ray spectrum of active galactic nuclei

NASA Technical Reports Server (NTRS)

Netzer, Hagai

1993-01-01

Broad absorption features are common in the X-ray spectrum of low-luminosity AGNs. The features have been modeled by leaky neutral absorbers or by highly ionized gas that completely occult the continuum source. Such models are incomplete since they do not take into account all the physical processes in the gas. In particular, no previous model included the X-ray emission by the ionized absorbing gas and the reflection of the continuum source radiation. The present work discusses the emission, absorption, and reflection properties of photoionized gases with emphasis on conditions thought to prevail in AGNs. It shows that such gas is likely to produce intense X-ray line and continuum radiation and to reflect a sizable fraction of the nonstellar continuum at all energies. If such gas is indeed responsible for the observed X-ray absorption, then absorption edges are much weaker than commonly assumed, and some residual X-ray continuum is likely to be observed even if the line of sight is completely blocked. Moreover, X-ray emission features may show up in sources not showing X-ray absorption. This has immense consequences for medium-resolution X-ray missions, such as BBXRT and Astro-D, and for the planned high-resolution experiments on board XMM and AXAF.

Large-Scale Structure of the Carina Nebula.

PubMed

Smith; Egan; Carey; Price; Morse; Price

2000-04-01

Observations obtained with the Midcourse Space Experiment (MSX) satellite reveal for the first time the complex mid-infrared morphology of the entire Carina Nebula (NGC 3372). On the largest size scale of approximately 100 pc, the thermal infrared emission from the giant H ii region delineates one coherent structure: a (somewhat distorted) bipolar nebula with the major axis perpendicular to the Galactic plane. The Carina Nebula is usually described as an evolved H ii region that is no longer actively forming stars, clearing away the last vestiges of its natal molecular cloud. However, the MSX observations presented here reveal numerous embedded infrared sources that are good candidates for sites of current star formation. Several compact infrared sources are located at the heads of dust pillars or in dark globules behind ionization fronts. Because their morphology suggests a strong interaction with the peculiar collection of massive stars in the nebula, we speculate that these new infrared sources may be sites of triggered star formation in NGC 3372.

High-resolution soft X-ray spectra of Scorpius X-1 - The structure of circumsource accreting material

NASA Technical Reports Server (NTRS)

Kahn, S. M.; Seward, F. D.; Chlebowski, T.

1984-01-01

Four observations of Scorpius X-1 with the Objective Grating Spectrometer of the Einstein Observatory have provided high-resolution spectra (lambda/Delta lambda = approximately 20-50) in the wavelength range 7-46 A. The spectra reveal the presence of absorption structure due to oxygen, nitrogen, and iron, and variable emission structure associated with ionized iron and nitrogen. The strengths of these features suggest that the N/O abundance ratio in the absorbing and line emitting gas is anomalously high, which might indicate that these spectral components are associated with processed material, probably accreting matter transferred from the surface of an evolved companion. Constraints on the inclination of the system, however, imply that this cool, dense, accreting material must be well out of the plane of the binary system. Possible models for the origin and nature of this circumsource medium are discussed. An extensive discussion of the calibration of the Objective Grating Spectrometer and of the analysis of spectra acquired by that instrument is also provided.

Evolution of the symbiotic binary system AG Pegasi - The slowest classical nova eruption ever recorded

NASA Technical Reports Server (NTRS)

Kenyon, Scott J.; Mikolajewska, Joanna; Mikolajewski, Maciej; Polidan, Ronald S.; Slovak, Mark H.

1993-01-01

We present an analysis of new and existing photometric and spectroscopic observations of the ongoing eruption in the symbiotic star AG Pegasi, showing that this binary has evolved considerably since the turn of the century. Recent dramatic changes in both the UV continuum and the wind from the hot component allow a more detailed analysis than in previous papers. AG Peg is composed of a normal M3 giant and a hot, compact star embedded in a dense, ionized nebula. The hot component powers the activity observed in this system, including a dense wind and a photoionized region within the outer atmosphere of the red giant. The hot component contracted in radius at roughly constant luminosity from 1850 to 1985. Its bolometric luminosity declined by a factor of about 4 during the past 5 yr. Both the mass loss rate from the hot component and the emission activity decreased in step with the hot component's total luminosity, while photospheric radiation from the red giant companion remained essentially constant.

CHEERS Results on Mrk 573: A Study of Deep Chandra Observations

NASA Astrophysics Data System (ADS)

Paggi, Alessandro; Wang, Junfeng; Fabbiano, Giuseppina; Elvis, Martin; Karovska, Margarita

2012-09-01

We present results on Mrk 573 obtained as part of the CHandra survey of Extended Emission-line Regions in nearby Seyfert galaxies (CHEERS). Previous studies showed that this source features a biconical emission in the soft X-ray band closely related to the narrow-line region as mapped by the [O III] emission line and the radio emission, though on a smaller scale; we investigate the properties of soft X-ray emission from this source with new deep Chandra observations. Making use of the subpixel resolution of the Chandra/ACIS image and point-spread function deconvolution, we resolve and study substructures in each ionizing cone. The two cone spectra are fitted with a photoionization model, showing a mildly photoionized phase diffused over the bicone. Thermal collisional gas at about ~1.1 keV and ~0.8 keV appears to be located between the nucleus and the "knots" resolved in radio observations, and between the "arcs" resolved in the optical images, respectively; this can be interpreted in terms of shock interaction with the host galactic plane. The nucleus shows a significant flux decrease across the observations indicating variability of the active galactic nucleus (AGN), with the nuclear region featuring a higher ionization parameter with respect to the bicone region. The long exposure allows us to find extended emission up to ~7 kpc from the nucleus along the bicone axis. Significant emission is also detected in the direction perpendicular to the ionizing cones, disagreeing with the fully obscuring torus prescribed in the AGN unified model and suggesting instead the presence of a clumpy structure.

Collision energy-resolved study of the emission cross-section and the Penning ionization cross-section in the reaction of BrCN with He*(2 3S)

NASA Astrophysics Data System (ADS)

Kanda, Kazuhiro; Yamakita, Yoshihiro; Ohno, Koichi

2001-12-01

The dissociative excitation of BrCN producing CN(B 2Σ +) fragment by the collision of He *(2 3S) was investigated by the collision energy-resolved electron and emission spectroscopy using time-of-flight method with a high-intensity He * beam. The Penning electrons ejected from BrCN and the subsequent CN ( B2Σ +- X2Σ +) emission were measured as a function of collision energy in the range of 90-180 meV. The formation of CN ( B2Σ +) is concluded to proceed dominantly via the promotion of an electron from Π-character orbital, by comparison between the collision energy dependence of the partial Penning ionization cross-sections and the CN ( B2Σ +- X2Σ +) emission cross-section.

Ionization equilibrium and radiative energy loss rates for C, N, and O ions in low-density plasmas

NASA Technical Reports Server (NTRS)

Jacobs, V. L.; Davis, J.; Rogerson, J. E.; Blaha, M.

1978-01-01

The results of calculations of the ionization equilibrium and radiative energy loss rates for C, N and O ions in low-density plasmas are presented for electron temperatures in the range 10,000-10,000,000 K. The ionization structure is determined by using the steady-state corona model, in which electron impact ionization from the ground states is balanced by direct radiative and dielectronic recombination. With an improved theory, detailed calculations are carried out for the dielectronic recombination rates in which account is taken of all radiative and autoionization processes involving a single-electron electric-dipole transition of the recombining ion. The radiative energy loss processes considered are electron-impact excitation of resonance line emission, direct radiative recombination, dielectronic recombination, and electron-ion bremsstrahlung. For all three elements, resonance line emission resulting from 2s-2p transitions produces a broad maximum in the energy loss rate near 100,000 K.

Observations of 85. cap alpha. recombination lines from M16

DOE Office of Scientific and Technical Information (OSTI.GOV)

Higgs, L.A.; Doherty, L.H.; MacLeod, J.M.

1979-01-01

Hydrogen and helium recombination-line observations have been made at eight positions in M16. These observations are compatible with a two-component model of the ionized gas, one component being an extended low-excitation region, the other being a higher-excitation region (with the helium ionized) at a radial velocity about 10 km s/sup -1/ greater than the mean velocity of the first component. The observed radial-velocity variations in the first component appear to be related to streaming motions from ionization fronts. The helium line emission is at a velocity comparable to that of the hottest exciting stars. The continuum radio emission is verymore » low considering the number of O stars in the nebula, indicating that it is probably density bounded.« less

The plasma properties and electron emission characteristics of near-zero differential resistance of hollow cathode-based plasma contactors with a discharge chamber

NASA Astrophysics Data System (ADS)

Xie, Kan; Farnell, Casey C.; Williams, John D.

2014-08-01

The formation of electron emission-bias voltage (I-V) characteristics of near-zero differential resistance in the cathodic plasma contactor for bare electrodynamic tether applications, based on a hollow cathode embedded in a ring-cusp ionization stage, is studied. The existence of such an I-V regime is important to achieve low impedance performance without being affected by the space plasma properties for a cathodic plasma contactor. Experimental data on the plasma structure and properties downstream from the ionization stage are presented as functions of the xenon flow rate and the electron emission current. The electrons were emitted from the cathode to the cylindrical vacuum chamber wall (r = 0.9 m) under ≈10-5 Torr of vacuum pressure. The ring-cusp configuration selected for the plasma contactor created a 125-Gauss axial field near the cathode orifice, along with a large-volume 50-Gauss magnitude pocket in the stage. A baseline ion energy cost of ≈300 eV/ion was measured in the ionization stage when no electrons were emitted to the vacuum chamber wall. In addition, the anode fall growth limited the maximum propellant unitization to below ≈75% in the discharge loss curves for this ion stage. Detailed measurements on the plasma properties were carried out for the no-electron emission and 3 A emission conditions. The experimental data are compared with 1-D models, and the effectiveness of the model is discussed. The four key issues that played important roles in the process of building the near-zero different resistance I-V regime are: a significant amount of ionization by the emission electrons, a decrease in the number of reflected electrons in the plume, the electron-temperature increment, and low initial ion energy at the source outlet.

Terahertz emission from ultrafast ionizing air in symmetry-broken laser fields

NASA Astrophysics Data System (ADS)

Kim, Ki-Yong; Glownia, James H.; Taylor, Antoinette J.; Rodriguez, George

2007-04-01

A transient photocurrent model is developed to explain coherent terahertz emission from air irradiated by a symmetry-broken laser field composed of the fundamental and its second harmonic laser pulses. When the total laser field is asymmetric across individual optical cycles, a nonvanishing electron current surge can arise during optical field ionization of air, emitting a terahertz electromagnetic pulse. Terahertz power scalability is also investigated, and with optical pump energy of tens of millijoules per pulse, peak terahertz field strengths in excess of 150 kV/cm are routinely produced.

Terahertz emission from ultrafast ionizing air in symmetry-broken laser fields.

PubMed

Kim, Ki-Yong; Glownia, James H; Taylor, Antoinette J; Rodriguez, George

2007-04-16

A transient photocurrent model is developed to explain coherent terahertz emission from air irradiated by a symmetry-broken laser field composed of the fundamental and its second harmonic laser pulses. When the total laser field is asymmetric across individual optical cycles, a nonvanishing electron current surge can arise during optical field ionization of air, emitting a terahertz electromagnetic pulse. Terahertz power scalability is also investigated, and with optical pump energy of tens of millijoules per pulse, peak terahertz field strengths in excess of 150 kV/cm are routinely produced.

On the Nature of Orion Source I

NASA Astrophysics Data System (ADS)

Báez-Rubio, A.; Jiménez-Serra, I.; Martín-Pintado, J.; Zhang, Q.; Curiel, S.

2018-01-01

The Kleinmann–Low nebula in Orion, the closest region of massive star formation, harbors Source I, whose nature is under debate. Knowledge of this source may have profound implications for our understanding of the energetics of the hot core in Orion KL since it might be the main heating source in the region. The spectral energy distribution of this source in the radio is characterized by a positive spectral index close to 2, which is consistent with (i) thermal bremsstrahlung emission of ionized hydrogen gas produced by a central massive protostar, or (ii) photospheric bremsstrahlung emission produced by electrons when deflected by the interaction with neutral and molecular hydrogen like Mira-like variable stars. If ionized hydrogen gas were responsible for the observed continuum emission, its modeling would predict detectable emission from hydrogen radio recombination lines (RRLs). However, our SMA observations were obtained with a high enough sensitivity to rule out that the radio continuum emission arises from a dense hypercompact H II region because the H26α line would have been detected, in contrast with our observations. To explain the observational constraints, we investigate further the nature of the radio continuum emission from source I. We have compared available radio continuum data with the predictions from our upgraded non-LTE 3D radiative transfer model, MOdel for REcombination LInes, to show that radio continuum fluxes and sizes can only be reproduced by assuming both dust and bremsstrahlung emission from neutral gas. The dust emission contribution is significant at ν ≥ 43 GHz. In addition, our RRL peak intensity predictions for the ionized metals case are consistent with the nondetection of Na and K RRLs at millimeter and submillimeter wavelengths.

40 CFR 63.11507 - What are my standards and management practices?

Code of Federal Regulations, 2011 CFR

2011-07-01

... distilled/de-ionized water, water filtration, pre-cleaning of parts to be plated, and thorough rinsing of... emissions from the thermal spraying process and transports the emissions to a water curtain, fabric filter... and transports the emissions to a water curtain, fabric filter, cartridge, or HEPA filter, according...

Neutral ISM, Ly α , and Lyman-continuum in the Nearby Starburst Haro 11

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rivera-Thorsen, T. Emil; Östlin, Göran; Hayes, Matthew

2017-03-01

Star-forming galaxies are believed to be a major source of Lyman continuum (LyC) radiation responsible for reionizing the early universe. Direct observations of escaping ionizing radiation have however been sparse and with low escape fractions. In the local universe, only 10 emitters have been observed, with typical escape fractions of a few percent. The mechanisms regulating this escape need to be strongly evolving with redshift in order to account for the epoch of reionization. Gas content and star formation feedback are among the main suspects, known to both regulate neutral gas coverage and evolve with cosmic time. In this paper,more » we reanalyze Hubble Space Telescope ( HST )-Cosmic Origins Spectrograph (COS) spectrocopy of the first detected local LyC leaker, Haro 11. We examine the connection between LyC leakage and Ly α line shape, and feedback-influenced neutral interstellar medium (ISM) properties like kinematics and gas distribution. We discuss the two extremes of an optically thin, density bounded ISM and a riddled, optically thick, ionization bounded ISM, and how Haro 11 fits into theoretical predictions. We find that the most likely ISM model is a clumpy neutral medium embedded in a highly ionized medium with a combined covering fraction of unity and a residual neutral gas column density in the ionized medium high enough to be optically thick to Ly α , but low enough to be at least partly transparent to LyC and undetected in Si ii. This suggests that star formation feedback and galaxy-scale interaction events play a major role in opening passageways for ionizing radiation through the neutral medium.« less

Searching for the influence radius of AGN in nearby narrow emission-line galaxies using the CALIFA survey

NASA Astrophysics Data System (ADS)

Robleto-Orús, A. C.; Torres-Papaqui, J. P.; Coziol, R.; Morales-Vargas, A.; Romero-Cruz, F. J.; Ortega-Minakata, R. A.; Chow-Martinez, M.; Trejo-Alonso, J. J.

2017-07-01

In narrow emission-line galaxies, one important problem consists in discriminating gas ionization due to an AGN and gas ionization due to OB stars in active star-forming regions. This problem becomes more acute in case of AGNs classified as transition-type objects (TO), where star formation is relatively intense, and for LINERs, where the AGN is very weak. Thanks to the integral field spectroscopy, we have a new way to attack this problem. By definition, OB stars ionize a definite portion of space, the Strömgren's sphere, which size depends on the total luminosity of the star, its temperature, and the density of the surrounding gas. Therefore one expects gas ionized by OB stars to cover limited areas in a galaxy. On the other hand, due to the huge amount of ionizing photons emitted by an AGN, its "influence radius" is expected do be much more extended, in the order of kpc. Using a sample of galaxies from included in the CALIFA survey DR3, we will test a new way to measure the characteristic "influence radius" of AGN with different intensities.

Fast Atom Ionization in Strong Electromagnetic Radiation

NASA Astrophysics Data System (ADS)

Apostol, M.

2018-05-01

The Goeppert-Mayer and Kramers-Henneberger transformations are examined for bound charges placed in electromagnetic radiation in the non-relativistic approximation. The consistent inclusion of the interaction with the radiation field provides the time evolution of the wavefunction with both structural interaction (which ensures the bound state) and electromagnetic interaction. It is shown that in a short time after switching on the high-intensity radiation the bound charges are set free. In these conditions, a statistical criterion is used to estimate the rate of atom ionization. The results correspond to a sudden application of the electromagnetic interaction, in contrast with the well-known ionization probability obtained by quasi-classical tunneling through classically unavailable non-stationary states, or other equivalent methods, where the interaction is introduced adiabatically. For low-intensity radiation the charges oscillate and emit higher-order harmonics, the charge configuration is re-arranged and the process is resumed. Tunneling ionization may appear in these circumstances. Extension of the approach to other applications involving radiation-induced charge emission from bound states is discussed, like ionization of molecules, atomic clusters or proton emission from atomic nuclei. Also, results for a static electric field are included.

Carriers of the mid-IR emission bands in PNe reanalysed. Evidence of a link between circumstellar and interstellar aromatic dust

NASA Astrophysics Data System (ADS)

Joblin, C.; Szczerba, R.; Berné, O.; Szyszka, C.

2008-10-01

Context: It has been shown that the diversity of the aromatic emission features can be rationalized into different classes of objects, in which differences between circumstellar and interstellar matter are emphasised. Aims: We probe the links between the mid-IR emitters observed in planetary nebulae (PNe) and their counterparts in the interstellar medium in order to probe a scenario in which the latter have been formed in the circumstellar environment of evolved stars. Methods: The mid-IR (6-14 μm) emission spectra of PNe and compact H II regions were analysed on the basis of previous work on photodissociation regions (PDRs). Galactic, Large Magellanic Cloud (LMC), and Small Magellanic Cloud (SMC) objects were considered in our sample. Results: We show that the mid-IR emission of PNe can be decomposed as the sum of six components. Some components made of polycyclic aromatic hydrocarbon (PAH) and very small grain (VSG) populations are similar to those observed in PDRs. Others are fitted in an evolutionary scenario involving the destruction of the aliphatic component observed in the post-AGB stage, as well as strong processing of PAHs in the extreme conditions of PNe that leads to a population of very large ionized PAHs. This species called PAHx are proposed as the carriers of a characteristic band at 7.90 μm. This band can be used as part of diagnostics that identify PNe in nearby galaxies and is also observed in galactic compact H II regions. Conclusions: These results support the formation of the aromatic very small dust particles in the envelopes of evolved stars, in the Milky Way, as well as in the LMC and SMC, and their subsequent survival in the interstellar medium. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA. Tables A.1 and A.2 are only available in electronic form at http://www.aanda.org

DETECTION OF BROAD Hα EMISSION LINES IN THE LATE-TIME SPECTRA OF A HYDROGEN-POOR SUPERLUMINOUS SUPERNOVA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Lin; Masci, F.; Quimby, R.

2015-12-01

iPTF13ehe is a hydrogen-poor superluminous supernova (SLSN) at z = 0.3434, with a slow-evolving light curve and spectral features similar to SN2007bi. It rises in 83–148 days to reach a peak bolometric luminosity of ∼1.3 × 10{sup 44} erg s{sup −1}, then decays slowly at 0.015 mag day{sup −1}. The measured ejecta velocity is ∼ 13,000 km s{sup −1}. The inferred explosion characteristics, such as the ejecta mass (70–220 M{sub ⊙}), and the total radiative and kinetic energy (E{sub rad} ∼ 10{sup 51} erg, E{sub kin} ∼ 2 × 10{sup 53} erg), are typical of slow-evolving H-poor SLSN events. However,more » the late-time spectrum taken at +251 days (rest, post-peak) reveals a Balmer Hα emission feature with broad and narrow components, which has never been detected before among other H-poor SLSNe. The broad component has a velocity width of ∼4500 km s{sup −1} and a ∼300 km s{sup −1} blueward shift relative to the narrow component. We interpret this broad Hα emission with a luminosity of ∼2 × 10{sup 41} erg s{sup −1} as resulting from the interaction between the supernova ejecta and a discrete H-rich shell, located at a distance of ∼4 × 10{sup 16} cm from the explosion site. This interaction causes the rest-frame r-band LC to brighten at late times. The fact that the late-time spectra are not completely absorbed by the shock-ionized H-shell implies that its Thomson scattering optical depth is likely ≤1, thus setting upper limits on the shell mass ≤30 M{sub ⊙}. Of the existing models, a Pulsational Pair Instability supernova model can naturally explain the observed 30 M{sub ⊙} H-shell, ejected from a progenitor star with an initial mass of (95–150) M{sub ⊙} about 40 years ago. We estimate that at least ∼15% of all SLSNe-I may have late-time Balmer emission lines.« less

Density Bounded H II Regions: Ionization of the Diffuse Interstellar and Intergalactic Media

NASA Astrophysics Data System (ADS)

Zurita, A.; Rozas, M.; Beckman, J. E.

2000-05-01

We present a study of the diffuse ionized gas (DIG) for a sample of nearby spiral galaxies using Hα images, after constructing their H II region catalogues. The integrated Hα emission of the DIG accounts for between 25% to 60% of the total Hα of the galaxy and a high ionizing photon flux is necessary to keep this gas ionized. We suggest that Lyman photons leaking from the most luminous H II regions are the prime source of the ionization of the DIG; they are more than enough to ionize the measured DIG in the model in which H II regions with luminosity in Hα greater than LStr=1038.6 erg sme are density bounded. We go on to show that this model can quantify the ionization observed in the skins of the high velocity clouds well above the plane of our Galaxy and predicts the ionization of the intergalactic medium.

What Dominates the Coronal Emission Spectrum During the Cycle of Impulsive Heating and Cooling?

NASA Technical Reports Server (NTRS)

Bradshaw, Stephen J.; Klimchuk, James A.

2011-01-01

The smoking gun of small-scale, impulsive events heating the solar corona is expected to be the presence of a hot ( > 5 MK) plasma component. Evidence for this has been scarce, but has gradually begun to accumulate due to recent studies designed to constrain the high temperature part of the emission measure distribution. However, the detected hot component is often weaker than models predict and this is due in part to the common modeling assumption that the ionization balance remains in equilibrium. The launch of the latest generation of space-based observing instrumentation aboard Hinode and the Solar Dynamics Observatory (SDO) has brought the matter of the ionization state of the plasma firmly to the forefront. It is timely to consider exactly what emission current instruments would detect when observing a corona heated impulsively on small-scales by nanoflares. Only after we understand the full effects of nonequilibrium ionization can we draw meaningful conclusions about the plasma that is (or is not) present. We have therefore performed a series of hydrodynamic simulations for a variety of different nanoflare properties and initial conditions. Our study has led to several key conclusions. 1. Deviations from equilibrium are greatest for short-duration nanoflares at low initial coronal densities. 2. Hot emission lines are the most affected and are suppressed sometimes to the point of being invisible. 3. The emission detected in all of the SDO-AIA channels is generally dominated by warm, over-dense, cooling plasma. 4. It is difficult not to create coronal loops that emit strongly at 1.5 MK and in the range 2 to 5 MK, which are the most commonly observed kind, for a broad range of nanoflare scenarios. 5. The Fe XV (284.16 ) emission in most of our models is about 10 times brighter than the Ca XVII (192.82 ) emission, consistent with observations. Our overarching conclusion is that small-scale, impulsive heating inducing a nonequilibrium ionization state leads to predictions for observable quantities that are entirely consistent with what is actually observed.

Structure and physical conditions in the Huygens region of the Orion nebula

NASA Astrophysics Data System (ADS)

O'Dell, C. R.; Ferland, G. J.; Peimbert, M.

2017-02-01

Hubble Space Telescope images, MUSE maps of emission lines, and an atlas of high velocity resolution emission-line spectra have been used to establish for the first time correlations of the electron temperature, electron density, radial velocity, turbulence, and orientation within the main ionization front of the nebula. From the study of the combined properties of multiple features, it is established that variations in the radial velocity are primarily caused by the photoevaporating ionization front being viewed at different angles. There is a progressive increase of the electron temperature and density with decreasing distance from the dominant ionizing star θ1 Ori C. The product of these characteristics (ne × Te) is the most relevant parameter in modelling a blister-type nebula like the Huygens region, where this quantity should vary with the surface brightness in Hα. Several lines of evidence indicate that small-scale structure and turbulence exist down to the level of our resolution of a few arcseconds. Although photoevaporative flow must contribute at some level to the well-known non-thermal broadening of the emission lines, comparison of quantitative predictions with the observed optical line widths indicates that it is not the major additive broadening component. Derivation of Te values for H+ from radio+optical and optical-only ionized hydrogen emission showed that this temperature is close to that derived from [N II] and that the transition from the well-known flat extinction curve which applies in the Huygens region to a more normal steep extinction curve occurs immediately outside of the Bright Bar feature of the nebula.

Atomic Data in X-Ray Astrophysics

NASA Technical Reports Server (NTRS)

Brickhouse, N. S.

2000-01-01

With the launches of the Chandra X-ray Observatory (CXO) and the X-ray Multimirror Mission (XMM) and the upcoming launch of the Japanese mission ASTRO-E, high resolution X-ray spectroscopy of cosmic sources has begun. Early, deep observations of three stellar coronal sources will provide not only invaluable calibration data, but will also give us benchmarks for the atomic data under collisional equilibrium conditions. Analysis of the Chandra X-ray Observatory data, and data from other telescopes taken simultaneously, for these stars is ongoing as part of the Emission Line Project. Goals of the Emission Line Project are: (1) to determine and verify accurate and robust diagnostics and (2) to identify and prioritize issues in fundamental spectroscopy which will require further theoretical and/or laboratory work. The Astrophysical Plasma Emission Database will be described in some detail, as it is introducing standardization and flexibility into X-ray spectral modeling. Spectral models of X-ray astrophysical plasmas can be generally classified as dominated by either collisional ionization or by X-ray photoionization. While the atomic data needs for spectral models under these two types of ionization are significantly different, there axe overlapping data needs, as I will describe. Early results from the Emission Line Project benchmarks are providing an invaluable starting place, but continuing work to improve the accuracy and completeness of atomic data is needed. Additionally, we consider the possibility that some sources will require that both collisional ionization and photoionization be taken into account, or that time-dependent ionization be considered. Thus plasma spectral models of general use need to be computed over a wide range of physical conditions.

THE COMPLEX CIRCUMNUCLEAR ENVIRONMENT OF THE BROAD-LINE RADIO GALAXY 3C 390.3 REVEALED BY CHANDRA HETG

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tombesi, F.; Kallman, T.; Leutenegger, M. A.

2016-10-20

We present the first high spectral resolution X-ray observation of the broad-line radio galaxy 3C 390.3 obtained with the high-energy transmission grating spectrometer on board the Chandra X-ray Observatory . The spectrum shows complex emission and absorption features in both the soft X-rays and Fe K band. We detect emission and absorption lines in the energy range E = 700–1000 eV associated with ionized Fe L transitions (Fe XVII–XX). An emission line at the energy of E ≃ 6.4 keV consistent with the Fe K α is also observed. Our best-fit model requires at least three different components: (i) amore » hot emission component likely associated with the hot interstellar medium in this elliptical galaxy with temperature kT = 0.5 ± 0.1 keV; (ii) a warm absorber with ionization parameter log ξ = 2.3 ± 0.5 erg s{sup −1} cm, column density log N {sub H} = 20.7 ± 0.1 cm{sup −2}, and outflow velocity v {sub out} < 150 km s{sup −1}; and (iii) a lowly ionized reflection component in the Fe K band likely associated with the optical broad-line region or the outer accretion disk. These evidences suggest the possibility that we are looking directly down the ionization cone of this active galaxy and that the central X-ray source only photoionizes along the unobscured cone. This is overall consistent with the angle-dependent unified picture of active galactic nuclei.« less

The Complex Circumnuclear Environment of the Broad-Line Radio Galaxy 3C 390.3 Revealed by Chandra HETG

NASA Technical Reports Server (NTRS)

Tombesi, F.; Reeves, J. N.; Kallman, Timothy R.; Reynolds, C. S.; Mushotzky, R. F.; Braito, V.; Behar, E.; Leutenegger, Maurice A.; Cappi, M.

2016-01-01

We present the first high spectral resolution X-ray observation of the broad-line radio galaxy 3C 390.3 obtained with the high-energy transmission grating spectrometer on board the Chandra X-ray Observatory. The spectrum shows complex emission and absorption features in both the soft X-rays and Fe K band. We detect emission and absorption lines in the energy range E = 700-1000 eV associated with ionized Fe L transitions (Fe XVIIXX). An emission line at the energy of E approximately equal to 6.4 keV consistent with the Fe K alpha is also observed. Our best-fit model requires at least three different components: (i) a hot emission component likely associated with the hot interstellar medium in this elliptical galaxy with temperature kT = 0.5 +/- 0.1 keV; (ii) a warm absorber with ionization parameter log Epislon = 2.3 +/- 0.5 erg s(exp 1) cm, column density logN(sub H) = 20.7 +/- 0.1 cm(exp -2), and outflow velocity v(sub out) less than 150 km s(exp -1); and (iii) a lowly ionized reflection component in the Fe K band likely associated with the optical broad-line region or the outer accretion disk. These evidences suggest the possibility that we are looking directly down the ionization cone of this active galaxy and that the central X-ray source only photoionizes along the unobscured cone. This is overall consistent with the angle-dependent unified picture of active galactic nuclei.

Infrared emission and mass loss from evolved stars in elliptical galaxies

NASA Technical Reports Server (NTRS)

Knapp, G. R.; Gunn, J. E.; Wynn-Williams, C. G.

1992-01-01

Small aperture 10.2-micron measurements of normal elliptical galaxies show that for almost all of these galaxies the 12-micron emission seen by IRAS is extended on the scale of the galaxy. NGC 1052 and NGC 3998 are exceptions to this; much of their 10-12-micron emission comes from the inner regions of the galaxies and may be associated with their active nuclei, as is the case for many radio galaxies. The distribution of the IR light and the IR colors of elliptical galaxies suggest that the most plausible source of the 12-micron emission is photospheric and circumstellear emission from cool evolved red giant stars. The 12-micron emission is well in excess of that expected from photospheric emission alone; about 40 percent of it probably comes from circumstellar dust.

Vibrationally excited water emission at 658 GHz from evolved stars

NASA Astrophysics Data System (ADS)

Baudry, A.; Humphreys, E. M. L.; Herpin, F.; Torstensson, K.; Vlemmings, W. H. T.; Richards, A. M. S.; Gray, M. D.; De Breuck, C.; Olberg, M.

2018-01-01

Context. Several rotational transitions of ortho- and para-water have been identified toward evolved stars in the ground vibrational state as well as in the first excited state of the bending mode (v2 = 1 in (0, 1, 0) state). In the latter vibrational state of water, the 658 GHz J = 11,0-10,1 rotational transition is often strong and seems to be widespread in late-type stars. Aims: Our main goals are to better characterize the nature of the 658 GHz emission, compare the velocity extent of the 658 GHz emission with SiO maser emission to help locate the water layers and, more generally, investigate the physical conditions prevailing in the excited water layers of evolved stars. Another goal is to identify new 658 GHz emission sources and contribute in showing that this emission is widespread in evolved stars. Methods: We have used the J = 11,0-10,1 rotational transition of water in the (0, 1, 0) vibrational state nearly 2400 K above the ground-state to trace some of the physical conditions of evolved stars. Eleven evolved stars were extracted from our mini-catalog of existing and potential 658 GHz sources for observations with the Atacama Pathfinder EXperiment (APEX) telescope equipped with the SEPIA Band 9 receiver. The 13CO J = 6-5 line at 661 GHz was placed in the same receiver sideband for simultaneous observation with the 658 GHz line of water. We have compared the ratio of these two lines to the same ratio derived from HIFI earlier observations to check for potential time variability in the 658 GHz line. We have compared the 658 GHz line properties with our H2O radiative transfer models in stars and we have compared the velocity ranges of the 658 GHz and SiO J = 2-1, v = 1 maser lines. Results: Eleven stars have been extracted from our catalog of known or potential 658 GHz evolved stars. All of them show 658 GHz emission with a peak flux density in the range ≈50-70 Jy (RU Hya and RT Eri) to ≈2000-3000 Jy (VY CMa and W Hya). Five Asymptotic Giant Branch (AGB) stars and one supergiant (AH Sco) are new detections. Three AGBs and one supergiant (VY CMa) exhibit relatively weak 13CO J = 6-5 line emission while o Ceti shows stronger 13CO emission. We have shown that the 658 GHz line is masing and we found that the 658 GHz velocity extent tends to be correlated with that of the SiO maser suggesting that both emission lines are excited in circumstellar layers close to the central star. Broad and stable line profiles are observed at 658 GHz. This could indicate maser saturation although we have tentatively provided first information on time variability at 658 GHz.

Verification Results of Jet Resonance-enhanced Multiphoton Ionization as a Real-time PCDD/F Emission Monitor

EPA Science Inventory

The Jet REMPI (Resonance Enhanced Multiphoton Ionization) monitor was tested on a hazardous waste firing boiler for its ability to determine concentrations of polychlorinated dibenzodioxins and dibenzofurans (PCDDs/Fs). Jet REMPI is a real time instrument capable of highly selec...

X-ray Excitation Triggers Ytterbium Anomalous Emission in CaF2:Yb but Not in SrF2:Yb.

PubMed

Hughes-Currie, Rosa B; Ivanovskikh, Konstantin V; Wells, Jon-Paul R; Reid, Michael F; Gordon, Robert A; Seijo, Luis; Barandiarán, Zoila

2017-03-16

Materials that luminesce after excitation with ionizing radiation are extensively applied in physics, medicine, security, and industry. Lanthanide dopants are known to trigger crystal scintillation through their fast d-f emissions; the same is true for other important applications as lasers or phosphors for lighting. However, this ability can be seriously compromised by unwanted anomalous emissions often found with the most common lanthanide activators. We report high-resolution X-ray-excited optical (IR to UV) luminescence spectra of CaF 2 :Yb and SrF 2 :Yb samples excited at 8949 eV and 80 K. Ionizing radiation excites the known anomalous emission of ytterbium in the CaF 2 host but not in the SrF 2 host. Wave function-based ab initio calculations of host-to-dopant electron transfer and Yb 2+ /Yb 3+ intervalence charge transfer explain the difference. The model also explains the lack of anomalous emission in Yb-doped SrF 2 excited by VUV radiation.

THE KINEMATICS AND IONIZATION OF NUCLEAR GAS CLOUDS IN CENTAURUS A

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bicknell, Geoffrey V.; Sutherland, Ralph S.; Neumayer, Nadine, E-mail: Geoff.Bicknell@anu.edu.au, E-mail: Ralph.Sutherland@anu.edu.au, E-mail: nadine.neumayer@universe-cluster.de

2013-03-20

Neumayer et al. established the existence of a blueshifted cloud in the core of Centaurus A, within a few parsecs of the nucleus and close to the radio jet. We propose that the cloud has been impacted by the jet, and that it is in the foreground of the jet, accounting for its blueshifted emission on the southern side of the nucleus. We consider both shock excitation and photoionization models for the excitation of the cloud. Shock models do not account for the [Si VI] and [Ca VIII] emission line fluxes. However, X-ray observations indicate a source of ionizing photonsmore » in the core of Centaurus A; photoionization by the inferred flux incident on the cloud can account for the fluxes in these lines relative to Brackett-{gamma}. The power-law slope of the ionizing continuum matches that inferred from synchrotron models of the X-rays. The logarithm of the ionization parameter is -1.9, typical of that in Seyfert galaxies and consistent with the value proposed for dusty ionized plasmas. The model cloud density depends upon the Lorentz factor of the blazar and the inclination of our line of sight to the jet axis. For acute inclinations, the inferred density is consistent with expected cloud densities. However, for moderate inclinations of the jet to the line of sight, high Lorentz factors imply cloud densities in excess of 10{sup 5} cm{sup -3} and very low filling factors, suggesting that models of the gamma-ray emission should incorporate jet Lorentz factors {approx}< 5.« less

Efficient Ionization Investigation for Flow Control and Energy Extraction

NASA Technical Reports Server (NTRS)

Schneider, Steven J.; Kamhawi, Hani; Blankson, Isaiah M.

2009-01-01

Nonequilibrium ionization of air by nonthermal means is explored for hypersonic vehicle applications. The method selected for evaluation generates a weakly ionized plasma using pulsed nanosecond, high-voltage discharges sustained by a lower dc voltage. These discharges promise to provide a means of energizing and sustaining electrons in the air while maintaining a nearly constant ion/neutral molecule temperature. This paper explores the use of short approx.5 nsec, high-voltage approx.12 to 22 kV, repetitive (40 to 100 kHz) discharges in generating a weakly ionized gas sustained by a 1 kV dc voltage in dry air at pressures from 10 to 80 torr. Demonstrated lifetimes of the sustainer discharge current approx.10 to 25 msec are over three orders of magnitude longer than the 5 nsec pulse that generates the electrons. This life is adequate for many high speed flows, enabling the possibility of exploiting weakly ionized plasma phenomena in flow-fields such as those in hypersonic inlets, combustors, and nozzles. Results to date are obtained in a volume of plasma between electrodes in a bell jar. The buildup and decay of the visible emission from the pulser excited air is photographed on an ICCD camera with nanosecond resolution and the time constants for visible emission decay are observed to be between 10 to 15 nsec decreasing as pressure increases. The application of the sustainer voltage does not change the visible emission decay time constant. Energy consumption as indicated by power output from the power supplies is 194 to 669 W depending on pulse repetition rate.

Multiband counterparts of two eclipsing ultraluminous X-ray sources in M 51

NASA Astrophysics Data System (ADS)

Urquhart, R.; Soria, R.; Johnston, H. M.; Pakull, M. W.; Motch, C.; Schwope, A.; Miller-Jones, J. C. A.; Anderson, G. E.

2018-04-01

We present the discovery and interpretation of ionized nebulae around two ultraluminous X-ray sources in M 51; both sources share the rare property of showing X-ray eclipses by their companion stars and are therefore prime targets for follow-up studies. Using archival Hubble Space Telescope images, we found an elongated, 100-pc-long emission-line structure associated with one X-ray source (CXOM51 J132940.0+471237; ULX-1 for simplicity), and a more circular, ionized nebula at the location of the second source (CXOM51 J132939.5+471244; ULX-2 for simplicity). We observed both nebulae with the Large Binocular Telescope's Multi-Object Double Spectrograph. From our analysis of the optical spectra, we argue that the gas in the ULX-1 bubble is shock-ionized, consistent with the effect of a jet with a kinetic power of ≈2 × 1039 erg s-1. Additional X-ray photoionization may also be present, to explain the strength of high-ionization lines such as He II λ4686 and [Ne V] λ3426. On the other hand, the emission lines from the ULX-2 bubble are typical for photoionization by normal O stars suggesting that the nebula is actually an H II region not physically related to the ULX but is simply a chance alignment. From archival Very Large Array data, we also detect spatially extended, steep-spectrum radio emission at the location of the ULX-1 bubble (consistent with its jet origin), but no radio counterpart for ULX-2 (consistent with the lack of shock-ionized gas around that source).

Interstellar matter in Shapley-Ames elliptical galaxies. II. The distribution of dust and ionized gas

NASA Astrophysics Data System (ADS)

Goudfrooij, P.; Hansen, L.; Jorgensen, H. E.; Norgaard-Nielsen, H. U.

1994-06-01

We present results of deep optical CCD imaging for a complete, optical magnitude-limited sample of 56 elliptical galaxies from the RSA catalog. For each galaxy we have obtained broad-band images (in B, V, and I) and narrow-band images using interference filters isolating the Hα+[NII] emission lines to derive the amount and morphology of dust and ionized gas. Detailed consideration of systematic errors due to effects of sky background subtraction and removal of stellar continuum light from the narrow-band images is described. The flux calibration of the narrow-band images is performed by deconvolving actually measured spectral energy distributions with the filter transmission curves. We also present optical long-slit spectroscopy to determine the [NII]/Hα intensity ratio of the ionized gas. Dust lanes and/or patches have been detected in 23 galaxies (41%) from this sample using both colour-index images and division by purely elliptical model images. We achieved a detection limit for dust absorption of A_B_~0.02. Accounting for selection effects, the true fraction of elliptical galaxies containing dust is estimated to be of order 80%. This detection rate is comparable to that of the IRAS satellite, and significantly larger than results of previous optical studies. Ionized gas has been detected in 32 galaxies (57%). The spectroscopic data confirm the presence and distribution of ionized gas as seen in the direct imaging. All elliptical galaxies in our sample in which a number of emission lines is detected show very similar emission-line intensity ratios, which are typical of LINER nuclei. The amounts of detectable dust and ionized gas are generally small--of order 10^4^-10^5^Msun_ of dust and 10^3^-10^4^Msun_ of ionized gas. The dust and ionized gas show a wide variety of distributions-extended along either the apparent major axis, or the minor axis, or a skewed axis, indicating that triaxiality is in general required as a galaxy figure. In some cases (NGC 1275, NGC 2325, NGC 3136, NGC 3962, NGC 4696, NGC 5018, NGC 5044, NGC 5813, IC 1459) the interstellar matter has a patchy or filamentary distribution, suggestive of a recent interaction event. The distributions of dust and ionized gas are consistent with being physically associated with each other.

How A Black Hole Lights Up Its Surroundings

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-10-01

How do the supermassive black holes that live at the centers of galaxies influence their environments? New observations of a distant active galaxy offer clues about this interaction.Signs of CoevolutionPlot demonstrating the m-sigma relation, the empirical correlation between the stellar velocity dispersion of a galactic bulge and the mass of the supermassive black hole at its center. [Msigma]We know that the centers of active galaxies host supermassive black holes with masses of millions to billions of suns. One mystery surrounding these beasts is that they are observed to evolve simultaneously with their host galaxies for instance, an empirical relationship is seen between the growth of a black hole and the growth of its host galaxys bulge. This suggests that there must be a feedback mechanism through which the evolution of a black hole is linked to that of its host galaxy.One proposed source of this coupling is the powerful jets emitted from the poles of these supermassive black holes. These jets are thought to be produced as some of the material accreting onto the black hole is flung out, confined by surrounding gas and magnetic fields. Because the jets of hot gas and radiation extend outward through the host galaxy, they provide a means for the black hole to influence the gas and dust of its surroundings.In our current model of a radio-loud active galactic nuclei,a region of hot, ionized gas the narrow-line region lies beyond the sphere of influence of the supermassive black hole. [C.M. Urry and P. Padovani]Clues in the Narrow-Line RegionThe region of gas thought to sit just outside of the black holes sphere of influence (at a distance of perhaps a thousand to a few thousand light-years) is known as the narrow line region so named because we observe narrow emission lines from this gas. Given its hot, ionized state, this gas must somehow be being pummeled with energy. In the canonical picture, radiation from the black hole heats the gas directly in a process called photoionization. But could jets also be involved?In a recent study led by kos Bogdn, a team of scientists at the Harvard-Smithsonian Center for Astrophysics used X-ray observations of a galaxys nucleus to explore the possibility that its narrow-line region is heated and ionized not only by radiation, but also by the shocks produced as radio jets collide with their surrounding environment.Heating from JetsChandra X-ray data for Mrk 3, with radio contours overplotted. Both wavelengths show S-shaped morphology of the jets, with the X-ray emission enveloping the radio emission. A strong shock is present in the west and a weaker shock toward the east. [Bogdn et al. 2017]Bogdn and collaborators analyzed deep Chandra X-ray observations of the center of Mrk 3, an early-type galaxy located roughly 200 million light-years away. Chandras imaging and high-resolution spectroscopy of the galaxys narrow-line region allowed the team to build a detailed picture of the hot gas, demonstrating that it shows similar S-shaped morphology to the gas emitting at radio wavelengths, but its more broadly distributed.The authors demonstrate the presence of shocks in the X-ray gas both toward the west and toward the east of the nucleus. These shocks, combined with the broadening of the X-ray emission and other signs, strongly support the idea that collisions of the jets with the surrounding environment heat the narrow-line-region gas, contributing to its ionization. The authors argue that, given how common small-scale radio jets are in galaxies such as Mrk 3, its likely that collisional ionization plays an important role in how the black holes in these galaxies impart energy to their surrounding environments.Citationkos Bogdn et al 2017 ApJ 848 61. doi:10.3847/1538-4357/aa8c76

Characterization of photomultiplier tubes in a novel operation mode for Secondary Emission Ionization Calorimetry

NASA Astrophysics Data System (ADS)

Tiras, E.; Dilsiz, K.; Ogul, H.; Southwick, D.; Bilki, B.; Wetzel, J.; Nachtman, J.; Onel, Y.; Winn, D.

2016-10-01

Hamamatsu single anode R7761 and multi-anode R5900-00-M16 Photomultiplier Tubes have been characterized for use in a Secondary Emission (SE) Ionization Calorimetry study. SE Ionization Calorimetry is a novel technique to measure electromagnetic shower particles in extreme radiation environments. The different operation modes used in these tests were developed by modifying the conventional PMT bias circuit. These modifications were simple changes to the arrangement of the voltage dividers of the baseboard circuits. The PMTs with modified bases, referred to as operating in SE mode, are used as an SE detector module in an SE calorimeter prototype, and placed between absorber materials (Fe, Cu, Pb, W, etc.). Here, the technical design of different operation modes, as well as the characterization measurements of both SE modes and the conventional PMT mode are reported.

The Interaction Between Accretion from the Interstellar Medium and Accretion from the Evolved Binary Component in Barium Stars

NASA Astrophysics Data System (ADS)

Jeong, Yeuncheol; Yushchenko, Alexander V.; Doikov, Dmytry N.

2018-03-01

The reanalysis of the previously published abundance pattern of mild barium star HD202109 (ζ Cyg) and the chemical compositions of 129 thin disk barium stars facilitated the search for possible correlations of different stellar parameters with second ionization potentials of chemical elements. Results show that three valuable correlations exist in the atmospheres of barium stars. The first is the relationship between relative abundances and second ionization potentials. The second is the age dependence of mean correlation coefficients of relative abundances vs. second ionization potentials, and the third one is the changes in correlation coefficients of relative abundances vs. second ionization potentials as a function of stellar spatial velocities and overabundances of s-process elements. These findings demonstrate the possibility of hydrogen and helium accretion from the interstellar medium on the atmospheres of barium stars.

Analyzing the Signatures of High Red-shift Hydrogen: The Lyman Alpha and 21cm Emission Lines

NASA Astrophysics Data System (ADS)

Hansen, Matthew

Hydrogen line emission is an important window on galaxy formation due to the large abundance of neutral hydrogen in the early Universe. This dissertation comprises two theoretical/computational studies of two types of hydrogen line emission: Lyman alpha emission and escape from young stellar populations, and 21cm radiation from neutral hydrogen clouds at the time of the first luminous objects. The Lyman alpha research concerns the radiative transfer of resonant line radiation from a central source escaping from a multi-phase medium appropriate to young star forming regions. To analyze the properties of this novel radiative transfer problem I develop new theoretical formulations of the problem, substantiated by physically accurate monte carlo simulations of photon scattering and absorption through multi-phase gas geometries. I find that the escape fraction of resonant line photons from young star forming regions--ionized gas filled with neutral hydrogen clouds with low dust content--can exceed the continuum photon escape fraction by up to an order of magnitude. Additionally, I study the effect of gas outflow on the line profile of escaping resonant photons. In light of these results, I discuss why a young normal stellar populations surrounded by a clumpy multi-phase gas outflow can explain the Lyman alpha spectra seen from high red-shift Lyman Alpha Emitters (LAEs). The 21cm research concerns the ionization evolution of the Intergalactic Medium (IGM) during the era of the first luminous objects in the Universe. Large radio-array observatories are currently being built to specifically detect the red-shifted 21cm radiation from neutral hydrogen at red-shifts z ˜ 12 - - 6; the output will be three dimensional maps of ionized regions across the plane of the sky at various red-shift depths. The signal in the resulting ionization maps will be limited by observational noise, mainly from foreground galactic emission in radio frequencies. The research presented here is a unique approach to data mining the planned observational ionization map data. I develop the one-point statistics of the observed 21cm intensity appropriate for the IGM at high red-shifts using a mixture model technique. I show that physically interesting parameters of such mixture models, such as the total ionized gas fraction at a given red-shift slice, can be estimated by applying Maximum Likelihood Expectation to the mixture model of the observed 21cm intensity distribution. The confidence intervals on the expected model parameters are rigorously calculated, and applied to expected detection capabilities of the planned radio-array observatories. I find that at least one of the observatories, the Low Frequency Array (LOFAR), will be able to statistically detect the evolution of the total ionized gas fraction with good precision.

The Influence of Emission Location on the Magnitude and Spatial Distribution of Aerosols' Climate Effects

NASA Astrophysics Data System (ADS)

Persad, G.; Caldeira, K.

2017-12-01

The global distribution of anthropogenic aerosol emissions has evolved continuously since the preindustrial era - from 20th century North American and Western European emissions hotspots to present-day South and East Asian ones. With this comes a relocation of the regional radiative, dynamical, and hydrological impacts of aerosol emissions, which may influence global climate differently depending on where they occur. A lack of understanding of this relationship between aerosol emissions' location and their global climate effects, however, obscures the potential influence that aerosols' evolving geographic distribution may have on global and regional climate change—a gap which we address in this work. Using a novel suite of experiments in the CESM CAM5 atmospheric general circulation model coupled to a slab ocean, we systematically test and analyze mechanisms behind the relative climate impact of identical black carbon and sulfate aerosol emissions located in each of 8 past, present, or projected future major emissions regions. Results indicate that historically high emissions regions, such as North America and Western Europe, produce a stronger cooling effect than current and projected future high emissions regions. Aerosol emissions located in Western Europe produce 3 times the global mean cooling (-0.34 °C) as those located in East Africa or India (-0.11 °C). The aerosols' in-situ radiative effects remain relatively confined near the emissions region, but large distal cooling results from remote feedback processes - such as ice albedo and cloud changes - that are excited more strongly by emissions from certain regions than others. Results suggest that aerosol emissions from different countries should not be considered equal in the context of climate mitigation accounting, and that the evolving geographic distribution of aerosol emissions may have a substantial impact on the magnitude and spatial distribution of global climate change.

A Modified Kinematic Model of Neutral and Ionized Gas in Galactic Center

NASA Astrophysics Data System (ADS)

Krishnarao, Dhanesh; Benjamin, Robert A.; Haffner, L. Matthew

2018-01-01

Gas near the center of the Milky Way is very complex across all phases (cold, warm, neutral, ionized, atomic, molecular, etc.) and shows strong observational evidence for warping, lopsided orientations and strongly non-circular kinematics. Historically, the kinematic complexities were modeled with many discrete features involved with expulsive phenomena near Galactic Center. However, much of the observed emission can be explained with a single unified and smooth density structure when geometrical and perspective effects are accounted for. Here we present a new model for a tilted, elliptical disk of gas within the inner 2 kpc of Galactic center based on the series of models following Burton & Liszt (1978 - 1992, Papers I- V). Machine learning techniques such as the Histogram of Oriented Gradients image correlation statistic are used to optimize the geometry and kinematics of neutral and ionized gas in 3D observational space (position,position, velocity). The model successfully predicts emission from neutral gas as seen by HI (Hi4Pi) and explains anomalous ionized gas features in H-Alpha emission (Wisconsin H-Alpha Mapper) and UV absorption lines (Hubble Space Telescope - Space Telescope Imaging Spectrograph). The modeled distribution of this tilted gas disk along with its kinematics of elliptical x1 orbits can reveal new insight about the Galactic Bar, star formation, and high-velocity gas near Galactic Center and its relation with the Fermi Bubble.

NEBULAR: Spectrum synthesis for mixed hydrogen-helium gas in ionization equilibrium

NASA Astrophysics Data System (ADS)

Schirmer, Mischa

2016-08-01

NEBULAR synthesizes the spectrum of a mixed hydrogen helium gas in collisional ionization equilibrium. It is not a spectral fitting code, but it can be used to resample a model spectrum onto the wavelength grid of a real observation. It supports a wide range of temperatures and densities. NEBULAR includes free-free, free-bound, two-photon and line emission from HI, HeI and HeII. The code will either return the composite model spectrum, or, if desired, the unrescaled atomic emission coefficients. It is written in C++ and depends on the GNU Scientific Library (GSL).

Direct spectroscopic evidence for ionized polycyclic aromatic hydrocarbons in the interstellar medium.

PubMed

Sloan, G C; Hayward, T L; Allamandola, L J; Bregman, J D; DeVito, B; Hudgins, D M

1999-03-01

Long-slit 8-13 micrometers spectroscopy of the nebula around NGC 1333 SVS 3 reveals spatial variations in the strength and shape of emission features that are probably produced by polycyclic aromatic hydrocarbons (PAHs). Close to SVS 3, the 11.2 micrometers feature develops an excess at approximately 10.8-11.0 micrometers and a feature appears at approximately 10 micrometers. These features disappear with increasing distance from the central source, and they show striking similarities to recent laboratory data of PAH cations, providing the first identification of emission features arising specifically from ionized PAHs in the interstellar medium.

Characterization of Novel Operation Modes for Secondary Emission Ionization Calorimetry

NASA Astrophysics Data System (ADS)

Tiras, Emrah; Dilsiz, Kamuran; Ogul, Hasan; Snyder, Christina; Bilki, Burak; Onel, Yasar; Winn, David

2017-01-01

Secondary Emission (SE) Ionization Calorimetry is a novel technique to measure electromagnetic showers in high radiation environments. We have developed new operation modes by modifying the bias of the conventional PMT circuits. Hamamatsu single anode R7761 and multi-anode R5900-00-M16 Photomultiplier Tubes (PMTs) with modified bases are used as SE detector modules in our SE calorimetry prototype. In this detector module, the first dynode is used as the active media as opposed to photocathode. Here, we report the technical design of new modes and characterization measurements for both SE and PMT modes.

The stellar content of the nuclear regions of Sc galaxies

NASA Technical Reports Server (NTRS)

Turnrose, B. E.

1976-01-01

Stellar-population syntheses based on absolute spectral energy distributions over the wavelength range from 3300 to 10,400 A are used to determine the stellar content of the nuclear regions of seven nearby Sc galaxies (NGC 628, 1073, 1084, 1637, 2903, 4321, and 5194). A linear-programming procedure is employed to construct models of the overall stellar populations whose spectra closely match those of the seven galaxies. Absolute measurements of the emission-line spectra of the nuclear regions are also provided. It is found that: (1) intrinsic reddening is probably present in each nuclear region; (2) the upper main sequence is substantially populated in most of the models; (3) the lower main sequence contributes insignificantly to the luminosity in all optimal solutions; (4) substantial contributions are made by evolved M stars at long wavelengths in all the models; (5) the model photometric M/L ratios are low, of the order of unity; and (6) the O-B stars arising naturally in the population models are just sufficient to provide the observed nuclear ionization in all the galaxies except NGC 5194, which may be collisionally ionized. The properties of the nuclear regions are shown to be consistent with the existence of a common initial mass function for star formation and a variety of time dependences for the star-formation process. A possibly significant correlation is noted between nuclear stellar content and overall dynamical properties in four of the galaxies.

Nebular Continuum and Line Emission in Stellar Population Synthesis Models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Byler, Nell; Dalcanton, Julianne J.; Conroy, Charlie

Accounting for nebular emission when modeling galaxy spectral energy distributions (SEDs) is important, as both line and continuum emissions can contribute significantly to the total observed flux. In this work, we present a new nebular emission model integrated within the Flexible Stellar Population Synthesis code that computes the line and continuum emission for complex stellar populations using the photoionization code Cloudy. The self-consistent coupling of the nebular emission to the matched ionizing spectrum produces emission line intensities that correctly scale with the stellar population as a function of age and metallicity. This more complete model of galaxy SEDs will improvemore » estimates of global gas properties derived with diagnostic diagrams, star formation rates based on H α , and physical properties derived from broadband photometry. Our models agree well with results from other photoionization models and are able to reproduce observed emission from H ii regions and star-forming galaxies. Our models show improved agreement with the observed H ii regions in the Ne iii/O ii plane and show satisfactory agreement with He ii emission from z = 2 galaxies, when including rotating stellar models. Models including post-asymptotic giant branch stars are able to reproduce line ratios consistent with low-ionization emission regions. The models are integrated into current versions of FSPS and include self-consistent nebular emission predictions for MIST and Padova+Geneva evolutionary tracks.« less

Understanding Emission From The Ism In The Milky Way And Other Galaxies Using [Nii] And Other Tracers

NASA Astrophysics Data System (ADS)

Goldsmith, Paul

We propose to combine recently-obtained data on the far-infrared fine structure lines of ionized nitrogen ([NII]) with studies of radio continuum and other far-infrared lines, to address a number of key questions about the structure of the interstellar medium, star formation, and to bootstrap our detailed understanding of processes in the Milky Way to more distant galaxies. The [CII] 158 μm line is the most powerful single far-infrared line emitted by galaxies, but since carbon can be ionized by photons having wavelengths longer than required to ionized hydrogen, [CII] emission can originate in atomic, molecular, and ionized regions. Due to its ionization potential being higher than that of hydrogen, nitrogen is a more selective tracer than carbon, and can serve as a critical ingredient to determine how much of the [CII] emission is produced in HII regions powered by massive young stars. We propose to take advantage of a newly-completed Herschel survey of the Galactic plane in both of the [NII] lines at 205 μm and 122 μm wavelength, complementing the GOT C+ survey of [CII]. The relative intensity of the two [NII] lines is a direct indicator of the electron density, and thus allows determination of the N+ column density. With the two data sets we can then determine what fraction of the [CII] emission is produced in HII regions, and what may be from the more diffuse components, thus enabling reconciliation of the Herschel and COBE measurements of this critical tracer. We also propose to use Planck and WMAP all-sky maps of the radio free-free emission to determine the emission measure. Comparison with the electron density and ionized nitrogen column density enables a novel probe of clumpiness in this component of the interstellar medium in addition to giving an improved method of determining the overall Galactic electron density distribution. A second aspect of our investigation of clumpiness will be to utilize the fact that each [NII] observation with the PACS instrument on Herschel consists of 25 spectra on a 5x5 grid. Using these, we will compare derived column densities and electron densities over these small regions to assess the degree of clumpiness. A third input to our analysis of inhomogeneities will be to compare the Planck & WMAP images of selected regions with much higher resolution ground-based data from survey such as CORNISH and GALFACTS. We also will use the improved understanding of [CII] and [NII] emission to develop a template for use in interpreting emission of these (and possibly other) tracers from other galaxies. We will be able to calculate the relative luminosities of these two tracers as a function of Galactocentric distance in the Milky Way, which will be available for comparison with existing and future data on other galaxies. This very active field suffers from an inability to distinguish the multiple sources of [CII] emission, and the understanding of how this spectral line works as a tracer of star formation is of very great interest to a large community of extragalactic astronomers. Together these studies will significantly improve our understanding of [CII] emission and its role as a coolant of the ISM, and the role of HII regions produced by massive young stars as sources of far-infrared line emission. In addition to a better appreciation of the life cycle of the interstellar medium, this work will also set the stage for better understanding of far-infrared emission from other galaxies though development of an improved Milky Way template. All of the data have been taken and are available including our own Herschel [NII] data, which have been reduced. As indicated in the proposal, we have made a limited demonstration of the required techniques, so that we are confident that this proposal will yield the desired new information and astrophysical results.

The Contribution of Ionizing Stars to the Far-Infrared and Radio Emission in the Galaxy

NASA Astrophysics Data System (ADS)

Terebey, S.; Fich, M.; Taylor, R.

1999-12-01

A summary of research activities carried out in this eighth and final progress report. The final report includes: this summary document, copies of three published research papers, plus a draft manuscript of a fourth research paper entitled "The Contribution of Ionizing Stars to the FarInfrared and Radio Emission in the Milky Way; Evidence for a Swept-up Shell and Diffuse Ionized Halo around the W4 Chimney/Supershell." The main activity during the final quarterly reporting period was research on W4, including analysis of the radio and far-infrared images, generation of shell models, a literature search, and preparation of a research manuscript. There will be additional consultation with co-authors prior to submission of the paper to the Astrophysical Journal. The results will be presented at the 4th Tetons Summer Conference on "Galactic Structure, Stars, and the ISM" in May 2000. In this fourth and last paper we show W4 has a swept-up partially ionized shell of gas and dust which is powered by the OCl 352 star cluster. Analysis shows there is dense interstellar material directly below the shell, evidence that that the lower W4 shell "ran into a brick wall" and stalled, whereas the upper W4 shell achieved "breakout" to form a Galactic chimney. An ionized halo is evidence of Lyman continuum leakage which ionizes the WIM (warm ionized medium). It has long been postulated that the strong winds and abundant ionizing photons from massive stars are responsible for much of the large scale structure in the interstellar medium (ISM), including the ISM in other galaxies. However standard HII region theory predicts few photons will escape the local HII region. The significance of W4 and this work is it provides a direct example of how stellar winds power a galactic chimney, which in turn leads to a low density cavity from which ionizing photons can escape to large distances to ionize the WIM.

The Contribution of Ionizing Stars to the Far-Infrared and Radio Emission in the Galaxy

NASA Technical Reports Server (NTRS)

Terebey, S.; Fich, M.; Taylor, R.

1999-01-01

A summary of research activities carried out in this eighth and final progress report. The final report includes: this summary document, copies of three published research papers, plus a draft manuscript of a fourth research paper entitled "The Contribution of Ionizing Stars to the FarInfrared and Radio Emission in the Milky Way; Evidence for a Swept-up Shell and Diffuse Ionized Halo around the W4 Chimney/Supershell." The main activity during the final quarterly reporting period was research on W4, including analysis of the radio and far-infrared images, generation of shell models, a literature search, and preparation of a research manuscript. There will be additional consultation with co-authors prior to submission of the paper to the Astrophysical Journal. The results will be presented at the 4th Tetons Summer Conference on "Galactic Structure, Stars, and the ISM" in May 2000. In this fourth and last paper we show W4 has a swept-up partially ionized shell of gas and dust which is powered by the OCl 352 star cluster. Analysis shows there is dense interstellar material directly below the shell, evidence that that the lower W4 shell "ran into a brick wall" and stalled, whereas the upper W4 shell achieved "breakout" to form a Galactic chimney. An ionized halo is evidence of Lyman continuum leakage which ionizes the WIM (warm ionized medium). It has long been postulated that the strong winds and abundant ionizing photons from massive stars are responsible for much of the large scale structure in the interstellar medium (ISM), including the ISM in other galaxies. However standard HII region theory predicts few photons will escape the local HII region. The significance of W4 and this work is it provides a direct example of how stellar winds power a galactic chimney, which in turn leads to a low density cavity from which ionizing photons can escape to large distances to ionize the WIM.

Line formation in the hot spot region of cataclysmic variable accretion disks

NASA Technical Reports Server (NTRS)

Elitzur, Moshe; Clarke, John T.; Kallman, T. R.

1988-01-01

The paper presents a theoretical analysis of the emission lines observed in the cataclysmic variable A0 Psc (=H2252-035), including detailed modeling of the hydrogen Balmer line emission. The analysis makes it possible to deduce the physical conditions in the so called 'hot spot', or 'bulge' region where the accretion column hits the rim of the accretion disk. It is concluded that the bulge is optically thick to the ionizing disk radiation. Consequently, its disk illuminated face is fully ionized whereas the side facing away from the disk is neutral, resulting in modulation of the observed emission lines with the orbital period. The density in the hot spot is about 5 x 10 to the 12th to 10 to the 13th/cu cm.

On the density and field sensitivities of dielectronic recombination. [rates in coronal plasmas of late stars and sun

NASA Technical Reports Server (NTRS)

Reisenfeld, Daniel B.; Raymond, John C.; Young, Albert R.; Kohl, John L.

1992-01-01

Dielectronic recombination dominates the recombination rates of most ions in coronal plasmas at their temperatures of peak concentration. Because dielectronic recombination goes by way of high nl doubly excited levels, it is susceptible to collisional excitation and ionization, leading to a decreased rate. On the other hand, theoretical studies show that Stark mixing of the nl levels by a modest electric field enhances the dielectronic recombination rate severalfold. The ionization balance is computed here as as function of density, and it is found that the new results require increased emission measures to match the C IV emission line intensities observed in the sun and in late-type stars. They also make it more difficult to interpret the overall EUV emission line spectrum of the sun.

A Physically based Model of the Ionizing Radiation from Active Galaxies for Photoionization Modeling

NASA Astrophysics Data System (ADS)

Thomas, A. D.; Groves, B. A.; Sutherland, R. S.; Dopita, M. A.; Kewley, L. J.; Jin, C.

2016-12-01

We present a simplified model of active galactic nucleus (AGN) continuum emission designed for photoionization modeling. The new model oxaf reproduces the diversity of spectral shapes that arise in physically based models. We identify and explain degeneracies in the effects of AGN parameters on model spectral shapes, with a focus on the complete degeneracy between the black hole mass and AGN luminosity. Our reparametrized model oxaf removes these degeneracies and accepts three parameters that directly describe the output spectral shape: the energy of the peak of the accretion disk emission {E}{peak}, the photon power-law index of the non-thermal emission Γ, and the proportion of the total flux that is emitted in the non-thermal component {p}{NT}. The parameter {E}{peak} is presented as a function of the black hole mass, AGN luminosity, and “coronal radius” of the optxagnf model upon which oxaf is based. We show that the soft X-ray excess does not significantly affect photoionization modeling predictions of strong emission lines in Seyfert narrow-line regions. Despite its simplicity, oxaf accounts for opacity effects where the accretion disk is ionized because it inherits the “color correction” of optxagnf. We use a grid of mappings photoionization models with oxaf ionizing spectra to demonstrate how predicted emission-line ratios on standard optical diagnostic diagrams are sensitive to each of the three oxaf parameters. The oxaf code is publicly available in the Astrophysics Source Code Library.

29 CFR 1910.16 - Longshoring and marine terminals.

Code of Federal Regulations, 2010 CFR

2010-07-01

...) Ionizing radiation. Subpart Z, § 1910.1096; (vi) Noise. Subpart G, § 1910.95; (vii) Nonionizing radiation. Subpart G, § 1910.97; Note to paragraph (a)(2)(vii): Exposures to nonionizing radiation emissions from.... Subpart Z, § 1910.1200; (vii) Ionizing radiation. Subpart Z, § 1910.1096; (viii) Noise. Subpart G, § 1910...

Solar coronal temperature diagnostics using emission line from multiple stages of ionization of iron

NASA Technical Reports Server (NTRS)

Brosius, Jeffrey W.; Davila, Joseph M.; Thomas, Roger J.; Thompson, William T.

1994-01-01

We obtained spatially resolved extreme-ultraviolet (EUV) spectra of AR 6615 on 1991 May 7 with NASA/ Goddard Space Flight Center's Solar EUV Rocket Telescope and Spectrograph (SERTS). Included are emission lines from four different stages of ionization of iron: Fe(+15) lambda 335 A, Fe(+14) lambda 327 A, Fe(+13) lambda 334 A, and Fe(+12) lambda 348 A. Using intensity ratios from among these lines, we have calculated the active region coronal temperature along the Solar Extreme Ultraviolet Telescope and Spectrograph (SERTS) slit. Temperatures derived from line ratios which incorporate adjacent stages of ionization are most sensitive to measurement uncertainties and yield the largest scatter. Temperatures derived from line ratios which incorporate nonadjacent stages of ionization are less sensitive to measurement uncertainties and yield little scatter. The active region temperature derived from these latter ratios has an average value of 2.54 x 10(exp 6) K, with a standard deviation approximately 0.12 x 10(exp 6) K, and shows no significant variation with position along the slit.

Quantitative measurements of vaporization, burst ionization, and emission characteristics of shaped charge barium releases

NASA Technical Reports Server (NTRS)

Hoch, Edward L.; Hallinan, Thomas J.; Stenbaek-Nielsen, Hans C.

1994-01-01

Intensity-calibrated color video recordings of three barium-shaped charge injections in the ionopshere were used to determine the initial ionization, the column density corresponding to unity optical depth, and the yield of vaporized barium in the fast jet. It was found that the initial ionization at the burst was less than 1% and that 0% burst ionization was consistent with the observations. Owing to the Doppler shift, the column density for optical thickness in the neutral barium varies somewhat according to the velocity distribution. For the cases examined here, the column density was 2-5 x 10(exp 10) atoms/sq cm. This value, which occurred 12 to 15 s after release, should be approximately valid for most shaped charge experiments. The yield was near 30% (15% in the fast jet) for two of the releases and was somewhat lower in the third, which also had a lower peak velocity. This study also demonstrated the applicability of the computer simulation code developed for chemical releases by Stenbaek-Nielsen and provided experimental verification of the Doppler-corrected emission rates calculated b Stenbaek-Nielsen (1989).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Howard, T. A., E-mail: howard@boulder.swri.edu

Measurements of Hα emission within an eruptive solar prominence are presented, using white light polarization properties as a proxy for the presence of Hα in the STEREO COR1 and COR2 coronagraphs. The transition from Hα emission to Thomson scattering radiance serves as an indicator of the ionization of the prominence, and I discuss the physical implications regarding the behavior of the neutrals and ions, and also for the measurement of coronal mass ejection properties using the Thomson scattering assumption. I find that the prominence has a high concentration of neutrals at around two solar radii that gradually exhibit ionization characteristics atmore » it moves away from the Sun. The prominence reaches complete ionization, or at least a state where the Thomson-scattered brightness dominates, by the time it reaches around seven solar radii. This is consistent with predictions inferred from direct Hα measurements made from earlier studies in the 1980s and with the predicted ionization rate of neutral hydrogen near solar maximum. These results pave the way for an accompanying paper that reports on measurements of the prominence at large distances from the Sun using the assumptions verified here.« less

Non-methane organic gas emissions from biomass burning: identification, quantification, and emission factors from PTR-ToF during the FIREX 2016 laboratory experiment

NASA Astrophysics Data System (ADS)

Koss, Abigail R.; Sekimoto, Kanako; Gilman, Jessica B.; Selimovic, Vanessa; Coggon, Matthew M.; Zarzana, Kyle J.; Yuan, Bin; Lerner, Brian M.; Brown, Steven S.; Jimenez, Jose L.; Krechmer, Jordan; Roberts, James M.; Warneke, Carsten; Yokelson, Robert J.; de Gouw, Joost

2018-03-01

Volatile and intermediate-volatility non-methane organic gases (NMOGs) released from biomass burning were measured during laboratory-simulated wildfires by proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF). We identified NMOG contributors to more than 150 PTR ion masses using gas chromatography (GC) pre-separation with electron ionization, H3O+ chemical ionization, and NO+ chemical ionization, an extensive literature review, and time series correlation, providing higher certainty for ion identifications than has been previously available. Our interpretation of the PTR-ToF mass spectrum accounts for nearly 90 % of NMOG mass detected by PTR-ToF across all fuel types. The relative contributions of different NMOGs to individual exact ion masses are mostly similar across many fires and fuel types. The PTR-ToF measurements are compared to corresponding measurements from open-path Fourier transform infrared spectroscopy (OP-FTIR), broadband cavity-enhanced spectroscopy (ACES), and iodide ion chemical ionization mass spectrometry (I- CIMS) where possible. The majority of comparisons have slopes near 1 and values of the linear correlation coefficient, R2, of > 0.8, including compounds that are not frequently reported by PTR-MS such as ammonia, hydrogen cyanide (HCN), nitrous acid (HONO), and propene. The exceptions include methylglyoxal and compounds that are known to be difficult to measure with one or more of the deployed instruments. The fire-integrated emission ratios to CO and emission factors of NMOGs from 18 fuel types are provided. Finally, we provide an overview of the chemical characteristics of detected species. Non-aromatic oxygenated compounds are the most abundant. Furans and aromatics, while less abundant, comprise a large portion of the OH reactivity. The OH reactivity, its major contributors, and the volatility distribution of emissions can change considerably over the course of a fire.

REAL-TIME EMISSION CHARACTERIZATION OF ORGANIC AIR TOXIC POLLUTANTS DURING STEADY STATE AND TRANSIENT OPERATION OF A MEDIUM DUTY DIESEL ENGINE

EPA Science Inventory

An on-line monitoring method, jet resonance-enhanced multi-photon ionization (REMPI) with time-of-flight mass spectrometry (TOFMS) was used to measure emissions of organic air toxics from a medium-duty (60 kW)diesel generator during transient and steady state operations. Emission...

DOE Office of Scientific and Technical Information (OSTI.GOV)

Devereux, Nick, E-mail: devereux@erau.edu

Dual epoch spectroscopy of the lenticular galaxy, NGC 4203, obtained with the Hubble Space Telescope has revealed that the double-peaked component of the broad H{alpha} emission line is time variable, increasing by a factor of 2.2 in brightness between 1999 and 2010. Modeling the gas distribution responsible for the double-peaked profiles indicates that a ring is a more appropriate description than a disk and most likely represents the contrail of a red supergiant star that is being tidally disrupted at a distance of {approx}1500 AU from the central black hole. There is also a bright core of broad H{alpha} linemore » emission that is not time variable and identified with a large-scale inflow from an outer radius of {approx}1 pc. If the gas number density is {>=}10{sup 6} cm{sup -3}, as suggested by the absence of similarly broad [O I] and [O III] emission lines, then the steady state inflow rate is {approx} 2 Multiplication-Sign 10{sup -2} M{sub Sun} yr{sup -1}, which exceeds the inflow requirement to explain the X-ray luminosity in terms of radiatively inefficient accretion by a factor of {approx}6. The central active galactic nucleus (AGN) is unable to sustain ionization of the broad-line region; the discrepancy is particularly acute in 2010 when the broad H{alpha} emission line is dominated by the contrail of the infalling supergiant star. However, ram pressure shock ionization produced by the interaction of the infalling supergiant with the ambient interstellar medium may help alleviate the ionizing deficit by generating a mechanical source of ionization supplementing the photoionization provided by the AGN.« less

Can the Lyman Continuum Leaked Out of H II Regions Explain Diffuse Ionized Gas?

NASA Astrophysics Data System (ADS)

Seon, Kwang-Il

2009-09-01

We present an attempt to explain the diffuse Hα emission of a face-on galaxy M 51 with the "standard" photoionization model, in which the Lyman continuum (Lyc) escaping from H II regions propagates large distances into the diffuse interstellar medium (ISM). The diffuse Hα emission of M 51 is analyzed using thin slab models and exponential disk models in the context of the "on-the-spot" approximation. The scale height of the ionized gas needed to explain the diffuse Hα emission with the scenario is found to be of the order of ~1-2 kpc, consistent with those of our Galaxy and edge-on galaxies. The model also provides a vertical profile, when the galaxy is viewed edge-on, consisting of two-exponential components. However, it is found that an incredibly low absorption coefficient of κ0 ≈ 0.4-0.8 kpc-1 at the galactic plane, or, equivalently, an effective cross section as low as σeff ~ 10-5 of the photoionization cross section at 912 Å is required to allow the stellar Lyc photons to travel through the H I disk. Such a low absorption coefficient is out of accord with the properties of the ISM. Furthermore, we found that even the model that has the diffuse ionized gas (DIG) phase only and no H I gas phase shows highly concentrated Hα emissions around H II regions, and can account for only lsim26% of the Hα luminosity of the DIG. This result places a strong constraint on the ionizing source of the DIG. We also report that the Hα intensity distribution functions not only of the DIG, but also of H II regions in M 51, appear to be lognormal.

Constraining the contribution of active galactic nuclei to reionization

NASA Astrophysics Data System (ADS)

Hassan, Sultan; Davé, Romeel; Mitra, Sourav; Finlator, Kristian; Ciardi, Benedetta; Santos, Mario G.

2018-01-01

Recent results have suggested that active galactic nuclei (AGN) could provide enough photons to reionize the Universe. We assess the viability of this scenario using a semi-numerical framework for modelling reionization, to which we add a quasar contribution by constructing a Quasar Halo Occupancy Distribution (QHOD) based on Giallongo et al. observations. Assuming a constant QHOD, we find that an AGN-only model cannot simultaneously match observations of the optical depth τe, neutral fraction and ionizing emissivity. Such a model predicts τe too low by ∼2σ relative to Planck constraints, and reionizes the Universe at z ≲ 5. Arbitrarily increasing the AGN emissivity to match these results yields a strong mismatch with the observed ionizing emissivity at z ∼ 5. If we instead assume a redshift-independent AGN luminosity function yielding an emissivity evolution like that assumed in Madau & Haardt model, then we can match τe albeit with late reionization; however, such evolution is inconsistent with observations at z ∼ 4-6 and poorly motivated physically. These results arise because AGN are more biased towards massive haloes than typical reionizing galaxies, resulting in stronger clustering and later formation times. AGN-dominated models produce larger ionizing bubbles that are reflected in ∼×2 more 21 cm power on all scales. A model with equal part galaxies and AGN contribution is still (barely) consistent with observations, but could be distinguished using next-generation 21 cm experiments such as Hydrogen Epoch of Reionization Array and SKA-low. We conclude that, even with recent claims of more faint AGN than previously thought, AGN are highly unlikely to dominate the ionizing photon budget for reionization.

Study of the molecular and ionized gas in a possible precursor of an ultra-compact H II region

NASA Astrophysics Data System (ADS)

Ortega, M. E.; Paron, S.; Giacani, E.; Celis Peña, M.; Rubio, M.; Petriella, A.

2017-10-01

Aims: We aim to study the molecular and the ionized gas in a possible precursor of an ultra-compact H II region to contribute to the understanding of how high-mass stars build-up their masses once they have reached the zero-age main sequence. Methods: We carried out molecular observations toward the position of the Red MSX source G052.9221-00.4892, using the Atacama Submillimeter Telescope Experiment (ASTE; Chile) in the 12CO J = 3-2, 13CO J = 3-2, C18O J = 3-2, and HCO+J = 4-3 lines with an angular resolution of about 22''. We also present radio continuum observations at 6 GHz carried out with the Jansky Very Large Array (JVLA; USA) interferometer with a synthesized beam of 4.8 arcsec × 4.1 arcsec. The molecular data were used to study the distribution and kinematics of the molecular gas, while the radio continuum data were used to characterize the ionized gas in the region. Combining these observations with public infrared data allowed us to inquire about the nature of the source. Results: The analysis of the molecular observations reveals the presence of a kinetic temperature and H2 column density gradients across the molecular clump in which the Red MSX source G052.9221-00.4892 is embedded, with the hotter and less dense gas in the inner region. The 12CO J = 3-2 emission shows evidence of misaligned massive molecular outflows, with the blue lobe in positional coincidence with a jet-like feature seen at 8 μm. The radio continuum emission shows a slightly elongated compact radio source, with a flux density of about 0.9 mJy, in positional coincidence with the Red MSX source. The polar-like morphology of this compact radio source perfectly matches the hourglass-like morphology exhibited by the source in the Ks band. Moreover, the axes of symmetry of the radio source and the near-infrared nebula are perfectly aligned. Thus, based on the presence of molecular outflows, the slightly elongated morphology of the compact radio source matching the hourglass-like morphology of the source at the Ks band, and the lack of evidence of collimated jets in the near-infrared spectrum, one interpretation for the nature of the source, is that the Red MSX source G052.9221-00.4892 could be transiting a hyper-compact H II region phase, in which the young central star emits winds and ionizing radiation through the poles. On the other hand, according to a comparison between the Brγ intensity and the radio flux density at 6 GHz, the source would be in a more evolved evolutionary stage of an optically thin UC H II region in photoionization equilibrium. If this is the case, from the radio continuum emission, we can conjecture upon the spectral type of its exciting star which would be a B0.5V.

First Detections of the [N II] 122 micron Line at High Redshift: Demonstrating the Utility of the Line for Studying Galaxies in the Early Universe

NASA Technical Reports Server (NTRS)

Ferkinhoff, Carl; Brisbin, Drew; Nikola, Thomas; Parshley, Stephen C.; Stacey, Gordon J.; Phillips, Thomas G.; Falgarone, Edith; Benford, Dominic J.; Staguhn, Johannes G.; Tucker, Carol E.

2011-01-01

We report the first detections of the [N II] 122 micron line from a high-redshift galaxy. The line was strongly (>6(sigma)) detected from SMMJ02399-0136, and H1413 + 117 (the Cloverleaf QSO) using the Redshift (zeta) and Early Universe Spectrometer on the Caltech Submillimeter Observatory. The lines from both sources are quite bright with line to far-infrared (FIR) continuum luminosity ratios that are approx.7.0 x 10(exp -4) (Cloverleaf) and 2.1 x 10(exo -3) (SMMJ02399). With ratios 2-10 times larger than the average value for nearby galaxies, neither source exhibits the line to continuum deficits seen in nearby sources. The line strengths also indicate large ionized gas fractions, approx.8%-17% of the molecUlar gas mass. The [O III]/[N II] line ratio is very sensitive to the effective temperature of ionizing stars and the ionization parameter for emission arising in the narrow-line region (NLR) of an active galactic nucleus (AGN). Using Our previous detection of the [O III] 88 micron line, the [O III]/[N II]line ratio for SMMJ02399-0136 indicates that the dominant source of the line emission is either stellar H II regions ionized by O9.5 stars, or the NLR of the AGN with ionization parameter log(U) = -3.3 to -4.0. A composite system, where 30%-50% of the FIR lines arise in the NLR also matches the data. The Cloverleaf is best modeled by a superposition of approx.200 M82-like starbursts accounting for all of the FIR emission and 43% of the [N II]line. The remainder may come from the NLR. This war!< demonstrates the utility of the [N II] and [O III] lines in constraining properties of the ionized medium.

Mapping Excitation in the Inner Regions of the Planetary Nebula NGC 5189 Using HST WFC3 Imaging

NASA Astrophysics Data System (ADS)

Danehkar, Ashkbiz; Karovska, Margarita; Maksym, W. Peter; Montez, Rodolfo, Jr.

2018-01-01

The planetary nebula (PN) NGC 5189 around a Wolf–Rayet [WO] central star demonstrates one of the most remarkable complex morphologies among PNe with many multiscale structures, showing evidence of multiple outbursts from an asymptotic giant branch (AGB) progenitor. In this study, we use multiwavelength Hubble Space Telescope Wide Field Camera 3 observations to study the morphology of the inner 0.3 pc × 0.2 pc region surrounding the central binary that appears to be a relic of a more recent outburst of the progenitor AGB star. We applied diagnostic diagrams based on emission-line ratios of Hα λ6563, [O III] λ5007, and [S II] λ λ 6716,6731 images to identify the location and morphology of low-ionization structures within the inner nebula. We distinguished two inner, low-ionization envelopes from the ionized gas, within a radius of 55 arcsec (∼0.15 pc) extending from the central star: a large envelope expanding toward the northeast, and its smaller counterpart envelope in the opposite direction toward the southwest of the nebula. These low-ionization envelopes are surrounded by a highly ionized gaseous environment. We believe that these low-ionization expanding envelopes are a result of a powerful outburst from the post-AGB star that created shocked wind regions as they propagate through the previously expelled material along a symmetric axis. Our diagnostic mapping using high-angular resolution line-emission imaging can provide a novel approach to detection of low-ionization regions in other PNe, especially those showing a complex multiscale morphology.

The size-luminosity relationship of quasar narrow-line regions

NASA Astrophysics Data System (ADS)

Dempsey, Ross; Zakamska, Nadia L.

2018-07-01

The presence of an active galactic nucleus (AGN) can strongly affect its host. Due to the copious radiative power of the nucleus, the effects of radiative feedback can be detected over the entire host galaxy and sometimes well into the intergalactic space. In this paper we model the observed size-luminosity relationship of the narrow-line regions (NLRs) of AGN. We model the NLR as a collection of clouds in pressure equilibrium with the ionizing radiation, with each cloud producing line emission calculated by Cloudy. The sizes of the NLRs of powerful quasars are reproduced without any free parameters, as long as they contain massive (105-107 M⊙) ionization-bounded clouds. At lower AGN luminosities the observed sizes are larger than the model sizes, likely due to additional unmodeled sources of ionization (e.g. star formation). We find that the observed saturation of sizes at ˜10 kpc which is observed at high AGN luminosities (Lion ≃ 1046 erg s-1) is naturally explained by optically thick clouds absorbing the ionizing radiation and preventing illumination beyond a critical distance. Using our models in combination with observations of the [O III]/IR ratio and the [O III] size-IR luminosity relationship, we calculate the covering factor of the obscuring torus (and therefore the type 2 fraction within the quasar population) to be f = 0.5, though this is likely an upper bound. Finally, because the gas behind the ionization front is invisible in ionized gas transitions, emission-based NLR mass calculations underestimate the mass of the NLR and therefore of the energetics of ionized-gas winds.

The Size-Luminosity Relationship of Quasar Narrow-Line Regions

NASA Astrophysics Data System (ADS)

Dempsey, Ross; Zakamska, Nadia L.

2018-04-01

The presence of an active galactic nucleus (AGN) can strongly affect its host. Due to the copious radiative power of the nucleus, the effects of radiative feedback can be detected over the entire host galaxy and sometimes well into the intergalactic space. In this paper we model the observed size-luminosity relationship of the narrow-line regions (NLRs) of AGN. We model the NLR as a collection of clouds in pressure equilibrium with the ionizing radiation, with each cloud producing line emission calculated by Cloudy. The sizes of the NLRs of powerful quasars are reproduced without any free parameters, as long as they contain massive (105M⊙ to 107M⊙) ionization-bounded clouds. At lower AGN luminosities the observed sizes are larger than the model sizes, likely due to additional unmodeled sources of ionization (e.g., star formation). We find that the observed saturation of sizes at ˜10kpc which is observed at high AGN luminosities (Lion ≃ 1046erg/s) is naturally explained by optically thick clouds absorbing the ionizing radiation and preventing illumination beyond a critical distance. Using our models in combination with observations of the [O III]/IR ratio and the [O III] size - IR luminosity relationship, we calculate the covering factor of the obscuring torus (and therefore the type 2 fraction within the quasar population) to be f = 0.5, though this is likely an upper bound. Finally, because the gas behind the ionization front is invisible in ionized gas transitions, emission-based NLR mass calculations underestimate the mass of the NLR and therefore of the energetics of ionized-gas winds.

Flash photoionization of gamma-ray burst environments

NASA Technical Reports Server (NTRS)

Band, David L.; Hartmann, Dieter H.

1992-01-01

The H-alpha line emission that a flash-photoionized region emits is calculated. Archival transients, as well as various theoretical predictions, suggest that there may be significant ionizing flux. The limits on the line flux which might be observable indicate that the density must be fairly high for the recombination radiation to be observable. The intense burst radiation is insufficient to melt the dust which will be present in such a dense medium. This dust may attenuate the observable line emission, but does not attenuate the ionizing radiation before it ionizes the neutral medium surrounding the burst source. The dust can also produce a light echo. If there are indeed gamma-ray bursts in dense clouds, then it is possible that the burst was triggered by Bondi-Hoyle accretion from the dense medium, although it is unlikely on statistical grounds that all bursts occur in clouds.

Preliminary Experimental Measurements for a Gallium Electromagnetic (GEM) Thruster

NASA Technical Reports Server (NTRS)

Thomas, Robert E.; Burton, Rodney L.; Glumac, Nick G.; Polzin, Kurt A.

2007-01-01

A low-energy gallium plasma source is used to perform a spatially and temporally broad spectroscopic survey in the 220-520 nm range. Neutral, singly, and doubly ionized gallium are present in a 20 J, 1.8 kA (peak) arc discharge operating with a central cathode. When the polarity of the inner electrode is reversed the discharge current and arc voltage waveforms remain similar. Utilizing a central anode configuration, multiple Ga lines are absent in the 270-340 nm range. In addition, neutral and singly ionized Fe spectral lines are present, indicating erosion of the outer electrode. With graphite present on the insulator to facilitate breakdown, line emission from the gallium species is further reduced and while emissions from singly and doubly ionized carbon atoms and molecular carbon (C2) radicals are observed. These data indicate that a significant fraction of energy is shifted from the gallium and deposited into the various carbon species.

Evidence for a warm wind from the red star in symbiotic binaries

NASA Technical Reports Server (NTRS)

Friedjung, M.; Stencel, R. E.; Viotti, R.

1983-01-01

A systematic redshift of the high ionization resonance emission lines with respect to the intercombination lines is found from an examination of the ultraviolet spectra of symbiotic stars obtained with IUE. After consideration of other possibilities, this is most probably explained by photon scattering in an expanding envelope optically thick to the resonance lines. Line formation in a wind, or at the base of a wind is therefore suggested. Reasons are also given indicating line formation of the most ionized species in a region with an electron temperature of the order of 100,000 K, probably around the cool star. The behavior of the emission line width with ionization energy seems to support this model. The cool components of symbiotic stars appear to differ from normal red giants, which do not have winds of this temperature. An explanation in terms of a higher rotation velocity due to the binary nature of these stars is suggested.

Heating of H II regions with application to the Galactic center

NASA Technical Reports Server (NTRS)

Maloney, Philip R.; Hollenbach, David J.; Townes, Charles H.

1992-01-01

The heating and thermal equilibrium of photoionized gas is reviewed. Photon-heating mechanisms (UV photoionization heating, grain photoelectric heating, and X-ray heating) either fail to provide the required heating rates or else require that the ionization state of the gas is very high. Specific application to the Galactic center observations show that the total heating power required to maintain the gas at the derived temperatures, using the observed emission measure in the bar and the temperature distribution derived from the radio recombination lines, is about 7 x 10 exp 6 solar luminosities, comparable to the bolometric luminosity of the central source as measured by the FIR flux from grains. Thus, the cooling emission from this hot gas, if LTE-derived temperatures are correct, would supply a major fraction of the bolometric and ionizing luminosity inferred from the ionized gas in the central 1 pc cavity and the dust and neutral gas in the surrounding torus.

The ionization parameter of star-forming galaxies evolves with the specific star formation rate

NASA Astrophysics Data System (ADS)

Kaasinen, Melanie; Kewley, Lisa; Bian, Fuyan; Groves, Brent; Kashino, Daichi; Silverman, John; Kartaltepe, Jeyhan

2018-07-01

We investigate the evolution of the ionization parameter of star-forming galaxies using a high-redshift (z˜ 1.5) sample from the FMOS-COSMOS (Fibre Multi-Object Spectrograph-COSMic evOlution Survey) and matched low-redshift samples from the Sloan Digital Sky Survey. By constructing samples of low-redshift galaxies for which the stellar mass (M*), star formation rate (SFR), and specific star formation rate (sSFR) are matched to the high-redshift sample, we remove the effects of an evolution in these properties. We also account for the effect of metallicity by jointly constraining the metallicity and ionization parameter of each sample. We find an evolution in the ionization parameter for main-sequence, star-forming galaxies and show that this evolution is driven by the evolution of sSFR. By analysing the matched samples as well as a larger sample of z< 0.3, star-forming galaxies we show that high ionization parameters are directly linked to high sSFRs and are not simply the by-product of an evolution in metallicity. Our results are physically consistent with the definition of the ionization parameter, a measure of the hydrogen ionizing photon flux relative to the number density of hydrogen atoms.

Multiwavelength campaign on Mrk 509. XIII. Testing ionized-reflection models on Mrk 509

NASA Astrophysics Data System (ADS)

Boissay, R.; Paltani, S.; Ponti, G.; Bianchi, S.; Cappi, M.; Kaastra, J. S.; Petrucci, P.-O.; Arav, N.; Branduardi-Raymont, G.; Costantini, E.; Ebrero, J.; Kriss, G. A.; Mehdipour, M.; Pinto, C.; Steenbrugge, K. C.

2014-07-01

Active galactic nuclei (AGN) are the most luminous persistent objects in the universe. The X-ray domain is particularly important because the X-ray flux represents a significant fraction of the bolometric emission from such objects and probes the innermost regions of accretion disks, where most of this power is generated. An excess of X-ray emission below ~2 keV, called soft-excess, is very common in Type 1 AGN spectra. The origin of this feature remains debated. Originally modeled with a blackbody, there are now several possibilities to model the soft-excess, including warm Comptonization and blurred ionized reflection. In this paper, we test ionized-reflection models on Mrk 509, a bright Seyfert 1 galaxy for which we have a unique data set, in order to determine whether it can be responsible for the strong soft-excess. We use ten simultaneous XMM-Newton and INTEGRAL observations performed every four days. We present here the results of the spectral analysis, the evolution of the parameters, and the variability properties of the X-ray emission. The application of blurred ionized-reflection models leads to a very strong reflection and an extreme geometry, but fails to reproduce the broad-band spectrum of Mrk 509. Two different scenarios for blurred ionized reflection are discussed: stable geometry and lamp-post configuration. In both cases we find that the model parameters do not follow the expected relations, indicating that the model is fine-tuned to fit the data without physical justification. A large, slow variation in the soft-excess without a counterpart in the hard X-rays could be explained by a change in ionization of the reflector. However, such a change does not naturally follow from the assumed geometrical configuration. Warm Comptonization remains the most probable origin of the soft-excess in this object. Nevertheless, it is possible that both ionized reflection and warm Comptonization mechanisms can explain the soft-excess in all objects, one dominating the other one, depending on the physical conditions of the disk and the corona.

On the Decreasing Fraction of Strong Ly α Emitters around z ∼ 6-7

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sadoun, Raphael; Zheng, Zheng; Miralda-Escudé, Jordi, E-mail: raphael.sadoun@utah.edu

2017-04-10

The fraction of galaxies with strong Ly α emission has been observed to decrease rapidly with redshift at z ≳ 6, after a gradual increase at z < 6. This has been interpreted as being a trace of the reionization of the intergalactic medium (IGM): the emitted Ly α photons would be scattered by an increasingly neutral IGM at z > 6. We study this effect by modeling the ionization and Ly α radiative transfer in the infall region and the IGM around a Ly α emitting galaxy (LAE), for a spherical halo model with the mean density and radialmore » velocity profiles in the standard ΛCDM cosmological scenario. We find that the expected fast increase of the ionizing background intensity toward the end of the reionization epoch implies a rapid evolution of halo infall regions from being self-shielded against the external ionizing background to being mostly ionized. Whereas self-shielded infall regions can scatter the Ly α photons over a much larger area than the commonly used apertures for observing LAEs, the same infalling gas is no longer optically thick to the Ly α emission line after it is ionized by the external background, making the Ly α emission more compact and brighter within the observed apertures. Based on this simple model, we show that the observed drop in the abundance of LAEs at z > 6 does not imply a rapid increase with redshift of the fraction of the whole IGM volume that is atomic, but is accounted for by a rapid increase of the neutral fraction in the infall regions around galaxy host halos.« less

The Grism Lens-Amplified Survey from Space (GLASS). XI. Detection of C IV in Multiple Images of the z = 6.11 Lyα Emitter behind RXC J2248.7-4431

NASA Astrophysics Data System (ADS)

Schmidt, K. B.; Huang, K.-H.; Treu, T.; Hoag, A.; Bradač, M.; Henry, A. L.; Jones, T. A.; Mason, C.; Malkan, M.; Morishita, T.; Pentericci, L.; Trenti, M.; Vulcani, B.; Wang, X.

2017-04-01

The C III] and C IV rest-frame UV emission lines are powerful probes of the ionization states of galaxies. They have furthermore been suggested as alternatives for spectroscopic redshift confirmation of objects at the epoch of reionization (z> 6), where the most frequently used redshift indicator, Lyα, is attenuated by the high fraction of neutral hydrogen in the intergalactic medium. However, currently only very few confirmations of carbon UV lines at these high redshifts exist, making it challenging to quantify these claims. Here, we present the detection of C IV λλ1548, 1551 Å in Hubble Space Telescope slitless grism spectroscopy obtained by GLASS of a Lyα emitter at z = 6.11 multiply imaged by the massive foreground galaxy cluster RXC J2248.7-4431. The C IV emission is detected at the 3σ-5σ level in two images of the source, with marginal detection in two other images. We do not detect significant C III]λλ1907, 1909 Å emission implying an equivalent width {{EW}}{{C}{{III}}]}< 20 Å (1σ) and {{C}} {{IV}}/{{C}} {{III}}> 0.7 (2σ). Combined with limits on the rest-frame UV flux from the He II λ1640 Å emission line and the O III]λλ1661, 1666 Å doublet, we put constraints on the metallicity and the ionization state of the galaxy. The estimated line ratios and equivalent widths do not support a scenario where an AGN is responsible for ionizing the carbon atoms. SED fits, including nebular emission lines, imply a source with a mass of log(M/M ⊙) ˜ 9, SFR of around 10 M ⊙ yr-1, and a young stellar population < 50 {Myr} old. The source shows a stronger ionizing radiation field than objects with detected C IV emission at z< 2 and adds to the growing sample of low-mass (log(M/M ⊙) ≲ 9) galaxies at the epoch of reionization with strong radiation fields from star formation.

Electron emission from transfer ionization reaction in 30 keV amu‑1 He 2+ on Ar collision

NASA Astrophysics Data System (ADS)

Amaya-Tapia, A.; Antillón, A.; Estrada, C. D.

2018-06-01

A model is presented that describes the transfer ionization process in H{e}2++Ar collision at a projectile energy of 30 keV amu‑1. It is based on a semiclassical independent-particle close-coupling method that yields a reasonable agreement between calculated and experimental values of the total single-ionization and single-capture cross sections. It is found that the transfer ionization reaction is predominantly carried out through simultaneous capture and ionization, rather than by sequential processes. The transfer-ionization differential cross section in energy that is obtained satisfactorily reproduces the global behavior of the experimental data. Additionally, the probabilities of capture and ionization as function of the impact parameter for H{e}2++A{r}+ and H{e}++A{r}+ collisions are calculated, as far as we know, for the first time. The results suggest that the model captures essential elements that describe the two-electron transfer ionization process and could be applied to systems and processes of two electrons.

FORCAST Observations of Galactic Evolved Stars: Measurements of Carbonaceous Dust, Crystalline Silicates, and Fullerenes from SOFIA

NASA Astrophysics Data System (ADS)

Kraemer, Kathleen; Sloan, G. C.; Keller, L. D.; Groenewegen, M. A. T.

2018-01-01

We present preliminary results from two projects to observe the mid-infrared spectra of evolved stars in the Milky Way using the FORCAST instrument on SOFIA. In the first project, we observed a set of 31 carbon stars over the course of three cycles (government shutdowns contributed to the delays in the program execution), covering a wavelength range of 5-13.7 μm, which includes prominent dust and gas diagnostics. The sources were selected to sample portions of period and flux phase space which were not covered in existing samples from older telescopes such as the Infrared Space Observatory (ISO) or Infrared Astronomical Satellite (IRAS). In the second project, we searched for fullerene emission (C60) at 18.9 μm in Galactic sources with crystalline silicate emission. Although most evolved stars are either carbon-rich or oxygen- (silicate-) rich, fullerenes, a carbon-rich molecule, have been observed in several oxygen-rich evolved stars whose silicate emission features are crystalline rather than the more usual amorphous types. None of our targets show clear signatures of fullerene emission.Support for this work was provided by NASA through awards SOF 03-0079, SOF 03-0104, and SOF 04-0129 issued by USRA.

SPATIALLY RESOLVED SPECTROSCOPY AND CHEMICAL HISTORY OF STAR-FORMING GALAXIES IN THE HERCULES CLUSTER: THE EFFECTS OF THE ENVIRONMENT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petropoulou, V.; Vilchez, J.; Iglesias-Paramo, J.

2011-06-10

Spatially resolved spectroscopy has been obtained for a sample of 27 star-forming (SF) galaxies selected from our deep H{alpha} survey of the Hercules cluster. We have applied spectral synthesis models to all emission-line spectra of this sample using the population synthesis code STARLIGHT and have obtained fundamental parameters of stellar components such as mean metallicity and age. The emission-line spectra were corrected for underlying stellar absorption using these spectral synthesis models. Line fluxes were measured and O/H and N/O gas chemical abundances were obtained using the latest empirical calibrations. We have derived the masses and total luminosities of the galaxiesmore » using available Sloan Digital Sky Survey broadband photometry. The effects of cluster environment on the chemical evolution of galaxies and on their mass-metallicity (MZ) and luminosity-metallicity (LZ) relations were studied by combining the derived gas metallicities, the mean stellar metallicities and ages, the masses and luminosities of the galaxies, and their existing H I data. Our Hercules SF galaxies are divided into three main subgroups: (1) chemically evolved spirals with truncated ionized-gas disks and nearly flat oxygen gradients, demonstrating the effect of ram-pressure stripping; (2) chemically evolved dwarfs/irregulars populating the highest local densities, possible products of tidal interactions in preprocessing events; and (3) less metallic dwarf galaxies that appear to be 'newcomers' to the cluster and are experiencing pressure-triggered star formation. Most Hercules SF galaxies follow well-defined MZ and LZ sequences (for both O/H and N/O), though the dwarf/irregular galaxies located at the densest regions appear to be outliers to these global relations, suggesting a physical reason for the dispersion in these fundamental relations. The Hercules cluster appears to be currently assembling via the merger of smaller substructures, providing an ideal laboratory where the local environment has been found to be a key parameter in understanding the chemical history of galaxies.« less

Ionization studies in laser-excited alkaline-earth vapors.

PubMed

Hermann, J P; Wynne, J J

1980-06-01

We report on the time behavior of ionization signals produced by laser excitation of Ca and Ba atomic vapor to high-Rydberg states. A space-charge-limited thermionic diode detector shows a long-lived (>I-msec) ionization signal. However, optical detection of atomic ions (Ca+, Ba+) shows that these species live for much shorter times (<100 microsec). These results, in conjunction with published results on mass-spectrometric studies of high-density atomic beams, suggest that our ionization signal is primarily due to molecular species (Ca2+, Ba2+). We also observed optically pumped amplified spontaneous emission and stimulated electronic Raman scattering in Ca+ and Ba+.

ETA CARINAE’S THERMAL X-RAY TAIL MEASURED WITH XMM-NEWTON AND NuSTAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamaguchi, Kenji; Corcoran, Michael F.; Gull, Theodore R.

The evolved, massive highly eccentric binary system, η Car, underwent a periastron passage in the summer of 2014. We obtained two coordinated X-ray observations with XMM-Newton and NuSTAR during the elevated X-ray flux state and just before the X-ray minimum flux state around this passage. These NuSTAR observations clearly detected X-ray emission associated with η Car extending up to ∼50 keV for the first time. The NuSTAR spectrum above 10 keV can be fit with the bremsstrahlung tail from a kT ∼ 6 keV plasma. This temperature is ΔkT ∼ 2 keV higher than those measured from the iron K emission line complex, if the shockedmore » gas is in collisional ionization equilibrium. This result may suggest that the companion star's pre-shock wind velocity is underestimated. The NuSTAR observation near the X-ray minimum state showed a gradual decline in the X-ray emission by 40% at energies above 5 keV in a day, the largest rate of change of the X-ray flux yet observed in individual η Car observations. The column density to the hardest emission component, N{sub H} ∼ 10{sup 24} H cm{sup −2}, marked one of the highest values ever observed for η Car, strongly suggesting increased obscuration of the wind–wind colliding X-ray emission by the thick primary stellar wind prior to superior conjunction. Neither observation detected the power-law component in the extremely hard band that INTEGRAL and Suzaku observed prior to 2011. If the non-detection by NuSTAR is caused by absorption, the power-law source must be small and located very near the wind–wind collision apex. Alternatively, it may be that the power-law source is not related to either η Car or the GeV γ-ray source.« less

ENVIRONMENTAL TECHNOLOGY VERIFICATION (ETV) TEST OF DIOXIN EMISSION MONITORS

EPA Science Inventory

The performance of four dioxin emission monitors including two long-term sampling devices, the DMS (DioxinMonitoringSystem) and AMESA (Adsorption Method for Sampling Dioxins and Furans), and two semi-real-time continuous monitors, RIMMPA-TOFMS (Resonance Ionization with Multi-Mir...

Battery-Powered RF Pre-Ionization System for the Caltech Magnetohydrodynamically-Driven Jet Experiment: RF Discharge Properties and MHD-Driven Jet Dynamics

NASA Astrophysics Data System (ADS)

Chaplin, Vernon H.

This thesis describes investigations of two classes of laboratory plasmas with rather different properties: partially ionized low pressure radiofrequency (RF) discharges, and fully ionized high density magnetohydrodynamically (MHD)-driven jets. An RF pre-ionization system was developed to enable neutral gas breakdown at lower pressures and create hotter, faster jets in the Caltech MHD-Driven Jet Experiment. The RF plasma source used a custom pulsed 3 kW 13.56 MHz RF power amplifier that was powered by AA batteries, allowing it to safely float at 4-6 kV with the cathode of the jet experiment. The argon RF discharge equilibrium and transport properties were analyzed, and novel jet dynamics were observed. Although the RF plasma source was conceived as a wave-heated helicon source, scaling measurements and numerical modeling showed that inductive coupling was the dominant energy input mechanism. A one-dimensional time-dependent fluid model was developed to quantitatively explain the expansion of the pre-ionized plasma into the jet experiment chamber. The plasma transitioned from an ionizing phase with depressed neutral emission to a recombining phase with enhanced emission during the course of the experiment, causing fast camera images to be a poor indicator of the density distribution. Under certain conditions, the total visible and infrared brightness and the downstream ion density both increased after the RF power was turned off. The time-dependent emission patterns were used for an indirect measurement of the neutral gas pressure. The low-mass jets formed with the aid of the pre-ionization system were extremely narrow and collimated near the electrodes, with peak density exceeding that of jets created without pre-ionization. The initial neutral gas distribution prior to plasma breakdown was found to be critical in determining the ultimate jet structure. The visible radius of the dense central jet column was several times narrower than the axial current channel radius, suggesting that the outer portion of the jet must have been force free, with the current parallel to the magnetic field. The studies of non-equilibrium flows and plasma self-organization being carried out at Caltech are relevant to astrophysical jets and fusion energy research.

Cosmic Feast of the Elements

NASA Astrophysics Data System (ADS)

Morisset, C.; Delgado-Inglada, G.; García-Rojas, J.

2017-11-01

In the past few decades most of our understanding of the history and chemical evolution of galaxies has been guided by the study of their stars and gaseous nebulae. Nebulae, thanks to their bright emission lines, are especially useful tracers of chemical elements from the very center to the outskirts of galaxies. In order to pin down the chemical abundances in nebulae, we must rely on careful analysis of emission lines combined with detailed models of the microscopic physical processes inside nebulae and state-of-the-art atomic data. Another important piece of the puzzle is the interplay between galaxy evolution and the activity of their central engines either as optical AGNs or radio jets. Last but not least, let us not forget the huge population of lineless, retired galaxies ionized by hot low-mass evolved stars: after nuclear and star formation activity quiets down, retired galaxies are the natural consequence of galaxy evolution. Grażyna Stasińska has made important contributions to each and every one of those aspects. This conference is to honor her work. We invite you to take part and share the latest news on this cosmic feast that transmutes chemical species, the onward journey of elements inside and outside galaxies either as lonely atoms or gregarious molecules and crystals, and their recycling in stars, which starts the cosmic feast all over again.

A black-hole mass measurement from molecular gas kinematics in NGC4526.

PubMed

Davis, Timothy A; Bureau, Martin; Cappellari, Michele; Sarzi, Marc; Blitz, Leo

2013-02-21

The masses of the supermassive black holes found in galaxy bulges are correlated with a multitude of galaxy properties, leading to suggestions that galaxies and black holes may evolve together. The number of reliably measured black-hole masses is small, and the number of methods for measuring them is limited, holding back attempts to understand this co-evolution. Directly measuring black-hole masses is currently possible with stellar kinematics (in early-type galaxies), ionized-gas kinematics (in some spiral and early-type galaxies) and in rare objects that have central maser emission. Here we report that by modelling the effect of a black hole on the kinematics of molecular gas it is possible to fit interferometric observations of CO emission and thereby accurately estimate black-hole masses. We study the dynamics of the gas in the early-type galaxy NGC 4526, and obtain a best fit that requires the presence of a central dark object of 4.5(+4.2)(-3.1) × 10(8) solar masses (3σ confidence limit). With the next-generation millimetre-wavelength interferometers these observations could be reproduced in galaxies out to 75 megaparsecs in less than 5 hours of observing time. The use of molecular gas as a kinematic tracer should thus allow one to estimate black-hole masses in hundreds of galaxies in the local Universe, many more than are accessible with current techniques.

The Luminous Blue Variable RMC 127 as Seen with ALMA and ATCA

NASA Astrophysics Data System (ADS)

Agliozzo, C.; Trigilio, C.; Pignata, G.; Phillips, N. M.; Nikutta, R.; Leto, P.; Umana, G.; Ingallinera, A.; Buemi, C.; Bauer, F. E.; Paladini, R.; Noriega-Crespo, A.; Prieto, J. L.; Massardi, M.; Cerrigone, L.

2017-06-01

We present ALMA and ATCA observations of the luminous blue variable RMC 127. The radio maps show for the first time the core of the nebula and evidence that the nebula is strongly asymmetric with a Z-pattern shape. Hints of this morphology are also visible in the archival Hubble Space Telescope {{H}}α image, which overall resembles the radio emission. The emission mechanism in the outer nebula is optically thin free-free in the radio. At high frequencies, a component of point-source emission appears at the position of the star, up to the ALMA frequencies. The rising flux density distribution ({S}ν ˜ {ν }0.78+/- 0.05) of this object suggests thermal emission from the ionized stellar wind and indicates a departure from spherical symmetry with {n}e(r)\\propto {r}-2. We examine different scenarios to explain this excess of thermal emission from the wind and show that this can arise from a bipolar outflow, supporting the suggestion by other authors that the stellar wind of RMC 127 is aspherical. We fit the data with two collimated ionized wind models, and we find that the mass-loss rate can be a factor of two or more smaller than in the spherical case. We also fit the photometry obtained by IR space telescopes and deduce that the mid- to far-IR emission must arise from extended, cool (˜ 80 {{K}}) dust within the outer ionized nebula. Finally, we discuss two possible scenarios for the nebular morphology: the canonical single-star expanding shell geometry and a precessing jet model assuming the presence of a companion star.

A Spectroscopic Search for AGN Activity in the Reionization Era

NASA Astrophysics Data System (ADS)

Laporte, Nicolas; Nakajima, Kimihiko; Ellis, Richard S.; Zitrin, Adi; Stark, Daniel P.; Mainali, Ramesh; Roberts-Borsani, G. W.

2017-12-01

The ubiquity of Lyman alpha (Lyα) emission in a sample of four bright [O III]-strong star-forming galaxies with redshifts above seven has led to the suggestion that such luminous sources represent a distinct population compared with their fainter, more numerous counterparts. The presence of Lyα emission within the reionization era could indicate that these sources created early ionized bubbles due to their unusually strong radiation, possibly because of the presence of active galactic nuclei. To test this hypothesis, we secured long integration spectra with XSHOOTER on the VLT for three z≃ 7 sources selected to have similar luminosities and prominent excess fluxes in the IRAC 3.6 or 4.5 μm band, usually attributed to strong [O III] emission. We secured additional spectroscopy for one of these galaxies at z = 7.15 using MOSFIRE at the Keck telescope. For the most well-studied source in our sample with the strongest IRAC excess, we detect significant nebular emission from He II and N V indicative of a non-thermal source. For the other two sources at z = 6.81 and z = 6.85, for which no previous optical/near-infrared spectroscopy was available, Lyα is seen in one and C III] emission in the other. Although based on a modest sample, our results further support the hypothesis that the phenomenon of intense [O III] emission is associated preferentially with sources lying in early ionized bubbles. However, even though one of our sources at z = 7.15 suggests the presence of non-thermal radiation, such ionized bubbles may not uniquely arise in this manner. We discuss the unique advantages of extending such challenging diagnostic studies with JWST.

A Gemini view of the galaxy cluster RXC J1504-0248: insights on the nature of the central gaseous filaments

NASA Astrophysics Data System (ADS)

Soja, A. C.; Sodré, L., Jr.; Monteiro-Oliveira, R.; Cypriano, E. S.; Lima Neto, G. B.

2018-03-01

We revisit the galaxy cluster RXC J1504-0248, a remarkable example of a structure with a strong cool core in a near redshift (z = 0.216). We performed a combined analysis using photometric and spectroscopic data obtained at Gemini South Telescope. We estimated the cluster mass through gravitational lensing, obtaining M200 = 5.3 ± 0.4 × 1014h_{70}^{-1} M⊙ within R200 = 1.56 ± 0.04 h^{-1}_{70} Mpc, in agreement with a virial mass estimate. This cluster presents a prominent filamentary structure associated to its BCG, located mainly along its major axis and aligned with the X-ray emission. A combined study of three emission line diagnostic diagrams has shown that the filament emission falls in the so-called transition region of these diagrams. Consequently, several ionizing sources should be playing an meaningful role. We have argued that old stars, often invoked to explain LINER emission, should not be the major source of ionization. We have noticed that most of the filamentary emission has line ratios consistent with the shock excitation limits obtained from shock models. We also found that line fluxes are related to gas velocities (here estimated from line widths) by power-laws with slopes in the range expected from shock models. These models also show, however, that only ˜10% of Hα luminosity can be explained by shocks. We conclude that shocks probably associated to the cooling of the intracluster gas in a filamentary structure may indeed be contributing to the filament nebular emission, but can not be the major source of ionizing photons.

REAL TIME, ON-LINE CHARACTERIZATION OF DIESEL GENERATOR AIR TOXIC EMISSIONS BY RESONANCE ENHANCED MULTI-PHOTON IONIZATION TIME OF FLIGHT MASS SPECTROMETRY

EPA Science Inventory

The laser based resonance, enhanced multi-photon ionization time-of-flight mass spectrometry (REMPI-TOFMS) technique has been applied to the exhaust gas stream of a diesel generator to measure, in real time, concentration levels of aromatic air toxics. Volatile organic compounds ...

Stationary Plasma Thruster Plume Emissions

NASA Technical Reports Server (NTRS)

Manzella, David H.

1994-01-01

The emission spectrum from a xenon plasma produced by a Stationary Plasma Thruster provided by the Ballistic Missile Defense Organization (BMDO) was measured. Approximately 270 individual Xe I, Xe II, and XE III transitions were identified. A total of 250 mW of radiated optical emission was estimated from measurements taken at the thruster exit plane. There was no evidence of erosion products in the emission signature. Ingestion and ionization of background gas at elevated background pressure was detected. The distribution of excited states could be described by temperatures ranging from fractions of 1 eV to 4 eV with a high degree of uncertainty due to the nonequilibrium nature of this plasma. The plasma was over 95 percent ionized at the thruster exit plane. Between 10 and 20 percent of the ions were doubly charged. Two modes of operation were identified. The intensity of plasma emission increased by a factor of two during operation in an oscillatory mode. The transfer between the two modes of operation was likely related to unidentified phenomena occurring on a time scale of minutes.

Shock Waves in Supernova Ejecta

NASA Astrophysics Data System (ADS)

Raymond, J. C.

2018-02-01

Astrophysical shock waves are a major mechanism for dissipating energy, and by heating and ionizing the gas they produce emission spectra that provide valuable diagnostics for the shock parameters, for the physics of collisionless shocks, and for the composition of the shocked material. Shocks in SN ejecta in which H and He have been burned to heavier elements behave differently than shocks in ordinary astrophysical gas because of their very large radiative cooling rates. In particular, extreme departures from thermal equilibrium among ions and electrons and from ionization equilibrium may arise. This paper discusses the consequences of the enhanced metal abundances for the structure and emission spectra of those shocks.

Stochastic treatment of electron multiplication without scattering in dielectrics

NASA Technical Reports Server (NTRS)

Lin, D. L.; Beers, B. L.

1981-01-01

By treating the emission of optical phonons as a Markov process, a simple analytic method is developed for calculating the electronic ionization rate per unit length for dielectrics. The effects of scattering from acoustic and optical phonons are neglected. The treatment obtains universal functions in recursive form, the theory depending on only two dimensionless energy ratios. A comparison of the present work with other numerical approaches indicates that the effect of scattering becomes important only when the electric potential energy drop in a mean free path for optical-phonon emission is less than about 25% of the ionization potential. A comparison with Monte Carlo results is also given for Teflon.

Double ionization of helium by ion impact: second Born order treatment at the fully differential level

NASA Astrophysics Data System (ADS)

López, S. D.; Otranto, S.; Garibotti, C. R.

2015-01-01

In this work, a theoretical study of the double ionization of He by ion impact at the fully differential level is presented. Emphasis is made in the role played by the projectile in the double emission process depending on its charge and the amount of momentum transferred to the target. A Born-CDW model including a second-order term in the projectile charge is introduced and evaluated within an on-shell treatment. We find that emission geometries for which the second-order term dominates lead to asymmetric structures around the momentum transfer direction, a typical characteristic of higher order transitions.

Interaction of the 100-year old X-Ray flare produced by a central black hole with diffuse gas in the Galactic center

NASA Astrophysics Data System (ADS)

Chernyshov, D.; Cheng, K.; Dogiel, V.; Kong, A.; Ko, C.; Tatischeff, V.; Terrier, R.

2017-10-01

We investigate an old X-Ray flare produced by a central black hole which is most likely responsible for the transient X-Ray emission from massive molecular clouds in the Galactic center. This flare should ionize diffuse molecular gas and also excite fluorescence lines e.g. neutral iron line at 6.4 keV. It turns out that the observed diffuse 6.4 keV line can be explained by the same X-Ray flare which illuminates dense molecular clouds. The diffuse emission can also be considered as a tool to limit potential duration and intensity of the primary X-Ray flare. We show that charged particles cannot provide necessary iron ionization rate to reproduce the observed emission. On the other hand ionization of neutral hydrogen cannot be provided by a primary flare and should be done by other mechanisms like for example charged particles. We also claim that recently found afterglow from Swift J1644+57 can be produced by similar event and can be a nice example of a Compton echo observed in a distant galaxy.

Results of the WHAM Hα survey of the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Smart, Brianna Marie; Haffner, Lawrence Matthew; Barger, Kat; Madsen, Greg

2018-01-01

We present the results of an Hα survey of the Small Magellanic Cloud (SMC) using the Wisconsin H-Alpha Mapper (WHAM) as the initial component of our WHAM Magellanic System Survey (SMC/LMC/Stream). Previous surveys of the SMC have focused on the bright H II regions (supernovae remnants/ HII bubbles, etc) centered around the stellar component of the galaxy. These surveys were not sensitive to the fainter Diffuse Ionized Gas (DIG) within and surrounding the galaxy. With WHAM, we detect a halo of diffuse Hα emission extending to radii well beyond the bright H II regions and comparable to extents of observed HI. Using WHAM's unprecedented sensitivity to trace diffuse emission (~ tens of mR) with a velocity resolution of 12 km/s, we have compiled the first comprehensive spatial and kinematic map of the extended Hα emission. With these new data in hand, we are able to delineate the considerable warm ionized component associated with the SMC, leading to better calculations of its present-day mass and providing new constraints for dynamical evolution simulations of the Magellanic System. Similar WHAM surveys of the diffuse ionized content of the LMC and Stream are also underway.

Discovery of Ionized Gas Associated with the Tilted Inner Disk of the Milky Way

NASA Astrophysics Data System (ADS)

Haffner, L. Matthew; Benjamin, Robert A.; Krishnarao, Dhanesh

2018-01-01

The complex distribution and motion of gas within the central few kiloparsecs of our Galaxy does not follow the more regular patterns seen throughout the rest of its gaseous disk. Sensitive observations of the neutral and molecular gas over the past 40 years reveal emission intensities and velocities that are far from symmetric about the Galactic equator and the line at zero longitude. Burton and Liszt (1978-1992) show that much of the anomalous behavior is well explained by an elliptical disk, tilted with respect to the Galactic plane and our line of sight.Using the Wisconsin Hα Mapper (WHAM), we report the discovery of ionized gas near the Galactic center (l = 0° - 14° b = -8° to +4°) with a distribution and velocities also explained by this creative model. Emission from distant regions near the Galactic plane is typically blocked by a thick band of interstellar dust. However, a portion of the tilted disk is behind Baade's Window, a hole in the thick dust near the Galactic center. Combined with the unparalleled sensitivity of the WHAM Sky Survey (IHα ~ 0.1 R; EM ~ 0.2 pc cm-6), we are able to trace the distribution and kinematics of the ionized phase of this structure for the first time. The relationship between this multi-phase inner disk, outflow from the Galactic center, and the Fermi bubbles is not yet clear.In several directions around the disk, WHAM captures emission from Hα, Hβ, and several ions (N, S, and O) to explore the state and source of the ionized gas. [N II]/Hα, [S II]/Hα, and [S II]/[N II] line ratios are much different than classical H II regions and diffuse gas near the plane but are similar to those seen at high-|z| (> 1.5 kpc) in the Perseus arm. We will also compare this emission to multi-phase absorption components revealed in a recent UV absorption-line study through the low halo (z ~ -1 kpc) in this direction (Savage et al. 2017) and to emission seen near nuclear regions of other spiral galaxies, where high low-ionization-species to Hα ratios have also been observed.WHAM has been designed, built, and operated primarily through support of the National Science Foundation. The research presented here has been funded by awards AST-1108911 and AST-1714472.

A simple way to model nebulae with distributed ionizing stars

NASA Astrophysics Data System (ADS)

Jamet, L.; Morisset, C.

2008-04-01

Aims: This work is a follow-up of a recent article by Ercolano et al. that shows that, in some cases, the spatial dispersion of the ionizing stars in a given nebula may significantly affect its emission spectrum. The authors found that the dispersion of the ionizing stars is accompanied by a decrease in the ionization parameter, which at least partly explains the variations in the nebular spectrum. However, they did not research how other effects associated to the dispersion of the stars may contribute to those variations. Furthermore, they made use of a unique and simplified set of stellar populations. The scope of the present article is to assess whether the variation in the ionization parameter is the dominant effect in the dependence of the nebular spectrum on the distribution of its ionizing stars. We examined this possibility for various regimes of metallicity and age. We also investigated a way to model the distribution of the ionizing sources so as to bypass expensive calculations. Methods: We wrote a code able to generate random stellar populations and to compute the emission spectra of their associated nebulae through the widespread photoionization code cloudy. This code can process two kinds of spatial distributions of the stars: one where all the stars are concentrated at one point, and one where their separation is such that their Strömgren spheres do not overlap. Results: We found that, in most regimes of stellar population ages and gas metallicities, the dependence of the ionization parameter on the distribution of the stars is the dominant factor in the variation of the main nebular diagnostics with this distribution. We derived a method to mimic those effects with a single calculation that makes use of the common assumptions of a central source and a spherical nebula, in the case of constant density objects. This represents a computation time saving by a factor of at least several dozen in the case of H ii regions ionized by massive clusters.

Comparison of direct and alternating current vacuum ultraviolet lamps in atmospheric pressure photoionization.

PubMed

Vaikkinen, Anu; Haapala, Markus; Kersten, Hendrik; Benter, Thorsten; Kostiainen, Risto; Kauppila, Tiina J

2012-02-07

A direct current induced vacuum ultraviolet (dc-VUV) krypton discharge lamp and an alternating current, radio frequency (rf) induced VUV lamp that are essentially similar to lamps in commercial atmospheric pressure photoionization (APPI) ion sources were compared. The emission distributions along the diameter of the lamp exit window were measured, and they showed that the beam of the rf lamp is much wider than that of the dc lamp. Thus, the rf lamp has larger efficient ionization area, and it also emits more photons than the dc lamp. The ionization efficiencies of the lamps were compared using identical spray geometries with both lamps in microchip APPI mass spectrometry (μAPPI-MS) and desorption atmospheric pressure photoionization-mass spectrometry (DAPPI-MS). A comprehensive view on the ionization was gained by studying six different μAPPI solvent compositions, five DAPPI spray solvents, and completely solvent-free DAPPI. The observed reactant ions for each solvent composition were very similar with both lamps except for toluene, which showed a higher amount of solvent originating oxidation products with the rf lamp than with the dc lamp in μAPPI. Moreover, the same analyte ions were detected with both lamps, and thus, the ionization mechanisms with both lamps are similar. The rf lamp showed a higher ionization efficiency than the dc lamp in all experiments. The difference between the lamp ionization efficiencies was greatest when high ionization energy (IE) solvent compositions (IEs above 10 eV), i.e., hexane, methanol, and methanol/water, (1:1 v:v) were used. The higher ionization efficiency of the rf lamp is likely due to the larger area of high intensity light emission, and the resulting larger efficient ionization area and higher amount of photons emitted. These result in higher solvent reactant ion production, which in turn enables more efficient analyte ion production. © 2012 American Chemical Society

Detection of a noble gas molecular ion, 36ArH+, in the Crab Nebula.

PubMed

Barlow, M J; Swinyard, B M; Owen, P J; Cernicharo, J; Gomez, H L; Ivison, R J; Krause, O; Lim, T L; Matsuura, M; Miller, S; Olofsson, G; Polehampton, E T

2013-12-13

Noble gas molecules have not hitherto been detected in space. From spectra obtained with the Herschel Space Observatory, we report the detection of emission in the 617.5- and 1234.6-gigahertz J = 1-0 and 2-1 rotational lines of (36)ArH(+) at several positions in the Crab Nebula, a supernova remnant known to contain both molecular hydrogen and regions of enhanced ionized argon emission. Argon-36 is believed to have originated from explosive nucleosynthesis in massive stars during core-collapse supernova events. Its detection in the Crab Nebula, the product of such a supernova event, confirms this expectation. The likely excitation mechanism for the observed (36)ArH(+) emission lines is electron collisions in partially ionized regions with electron densities of a few hundred per centimeter cubed.

Color gradients in cooling flow cluster central galaxies and the ionization of cluster emission line systems

NASA Technical Reports Server (NTRS)

Romanishin, W.

1988-01-01

Preliminary results are given for a program to measure color gradients in the central galaxies in clusters with a variety of cooling flow rates. The objectives are to search for extended blue continuum regions indicative of star formation, to study the spatial distribution of star formation, and to make a quantitative measure of the amount of light from young stars, which can lead to a measure of the star formation rate (for an assumed initial mass function). Four clusters with large masses and large cluster H-alpha emission fluxes are found to have an excess of blue light concentrated to the centers of the cluster central galaxy. Assumption of a disk IMF leads to the conclusion that the starlight might play a major role in ionizing the emission line gas in these clusters.

The influence of the ionized medium on synchrotron emission in interstellar space.

NASA Technical Reports Server (NTRS)

Ramaty, R.

1972-01-01

The effect of the ionized gas on synchrotron emission in the interstellar medium is investigated. A detailed calculation of the synchrotron emissivity of cosmic electrons, assumed to have an isotropic pitch-angle distribution in a uniform magnetic field, is made as a function of frequency and observation angle with respect to the field. The results are presented both as a local emissivity and as an intensity, the latter obtained by neglecting free-free absorption in the interstellar medium and by assuming that the emissivity is constant along the line of sight. The comparison of these results with previous studies on the nature of the low-frequency turnover of the galactic nonthermal radio background reveals that, except if the component perpendicular to the line of sight of the interstellar magnetic field is small (less than 1 microgauss), or if the cosmic-ray electron spectrum is cut off at energies below a few hundred MeV, the suppression of synchrotron emission by the ambient electrons has in general a lesser effect than free-free absorption by these electrons, and that in some cases this suppression effect is almost entirely negligible.

Emission and chemistry of organic compounds from biomass burning: measurements from an iodide time-of-flight chemical ionization mass spectrometer (I- ToF-CIMS) during the FIREX FireLab 2016 intensive

NASA Astrophysics Data System (ADS)

Yuan, B.; Krechmer, J. E.; Warneke, C.; Coggon, M.; Koss, A.; Lim, C. Y.; Selimovic, V.; Gilman, J.; Lerner, B. M.; Stark, H.; Kang, H.; Jimenez, J. L.; Yokelson, R. J.; Liggio, J.; Roberts, J. M.; Kroll, J. H.; De Gouw, J. A.

2017-12-01

Biomass burning can emit large amounts of many different organic compounds to the atmosphere. The emission strengths of these emitted organic compounds and their subsequent atmospheric chemistry are not well known. In this study, we deployed a time-of-flight chemical ionization mass spectrometer using iodide as reagent ions (Iodide ToF-CIMS) to measure direct emissions of organic compounds during the FIREX laboratory 2016 intensive in the USDA Fire Sciences Lab in Missoula, MT. An interpretation of the I­- TOF-CIMS mass spectra from biomass burning emissions will be presented. The dependence of the emissions of selected organic compounds with fuel types, combustion efficiency and fuel chemical compositions will be discussed. The I- TOF-CIMS also measured aged biomass burning smoke from a small smog chamber and an oxidative flow reactor (OFR). The I- TOF-CIMS consistently observed much higher signals of highly oxygenated organic compounds in the aged biomass burning smoke than in fresh emissions, indicative of strong secondary formation of these organic compounds in biomass burning plumes.

Simulation of K-α Emission from Highly Charged Cu ions for Pinches on ZR

NASA Astrophysics Data System (ADS)

Dasgupta, A.; Giuliani, J. L.; Clark, R. W.; Ouart, N. D.; Jones, B.; Ampleford, D. J.

2012-10-01

Recent spectral data of Cu shots Z1975 and Z2122 from Sandia's ZR machine are believed to show strong K-α emissions. As these K-α lines provide good diagnostics, a detailed spectral model will be developed to investigate these line emissions for analyzing the data. In a Z pinch plasma, K-α emission can occur due to e-beams, hot electrons at the tail of a Maxwellian and also pumping from hot photons emitted near the axis. K-α emission that originates from collisional processes involving hot electrons in the final phase of the pinching plasmas are associated with radiationless electron capture, inner-shell electron collisional excitation and ionization. K-α lines from various ionization stages of various materials such as Fe, Cr, Ni, and Mn were also observed in the ZR data. Contributions from ions with strong K-α transitions will be included for this study which is a preliminary attempt to investigate Cu K-α lines due to hot electrons and photons. Photo-pumped K-α emission from an outer shell is spatially distinguishable from that produced by e-beam on axis.

Large-scale Map of Millimeter-wavelength Hydrogen Radio Recombination Lines around a Young Massive Star Cluster

NASA Astrophysics Data System (ADS)

Nguyen-Luong, Q.; Anderson, L. D.; Motte, F.; Kim, Kee-Tae; Schilke, P.; Carlhoff, P.; Beuther, H.; Schneider, N.; Didelon, P.; Kramer, C.; Louvet, F.; Nony, T.; Bihr, S.; Rugel, M.; Soler, J.; Wang, Y.; Bronfman, L.; Simon, R.; Menten, K. M.; Wyrowski, F.; Walmsley, C. M.

2017-08-01

We report the first map of large-scale (10 pc in length) emission of millimeter-wavelength hydrogen recombination lines (mm-RRLs) toward the giant H II region around the W43-Main young massive star cluster (YMC). Our mm-RRL data come from the IRAM 30 m telescope and are analyzed together with radio continuum and cm-RRL data from the Karl G. Jansky Very Large Array and HCO+ 1-0 line emission data from the IRAM 30 m. The mm-RRLs reveal an expanding wind-blown ionized gas shell with an electron density ˜70-1500 cm-3 driven by the WR/OB cluster, which produces a total Lyα photon flux of 1.5× {10}50 s-1. This shell is interacting with the dense neutral molecular gas in the W43-Main dense cloud. Combining the high spectral and angular resolution mm-RRL and cm-RRL cubes, we derive the two-dimensional relative distributions of dynamical and pressure broadening of the ionized gas emission and find that the RRL line shapes are dominated by pressure broadening (4-55 {km} {{{s}}}-1) near the YMC and by dynamical broadening (8-36 {km} {{{s}}}-1) near the shell’s edge. Ionized gas clumps hosting ultra-compact H II regions found at the edge of the shell suggest that large-scale ionized gas motion triggers the formation of new star generation near the periphery of the shell.

[C ii] 158 μm line detection of the warm ionized medium in the Scutum-Crux spiral arm tangency

NASA Astrophysics Data System (ADS)

Velusamy, T.; Langer, W. D.; Pineda, J. L.; Goldsmith, P. F.

2012-05-01

Context. The Herschel HIFI GOT C+ Galactic plane [C ii] spectral survey has detected strong emission at the spiral arm tangencies. Aims: We use the unique viewing geometry of the Scutum-Crux (S-C) tangency nearl = 30° to detect the warm ionized medium (WIM) component traced by [CII] and to study the effects of spiral density waves on Interstellar Medium (ISM) gas. Methods: We compare [C ii] velocity features with ancillary H i, 12CO and 13CO data near tangent velocities at each longitude to separate the cold neutral medium and the warm neutral + ionized components in the S-C tangency, then we identify [C ii] emission at the highest velocities without any contribution from 12CO clouds, as WIM. Results: We present the GOT C+ results for the S-C tangency. We interpret the diffuse and extended excess [C ii] emission at and above the tangent velocities as arising in the electron-dominated warm ionized gas in the WIM. We derive an electron density in the range of 0.2-0.9 cm-3 at each longitude, a factor of several higher than the average value from Hα and pulsar dispersion. Conclusions: We interpret the excess [C ii] in S-C tangency as shock compression of the WIM induced by the spiral density waves. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Wind-embedded shocks in FASTWIND: X-ray emission and K-shell absorption

NASA Astrophysics Data System (ADS)

Carneiro, L. P.; Puls, J.; Sundqvist, J. O.; Hoffmann, T. L.

2017-11-01

EUV and X-ray radiation emitted from wind-embedded shocks can affect the ionization balance in the outer atmospheres of massive stars, and can also be the mechanism responsible for producing highly ionized atoms detected in the wind UV spectra. To investigate these processes, we implemented the emission from wind-embedded shocks and related physics into our atmosphere/spectrum synthesis code FASTWIND. We also account for the high energy absorption of the cool wind, by adding important K-shell opacities. Various tests justfying our approach have been described by Carneiro+(2016, A&A 590, A88). In particular, we studied the impact of X-ray emission on the ionization balance of important elements. In almost all the cases, the lower ionization stages (O iv, N iv, P v) are depleted and the higher stages (N v, O v, O vi) become enhanced. Moreover, also He lines (in particular He ii 1640 and He ii 4686) can be affected as well. Finally, we carried out an extensive discussion of the high-energy mass absorption coefficient, κν, regarding its spatial variation and dependence on T eff. We found that (i) the approximation of a radially constant κν can be justified for r >= 1.2R * and λ <= 18 Å, and also for many models at longer wavelengths. (ii) In order to estimate the actual value of this quantity, however, the He ii background needs to be considered from detailed modeling.

Analysis of the diffuse ionized gas database: DIGEDA

NASA Astrophysics Data System (ADS)

Flores-Fajardo, N.; Morisset, C.; Binette, L.

2009-10-01

Studies of the Diffuse Ionized Gas (DIG) have progressed without providing so far any strict criterion to distinguish DIGs from H II regions. In this work, we compile the emission line measurements of 29 galaxies that are available in the scientific literature, thereby setting up the first DIG database (DIGEDA). Making use of this database, we proceed to analyze the global properties of the DIG using the [NII]λ6583/Hα, [O I]λ6300/Hα, [O III]λ5007/Hβ and [SII]λ6716/Hα lines ratios, including the H α emission measure. This analysis leads us to conclude that the [N II]/Hα ratio provides an objective criterion for distinguishing whether an emission region is a DIG or an H II region, while the EM(Hα) is a useful quantity only when the galaxies are considered individually. Finally, we find that the emission regions of Irr galaxies classified as DIG in the literature appear in fact to be much more similar to H II regions than to the DIGs of spiral galaxies.

Theory of terahertz emission from femtosecond-laser-induced microplasmas

NASA Astrophysics Data System (ADS)

Thiele, I.; Nuter, R.; Bousquet, B.; Tikhonchuk, V.; Skupin, S.; Davoine, X.; Gremillet, L.; Bergé, L.

2016-12-01

We present a theoretical investigation of terahertz (THz) generation in laser-induced gas plasmas. The work is strongly motivated by recent experimental results on microplasmas, but our general findings are not limited to such a configuration. The electrons and ions are created by tunnel ionization of neutral atoms, and the resulting plasma is heated by collisions. Electrons are driven by electromagnetic, convective, and diffusive sources and produce a macroscopic current which is responsible for THz emission. The model naturally includes both ionization current and transition-Cherenkov mechanisms for THz emission, which are usually investigated separately in the literature. The latter mechanism is shown to dominate for single-color multicycle laser pulses, where the observed THz radiation originates from longitudinal electron currents. However, we find that the often discussed oscillations at the plasma frequency do not contribute to the THz emission spectrum. In order to predict the scaling of the conversion efficiency with pulse energy and focusing conditions, we propose a simplified description that is in excellent agreement with rigorous particle-in-cell simulations.

Coherent electron emission from O2 in collisions with fast electrons

NASA Astrophysics Data System (ADS)

Chowdhury, Madhusree Roy; Stia, Carlos R.; Tachino, Carmen A.; Fojón, Omar A.; Rivarola, Roberto D.; Tribedi, Lokesh C.

2017-08-01

Absolute double differential cross sections (DDCS) of secondary electrons emitted in ionization of O2 by fast electrons have been measured for different emission angles. Theoretical calculations of atomic DDCS were obtained using the first Born approximation with an asymptotic charge of Z T = 1. The measured molecular DDCS were divided by twice the theoretical atomic DDCS to detect the presence of interference effects which was the aim of the experiment. The experimental to theoretical DDCS ratios showed clear signature of first order interference oscillation for all emission angles. The ratios were fitted by a first order Cohen-Fano type model. The variation of the oscillation amplitudes as a function of the electron emission angle showed a parabolic behaviour which goes through a minimum at 90°. The single differential and total ionization cross sections have also been deduced, besides the KLL Auger cross sections. In order to make a comparative study, we have discussed these results along with our recent experimental data obtained for N2 molecule.

The nuclear region of low luminosity flat radio spectrum sources. II. Emission-line spectra

NASA Astrophysics Data System (ADS)

Gonçalves, A. C.; Serote Roos, M.

2004-01-01

We report on the spectroscopic study of 19 low luminosity Flat Radio Spectrum (LL FRS) sources selected from Marchã's et al. (\\cite{March96}) 200 mJy sample. In the optical, these objects are mainly dominated by the host galaxy starlight. After correcting the data for this effect, we obtain a new set of spectra clearly displaying weak emission lines; such features carry valuable information concerning the excitation mechanisms at work in the nuclear regions of LL FRS sources. We have used a special routine to model the spectra and assess the intensities and velocities of the emission lines; we have analyzed the results in terms of diagnostic diagrams. Our analysis shows that 79% of the studied objects harbour a Low Ionization Nuclear Emission-line Region (or LINER) whose contribution was swamped by the host galaxy starlight. The remaining objects display a higher ionization spectrum, more typical of Seyferts; due to the poor quality of the spectra, it was not possible to identify any possible large Balmer components. The fact that we observe a LINER-type spectrum in LL FRS sources supports the idea that some of these objects could be undergoing an ADAF phase; in addition, such a low ionization emission-line spectrum is in agreement with the black hole mass values and sub-Eddington accretion rates published for some FRS sources. Based on observations collected at the Multiple Mirror Telescope on Mt. Hopkins. Full Fig. 1 is only available in electronic form at http://www.edpsciences.org

Fe XXV and Fe XXVI Diagnostics of the Black Hole and Accretion Disk in Active Galaxies: Chandra Time-Resolved Spectroscopy of NGC 7314

NASA Technical Reports Server (NTRS)

Yaqoob, Tahir; George, Ian M.; Kallman, Timothy R.; Padmanabhan, Urmila; Weaver, Kimberly A.; Turner, T. Jane

2003-01-01

We report the detection of Fe xxv and Fe XXVI Ka emission lines from a Chandra High Energy Grating Spectrometer (HETGS) observation of the narrow-line Seyfert 1 galaxy NGC 7314, made simultaneously with RXTE. The lines are redshifted (cz approximately 1500 kilometers per second) relative to the systemic velocity and unresolved by the gratings. We argue that the lines originate in a near face-on (less than 7 deg) disk having a radial line emissivity flatter than r(exp -2). Line emission from ionization states of Fe in the range approximately Fe I a up to Fe XXVI is observed. The ionization balance of Fe responds to continuum variations on timescales less than 12.5 ks, supporting an origin of the lines close to the X-ray source. We present additional, detailed diagnostics from this rich data set. These results identify NGC 7314 as a key source to study in the future if we are to pursue reverberation mapping of space-time near black-hole event horizons. This is because it is first necessary to understand the ionization structure of accretion disks and the relation between the X-ray continuum and Fe Ka line emission. However, we also describe how our results are suggestive of a means of measuring black-hole spin without a knowledge of the relation between the continuum and line emission. Finally, these data emphasize that one can study strong gravity with narrow (as opposed to very broad) disk lines. In fact narrow lines offer higher precision, given sufficient energy resolution.

Observing Supernova 1987A with the Refurbished Hubble Space Telescope

NASA Technical Reports Server (NTRS)

France, Kevin; McCray, Richard; Heng, Kevin; Kirshner, Robert P.; Challis, Peter; Bouchet, Patrice; Crotts, Arlin; Dwek, Eli; Fransson, Claes; Garnavich, Peter M.;

Analysis of the 3C 445 soft X-ray spectrum as observed by Chandra high-energy gratings

NASA Astrophysics Data System (ADS)

Dong, Fu-Tong; Shao, Shu-Hua; Cheng, Yan; Zeng, Jiao-Long

2018-05-01

We present a detailed analysis of the soft X-ray emission of 3C 445 using an archival Chandra High Energy Transmission Grating (HETG) spectrum. Highly-ionized H- and He-like Mg, Si and S lines, as well as a resolved low-ionized Si Kα line, are detected in the high resolution spectrum. The He-like triplets of Mg and Si are resolved into individual lines, and the calculated R ratios indicate a high density for the emitter. The low values of G ratios indicate the lines originate from collisionally ionized plasmas. However, the detection of a resolved narrow Ne X radiative recombination continua (RRC) feature in the spectrum seems to prefer a photoionized environment. The spectrum is subsequently modeled with a photoionization model, and the results are compared with those of a collisional model. Through a detailed analysis of the spectrum, we exclude a collisional origin for these emission lines. A one-component photoionization model provides a great fit to the emission features. The best-fit parameters are {log} ξ ={3.3}-0.3+0.4 erg cm s‑1, {n}{{H}}={5}-4.5+15× {10}10 cm‑3 and {N}{{H}}={2.5}-1.7+3.8× {10}20 cm‑2. According to the calculated high density for the emitter, the measured velocity widths of the emission lines and the inferred radial distance (6 × 1014 – 8 × 1015 cm), we suggest the emission lines originating from matter are located in the broad line region (BLR).

Physical conditions of the interstellar medium in star-forming galaxies at z ˜ 1.5

NASA Astrophysics Data System (ADS)

Hayashi, Masao; Ly, Chun; Shimasaku, Kazuhiro; Motohara, Kentaro; Malkan, Matthew A.; Nagao, Tohru; Kashikawa, Nobunari; Goto, Ryosuke; Naito, Yoshiaki

2015-10-01

We present results from Subaru Fiber Multi Object Spectrograph near-infrared spectroscopy of 118 star-forming galaxies at z ˜ 1.5 in the Subaru Deep Field. These galaxies are selected as [O II]λ3727 emitters at z ≈ 1.47 and 1.62 from narrow-band imaging. We detect the Hα emission line in 115 galaxies, the [O III]λ5007 emission line in 45 galaxies, and Hβ, [N II]λ6584, and [S II]λλ6716, 6731 in 13, 16, and 6 galaxies, respectively. Including the [O II] emission line, we use the six strong nebular emission lines in the individual and composite rest-frame optical spectra to investigate the physical conditions of the interstellar medium in star-forming galaxies at z ˜ 1.5. We find a tight correlation between Hα and [O II], which suggests that [O II] can be a good star formation rate indicator for galaxies at z ˜ 1.5. The line ratios of Hα/[O II] are consistent with those of local galaxies. We also find that [O II] emitters have strong [O III] emission lines. The [O III]/[O II] ratios are larger than normal star-forming galaxies in the local universe, suggesting a higher ionization parameter. Less massive galaxies have larger [O III]/[O II] ratios. With evidence that the electron density is consistent with local galaxies, the high ionization of galaxies at high redshifts may be attributed to a harder radiation field by a young stellar population and/or an increase in the number of ionizing photons from each massive star.

Population kinetics on K alpha lines of partially ionized Cl atoms.

PubMed

Kawamura, Tohru; Nishimura, Hiroaki; Koike, Fumihiro; Ochi, Yoshihiro; Matsui, Ryoji; Miao, Wen Yong; Okihara, Shinichiro; Sakabe, Shuji; Uschmann, Ingo; Förster, Eckhart; Mima, Kunioki

2002-07-01

A population kinetics code was developed to analyze K alpha emission from partially ionized chlorine atoms in hydrocarbon plasmas. Atomic processes are solved under collisional-radiative equilibrium for two-temperature plasmas. It is shown that the fast electrons dominantly contribute to ionize the K-shell bound electrons (i.e., inner-shell ionization) and the cold electrons to the outer-shell bound ones. Ratios of K alpha lines of partially ionized atoms are presented as a function of cold-electron temperature. The model was validated by observation of the K alpha lines from a chlorinated plastic target irradiated with 1 TW Ti:sapphire laser pulses at 1.5 x 10(17) W/cm(2), inferring a plasma temperature of about 100 eV on the target surface.

Probing electron delays in above-threshold ionization

DOE PAGES

Zipp, Lucas J.; Natan, Adi; Bucksbaum, Philip H.

2014-11-21

Recent experiments have revealed attosecond delays in the emission of electrons from atoms ionized by extreme UV light, offering a glimpse into the ultrafast nature of light-induced electron dynamics. In this work, we extend these measurements to the strong-field above-threshold ionization (ATI) regime, by measuring delays in the photoemission of electrons from argon in the presence of an intense laser field. We probe the ATI process with a weak coherent reference, at half the laser frequency. The interfering ionization signal reveals the relative spectral phase of adjacent ATI channels, with an equivalent resolution of a few attoseconds. These relative delaysmore » depend on the strong field, and approach zero at higher intensity. Our phase measurements of ATI electrons show how strong fields alter ionization dynamics in atoms.« less

Coulomb-repulsion-assisted double ionization from doubly excited states of argon

NASA Astrophysics Data System (ADS)

Liao, Qing; Winney, Alexander H.; Lee, Suk Kyoung; Lin, Yun Fei; Adhikari, Pradip; Li, Wen

2017-08-01

We report a combined experimental and theoretical study to elucidate nonsequential double-ionization dynamics of argon atoms at laser intensities near and below the recollision-induced ionization threshold. Three-dimensional momentum measurements of two electrons arising from strong-field nonsequential double ionization are achieved with a custom-built electron-electron-ion coincidence apparatus, showing laser intensity-dependent Coulomb repulsion effect between the two outgoing electrons. Furthermore, a previously predicted feature of double ionization from doubly excited states is confirmed in the distributions of sum of two-electron momenta. A classical ensemble simulation suggests that Coulomb-repulsion-assisted double ionization from doubly excited states is at play at low laser intensity. This mechanism can explain the dependence of Coulomb repulsion effect on the laser intensity, as well as the transition from side-by-side to back-to-back dominant emission along the laser polarization direction.

Heater-induced ionization inferred from spectrometric airglow measurements

NASA Astrophysics Data System (ADS)

Hysell, D. L.; Miceli, R. J.; Varney, R. H.; Schlatter, N.; Huba, J. D.

2013-12-01

Spectrographic airglow measurements were made during an ionospheric modification experiment at HAARP on March 12, 2013. Artificial airglow enhancements at 427.8, 557.7, 630.0, 777.4, and 844.6 nm were observed. On the basis of these emissions and using a methodology based on the method of Backus and Gilbert [1968, 1970], we estimate the suprathermal electron population and the subsequent equilibrium electron density profile, including contributions from electron impact ionization. We find that the airglow is consistent with significant induced ionization in view of the spatial intermittency of the airglow.

Characterization of weakly ionized argon flows for radio blackout mitigation experiments

NASA Astrophysics Data System (ADS)

Steffens, L.; Koch, U.; Esser, B.; Gülhan, A.

2017-06-01

For reproducing the so-called E × B communication blackout mitigation scheme inside the L2K arc heated facility of the DLR in weakly ionized argon §ows, a §at plate model has been equipped with a superconducting magnet, electrodes, and a setup comprising microwave plasma transmission spectroscopy (MPTS). A thorough characterization of the weakly ionized argon §ow has been performed including the use of microwave interferometry (MWI), Langmuir probe measurements, Pitot probe pro¦les, and spectroscopic methods like diode laser absorption spectroscopy (DLAS) and emission spectroscopy.

Physical parameters for proton induced K-, L-, and M-shell ionization processes

NASA Astrophysics Data System (ADS)

Shehla; Puri, Sanjiv

2016-10-01

The proton induced atomic inner-shell ionization processes comprising radiative and non-radiative transitions are characterized by physical parameters, namely, the proton ionization cross sections, X-ray emission rates, fluorescence yields and Coster-Kronig (CK) transition probabilities. These parameters are required to calculate the K/L/M shell X-ray production (XRP) cross sections and relative X-ray intensity ratios, which in turn are required for different analytical applications. The current status of different physical parameters is presented in this report for use in various applications.

A Mass Spectrometer Simulator in Your Computer

ERIC Educational Resources Information Center

Gagnon, Michel

2012-01-01

Introduced to study components of ionized gas, the mass spectrometer has evolved into a highly accurate device now used in many undergraduate and research laboratories. Unfortunately, despite their importance in the formation of future scientists, mass spectrometers remain beyond the financial reach of many high schools and colleges. As a result,…

Temporal and modal characterization of DoD source air toxic emission factors: final report

EPA Science Inventory

This project tested three, real-/near real-time monitoring techniques to develop air toxic emission factors for Department of Defense (DoD) platform sources. These techniques included: resonance enhanced multi photon ionization time of flight mass spectrometry (REMPI-TOFMS) for o...

Monitoring of Hazardous Air Pollutant Surrogates Using Resonance Enhanced Multiphoton Ionization/Time of Flight Mass Spectrometry

EPA Science Inventory

EPA’s preferred approach for regulatory emissions compliance is based upon real-time monitoring of individual hazardous air pollutants (HAPs). Real-time, continuous monitoring not only provides the most comprehensive assurance of emissions compliance, but also can serve as...

A Deep Chandra ACIS Study of NGC 4151. II. The Innermost Emission Line Region and Strong Evidence for Radio Jet-NLR Cloud Collision

NASA Astrophysics Data System (ADS)

Wang, Junfeng; Fabbiano, Giuseppina; Elvis, Martin; Risaliti, Guido; Mundell, Carole G.; Karovska, Margarita; Zezas, Andreas

2011-07-01

We have studied the X-ray emission within the inner ~150 pc radius of NGC 4151 by constructing high spatial resolution emission line images of blended O VII, O VIII, and Ne IX. These maps show extended structures that are spatially correlated with the radio outflow and optical [O III] emission. We find strong evidence for jet-gas cloud interaction, including morphological correspondences with regions of X-ray enhancement, peaks of near-infrared [Fe II] emission, and optical clouds. In these regions, moreover, we find evidence of elevated Ne IX/O VII ratios; the X-ray emission of these regions also exceeds that expected from nuclear photoionization. Spectral fitting reveals the presence of a collisionally ionized component. The thermal energy of the hot gas suggests that >~ 0.1% of the estimated jet power is deposited into the host interstellar medium through interaction between the radio jet and the dense medium of the circumnuclear region. We find possible pressure equilibrium between the collisionally ionized hot gas and the photoionized line-emitting cool clouds. We also obtain constraints on the extended iron and silicon fluorescent emission. Both lines are spatially unresolved. The upper limit on the contribution of an extended emission region to the Fe Kα emission is <~ 5% of the total, in disagreement with a previous claim that 65% of the Fe Kα emission originates in the extended narrow line region.

Correlated electronic decay in expanding clusters triggered by intense XUV pulses from a Free-Electron-Laser

PubMed Central

Oelze, Tim; Schütte, Bernd; Müller, Maria; Müller, Jan P.; Wieland, Marek; Frühling, Ulrike; Drescher, Markus; Al-Shemmary, Alaa; Golz, Torsten; Stojanovic, Nikola; Krikunova, Maria

2017-01-01

Irradiation of nanoscale clusters and large molecules with intense laser pulses transforms them into highly-excited non- equilibrium states. The dynamics of intense laser-cluster interaction is encoded in electron kinetic energy spectra, which contain signatures of direct photoelectron emission as well as emission of thermalized nanoplasma electrons. In this work we report on a so far not observed spectrally narrow bound state signature in the electron kinetic energy spectra from mixed Xe core - Ar shell clusters ionized by intense extreme-ultraviolet (XUV) pulses from a free-electron-laser. This signature is attributed to the correlated electronic decay (CED) process, in which an excited atom relaxes and the excess energy is used to ionize the same or another excited atom or a nanoplasma electron. By applying the terahertz field streaking principle we demonstrate that CED-electrons are emitted at least a few picoseconds after the ionizing XUV pulse has ended. Following the recent finding of CED in clusters ionized by intense near-infrared laser pulses, our observation of CED in the XUV range suggests that this process is of general relevance for the relaxation dynamics in laser produced nanoplasmas. PMID:28098175

Experimental investigation on large-area dielectric barrier discharge in atmospheric nitrogen and air assisted by the ultraviolet lamp.

PubMed

Zhang, Yan; Gu, Biao; Wang, Wenchun; Wang, Dezhen; Peng, Xuwen

2009-04-01

In this paper, ultraviolet radiation produced by the ultraviolet lamp is employed to supply pre-ionization for the dielectric barrier discharge in N(2) or air at atmospheric pressure. The effect of the ultraviolet pre-ionization on improving the uniformity of the dielectric barrier discharge is investigated experimentally. The atmospheric pressure glow discharge of the large area (270 mm x 120 mm) is obtained successfully via the ultraviolet pre-ionization in atmospheric DBD in N(2) when the gas gap decrease to 3mm. Based on the emission spectra, the mechanism which ultraviolet pre-ionization improves the uniformity of the dielectric barrier discharge is discussed.

Characterization of direct-current atmospheric-pressure discharges useful for ambient desorption/ionization mass spectrometry.

PubMed

Shelley, Jacob T; Wiley, Joshua S; Chan, George C Y; Schilling, Gregory D; Ray, Steven J; Hieftje, Gary M

2009-05-01

Two relatively new ambient ionization sources, direct analysis in real time (DART) and the flowing atmospheric-pressure afterglow (FAPA), use direct current, atmospheric-pressure discharges to produce reagent ions for the direct ionization of a sample. Although at a first glance these two sources appear similar, a fundamental study reveals otherwise. Specifically, DART was found to operate with a corona-to-glow transition (C-G) discharge whereas the FAPA was found to operate with a glow-to-arc transition (G-A) discharge. The characteristics of both discharges were evaluated on the basis of four factors: reagent-ion production, response to a model analyte (ferrocene), infrared (IR) thermography of the gas used for desorption and ionization, and spatial emission characteristics. The G-A discharge produced a greater abundance and a wider variety of reagent ions than the C-G discharge. In addition, the discharges yielded different adducts and signal strengths for ferrocene. It was also found that the gas exiting the discharge chamber reached a maximum of 235 degrees C and 55 degrees C for the G-A and C-G discharges, respectively. Finally, spatially resolved emission maps of both discharges showed clear differences for N(2)(+) and O(I). These findings demonstrate that the discharges used by FAPA and DART are fundamentally different and should have different optimal applications for ambient desorption/ionization mass spectrometry (ADI-MS).

Line Identifications in the Far Ultraviolet Spectrum of the Eclipsing Binary System 31 Cygni

NASA Astrophysics Data System (ADS)

Hagen Bauer, Wendy; Bennett, P. D.

2011-05-01

The eclipsing binary system 31 Cygni (K4 Ib + B3 V) was observed at several phases with the Far Ultraviolet Spectrosocopic Explorer (FUSE) satellite. During total eclipse, a rich emission spectrum was observed, produced by scattering of hot star photons in the extended wind of the K supergiant. The system was observed during deep chromospheric eclipse, and 2.5 months after total eclipse ended. We present an atlas of line identifications in these spectra. During total eclipse, emission features from C II , C III, N I, N II, N III, O I, Si II, P II, P III, S II, S III, Ar I, Cr III, Fe II, Fe III, and Ni II were detected. The strongest emission features arise from N II. These lines appear strongly in absorption during chromospheric eclipse, and even 2.5 months after total eclipse, the absorption bottoms out on the underlying emission seen during total eclipse. The second strongest features in the emission spectrum arise from Fe III. Any chromospheric Fe III absorption is buried within strong chromospheric absorption from other species, mainly Fe II. The emission profiles of most of the doubly-ionized species are red-shifted relative to the systemic velocity, with asymmetric profiles with a steeper long-wavelength edge. Emission profiles from singly-ionized species tend to be more symmetric and centered near the systemic velocity. In deep chromospheric eclipse, absorption features are seen from neutral and singly-ionized species, arising from lower levels up to 3 eV. Many strong chromospheric features are doubled in the observation obtained during egress from eclipse. The 31 Cygni spectrum taken 2.5 months after total eclipse ended ws compared to single-star B spectra from the FUSE archives. There was still some additional chromospheric absorption from strong low-excitation Fe II, O I and Ar I.

The Far-Infrared Emission Line and Continuum Spectrum of the Seyfert Galaxy NGC 1068

NASA Technical Reports Server (NTRS)

Spinoglio, Luigi; Smith, Howard A.; Gonzalez-Alfonso, Eduardo; Fisher, Jacqueline

2005-01-01

We report on the analysis of the first complete far-infrared spectrum (43-197 microns) of the Seyfert 2 galaxy NGC 1068 as observed with the Long Wavelength Spectrometer (LWS) onboard the Infrared Space Observatory (ISO). In addition to the 7 expected ionic fine structure emission lines, the OH rotational lines at 79, 119 and 163 microns were all detected in emission, which is unique among galaxies with full LWS spectra, where the 119 micron line, where detected, is always in absorption. The observed line intensities were modelled together with IS0 Short Wavelength Spectrometer (SWS) and optical and ultraviolet line intensities from the literature, considering two independent emission components: the AGN component and the starburst component in the circumnuclear ring of approximately 3kpc in size. Using the UV to mid-IR emission line spectrum to constrain the nuclear ionizing continuum, we have confirmed previous results: a canonical power-law ionizing spectrum is a poorer fit than one with a deep absorption trough, while the presence of a big blue bump is ruled out. Based on the instantaneous starburst age of 5 Myr constrained by the Br gamma equivalent width in the starburst ring, and starburst synthesis models of the mid- and far-infrared fine-structure line emission, a low ionization parameter (U=10(exp -3.5)) and low densities (n=100 cm (exp -3)) are derived. Combining the AGN and starburst components, we succeed in modeling the overall UV to far-IR atomic spectrum of SGC 1068, reproducing the line fluxes to within a factor 2.0 on average with a standard deviation of 1.4. The OH 119 micron emission indicates that the line is collisionally excited, and arises in a warm and dense region. The OH emission has been modeled using spherically symmetric, non-local, non-LTE radiative transfer models. The models indicate that the bulk of the emission arises from the nuclear region, although some extended contribution from the starburst is not ruled out. The OH abundance in the nuclear region is expected to be approximately 10(exp -5), characteristic of X-ray dominated regions.

Solar flare model atmospheres

NASA Technical Reports Server (NTRS)

Hawley, Suzanne L.; Fisher, George H.

1993-01-01

Solar flare model atmospheres computed under the assumption of energetic equilibrium in the chromosphere are presented. The models use a static, one-dimensional plane parallel geometry and are designed within a physically self-consistent coronal loop. Assumed flare heating mechanisms include collisions from a flux of non-thermal electrons and x-ray heating of the chromosphere by the corona. The heating by energetic electrons accounts explicitly for variations of the ionized fraction with depth in the atmosphere. X-ray heating of the chromosphere by the corona incorporates a flare loop geometry by approximating distant portions of the loop with a series of point sources, while treating the loop leg closest to the chromospheric footpoint in the plane-parallel approximation. Coronal flare heating leads to increased heat conduction, chromospheric evaporation and subsequent changes in coronal pressure; these effects are included self-consistently in the models. Cooling in the chromosphere is computed in detail for the important optically thick HI, CaII and MgII transitions using the non-LTE prescription in the program MULTI. Hydrogen ionization rates from x-ray photo-ionization and collisional ionization by non-thermal electrons are included explicitly in the rate equations. The models are computed in the 'impulsive' and 'equilibrium' limits, and in a set of intermediate 'evolving' states. The impulsive atmospheres have the density distribution frozen in pre-flare configuration, while the equilibrium models assume the entire atmosphere is in hydrostatic and energetic equilibrium. The evolving atmospheres represent intermediate stages where hydrostatic equilibrium has been established in the chromosphere and corona, but the corona is not yet in energetic equilibrium with the flare heating source. Thus, for example, chromospheric evaporation is still in the process of occurring.

A Dynamic/Anisotropic Low Earth Orbit (LEO) Ionizing Radiation Model

NASA Technical Reports Server (NTRS)

Badavi, Francis F.; West, Katie J.; Nealy, John E.; Wilson, John W.; Abrahms, Briana L.; Luetke, Nathan J.

2006-01-01

The International Space Station (ISS) provides the proving ground for future long duration human activities in space. Ionizing radiation measurements in ISS form the ideal tool for the experimental validation of ionizing radiation environmental models, nuclear transport code algorithms, and nuclear reaction cross sections. Indeed, prior measurements on the Space Transportation System (STS; Shuttle) have provided vital information impacting both the environmental models and the nuclear transport code development by requiring dynamic models of the Low Earth Orbit (LEO) environment. Previous studies using Computer Aided Design (CAD) models of the evolving ISS configurations with Thermo Luminescent Detector (TLD) area monitors, demonstrated that computational dosimetry requires environmental models with accurate non-isotropic as well as dynamic behavior, detailed information on rack loading, and an accurate 6 degree of freedom (DOF) description of ISS trajectory and orientation.

Determination of Hazardous Air Pollutant Surrogates Using Resonance Enhanced Multi Photon Ionization - Time of Flight Mass Spectrometry

EPA Science Inventory

EPA?s preferred approach for regulatory emissions compliance is based upon real-time monitoring of individual hazardous air pollutants (HAPs). Real-time, continuous monitoring not only provides the most comprehensive assurance of emissions compliance, but also can serve as a pro...

On the detectability of key-MeV solar protons through their nonthermal Lyman-alpha emission

NASA Technical Reports Server (NTRS)

Canfield, R. C.; Chang, C. R.

1985-01-01

The intensity and timescale of nonthermal Doppler-shifted hydrogen L alpha photon emission as diagnostics of 10 keV to 10 MeV protons bombarding the solar chromosphere during flares are investigated. The steady-state excitation and ionization balance of the proton beam are determined, taking into account all important atomic interactions with the ambient chromosphere. For a proton energy flux comparable to the electron energy flux commonly inferred for large flares, L alpha wing intensities orders of magnitude larger than observed nonflaring values were found. Investigation of timescales for ionization and charge exchange leads researchers to conclude that over a wide range of values of mean proton energy and beam parameters, Doppler-shifted nonthermal L alpha emission is a useful observational diagnostic of the presence of 10 keV to 10 MeV superthermal proton beams in the solar flare chromosphere.

Vanishing absorption and blueshifted emission in FeLoBAL quasars

NASA Astrophysics Data System (ADS)

Rafiee, Alireza; Pirkola, Patrik; Hall, Patrick B.; Galati, Natalee; Rogerson, Jesse; Ameri, Abtin

2016-07-01

We study the dramatic decrease in iron absorption strength in the iron low-ionization broad absorption line quasar SDSS J084133.15+200525.8. We report on the continued weakening of absorption in the prototype of this class of variable broad absorption line quasar, FBQS J140806.2+305448. We also report a third example of this class, SDSS J123103.70+392903.6; unlike the other two examples, it has undergone an increase in observed continuum brightness (at 3000 Å rest frame) as well as a decrease in iron absorption strength. These changes could be caused by absorber transverse motion or by ionization variability. We note that the Mg II and UV Fe II lines in several FeLoBAL quasars are blueshifted by thousands of km s-1 relative to the H β emission line peak. We suggest that such emission arises in the outflowing winds normally seen only in absorption.

Detailed non-LTE calculations of the iron emission from NGC 1068

NASA Technical Reports Server (NTRS)

Band, David L.; Klein, Richard I.; Castor, John I.; Nash, J. K.

1989-01-01

The X-ray iron line emission from NGC 1068 observed by the Ginga satellite is modeled using the new multiline, multilevel, non-LTE radiative transport code ALTAIR and a detailed atomic model for Ne-like through stripped iron. The parameter space of the obscured type 1 Seyfert nucleus model for this object is studied. The equivalent width is greater than previously predicted. It is found that detailed radiative transfer can have a significant effect on the observed line flux both for the K alpha line and for the L-shell emission. The ionization of the iron increases with temperature. Therefore the K alpha equivalent width and energy is a function not only of the ionization parameter, but also of the column depth and temperature. For a likely model of NGC 1068 it is found that the iron abundance is about twice solar, but that modifications of this model may permit a smaller abundance.

Can a Penning ionization discharge simulate the tokamak scrape-off plasma conditions?

NASA Technical Reports Server (NTRS)

Finkenthal, M.; Littman, A.; Stutman, D.; Kovnovich, S.; Mandelbaum, P.; Schwob, J. L.; Bhatia, A. K.

1990-01-01

The tokamak scrape-off (the region between the vacuum vessel wall and the magnetically confined fusion plasma edge), represents a source/sink for the hot fusion plasma. The electron densities and temperatures are in the ranges 10 to the 11th - 10 to the 13th/cu cm and 1-40 eV, respectively (depending on the size, magnetic field intensity and configuration, plasma current, etc). In the work reported, the electron temperature and density have been estimated in a Penning ionization discharge by comparing its spectroscopic emission in the VUV with that predicted by a collisional radiative model. An attempt to directly compare this emission with that of the tokamak edge is briefly described.

Understanding the flowing atmospheric-pressure afterglow (FAPA) ambient ionization source through optical means.

PubMed

Shelley, Jacob T; Chan, George C-Y; Hieftje, Gary M

2012-02-01

The advent of ambient desorption/ionization mass spectrometry (ADI-MS) has led to the development of a large number of atmospheric-pressure ionization sources. The largest group of such sources is based on electrical discharges; yet, the desorption and ionization processes that they employ remain largely uncharacterized. Here, the atmospheric-pressure glow discharge (APGD) and afterglow of a helium flowing atmospheric-pressure afterglow (FAPA) ionization source were examined by optical emission spectroscopy. Spatial emission profiles of species created in the APGD and afterglow were recorded under a variety of operating conditions, including discharge current, electrode polarity, and plasma-gas flow rate. From these studies, it was found that an appreciable amount of atmospheric H(2)O vapor, N(2), and O(2) diffuses through the hole in the plate electrode into the discharge to become a major source of reagent ions in ADI-MS analyses. Spatially resolved plasma parameters, such as OH rotational temperature (T(rot)) and electron number density (n(e)), were also measured in the APGD. Maximum values for T(rot) and n(e) were found to be ~1100 K and ~4×10(19) m(-3), respectively, and were both located at the pin cathode. In the afterglow, rotational temperatures from OH and N(2)(+) yielded drastically different values, with OH temperatures matching those obtained from infrared thermography measurements. The higher N(2)(+) temperature is believed to be caused by charge-transfer ionization of N(2) by He(2)(+). These findings are discussed in the context of previously reported ADI-MS analyses with the FAPA source. © American Society for Mass Spectrometry, 2011

Understanding the Flowing Atmospheric-Pressure Afterglow (FAPA) Ambient Ionization Source through Optical Means

NASA Astrophysics Data System (ADS)

Shelley, Jacob T.; Chan, George C.-Y.; Hieftje, Gary M.

2012-02-01

The advent of ambient desorption/ionization mass spectrometry (ADI-MS) has led to the development of a large number of atmospheric-pressure ionization sources. The largest group of such sources is based on electrical discharges; yet, the desorption and ionization processes that they employ remain largely uncharacterized. Here, the atmospheric-pressure glow discharge (APGD) and afterglow of a helium flowing atmospheric-pressure afterglow (FAPA) ionization source were examined by optical emission spectroscopy. Spatial emission profiles of species created in the APGD and afterglow were recorded under a variety of operating conditions, including discharge current, electrode polarity, and plasma-gas flow rate. From these studies, it was found that an appreciable amount of atmospheric H2O vapor, N2, and O2 diffuses through the hole in the plate electrode into the discharge to become a major source of reagent ions in ADI-MS analyses. Spatially resolved plasma parameters, such as OH rotational temperature (Trot) and electron number density (ne), were also measured in the APGD. Maximum values for Trot and ne were found to be ~1100 K and ~4 × 1019 m-3, respectively, and were both located at the pin cathode. In the afterglow, rotational temperatures from OH and N{2/+} yielded drastically different values, with OH temperatures matching those obtained from infrared thermography measurements. The higher N{2/+} temperature is believed to be caused by charge-transfer ionization of N2 by He{2/+}. These findings are discussed in the context of previously reported ADI-MS analyses with the FAPA source.

The mid-infrared properties and gas content of active galaxies over large lookback times

NASA Astrophysics Data System (ADS)

Curran, S. J.; Duchesne, S. W.

2018-05-01

Upon an expansion of all of the searches for redshifted H I 21-cm absorption (0.002 1 ≤ z ≤ 5.19), we update recent results regarding the detection of 21-cm in the non-local Universe. Specifically, we confirm that photo-ionization of the gas is the mostly likely cause of the low detection rate at high redshift, in addition to finding that at z ≲ 0.1 there may also be a decrease in the detection rate, which we suggest is due to the dilution of the absorption strength by 21-cm emission. By assuming that associated and intervening absorbers have similar cosmological mass densities, we find evidence that the spin temperature of the gas evolves with redshift, consistent with heating by ultraviolet photons. From the near-infrared (λ = 3.4, 4.6 and 12 μm) colours, we see that radio galaxies become more quasar-like in their activity with increasing redshift. We also find that the non-detection of 21-cm absorption at high redshift is not likely to be due to the selection of gas-poor ellipticals, in addition to a strong correlation between the ionizing photon rate and the [3.4] - [4.6] colour, indicating that the UV photons arise from AGN activity. Like previous studies, we find a correlation between the detection of 21-cm absorption and the [4.6] - [12] colour, which is a tracer of star-forming activity. However, this only applies at the lowest redshifts (z ≲ 0.1), the range considered by the other studies.

Disentangling the outflow and protostars in HH 900 in the Carina Nebula

NASA Astrophysics Data System (ADS)

Reiter, Megan; Smith, Nathan; Kiminki, Megan M.; Bally, John; Anderson, Jay

2015-04-01

HH 900 is a peculiar protostellar outflow emerging from a small, tadpole-shaped globule in the Carina Nebula. Previous Hα imaging with Hubble Space Telescope (HST)/Advanced Camera for Surveys showed an ionized outflow with a wide opening angle that is distinct from the highly collimated structures typically seen in protostellar jets. We present new narrowband near-IR [Fe II] images taken with the Wide Field Camera 3 on the HST that reveal a remarkably different structure than Hα. In contrast to the unusual broad Hα outflow, the [Fe II] emission traces a symmetric, collimated bipolar jet with the morphology and kinematics that are more typical of protostellar jets. In addition, new Gemini adaptive optics images reveal near-IR H2 emission coincident with the Hα emission, but not the [Fe II]. Spectra of these three components trace three separate and distinct velocity components: (1) H2 from the slow, entrained molecular gas, (2) Hα from the ionized skin of the accelerating outflow sheath, and (3) [Fe II] from the fast, dense, and collimated protostellar jet itself. Together, these data require a driving source inside the dark globule that remains undetected behind a large column density of material. In contrast, Hα and H2 emission trace the broad outflow of material entrained by the jet, which is irradiated outside the globule. As it get dissociated and ionized, it remains visible for only a short time after it is dragged into the H II region.

Highly ionized atoms in cooling gas

NASA Technical Reports Server (NTRS)

Edgar, R. J.; Chevalier, R. A.

1986-01-01

The ionization of low density gas cooling from a high temperature was calculated. The evolution during the cooling is assumed to be isochoric, isobaric, or a combination of these cases. The calculations are used to predict the column densities and ultraviolet line luminosities of highly ionized atoms in cooling gas. In a model for cooling of a hot galactic corona, it is shown that the observed value of N(N V) can be produced in the cooling gas, while the predicted value of N(Si IV) falls short of the observed value by a factor of about 5. The same model predicts fluxes of ultraviolet emission lines that are a factor of 10 lower than the claimed detections of Feldman, Brune, and Henry. Predictions are made for ultraviolet lines in cooling flows in early-type galaxies and clusters of galaxies. It is shown that the column densities of interest vary over a fairly narrow range, while the emission line luminosities are simply proportional to the mass inflow rate.

Highly ionized atoms in cooling gas. [in model for cooling of hot Galactic corona

NASA Technical Reports Server (NTRS)

Edgar, Richard J.; Chevalier, Roger A.

1986-01-01

The ionization of low density gas cooling from a high temperature was calculated. The evolution during the cooling is assumed to be isochoric, isobaric, or a combination of these cases. The calculations are used to predict the column densities and ultraviolet line luminosities of highly ionized atoms in cooling gas. In a model for cooling of a hot galactic corona, it is shown that the observed value of N(N V) can be produced in the cooling gas, while the predicted value of N(Si IV) falls short of the observed value by a factor of about 5. The same model predicts fluxes of ultraviolet emission lines that are a factor of 10 lower than the claimed detections of Feldman, Bruna, and Henry. Predictions are made for ultraviolet lines in cooling flows in early-type galaxies and clusters of galaxies. It is shown that the column densities of interest vary over a fairly narrow range, while the emission line luminosities are simply proportional to the mass inflow rate.

Resonantly Enhanced Betatron Hard X-rays from Ionization Injected Electrons in a Laser Plasma Accelerator

PubMed Central

Huang, K.; Li, Y. F.; Li, D. Z.; Chen, L. M.; Tao, M. Z.; Ma, Y.; Zhao, J. R.; Li, M. H.; Chen, M.; Mirzaie, M.; Hafz, N.; Sokollik, T.; Sheng, Z. M.; Zhang, J.

2016-01-01

Ultrafast betatron x-ray emission from electron oscillations in laser wakefield acceleration (LWFA) has been widely investigated as a promising source. Betatron x-rays are usually produced via self-injected electron beams, which are not controllable and are not optimized for x-ray yields. Here, we present a new method for bright hard x-ray emission via ionization injection from the K-shell electrons of nitrogen into the accelerating bucket. A total photon yield of 8 × 108/shot and 108 photons with energy greater than 110 keV is obtained. The yield is 10 times higher than that achieved with self-injection mode in helium under similar laser parameters. The simulation suggests that ionization-injected electrons are quickly accelerated to the driving laser region and are subsequently driven into betatron resonance. The present scheme enables the single-stage betatron radiation from LWFA to be extended to bright γ-ray radiation, which is beyond the capability of 3rd generation synchrotrons. PMID:27273170

An Atlas of Far-ultraviolet Spectra of the Zeta Aurigae Binary 31 Cygni with Line Identifications

NASA Astrophysics Data System (ADS)

Hagen Bauer, Wendy; Bennett, Philip D.

2014-04-01

The ζ Aurigae system 31 Cygni (K4 Ib + B4 V) was observed by the FUSE satellite during total eclipse and at three phases during chromospheric eclipse. We present the coadded, calibrated spectra and atlases with line identifications. During total eclipse, emission from high ionization states (e.g., Fe III and Cr III) shows asymmetric profiles redshifted from the systemic velocity, while emission from lower ionization states (e.g., Fe II and O I) appears more symmetric and is centered closer to the systemic velocity. Absorption from neutral and singly ionized elements is detected during chromospheric eclipse. Late in chromospheric eclipse, absorption from the K star wind is detected at a terminal velocity of ~80 km s-1. These atlases will be useful for interpreting the far-UV spectra of other ζ Aur systems, as the observed FUSE spectra of 32 Cyg, KQ Pup, and VV Cep during chromospheric eclipse resemble that of 31 Cyg.

Local thermodynamic equilibrium in rapidly heated high energy density plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aslanyan, V.; Tallents, G. J.

Emission spectra and the dynamics of high energy density plasmas created by optical and Free Electron Lasers (FELs) depend on the populations of atomic levels. Calculations of plasma emission and ionization may be simplified by assuming Local Thermodynamic Equilibrium (LTE), where populations are given by the Saha-Boltzmann equation. LTE can be achieved at high densities when collisional processes are much more significant than radiative processes, but may not be valid if plasma conditions change rapidly. A collisional-radiative model has been used to calculate the times taken by carbon and iron plasmas to reach LTE at varying densities and heating rates.more » The effect of different energy deposition methods, as well as Ionization Potential Depression are explored. This work shows regimes in rapidly changing plasmas, such as those created by optical lasers and FELs, where the use of LTE is justified, because timescales for plasma changes are significantly longer than the times needed to achieve an LTE ionization balance.« less

On the nature of the symbiotic binary AX Persei

NASA Technical Reports Server (NTRS)

Mikolajewska, Joanna; Kenyon, Scott J.

1992-01-01

Photometric and spectroscopic observations of the symbiotic binary AX Persei are presented. This system contains a red giant that fills its tidal lobe and transfers material into an accretion disk surrounding a low-mass main-sequence star. The stellar masses - 1 solar mass for the red giant and about 0.4 solar mass for the companion - suggest AX Per is poised to enter a common envelope phase of evolution. The disk luminosity increases from L(disk) about 100 solar luminosity in quiescence to L(disk) about 5700 solar luminosity in outburst for a distance of d = 2.5 kpc. Except for visual maximum, high ionization permitted emission lines - such as He II - imply an EUV luminosity comparable to the disk luminosity. High-energy photons emitted by a hot boundary layer between the disk and central star ionize a surrounding nebula to produce this permitted line emission. High ionization forbidden lines form in an extended, shock-excited region well out of the binary's orbital plane and may be associated with mass loss from the disk.

Gemini Near Infrared Field Spectrograph Observations of the Seyfert 2 Galaxy MRK 573: In Situ Acceleration of Ionized and Molecular Gas Off Fueling Flows

NASA Technical Reports Server (NTRS)

Fischer, Travis C.; Machuca, C.; Diniz, M. R.; Crenshaw, D. M.; Kraemer, S. B.; Riffel, R. A.; Schmitt, H. R.; Baron, F.; Storchi-Bergmann, T.; Straughn, A. N.;

The effects of pre-ionization using a shunt resistor on reproducibility of the x-ray emission in a dense plasma focus device

NASA Astrophysics Data System (ADS)

Piriaei, D.; Yousefi, H. R.; Mahabadi, T. D.; SalarElahi, A.; Ghoranneviss, M.

2017-08-01

In this research, the effects of pre-ionization using a shunt resistor on reproducibility of x-ray emission in a Mather type plasma focus device have been studied. This technique increased the intensities of the emitted x-rays from argon as the filling gas of the device and made the x-ray yields with similar intensities reproducible. A Mirnov coil was also used to record the variations of the plasma's magnetic field, and the wavelet spectrums of these recorded signals showed the reduced instabilities due to the application of the pre-ionization technique. Moreover, it was demonstrated that this technique was capable of reducing the number of initial runaway electrons that could increase the impurities and instabilities inside the plasma. In addition to the above-mentioned features, this technique could improve the uniform formation of the current sheath during the breakdown phase that might later lead to a high quality pinch and high intensity emitted x-rays.

Delayed Ionization in Transition Metal Carbon Clusters

NASA Astrophysics Data System (ADS)

Kooi, S. E.; Castleman, A. W., Jr.

1997-03-01

Mass spectrometric studies of several single and binary transition metal carbon cluster systems, produced in a laser vaporization source, reveal several species that undergo delayed ionization. Pulsed extraction and blocking electric fields, in a time-of-flight mass spectrometer, allow the study of delayed ionization over a time window after excitation with a pulsed laser. In systems where metallocarbohedrenes (Met-Cars) are produced, the Met-Cars are the dominate delayed species. Delayed ionization of binary metal Met-Cars Ti_xM_yC_12 (M=Zr,Nb,Y; x+y=8) is dependent on the ratio of the two metals. Delayed behavior is investigated over a range of photoionization wavelengths and fluences. In order to determine the degree to which the delayed ionization is thermionic in character, the experimental data have been compared to Klots's model for thermionic emission from small particles.

Spontaneous-Desorption Ionizer for a TOF-MS

NASA Technical Reports Server (NTRS)

Schultz, J. Albert

2006-01-01

A time-of-flight mass spectrometer (TOF-MS) like the one mentioned in the immediately preceding article has been retrofitted with an ionizer based on a surface spontaneous-desorption process. This ionizer includes an electron multiplier in the form of a microchannel plate (MCP). Relative to an ionizer based on a hot-filament electron source, this ionizer offers advantages of less power consumption and greater mechanical ruggedness. The current density and stability characteristics of the electron emission of this ionizer are similar to those of a filament-based ionizer. In tests of various versions of this ionizer in the TOF-MS, electron currents up to 100 nA were registered. Currents of microamperes or more - great enough to satisfy requirements in most TOFMS applications - could be obtained by use of MCPs different from those used in the tests, albeit at the cost of greater bulk. One drawback of this ionizer is that the gain of the MCP decreases as a function of the charge extracted thus far; the total charge that can be extracted over the operational lifetime is about 1 coulomb. An MCP in the ion-detector portion of the TOF-MS is subject to the same limitation.

The mean ultraviolet spectrum of a representative sample of faint z ˜ 3 Lyman alpha emitters

NASA Astrophysics Data System (ADS)

Nakajima, Kimihiko; Fletcher, Thomas; Ellis, Richard S.; Robertson, Brant E.; Iwata, Ikuru

2018-06-01

We discuss the rest-frame ultraviolet (UV) emission line spectra of a large (˜100) sample of low luminosity redshift z ˜ 3.1 Lyman alpha emitters (LAEs) drawn from a Subaru imaging survey in the SSA22 survey field. Our earlier work based on smaller samples indicated that such sources have high [O III]/[O II] line ratios possibly arising from a hard ionizing spectrum that may be typical of similar sources in the reionization era. With optical spectra secured from VLT/VIMOS, we re-examine the nature of the ionizing radiation in a larger sample using the strength of the high ionization diagnostic emission lines of CIII]λ1909, CIVλ1549, HEIIλ1640, and O III]λλ1661, 1666 Å in various stacked subsets. Our analysis confirms earlier suggestions of a correlation between the strength of Ly α and CIII] emission and we find similar trends with broad-band UV luminosity and rest-frame UV colour. Using various diagnostic line ratios and our stellar photoionization models, we determine both the gas phase metallicity and hardness of the ionization spectrum characterized by ξion - the number of Lyman continuum photons per UV luminosity. We confirm our earlier suggestion that ξion is significantly larger for LAEs than for continuum-selected Lyman break galaxies, particularly for those LAEs with the faintest UV luminosities. We briefly discuss the implications for cosmic reionization if the metal-poor intensely star-forming systems studied here are representative examples of those at much higher redshift.

LMC X-1: A New Spectral Analysis of the O-star in the Binary and Surrounding Nebula

NASA Astrophysics Data System (ADS)

Hyde, E. A.; Russell, D. M.; Ritter, A.; Filipović, M. D.; Kaper, L.; Grieve, K.; O'Brien, A. N.

2017-09-01

We provide new observations of the LMC X-1 O star and its extended nebula structure using spectroscopic data from VLT/UVES as well as Hα imaging from the Wide Field Imager on the Max Planck Gesellschaft/European Southern Observatory 2.2 m telescope and ATCA imaging of the 2.1 GHz radio continuum. This nebula is one of the few known to be energized by an X-ray binary. We use a new spectrum extraction technique that is superior to other methods used to obtain both radial velocities and fluxes. This provides an updated spatial velocity of ≃ 21.0 +/- 4.8 km s-1 for the O star. The slit encompasses both the photo-ionized and shock-ionized regions of the nebula. The imaging shows a clear arc-like structure reminiscent of a wind bow shock in between the ionization cone and shock-ionized nebula. The observed structure can be fit well by the parabolic shape of a wind bow shock. If an interpretation of a wind bow shock system is valid, we investigate the N159-O1 star cluster as a potential parent of the system, suggesting a progenitor mass of ˜60 M ⊙ for the black hole. We further note that the radio emission could be non-thermal emission from the wind bow shock, or synchrotron emission associated with the jet-inflated nebula. For both wind- and jet-powered origins, this would represent one of the first radio detections of such a structure.

Ejection-ionization of molecules from free standing graphene

NASA Astrophysics Data System (ADS)

Verkhoturov, Stanislav V.; Czerwinski, Bartlomiej; Verkhoturov, Dmitriy S.; Geng, Sheng; Delcorte, Arnaud; Schweikert, Emile A.

2017-02-01

We present the first data on emission of -C60 stimulated by single impacts of 50 keV C60+2 on the self-assembled molecular layer of C60 deposited on free standing 2 layer graphene. The yield, Y, of -C60 emitted in the transmission direction is 1.7%. To characterize the ejection and ionization of molecules, we have measured the emission of -C60 from the surface of bulk C60 (Y = 3.7%) and from a single layer of C60 deposited on bulk pyrolytic graphite (Y = 3.3%). To gain insight into the mechanism(s) of ejection, molecular dynamic simulations were performed. The scenario of the energy deposition and ejection of molecules is different for the case of graphene due to the confined volume of projectile-analyte interaction. In the case of 50 keV C60+2 impacts on graphene plus C60, the C atoms of the projectile collide with those of the target. The knocked-on atoms take on a part of the kinetic energy of the projectile atoms. Another part of the kinetic energy is deposited into the rim around the impact site. The ejection of molecules from the rim is a result of collective movement of the molecules and graphene membrane, where the membrane movement provides the impulse for ejection. The efficient emission of the intact molecular ions implies an effective ionization probability of intact C60. The proposed mechanism of ionization involves the tunneling of electrons from the vibrationally exited area around the hole to the ejecta.

Variations in the 3 micron spectrum across the Orion Bar: polycyclic aromatic hydrocarbons and related molecules

NASA Technical Reports Server (NTRS)

Sloan, G. C.; Bregman, J. D.; Geballe, T. R.; Allamandola, L. J.; Woodward, C. E.

1997-01-01

Long-slit spectra across the Orion Bar reveal significant differences in the spatial behavior of the components of the 3 microns polycyclic aromatic hydrocarbon (PAH) spectrum. The strong PAH band at 3.29 microns generally decreases exponentially with distance from the ionization front into the molecular cloud (scale height approximately 12"), although excesses appear approximately 10" and 20" behind the ionization front, close to layers of H2 and CO emission, respectively. The 3.40 microns PAH feature separates into two components with very different spatial distributions. The main component (at 3.395 microns), along with the 3.51 microns band and the PAH plateau (3.3-3.6 microns), shows excess emission approximately 10" and approximately 20" behind the ionization front, stronger than the excesses in the 3.29 microns band. The extra component of the 3.40 microns band, which peaks at approximately 3.405 microns, has a spatial distribution very similar to the H2 emission. Aromatic C-H stretches in PAHs most likely produce the 3.29 microns feature. Aliphatic C-H stretches in either attached methyl side-groups or superhydrogenated PAHs, or perhaps both, could produce the complicated spectral and spatial structure at 3.40 microns.

Investigating the temporal domain of massive ionized jets - I. A pilot study

NASA Astrophysics Data System (ADS)

Purser, S. J. D.; Lumsden, S. L.; Hoare, M. G.; Cunningham, N.

2018-03-01

We present sensitive (σ < 10 μJy beam- 1), radio continuum observations using the Australian Telescope Compact Array at frequencies of 6 and 9 GHz towards four massive young stellar objects (MYSOs). From a previous, less sensitive work, these objects are known to harbour ionized jets associated with radio lobes, which result from shock processes. In comparison with that work, further emission components are detected towards each MYSO. These include extended, direct, thermal emission from the ionized jet's stream, new radio lobes indicative of shocks close (<105 au) to the MYSO, three radio Herbig-Haro objects separated by up to 3.8 pc from the jet's launching site, and an IR-dark source coincident with CH3OH maser emission. No significant, integrated flux variability is detected towards any jets or shocked lobes, and only one proper motion is observed (1806± 596{{ km}{ s}^{-1}{ }} parallel to the jet axis of G310.1420+00.7583A). Evidence for precession is detected in all four MYSOs with precession periods and angles within the ranges 66-15 480 yr and 6°-36°, respectively. Should precession be the result of the influence from a binary companion, we infer orbital radii of 30-1800 au.

Detection of Thermal Water Vapor Emission from W Hydrae

NASA Technical Reports Server (NTRS)

Neufeld, David A.; Chen, Wesley; Melnick, Gary J.; DeGraauw, Thijs; Feuchtgruber, Helmut; Harwitt, Martin

1997-01-01

We have detected four far-infrared emission lines of water vapor toward the evolved star W Hydrae, using the Short Wavelength Spectrometer (SWS) of the Infrared Space Observatory (ISO). This is the first detection of thermal water vapor emission from a circumstellar outflow.

An Outburst Scenario for the X-ray Spectral Variability in 3C 111

NASA Technical Reports Server (NTRS)

Tombesi, Francesco; Reeves, J. N.; Reynolds, Christopher S.; Garcia, J.; Lohfink, A.

2013-01-01

We present a combined Suzaku and Swift BAT broad-band E=0.6-200 keV spectral analysis of three 3C 111 observations obtained in 2010. The data are well described with an absorbed power-law continuum and a weak (R approximately equal to 0.2) cold reflection component from distant material. We constrain the continuum cutoff at E(sub C) approximately equal to 150- 200 keV, which is in accordance with X-ray Comptonization corona models and supports claims that the jet emission is only dominant at much higher energies. Fe XXVI Ly alpha emission and absorption lines are also present in the first and second observations, respectively. The modelling and interpretation of the emission line is complex and we explore three possibilities. If originating from ionized disc reflection, this should be emitted at r(sub in) greater than or equal to 50 r(sub g) or, in the lamp-post configuration, the illuminating source should be at a height of h greater than or equal to 30 r(sub g) over the black hole. Alternatively, the line could be modeled with a hot collisionally ionized plasma with temperature kT = 22.0(sup +6.1)(sub -3.2) keV or a photo-ionized plasma with logXi=4.52(sup +0.10)(sub -0.16) erg per second cm, and column density N(sub H) greater than 3×10(sup 23) per square centimeter. However, the first and second scenarios are less favored on statistical and physical grounds, respectively. The blue-shifted absorption line in the second observation can be modelled as an ultra-fast outflow (UFO) with ionization parameter logXi=4.47(sup +0.76) (sub -0.04) erg per second cm, column density NH=(5.3(sup +1.8)(sub -1.3))×10(sup 22) per square centimeter and outflow velocity v(sub out) = 0.104+/-0.006c. Interestingly, the parameters of the photoionized emission model remarkably match those of the absorbing UFO, supporting the possibility that the same material could be responsible for both emission and absorption. We suggest an outburst scenario in which an accretion disc wind, initially lying out of the line of sight and observed in emission, then crosses our view to the source and it is observed in absorption as a mildly-relativistic UFO.

Infrared dust bubble CS51 and its interaction with the surrounding interstellar medium

NASA Astrophysics Data System (ADS)

Das, Swagat R.; Tej, Anandmayee; Vig, Sarita; Liu, Hong-Li; Liu, Tie; Ishwara Chandra, C. H.; Ghosh, Swarna K.

2017-12-01

A multiwavelength investigation of the southern infrared dust bubble CS51 is presented in this paper. We probe the associated ionized, cold dust, molecular and stellar components. Radio continuum emission mapped at 610 and 1300 MHz, using the Giant Metrewave Radio Telescope, India, reveals the presence of three compact emission components (A, B, and C) apart from large-scale diffuse emission within the bubble interior. Radio spectral index map shows the co-existence of thermal and non-thermal emission components. Modified blackbody fits to the thermal dust emission using Herschel Photodetector Array Camera and Spectrometer and Spectral and Photometric Imaging Receiver data is performed to generate dust temperature and column density maps. We identify five dust clumps associated with CS51 with masses and radius in the range 810-4600 M⊙ and 1.0-1.9 pc, respectively. We further construct the column density probability distribution functions of the surrounding cold dust which display the impact of ionization feedback from high-mass stars. The estimated dynamical and fragmentation time-scales indicate the possibility of collect and collapse mechanism in play at the bubble border. Molecular line emission from the Millimeter Astronomy Legacy Team 90 GHz survey is used to understand the nature of two clumps which show signatures of expansion of CS51.

Current conduction mechanism and electrical break-down in InN grown on GaN

NASA Astrophysics Data System (ADS)

Kuzmik, J.; Fleury, C.; Adikimenakis, A.; Gregušová, D.; Ťapajna, M.; Dobročka, E.; Haščík, Š.; Kučera, M.; Kúdela, R.; Androulidaki, M.; Pogany, D.; Georgakilas, A.

2017-06-01

Current conduction mechanism, including electron mobility, electron drift velocity (vd) and electrical break-down have been investigated in a 0.5 μm-thick (0001) InN layer grown by molecular-beam epitaxy on a GaN/sapphire template. Electron mobility (μ) of 1040 cm2/Vs and a free electron concentration (n) of 2.1 × 1018 cm-3 were measured at room temperature with only a limited change down to 20 K, suggesting scattering on dislocations and ionized impurities. Photoluminescence spectra and high-resolution X-ray diffraction correlated with the Hall experiment showing an emission peak at 0.69 eV, a full-width half-maximum of 30 meV, and a dislocation density Ndis ˜ 5.6 × 1010 cm-2. Current-voltage (I-V) characterization was done in a pulsed (10 ns-width) mode on InN resistors prepared by plasma processing and Ohmic contacts evaporation. Resistors with a different channel length ranging from 4 to 15.8 μm obeyed the Ohm law up to an electric field intensity Eknee ˜ 22 kV/cm, when vd ≥ 2.5 × 105 m/s. For higher E, I-V curves were nonlinear and evolved with time. Light emission with a photon energy > 0.7 eV has been observed already at modest Erad of ˜ 8.3 kV/cm and consequently, a trap-assisted interband tunneling was suggested to play a role. At Eknee ˜ 22 kV/cm, we assumed electron emission from traps, with a positive feed-back for the current enhancement. Catastrophic break-down appeared at E ˜ 25 kV/cm. Reduction of Ndis was suggested to fully exploit InN unique prospects for future high-frequency devices.

Haro 11: Where is the Lyman Continuum Source?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keenan, Ryan P.; Oey, M. S.; Jaskot, Anne E.

2017-10-10

Identifying the mechanism by which high-energy Lyman continuum (LyC) photons escaped from early galaxies is one of the most pressing questions in cosmic evolution. Haro 11 is the best known local LyC-leaking galaxy, providing an important opportunity to test our understanding of LyC escape. The observed LyC emission in this galaxy presumably originates from one of the three bright, photoionizing knots known as A, B, and C. It is known that Knot C has strong Ly α emission, and Knot B hosts an unusually bright ultraluminous X-ray source, which may be a low-luminosity active galactic nucleus. To clarify the LyCmore » source, we carry out ionization-parameter mapping (IPM) by obtaining narrow-band imaging from the Hubble Space Telescope WFC3 and ACS cameras to construct spatially resolved ratio maps of [O iii]/[O ii] emission from the galaxy. IPM traces the ionization structure of the interstellar medium and allows us to identify optically thin regions. To optimize the continuum subtraction, we introduce a new method for determining the best continuum scale factor derived from the mode of the continuum-subtracted, image flux distribution. We find no conclusive evidence of LyC escape from Knots B or C, but instead we identify a high-ionization region extending over at least 1 kpc from Knot A. This knot shows evidence of an extremely young age (≲1 Myr), perhaps containing very massive stars (>100 M {sub ⊙}). It is weak in Ly α , so if it is confirmed as the LyC source, our results imply that LyC emission may be independent of Ly α emission.« less

Physical Conditions of the Interstellar Medium in Star-forming Galaxies at z1.5

NASA Technical Reports Server (NTRS)

Hayashi, Masao; Ly, Chun; Shimasaku, Kazuhiro; Motohara, Kentaro; Malkan, Matthew A.; Nagao, Tohru; Kashikawa, Nobunari; Goto, Ryosuke; Naito, Yoshiaki

2015-01-01

We present results from Subaru/FMOS near-infrared (NIR) spectroscopy of 118 star-forming galaxies at z approximately equal to 1.5 in the Subaru Deep Field. These galaxies are selected as [O II] lambda 3727 emitters at z approximately equal to 1.47 and 1.62 from narrow-band imaging. We detect H alpha emission line in 115 galaxies, [O III] lambda 5007 emission line in 45 galaxies, and H Beta, [N II] lambda 6584, and [S II]lambda lambda 6716, 6731 in 13, 16, and 6 galaxies, respectively. Including the [O II] emission line, we use the six strong nebular emission lines in the individual and composite rest-frame optical spectra to investigate physical conditions of the interstellar medium in star-forming galaxies at z approximately equal to 1.5. We find a tight correlation between H alpha and [O II], which suggests that [O II] can be a good star formation rate (SFR) indicator for galaxies at z approximately equal to 1.5. The line ratios of H alpha / [O II] are consistent with those of local galaxies. We also find that [O II] emitters have strong [O III] emission lines. The [O III]/[O II] ratios are larger than normal star-forming galaxies in the local Universe, suggesting a higher ionization parameter. Less massive galaxies have larger [O III]/[O II] ratios. With evidence that the electron density is consistent with local galaxies, the high ionization of galaxies at high redshifts may be attributed to a harder radiation field by a young stellar population and/or an increase in the number of ionizing photons from each massive star.

Constraining the Accretion Mode in LINER 1.9s

NASA Astrophysics Data System (ADS)

Sabra, Bassem; Der Sahaguian, Elias; Badr, Elie

2016-01-01

The accretion mode and the dominant power source in low-ionization nuclear emission-line regions (LINERs), a class of active galactic nuclei (AGN), are still elusive. We focus on a sample of 22 LINER 1.9s (Ho et al. 1997), a subclass of LINERs that show broad Halpha lines, a signature of blackhole-powered accretion, to test the hypothesis that the ionizing continuum emitted by a radiatively inefficient accretion flow (RIAF) could lead to the LINER ultraviolet (UV) emission-line ratios. Optical line-ratio diagrams are a weak diagnostic tool in distinguishing between possible power sources (Sabra et al. 2003). We search the Mikulski Archive for Space Telescopes (MAST) for UV spectra of the objects in the above sample and also perform photoionization simulations using CLOUDY (Ferland et al. 2013). Unfortunately, only one object (NGC 1052; Gabel et al. 2000) of the 22 LINER 1.9s has UV spectra that cover many emission lines; the rest of the objects either do not have any UV spectra, the spectral coverage is in-adequate, or the spectra have very low signal-to-noise ratios. Our photoionization simulations set up two identical grids of clouds with a range of densities and ionization parameters. We illuminate one grid with radiation emitted by a thin accretion disk (AD) and we illuminate the other grid with radiation from a RIAF. We overplot the UV emission-line ratio predictions for AD and RIAF illumination, together with the available line ratios for NGC 1052. Initial results show that UV lines could be used as diagnostics for the accretion mode in AGN. More UV spectral coverage of LINER 1.9s is needed in order to more fully utilize the diagnostic powers of UV emission line ratios.

The Resolved Outflow from 3C 48

NASA Astrophysics Data System (ADS)

Shih, Hsin-Yi; Stockton, Alan

2014-10-01

We investigate the properties of the high-velocity outflow driven by the young radio jet of 3C 48, a compact-steep-spectrum source. We use the Space Telescope Imaging Spectrograph on board the Hubble Space Telecope to obtain (1) low-resolution UV and optical spectra and (2) multi-slit medium-resolution spectra of the ionized outflow. With supporting data from ground-based spectrographs, we are able to accurately measure the ratios of diagnostic emission lines such as [O III] λ5007, [O III] λ3727, [N II] λ6548, Hα, Hβ, [Ne V] λ3425, and [Ne III] λ3869. We fit the observed emission-line ratios using a range of ionization models, powered by active galactic nucleus (AGN) radiation and shocks, produced by the MAPPINGS code. We have determined that AGN radiation is likely the dominant ionization source. The outflow's density is estimated to be in the range n = 103-104 cm-3, the mass is ~6 × 106 M ⊙, and the metallicity is likely equal to or higher than solar. Compared with the typical outflows associated with more evolved radio jets, this young outflow is denser, less massive, and more metal rich. Multi-slit observations allow us to construct a two-dimensional velocity map of the outflow that shows a wide range of velocities with distinct velocity components, suggesting a wide-angle clumpy outflow. Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-11574. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Some of the observations included were obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).

A QUANTITATIVE STUDY OF THE EVOLUTION OF GASES FROM ELECTRON TUBES AND MATERIALS.

DTIC Science & Technology

spectrometer, ion pumps, ionization gauges and precision orifices to measure the flow rate of individual gases. It has been used to examine several...amounts comprise about 95% of the gas evolved during cathode conversion and activation. Additional experiments in the dynamic analysis of tube processes are suggested. (Author)

Biochemical characterization of RecA variants that contribute to extreme resistance to ionizing radiation

PubMed Central

Piechura, Joseph R.; Tseng, Tzu-Ling; Hsu, Hsin-Fang; Byrne, Rose T.; Windgassen, Tricia A.; Chitteni-Pattu, Sindhu; Battista, John R.; Li, Hung-Wen; Cox, Michael M.

2015-01-01

Among strains of Escherichia coli that have evolved to survive extreme exposure to ionizing radiation, mutations in the recA gene are prominent and contribute substantially to the acquired phenotype. Changes at amino acid residue 276, D276A and D276N, occur repeatedly and in separate evolved populations. RecA D276A and RecA D276N exhibit unique adaptations to an environment that can require the repair of hundreds of double strand breaks. These two RecA protein variants (a) exhibit a faster rate of filament nucleation on DNA, as well as a slower extension under at least some conditions, leading potentially to a distribution of the protein among a higher number of shorter filaments, (b) promote DNA strand exchange more efficiently in the context of a shorter filament, and (c) are markedly less inhibited by ADP. These adaptations potentially allow RecA protein to address larger numbers of double strand DNA breaks in an environment where ADP concentrations are higher due to a compromised cellular metabolism. PMID:25559557

A Physical Model for the Evolving Ultraviolet Luminosity Function of High Redshift Galaxies and their Contribution to the Cosmic Reionization

NASA Astrophysics Data System (ADS)

Cai, Zhen-Yi; Lapi, Andrea; Bressan, Alessandro; De Zotti, Gianfranco; Negrello, Mattia; Danese, Luigi

2014-04-01

We present a physical model for the evolution of the ultraviolet (UV) luminosity function of high-redshift galaxies, taking into account in a self-consistent way their chemical evolution and the associated evolution of dust extinction. Dust extinction is found to increase fast with halo mass. A strong correlation between dust attenuation and halo/stellar mass for UV selected high-z galaxies is thus predicted. The model yields good fits of the UV and Lyman-α (Lyα) line luminosity functions at all redshifts at which they have been measured. The weak observed evolution of both luminosity functions between z = 2 and z = 6 is explained as the combined effect of the negative evolution of the halo mass function; of the increase with redshift of the star formation efficiency due to the faster gas cooling; and of dust extinction, differential with halo mass. The slope of the faint end of the UV luminosity function is found to steepen with increasing redshift, implying that low luminosity galaxies increasingly dominate the contribution to the UV background at higher and higher redshifts. The observed range of the UV luminosities at high z implies a minimum halo mass capable of hosting active star formation M crit <~ 109.8 M ⊙, which is consistent with the constraints from hydrodynamical simulations. From fits of Lyα line luminosity functions, plus data on the luminosity dependence of extinction, and from the measured ratios of non-ionizing UV to Lyman-continuum flux density for samples of z ~= 3 Lyman break galaxies and Lyα emitters, we derive a simple relationship between the escape fraction of ionizing photons and the star formation rate. It implies that the escape fraction is larger for low-mass galaxies, which are almost dust-free and have lower gas column densities. Galaxies already represented in the UV luminosity function (M UV <~ -18) can keep the universe fully ionized up to z ~= 6. This is consistent with (uncertain) data pointing to a rapid drop of the ionization degree above z ~= 6, such as indications of a decrease of the comoving emission rate of ionizing photons at z ~= 6, a decrease of sizes of quasar near zones, and a possible decline of the Lyα transmission through the intergalactic medium at z > 6. On the other hand, the electron scattering optical depth, τes, inferred from cosmic microwave background (CMB) experiments favor an ionization degree close to unity up to z ~= 9-10. Consistency with CMB data can be achieved if M crit ~= 108.5 M ⊙, implying that the UV luminosity functions extend to M UV ~= -13, although the corresponding τes is still on the low side of CMB-based estimates.

Is there any pristine gas in nearby starburst galaxies?

NASA Astrophysics Data System (ADS)

Lebouteiller, Vianney; Kunth, Daniel

2008-12-01

We derive the chemical composition of the neutral gas in the blue compact dwarf (BCD) Pox 36 observed with FUSE. Metals (N, O, Ar, and Fe) are underabundant as compared to the ionized gas associated with H ii regions by a factor ~7. The neutral gas, although it is not pristine, is thus probably less chemically evolved than the ionized gas. This could be due to different dispersal and mixing timescales. Results are compared to those of other BCDs observed with FUSE. The metallicity of the neutral gas in BCDs seems to reach a lower threshold of ~1/50 Z⊙ for extremely-metal poor galaxies.

Metal enrichment in the neutral gas of star-forming galaxies

NASA Astrophysics Data System (ADS)

Lebouteiller, V.; Kunth, D.; Désert, J.-M.; Thuan, T. X.

2009-05-01

We derive the chemical composition of the neutral gas in the blue compact dwarf (BCD) Pox 36 observed with FUSE. Metals (N, O, Ar, and Fe) are underabundant as compared to the ionized gas associated with H II regions by a factor ~7. The neutral gas, although it is not pristine, is thus probably less chemically evolved than the ionized gas. This could be due to different dispersal and mixing timescales. Results are compared to those of other BCDs observed with FUSE. The metallicity of the neutral gas in BCDs seems to reach a lower threshold of ~1/50Zsolar for extremely-metal poor galaxies.

Excitation of higher lying energy states in a rubidium DPAL

NASA Astrophysics Data System (ADS)

Wallerstein, A. J.; Perram, Glen; Rice, Christopher A.

2018-02-01

The spontaneous emission in a cw rubidium diode dumped alkali laser (DPAL) system was analyzed. The fluorescence from higher lying states decreases with additional buffer gas. The intermediate states (7S, 6P, 5D) decay more slowly with buffer gas and scale super-linearly with alkali density. A detailed kinetic model has been constructed, where the dominant mechanisms are energy pooling and single photon ionization. It also includes pumping into the non-Lorentzian wings of absorption profiles, fine structure mixing, collisional de-excitation, and Penning ionization. Effects of ionization in a high powered CW rubidium DPAL were assessed.

Heater-induced ionization inferred from spectrometric airglow measurements

NASA Astrophysics Data System (ADS)

Hysell, D. L.; Miceli, R. J.; Kendall, E. A.; Schlatter, N. M.; Varney, R. H.; Watkins, B. J.; Pedersen, T. R.; Bernhardt, P. A.; Huba, J. D.

2014-03-01

Spectrographic airglow measurements were made during an ionospheric modification experiment at High Frequency Active Auroral Research Program on 12 March 2013. Artificial airglow enhancements at 427.8, 557.7, 630.0, 777.4, and 844.6 nm were observed. On the basis of these emissions and using a methodology based on the method of Backus and Gilbert (1968, 1970), we estimate the suprathermal electron population and the subsequent equilibrium electron density profile, including contributions from electron impact ionization. We find that the airglow is consistent with heater-induced ionization in view of the spatial intermittency of the airglow.

Spatially resolved density and ionization measurements of shocked foams using x-ray fluorescence

DOE Office of Scientific and Technical Information (OSTI.GOV)

MacDonald, M. J.; Keiter, P. A.; Montgomery, D. S.

2016-09-28

We present experiments at the Trident laser facility demonstrating the use of x-ray fluorescence (XRF) to simultaneously measure density, ionization state populations, and electron temperature in shocked foams. An imaging x-ray spectrometer obtained spatially resolved measurements of Ti K-α emission. Density profiles were measured from K-α intensity. Ti ionization state distributions and electron temperatures were inferred by fitting K-α spectra to spectra from CRETIN simulations. This work shows that XRF provides a powerful tool to complement other diagnostics to make equation of state measurements of shocked materials containing a suitable tracer element.

The effect of nonequilibrium ionization on ultraviolet line shifts in the solar transition region

NASA Technical Reports Server (NTRS)

Spadaro, D.; Noci, G.; Zappala, R. A.; Antiochos, S. K.

1990-01-01

The line profiles and wavelength positions of all the important emission lines due to carbon were computed for a variety of steady state siphon flow loop models. For the lines from the lower ionization states (C II-C IV) a preponderance of blueshifts was found, contrary to the observations. The lines from the higher ionization states can show either a net red- or blueshift, depending on the position of the loop on the solar disk. Similar results are expected for oxygen. It is concluded that the observed redshifts cannot be explained by the models proposed here.

Observations of extended and counterrotating disks of ionized gas in S0 galaxies

NASA Technical Reports Server (NTRS)

Dettmar, Ralf-Juergen; Jullien-Dettmar, Marlies; Barteldrees, Andreas

1990-01-01

While many E/S0 galaxies have been found to show emission line spectra in their nuclear regions, the question of the presence and nature of extended disks of ionized gas in these galaxies has been addressed only in recent years. Typically the ionized gas is detected in the inner region on a scale of approx. 1 kpc (e.g., Phillips et al. 1986, Caldwell 1984). Here researchers present evidence that the disks of ionized gas of at least some S0 galaxies are much more extended than previously believed. In addition, with the detection of the counterrotation of gas and stars in NGC 7007 they strengthen the basis for arguments that the source of gas in S0 galaxies is external

Ionized gas at the edge of the central molecular zone

NASA Astrophysics Data System (ADS)

Langer, W. D.; Goldsmith, P. F.; Pineda, J. L.; Velusamy, T.; Requena-Torres, M. A.; Wiesemeyer, H.

2015-04-01

Context. The edge of the central molecular zone (CMZ) is the location where massive dense molecular clouds with large internal velocity dispersions transition to the surrounding more quiescent and lower CO emissivity region of the Galaxy. Little is known about the ionized gas surrounding the molecular clouds and in the transition region. Aims: We determine the properties of the ionized gas at the edge of the CMZ near Sgr E using observations of N+ and C+. Methods: We observed a small portion of the edge of the CMZ near Sgr E with spectrally resolved [C ii] 158 μm and [N ii] 205 μm fine structure lines at six positions with the GREAT instrument on SOFIA and in [C ii] using Herschel HIFI on-the-fly strip maps. We use the [N ii] spectra along with a radiative transfer model to calculate the electron density of the gas and the [C ii] maps to illuminate the morphology of the ionized gas and model the column density of CO-dark H2. Results: We detect two [C ii] and [N ii] velocity components, one along the line of sight to a CO molecular cloud at - 207 km s-1 associated with Sgr E and the other at -174 km s-1 outside the edge of another CO cloud. From the [N ii] emission we find that the average electron density is in the range of ~5 to 21 cm-3 for these features. This electron density is much higher than that of the disk's warm ionized medium, but is consistent with densities determined for bright diffuse H ii nebula. The column density of the CO-dark H2 layer in the -207 km s-1 cloud is ~1-2 × 1021 cm-2 in agreement with theoretical models. The CMZ extends further out in Galactic radius by ~7 to 14 pc in ionized gas than it does in molecular gas traced by CO. Conclusions: The edge of the CMZ likely contains dense hot ionized gas surrounding the neutral molecular material. The high fractional abundance of N+ and high electron density require an intense EUV field with a photon flux of order 106 to 107 photons cm-2 s-1, and/or efficient proton charge exchange with nitrogen, at temperatures of order 104 K, and/or a large flux of X-rays. Sgr E is a region of massive star formation as indicated by the presence of numerous compact H ii regions. The massive stars are potential sources of the EUV radiation that ionizes and heat the gas. In addition, X-ray sources and the diffuse X-ray emission in the CMZ are candidates for ionizing nitrogen.

Strong optical and UV intermediate-width emission lines in the quasar SDSS J232444.80-094600.3: dust-free and intermediate-density gas at the skin of dusty torus?

NASA Astrophysics Data System (ADS)

Li, Zhen-Zhen; Zhou, Hong-Yan; Hao, Lei; Wang, Shu-Fen; Ji, Tuo; Liu, Bo

2016-09-01

Emission lines from the broad emission line region (BELR) and the narrow emission line region (NELR) of active galactic nuclei (AGNs) have been extensively studied. However, emission lines are rarely detected between these two regions. We present a detailed analysis of quasar SDSS J232444.80-094600.3 (SDSS J2324-0946), which is remarkable for its strong intermediate-width emission lines (IELs) with FWHM ≈ 1800 km s-1. The IEL component is present in different emission lines, including the permitted lines Lyα λ1216, CIV λ1549, semiforbidden line [CIII] λ1909, and forbidden lines [OIII] λλ4959, 5007. With the aid of photo-ionization models, we found that the IELs are produced by gas with a hydrogen density of nH ˜ 106.2 ˜ 106.3 cm-3, a distance from the central ionizing source of R ˜ 35 - 50 pc, a covering factor of ˜ 6%, and a dust-to-gas ratio of ≤ 4% that of the SMC. We suggest that the strong IELs of this quasar are produced by nearly dust-free and intermediate-density gas located at the skin of the dusty torus. Such strong IELs, which serve as a useful diagnostic, can provide an avenue to study the properties of gas between the BELR and the NELR.

Red Geyser: A New Class of Galaxy with Large-scale AGN-driven Winds

NASA Astrophysics Data System (ADS)

Roy, Namrata; Bundy, Kevin; Cheung, Edmond; MaNGA Team

2018-01-01

A new class of quiescent (non-star-forming) galaxies harboring possible AGN-driven winds have been discovered using the spatially resolved optical spectroscopy from the ongoing SDSS-IV MaNGA (Sloan Digital Sky Survey-IV Mapping Nearby Galaxies at Apache Point Observatory) survey. These galaxies named "red geysers" constitute 5%-10% of the local quiescent galaxy population and are characterized by narrow bisymmetric ionized gas emission patterns. These enhanced patterns are seen in equivalent width maps of Hα, [OIII] and other strong emission lines. They are co-aligned with the ionized gas velocity gradients but significantly misaligned with stellar velocity gradients. They also show very high gas velocity dispersions (~200 km/s). Considering these observations in light of models of the gravitational potential, Cheung et al. argued that red geysers host large-scale AGN-driven winds of ionized gas that may play a role in suppressing star formation at late times. In this work, we test the hypothesis that AGN activity is ultimately responsible for the red geyser phenomenon. We compare the nuclear radio activity of the red geysers to a matched control sample of galaxies of similar stellar mass, redshift, rest frame NUV–r color and axis ratio. and additionally, control for the presence of ionized gas. We have used 1.4 GHz radio continuum data from the VLA FIRST Survey to stack the radio flux from the red geyser sample and control sample. We find that the red geysers have a higher average radio flux than the control galaxies at > 3σ significance. Our sample is restricted to rest-frame NUV–r color > 5, thus ruling out possible radio emission due to star formation activity. We conclude that red geysers are associated with more active AGN, supporting a feedback picture in which episodic AGN activity drives large-scale but relatively weak ionized winds in many in many early-type galaxies.

DEVELOPMENT OF HAZARDOUS AIR POLLUTANT EMISSION FACTORS FROM STATE SOURCE TEST PROGRAMS

EPA Science Inventory

The report gives results of a study in which emission factors were evolved from test data obtained from several Air Quality Management Districts in California and from state environmental agencies in Louisiana, Maryland, New Jersey, and Texas. The emission factors were developed...

Gold emissivities for hydrocode applications

NASA Astrophysics Data System (ADS)

Bowen, C.; Wagon, F.; Galmiche, D.; Loiseau, P.; Dattolo, E.; Babonneau, D.

2004-10-01

The Radiom model [M. Busquet, Phys Fluids B 5, 4191 (1993)] is designed to provide a radiative-hydrodynamic code with non-local thermodynamic equilibrium (non-LTE) data efficiently by using LTE tables. Comparison with benchmark data [M. Klapisch and A. Bar-Shalom, J. Quant. Spectrosc. Radiat. Transf. 58, 687 (1997)] has shown Radiom to be inaccurate far from LTE and for heavy ions. In particular, the emissivity was found to be strongly underestimated. A recent algorithm, Gondor [C. Bowen and P. Kaiser, J. Quant. Spectrosc. Radiat. Transf. 81, 85 (2003)], was introduced to improve the gold non-LTE ionization and corresponding opacity. It relies on fitting the collisional ionization rate to reproduce benchmark data given by the Averroès superconfiguration code [O. Peyrusse, J. Phys. B 33, 4303 (2000)]. Gondor is extended here to gold emissivity calculations, with two simple modifications of the two-level atom line source function used by Radiom: (a) a larger collisional excitation rate and (b) the addition of a Planckian source term, fitted to spectrally integrated Averroès emissivity data. This approach improves the agreement between experiments and hydrodynamic simulations.

Effects of stellar evolution and ionizing radiation on the environments of massive stars

NASA Astrophysics Data System (ADS)

Mackey, J.; Langer, N.; Mohamed, S.; Gvaramadze, V. V.; Neilson, H. R.; Meyer, D. M.-A.

2014-09-01

We discuss two important effects for the astrospheres of runaway stars: the propagation of ionizing photons far beyond the astropause, and the rapid evolution of massive stars (and their winds) near the end of their lives. Hot stars emit ionizing photons with associated photoheating that has a significant dynamical effect on their surroundings. 3-D simulations show that H ii regions around runaway O stars drive expanding conical shells and leave underdense wakes in the medium they pass through. For late O stars this feedback to the interstellar medium is more important than that from stellar winds. Late in life, O stars evolve to cool red supergiants more rapidly than their environment can react, producing transient circumstellar structures such as double bow shocks. This provides an explanation for the bow shock and linear bar-shaped structure observed around Betelgeuse.

Seyfert galaxy ultraviolet emission-line intensities and variability - A self-consistent photoionization analysis applied to broad-line-emitting gas in NGC 3783

NASA Technical Reports Server (NTRS)

Koratkar, Anuradha P.; Macalpine, Gordon M.

1992-01-01

Well-constrained photoionization models for the Seyfert I galaxy NGC 3783 are developed. Both cross-correlation analyses and line variability trends with varying ionizing radiation flux require a multicomponent picture. All the data for He II 1640 A, C IV 1549 A, and semiforbidden C III 1909 A can be reasonably well reproduced by two cloud components. One has a source-cloud distance of 24 lt-days, gas density around 3 x 10 exp 10/cu cm, ionization parameter range of 0.04-0.2, and cloud thickness such that about half of the carbon is doubly ionized and about half is triply ionized. The other component is located approximately 96 lt-days from the source, is shielded from the source by the inner cloud, has a density about 3 x 10 to the 9th/cu cm, and is characterized by an ionization parameter range of 0.001-0.03, The cloud thickness is such that about 45 percent carbon is doubly ionized and about 55 percent is singly ionized.

Morphology of the interstellar cooling lines detected by COBE

NASA Technical Reports Server (NTRS)

Bennett, C. L.; Fixsen, D. J.; Hinshaw, G.; Mather, J. C.; Moseley, S. H.; Wright, E. L.; Eplee, R. E., Jr.; Gales, J.; Hewagama, T.; Isaacman, R. B.

1994-01-01

The Far-Infrared Absolute Spectrophotometer (FIRAS) on the COBE satellite has conducted an unbiased survey of the far-infrared emission from our Galaxy. The first results of this survey were reported by Wright et al. (1991). We report the results of new analyses of this spectral survey, which includes emission lines from 158 micrometer C(+), 122 and 205 micrometer N(+), 370 and 609 micrometer C(0), and CO J = 2 goes to 1 through J = 5 goes to 4. We report the morphological distribution along the Galactic plane (b = 0 deg) of the spectral line emission, and the high Galactic latitude intensities of the C(+) and 205 micrometer N(+) emission. In the Galactic plane the 205 micrometer line of N(+) generally follows the 158 micrometer C(+) line distribution, but the intensities scale as I(N(+) 205 micrometer) varies as I(C(+) 158 micrometer)(exp 1.5) toward the inner Galaxy. The high Galactic latitude intensity of the 158 micrometer fine-structure transition from C(+) is I(C(+) 158 micrometer) = (1.43 +/- 0.12) x 10(exp -6) csc (absolute value of b) ergs/sq cm s sr for absolute value of b greater than 15 deg, and it decreases more rapidly than the far-infrared intensity with increasing Galactic latitude. C(+) and neutral atomic hydrogen emission are closely correlated with a C(+) cooling rate of (2.65 +/- 0.15) x 10(exp -26) ergs/s. We conclude that this emission arises almost entirely from the cold neutral medium. The high Galactic latitude intensity of the 205 micrometer fine-structure transition from N(+) is I(N(+) 205 micrometer) = (4 +/- 1) x 10(exp -8) csc (absolute value of b) ergs/((sq cm)(s)(sr)) arising entirely from the warm ionized medium. We estimate the total ionizing photon rate in the Galaxy to be phi = 3.5 x 10(exp 53) ionizing photons per second, based on the 205 micrometer N(+) transition.

Cross sections for ionization of tetrahydrofuran by protons at energies between 300 and 3000 keV

NASA Astrophysics Data System (ADS)

Wang, Mingjie; Rudek, Benedikt; Bennett, Daniel; de Vera, Pablo; Bug, Marion; Buhr, Ticia; Baek, Woon Yong; Hilgers, Gerhard; Rabus, Hans

2016-05-01

Double-differential cross sections for ionization of tetrahydrofuran by protons with energies from 300 to 3000 keV were measured at the Physikalisch-Technische Bundesanstalt ion accelerator facility. The electrons emitted at angles between 15∘ and 150∘ relative to the ion-beam direction were detected with an electrostatic hemispherical electron spectrometer. Single-differential and total ionization cross sections have been derived by integration. The experimental results are compared to the semiempirical Hansen-Kocbach-Stolterfoht model as well as to the recently reported method based on the dielectric formalism. The comparison to the latter showed good agreement with experimental data in a broad range of emission angles and energies of secondary electrons. The scaling property of ionization cross sections for tetrahydrofuran was also investigated. Compared to molecules of different size, the ionization cross sections of tetrahydrofuran were found to scale with the number of valence electrons at large impact parameters.

The Tomographic Ionized-Carbon Mapping Experiment (TIME) CII Imaging Spectrometer

NASA Astrophysics Data System (ADS)

Staniszewski, Z.; Bock, J. J.; Bradford, C. M.; Brevik, J.; Cooray, A.; Gong, Y.; Hailey-Dunsheath, S.; O'Brient, R.; Santos, M.; Shirokoff, E.; Silva, M.; Zemcov, M.

2014-09-01

The Tomographic Ionized-Carbon Mapping Experiment (TIME) and TIME-Pilot are proposed imaging spectrometers to measure reionization and large scale structure at redshifts 5-9. We seek to exploit the 158 restframe emission of [CII], which becomes measurable at 200-300 GHz at reionization redshifts. Here we describe the scientific motivation, give an overview of the proposed instrument, and highlight key technological developments underway to enable these measurements.

INVESTIGATION OF DENSITY EFFECT IN SOLIDS AND GASES.

DTIC Science & Technology

electron-positron pair production by 150 MeV electrons. (5) Investiga tion of the density effect in C, Al, Fe, Cu, Ni, Ag, Ta, and Au. (Author)...This report describes the results obtained for the following experiments: (1) The pressure dependence of ionization by relativistic elec trons. (2...Ionization by relativistic particles in helium-hydrogen gas mixtures. (3) Investiga tion of the operation of secondary emission monitors. (4) Direct

Nonperturbative Time Dependent Solution of a Simple Ionization Model

NASA Astrophysics Data System (ADS)

Costin, Ovidiu; Costin, Rodica D.; Lebowitz, Joel L.

2018-02-01

We present a non-perturbative solution of the Schrödinger equation {iψ_t(t,x)=-ψ_{xx}(t,x)-2(1 +α sinω t) δ(x)ψ(t,x)} , written in units in which \\hbar=2m=1, describing the ionization of a model atom by a parametric oscillating potential. This model has been studied extensively by many authors, including us. It has surprisingly many features in common with those observed in the ionization of real atoms and emission by solids, subjected to microwave or laser radiation. Here we use new mathematical methods to go beyond previous investigations and to provide a complete and rigorous analysis of this system. We obtain the Borel-resummed transseries (multi-instanton expansion) valid for all values of α, ω, t for the wave function, ionization probability, and energy distribution of the emitted electrons, the latter not studied previously for this model. We show that for large t and small α the energy distribution has sharp peaks at energies which are multiples of ω, corresponding to photon capture. We obtain small α expansions that converge for all t, unlike those of standard perturbation theory. We expect that our analysis will serve as a basis for treating more realistic systems revealing a form of universality in different emission processes.

The slow ionized wind and rotating disklike system that are associated with the high-mass young stellar object G345.4938+01.4677

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guzmán, Andrés E.; Garay, Guido; Bronfman, Leonardo

2014-12-01

We report the detection, made using ALMA, of the 92 GHz continuum and hydrogen recombination lines (HRLs) H40α, H42α, and H50β emission toward the ionized wind associated with the high-mass young stellar object G345.4938+01.4677. This is the luminous central dominating source located in the massive and dense molecular clump associated with IRAS 16562–3959. The HRLs exhibit Voigt profiles, which is a strong signature of Stark broadening. We successfully reproduce the observed continuum and HRLs simultaneously using a simple model of a slow ionized wind in local thermodynamic equilibrium, with no need for a high-velocity component. The Lorentzian line wings implymore » electron densities of 5 × 10{sup 7} cm{sup –3} on average. In addition, we detect SO and SO{sub 2} emission arising from a compact (∼3000 AU) molecular core associated with the central young star. The molecular core exhibits a velocity gradient that is perpendicular to the jet-axis, which we interpret as evidence of rotation. The set of observations toward G345.4938+01.4677 are consistent with it being a young high-mass star associated with a slow photo-ionized wind.« less

Radiative transfer calculations of the diffuse ionized gas in disc galaxies with cosmic ray feedback

NASA Astrophysics Data System (ADS)

Vandenbroucke, Bert; Wood, Kenneth; Girichidis, Philipp; Hill, Alex S.; Peters, Thomas

2018-05-01

The large vertical scale heights of the diffuse ionized gas (DIG) in disc galaxies are challenging to model, as hydrodynamical models including only thermal feedback seem to be unable to support gas at these heights. In this paper, we use a three-dimensional Monte Carlo radiation transfer code to post-process disc simulations of the Simulating the Life-Cycle of Molecular Clouds project that include feedback by cosmic rays. We show that the more extended discs in simulations including cosmic ray feedback naturally lead to larger scale heights for the DIG which are more in line with observed scale heights. We also show that including a fiducial cosmic ray heating term in our model can help to increase the temperature as a function of disc scale height, but fails to reproduce observed DIG nitrogen and sulphur forbidden line intensities. We show that, to reproduce these line emissions, we require a heating mechanism that affects gas over a larger density range than is achieved by cosmic ray heating, which can be achieved by fine tuning the total luminosity of ionizing sources to get an appropriate ionizing spectrum as a function of scale height. This result sheds a new light on the relation between forbidden line emissions and temperature profiles for realistic DIG gas distributions.

Detection of Heating Processes in Coronal Loops by Soft X-ray Spectroscopy

NASA Astrophysics Data System (ADS)

Kawate, Tomoko; Narukage, Noriyuki; Ishikawa, Shin-nosuke; Imada, Shinsuke

2017-08-01

Imaging and Spectroscopic observations in the soft X-ray band will open a new window of the heating/acceleration/transport processes in the solar corona. The soft X-ray spectrum between 0.5 and 10 keV consists of the electron thermal free-free continuum and hot coronal lines such as O VIII, Fe XVII, Mg XI, Si XVII. Intensity of free-free continuum emission is not affected by the population of ions, whereas line intensities especially from highly ionized species have a sensitivity of the timescale of ionization/recombination processes. Thus, spectroscopic observations of both continuum and line intensities have a capability of diagnostics of heating/cooling timescales. We perform a 1D hydrodynamic simulation coupled with the time-dependent ionization, and calculate continuum and line intensities under different heat input conditions in a coronal loop. We also examine the differential emission measure of the coronal loop from the time-integrated soft x-ray spectra. As a result, line intensity shows a departure from the ionization equilibrium and shows different responses depending on the frequency of the heat input. Solar soft X-ray spectroscopic imager will be mounted in the sounding rocket experiment of the Focusing Optics X-ray Solar Imager (FOXSI). This observation will deepen our understanding of heating processes to solve the “coronal heating problem”.

A Global Photoionization Response to Prompt Emission and Outliers: Different Origin of Long Gamma-ray Bursts?

NASA Astrophysics Data System (ADS)

Wang, J.; Xin, L. P.; Qiu, Y. L.; Xu, D. W.; Wei, J. Y.

2018-03-01

By using the line ratio C IV λ1549/C II λ1335 as a tracer of the ionization ratio of the interstellar medium (ISM) illuminated by a long gamma-ray burst (LGRB), we identify a global photoionization response of the ionization ratio to the photon luminosity of the prompt emission assessed by either L iso/E peak or {L}iso}/{E}peak}2. The ionization ratio increases with both L iso/E peak and L iso/E 2 peak for a majority of the LGRBs in our sample, although there are a few outliers. The identified dependence of C IV/C II on {L}iso}/{E}peak}2 suggests that the scatter of the widely accepted Amati relation is related to the ionization ratio in the ISM. The outliers tend to have relatively high C IV/C II values as well as relatively high C IV λ1549/Si IV λ1403 ratios, which suggests an existence of Wolf–Rayet stars in the environment of these LGRBs. We finally argue that the outliers and the LGRBs following the identified C IV/C II‑L iso/E peak ({L}iso}/{E}peak}2) correlation might come from different progenitors with different local environments.

VizieR Online Data Catalog: SPOGS. I. SDSS Shocked POststarburst Galaxy cand. (Alatalo+, 2016)

NASA Astrophysics Data System (ADS)

Alatalo, K.; Cales, S. L.; Rich, J. A.; Appleton, P. N.; Kewley, L. J.; Lacy, M.; Lanz, L.; Medling, A. M.; Nyland, K.

2016-07-01

There are many mechanisms by which galaxies can transform from blue, star-forming spirals, to red, quiescent early-type galaxies, but our current census of them does not form a complete picture. Recent observations of nearby case studies have identified a population of galaxies that quench "quietly". Traditional poststarburst searches seem to catch galaxies only after they have quenched and transformed, and thus miss any objects with additional ionization mechanisms exciting the remaining gas. The Shocked POststarburst Galaxy Survey (SPOGS) aims to identify transforming galaxies, in which the nebular lines are excited via shocks instead of through star formation processes. Utilizing the Oh-Sarzi-Schawinski-Yi (OSSY, 2011ApJS..195...13O) measurements on the Sloan Digital Sky Survey Data Release 7 catalog, we applied Balmer absorption and shock boundary criteria to identify 1067 SPOG candidates (SPOGs*) within z=0.2. SPOGs* represent 0.2% of the OSSY sample galaxies that exceed the continuum signal-to-noise cut (and 0.7% of the emission line galaxy sample). SPOGs* colors suggest that they are in an earlier phase of transition than OSSY galaxies that meet an "E+A" selection. SPOGs* have a 13% 1.4GHz detection rate from the Faint Images of the Radio Sky at Twenty Centimeters Survey, higher than most other subsamples, and comparable only to low-ionization nuclear emission line region hosts, suggestive of the presence of active galactic nuclei (AGNs). SPOGs* also have stronger Na i D absorption than predicted from the stellar population, suggestive of cool gas being driven out in galactic winds. It appears that SPOGs* represent an earlier phase in galaxy transformation than traditionally selected poststarburst galaxies, and that a large proportion of SPOGs* also have properties consistent with disruption of their interstellar media, a key component to galaxy transformation. It is likely that many of the known pathways to transformation undergo a SPOG phase. Studying this sample of SPOGs* further, including their morphologies, AGN properties, and environments, has the potential for us to build a more complete picture of the initial conditions that can lead to a galaxy evolving. (1 data file).

A ROSAT high resolution x ray image of NGC 1068

NASA Technical Reports Server (NTRS)

Halpern, J.

1993-01-01

The soft x ray properties of the Seyfert 2 galaxy NGC 1068 are a crucial test of the 'hidden Seyfert 1' model. It is important to determine whether the soft x rays come from the nucleus, or from a number of other possible regions in the circumnuclear starburst disk. We present preliminary results of a ROSAT HRI observation of NGC 1068 obtained during the verification phase. The fraction of x rays that can be attributed to the nucleus is about 70 percent so the 'soft x ray problem' remains. There is also significant diffuse x ray flux on arcminute scales, which may be related to the 'diffuse ionized medium' seen in optical emission lines, and the highly ionized Fe K(alpha) emission seen by BBXRT.

Observation of emission process in hydrogen-like nitrogen Z-pinch discharge with time integrated soft X-ray spectrum pinhole image

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sakai, Y.; Kumai, H.; Nakanishi, Y.

2013-02-15

The emission spectra of hydrogen-like nitrogen Balmer at the wavelength of 13.4 nm in capillary Z-pinch discharge plasma are experimentally examined. Ionization to fully strip nitrogen at the pinch maximum, and subsequent rapid expansion cooling are required to establish the population inversion between the principal quantum number of n = 2 and n = 3. The ionization and recombination processes with estimated plasma parameters are evaluated by utilizing a time integrated spectrum pinhole image containing radial spatial information. A cylindrical capillary plasma is pinched by a triangular pulsed current with peak amplitude of 50 kA and pulse width of 50more » ns.« less

Molecular three-body Brauner-Briggs-Klar theory for ion-impact ionization of molecules

NASA Astrophysics Data System (ADS)

Ghanbari-Adivi, E.

2016-12-01

Molecular three-body Brauner-Briggs-Klar (M3BBK) theory is developed to study the single ionization of diatomic molecules by ion impact. The orientation-averaged molecular orbital (OAMO) approximation is used to reduce the required computer time without sacrificing the performance of the method. The post-collision interaction (PCI) between the scattered projectile and the ejected electron is included. The theory is applied to collision of protons with hydrogen molecules. Results are obtained for two different kinematical regimes: i) fast collisions and low emission energies, and ii) not so fast collisions and higher emission energies. For both considered regimes, experimental fully differential cross-sections as well as different theoretical calculations are available for comparison. These comparisons are carried out and discussed.

Pillars of Creation among Destruction: Star Formation in Molecular Clouds near R136 in 30 Doradus

NASA Astrophysics Data System (ADS)

Kalari, Venu M.; Rubio, Mónica; Elmegreen, Bruce G.; Guzmán, Viviana V.; Zinnecker, Hans; Herrera, Cinthya N.

2018-01-01

We present new sensitive CO(2–1) observations of the 30 Doradus region in the Large Magellanic Cloud. We identify a chain of three newly discovered molecular clouds that we name KN1, KN2, and KN3 lying within 2–14 pc in projection from the young massive cluster R136 in 30 Doradus. Excited H2 2.12 μm emission is spatially coincident with the molecular clouds, but ionized Brγ emission is not. We interpret these observations as the tails of pillar-like structures whose ionized heads are pointing toward R136. Based on infrared photometry, we identify a new generation of stars forming within this structure.

Waveform control of orientation-dependent ionization of DCl in few-cycle laser fields.

PubMed

Znakovskaya, I; von den Hoff, P; Schirmel, N; Urbasch, G; Zherebtsov, S; Bergues, B; de Vivie-Riedle, R; Weitzel, K-M; Kling, M F

2011-05-21

Strong few-cycle light fields with stable electric field waveforms allow controlling electrons on time scales down to the attosecond domain. We have studied the dissociative ionization of randomly oriented DCl in 5 fs light fields at 720 nm in the tunneling regime. Momentum distributions of D(+) and Cl(+) fragments were recorded via velocity-map imaging. A waveform-dependent anti-correlated directional emission of D(+) and Cl(+) fragments is observed. Comparison of our results with calculations indicates that tailoring of the light field via the carrier envelope phase permits the control over the orientation of DCl(+) and in turn the directional emission of charged fragments upon the breakup of the molecular ion. © The Owner Societies 2011

The effect of extreme ionization rates during the initial collapse of a molecular cloud core

NASA Astrophysics Data System (ADS)

Wurster, James; Bate, Matthew R.; Price, Daniel J.

2018-05-01

What cosmic ray ionization rate is required such that a non-ideal magnetohydrodynamics (MHD) simulation of a collapsing molecular cloud will follow the same evolutionary path as an ideal MHD simulation or as a purely hydrodynamics simulation? To investigate this question, we perform three-dimensional smoothed particle non-ideal MHD simulations of the gravitational collapse of rotating, one solar mass, magnetized molecular cloud cores, which include Ohmic resistivity, ambipolar diffusion, and the Hall effect. We assume a uniform grain size of ag = 0.1 μm, and our free parameter is the cosmic ray ionization rate, ζcr. We evolve our models, where possible, until they have produced a first hydrostatic core. Models with ζcr ≳ 10-13 s-1 are indistinguishable from ideal MHD models, and the evolution of the model with ζcr = 10-14 s-1 matches the evolution of the ideal MHD model within 1 per cent when considering maximum density, magnetic energy, and maximum magnetic field strength as a function of time; these results are independent of ag. Models with very low ionization rates (ζcr ≲ 10-24 s-1) are required to approach hydrodynamical collapse, and even lower ionization rates may be required for larger ag. Thus, it is possible to reproduce ideal MHD and purely hydrodynamical collapses using non-ideal MHD given an appropriate cosmic ray ionization rate. However, realistic cosmic ray ionization rates approach neither limit; thus, non-ideal MHD cannot be neglected in star formation simulations.

Determination of the Far-Infrared Cosmic Background Using COBE/DIRBE and WHAM Data

NASA Technical Reports Server (NTRS)

Odegard, N.; Arendt, R. G.; Dwek, E.; Haffner, L. M.; Hauser, M. G.; Reynolds, R. J.

2007-01-01

Determination of the cosmic infrared background (CIB) at far infrared wavelengths using COBE/DIRBE data is limited by the accuracy to which foreground interplanetary and Galactic dust emission can be modeled and subtracted. Previous determinations of the far infrared CIB (e.g., Hauser et al. 1998) were based on the detection of residual isotropic emission in skymaps from which the emission from interplanetary dust and the neutral interstellar medium were removed. In this paper we use the Wisconsin H(alpha) Mapper (WHAM) Northern Sky Survey as a tracer of the ionized medium to examine the effect of this foreground component on determination of the CIB. We decompose the DIRBE far infrared data for five high Galactic latitude regions into HI- and H(alpha)- correlated components and a residual component. Eased on FUSE H2 absorption line observations, the contribution of a11 H2-correlated component is expected to he negligible. We find the H(alpha)-correlated component to be consistent with zero for each region, and we find that addition of an H(alpha)-correlated component in modeling the foreground emission has negligible effect on derived CIB results. Our CIB detections and 2(sigma) upper limits are essentially the same as those derived by Hauser et al. and are given by (nu)I(sub nu)(nW/sq m/sr) < 75, < 32, 25+/-8, and 13+/-3 at gamma = 60, 100, 140, and 240 microns, respectively. Our residuals have not been subjected to a detailed anisotropy test, so our CIB results do not supersede those of Hauser et al. Mie derive upper limits on the 100 micron emissivity of the ionized medium that are typically about 40% of the 100 micron emissivity of the neutral atomic medium. This low value may be caused in part by a lower dust-to-gas mass ratio in the ionized medium than in the neutral medium, and in part by a shortcoming of using H(alpha) intensity as a tracer of far infrared emission. If H(alpha) is not a reliable tracer, our analysis would underestimate the emissivity of the ionized medium, and both our analysis and the Hauser et al. analysis may slightly overestimate the CIB. We estimate the possible effect for the CIB to be only about 5%, which is much smaller than the quoted uncertainties. From a comparison of the Hauser et al. CIB results with the integrated galaxy brightness from Spitzer source counts, we obtain 2(sigma) upper limits on a possible diffuse CIB component that are 26 nW/sq m/sr at 140 microns and 8.5 nW/sq m/sr at 240 microns.

Modelling massive star feedback with Monte Carlo radiation hydrodynamics: photoionization and radiation pressure in a turbulent cloud

NASA Astrophysics Data System (ADS)

Ali, Ahmad; Harries, Tim J.; Douglas, Thomas A.

2018-07-01

We simulate a self-gravitating, turbulent cloud of 1000 M⊙ with photoionization and radiation pressure feedback from a 34 M⊙ star. We use a detailed Monte Carlo radiative transfer scheme alongside the hydrodynamics to compute photoionization and thermal equilibrium with dust grains and multiple atomic species. Using these gas temperatures, dust temperatures, and ionization fractions, we produce self-consistent synthetic observations of line and continuum emission. We find that all material is dispersed from the (15.5 pc)3 grid within 1.6 Myr or 0.74 free-fall times. Mass exits with a peak flux of 2 × 10-3 M⊙ yr-1, showing efficient gas dispersal. The model without radiation pressure has a slight delay in the breakthrough of ionization, but overall its effects are negligible. 85 per cent of the volume, and 40 per cent of the mass, become ionized - dense filaments resist ionization and are swept up into spherical cores with pillars that point radially away from the ionizing star. We use free-free emission at 20 cm to estimate the production rate of ionizing photons. This is almost always underestimated: by a factor of a few at early stages, then by orders of magnitude as mass leaves the volume. We also test the ratio of dust continuum surface brightnesses at 450 and 850 µm to probe dust temperatures. This underestimates the actual temperature by more than a factor of 2 in areas of low column density or high line-of-sight temperature dispersion; the H II region cavity is particularly prone to this discrepancy. However, the probe is accurate in dense locations such as filaments.

SOLAR HARD X-RAY SOURCE SIZES IN A BEAM-HEATED AND IONIZED CHROMOSPHERE

DOE Office of Scientific and Technical Information (OSTI.GOV)

O'Flannagain, Aidan M.; Gallagher, Peter T.; Brown, John C.

2015-02-01

Solar flare hard X-rays (HXRs) are produced as bremsstrahlung when an accelerated population of electrons interacts with the dense chromospheric plasma. HXR observations presented by Kontar et al. using the Ramaty High-Energy Solar Spectroscopic Imager have shown that HXR source sizes are three to six times more extended in height than those predicted by the standard collisional thick target model (CTTM). Several possible explanations have been put forward including the multi-threaded nature of flare loops, pitch-angle scattering, and magnetic mirroring. However, the nonuniform ionization (NUI) structure along the path of the electron beam has not been fully explored as amore » solution to this problem. Ionized plasma is known to be less effective at producing nonthermal bremsstrahlung HXRs when compared to neutral plasma. If the peak HXR emission was produced in a locally ionized region within the chromosphere, the intensity of emission will be preferentially reduced around this peak, resulting in a more extended source. Due to this effect, along with the associated density enhancement in the upper chromosphere, injection of a beam of electrons into a partially ionized plasma should result in an HXR source that is substantially more vertically extended relative to that for a neutral target. Here we present the results of a modification to the CTTM, which takes into account both a localized form of chromospheric NUI and an increased target density. We find 50 keV HXR source widths, with and without the inclusion of a locally ionized region, of ∼3 Mm and ∼0.7 Mm, respectively. This helps to provide a theoretical solution to the currently open question of overly extended HXR sources.« less

Modelling massive-star feedback with Monte Carlo radiation hydrodynamics: photoionization and radiation pressure in a turbulent cloud

NASA Astrophysics Data System (ADS)

Ali, Ahmad; Harries, Tim J.; Douglas, Thomas A.

2018-04-01

We simulate a self-gravitating, turbulent cloud of 1000M⊙ with photoionization and radiation pressure feedback from a 34M⊙ star. We use a detailed Monte Carlo radiative transfer scheme alongside the hydrodynamics to compute photoionization and thermal equilibrium with dust grains and multiple atomic species. Using these gas temperatures, dust temperatures, and ionization fractions, we produce self-consistent synthetic observations of line and continuum emission. We find that all material is dispersed from the (15.5pc)3 grid within 1.6Myr or 0.74 free-fall times. Mass exits with a peak flux of 2× 10-3M⊙yr-1, showing efficient gas dispersal. The model without radiation pressure has a slight delay in the breakthrough of ionization, but overall its effects are negligible. 85 per cent of the volume, and 40 per cent of the mass, become ionized - dense filaments resist ionization and are swept up into spherical cores with pillars that point radially away from the ionizing star. We use free-free emission at 20cm to estimate the production rate of ionizing photons. This is almost always underestimated: by a factor of a few at early stages, then by orders of magnitude as mass leaves the volume. We also test the ratio of dust continuum surface brightnesses at 450 and 850μ to probe dust temperatures. This underestimates the actual temperature by more than a factor of 2 in areas of low column density or high line-of-sight temperature dispersion; the HII region cavity is particularly prone to this discrepancy. However, the probe is accurate in dense locations such as filaments.

Indirect contributions to electron-impact ionization of Li+ (1 s 2 s S31 ) ions: Role of intermediate double-K -vacancy states

NASA Astrophysics Data System (ADS)

Müller, A.; Borovik, A.; Huber, K.; Schippers, S.; Fursa, D. V.; Bray, I.

2018-02-01

Fine details of the cross section for electron-impact ionization of metastable two-electron Li+(1 s 2 s S31) ions are scrutinized by both experiment and theory. Beyond direct knockoff ionization, indirect ionization mechanisms proceeding via formation of intermediate double-K-vacancy (hollow) states either in a Li+ ion or in a neutral lithium atom and subsequent emission of one or two electrons, respectively, can contribute to the net production of Li2 + ions. The partial cross sections for such contributions are less than 4% of the total single-ionization cross section. The characteristic steps, resonances, and interference phenomena in the indirect ionization contribution are measured with an experimental energy spread of less than 0.9 eV and with a statistical relative uncertainty of the order of 1.7%, requiring a level of statistical uncertainty in the total single-ionization cross section of better than 0.05%. The measurements are accompanied by convergent-close-coupling calculations performed on a fine energy grid. Theory and experiment are in remarkable agreement concerning the fine details of the ionization cross section. Comparison with previous R-matrix results is less favorable.

GUM 48d: AN EVOLVED H II REGION WITH ONGOING STAR FORMATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karr, J. L.; Ohashi, N.; Manoj, P.

2009-05-20

High-mass star formation and the evolution of H II regions have a substantial impact on the morphology and star formation history of molecular clouds. The H II region Gum 48d, located in the Centaurus Arm at a distance of 3.5 kpc, is an old, well evolved H II region whose ionizing stars have moved off the main sequence. As such, it represents a phase in the evolution of H II regions that is less well studied than the earlier, more energetic, main-sequence phase. In this paper, we use multiwavelength archive data from a variety of sources to perform a detailedmore » study of this interesting region. Morphologically, Gum 48d displays a ring-like faint H II region associated with diffuse emission from the associated photodissociation region, and is formed from part of a large, massive molecular cloud complex. There is extensive ongoing star formation in the region, at scales ranging from low to high mass, which is consistent with triggered star formation scenarios. We investigate the dynamical history and evolution of this region, and conclude that the original H II region was once larger and more energetic than the faint region currently seen. The proposed history of this molecular cloud complex is one of multiple, linked generations of star formation, over a period of 10 Myr. Gum 48d differs significantly in morphology and star formation from the other H II regions in the molecular cloud; these differences are likely the result of the advanced age of the region, and its different evolutionary status.« less

Optimizing convergence rates of alternating minimization reconstruction algorithms for real-time explosive detection applications

NASA Astrophysics Data System (ADS)

Bosch, Carl; Degirmenci, Soysal; Barlow, Jason; Mesika, Assaf; Politte, David G.; O'Sullivan, Joseph A.

2016-05-01

X-ray computed tomography reconstruction for medical, security and industrial applications has evolved through 40 years of experience with rotating gantry scanners using analytic reconstruction techniques such as filtered back projection (FBP). In parallel, research into statistical iterative reconstruction algorithms has evolved to apply to sparse view scanners in nuclear medicine, low data rate scanners in Positron Emission Tomography (PET) [5, 7, 10] and more recently to reduce exposure to ionizing radiation in conventional X-ray CT scanners. Multiple approaches to statistical iterative reconstruction have been developed based primarily on variations of expectation maximization (EM) algorithms. The primary benefit of EM algorithms is the guarantee of convergence that is maintained when iterative corrections are made within the limits of convergent algorithms. The primary disadvantage, however is that strict adherence to correction limits of convergent algorithms extends the number of iterations and ultimate timeline to complete a 3D volumetric reconstruction. Researchers have studied methods to accelerate convergence through more aggressive corrections [1], ordered subsets [1, 3, 4, 9] and spatially variant image updates. In this paper we describe the development of an AM reconstruction algorithm with accelerated convergence for use in a real-time explosive detection application for aviation security. By judiciously applying multiple acceleration techniques and advanced GPU processing architectures, we are able to perform 3D reconstruction of scanned passenger baggage at a rate of 75 slices per second. Analysis of the results on stream of commerce passenger bags demonstrates accelerated convergence by factors of 8 to 15, when comparing images from accelerated and strictly convergent algorithms.

Tracking Filament Evolution in the Low Solar Corona Using Remote Sensing and In Situ Observations

NASA Astrophysics Data System (ADS)

Kocher, Manan; Landi, Enrico; Lepri, Susan. T.

2018-06-01

In the present work, we analyze a filament eruption associated with an interplanetary coronal mass ejection that arrived at L1 on 2011 August 5. In multiwavelength Solar Dynamic Observatory/Advanced Imaging Assembly (AIA) images, three plasma parcels within the filament were tracked at high cadence along the solar corona. A novel absorption diagnostic technique was applied to the filament material traveling along the three chosen trajectories to compute the column density and temperature evolution in time. Kinematics of the filamentary material were estimated using STEREO/Extreme Ultraviolet Imager and STEREO/COR1 observations. The Michigan Ionization Code used inputs of these density, temperature, and speed profiles for the computation of ionization profiles of the filament plasma. Based on these measurements, we conclude that the core plasma was in near ionization equilibrium, and the ionization states were still evolving at the altitudes where they were visible in absorption in AIA images. Additionally, we report that the filament plasma was heterogeneous, and the filamentary material was continuously heated as it expanded in the low solar corona.

Transition in discharge plasma of Hall thruster type in presence of secondary electron emissive surface

NASA Astrophysics Data System (ADS)

Schweigert, I. V.; Yadrenkin, M. A.; Fomichev, V. P.

2017-11-01

Modification of the sheath structure near the emissive plate placed in magnetized DC discharge plasma of Hall thruster type was studied in the experiment and in kinetic simulations. The plate is made from Al2O3 which has enhanced secondary electron emission yield. The energetic electrons emitted by heated cathode provide the volume ionization and the secondary electron emission from the plate. An increase of the electron beam energy leads to an increase of the secondary electron generation, which initiates the transition in sheath structure over the emissive plate.

Photometric properties of stars clusters with young or mixed age stellar populations

NASA Astrophysics Data System (ADS)

Mollá, M.; García-Vargas, M. L.; Martín-Manjón, M. L.

2013-05-01

The main goal of this work is to present and discuss the synthetic photometrical properties of stellar clusters resulting from the PopStar code. Colors in Johnson and SDSS systems, Hα and Hβ luminosities and equivalent widths, and ionizing region size, have been computed for a wide range of metallicities Z = 0.0001, 0.0004, 0.004,0.008,0.02 and 0.05, and ages, from 0.1 Myr to 20 Gyr in Mollá, Garc{í}a-Vargas, & Bressan (2009, MNRAS, 398, 451). Emission lines are shown in Mart{í}n-Manj{ó}n et al. (2010, MNRAS, 403, 2012). Now we calculate colors with the emission lines contribution to the broad band color, so colors include stellar and nebular components, plus the emission lines following the evolution of the cluster and the region geometry in a consistent way. We compare the Single Stellar Populations contaminated and uncontaminated colors (in both Johnson and SDSS systems) and show the importance of emission lines contribution when photometry is used as a tool to characterize stellar populations. With these models we may determine the physical properties of young ionizing clusters when only photometrical observations are available and these correspond to the isolated star forming regions, subtracted the contribution of the underlying population In most cases, however, the ionizing population is usually embedded in a large and complex system, and the observed photometrical properties are the result of the combination of both the young star-forming burst and the host-underlying older population. The second objective of our work is therefore to provide a grid of models for nearby galaxies able to interpret mixed regions where the separation of young and old population is not possible or reliable enough. We obtain a set of PopStar Spectral Energy Distributions (available at PopStar site and also in VO) and derived colors for mixed populations where an underlying host population is combined in different mass ratios with a recent, metal-rich ionizing burst. These colors, together with other photometrical parameters, like Hα radius of the ionized region, and Balmer lines equivalent width and luminosity allow to infer the physical properties of star-forming regions without any spectroscopic information. For details and a complete set of tables and figures see Mollá, García-Vargas, & Martín-Manjón (2012, MNRAS, submitted).

Imaging a Central Ionized Component, a Narrow Ring, and the CO Snowline in the Multigapped Disk of HD 169142

NASA Astrophysics Data System (ADS)

Macías, Enrique; Anglada, Guillem; Osorio, Mayra; Torrelles, José M.; Carrasco-González, Carlos; Gómez, José F.; Rodríguez, Luis F.; Sierra, Anibal

2017-04-01

We report Very Large Array observations at 7 mm, 9 mm, and 3 cm toward the pre-transitional disk of the Herbig Ae star HD 169142. These observations have allowed us to study the millimeter emission of this disk with the highest angular resolution so far (0.″12 × 0.″09, or 14 au × 11 au, at 7 mm). Our 7 and 9 mm images show a narrow ring of emission at a radius of ˜25 au tracing the outer edge of the inner gap. This ring presents an asymmetric morphology that could be produced by dynamical interactions between the disk and forming planets. Additionally, the azimuthally averaged radial intensity profiles of the 7 and 9 mm images confirm the presence of the previously reported gap at ˜45 au and reveal a new gap at ˜85 au. We analyzed archival DCO+(3-2) and C18O(2-1) ALMA observations, showing that the CO snowline is located very close to this third outer gap. This suggests that growth and accumulation of large dust grains close to the CO snowline could be the mechanism responsible for this proposed outer gap. Finally, a compact source of emission is detected at 7 mm, 9 mm, and 3 cm toward the center of the disk. Its flux density and spectral index indicate that it is dominated by free-free emission from ionized gas, which could be associated with the photoionization of the inner disk, an independent object, or an ionized jet.

Chandra High Resolution Spectroscopy of the Circumnuclear Matter in the Broad Line Radio Galaxy, 3C 445

NASA Technical Reports Server (NTRS)

Reeves, J. N.; Gofford, J.; Braito, V.; Sambruna, R.

2010-01-01

We present evidence for X-ray line emitting and absorbing gas in the nucleus of the Broad-Line Radio Galaxy (BLRG), 3C445. A 200 ks Chandra LETG observation of 3C 445 reveals the presence of several highly ionized emission lines in the soft X-ray spectrum, primarily from the He and H-like ions of O, Ne, Mg and Si. Radiative recombination emission is detected from O VII and O VIII, indicating that the emitting gas is photoionized. The He-like emission appears to be resolved into forbidden and intercombination line components, which implies a high density of greater than 10(sup 10) cm(sup -3), while the lines are velocity broadened with a mean width of 2600 km s(sup -1). The density and widths of the ionized lines indicate an origin of the gas on sub-parsec scales in the Broad Line Region (BLR). The X-ray continuum of 3C 445 is heavily obscured by a photoionized absorber of column density N(sub H) = 2 x 10(sup 23) cm(sup -2) and ionization parameter log xi = 1.4 erg cm s(sup -1). However the view of the X-ray line emission is unobscured, which requires the absorber to be located at radii well within any parsec scale molecular torus. Instead we suggest that the X-ray absorber in 3C 445 may be associated with an outflowing, but clumpy accretion disk wind, with an observed outflow velocity of approximately 10000 km s(sup -1).

IRAS observations of extended dust envelopes around evolved stars

NASA Technical Reports Server (NTRS)

Hawkins, George

1990-01-01

Deconvolved IRAS profiles, with resolution 2-3 time better than detector sizes 1.5 and 3 arcmin at 60 and 100 microns, are presented for a number of evolved stars with extended emission. These include VY UMa, Mu Cep, S Sct, U Hya, Y CVn, U Ant, alpha Ori, Y Pav, UU aur, IRC + 10216, RZ Sgr, and R Lyr. Simple models suggest that extended IRAS emission results from stars which greater mass loss rates in the past, rather than from stars with large current mass loss rates.

Ratios of double to single ionization of He and Ne by strong 400-nm laser pulses using the quantitative rescattering theory

NASA Astrophysics Data System (ADS)

Chen, Zhangjin; Li, Xiaojin; Zatsarinny, Oleg; Bartschat, Klaus; Lin, C. D.

2018-01-01

We present numerical simulations of the ratio between double and single ionization of He and Ne by intense laser pulses at wavelengths of 390 and 400 nm, respectively. The yields of doubly charged ions due to nonsequential double ionization (NSDI) are obtained by employing the quantitative rescattering (QRS) model. In this model, the NSDI ionization probability is expressed as a product of the returning electron wave packet (RWP) and the total scattering cross sections for laser-free electron impact excitation and electron impact ionization of the parent ion. According to the QRS theory, the same RWP is also responsible for the emission of high-energy above-threshold ionization photoelectrons. To obtain absolute double-ionization yields, the RWP is generated by solving the time-dependent Schrödinger equation (TDSE) within a one-electron model. The same TDSE results can also be taken to obtain single-ionization yields. By using the TDSE results to calibrate single ionization and the RWP obtained from the strong-field approximation, we further simplify the calculation such that the nonuniform laser intensity distribution in the focused laser beam can be accounted for. In addition, laser-free electron impact excitation and ionization cross sections are calculated using the state-of-the-art many-electron R -matrix theory. The simulation results for double-to-single-ionization ratios are found to compare well with experimental data and support the validity of the nonsequential double-ionization mechanism for the covered intensity region.

The ratio of neutral hydrogen to neutral helium in the local interstellar medium

NASA Astrophysics Data System (ADS)

Green, James Carswell

The results are described from a sounding rocket borne EUV spectrometer that was designed and built. This instrument operated from 400 to 1150A with a spectral resolution of approx. 15A. The instrument effective area was about 1 sq cm. The instrument was successfully launched, and observed the nearby DA white dwarf G191-B2B. From this observation, it was determined that the stellar effective temperature is 61,000 + or -4000 to 6000K, and the ratio of helium to hydrogen in the stellar photosphere is 1.0 + or -0.68 to 2.2 x 10-4. Additionally, the neutral column densities of helium and hydrogen were measured to the star. The neutral helium column density was determined from the first observation of the interstellar absorption edge at 504A. The ratio of neutral helium to neutral hydrogen constrains the mean ionization of the warm gas along the line of sight to G191-B2B. The fractional ionization of hydrogen (H II/H) is approx. less than 20 percent, unless significant helium ionization is present as well. The scenario where the fractional ionization of hydrogen is high (H II/H) approx. less than 40 percent and the helium is neutral is ruled out with 99 percent certainty. This result is consistent with some recent theoretical calculations. Using these results, a self-consistent model of the local interstellar medium along the line of sight to G191-B2B is developed. In addition, an unexpected emission feature at 584A was detected in this observation with a high level of significance. Possible sources of this emission are examined, including the companion K dwarf G191-B2A, and an emission nebula near or around G191-B2B.

High-resolution Observations of the Massive Protostar in IRAS 18566+0408

NASA Astrophysics Data System (ADS)

Hofner, P.; Cesaroni, R.; Kurtz, S.; Rosero, V.; Anderson, C.; Furuya, R. S.; Araya, E. D.; Molinari, S.

2017-07-01

We report 3 mm continuum, CH3CN(5-4) and 13CS(2-1) line observations with CARMA (Combined Array for Research in Millimeter-wave Astronomy), in conjunction with 6 and 1.3 cm continuum VLA data, and 12 and 25 μm broadband data from the Subaru Telescope toward the massive proto-star IRAS 18566+0408. The VLA data resolve the ionized jet into four components aligned in the E-W direction. Radio components A, C, and D have flat centimeter SEDs indicative of optically thin emission from ionized gas, and component B has a spectral index α = 1.0, and a decreasing size with frequency \\propto {ν }-0.5. Emission from the CARMA 3 mm continuum and from the 13CS(2-1) and CH3CN(5-4) spectral lines is compact (I.e., < 6700 {au}) and peaks near the position of the VLA centimeter source, component B. Analysis of these lines indicates hot and dense molecular gas, which is typical for HMCs. Our Subaru telescope observations detect a single compact source, coincident with radio component B, demonstrating that most of the energy in IRAS 18566+0408 originates from a region of size < 2400 {au}. We also present UKIRT near-infrared archival data for IRAS 18566+0408, which show extended K-band emission along the jet direction. We detect an E-W velocity shift of about 10 km s-1 over the HMC in the CH3CN lines possibly tracing the interface of the ionized jet with the surrounding core gas. Our data demonstrate the presence of an ionized jet at the base of the molecular outflow and support the hypothesis that massive protostars with O-type luminosity form with a mechanism similar to lower mass stars.

The Embedded Ring-like Feature and Star Formation Activities in G35.673-00.847

NASA Astrophysics Data System (ADS)

Dewangan, L. K.; Devaraj, R.; Ojha, D. K.

2018-02-01

We present a multiwavelength study to probe the star formation (SF) process in the molecular cloud linked with the G35.673-00.847 site (hereafter MCG35.6), which is traced in a velocity range of 53–62 km s‑1. Multiwavelength images reveal a semi-ring-like feature (associated with ionized gas emission) and an embedded face-on ring-like feature (without the NVSS 1.4 GHz radio emission, where 1σ ∼ 0.45 mJy beam‑1) in MCG35.6. The semi-ring-like feature is originated by the ionizing feedback from a star with spectral type B0.5V–B0V. The central region of the ring-like feature does not contain detectable ionized gas emission, indicating that the ring-like feature is unlikely to be produced by the ionizing feedback from a massive star. Several embedded Herschel clumps and young stellar objects (YSOs) are identified in MCG35.6, tracing the ongoing SF activities within the cloud. The polarization information from the Planck and GPIPS data trace the plane-of-sky magnetic field, which is oriented parallel to the major axis of the ring-like feature. At least five clumps (having M clump ∼ 740–1420 M ⊙) seem to be distributed in an almost regularly spaced manner along the ring-like feature and contain noticeable YSOs. Based on the analysis of the polarization and molecular line data, three subregions containing the clumps are found to be magnetically supercritical in the ring-like feature. Altogether, the existence of the ring-like feature and the SF activities on its edges can be explained by the magnetic field mediated process as simulated by Li & Nakamura.

Making fate and exposure models for freshwater ecotoxicity in life cycle assessment suitable for organic acids and bases.

PubMed

van Zelm, Rosalie; Stam, Gea; Huijbregts, Mark A J; van de Meent, Dik

2013-01-01

Freshwater fate and exposure factors were determined for organic acids and bases, making use of the knowledge on electrical interaction of ionizing chemicals and their sorption to particles. The fate factor represents the residence time in the environment whereas exposure factors equal the dissolved fraction of a chemical. Multimedia fate, exposure, and effect model USES-LCA was updated to take into account the influence of ionization, based upon the acid dissociation constant (pK(a)) of a chemical, and the environmental pH. Freshwater fate (FF) and exposure (XF) factors were determined for 415 acids and 496 bases emitted to freshwater, air, and soil. The relevance of taking account of the degree of ionization of chemicals was tested by determining the ratio (R) of the new vs. fate and exposure factors determined with USES-LCA suitable for neutral chemicals only. Our results show that the majority of freshwater fate and exposure factors of chemicals that are largely ionized in the environment are larger with the ionics model compared to the factors determined with the neutrals model version. R(FF) ranged from 2.4×10(-1) to 1.6×10(1) for freshwater emissions, from 1.2×10(-2) to 2.0×10(4) for soil emissions and from 5.8×10(-2) to 6.0×10(3) for air emissions, and R(XF) from 5.3×10(-1) to 2.2×10(1). Prediction of changed solid-water partitioning, implying a change in runoff and in removal via sedimentation, and prediction of negligible air-water partition coefficient, leading to negligible volatilization were the main contributors to the changes in freshwater fate factors. Copyright © 2012 Elsevier Ltd. All rights reserved.

Early Results from the Wisconsin H-Alpha Mapper Southern Sky Survey

NASA Astrophysics Data System (ADS)

Haffner, L. Matthew; Reynolds, R. J.; Madsen, G. J.; Hill, A. S.; Barger, K. A.; Jaehnig, K. P.; Mierkiewicz, E. J.; Percival, J. W.

2010-01-01

After a successful eleven-year campaign at Kitt Peak, we moved the Wisconsin H-Alpha Mapper (WHAM) to Cerro Tololo in early 2009. Here we present some of the early data after the first nine months under southern skies. These maps begin to complete the first all-sky, kinematic survey of the diffuse Hα emission from the Milky Way. Much of this emission arises from the Warm Ionized Medium (WIM), a significant component of the ISM that extends a few kiloparsecs above the Galactic disk. The WHAM instrument consists of a 0.6 m primary lens housed in a steerable siderostat coupled to a 15 cm dual-etalon Fabry-Perot spectrometer. The optical configuration delivers a spatially integrated spectrum from a one-degree beam on the sky covering 200 km/s with 12 km/s spectral resolution. Short, 30-second exposures allow us to cover the observable sky in about two years at sensitivity levels of about 0.1 R (EM 0.2 pc cm-6). While this first look at the data focuses on the Hα survey, WHAM is also capable of observing many other optical emission lines, revealing fascinating trends in the temperature and ionization state of the WIM. Our ongoing studies of the physical conditions of diffuse ionized gas will continue in the south following the Hα survey. In addition, future observations using our survey mode will cover the full velocity range of the Magellanic Stream, Bridge, and Clouds to trace the ionized gas associated with these neighboring systems. WHAM is supported by NSF award AST-0607512 and has made this smooth relocation south due to the excellent staff at KPNO and CTIO.

A TALE OF TWO NARROW-LINE REGIONS: IONIZATION, KINEMATICS, AND SPECTRAL ENERGY DISTRIBUTIONS FOR A LOCAL PAIR OF MERGING OBSCURED ACTIVE GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hainline, Kevin N.; Hickox, Ryan C.; Chen, Chien-Ting

2016-05-20

We explore the gas ionization and kinematics, as well as the optical-IR spectral energy distributions for UGC 11185, a nearby pair of merging galaxies hosting obscured active galactic nuclei (AGNs), also known as SDSS J181611.72+423941.6 and J181609.37+423923.0 (J1816NE and J1816SW, z ≈ 0.04). Due to the wide separation between these interacting galaxies (∼23 kpc), observations of these objects provide a rare glimpse of the concurrent growth of supermassive black holes at an early merger stage. We use BPT line diagnostics to show that the full extent of the narrow-line emission in both galaxies is photoionized by an AGN, and confirmmore » the existence of a 10 kpc-scale ionization cone in J1816NE, while in J1816SW the AGN narrow-line region is much more compact (1–2 kpc) and relatively undisturbed. Our observations also reveal the presence of ionized gas that nearly spans the entire distance between the galaxies, which is likely in a merger-induced tidal stream. In addition, we carry out a spectral analysis of the X-ray emission using data from XMM-Newton . These galaxies represent a useful pair to explore how the [O iii] luminosity of an AGN is dependent on the size of the region used to explore the extended emission. Given the growing evidence for AGN “flickering” over short timescales, we speculate that the appearances and impacts of these AGNs may change multiple times over the course of the galaxy merger, which is especially important given that these objects are likely the progenitors of the types of systems commonly classified as “dual AGNs.”.« less

The ionizing radiation of Seyfert 2 galactic nuclei

NASA Technical Reports Server (NTRS)

Ho, Luis C.; Shields, Joseph C.; Filippenko, Alexei V.

1993-01-01

We report the discovery of a nonrandom trend in the dispersion of emission-line intensity ratios for Seyfert 2 galaxies. The sense of this pattern suggests the influence of a single physical parameter, the hardness of the ionizing continuum, which controls the heating energy per ionizing photon. We compare the observed line ratios with new photoionization calculations and find that the observed distributions can be reproduced if the ionizing continuum is parametrized by a power law. Our results also suggest an inverse correlation between luminosity and continuum hardness for Seyfert 2 nuclei; if true, this trend extends a similar pattern known in quasars and Seyfert 1 galaxies to active galactic nuclei of lower luminosity. Samples of Seyfert 2 nuclei with improved selection uniformity are desirable for elaboration of these findings.

Well-ionization chamber response relative to NIST air-kerma strength standard for prostate brachytherapy seeds.

PubMed

Mitch, M G; Zimmerman, B E; Lamperti, P J; Seltzer, S M; Coursey, B M

2000-10-01

The response of well-ionization chambers to the emissions of 103Pd and 125I radioactive seed sources used in prostate cancer brachytherapy has been measured. Calibration factors relating chamber response (current or dial setting) to measured air-kerma strength have been determined for seeds from nine manufacturers, each with different designs. Variations in well-ionization chamber response relative to measured air-kerma strength have been observed because of differences in the emitted energy spectrum due to both the radionuclide support material (125I seeds) and the mass ratio of 103Pd to 102Pd (103Pd seeds). Obtaining accurate results from quality assurance measurements using well-ionization chambers at a therapy clinic requires knowledge of such differences in chamber response as a function of seed design.

β -delayed neutron emission from 85Ga

NASA Astrophysics Data System (ADS)

Miernik, K.; Rykaczewski, K. P.; Grzywacz, R.; Gross, C. J.; Madurga, M.; Miller, D.; Stracener, D. W.; Batchelder, J. C.; Brewer, N. T.; Korgul, A.; Mazzocchi, C.; Mendez, A. J.; Liu, Y.; Paulauskas, S. V.; Winger, J. A.; Wolińska-Cichocka, M.; Zganjar, E. F.

2018-05-01

Decay of 85Ga was studied by means of β -neutron-γ spectroscopy. A pure beam of 85Ga was produced at the Holifield Radioactive Ion Beam Facility using a resonance ionization laser ion source and a high-resolution electromagnetic separator. The β -delayed neutron emission probability was measured for the first time, yielding 70(5)%. An upper limit of 0.1% for β -delayed two-neutron emission was also experimentally established for the first time. A detailed decay scheme including absolute γ -ray intensities was obtained. Results are compared with theoretical β -delayed emission models.

A survey for PAH emission in H II regions, planetary and proto-planetary nebulae

NASA Technical Reports Server (NTRS)

Demuizon, M.; Cox, P.; Lequeux, J.

1989-01-01

The results of a systematic investigation of polycyclic aromatic hydrocarbon (PAH) emission in H II regions, planetary nebulae (PN), and proto-planetary nebulae (PNN), are reported. Data is obtained from the low resolution spectra (LRS) of IRAS. The results show that: PAHs are formed in carbon rich objects; and PAH emission is ubiquitous in general interstellar medium and requires the presence of ultraviolet photons, in planetary and proto-planetary nebulae, PAH emission is seen only where an ionizing flux is present and in carbon rich objects.

Kinematic Study of Ionized and Molecular Gases in Ultracompact HII Region in Monoceros R2

NASA Astrophysics Data System (ADS)

Kim, Hwihyun; Lacy, John H.; Jaffe, Daniel Thomas

2017-06-01

Monoceros R2 (Mon R2) is an UltraCompact HII region (UCHII) surrounded by several PhotoDissociation Regions (PDRs). It is an excellent example to investigate the chemistry and physics of early stage of massive star formation due to its proximity (830pc) and brightness. Previous studies suggest that the wind from the star holds the ionized gas up against the dense molecular core and the higher pressure at the head drives the ionized gas along the shell. In order for the model to work, there should be evidence for dense molecular gas along the shell walls, irradiated by the UCHII region and perhaps entrained into the flow along the walls.We obtained the Immersion Grating INfrared Spectrograph (IGRINS) spectra of Mon R2 to study the kinematic patterns in the areas where ionized and molecular gases interact. The position-velocity maps from the high resolution (R~45,000) H- and K-band (1.4-2.5μm) IGRINS spectra demonstrate that the ionized gases (Brackett and Pfund series, He and Fe emission lines; Δv ≈ 40km/s) flow along the walls of the surrounding clouds. This is consistent with the model by Zhu et al. (2008). In the PV maps of the H2 emission lines there is no obvious motion (Δv ≈ 10km/s) of the molecular hydrogen right at the ionization boundary. This implies that the molecular gas is not taking part in the flow as the ionized gas is moving along the cavity walls.This work used the Immersion Grating Infrared Spectrograph (IGRINS) that was developed under a collaboration between the University of Texas at Austin and the Korea Astronomy and Space Science Institute (KASI) with the financial support of the US National Science Foundation (NSF; grant AST-1229522), of the University of Texas at Austin, and of the Korean GMTProject of KASI.

Synthetic nebular emission from massive galaxies - I: origin of the cosmic evolution of optical emission-line ratios

NASA Astrophysics Data System (ADS)

Hirschmann, Michaela; Charlot, Stephane; Feltre, Anna; Naab, Thorsten; Choi, Ena; Ostriker, Jeremiah P.; Somerville, Rachel S.

2017-12-01

Galaxies occupy different regions of the [O III]λ5007/H β-versus-[N II]λ6584/H α emission-line ratio diagram in the distant and local Universe. We investigate the origin of this intriguing result by modelling self-consistently, for the first time, nebular emission from young stars, accreting black holes (BHs) and older, post-asymptotic giant branch (post-AGB) stellar populations in galaxy formation simulations in a full cosmological context. In post-processing, we couple new-generation nebular-emission models with high-resolution, cosmological zoom-in simulations of massive galaxies to explore which galaxy physical properties drive the redshift evolution of the optical-line ratios [O III]λ5007/H β, [N II]λ6584/H α, [S II]λλ6717, 6731/H α and [O I]λ6300/H α. The line ratios of simulated galaxies agree well with observations of both star-forming and active local Sloan Digital Sky Survey galaxies. Towards higher redshifts, at fixed galaxy stellar mass, the average [O III]/H β is predicted to increase and [N II]/H α, [S II]/H α and [O I]/H α to decrease - widely consistent with observations. At fixed stellar mass, we identify star formation history, which controls nebular emission from young stars via the ionization parameter, as the primary driver of the cosmic evolution of [O III]/H β and [N II]/H α. For [S II]/H α and [O I]/H α, this applies only to redshifts greater than z = 1.5, the evolution at lower redshift being driven in roughly equal parts by nebular emission from active galactic nuclei and post-AGB stellar populations. Instead, changes in the hardness of ionizing radiation, ionized-gas density, the prevalence of BH accretion relative to star formation and the dust-to-metal mass ratio (whose impact on the gas-phase N/O ratio we model at fixed O/H) play at most a minor role in the cosmic evolution of simulated galaxy line ratios.

Angle-resolved high-order above-threshold ionization of a molecule: sensitive tool for molecular characterization.

PubMed

Busuladzić, M; Gazibegović-Busuladzić, A; Milosević, D B; Becker, W

2008-05-23

The strong-field approximation for ionization of diatomic molecules by an intense laser field is generalized to include rescattering of the ionized electron off the various centers of its molecular parent ion. The resulting spectrum and its interference structure strongly depend on the symmetry of the ground state molecular orbital. For N2, if the laser polarization is perpendicular to the molecular axis, we observe a distinct minimum in the emission spectrum, which survives focal averaging and allows determination of, e.g., the internuclear separation. In contrast, for O2, rescattering is absent in the same situation.

Spatially resolved density and ionization measurements of shocked foams using x-ray fluorescence

DOE Office of Scientific and Technical Information (OSTI.GOV)

MacDonald, M. J.; Keiter, P. A.; Montgomery, D. S.

2016-09-22

We present experiments at the Trident laser facility demonstrating the use of x-ray fluorescence (XRF) to simultaneously measure density, ionization state populations, and electron temperature in shocked foams. An imaging x-ray spectrometer was used to obtain spatially-resolved measurements of Ti K-more » $$\\alpha$$ emission. Density profiles were measured from K-$$\\alpha$$ intensity. Ti ionization state distributions and electron temperatures were inferred by fitting K-$$\\alpha$$ spectra to spectra from CRETIN simulations. This study shows that XRF provides a powerful tool to complement other diagnostics to make equation of state measurements of shocked materials containing a suitable tracer element.« less

Numerical study of electronic impact and radiation in sonoluminescence

NASA Astrophysics Data System (ADS)

Xu, Ning; Wang, Long; Hu, Xiwei

1998-02-01

A hydrodynamic simulation of pure argon single-bubble sonoluminescence including electron collisional ionization, recombination, and radiative energy loss has been performed. We find that near the moment that the bubble reaches its minimum radius the atoms inside a very thin layer around the origin of the bubble are strongly ionized, and the light emission occurs nearly simultaneously. Therefore we conclude that multiple ionization and recombination, which mainly occur in the thin layer of plasma, play a dramatically important role in the noble gas sonoluminescence. We also find that the temperature and the intensity of luminescence are not so high as those predicted by previous models, which consider only neutral gases.

Exploring the Diffuse X-ray Emission of Supernova Remnant Kesteven 69 with XMM-Newton

NASA Astrophysics Data System (ADS)

Seo, Kyoung-Ae; Hui, Chung Yue

2013-06-01

We have investigated the X-ray emission from the shock-heated plasma of the Galactic supernova remnant Kesteven 69 with XMM-Newton. Assuming the plasma is at collisional ionization equilibrium, a plasma temperature and a column absorption are found to be kT ~ 0.62 keV and NH ~ 2.85 ×10^22 cm-2 respectively by imaging spectroscopy. Together with the deduced emission measure, we place constraints on its Sedov parameters.

NGC 3393: multi-component AGN feedback as seen by CHEERS

NASA Astrophysics Data System (ADS)

Maksym, W. Peter; Fabbiano, Giuseppina; Elvis, Martin; Karovska, Margarita; Raymond, John C.; Storchi-Bergmann, Thaisa; Paggi, Alessandro; Wang, Junfeng; Risaliti, Guido

2017-01-01

Due to its low density, moderate ionization, and weak kinematics, the narrow line region (NLR) of active galactic nuclei (AGN) provides poweful diagnostics for investigating AGN feedback. The CHandra Extended Emission line Region Survey (CHEERS) is the ultimate investigation into resolved feedback in the NLR. We present results from our CHEERS investigations of NGC 3393. By imaging extended X-ray line emission of NGC 3393 with Chandra and optical line emission with Hubble's narrow-band filters, we are able to map out the simultaneous impact of photoionization, jets and an AGN disk-wind. When resolved on scales of ~10s of parsecs, the NLR of NGC 3393 shows a complex multi-component medium. Diagnostic line mapping indicates a Low-ionization Emmision Line Region (LINER) cocoon surrounding the outflow-evacuated cavities (in optical) and surrounding the supports the presence of collisional plasma (in X-rays). These physically distinct constituent regions can only be resolved by the high-resolution imaging that Chandra and HST enable.

Infrared fine-structure line diagnostics of shrouded active galactic nuclei

NASA Technical Reports Server (NTRS)

Voit, G. M.

1993-01-01

Far-infrared spectroscopy of celestial objects will improve dramatically in the coming decade, allowing astronomers to use fine-structure line emission to probe photoionized regions obscured in the optical band by thick clouds of dust. The ultraluminous far-IR galaxies revealed by IRAS, quasar-like in luminosity but smothered in molecular gas, probably conceal either immense starbursts or luminous active nuclei. In both scenarios, these objects ought to produce copious infrared fine-structure emission with several lines comparable to H(beta) in luminosity. This paper shows how these lines, if detected, can be used to determine the electron densities and far-IR obscurations of shrouded photoionized regions and to constrain the shape and ionization parameter of the ionizing spectra. The presence of (Ne V) emission in particular will distinguish shrouded AGN's from shrouded starbursts. Since all active galaxies photoionize at least some surrounding material, these diagnostics can also be applied to active galaxies in general and will aid in studying how an active nucleus interacts with the interstellar medium of its host galaxy.

Effects of Mg II and Ca II ionization on ab-initio solar chromosphere models

NASA Technical Reports Server (NTRS)

Rammacher, W.; Cuntz, M.

1991-01-01

Acoustically heated solar chromosphere models are computed considering radiation damping by (non-LTE) emission from H(-) and by Mg II and Ca II emission lines. The radiative transfer equations for the Mg II k and Ca II K emission lines are solved using the core-saturation method with complete redistribution. The Mg II k and Ca II K cooling rates are compared with the VAL model C. Several substantial improvements over the work of Ulmschneider et al. (1987) are included. It is found that the rapid temperature rises caused by the ionization of Mg II are not formed in the middle chromosphere, but occur at larger atmospheric heights. These models represent the temperature structure of the 'real' solar chromosphere much better. This result is a major precondition for the study of ab-initio models for solar flux tubes based on MHD wave propagation and also for ab-initio models for the solar transition layer.

History of Hubble Space Telescope (HST)

NASA Image and Video Library

1995-01-01

These eerie, dark, pillar-like structures are actually columns of cool interstellar hydrogen gas and dust that are also incubators for new stars. The pillars protrude from the interior wall of a dark molecular cloud like stalagmites from the floor of a cavern. They are part of the Eagle Nebula (also called M16), a nearby star-forming region 7,000 light-years away, in the constellation Serpens. The ultraviolet light from hot, massive, newborn stars is responsible for illuminating the convoluted surfaces of the columns and the ghostly streamers of gas boiling away from their surfaces, producing the dramatic visual effects that highlight the three-dimensional nature of the clouds. This image was taken on April 1, 1995 with the Hubble Space Telescope Wide Field Planetary Camera 2. The color image is constructed from three separate images taken in the light of emission from different types of atoms. Red shows emissions from singly-ionized sulfur atoms, green shows emissions from hydrogen, and blue shows light emitted by doubly-ionized oxygen atoms.

Fundamental Scaling of Microplasmas and Tunable UV Light Generation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manginell, Ronald P.; Sillerud, Colin Halliday; Hopkins, Matthew M.

2016-11-01

The temporal evolution of spectral lines from microplasma devices (MD) was studied, including impurity transitions. Long-wavelength emission diminishes more rapidly than deep UV with decreasing pulse width and RF operation. Thus, switching from DC to short pulsed or RF operation, UV emissions can be suppressed, allowing for real-time tuning of the ionization energy of a microplasma photo-ionization source, which is useful for chemical and atomic physics. Scaling allows MD to operate near atmospheric pressure where excimer states are efficiently created and emit down to 65 nm; laser emissions fall off below 200 nm, making MD light sources attractive for deepmore » UV use. A first fully-kinetic three-dimensional model was developed that explicitly calculates electron-energy distribution function. This, and non-continuum effects, were studied with the model and how they are impacted by geometry and transient or DC operation. Finally, a global non-dimensional model was developed to help explain general trends MD physics.« less

The Fe K Line Region Of η Carinae Around The X-ray Minima

NASA Astrophysics Data System (ADS)

Leyder, Jean-Christophe; Corcoran, M. F.; Henley, D. B.; Hamaguchi, K.; Ishibashi, K.; Pittard, J.

2011-09-01

We studied the Fe K line region of η Carinae with high-resolution X-ray Chandra grating spectra, using observations covering key phases around the last two X-ray minima (i.e. in 2003.5 and 2009). The line centroids are slightly redshifted, as opposed to the blueshifted lines observed at lower X-ray energies. This is the first observational evidence that the plasma producing the iron line emission is dynamically distinct from the plasma responsible for K-shell emission at lower energies, and is in agreement with the general colliding wind shock model. Gaussian modeling of the Fe XXV K-shell triplet blend shows apparent variations in centroid velocity, which are difficult to interpret as orbital motion of the companion star. Significant variability in the doppler broadening of the Fe K fluorescence emission line at 6.4 keV suggests that the formation of this line occurs in the wind of η Carinae at some particular phases. Of particular interest is the presence of a red wing in the profile of the Fe XXV triplet. This emission probably arises from iron in ionization states below Fe XXIV. Different mechanisms that might explain this emission will be discussed, e.g. an extremely bright, relatively cool, and heavily absorbed equilibrium plasma; emission from unshocked photoionized wind material; or assuming a fraction of the thermal plasma is not in ionization equilibrium.

XMM-Newton Observations of NGC 253: Resolving the Emission Components in the Disk and Nuclear Area

NASA Technical Reports Server (NTRS)

Pietsch, W.; Borozdin, K. N.; Branduardi-Raymont, G.; Cappi, M.; Ehle, M.; Ferrando, P.; Freyberg, M. J.; Kahn, S. M.; Ponman, T. J.; Ptak, A.

2000-01-01

We describe the first XMM-Newton observations of the starburst galaxy NGC 253. As known from previous X-ray observations, NGC 253 shows a mixture of extended (disk and halo) and point-source emission. The high XMM-Newton throughput allows for the first time a detailed investigation of the spatial, spectral and variability properties of these components simultaneously. We detect a bright X-ray transient approx. 70 sec SSW of the nucleus and show the spectrum and light curve of the brightest point source (approx. 30 sec S of the nucleus, most likely a black-hole X-ray binary, BHXRB). The unprecedented combination of RGS and EPIC also sheds new light on the emission of the complex nuclear region, the X-ray plume and the disk diffuse emission. In particular, EPIC images reveal that the limb-brightening of the plume is mostly seen in higher ionization emission lines, while in the lower ionization lines, and below 0.5 keV, the plume is more homo- geneously structured, pointing to new interpretations as to the make up of the starburst-driven outflow. Assuming that type IIa supernova remnants (SNRs) are mostly responsible for the E greater than 4 keV emission, the detection with EPIC of the 6.7 keV line allows us to estimate a supernova rate within the nuclear starburst of 0.2 /yr.

Ionization of elements in medium power capacitively coupled argon plasma torch with single and double ring electrodes.

PubMed

Ponta, Michaela; Frentiu, Maria; Frentiu, Tiberiu

2012-06-01

A medium power, low Ar consumption capacitively coupled plasma torch (275 W, 0.4 L min-1) with molybdenum tubular electrode and single or two ring electrodes in non-local thermodynamic equilibrium (LTE) was characterized with respect to its ability to achieve element ionization. Ionization degrees of Ca, Mg, Mn and Cd were determined from ionic-to-atomic emission ratio and ionization equilibrium according to Saha's equation. The ionization degrees resulted from the Saha equation were higher by 9-32% than those obtained from spectral lines intensity in LTE regime and closer to reality. A linear decrease of ionization with increase of ionization energy of elements was observed. Plasma torch with two ring electrodes provided higher ionization degrees (85 ± 7% Ca, 79 ± 7% Mn, 80 ± 7% Mg and 73 ± 8% Cd) than those in single ring arrangement (70 ± 6% Ca, 57 ± 7% Mn, 57 ± 8% Mg and 42 ± 9% Cd). The Ca ionization decreased linearly by up to 79 ± 4% and 53 ± 6% in plasma with two ring electrodes and single ring respectively in the presence of up to 400 µg mL-1 Na as interferent. The studied plasma was effective in element ionization and could be a potential ion source in mass spectrometry.

Measurement of HONO, HNCO, and other inorganic acids by negative-ion proton-transfer chemical-ionization mass spectrometry (NI-PT-CIMS): application to biomass burning emissions

Treesearch

J. M. Roberts; P. Veres; C. Warneke; J. A. Neuman; R. A. Washenfelder; S. S. Brown; M. Baasandorj; J. B. Burkholder; I. R. Burling; T. J. Johnson; R. J. Yokelson; J. de Gouw

2010-01-01

A negative-ion proton transfer chemical ionization mass spectrometric technique (NI-PT-CIMS), using acetate as the reagent ion, was applied to the measurement of volatile inorganic acids of atmospheric interest: hydrochloric (HCl), nitrous (HONO), nitric 5 (HNO3), and isocyanic (HNCO) acids. Gas phase calibrations through the sampling inlet showed the method to be...

Touch Spray Mass Spectrometry for In Situ Analysis of Complex Samples

PubMed Central

Kerian, Kevin S.; Jarmusch, Alan K.; Cooks, R. Graham

2014-01-01

Touch spray, a spray-based ambient in-situ ionization method, uses a small probe, e.g. a teasing needle to pick up sample and the application of voltage and solvent to cause field-induced droplet emission. Compounds extracted from the microsample are incorporated into the sprayed micro droplets. Performance tests include disease state of tissue, microorganism identification, and therapeutic drug quantitation. Chemical derivatization is performed simultaneously with ionization. PMID:24756256

Neutral ISM, Lyα, and Lyman-continuum in the Nearby Starburst Haro11

NASA Astrophysics Data System (ADS)

Rivera-Thorsen, T. Emil; Östlin, Göran; Hayes, Matthew; Puschnig, Johannes

2017-03-01

Star-forming galaxies are believed to be a major source of Lyman continuum (LyC) radiation responsible for reionizing the early universe. Direct observations of escaping ionizing radiation have however been sparse and with low escape fractions. In the local universe, only 10 emitters have been observed, with typical escape fractions of a few percent. The mechanisms regulating this escape need to be strongly evolving with redshift in order to account for the epoch of reionization. Gas content and star formation feedback are among the main suspects, known to both regulate neutral gas coverage and evolve with cosmic time. In this paper, we reanalyze Hubble Space Telescope (HST)-Cosmic Origins Spectrograph (COS) spectrocopy of the first detected local LyC leaker, Haro 11. We examine the connection between LyC leakage and Lyα line shape, and feedback-influenced neutral interstellar medium (ISM) properties like kinematics and gas distribution. We discuss the two extremes of an optically thin, density bounded ISM and a riddled, optically thick, ionization bounded ISM, and how Haro 11 fits into theoretical predictions. We find that the most likely ISM model is a clumpy neutral medium embedded in a highly ionized medium with a combined covering fraction of unity and a residual neutral gas column density in the ionized medium high enough to be optically thick to Lyα, but low enough to be at least partly transparent to LyC and undetected in Si II. This suggests that star formation feedback and galaxy-scale interaction events play a major role in opening passageways for ionizing radiation through the neutral medium. Based on observations with HST-COS, program GO 13017, obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts.

Single impacts of keV fullerene ions on free standing graphene: Emission of ions and electrons from confined volume

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verkhoturov, Stanislav V.; Geng, Sheng; Schweikert, Emile A., E-mail: schweikert@chem.tamu.edu

We present the first data from individual C{sub 60} impacting one to four layer graphene at 25 and 50 keV. Negative secondary ions and electrons emitted in transmission were recorded separately from each impact. The yields for C{sub n}{sup −} clusters are above 10% for n ≤ 4, they oscillate with electron affinities and decrease exponentially with n. The result can be explained with the aid of MD simulation as a post-collision process where sufficient vibrational energy is accumulated around the rim of the impact hole for sputtering of carbon clusters. The ionization probability can be estimated by comparing experimentalmore » yields of C{sub n}{sup −} with those of C{sub n}{sup 0} from MD simulation, where it increases exponentially with n. The ionization probability can be approximated with ejecta from a thermally excited (3700 K) rim damped by cluster fragmentation and electron detachment. The experimental electron probability distributions are Poisson-like. On average, three electrons of thermal energies are emitted per impact. The thermal excitation model invoked for C{sub n}{sup −} emission can also explain the emission of electrons. The interaction of C{sub 60} with graphene is fundamentally different from impacts on 3D targets. A key characteristic is the high degree of ionization of the ejecta.« less

FAST, LOW-IONIZATION EMISSION REGIONS OF THE PLANETARY NEBULA M2-42

DOE Office of Scientific and Technical Information (OSTI.GOV)

Danehkar, A.; Parker, Q. A.; Steffen, W., E-mail: ashkbiz.danehkar@cfa.harvard.edu

Spatially resolved observations of the planetary nebula M2-42 (PN G008.2−04.8) obtained with the Wide Field Spectrograph on the Australian National University 2.3 m telescope have revealed the remarkable features of bipolar collimated jets emerging from its main structure. Velocity-resolved channel maps derived from the [N ii] λ6584 emission line disentangle different morphological components of the nebula. This information is used to develop a three-dimensional morpho-kinematic model, which consists of an equatorial dense torus and a pair of asymmetric bipolar outflows. The expansion velocity of about 20 km s{sup −1} is measured from the spectrum integrated over the main shell. However,more » the deprojected velocities of the jets are found to be in the range of 80–160 km s{sup −1} with respect to the nebular center. It is found that the mean density of the collimated outflows, 595 ± 125 cm{sup −3}, is five times lower than that of the main shell, 3150 cm{sup −3}, whereas their singly ionized nitrogen and sulfur abundances are about three times higher than those determined from the dense shell. The results indicate that the features of the collimated jets are typical of fast, low-ionization emission regions.« less

Line Emission and X-ray Line Polarization of Multiply Ionized Mo Ions

NASA Astrophysics Data System (ADS)

Petkov, E. E.; Safronova, A. S.; Kantsyrev, V. L.; Shlyaptseva, V. V.; Stafford, A.; Safronova, U. I.; Shrestha, I. K.; Schultz, K. A.; Childers, R.; Cooper, M. C.; Beiersdorfer, P.; Hell, N.; Brown, G. V.

2016-10-01

We present a comprehensive experimental and theoretical study of the line emission from multiply ionized Mo ions produced by two different sets of experiments: at LLNL EBIT and the pulsed power generator Zebra at UNR. Mo line emission and polarization measurements were accomplished at EBIT for the first time. In particular, benchmarking experiments at the LLNL EBIT with Mo ions produced at electron beam energies from 2.75 keV up to 15 keV allowed us to break down these very complicated spectra into spectra with only few ionization stages and to select processes that influence them as well as to measure line polarization. The EBIT data were recorded using the EBIT Calorimeter Spectrometer and a crystal spectrometer with a Ge crystal. X-ray Mo spectra and pinhole images were collected from Z-pinch plasmas produced from various wire loads. Non-LTE modeling, high-precision relativistic atomic and polarization data were used to analyze L-shell Mo spectra. The influence of different plasma processes including electron beams on Mo line radiation is summarized. This work was supported by NNSA under DOE Grant DE-NA0002954. Experiments at the NTF/UNR were funded in part by DE-NA0002075. Work at LLNL was performed under the auspices of the U.S. DOE under contract DE-AC52-07NA27344.

Origin of X-Ray and Gamma-Ray Emission from the Galactic Central Region

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chernyshov, D. O.; Dogiel, V. A.; Cheng, K.-S.

We study a possible connection between different non-thermal emissions from the inner few parsecs of the Galaxy. We analyze the origin of the gamma-ray source 2FGL J1745.6−2858 (or 3FGL J1745.6−2859c) in the Galactic Center (GC) and the diffuse hard X-ray component recently found by the Nuclear Spectroscopic Telescope Array , as well as the radio emission and processes of hydrogen ionization from this area. We assume that a source in the GC injected energetic particles with power-law spectrum into the surrounding medium in the past or continues to inject until now. The energetic particles may be protons, electrons, or amore » combination of both. These particles diffuse to the surrounding medium and interact with gas, magnetic field, and background photons to produce non-thermal emissions. We study the spectral and spatial features of the hard X-ray emission and gamma-ray emission by the particles from the central source. Our goal is to examine whether the hard X-ray and gamma-ray emissions have a common origin. Our estimations show that, in the case of pure hadronic models, the expected flux of hard X-ray emission is too low. Despite the fact that protons can produce a non-zero contribution in gamma-ray emission, it is unlikely that they and their secondary electrons can make a significant contribution in hard X-ray flux. In the case of pure leptonic models, it is possible to reproduce both X-ray and gamma-ray emissions for both transient and continuous supply models. However, in the case of the continuous supply model, the ionization rate of molecular hydrogen may significantly exceed the observed value.« less

GEMINI NEAR INFRARED FIELD SPECTROGRAPH OBSERVATIONS OF THE SEYFERT 2 GALAXY MRK 573: IN SITU ACCELERATION OF IONIZED AND MOLECULAR GAS OFF FUELING FLOWS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fischer, Travis C.; Straughn, A. N.; Machuca, C.

2017-01-01

We present near-infrared and optical emission-line and stellar kinematics of the Seyfert 2 galaxy Mrk 573 using the Near-Infrared Field Spectrograph (NIFS) at Gemini North and Dual Imaging Spectrograph at Apache Point Observatory, respectively. By obtaining full kinematic maps of the infrared ionized and molecular gas and stellar kinematics in a ∼700 × 2100 pc{sup 2} circumnuclear region of Mrk 573, we find that kinematics within the Narrow-Line Region are largely due to a combination of both rotation and in situ acceleration of material originating in the host disk. Combining these observations with large-scale, optical long-slit spectroscopy that traces ionized gas emission out tomore » several kpcs, we find that rotation kinematics dominate the majority of the gas. We find that outflowing gas extends to distances less than 1 kpc, suggesting that outflows in Seyfert galaxies may not be powerful enough to evacuate their entire bulges.« less

Nyx: Adaptive mesh, massively-parallel, cosmological simulation code

NASA Astrophysics Data System (ADS)

Almgren, Ann; Beckner, Vince; Friesen, Brian; Lukic, Zarija; Zhang, Weiqun

2017-12-01

Nyx code solves equations of compressible hydrodynamics on an adaptive grid hierarchy coupled with an N-body treatment of dark matter. The gas dynamics in Nyx use a finite volume methodology on an adaptive set of 3-D Eulerian grids; dark matter is represented as discrete particles moving under the influence of gravity. Particles are evolved via a particle-mesh method, using Cloud-in-Cell deposition/interpolation scheme. Both baryonic and dark matter contribute to the gravitational field. In addition, Nyx includes physics for accurately modeling the intergalactic medium; in optically thin limits and assuming ionization equilibrium, the code calculates heating and cooling processes of the primordial-composition gas in an ionizing ultraviolet background radiation field.

Radioactive Decay

EPA Pesticide Factsheets

Radioactive decay is the emission of energy in the form of ionizing radiation. Example decay chains illustrate how radioactive atoms can go through many transformations as they become stable and no longer radioactive.

The argument for a unified approach to non-ionizing radiation protection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perala, R.A.; Rigden, G.J.; Pfeffer, R.A.

1993-12-01

In the next decade military equipment will be required to operate in severe electromagnetic environments. These environments are expected to contain most non-ionizing frequencies (D.C. to GHz), from hostile and/or non-hostile sources, and be severe enough to cause temporary upset or even catastrophic failure of electronic equipment. Over the past thirty years considerable emphasis has been placed on hardening critical systems to one or more of these non-ionizing radiation environments, the most prevalent being the nuclear-induced electromagnetic pulse (EMD). From this technology development there has evolved a hardening philosophy that applies to most of these non-ionizing radiation environments. The philosophy,more » which stresses the application of zonal shields plus penetration protection, can provide low-cost hardening against such diverse non-ionizing radiation as p-static, lightning, electromagnetic interference (EMI), EMP, high intensity radiated fields (HIRF), electromagnetic radiation (EMR), and high power microwaves (HPM). The objective in this paper is to describe the application of this philosophy to Army helicopters. The authors develop a unified specification complete with threat definitions and test methods which illustrates integration of EMP, lightning, and HIRF at the box qualification level. This paper is a summary of the effort documented in a cited reference.« less

Direct Roadside Measurements of Volatile Organic Compounds in Vehicle Emissions Using NO+ Time-of-Flight Chemical Ionization Mass Spectrometry

NASA Astrophysics Data System (ADS)

Warneke, C.; Finewax, Z.; Koss, A.; Coggon, M.; Gilman, J.; Ziemann, P. J.; De Gouw, J. A.

2017-12-01

Vehicle emissions are a large source of volatile organic compounds (VOCs) in urban areas. As vehicle emissions have strongly decreased over the last few decades, several studies have shown that a relatively small fraction of vehicles are now responsible for total mobile emissions. While tunnel studies have measured on-road vehicular emissions representative of a vehicular fleet, there is limited data describing vehicle-specific, on-road VOC profiles. In this study VOCs were measured in real-time at one-second time resolution using NO+ time-of-flight chemical ionization mass spectrometry (NO+ ToF-CIMS) on a Denver Metro freeway ramp for several hours in the summer of 2016 and on Highway 7, east of Boulder, Colorado, in the summer of 2017. With this setup plumes from single vehicles were successfully measured. Using positive matrix factorization (PMF), three VOC sources were obtained from the data: gasoline vapor, gasoline exhaust and diesel exhaust, which were validated by laboratory samples of gasoline and diesel headspace, of vehicle exhaust and from literature. Chemical identification of the PMF factors was further aided by authentic samples of canisters via improved Whole Air Sampling (iWAS) and Gas Chromatography - NO+ ToF-CIMS. A small portion of total vehicles measured had VOC emissions greatly exceeding the average vehicle sampled. These high-emitting vehicles will be investigated to determine the relative importance of high-emitting vehicles to overall emissions in urban areas, and how the emissions composition of high-emitting vehicles is different from the average vehicle.

The dependence on optical energy of terahertz emission from air plasma induced by two-color femtosecond laser-pulses

NASA Astrophysics Data System (ADS)

Wu, Si-Qing; Liu, Jin-Song; Wang, Sheng-Lie; Hu, Bing

2013-10-01

The generation of terahertz (THz) emission from air plasma induced by two-color femtosecond laser pulses is studied on the basis of a transient photocurrent model. While the gas is ionized by the two-color femtosecond laser-pulses composed of the fundamental and its second harmonic, a non-vanishing directional photoelectron current emerges, radiating a THz electromagnetic pulse. The gas ionization processes at three different laser-pulse energies are simulated, and the corresponding THz waveforms and spectra are plotted. The results demonstrate that, by keeping the laser-pulse width and the relative phase between two pulses invariant when the laser energy is at a moderate value, the emitted THz fields are significantly enhanced with a near-linear dependence on the optical energy.

Spectral self-action of THz emission from ionizing two-color laser pulses in gases

NASA Astrophysics Data System (ADS)

Cabrera-Granado, Eduardo; Chen, Yxing; Babushkin, Ihar; Bergé, Luc; Skupin, Stefan

2015-02-01

The spectrum of terahertz (THz) emission in gases via ionizing two-color femtosecond pulses is analyzed by means of a semi-analytic model and numerical simulations in 1D, 2D and 3D geometries taking into account propagation effects of both pump and THz fields. We show that produced THz signals interact with free electron trajectories and thus significantly influence further THz generation upon propagation, i.e., make the process inherently nonlocal. This self-action contributes to the observed strong spectral broadening of the generated THz field. We show that diffraction of the generated THz radiation is the limiting factor for the co-propagating low frequency amplitudes and thus for the self-action mechanism in 2D and 3D geometries.

Strange doings on Io. [Jupiter radio emission modification, sodium cloud, ionized sulfur and extreme brightness

NASA Technical Reports Server (NTRS)

Goody, R.

1978-01-01

Some unusual properties of Io are discussed, and possible explanations for these are considered. The properties discussed include Io's ability to modify radio waves emitted by Jupiter in the decametric band, the satellite's ionosphere and sodium cloud, its extraordinary brightness, and the presence of ionized sulfur just inside the satellite's orbit. Io's ability to modulate Jovian decametric radio emission is explained on the basis of the hypothesis that the satellite conducts electricity and interacts with Jupiter's magnetic field. Characteristics of the sodium cloud are reviewed, and the probable mechanism responsible for this cloud is outlined. It is concluded that the only plausible explanation for the brightness of Io is the presence of cat's-eye-type reflectors, possibly composed of crystalline deposits, on the satellite's surface.

A 205 {mu}m [N II] MAP OF THE CARINA NEBULA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oberst, T. E.; Parshley, S. C.; Nikola, T.

We present the results of a {approx}250 arcmin{sup 2} mapping of the 205 {mu}m [N II] fine-structure emission over the northern Carina Nebula, including the Car I and Car II H II regions. Spectra were obtained using the South Pole Imaging Fabry-Perot Interferometer (SPIFI) at the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) at the South Pole. We supplement the 205 {mu}m data with new reductions of far-IR fine-structure spectra from the Infrared Space Observatory (ISO) Long Wavelength Spectrometer (LWS) in 63 {mu}m [O I], 122 {mu}m [N II], 146 {mu}m [O I], and 158 {mu}m [C II]; the 146more » {mu}m [O I] data include 90 raster positions which have not been previously published. Morphological comparisons are made with optical, radio continuum, and CO maps. The 122/205 line ratio is used to probe the density of the low-ionization gas, and the 158/205 line ratio is used to probe the fraction of C{sup +} arising from photodissociation regions (PDRs). The [O I] and [C II] lines are used to construct a PDR model of Carina. When the PDR properties are compared with other sources, Carina is found to be more akin to 30 Doradus than galactic star-forming regions such as Orion, M17, or W49; this is consistent with the view of Carina as a more evolved region, where much of the parent molecular cloud has been ionized or swept away. These data constitute the first ground-based detection of the 205 {mu}m [N II] line, and the third detection overall since those of COBE FIRAS and the Kuiper Airborne Observatory in the early 1990s.« less

Dark-ages reionization and galaxy formation simulation - III. Modelling galaxy formation and the epoch of reionization

NASA Astrophysics Data System (ADS)

Mutch, Simon J.; Geil, Paul M.; Poole, Gregory B.; Angel, Paul W.; Duffy, Alan R.; Mesinger, Andrei; Wyithe, J. Stuart B.

2016-10-01

We introduce MERAXES, a new, purpose-built semi-analytic galaxy formation model designed for studying galaxy growth during reionization. MERAXES is the first model of its type to include a temporally and spatially coupled treatment of reionization and is built upon a custom (100 Mpc)3 N-body simulation with high temporal and mass resolution, allowing us to resolve the galaxy and star formation physics relevant to early galaxy formation. Our fiducial model with supernova feedback reproduces the observed optical depth to electron scattering and evolution of the galaxy stellar mass function between z = 5 and 7, predicting that a broad range of halo masses contribute to reionization. Using a constant escape fraction and global recombination rate, our model is unable to simultaneously match the observed ionizing emissivity at z ≲ 6. However, the use of an evolving escape fraction of 0.05-0.1 at z ˜ 6, increasing towards higher redshift, is able to satisfy these three constraints. We also demonstrate that photoionization suppression of low-mass galaxy formation during reionization has only a small effect on the ionization history of the intergalactic medium. This lack of `self-regulation' arises due to the already efficient quenching of star formation by supernova feedback. It is only in models with gas supply-limited star formation that reionization feedback is effective at regulating galaxy growth. We similarly find that reionization has only a small effect on the stellar mass function, with no observationally detectable imprint at M* > 107.5 M⊙. However, patchy reionization has significant effects on individual galaxy masses, with variations of factors of 2-3 at z = 5 that correlate with environment.

Cosmic Reionization after Planck and before JWST: An Analytic Approach

NASA Astrophysics Data System (ADS)

Madau, Piero

2017-12-01

The reionization of cosmic hydrogen marks a critical juncture in the history of structure formation. Here we present a new formulation of the standard reionization equation for the evolution of the volume-averaged H II fraction that is more consistent with the accepted conceptual model of inhomogeneous intergalactic absorption. The revised equation explicitly accounts for the presence of the optically thick “Lyman-limit systems” that are known to determine the mean-free path of ionizing radiation after overlap. Integration of this equation provides a better characterization of the timing of reionization by smoothly linking the pre-overlap with the post-overlap phases of such a process. We confirm the validity of the quasi-instantaneous approximation as a predictor of reionization completion/maintenance and discuss new insights on the sources of cosmic reionization using the improved formalism. A constant emission rate into the intergalactic medium (IGM) of three Lyman continuum (LyC) photons per atom per gigayear leads to a reionization history that is consistent with a number of observational constraints on the ionization state of the z = 5–9 universe. While star-forming galaxies can dominate the reionization process if the luminosity-weighted fraction of LyC photons that escape into the IGM, {f}{esc}, exceeds 15% (for a faint magnitude cut-off of the galaxy UV luminosity function of {M}{lim}=-13 and a LyC photon yield per unit 1500 Å luminosity of {ξ }{ion}={10}25.3 {{erg}}-1 {Hz}), simple models where the product of the two unknowns {f}{esc}{ξ }{ion} is not evolving with redshift fail to reproduce the changing neutrality of the IGM observed at these epochs.

Diffuse ionized gas in galaxies across the Hubble sequence at the CALIFA resolution

NASA Astrophysics Data System (ADS)

Lacerda, E. A. D.; Cid Fernandes, R.; Couto, G. S.; Stasińska, G.; García-Benito, R.; Vale Asari, N.; Pérez, E.; González Delgado, R. M.; Sánchez, S. F.; de Amorim, A. L.

2018-03-01

We use spatially resolved spectroscopy from the Calar Alto Legacy Integral Field Area (CALIFA) survey to study the nature of the line emitting gas in galaxies of different Hubble types, focusing on the separation of star-forming (SF) regions from those better characterized as diffuse ionized gas (DIG). The diagnosis is carried out in terms of the equivalent width of H α (WH α). Three nebular regimes are identified. Regions where WH α < 3 Å define what we call the hDIG, the component of the DIG where photoionization is dominated by hot, low-mass, evolved stars. Regions where WH α > 14 Å trace SF complexes. WH α values in the intermediate 3-14 Å range reflect a mixed regime (mDIG) where more than one process contributes. This three-tier scheme is inspired both by theoretical and empirical considerations. Its application to CALIFA galaxies of different types and inclinations leads to the following results: (i) the hDIG component is prevalent throughout ellipticals and S0's as well as in bulges, and explains the strongly bimodal distribution of WH α both among and within galaxies. (ii) Early-type spirals have some hDIG in their discs, but this component becomes progressively less relevant for later Hubble types. (iii) hDIG emission is also present above and below galactic discs, as seen in several edge-on spirals in our sample. (iv) The SF/mDIG proportion grows steadily from early- to late-type spirals, and from inner to outer radii. (v) Besides circumventing basic inconsistencies in conventional DIG/SF separation criteria based on the H α surface brightness, our WH α-based method produces results in agreement with a classical excitation diagram analysis.

Diffuse ionized gas in galaxies across the Hubble sequence at the CALIFA resolution

NASA Astrophysics Data System (ADS)

Lacerda, E. A. D.; Cid Fernandes, R.; Couto, G. S.; Stasińska, G.; García-Benito, R.; Vale Asari, N.; Pérez, E.; Gonzalez Delgado, R. M.; Sánchez, S. F.; de Amorim, A. L.

2017-11-01

We use spatially resolved spectroscopy from the CALIFA survey to study the nature of the line emitting gas in galaxies of different Hubble types, focusing on the separation of star-forming (SF) regions from those better characterized as diffuse ionized gas (DIG). The diagnosis is carried out in terms of the equivalent width of Hα (W_{Hα}). Three nebular regimes are identified: Regions where W_{Hα} < 3 Å define what we call the hDIG, the component of the DIG where photoionization is dominated by hot, low mass, evolved stars. Regions where W_{Hα} > 14 Å trace SF complexes. W_{Hα} values in the intermediate 3-14 Å range reflect a mixed regime (mDIG) where more than one process contributes.This three-tier scheme is inspired both by theoretical and empirical considerations. Its application to CALIFA galaxies of different types and inclinations leads to the following results: (i) The hDIG component is prevalent throughout ellipticals and S0's as well as in bulges, and explains the strongly bimodal distribution of W_{{Hα} both among and within galaxies. (ii) Early type spirals have some hDIG in their disks, but this component becomes progressively less relevant for later Hubble types. (iii) hDIG emission is also present above and below galactic disks, as seen in several edge-on spirals in our sample. (iv) The SF/mDIG proportion grows steadily from early to late types spirals, and from inner to outer radii. (v) Besides circumventing basic inconsistencies in conventional DIG/SF separation criteria based on the &Hα surface brightness, our W_{Hα}-based method produces results in agreement with a classical excitation diagram analysis.

Radio Recombination Line Surveys of the inner Galactic Plane: SIGGMA and GDIGS

NASA Astrophysics Data System (ADS)

Liu, Bin; Anderson, Loren Dean; Luisi, Matteo; Balser, Dana; Bania, Thomas; Wenger, Trey; Haffner, Lawrence Matthew; Minchin, Robert; Roshi, Anish; Churchwell, Edward; Terzian, Yervant; McIntyre, Travis; Lebron, Mayra; SIGGMA team, GDIGS team

2018-01-01

Ionized gas is one of the primary components of the interstellar medium (ISM) and plays a crucial role in star formation and galaxy evolution. Radio recombination lines (RRLs) can directly trace ionized gas in HII regions and warm ionized medium (WIM) without being affected by interstellar extinction. Single-dish telescopes like Arecibo Observatory and the Green Bank Telescope (GBT) are sensitive to low surface brightness emission, and are therefore powerful tools for the study of HII regions and the WIM. We report here on two large surveys of RRL emission: The Survey of Ionized Gas in the Galaxy, Made with the Arecibo telescope (SIGGMA) and the GBT Diffuse Ionized Gas Survey (GDIGS). These are the first large-scale fully-sampled RRL surveys, and together cover nearly the entire first quadrant of the Galactic plane at ~arcmin spatial resolution (l = -5 - 32 deg. for GDIGS and l = 32 - 70 deg. for SIGGMA). SIGGMA is performed with the Arecibo L-band Feed Array (ALFA) receiver, whose bandpass covers twelve hydrogen alpha lines from H163α to H174α. By stacking the α-lines and smoothing to 4 km/s velocity resolution, the final SIGGMA spectra have a mean rms level of ~0.65 mJy per beam. The GDIGS data were taken with the GBT C-band receiver and the VEGAS backend and include RRLs from H95α to H117α, and when stacked and smoothed to 5 km/s resolution achieve 1 mJy per beam rms. Here, we report on early analysis of the SIGGMA and GDIGS data, and present first scientific results.

Spitzer Infrared Spectrograph Observations of the Galactic Center: Quantifying the Extreme Ultraviolet/Soft X-ray Fluxes

NASA Astrophysics Data System (ADS)

Simpson, Janet P.

2018-04-01

It has long been shown that the extreme ultraviolet spectrum of the ionizing stars of H II regions can be estimated by comparing the observed line emission to detailed models. In the Galactic Center (GC), however, previous observations have shown that the ionizing spectral energy distribution (SED) of the local photon field is strange, producing both very low excitation ionized gas (indicative of ionization by late O stars) and also widespread diffuse emission from atoms too highly ionized to be found in normal H II regions. This paper describes the analysis of all GC spectra taken by Spitzer's Infrared Spectrograph and downloaded from the Spitzer Heritage Archive. In it, H II region densities and abundances are described, and serendipitously discovered candidate planetary nebulae, compact shocks, and candidate young stellar objects are tabulated. Models were computed with Cloudy, using SEDs from Starburst99 plus additional X-rays, and compared to the observed mid-infrared forbidden and recombination lines. The ages inferred from the model fits do not agree with recent proposed star formation sequences (star formation in the GC occurring along streams of gas with density enhancements caused by close encounters with the black hole, Sgr A*), with Sgr B1, Sgr C, and the Arches Cluster being all about the same age, around 4.5 Myr old, with similar X-ray requirements. The fits for the Quintuplet Cluster appear to give a younger age, but that could be caused by higher-energy photons from shocks from stellar winds or from a supernova.

Infrared coronal emission lines and the possibility of their maser emission in Seyfert nuclei

NASA Technical Reports Server (NTRS)

Greenhouse, Matthew A.; Feldman, Uri; Smith, Howard A.; Klapisch, Marcel; Bhatia, Anand K.; Bar-Shalom, Abi

1993-01-01

Energetic emitting regions have traditionally been studied via x-ray, UV and optical emission lines of highly ionized intermediate mass elements. Such lines are often referred to as 'coronal lines' since the ions, when produced by collisional ionization, reach maximum abundance at electron temperatures of approx. 10(exp 5) - 10(exp 6) K typical of the sun's upper atmosphere. However, optical and UV coronal lines are also observed in a wide variety of Galactic and extragalactic sources including the Galactic interstellar medium, nova shells, supernova remnants, galaxies and QSOs. Infrared coronal lines are providing a new window for observation of energetic emitting regions in heavily dust obscured sources such as infrared bright merging galaxies and Seyfert nuclei and new opportunities for model constraints on physical conditions in these sources. Unlike their UV and optical counterparts, infrared coronal lines can be primary coolants of collisionally ionized plasmas with 10(exp 4) less than T(sub e)(K) less than 10(exp 6) which produce little or no optical or shorter wavelength coronal line emission. In addition, they provide a means to probe heavily dust obscured emitting regions which are often inaccessible to optical or UV line studies. In this poster, we provide results from new model calculations to support upcoming Infrared Space Observatory (ISO) and current ground-based observing programs involving infrared coronal emission lines in AGN. We present a complete list of infrared (lambda greater than 1 micron) lines due to transitions within the ground configurations 2s(2)2p(k) and 3s(2)3p(k) (k = 1 to 5) or the first excited configurations 2s2p and 3s3p of highly ionized (x greater than or equal to 100 eV) astrophysically abundant (n(X)/n(H) greater than or equal to 10(exp -6)) elements. Included are approximately 74 lines in ions of O, Ne, Na, Mg, Al, Si, S, Ar, Ca, Fe, and Ni spanning a wavelength range of approximately 1 - 280 microns. We present new results from detailed balance calculations, new critical densities for collisional de-excitation, intrinsic photon rates, branching ratios, and excitation temperatures for the majority of the compiled transitions. The temperature and density parameter space for dominant cooling via infrared coronal lines is presented, and the relationship of infrared to optical coronal lines is discussed.

The Ionization Fraction in the Obscuring ``Torus'' of an Active Galactic Nucleus

NASA Astrophysics Data System (ADS)

Wilson, A. S.; Roy, A. L.; Ulvestad, J. S.; Colbert, E. J. M.; Weaver, K. A.; Braatz, J. A.; Henkel, C.; Matsuoka, M.; Xue, S.; Iyomoto, N.; Okada, K.

1998-10-01

The LINER galaxy NGC 2639 contains a water vapor megamaser, suggesting the presence of a nuclear accretion disk or torus viewed close to edge-on. This galaxy is thus a good candidate for revealing absorption by the torus of any compact nuclear continuum emission. In this paper, we report VLBA radio maps at three frequencies and an ASCA X-ray spectrum obtained to search for free-free and photoelectric absorptions, respectively. The radio observations reveal a compact (<0.2 pc) nuclear source with a spectrum that turns over sharply near 5 GHz. This turnover may reflect either synchrotron self-absorption or free-free absorption. The galaxy is detected by ASCA with an observed luminosity of 1.4 × 1041 ergs s-1 in the 0.6-10 keV band. The X-ray spectrum shows emission in excess of a power-law model at energies greater than 4 keV; we interpret this excess as compact, nuclear, hard X-ray emission with the lower energies photoelectrically absorbed by an equivalent hydrogen column of ~= 5 × 1023 cm-2. If we assume that the turnover in the radio spectrum is caused by free-free absorption and that both the free-free and photoelectric absorptions are produced by the same gaseous component, the ratio n2edl/nHdl may be determined. If the masing molecular gas is responsible for both absorptions, the required ionization fraction is >~1.3 × 10-5, which is comparable to the theoretical upper limit derived by Neufeld, Maloney, and Conger for X-ray heated molecular gas. The two values may be reconciled if the molecular gas is very dense: nH2>~109 cm-3. The measured ionization fraction is also consistent with the idea that both absorptions occur in a hot (~6000 K), weakly ionized (ionization fraction a few times 10-2) atomic region that may coexist with the warm molecular gas. If this is the case, the absorbing gas is ~1 pc from the nucleus. We rule out the possibility that both absorptions occur in a fully ionized gas near 104 K. If our line of sight passes through more than one phase, the atomic gas probably dominates the free-free absorption, while the molecular gas may dominate the photoelectric absorption.

First detection of 3He+ in the planetary nebula IC 418

NASA Astrophysics Data System (ADS)

Guzman-Ramirez, L.; Rizzo, J. R.; Zijlstra, A. A.; García-Miró, C.; Morisset, C.; Gray, M. D.

2016-07-01

The 3He isotope is important to many fields of astrophysics, including stellar evolution, chemical evolution, and cosmology. The isotope is produced in low-mass stars which evolve through the planetary nebula (PN) phase. 3He abundances in PNe can help test models of the chemical evolution of the Galaxy. We present the detection of the 3He+ emission line using the single dish Deep Space Station 63, towards the PN IC 418. We derived a 3He/H abundance in the range 1.74 ± 0.8 × 10-3 to 5.8 ± 1.7 × 10-3, depending on whether part of the line arises in an outer ionized halo. The lower value for 3He/H ratio approaches values predicted by stellar models which include thermohaline mixing, but requires that large amounts of 3He are produced inside low-mass stars which enrich the interstellar medium (ISM). However, this overpredicts the 3He abundance in H II regions, the ISM, and protosolar grains, which is known to be of the order of 10-5. This discrepancy questions our understanding of the evolution of the 3He, from circumstellar environments to the ISM.

AN X-RAY INVESTIGATION OF THREE SUPERNOVA REMNANTS IN THE LARGE MAGELLANIC CLOUD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klimek, Matthew D.; Points, S. D.; Smith, R. C.

2010-12-20

We have investigated three supernova remnants (SNRs) in the LMC using multi-wavelength data. These SNRs are generally fainter than the known sample (see Section 4) and may represent a previously missed population. One of our SNRs is the second LMC remnant analyzed which is larger than any Galactic remnant for which a definite size has been established. The analysis of such a large remnant contributes to the understanding of the population of highly evolved SNRs. We have obtained X-ray images and spectra of three of these recently identified SNRs using the XMM-Newton observatory. These data, in conjunction with pre-existing opticalmore » emission-line images and spectra, were used to determine the physical conditions of the optical- and X-ray-emitting gas in the SNRs. We have compared the morphologies of the SNRs in the different wavebands. The physical properties of the warm ionized shell were determined from the H{alpha} surface brightness and the SNR expansion velocity. The X-ray spectra were fit with a thermal plasma model and the physical conditions of the hot gas were derived from the model fits. Finally, we have compared our observations with simulations of SNR evolution.« less

Xenia: A Probe of Cosmic Chemical Evolution

NASA Technical Reports Server (NTRS)

Kouveliotou, Chryssa; Piro, L.

2008-01-01

Xenia is a concept study for a medium-size astrophysical cosmology mission addressing the Cosmic Origins key objective of NASA's Science Plan. The fundamental goal of this objective is to understand the formation and evolution of structures on various scales from the early Universe to the present time (stars, galaxies and the cosmic web). Xenia will use X-and y-ray monitoring and wide field X-ray imaging and high-resolution spectroscopy to collect essential information from three major tracers of these cosmic structures: the Warm Hot Intergalactic Medium (WHIM), Galaxy Clusters and Gamma Ray Bursts (GRBs). Our goal is to trace the chemo-dynamical history of the ubiquitous warm hot diffuse baryon component in the Universe residing in cosmic filaments and clusters of galaxies up to its formation epoch (at z =0-2) and to map star formation and galaxy metal enrichment into the re-ionization era beyond z 6. The concept of Xenia (Greek for "hospitality") evolved in parallel with the Explorer of Diffuse Emission and GRB Explosions (EDGE), a mission proposed by a multinational collaboration to the ESA Cosmic Vision 2015. Xenia incorporates the European and Japanese collaborators into a U.S. led mission that builds on the scientific objectives and technological readiness of EDGE.

Modeling Early Galaxies Using Radiation Hydrodynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

This simulation uses a flux-limited diffusion solver to explore the radiation hydrodynamics of early galaxies, in particular, the ionizing radiation created by Population III stars. At the time of this rendering, the simulation has evolved to a redshift of 3.5. The simulation volume is 11.2 comoving megaparsecs, and has a uniform grid of 10243 cells, with over 1 billion dark matter and star particles. This animation shows a combined view of the baryon density, dark matter density, radiation energy and emissivity from this simulation. The multi-variate rendering is particularly useful because is shows both the baryonic matter ("normal") and darkmore » matter, and the pressure and temperature variables are properties of only the baryonic matter. Visible in the gas density are "bubbles", or shells, created by the radiation feedback from young stars. Seeing the bubbles from feedback provides confirmation of the physics model implemented. Features such as these are difficult to identify algorithmically, but easily found when viewing the visualization. Simulation was performed on Kraken at the National Institute for Computational Sciences. Visualization was produced using resources of the Argonne Leadership Computing Facility at Argonne National Laboratory.« less

Xenia: A Probe of Cosmic Chemical Evolution

NASA Astrophysics Data System (ADS)

Kouveliotou, Chryssa; Piro, L.; Xenia Collaboration

2008-03-01

Xenia is a concept study for a medium-size astrophysical cosmology mission addressing the Cosmic Origins key objective of NASA's Science Plan. The fundamental goal of this objective is to understand the formation and evolution of structures on various scales from the early Universe to the present time (stars, galaxies and the cosmic web). Xenia will use X-and γ-ray monitoring and wide field X-ray imaging and high-resolution spectroscopy to collect essential information from three major tracers of these cosmic structures: the Warm Hot Intergalactic Medium (WHIM), Galaxy Clusters and Gamma Ray Bursts (GRBs). Our goal is to trace the chemo-dynamical history of the ubiquitous warm hot diffuse baryon component in the Universe residing in cosmic filaments and clusters of galaxies up to its formation epoch (at z =0-2) and to map star formation and galaxy metal enrichment into the re-ionization era beyond z 6. The concept of Xenia (Greek for "hospitality") evolved in parallel with the Explorer of Diffuse Emission and GRB Explosions (EDGE), a mission proposed by a multinational collaboration to the ESA Cosmic Vision 2015. Xenia incorporates the European and Japanese collaborators into a U.S. led mission that builds on the scientific objectives and technological readiness of EDGE.

Selectivity of Electronic Coherence and Attosecond Ionization Delays in Strong-Field Double Ionization

NASA Astrophysics Data System (ADS)

Kobayashi, Yuki; Reduzzi, Maurizio; Chang, Kristina F.; Timmers, Henry; Neumark, Daniel M.; Leone, Stephen R.

2018-06-01

Experiments are presented on real-time probing of coherent electron dynamics in xenon initiated by strong-field double ionization. Attosecond transient absorption measurements allow for characterization of electronic coherences as well as relative ionization timings in multiple electronic states of Xe+ and Xe2 + . A high degree of coherence g =0.4 is observed between P3 2 0-P3 0 0 of Xe2 + , whereas for other possible pairs of states the coherences are below the detection limits of the experiments. A comparison of the experimental results with numerical simulations based on an uncorrelated electron-emission model shows that the coherences produced by strong-field double ionization are more selective than predicted. Surprisingly short ionization time delays, 0.85 fs, 0.64 fs, and 0.75 fs relative to Xe+ formation, are also measured for the P2 3 , P0 3 , and P1 3 states of Xe2 + , respectively. Both the unpredicted selectivity in the formation of coherence and the subfemtosecond time delays of specific states provide new insight into correlated electron dynamics in strong-field double ionization.

Phonon-assisted field emission in silicon nanomembranes for time-of-flight mass spectrometry of proteins.

PubMed

Park, Jonghoo; Aksamija, Zlatan; Shin, Hyun-Cheol; Kim, Hyunseok; Blick, Robert H

2013-06-12

Time-of-flight (TOF) mass spectrometry has been considered as the method of choice for mass analysis of large intact biomolecules, which are ionized in low charge states by matrix-assisted-laser-desorption/ionization (MALDI). However, it remains predominantly restricted to the mass analysis of biomolecules with a mass below about 50,000 Da. This limitation mainly stems from the fact that the sensitivity of the standard detectors decreases with increasing ion mass. We describe here a new principle for ion detection in TOF mass spectrometry, which is based upon suspended silicon nanomembranes. Impinging ion packets on one side of the suspended silicon nanomembrane generate nonequilibrium phonons, which propagate quasi-diffusively and deliver thermal energy to electrons within the silicon nanomembrane. This enhances electron emission from the nanomembrane surface with an electric field applied to it. The nonequilibrium phonon-assisted field emission in the suspended nanomembrane connected to an effective cooling of the nanomembrane via field emission allows mass analysis of megadalton ions with high mass resolution at room temperature. The high resolution of the detector will give better insight into high mass proteins and their functions.

PAH 8μm Emission as a Diagnostic of HII Region Optical Depth

NASA Astrophysics Data System (ADS)

Oey, M. S.; Lopez-Hernandez, J.; Kellar, J. A.; Pellegrini, E. W.; Gordon, Karl D.; Jameson, Katherine; Li, Aigen; Madden, Suzanne C.; Meixner, Margaret; Roman-Duval, Julia; Bot, Caroline; Rubio, Monica; Tielens, A. G. G. M.

2017-01-01

PAHs are easily destroyed by Lyman continuum radiation and so in optically thick Stromgren spheres, they tend to be found only on the periphery of HII regions, rather than in the central volume. We therefore expect that in HII regions that are optically thin to ionizing radiation, PAHs would be destroyed beyond the primary nebular structure. Using data from the Spitzer SAGE survey of the Magellanic Clouds, we test whether 8 μm emission can serve as a diagnostic of optical depth in HII regions. We find that 8 μm emission does provide valuable constraints in the Large Magellanic Cloud, where objects identified as optically thick by their atomic ionization structure have 6 times higher median 8 μm surface brightness than optically thin objects. However, in the Small Magellanic Cloud, this differentiation is not observed. This appears to be caused by extremely low PAH production in this low-metallicity environment, such that any differentiation between optically thick and thin objects is washed out by stochastic variations, likely driven by the interplay between dust production and UV destruction. Thus, PAH emission is sensitive to nebular optical depth only at higher metallicities.

The Properties and the Evolution of the Highly Ionized Gas in MR 2251-178

NASA Technical Reports Server (NTRS)

Kaspi, Shai; Netzer, hagai; Chelouche, Doron; George, Ian M.; Nandra, Kirpal; Turner, T. J.

2004-01-01

We present the first XMM-Newton observations of the radio-quiet quasar MR 2251-178 obtained in 2000 and 2002. The EPIC-pn spectra show a power-law continuum with a slope of Gamma = 1.6 at high energies absorbed by at least two warm absorbers (WAs) intrinsic to the source. The underlying continuum in the earlier observation shows a soft excess at low X-ray energies which can be modeled as an additional power-law with Gamma = 2.9. The spectra also show a weak narrow iron K alpha emission line. The high-resolution grating spectrum obtained in 2002 shows emission lines from N VI, O VII, O VIII, Ne IX, and Ne X, as well as absorption lines from the low-ionization ions of O III, O IV, and O V, and other confirmed and suspected weaker absorption lines. The O III - O V lines are consistent with the properties of the emission line gas observed as extended optical (O III) emission in this source. The signal-to-noise of the 2000 grating data is too low to detect any lines. We suggest a model for the high-resolution spectrum which consist of two or three warm-absorber (WA) components. The two-components model has a high-ionization WA with a column density of 10(exp 21.5)-10 (exp 21.8) sq cm and a low-ionization absorber with a column density of 10(exp 20.3) sq cm. In the three-components model we add a lower ionization component that produces the observed iron M-shell absorption lines. We investigate the spectral variations in MR 2251-178 over a period of 8.5 years using data from ASCA, BeppoSAX, and XMM-Newton. All X-ray observations can be fitted with the above two power laws and the two absorbers. The observed luminosity variations seems to correlate with variations in the soft X-ray continuum. The 8.5 year history of the source suggests a changing X-ray absorber due to material that enters and disappears from the line-of-sight on timescales of several months. We also present, for the first time, the entire FUSE spectrum of MR 2251-178. We detect emission from N III, C III, and O VI and at least 4 absorption systems in C III, H I, and O VI, one at -580 km/s and at least 3 others which are blended together and form a wide trough covering the velocity range of 0 to -500 km/s. The general characteristics of the UV and X-ray absorbers are consistent with an origin in the same gas.

The Properties and Evolution of the Highly Ionized Gas in MR 2251-178

NASA Astrophysics Data System (ADS)

Kaspi, Shai; Netzer, Hagai; Chelouche, Doron; George, Ian M.; Nandra, Kirpal; Turner, T. J.

2004-08-01

We present the first XMM-Newton observations of the radio-quiet quasar MR 2251-178 obtained in 2000 and 2002. The EPIC pn spectra show a power-law continuum with a slope of Γ=1.6 at high energies absorbed by at least two warm absorbers (WAs) intrinsic to the source. The underlying continuum in the earlier observation shows a ``soft excess'' at low X-ray energies, which can be modeled as an additional power law with Γ=2.9. The spectra also show a weak narrow iron Kα emission line. The high-resolution grating spectrum obtained in 2002 shows emission lines from N VI, O VII, O VIII, Ne IX, and Ne X, as well as absorption lines from the low-ionization ions of O III, O IV, and O V, and other confirmed and suspected weaker absorption lines. The O III-O V lines are consistent with the properties of the emission-line gas observed as extended optical [O III] emission in this source. The signal-to-noise ratio of the 2000 grating data is too low to detect any lines. We suggest a model for the high-resolution spectrum that consists of two or three WA components. The two-component model has a high-ionization WA with a column density of 1021.5-1021.8 cm-2 and a low-ionization absorber with a column density of 1020.3 cm-2. In the three-component model we add a lower ionization component that produces the observed iron M shell absorption lines. We investigate the spectral variations in MR 2251-178 over a period of 8.5 yr using data from ASCA, BeppoSAX, and XMM-Newton. All X-ray observations can be fitted with the above two power laws and the two absorbers. The observed luminosity variations seem to correlate with variations in the soft X-ray continuum. The 8.5 yr history of the source suggests a changing X-ray absorber due to material that enters and disappears from the line of sight on timescales of several months. We also present, for the first time, the entire Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum of MR 2251-178. We detect emission from N III, C III, and O VI and at least four absorption systems in C III, H I, and O VI, one at -580 km s-1 and at least three others that are blended together and form a wide trough covering the velocity range of 0 to -500 km s-1. The general characteristics of the UV and X-ray absorbers are consistent with an origin in the same gas.

Photoluminescence properties of non-stoichiometric strontium zirconate powder phosphor

NASA Astrophysics Data System (ADS)

Jarý, V.; Boháček, P.; Mihóková, E.; Havlák, L.; Trunda, B.; Nikl, M.

2013-03-01

Excitation and emission spectra and decay kinetics of non-stoichiometric strontium zirconate powder phosphor were measured in the 8-500 K temperature interval. Phenomenological model was applied to extract quantitative parameters of the excited state levels and nonradiative quenching pathways related to the luminescence centre. Delayed recombination integrals measurement was employed to investigate the occurrence of thermally induced ionization of the excited state of the emission centre. The nature of the emission centre itself is suggested. Suitability for phosphor and scintillation application is discussed.

High efficiency photoionization detector

DOEpatents

Anderson, David F.

1984-01-01

A high efficiency photoionization detector using tetraaminoethylenes in a gaseous state having a low ionization potential and a relative photoionization cross section which closely matches the emission spectrum of xenon gas. Imaging proportional counters are also disclosed using the novel photoionization detector of the invention. The compound of greatest interest is TMAE which comprises tetrakis(dimethylamino)ethylene which has a measured ionization potential of 5.36.+-.0.02 eV, and a vapor pressure of 0.35 torr at 20.degree. C.

CMacIonize: Monte Carlo photoionisation and moving-mesh radiation hydrodynamics

NASA Astrophysics Data System (ADS)

Vandenbroucke, Bert; Wood, Kenneth

2018-02-01

CMacIonize simulates the self-consistent evolution of HII regions surrounding young O and B stars, or other sources of ionizing radiation. The code combines a Monte Carlo photoionization algorithm that uses a complex mix of hydrogen, helium and several coolants in order to self-consistently solve for the ionization and temperature balance at any given time, with a standard first order hydrodynamics scheme. The code can be run as a post-processing tool to get the line emission from an existing simulation snapshot, but can also be used to run full radiation hydrodynamical simulations. Both the radiation transfer and the hydrodynamics are implemented in a general way that is independent of the grid structure that is used to discretize the system, allowing it to be run both as a standard fixed grid code and also as a moving-mesh code.

Initiation of air ionization by ultrashort laser pulses: evidence for a role of metastable-state air molecules

NASA Astrophysics Data System (ADS)

Bulgakov, A. V.; Mirza, I.; Bulgakova, N. M.; Zhukov, V. P.; Machulka, R.; Haderka, O.; Campbell, E. E. B.; Mocek, T.

2018-06-01

Transmission measurements for femtosecond laser pulses focused in air with spectral analysis of emission from the focal region have been carried out for various pulse energies and air pressures. The air breakdown threshold and pulse attenuation due to plasma absorption are evaluated and compared with calculations based on the multiphoton ionization model. The plasma absorption is found to depend on the pulse repetition rate and is considerably stronger at 1 kHz than at 1–10 Hz. This suggests that accumulation of metastable states of air molecules plays an important role in initiation of air breakdown, enhancing the ionization efficiency at high repetition rates. Possible channels of metastable-state-assisted air ionization and the role of the observed accumulation effect in laser material processing are discussed.

Accurate Cross Sections for Microanalysis.

PubMed

Rez, Peter

2002-01-01

To calculate the intensity of x-ray emission in electron beam microanalysis requires a knowledge of the energy distribution of the electrons in the solid, the energy variation of the ionization cross section of the relevant subshell, the fraction of ionizations events producing x rays of interest and the absorption coefficient of the x rays on the path to the detector. The theoretical predictions and experimental data available for ionization cross sections are limited mainly to K shells of a few elements. Results of systematic plane wave Born approximation calculations with exchange for K, L, and M shell ionization cross sections over the range of electron energies used in microanalysis are presented. Comparisons are made with experimental measurement for selected K shells and it is shown that the plane wave theory is not appropriate for overvoltages less than 2.5 V.

ASCA Observations of "Type 2" LINERs Evidence for a Stellar Source of Ionization

NASA Technical Reports Server (NTRS)

Terashima, Yuichi; Ho, Luis C.; Ptak, Andrew F.; Mushotzky, Richard F.; Serlemitsos, Peter J.; Yaqoob, Tahir; Kunieda, Hideyo

1999-01-01

We present ASCA observations of LINERs without broad H.alpha emission in their optical spectra. The sample of "type 2" LINERs consists of NGC 404, 4111, 4192, 4457, and 4569. We have detected X-ray emission from all the objects except for NGC 404; among the detected objects are two so-called transition objects (NGC 4192 and NGC 4569), which have been postulated to be composite nuclei having both an H II region and a LINER component. The images of NGC 4111 and NGC 4569 in the soft (0.5-2 keV) and hard (2-7 keV) X-ray bands are extended on scales of several kpc. The X-ray spectra of NGC 4111, NGC 4457 and NGC 4569 are well fitted by a two-component model that consists of soft thermal emission with kT approximately 0.65 keV and a hard component represented by a power law (photon index approximately 2) or by thermal bremsstrahlung emission (kT approximately several keV). The extended hard X-rays probably come from discrete sources, while the soft emission most likely originates from hot gas produced by active star formation in the host galaxy. We have found no clear evidence for the presence of active galactic nuclei (AGNs) in the sample. Using black hole masses estimated from host galaxy bulge luminosities, we obtain an upper limit on the implied Eddington ratios less than 5 x 10(exp -5). If an AGN component is the primary ionization source of the optical emission lines, then it must be heavily obscured with a column density significantly larger than 10(exp 23)/sq cm, since the observed X-ray luminosity is insufficient to drive the luminosities of the optical emission lines. Alternatively, the optical emission could be ionized by a population of exceptionally hot stars. This interpretation is consistent with the small [O I] lambda6300/H.alpha ratios observed in these sources, the ultraviolet spectral characteristics in the cases where such information exists, and the X-ray results reported here. We also analyze the X-ray properties of NGC 4117, a low-luminosity Seyfert 2 galaxy serendipitously observed in the field of NGC 4111.

On- and off-axis spectral emission features from laser-produced gas breakdown plasmas

NASA Astrophysics Data System (ADS)

Harilal, S. S.; Skrodzki, P. J.; Miloshevsky, A.; Brumfield, B. E.; Phillips, M. C.; Miloshevsky, G.

2017-06-01

Laser-heated gas breakdown plasmas or sparks emit profoundly in the ultraviolet and visible region of the electromagnetic spectrum with contributions from ionic, atomic, and molecular species. Laser created kernels expand into a cold ambient with high velocities during their early lifetime followed by confinement of the plasma kernel and eventually collapse. However, the plasma kernels produced during laser breakdown of gases are also capable of exciting and ionizing the surrounding ambient medium. Two mechanisms can be responsible for excitation and ionization of the surrounding ambient: photoexcitation and ionization by intense ultraviolet emission from the sparks produced during the early times of their creation and/or heating by strong shocks generated by the kernel during its expansion into the ambient. In this study, an investigation is made on the spectral features of on- and off-axis emission of laser-induced plasma breakdown kernels generated in atmospheric pressure conditions with an aim to elucidate the mechanisms leading to ambient excitation and emission. Pulses from an Nd:YAG laser emitting at 1064 nm with a pulse duration of 6 ns are used to generate plasma kernels. Laser sparks were generated in air, argon, and helium gases to provide different physical properties of expansion dynamics and plasma chemistry considering the differences in laser absorption properties, mass density, and speciation. Point shadowgraphy and time-resolved imaging were used to evaluate the shock wave and spark self-emission morphology at early and late times, while space and time resolved spectroscopy is used for evaluating the emission features and for inferring plasma physical conditions at on- and off-axis positions. The structure and dynamics of the plasma kernel obtained using imaging techniques are also compared to numerical simulations using the computational fluid dynamics code. The emission from the kernel showed that spectral features from ions, atoms, and molecules are separated in time with early time temperatures and densities in excess of 35 000 K and 4 × 1018/cm3 with an existence of thermal equilibrium. However, the emission from the off-kernel positions from the breakdown plasmas showed enhanced ultraviolet radiation with the presence of N2 bands and is represented by non-local thermodynamic equilibrium (non-LTE) conditions. Our results also highlight that the ultraviolet radiation emitted during the early time of spark evolution is the predominant source of the photo-excitation of the surrounding medium.

On- and off-axis spectral emission features from laser-produced gas breakdown plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harilal, S. S.; Skrodzki, P. J.; Miloshevsky, A.

Laser-heated gas breakdown plasmas or sparks emit profoundly in the ultraviolet and visible region of the electromagnetic spectrum with contributions from ionic, atomic, and molecular species. Laser created kernels expand into a cold ambient with high velocities during its early lifetime followed by confinement of the plasma kernel and eventually collapse. However, the plasma kernels produced during laser breakdown of gases are also capable of exciting and ionizing the surrounding ambient medium. Two mechanisms can be responsible for excitation and ionization of surrounding ambient: viz. photoexcitation and ionization by intense ultraviolet emission from the sparks produced during the early timesmore » of its creation and/or heating by strong shocks generated by the kernel during its expansion into the ambient. In this study, an investigation is made on the spectral features of on- and off-axis emission features of laser-induced plasma breakdown kernels generated in atmospheric pressure conditions with an aim to elucidate the mechanisms leading to ambient excitation and emission. Pulses from an Nd:YAG laser emitting at 1064 nm with 6 ns pulse duration are used to generate plasma kernels. Laser sparks were generated in air, argon, and helium gases to provide different physical properties of expansion dynamics and plasma chemistry considering the differences in laser absorption properties, mass density and speciation. Point shadowgraphy and time-resolved imaging were used to evaluate the shock wave and spark self-emission morphology at early and late times while space and time resolved spectroscopy is used for evaluating the emission features as well as for inferring plasma fundaments at on- and off-axis. Structure and dynamics of the plasma kernel obtained using imaging techniques are also compared to numerical simulations using computational fluid dynamics code. The emission from the kernel showed that spectral features from ions, atoms and molecules are separated in time with an early time temperatures and densities in excess of 35000 K and 4×10 18 /cm 3 with an existence of thermal equilibrium. However, the emission from the off-kernel positions from the breakdown plasmas showed enhanced ultraviolet radiation with the presence of N 2 bands and represented by non-LTE conditions. Finally, our results also highlight that the ultraviolet radiation emitted during early time of spark evolution is the predominant source of the photo-excitation of the surrounding medium.« less

On- and off-axis spectral emission features from laser-produced gas breakdown plasmas

DOE PAGES

Harilal, S. S.; Skrodzki, P. J.; Miloshevsky, A.; ...

2017-06-01

Laser-heated gas breakdown plasmas or sparks emit profoundly in the ultraviolet and visible region of the electromagnetic spectrum with contributions from ionic, atomic, and molecular species. Laser created kernels expand into a cold ambient with high velocities during its early lifetime followed by confinement of the plasma kernel and eventually collapse. However, the plasma kernels produced during laser breakdown of gases are also capable of exciting and ionizing the surrounding ambient medium. Two mechanisms can be responsible for excitation and ionization of surrounding ambient: viz. photoexcitation and ionization by intense ultraviolet emission from the sparks produced during the early timesmore » of its creation and/or heating by strong shocks generated by the kernel during its expansion into the ambient. In this study, an investigation is made on the spectral features of on- and off-axis emission features of laser-induced plasma breakdown kernels generated in atmospheric pressure conditions with an aim to elucidate the mechanisms leading to ambient excitation and emission. Pulses from an Nd:YAG laser emitting at 1064 nm with 6 ns pulse duration are used to generate plasma kernels. Laser sparks were generated in air, argon, and helium gases to provide different physical properties of expansion dynamics and plasma chemistry considering the differences in laser absorption properties, mass density and speciation. Point shadowgraphy and time-resolved imaging were used to evaluate the shock wave and spark self-emission morphology at early and late times while space and time resolved spectroscopy is used for evaluating the emission features as well as for inferring plasma fundaments at on- and off-axis. Structure and dynamics of the plasma kernel obtained using imaging techniques are also compared to numerical simulations using computational fluid dynamics code. The emission from the kernel showed that spectral features from ions, atoms and molecules are separated in time with an early time temperatures and densities in excess of 35000 K and 4×1018 /cm3 with an existence of thermal equilibrium. However, the emission from the off-kernel positions from the breakdown plasmas showed enhanced ultraviolet radiation with the presence of N2 bands and represented by non-LTE conditions. Our results also highlight that the ultraviolet radiation emitted during early time of spark evolution is the predominant source of the photo-excitation of the surrounding medium.« less

Effect of geomagnetic storm conditions on the equatorial ionization anomaly and equatorial temperature anomaly

NASA Astrophysics Data System (ADS)

Bharti, Gaurav; Bag, T.; Sunil Krishna, M. V.

2018-03-01

The effect of the geomagnetic storm on the equatorial ionization anomaly (EIA) and equatorial temperature anomaly (ETA) has been studied using the atomic oxygen dayglow emissions at 577.7 nm (OI 557.7 nm) and 732.0 nm (OII 732.0 nm). For the purpose of this study, four intense geomagnetic storms during the ascending phase of solar cycle 24 have been considered. This study is primarily based on the results obtained using photochemical models with necessary inputs from theoretical studies and experimental observations. The latest reaction rate coefficients, quantum yields and the corresponding cross-sections have also been incorporated in these models. The volume emission rate of airglow emissions has been calculated using the neutral densities from NRLMSISE-00 and charged densities from IRI-2012 model. The modeled volume emission rate (VER) for OI 557.7 nm shows a positive correlation with the Dst index at 150 km and negative correlation with Dst at 250 and 280 km altitudes. Latitudinal profile of the greenline emission rate at different altitudes show a distinct behaviour similar to what has been observed in EIA with crests on either sides of the equator. The EIA crests are found to show poleward movement in the higher altitude regions. The volume emission rate of 732.0 nm emission shows a strong enhancement during the main phase of the storm. The changes observed in the airglow emission rates are explained with the help of variations induced in neutral densities and parameters related to EIA and ETA. The latitudinal variation of 732.0 nm emission rate is correlated to the variability in EIA during the storm period.

Local H i emissivity measured with FERMI-LAT and implications for Cosmic-ray spectra

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casandjian, Jean -Marc

Cosmic-ray (CR) electrons and nuclei interact with the Galactic interstellar gas and produce high-energy γ-rays. The γ-ray emission rate per hydrogen atom, called emissivity, provides a unique indirect probe of the CR flux. We present the measurement and the interpretation of the emissivity in the solar neighborhood for γ-ray energy from 50 MeV to 50 GeV. We analyzed a subset of 4 yr of observations from the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope ( Fermi) restricted to absolute latitudesmore » $$10^\\circ \\lt | b| \\lt 70^\\circ $$. From a fit to the LAT data including atomic, molecular, and ionized hydrogen column density templates, as well as a dust optical depth map, we derived the emissivities, the molecular hydrogen–to–CO conversion factor $${X}_{\\mathrm{CO}}=(0.902\\pm 0.007)\\times {10}^{20}$$ cm–2 (K km s–1)–1, and the dust-to-gas ratio $${X}_{\\mathrm{DUST}}=(41.4\\pm 0.3)\\times {10}^{20}$$ cm–2 mag–1. Moreover, we detected for the first time γ-ray emission from ionized hydrogen. We compared the extracted emissivities to those calculated from γ-ray production cross sections and to CR spectra measured in the heliosphere. We observed that the experimental emissivities are reproduced only if the solar modulation is accounted for. This provides a direct detection of solar modulation observed previously through the anticorrelation between CR fluxes and solar activity. Lastly, we fitted a parameterized spectral form to the heliospheric CR observations and to the Fermi-LAT emissivity and obtained compatible local interstellar spectra for proton and helium kinetic energy per nucleon between between 1 and 100 GeV and for electron–positrons between 0.1 and 100 GeV.« less

Local H i emissivity measured with FERMI-LAT and implications for Cosmic-ray spectra

DOE PAGES

Casandjian, Jean -Marc

2015-06-20

Cosmic-ray (CR) electrons and nuclei interact with the Galactic interstellar gas and produce high-energy γ-rays. The γ-ray emission rate per hydrogen atom, called emissivity, provides a unique indirect probe of the CR flux. We present the measurement and the interpretation of the emissivity in the solar neighborhood for γ-ray energy from 50 MeV to 50 GeV. We analyzed a subset of 4 yr of observations from the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope ( Fermi) restricted to absolute latitudesmore » $$10^\\circ \\lt | b| \\lt 70^\\circ $$. From a fit to the LAT data including atomic, molecular, and ionized hydrogen column density templates, as well as a dust optical depth map, we derived the emissivities, the molecular hydrogen–to–CO conversion factor $${X}_{\\mathrm{CO}}=(0.902\\pm 0.007)\\times {10}^{20}$$ cm–2 (K km s–1)–1, and the dust-to-gas ratio $${X}_{\\mathrm{DUST}}=(41.4\\pm 0.3)\\times {10}^{20}$$ cm–2 mag–1. Moreover, we detected for the first time γ-ray emission from ionized hydrogen. We compared the extracted emissivities to those calculated from γ-ray production cross sections and to CR spectra measured in the heliosphere. We observed that the experimental emissivities are reproduced only if the solar modulation is accounted for. This provides a direct detection of solar modulation observed previously through the anticorrelation between CR fluxes and solar activity. Lastly, we fitted a parameterized spectral form to the heliospheric CR observations and to the Fermi-LAT emissivity and obtained compatible local interstellar spectra for proton and helium kinetic energy per nucleon between between 1 and 100 GeV and for electron–positrons between 0.1 and 100 GeV.« less

Diffuse X-Ray Emission in the Milky Way

NASA Technical Reports Server (NTRS)

Snowden, Steve

2011-01-01

Our understanding of the diffuse X-ray emission from the Milky Way has evolved. extensively with time from when it was first observed in the 1960's, and its origin is still the subject of debate as much now as ever. This presentation will provide an overview of that evolution, the various emission components, emission mechanisms, an assessment of the current state of the field, and implications for eROSITA.

HEATING OF THE WARM IONIZED MEDIUM BY LOW-ENERGY COSMIC RAYS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walker, Mark A., E-mail: Mark.Walker@manlyastrophysics.org

2016-02-10

In light of evidence for a high ionization rate due to low-energy cosmic rays (LECR) in diffuse molecular gas in the solar neighborhood, we evaluate their heat input to the warm ionized medium (WIM). LECR are much more effective at heating plasma than they are at heating neutrals. We show that the upper end of the measured ionization rates corresponds to a local LECR heating rate sufficient to maintain the WIM against radiative cooling, independent of the nature of the ionizing particles or the detailed shape of their spectrum. Elsewhere in the Galaxy the LECR heating rates may be highermore » than those measured locally. In particular, higher fluxes of LECR have been suggested for the inner Galactic disk, based on the observed hard X-ray emission, with correspondingly larger heating rates implied for the WIM. We conclude that LECR play an important and perhaps dominant role in the thermal balance of the WIM.« less

Spectroscopic method to study low charge state ion and cold electron population in ECRIS plasma

NASA Astrophysics Data System (ADS)

Kronholm, R.; Kalvas, T.; Koivisto, H.; Tarvainen, O.

2018-04-01

The results of optical emission spectroscopy experiments probing the cold electron population of a 14 GHz Electron Cyclotron Resonance Ion Source (ECRIS) are reported. The study has been conducted with a high resolution spectrometer and data acquisition setup developed specifically for the diagnostics of weak emission line characteristic to ECRIS plasmas. The optical emission lines of low charge state ions and neutral atoms of neon have been measured and analyzed with the line-ratio method. The aforementioned electron population temperature of the cold electron population (Te < 100 eV) is determined for Maxwell-Boltzmann and Druyvesteyn energy distributions to demonstrate the applicability of the method. The temperature was found to change significantly when the extraction voltage of the ion source is turned on/off. In the case of the Maxwellian distribution, the temperature of the cold electron population is 20 ± 10 eV when the extraction voltage is off and 40 ± 10 eV when it is on. The optical emission measurements revealed that the extraction voltage also affects both neutral and ion densities. Based on the rate coefficient analysis with the aforementioned temperatures, switching the extraction voltage off decreases the rate coefficient of neutral to 1+ ionization to 42% and 1+ to 2+ ionization to 24% of the original. This suggests that switching the extraction voltage on favors ionization to charge states ≥2+ and, thus, the charge state distributions of ECRIS plasmas are probably different with the extraction voltage on/off. It is therefore concluded that diagnostics results of ECRIS plasmas obtained without the extraction voltage are not depicting the plasma conditions in normal ECRIS operation.

Imaging a Central Ionized Component, a Narrow Ring, and the CO Snowline in the Multigapped Disk of HD 169142

DOE Office of Scientific and Technical Information (OSTI.GOV)

Macías, Enrique; Anglada, Guillem; Osorio, Mayra

2017-04-01

We report Very Large Array observations at 7 mm, 9 mm, and 3 cm toward the pre-transitional disk of the Herbig Ae star HD 169142. These observations have allowed us to study the millimeter emission of this disk with the highest angular resolution so far (0.″12 × 0.″09, or 14 au × 11 au, at 7 mm). Our 7 and 9 mm images show a narrow ring of emission at a radius of ∼25 au tracing the outer edge of the inner gap. This ring presents an asymmetric morphology that could be produced by dynamical interactions between the disk andmore » forming planets. Additionally, the azimuthally averaged radial intensity profiles of the 7 and 9 mm images confirm the presence of the previously reported gap at ∼45 au and reveal a new gap at ∼85 au. We analyzed archival DCO{sup +}(3–2) and C{sup 18}O(2–1) ALMA observations, showing that the CO snowline is located very close to this third outer gap. This suggests that growth and accumulation of large dust grains close to the CO snowline could be the mechanism responsible for this proposed outer gap. Finally, a compact source of emission is detected at 7 mm, 9 mm, and 3 cm toward the center of the disk. Its flux density and spectral index indicate that it is dominated by free–free emission from ionized gas, which could be associated with the photoionization of the inner disk, an independent object, or an ionized jet.« less

Detection of Extraplanar Diffuse Ionized Gas in M83

NASA Astrophysics Data System (ADS)

Boettcher, Erin; Gallagher, J. S., III; Zweibel, Ellen G.

2017-08-01

We present the first kinematic study of extraplanar diffuse ionized gas (eDIG) in the nearby, face-on disk galaxy M83 using optical emission-line spectroscopy from the Robert Stobie Spectrograph on the Southern African Large Telescope. We use a Markov Chain Monte Carlo method to decompose the [N II]λ λ 6548, 6583, Hα, and [S II]λ λ 6717, 6731 emission lines into H II region and diffuse ionized gas emission. Extraplanar, diffuse gas is distinguished by its emission-line ratios ([N II]λ6583/Hα ≳ 1.0) and its rotational velocity lag with respect to the disk ({{Δ }}v=-24 km s-1 in projection). With interesting implications for isotropy, the velocity dispersion of the diffuse gas, σ =96 km s-1, is a factor of a few higher in M83 than in the Milky Way and nearby, edge-on disk galaxies. The turbulent pressure gradient is sufficient to support the eDIG layer in dynamical equilibrium at an electron scale height of {h}z=1 kpc. However, this dynamical equilibrium model must be finely tuned to reproduce the rotational velocity lag. There is evidence of local bulk flows near star-forming regions in the disk, suggesting that the dynamical state of the gas may be intermediate between a dynamical equilibrium and a galactic fountain flow. As one of the first efforts to study eDIG kinematics in a face-on galaxy, this study demonstrates the feasibility of characterizing the radial distribution, bulk velocities, and vertical velocity dispersions in low-inclination systems. Based on observations made with the Southern African Large Telescope (SALT) under program 2015-2-SCI-004 (PI: E. Boettcher).

The Galactic Centre Mini-Spiral in the MM-Regime

NASA Technical Reports Server (NTRS)

Kunneriath, D.; Eckart, A.; Vogel, S. N.; Teuben, P.; Muzic, I.; Schoedel, R.; Garcia-Marin, M.; Moultaka, J.; Staguhn, J.; Straubmeier, C.;

Constraining UV Continuum Slopes of Active Galactic Nuclei with CLOUDY Models of Broad-line Region Extreme-ultraviolet Emission Lines

NASA Astrophysics Data System (ADS)

Moloney, Joshua; Shull, J. Michael

2014-10-01

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 H >= 1012 cm-3) and hydrogen ionizing photon fluxes (ΦH >= 1022 cm-2 s-1). Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS5-26555.

The [CII]/[NII] far-infrared line ratio at z>5: extreme conditions for “normal” galaxies

NASA Astrophysics Data System (ADS)

Pavesi, Riccardo; Riechers, Dominik; Capak, Peter L.; Carilli, Chris Luke; Sharon, Chelsea E.; Stacey, Gordon J.; Karim, Alexander; Scoville, Nicholas; Smolcic, Vernesa

2017-01-01

Thanks to the Atacama Large (sub-)Millimeter Array (ALMA), observations of atomic far-infrared fine structure lines are a very productive way of measuring physical properties of the interstellar medium (ISM) in galaxies at high redshift, because they provide an unobscured view into the physical conditions of star formation. While the bright [CII] line has become a routine probe of the dynamical properties of the gas, its intensity needs to be compared to other lines in order to establish the physical origin of the emission. [NII] selectively traces the emission coming from the ionized fraction of the [CII]-emitting gas, offering insight into the phase structure of the ISM. Here we present ALMA measurements of [NII] 205 μm fine structure line emission from a representative sample of galaxies at z=5-6 spanning two orders of magnitude in star formation rate (SFR). Our results show at least two different regimes of ionized gas properties for galaxies in the first billion years of cosmic time, separated by their L[CII]/L[NII] ratio. First, we find extremely low [NII] emission compared to [CII] from a “typical” Lyman Break Galaxy (LBG-1), likely due to low dust content and reminiscent of local dwarfs. Second, the dusty Lyman Break Galaxy HZ10 and the extreme starburst AzTEC-3 show ionized gas fractions typical of local star-forming galaxies and show hints of spatial variations in their [CII]/[NII] line ratio. These observations of far-infrared lines in “normal” galaxies at z>5 yield some of the first constraints on ISM models for young galaxies in the first billion years of cosmic time and shed light on the observed evolution of the dust and gas properties.

Population inversions in ablation plasmas generated by intense electron beams. Final report, 1 November 1985-31 October 1988

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gilgenbach, R.M.; Kammash, T.; Brake, M.L.

1988-11-01

Experiments during the past three years have concerned the generation and spectroscopic study of electron beam-driven carbon plasmas in order to explore the production of optical and ultraviolet radiation from nonequilibrium populations. The output of MELBA (Michigan Electron Long Beam Accelerator), has been connected to an electron-beam diode consisting of an aluminum (or brass) cathode stalk and a carbon anode. Magnetic-field coils were designed, procured, and utilized to focus the electron beam. A side viewing port permitted spectroscopic diagnostics to view across the surface of the anode. Spectroscopic diagnosis was performed using a 1-m spectrograph capable of operation from themore » vacuum-ultraviolet through the visible. This spectrograph is coupled to a 1024-channel optical multichannel analyzer. Spectra taken during the initial 400-ns period of the e-beam pulse showed a low effective-charge plasma with primarily molecular components (C/sub 2/, CH) as well as atomic hydrogen and singly ionized carbon (CII). When the generator pulse was crowbarred after the first 400 ns, the spectra revealed a continuation of the low-charge-state plasma. At times greater than 400 ns in non-crowbarred shots, the spectra revealed a highly ionized plasma with a very large intensity line at 2530 Angstroms due to CIV (5g-4f), and lower-intensity lines due to CIII and CII. This CIV line emission increased with time, peaking sharply between 750 and 900 ns, and decayed rapidly in less than 100 ns. Emission from these high ionization states may be due to electron beam-plasma instabilities, as this emission was accompanied by high levels of radio frequency and microwave emission.« less

Mid-infrared imaging- and spectro-polarimetric subarcsecond observations of NGC 1068

NASA Astrophysics Data System (ADS)

Lopez-Rodriguez, E.; Packham, C.; Roche, P. F.; Alonso-Herrero, A.; Díaz-Santos, T.; Nikutta, R.; González-Martín, O.; Álvarez, C. A.; Esquej, P.; Espinosa, J. M. Rodríguez; Perlman, E.; Ramos Almeida, C.; Telesco, C. M.

2016-06-01

We present subarcsecond 7.5-13 μm imaging- and spectro-polarimetric observations of NGC 1068 using CanariCam on the 10.4-m Gran Telescopio CANARIAS. At all wavelengths, we find: (1) A 90 × 60 pc extended polarized feature in the northern ionization cone, with a uniform ˜44° polarization angle. Its polarization arises from dust and gas emission in the ionization cone, heated by the active nucleus and jet, and further extinguished by aligned dust grains in the host galaxy. The polarization spectrum of the jet-molecular cloud interaction at ˜24 pc from the core is highly polarized, and does not show a silicate feature, suggesting that the dust grains are different from those in the interstellar medium. (2) A southern polarized feature at ˜9.6 pc from the core. Its polarization arises from a dust emission component extinguished by a large concentration of dust in the galaxy disc. We cannot distinguish between dust emission from magnetically aligned dust grains directly heated by the jet close to the core, and aligned dust grains in the dusty obscuring material surrounding the central engine. Silicate-like grains reproduce the polarized dust emission in this feature, suggesting different dust compositions in both ionization cones. (3) An upper limit of polarization degree of 0.3 per cent in the core. Based on our polarization model, the expected polarization of the obscuring dusty material is ≲0.1 per cent in the 8-13 μm wavelength range. This low polarization may be arising from the passage of radiation through aligned dust grains in the shielded edges of the clumps.

Planck intermediate results: XXXIV. The magnetic field structure in the Rosette Nebula

DOE PAGES

Aghanim, N.; Alves, M. I. R.; Arnaud, M.; ...

2016-02-09

Planck has mapped the polarized dust emission over the whole sky, making it possible to trace the Galactic magnetic field structure that pervades the interstellar medium (ISM). In this paper, we combine polarization data from Planck with rotation measure (RM) observations towards a massive star-forming region, the Rosette Nebula in the Monoceros molecular cloud, to study its magnetic field structure and the impact of an expanding H ii region on the morphology of the field. We derive an analytical solution for the magnetic field, assumed to evolve from an initially uniform configuration following the expansion of ionized gas and themore » formation of a shell of swept-up ISM. From the RM data we estimate a mean value of the line-of-sight component of the magnetic field of about 3 μG (towards the observer) in the Rosette Nebula, for a uniform electron density of about 12 cm -3. The dust shell that surrounds the Rosette H ii region is clearly observed in the Planck intensity map at 353 GHz, with a polarization signal significantly different from that of the local background when considered asa whole. The Planck observations constrain the plane-of-the-sky orientation of the magnetic field in the Rosette’s parent molecular cloud to be mostly aligned with the large-scale field along the Galactic plane. The Planck data are compared with the analytical model, which predicts the mean polarization properties of a spherical and uniform dust shell for a given orientation of the field. This comparison leads to an upper limit of about 45° on the angle between the line of sight and the magnetic field in the Rosette complex, for an assumed intrinsic dust polarization fraction of 4%. This field direction can reproduce the RM values detected in the ionized region if the magnetic field strength in the Monoceros molecular cloud is in the range 6.5–9 μG. Finally, the present analytical model is able to reproduce the RM distribution across the ionized nebula, as well as the mean dust polarization properties of the swept-up shell, and can be directly applied to other similar objects.« less

Planck intermediate results: XXXIV. The magnetic field structure in the Rosette Nebula

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aghanim, N.; Alves, M. I. R.; Arnaud, M.

Planck has mapped the polarized dust emission over the whole sky, making it possible to trace the Galactic magnetic field structure that pervades the interstellar medium (ISM). In this paper, we combine polarization data from Planck with rotation measure (RM) observations towards a massive star-forming region, the Rosette Nebula in the Monoceros molecular cloud, to study its magnetic field structure and the impact of an expanding H ii region on the morphology of the field. We derive an analytical solution for the magnetic field, assumed to evolve from an initially uniform configuration following the expansion of ionized gas and themore » formation of a shell of swept-up ISM. From the RM data we estimate a mean value of the line-of-sight component of the magnetic field of about 3 μG (towards the observer) in the Rosette Nebula, for a uniform electron density of about 12 cm -3. The dust shell that surrounds the Rosette H ii region is clearly observed in the Planck intensity map at 353 GHz, with a polarization signal significantly different from that of the local background when considered asa whole. The Planck observations constrain the plane-of-the-sky orientation of the magnetic field in the Rosette’s parent molecular cloud to be mostly aligned with the large-scale field along the Galactic plane. The Planck data are compared with the analytical model, which predicts the mean polarization properties of a spherical and uniform dust shell for a given orientation of the field. This comparison leads to an upper limit of about 45° on the angle between the line of sight and the magnetic field in the Rosette complex, for an assumed intrinsic dust polarization fraction of 4%. This field direction can reproduce the RM values detected in the ionized region if the magnetic field strength in the Monoceros molecular cloud is in the range 6.5–9 μG. Finally, the present analytical model is able to reproduce the RM distribution across the ionized nebula, as well as the mean dust polarization properties of the swept-up shell, and can be directly applied to other similar objects.« less

Expansion of an ultracold Rydberg plasma

NASA Astrophysics Data System (ADS)

Forest, Gabriel T.; Li, Yin; Ward, Edwin D.; Goodsell, Anne L.; Tate, Duncan A.

2018-04-01

We report a systematic experimental and numerical study of the expansion of ultracold Rydberg plasmas. Specifically, we have measured the asymptotic expansion velocities, v0, of ultracold neutral plasmas (UNPs) which evolve from cold, dense samples of Rydberg rubidium atoms using ion time-of-flight spectroscopy. From this, we have obtained values for the effective initial plasma electron temperature, Te ,0=mionv02/kB (where mion is the Rb+ ion mass), as a function of the original Rydberg atom density and binding energy, Eb ,i. We have also simulated numerically the interaction of UNPs with a large reservoir of Rydberg atoms to obtain data to compare with our experimental results. We find that for Rydberg atom densities in the range 107-109 cm-3, for states with principal quantum number n >40 , Te ,0 is insensitive to the initial ionization mechanism which seeds the plasma. In addition, the quantity kBTe ,0 is strongly correlated with the fraction of atoms which ionize, and is in the range 0.6 ×| Eb ,i|≲ kBTe ,0≲2.5 ×|Eb ,i| . On the other hand, plasmas from Rydberg samples with n ≲40 evolve with no significant additional ionization of the remaining atoms once a threshold number of ions has been established. The dominant interaction between the plasma electrons and the Rydberg atoms is one in which the atoms are deexcited, a heating process for electrons that competes with adiabatic cooling to establish an equilibrium where Te ,0 is determined by their Coulomb coupling parameter, Γe˜0.01 .

The analysis of a rocket tomography measurement of the N2+3914A emission and N2 ionization rates in an auroral arc

NASA Technical Reports Server (NTRS)

Mcdade, Ian C.

1991-01-01

Techniques were developed for recovering two-dimensional distributions of auroral volume emission rates from rocket photometer measurements made in a tomographic spin scan mode. These tomographic inversion procedures are based upon an algebraic reconstruction technique (ART) and utilize two different iterative relaxation techniques for solving the problems associated with noise in the observational data. One of the inversion algorithms is based upon a least squares method and the other on a maximum probability approach. The performance of the inversion algorithms, and the limitations of the rocket tomography technique, were critically assessed using various factors such as (1) statistical and non-statistical noise in the observational data, (2) rocket penetration of the auroral form, (3) background sources of emission, (4) smearing due to the photometer field of view, and (5) temporal variations in the auroral form. These tests show that the inversion procedures may be successfully applied to rocket observations made in medium intensity aurora with standard rocket photometer instruments. The inversion procedures have been used to recover two-dimensional distributions of auroral emission rates and ionization rates from an existing set of N2+3914A rocket photometer measurements which were made in a tomographic spin scan mode during the ARIES auroral campaign. The two-dimensional distributions of the 3914A volume emission rates recoverd from the inversion of the rocket data compare very well with the distributions that were inferred from ground-based measurements using triangulation-tomography techniques and the N2 ionization rates derived from the rocket tomography results are in very good agreement with the in situ particle measurements that were made during the flight. Three pre-prints describing the tomographic inversion techniques and the tomographic analysis of the ARIES rocket data are included as appendices.

Ultraviolet emission lines in young low-mass galaxies at z ≃ 2: physical properties and implications for studies at z > 7

NASA Astrophysics Data System (ADS)

Stark, Daniel P.; Richard, Johan; Siana, Brian; Charlot, Stéphane; Freeman, William R.; Gutkin, Julia; Wofford, Aida; Robertson, Brant; Amanullah, Rahman; Watson, Darach; Milvang-Jensen, Bo

2014-12-01

We present deep spectroscopy of 17 very low mass (M⋆ ≃ 2.0 × 106-1.4 × 109 M⊙) and low luminosity (MUV ≃ -13.7 to -19.9) gravitationally lensed galaxies in the redshift range z ≃ 1.5-3.0. Deep rest-frame ultraviolet spectra reveal large equivalent width emission from numerous emission lines (N IV], O III], C IV, Si III], C III]) which are rarely seen in individual spectra of more massive star-forming galaxies. C III] is detected in 16 of 17 low-mass star-forming systems with rest-frame equivalent widths as large as 13.5 Å. Nebular C IV emission is present in the most extreme C III] emitters, requiring an ionizing source capable of producing a substantial component of photons with energies in excess of 47.9 eV. Photoionization models support a picture whereby the large equivalent widths are driven by the increased electron temperature and enhanced ionizing output arising from metal-poor gas and stars (0.04-0.13 Z⊙), young stellar populations (6-50 Myr), and large ionization parameters (log U = -2.16 to -1.84). The young ages implied by the emission lines and continuum spectral energy distributions (SEDs) indicate that the extreme line emitters in our sample are in the midst of a significant upturn in their star formation activity. The low stellar masses, blue UV colours, and large specific star formation rates of our sample are similar to those of typical z ≳ 6 galaxies. Given the strong attenuation of Lyα in z ≳ 6 galaxies, we suggest that C III] is likely to provide our best probe of early star-forming galaxies with ground-based spectrographs and one off the most efficient means of confirming z ≳ 10 galaxies with the James Webb Space Telescope.

Emission-line diagnostics of nearby H II regions including interacting binary populations

NASA Astrophysics Data System (ADS)

Xiao, Lin; Stanway, Elizabeth R.; Eldridge, J. J.

2018-06-01

We present numerical models of the nebular emission from H II regions around young stellar populations over a range of compositions and ages. The synthetic stellar populations include both single stars and interacting binary stars. We compare these models to the observed emission lines of 254 H II regions of 13 nearby spiral galaxies and 21 dwarf galaxies drawn from archival data. The models are created using the combination of the BPASS (Binary Population and Spectral Synthesis) code with the photoionization code CLOUDY to study the differences caused by the inclusion of interacting binary stars in the stellar population. We obtain agreement with the observed emission line ratios from the nearby star-forming regions and discuss the effect of binary-star evolution pathways on the nebular ionization of H II regions. We find that at population ages above 10 Myr, single-star models rapidly decrease in flux and ionization strength, while binary-star models still produce strong flux and high [O III]/H β ratios. Our models can reproduce the metallicity of H II regions from spiral galaxies, but we find higher metallicities than previously estimated for the H II regions from dwarf galaxies. Comparing the equivalent width of H β emission between models and observations, we find that accounting for ionizing photon leakage can affect age estimates for H II regions. When it is included, the typical age derived for H II regions is 5 Myr from single-star models, and up to 10 Myr with binary-star models. This is due to the existence of binary-star evolution pathways, which produce more hot Wolf-Rayet and helium stars at older ages. For future reference, we calculate new BPASS binary maximal starburst lines as a function of metallicity, and for the total model population, and present these in Appendix A.

Spectroscopic Constraints on UV Metal Line Emission at z ≃ 6 - 9 The Nature of Lyα Emitting Galaxies in the Reionization-Era

NASA Astrophysics Data System (ADS)

Mainali, Ramesh; Zitrin, Adi; Stark, Daniel P.; Ellis, Richard S.; Richard, Johan; Tang, Mengtao; Laporte, Nicolas; Oesch, Pascal; McGreer, Ian

2018-06-01

Recent studies have revealed intense UV metal emission lines in a modest sample of z > 7 Lyman-α emitters, indicating a hard ionizing spectrum is present. If such high ionization features are shown to be common, it may indicate that extreme radiation fields play a role in regulating the visibility of Lyα in the reionization era. Here we present deep near-infrared spectra of seven galaxies with Lyα emission at 5.4 < z < 8.7 (including a newly-confirmed lensed galaxy at zLyα = 6.031) and three bright z ≃ 7 photometric targets. In nine sources we do not detect UV metal lines. However in the zLyα = 8.683 galaxy EGSY8p7, we detect a 4.6σ emission line in the narrow spectral window expected for NVλ1243. The feature is unresolved (FWHM<90 km s-1) and is likely nebular in origin. A deep H-band spectrum of EGSY8p7 reveals non-detections of CIV, He II, and OIII]. The presence of NV requires a substantial flux of photons above 77 eV, pointing to a hard ionizing spectrum powered by an AGN or fast radiative shocks. Regardless of its origin, the intense radiation field of EGSY8p7 may aid the transmission of Lyα through what is likely a partially neutral IGM. With this new detection, five of thirteen known Lyα emitters at z > 7 have now been shown to have intense UV line emission, suggesting that extreme radiation fields are commonplace among the Lyα population. Future observations with JWST will eventually clarify the origin of these features and explain their role in the visibility of Lyα in the reionization era.

Scattering of hydrogen, nitrogen and water ions from micro pore optic plates for application in spaceborne plasma instrumentation

NASA Astrophysics Data System (ADS)

Stude, Joan; Wieser, Martin; Barabash, Stas

2016-10-01

Time-of-flight mass spectrometers for upcoming space missions into enhanced radiation environments need to be small, light weight and energy efficient. Time-of-flight systems using surface interactions as start-event generation can be smaller than foil-type instruments. Start surfaces for such applications need to provide narrow angular scattering, high ionization yields and high secondary electron emissions to be effective. We measured the angular scattering, energy distribution and positive ionization yield of micro pore optics for incident hydrogen, nitrogen and water ions at 2 keV. Positive ionization yields of 2% for H+ , 0.5% for N+ and 0.2% for H2O+ were detected.

Quantification of surface emissions: An historical perspective from GEIA

NASA Astrophysics Data System (ADS)

Granier, C.; Denier Van Der Gon, H.; Doumbia, E. H. T.; Frost, G. J.; Guenther, A. B.; Hassler, B.; Janssens-Maenhout, G. G. A.; Lasslop, G.; Melamed, M. L.; Middleton, P.; Sindelarova, K.; Tarrason, L.; van Marle, M.; W Kaiser, J.; van der Werf, G.

2015-12-01

Assessments of the composition of the atmosphere and its evolution require accurate knowledge of the surface emissions of atmospheric compounds. The first community development of global surface emissions started in 1990, when GEIA was established as a component of the International Global Atmospheric Chemistry (IGAC) project. At that time, GEIA meant "Global Emissions Inventory Activity". Since its inception, GEIA has brought together people to understand emissions from anthropogenic, biomass burning and natural sources. The first goal of GEIA was to establish a "best" inventory for the base year 1985 at 1x1 degree resolution. Since then many inventories have been developed by various groups at the global and regional scale at different temporal and spatial resolutions. GEIA, which now means the "Global Emissions Initiative", has evolved into assessing, harmonizing and distributing emissions datasets. We will review the main achievements of GEIA, and show how the development and evaluation of surface emissions has evolved during the last 25 years. We will discuss the use of surface, in-situ and remote sensing observations to evaluate and improve the quantification of emissions. We will highlight the main uncertainties currently limiting emissions datasets, such as the spatial and temporal evolution of emissions at different resolutions, the quantification of emerging emission sources (such as oil/gas extraction and distribution, biofuels, etc.), the speciation of the emissions of volatile organic compounds and of particulate matter, the capacity building necessary for organizing the development of regional emissions across the world, emissions from shipping, etc. We will present the ECCAD (Emissions of Atmospheric Compounds and Compilation of Ancillary Data) database, developed as part of GEIA to facilitate the access and evaluation of emission inventories.

Effects of ionization and ion loss on dust ion-acoustic solitary waves in a collisional dusty plasma with suprathermal electrons

NASA Astrophysics Data System (ADS)

Mayout, Saliha; Gougam, Leila Ait; Tribeche, Mouloud

2016-03-01

The combined effects of ionization, ion loss, and electron suprathermality on dust ion-acoustic solitary waves in a collisional dusty plasma are examined. Carrying out a small but finite amplitude analysis, a damped Korteweg-de Vries (dK-dV) equation is derived. The damping term decreases with the increase of the spectral index and saturates for Maxwellian electrons. Choosing typical plasma parameters, the analytical approximate solution of the dK-dV equation is numerically analyzed. We first neglect the ionization and ion loss effects and account only for collisions to estimate the relative importance between these damping terms which can act concurrently. Interestingly, we found that as the suprathermal character of the electrons becomes important, the strength of the collisions related dissipation becomes more important and causes the dust ion-acoustic solitary wave amplitude to decay more rapidly. Moreover, the collisional damping may largely prevail over the ionization and ion loss related damping. The latter becomes more effective as the electrons evolve far away from their thermal equilibrium. Our results complement and provide new insights into previously published work on this problem.

Effects of ionization and ion loss on dust ion- acoustic solitary waves in a collisional dusty plasma with suprathermal electrons

NASA Astrophysics Data System (ADS)

Tribeche, Mouloud; Mayout, Saliha

2016-07-01

The combined effects of ionization, ion loss and electron suprathermality on dust ion- acoustic solitary waves in a collisional dusty plasma are examined. Carrying out a small but finite amplitude analysis, a damped Korteweg- de Vries (dK-- dV) equation is derived. The damping term decreases with the increase of the spectral index and saturates for Maxwellian electrons. Choosing typical plasma parameters, the analytical approximate solution of the dK- dV equation is numerically analyzed. We first neglect the ionization and ion loss effects and account only for collisions to estimate the relative importance between these damping terms which can act concurrently. Interestingly, we found that as the suprathermal character of the electrons becomes important, the strength of the collisions related dissipation becomes more important and causes the DIA solitary wave amplitude to decay more rapidly. Moreover, the collisional damping may largely prevail over the ionization and ion loss related damping. The latter becomes more effective as the electrons evolve far away from their thermal equilibrium. Our results complement and provide new insights into previously published work on this problem.

Simulation of laser interaction with ablative plasma and hydrodynamic behavior of laser supported plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tong Huifeng; Yuan Hong; Tang Zhiping

When an intense laser beam irradiates on a solid target, ambient air ionizes and becomes plasma, while part of the target rises in temperature, melts, vaporizes, ionizes, and yet becomes plasma. A general Godunov finite difference scheme WENO (Weighted Essentially Non-Oscillatory Scheme) with fifth-order accuracy is used to simulate 2-dimensional axis symmetrical laser-supported plasma flow field in the process of laser ablation. The model of the calculation of ionization degree of plasma and the interaction between laser beam and plasma are considered in the simulation. The numerical simulations obtain the profiles of temperature, density, and velocity at different times whichmore » show the evolvement of the ablative plasma. The simulated results show that the laser energy is strongly absorbed by plasma on target surface and that the velocity of laser supported detonation (LSD) wave is half of the ideal LSD value derived from Chapman-Jouguet detonation theory.« less

The evolving intergalactic medium - The uncollapsed baryon fraction in a cold dark matter universe

NASA Technical Reports Server (NTRS)

Shapiro, Paul R.; Giroux, Mark L.; Babul, Arif

1991-01-01

The time-varying density of the intergalactic medium (IGM) is calculated by coupling detailed numerical calculations of the thermal and ionization balance and radiative transfer in a uniform IGM of H and He to the linearized equations for the growth of density fluctuations in both gases and a dark component in a cold dark matter universe. The IGM density is identified with the collapsed baryon fraction. It is found that even if the IGM is never reheated, a significant fraction of the baryons remain uncollapsed at redshifts of four. If instead the collapsed fraction releases enough ionizing radiation or thermal energy to reionize the IGM by z greater than four as required by the Gunn-Peterson (GP) constraint, the uncollapsed fraction at z of four is even higher. The known quasar distribution is insufficient to supply the ionizing radiation necessary to satisfy the GP constraint in this case and, if stars are instead responsible, a substantial metallicity must have been produced by z of four.

An outburst scenario for the X-ray spectral variability in 3C 111

NASA Astrophysics Data System (ADS)

Tombesi, F.; Reeves, J. N.; Reynolds, C. S.; García, J.; Lohfink, A.

2013-09-01

We present a combined Suzaku and Swift BAT broad-band E = 0.6-200 keV spectral analysis of three 3C 111 observations obtained in 2010. The data are well described with an absorbed power-law continuum and a weak (R ≃ 0.2) cold reflection component from distant material. We constrain the continuum cutoff at EC ≃ 150-200 keV, which is in accordance with X-ray Comptonization corona models and supports claims that the jet emission is only dominant at much higher energies. Fe XXVI Lyα emission and absorption lines are also present in the first and second observations, respectively. The modelling and interpretation of the emission line is complex and we explore three possibilities. If originating from ionized-disc reflection, this should be emitted at rin ≥ 50 rg or, in the lamp-post configuration, the illuminating source should be at a height of h ≥ 30 rg above the black hole. Alternatively, the line could be modelled with a hot collisionally ionized plasma with temperature kT = 22.0^{+6.1}_{-3.2} keV or a photoionized plasma with log ξ = 4.52^{+0.10}_{-0.16} erg s-1 cm and column density NH > 3 × 1023 cm-2. However, the first and second scenarios are less favoured on statistical and physical grounds, respectively. The blueshifted absorption line in the second observation can be modelled as an ultrafast outflow (UFO) with ionization parameter log ξ = 4.47^{+0.76}_{-0.04} erg s-1 cm, column density N_H = (5.3^{+1.8}_{-1.3})× 10^{22} cm-2 and outflow velocity vout = 0.104 ± 0.006c. Interestingly, the parameters of the photoionized emission model remarkably match those of the absorbing UFO, supporting the possibility that the same material could be responsible for both emission and absorption. We suggest an outburst scenario in which an accretion disc wind, initially lying out of the line of sight and observed in emission, then crosses our view to the source and it is observed in absorption as a mildly relativistic UFO.

Electron emission perpendicular to the polarization direction in laser-assisted XUV atomic ionization

NASA Astrophysics Data System (ADS)

Gramajo, A. A.; Della Picca, R.; Arbó, D. G.

2017-08-01

We present a theoretical study of ionization of the hydrogen atom due to an XUV pulse in the presence of an infrared (IR) laser with both fields linearly polarized in the same direction. In particular, we study the energy distribution of photoelectrons emitted perpendicularly to the polarization direction. As we previously showed in Gramajo et al. [Phys. Rev. A 94, 053404 (2016), 10.1103/PhysRevA.94.053404] for parallel emission, by means of a very simple semiclassical model which considers electron trajectories born at different ionization times, the electron energy spectrum can be interpreted as the interplay of intra- and intercycle interferences. However, contrary to the case of parallel emission the intracycle interference pattern stems from the coherent superposition of four electron trajectories giving rise to (i) interference of electron trajectories born during the same half cycle (intra-half-cycle interference) and (ii) interference between electron trajectories born during the first half cycle with those born during the second half cycle (inter-half-cycle interference). The intercycle interference is responsible for the formation of the sidebands. We also show that the destructive inter-half-cycle interference for the absorption and emission of an even number of IR laser photons is responsible for the characteristic sidebands in the perpendicular direction separated by twice the IR photon energy. This contrasts with the emission along the polarization axis (all sideband orders are present) since intra-half-cycle interferences do not exist in that case. The intracycle interference pattern works as a modulation of the sidebands and, in the same way, it is modulated by the intra-half-cycle interference pattern. We analyze the dependence of the energy spectrum on the laser intensity and the time delay between the XUV pulse and the IR laser. Finally, we show that our semiclassical simulations are in very good agreement with quantum calculations within the strong-field approximation and the numerical solution of the time-dependent Schrödinger equation, giving rise to nonzero emission, in contraposition to other theories.

High efficiency photoionization detector

DOEpatents

Anderson, D.F.

1984-01-31

A high efficiency photoionization detector is described using tetraaminoethylenes in a gaseous state having a low ionization potential and a relative photoionization cross section which closely matches the emission spectrum of xenon gas. Imaging proportional counters are also disclosed using the novel photoionization detector of the invention. The compound of greatest interest is TMAE which comprises tetrakis(dimethylamino)ethylene which has a measured ionization potential of 5.36 [+-] 0.02 eV, and a vapor pressure of 0.35 torr at 20 C. 6 figs.

The ionization structure of planetary nebulae. IX - NGC 1535

NASA Technical Reports Server (NTRS)

Barker, Timothy

1989-01-01

The ionization structure of planetary nebula NGC 1535 was investigated using spectrophotometric observations of emission-line intensities over the spectral range 1400-7200 A, which were carried out in five positions in this nebula. The results obtained on the ionic abundances of He, O, N, Ne, C, and Ar in NGC 1535 suggest that it is a planetary nebula that formed initially in a somewhat metal-poor region and has undergone little or no enhancement of its original abundances by mixing with nuclear-processed material.

Design and Installation of a Field Ionization Test Chamber for Ion Thrusters

DTIC Science & Technology

2011-12-01

where F is thrust, m& is the mass flow rate of the propellant, and go is the standard acceleration due to gravity at sea level [1]. It provides a...only one graphene wall, and multi- walled CNT ( MWCNT ), which consist of multiple, concentric walls of graphene (Figure 9). One of the most unique...ionization chamber to ensure the mass flow rate going into the chamber matches the mass flow rate leaving it. 46 B. FIELD EMISSION AND FIELD

A Study of Local Time Variations of Jupiter's Ultraviolet Aurora using Juno-UVS

NASA Astrophysics Data System (ADS)

Greathouse, T. K.; Gladstone, R.; Versteeg, M. H.; Hue, V.; Kammer, J.; Davis, M. W.; Bolton, S. J.; Levin, S.; Connerney, J. E. P.; Gerard, J. C. M. C.; Grodent, D. C.; Bonfond, B.; Bunce, E. J.

2017-12-01

Juno's Ultraviolet Spectrograph (Juno-UVS) offers unique views of Jupiter's auroras never before obtained in the UV, observing at all local times (unlike HST observations, limited to the illuminated disk). With Juno's 2-rpm spin period, the UVS long slit rapidly scans across Jupiter observing narrow stripes or swaths of Jupiter's poles, from 5 hours prior to perijove until 5 hours after perijove. By rotating a mirror interior to the instrument, UVS can view objects from 60 to 120 degrees off the spacecraft spin axis. This allows UVS to map out the entire auroral oval over multiple spins, even when Juno is very close to Jupiter. Using the first 8 perijove passes, we take a first look for local time effects in Jupiter's northern and southern auroras. We focus on the strength of auroral oval emissions and polar emissions found poleward of the main oval. Some unique polar emissions of interest include newly discovered polar flare emissions that start off as small localized points of emission but quickly (10's of sec) evolve into rings. These emissions evolve in such a way as to be reminiscent of raindrops striking a pond.

29 CFR 1918.1 - Scope and application.

Code of Federal Regulations, 2010 CFR

2010-07-01

...) Ionizing radiation. Subpart Z, § 1910.1096; (6) Noise. Subpart G, § 1910.95; (7) Nonionizing radiation. Subpart G, § 1910.97; Note to paragraph (b)(7): Exposures to nonionizing radiation emissions from...

Infrared fine-structure line diagnostics of shrouded active galactic nuclei

NASA Technical Reports Server (NTRS)

Voit, G. M.

1992-01-01

The ultraluminous far-IR galaxies revealed by IRAS, quasar-like in luminosity but smothered in molecular gas, probably conceal either immense starbursts or luminous active nuclei. In both scenarios, these objects ought to produce copious infrared fine-structure emission with several lines comparable to H-beta in luminosity. We show how these lines, if detected, can be used to determine the electron densities and far-IR obscurations of shrouded photoionized regions and to constrain the shape and ionization parameter of the ionizing spectra. The presence of Ne v emission in particular will distinguish shrouded AGNs from shrouded starbursts. Since all active galaxies photoionize at least some surrounding material, these diagnostics can also be applied to active galaxies in general and will aid in studying how an active nucleus interacts with the interstellar medium of its host galaxy.

Can Radio Emission From Luminous Obscured AGN Blow Kpc-scale Ionized Outflows?

NASA Astrophysics Data System (ADS)

Goulding, Andy

2017-09-01

We propose joint VLA radio and Chandra X-ray to observe 4 AGN selected from the SDSS-BOSS and the Hyper Suprime-Cam surveys that present spectacular extended outflowing [O III] regions, reaching up to 50kpc in diameter. Our proposed observations allow us to study the mechanical and kinematical output of the AGN through radio and X-ray observations, measure the fraction of the AGN bolometric luminosity that is transferred to the outflow, and to determine the morphology and spectral index (by producing high-res continuum maps) of the radio emission that may be co-spatial with the extended ionized AGN outflow. In turn, our study will determine what role the AGN plays in producing extended outflows, and hence, provide an in-depth understanding of the physical drivers of AGN feedback.

Estimación de la incerteza cinemática de los espectros obtenidos con REOSC (CAsLeo), Flamingos-2 y PHOENIX (Gemini) para observaciones de gas ionizado en galaxias

NASA Astrophysics Data System (ADS)

Gaspar, G.; Díaz, R. J.; Güunthardt, G.; Agüuero, M. P.; Camperi, J. A.; Gimeno, G.

The determination of the radial velocity curves of ionized gas in galaxies requires knowing the value of the internal kinematic uncertainly along the slit for the used spectrographs. We present preliminary results of the study of the variation of the measured radial velocity of both the telluric and comparison emission lines in the spatial direction. This was done for the spectrographs REOSC, Flamingos-2 (F2) and Phoenix. In particular we are interested in using this data to homogenize the rotation curves of nearby galaxies in large-scale ranges. These results will be also useful as references for those works that measure radial velocities of extended objects using only one emission line of ionized gas. FULL TEXT IN SPANISH

Infrared emission in Seyfert 2 galaxies - Reprocessed radiation from a dusty torus?

NASA Technical Reports Server (NTRS)

Storchi-Bergmann, Thaisa; Mulchaey, John S.; Wilson, Andrew S.

1992-01-01

New and existing data for a sample of nine Seyfert 2 galaxies with known 'ionization cones' are combined in order to test whether collimation results from shadowing of radiation from a small isotropic nuclear source by a thick dusty torus. The number of ionizing photons emitted by the compact nucleus is calculated from the emission-line ratios measured for gas within the cones. On the assumption that this compact nuclear source radiates isotropically, the optical-UV power incident on the torus, which is expected to be reradiated in the IR, is determined. It is found that the observed IRAS luminosities are consistent with the torus model in eight of the nine objects with sufficient data to perform the calculation. It is concluded that the data are generally consistent with collimation and reradiation by a dusty torus.

Polycyclic Aromatic Hydrocarbons

NASA Technical Reports Server (NTRS)

Salama, Farid

2010-01-01

Carbonaceous materials play an important role in space. Polycyclic Aromatic Hydrocarbons (PAHs) are a ubiquitous component of the carbonaceous materials. PAHs are the best-known candidates to account for the IR emission bands. They are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). PAH ionization states reflect the ionization balance of the medium while PAH size, composition, and structure reflect the energetic and chemical history of the medium. A major challenge is to reproduce in the laboratory the physical conditions that exist in the emission and absorption interstellar zones. The harsh physical conditions of the ISM -low temperature, collisionless, strong UV radiation fields- are simulated in the laboratory by associating a molecular beam with an ionizing discharge to generate a cold plasma expansion. PAH ions and radicals are formed from the neutral precursors in an isolated environment at low temperature and probed with high-sensitivity cavity ringdown spectroscopy in the NUV-NIR range. Carbon nanoparticles are also formed during the short residence time of the precursors in the plasma and are characterized with time-offlight mass spectrometry. These experiments provide unique information on the spectra of large carbonaceous molecules and ions in the gas phase that can now be directly compared to interstellar and circumstellar observations (IR emission bands, DIBs, extinction curve). These findings also hold great potential for understanding the formation process of interstellar carbonaceous grains. We will review recent progress in the experimental and theoretical studies of PAHs, compare the laboratory data with astronomical observations and discuss the global implications.

Properties of a weakly ionized NO gas sensor based on multi-walled carbon nanotubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Jingyuan; Zhang, Yong, E-mail: zhyong@mail.xjtu.edu.cn; Pan, Zhigang

2015-08-31

Nitric oxide NO is one of the major targets for environmental monitoring, but the existing NO sensors are limited by their low sensitivity and narrow test range. Here, a NO gas sensor employing multiwalled carbon nanotubes (MWCNTs) was fabricated, and its properties in NO–N{sub 2} mixture were investigated from both emission and ionization. The current I{sub e} passing through the nanotubes cathode was found to decrease with increasing NO concentration and increase linearly in different slopes with the extracting voltage U{sub e}. It is shown that the Schottky barrier of the MWCNTs calculated by I{sub e} increased with NO concentrationmore » due to the adsorption of NO gas, which restrained the electron emission and consequently weakened the ionization. The positive ion currents I{sub c} passing through the collecting electrode at different voltages of U{sub e} were found to monotonically decrease with increasing NO concentration, which was induced by both of the reduced electron emission and the consumption of the two excited metastable states N{sub 2}(A{sup 3}∑{sub u}{sup +}) and N{sub 2}(a′{sup 1}∑{sub u}{sup −}) by NO. The sensor exhibited high sensitivity at the low temperature of 30 °C. The calculated conductivity was found to be able to take place of I{sub c} for NO detection in a wide voltage range of 80–150 V U{sub e}.« less

PDR MODEL MAPPING OF OBSCURED H{sub 2} EMISSION AND THE LINE-OF-SIGHT STRUCTURE OF M17-SW

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheffer, Y.; Wolfire, M. G.

2013-09-01

We observed H{sub 2} line emission with Spitzer-IRS toward M17-SW and modeled the data with our photon-dominated region (PDR) code. Derived gas density values of up to few times 10{sup 7} cm{sup -3} indicate that H{sub 2} emission originates in high-density clumps. We discover that the PDR code can be utilized to map the amount of intervening extinction obscuring the H{sub 2} emission layers, and thus we obtain the radial profile of A{sub V} relative to the central ionizing cluster NGC 6618. The extinction has a positive radial gradient, varying between 15-47 mag over the projected distance of 0.9-2.5 pcmore » from the primary ionizer, CEN 1. These high extinction values are in good agreement with previous studies of A{sub V} toward stellar targets in M17-SW. The ratio of data to PDR model values is used to infer the global line-of-sight structure of the PDR surface, which is revealed to resemble a concave surface relative to NGC 6618. Such a configuration confirms that this PDR can be described as a bowl-shaped boundary of the central H II region in M17. The derived structure and physical conditions are important for interpreting the fine-structure and rotational line emission from the PDR.« less

Galaxy emission line classification using three-dimensional line ratio diagrams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vogt, Frédéric P. A.; Dopita, Michael A.; Kewley, Lisa J.

2014-10-01

Two-dimensional (2D) line ratio diagnostic diagrams have become a key tool in understanding the excitation mechanisms of galaxies. The curves used to separate the different regions—H II-like or excited by an active galactic nucleus (AGN)—have been refined over time but the core technique has not evolved significantly. However, the classification of galaxies based on their emission line ratios really is a multi-dimensional problem. Here we exploit recent software developments to explore the potential of three-dimensional (3D) line ratio diagnostic diagrams. We introduce the ZQE diagrams, which are a specific set of 3D diagrams that separate the oxygen abundance and themore » ionization parameter of H II region-like spectra and also enable us to probe the excitation mechanism of the gas. By examining these new 3D spaces interactively, we define the ZE diagnostics, a new set of 2D diagnostics that can provide the metallicity of objects excited by hot young stars and that cleanly separate H II region-like objects from the different classes of AGNs. We show that these ZE diagnostics are consistent with the key log [N II]/Hα versus log [O III]/Hβ diagnostic currently used by the community. They also have the advantage of attaching a probability that a given object belongs to one class or the other. Finally, we discuss briefly why ZQE diagrams can provide a new way to differentiate and study the different classes of AGNs in anticipation of a dedicated follow-up study.« less

Spectroscopic Characteristic and Analytical Capability of Ar-N₂ Inductively Coupled Plasma in Axially Viewing Optical Emission Spectrometry.

PubMed

Ohata, Masaki

2016-01-01

The spectroscopic characteristics and analytical capability of argon-nitrogen (Ar-N2) inductively coupled plasma (ICP) in axially viewing optical emission spectrometry (OES) were examined and figures of merit were determined in the present study. The spectroscopic characteristics such as the emission intensity profile and the excitation temperature observed from the analytical zone of Ar-N2 ICP in axially viewing ICPOES, in order to elucidate the enhancement of the emission intensity of elements obtained in our previous study, were evaluated and compared to those of the standard ICP. The background and emission intensities of elements as well as their excitation behavior for both atom and ion lines were also examined. As results, a narrower emission intensity profile and an increased excitation temperature as well as enhancements for both background and emission intensities of elements, which could be due to the ICP shrunken as well as the enhancement of the interaction between the central channel of the ICP and samples introduced, were observed for Ar-N2 ICP in axially viewing OES. In addition, the elements with relatively higher excitation and ionization energies such as As, Bi, Cd, Ni, P, and Zn revealed larger enhancements of the emission intensities as well as improved limits of detection (LODs), which were also attributed to the enhanced interaction between Ar-N2 ICP and the samples. Since the Ar-N2 ICP could be obtained easily only by the addition of a small amount of N2 gas to the Ar plasma gas of the standard ICP and no optimization on the alignment between Ar-N2 ICP and the spectrometer in commercially available ICPOES instruments was needed, it could be utilized as simple and optional excitation and ionization sources in axially viewing ICPOES.

Diffuse Ionized Gas in the Milky Way Disk

NASA Astrophysics Data System (ADS)

Luisi, Matteo; Anderson, L. D.; Balser, Dana S.; Wenger, Trey V.; Bania, T. M.

2017-11-01

We analyze the diffuse ionized gas (DIG) in the first Galactic quadrant from {\\ell }=18^\\circ to 40° using radio recombination line (RRL) data from the Green Bank Telescope. These data allow us to distinguish DIG emission from H II region emission and thus study the diffuse gas essentially unaffected by confusion from discrete sources. We find that the DIG has two dominant velocity components, one centered around 100 {km} {{{s}}}-1 associated with the luminous H II region W43, and the other centered around 45 {km} {{{s}}}-1 not associated with any large H II region. Our analysis suggests that the two velocity components near W43 may be caused by noncircular streaming motions originating near the end of the Galactic bar. At lower Galactic longitudes, the two velocities may instead arise from gas at two distinct distances from the Sun, with the most likely distances being ˜6 kpc for the 100 {km} {{{s}}}-1 component and ˜12 kpc for the 45 {km} {{{s}}}-1 component. We show that the intensity of diffuse Spitzer GLIMPSE 8.0 μm emission caused by excitation of polyaromatic hydrocarbons (PAHs) is correlated with both the locations of discrete H II regions and the intensity of the RRL emission from the DIG. This implies that the soft ultraviolet photons responsible for creating the infrared emission have a similar origin as the harder ultraviolet photons required for the RRL emission. The 8.0 μm emission increases with RRL intensity but flattens out for directions with the most intense RRL emission, suggesting that PAHs are partially destroyed by the energetic radiation field at these locations.

Deep Imaging of Extremely Metal-Poor Galaxies

NASA Astrophysics Data System (ADS)

Corbin, Michael

2006-07-01

Conflicting evidence exists regarding whether the most metal-poor and actively star-forming galaxies in the local universe such as I Zw 18 contain evolved stars. We propose to help settle this issue by obtaining deep ACS/HRC U, narrow-V, I, and H-alpha images of nine nearby {z < 0.01} extremely metal-poor {12 + O/H < 7.65} galaxies selected from the Sloan Digital Sky Survey. These objects are only marginally resolved from the ground and appear uniformly blue, strongly motivating HST imaging. The continuum images will establish: 1.} If underlying populations of evolved stars are present, by revealing the objects' colors on scales 10 pc, and 2.} The presence of any faint tidal features, dust lanes, and globular or super star clusters, all of which constrain the objects' evolutionary states. The H-alpha images, in combination with ground-based echelle spectroscopy, will reveal 1.} Whether the objects are producing "superwinds" that are depleting them of their metals; ground-based images of some of them indeed show large halos of ionized gas, and 2.} The correspondence of their nebular and stellar emission on scales of a few parsecs, which is important for understanding the "feedback" process by which supernovae and stellar winds regulate star formation. One of the sample objects, CGCG 269-049, lies only 2 Mpc away, allowing the detection of individual red giant stars in it if any are present. We have recently obtained Spitzer images and spectra of this galaxy to determine its dust content and star formation history, which will complement the proposed HST observations. [NOTE: THIS PROPOSAL WAS REDUCED TO FIVE ORBITS, AND ONLY ONE OF THE ORIGINAL TARGETS, CGCG 269-049, AFTER THE PHASE I REVIEW

The ionized gas at the centre of IC 10: a possible localized chemical pollution by Wolf-Rayet stars

NASA Astrophysics Data System (ADS)

López-Sánchez, Á. R.; Mesa-Delgado, A.; López-Martín, L.; Esteban, C.

2011-03-01

We present results from integral field spectroscopy with the Potsdam Multi-Aperture Spectrograph at the 3.5-m telescope at Calar Alto Observatory of the intense star-forming region [HL90] 111 at the centre of the starburst galaxy IC 10. We have obtained maps with a spatial sampling of 1 × 1 arcsec2= 3.9× 3.9 pc2 of different emission lines and analysed the extinction, physical conditions, nature of the ionization and chemical abundances of the ionized gas, as well determined locally the age of the most recent star formation event. By defining several apertures, we study the main integrated properties of some regions within [HL90] 111. Two contiguous spaxels show an unambiguous detection of the broad He IIλ4686 emission line, this feature seems to be produced by a single late-type WN star. We also report a probable N and He enrichment in the precise spaxels where the Wolf-Rayet (WR) features are detected. The enrichment pattern is roughly consistent with that expected for the pollution of the ejecta of a single or a very small number of WR stars. Furthermore, this chemical pollution is very localized (˜2 arcsec ˜7.8 pc) and it should be difficult to detect in star-forming galaxies beyond the Local Volume. We also discuss the use of the most common empirical calibrations to estimate the oxygen abundances of the ionized gas in nearby galaxies from 2D spectroscopic data. The ionization degree of the gas plays an important role when applying these empirical methods, as they tend to give lower oxygen abundances with increasing ionization degree. Based on observations collected at the Centro Astrónomico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Plank Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).Visiting Astronomer at the Instituto de Astrofísica de Canarias.

Nanocalorimetry-coupled time-of-flight mass spectrometry: identifying evolved species during high-rate thermal measurements.

PubMed

Yi, Feng; DeLisio, Jeffery B; Zachariah, Michael R; LaVan, David A

2015-10-06

We report on measurements integrating a nanocalorimeter sensor into a time-of-flight mass spectrometer (TOFMS) for simultaneous thermal and speciation measurements at high heating rates. The nanocalorimeter sensor was incorporated into the extraction region of the TOFMS system to provide sample heating and thermal information essentially simultaneously with the evolved species identification. This approach can be used to measure chemical reactions and evolved species for a variety of materials. Furthermore, since the calorimetry is conducted within the same proximal volume as ionization and ion extraction, evolved species detected are in a collision-free environment, and thus, the possibility exists to interrogate intermediate and radical species. We present measurements showing the decomposition of ammonium perchlorate, copper oxide nanoparticles, and sodium azotetrazolate. The rapid, controlled, and quantifiable heating rate capabilities of the nanocalorimeter coupled with the 0.1 ms temporal resolution of the TOFMS provides a new measurement capability and insight into high-rate reactions, such as those seen with reactive and energetic materials, and adsorption\\desorption measurements, critical for understanding surface chemistry and accelerating catalyst selection.

Markarian 315: A test case for the active galactic nucleus-merger hypothesis?

NASA Technical Reports Server (NTRS)

Mackenty, John W.; Simkin, Susan M.; Griffiths, Richard E.; Ulvestad, James S.; Wilson, Andrew S.

1994-01-01

Using the Hubble Space Telescope (HST) Wide Field/Planetary Camera, (WF/PC) we have detected a diffuse continuum knot in the inner regions of the Seyfert galaxy Markarian 315. This knot may be a remnant nucleus. It is associated with a complex, ringlike structure in both the continuum and ionized gas emission. We have measured the kinematics of the ionized gas in two position angles and find velocities which are consistent with a nonaxisymmetric gravitational disturbance. The galaxy is associated with an extended ionized filament, or tidal tail, and our measurements show that the ionized gas in this feature is redshifted by up to 500 km/s in the line of sight relative to the Seyfert nucleus. This combination of morphological and kinematic features suggests that Mrk 315 has suffered a disruptive, tidal interaction which has significantly influenced regions within 1 kpc of its nucleus.

Detection of polychlorinated biphenyls in transformer oils in Vietnam by multiphoton ionization mass spectrometry using a far-ultraviolet femtosecond laser as an ionization source.

PubMed

Duong, Vu Thi Thuy; Duong, Vu; Lien, Nghiem Thi Ha; Imasaka, Tomoko; Tang, Yuanyuan; Shibuta, Shinpei; Hamachi, Akifumi; Hoa, Do Quang; Imasaka, Totaro

2016-03-01

Polychlorinated biphenyls (PCBs) in transformer and food oils were measured using gas chromatography combined with multiphoton ionization mass spectroscopy. An ultrashort laser pulse emitting in the far-ultraviolet region was utilized for efficient ionization of the analytes. Numerous signal peaks were clearly observed for a standard sample mixture of PCBs when the third and fourth harmonic emissions (267 and 200nm) of a femtosecond Ti:sapphire laser (800nm) were employed. The signal intensities were found to be greater when measured at 200nm compared with those measured at 267nm, providing lower detection limits especially for highly chlorinated PCBs at shorter wavelengths. After simple pretreatment using disposable columns, PCB congeners were measured and found to be present in the transformer oils used in Vietnam. Copyright © 2015 Elsevier B.V. All rights reserved.

A rocket-borne airglow photometer

NASA Technical Reports Server (NTRS)

Paarmann, L. D.; Smith, L. G.

1977-01-01

The design of a rocket-borne photometer to measure the airglow emission of ionized molecular nitrogen in the 391.4 nm band is presented. This airglow is a well known and often observed phenomenon of auroras, where the principal source of ionization is energetic electrons. It is believed that at some midlatitude locations energetic electrons are also a source of nighttime ionization in the E region of the ionosphere. If this is so, then significant levels of 391.4 nm airglow should be present. The intensity of this airglow will be measured in a rocket payload which also contains instrumentation to measured in a rocket payload which also contains instrumentation to measure energetic electron differential flux and the ambient electron density. An intercomparison of the 3 experiments in a nightime launch will allow a test of the importance of energetic electrons as a nighttime source of ionization in the upper E region.