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NASA NTRS1993

Infrared coronal emission lines and the possibility of their maser emission in Seyfert nuclei

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.

Greenhouse, Matthew A.↗

NASA NTRS1994

Carbon recombination lines as a diagnostic of photodissociation regions

We have observed the C91 alpha radio recombination line toward the Orion H II region. This narrow (approximately 3-5 km per sec full width at half maximum (FWHM)) line is spatially very extended (approximately 8 arcmin or 1 pc). These charateristics compare well with the observed characteristics of the C II fine structure line at 158 microns. Thus, the C91 alpha line originates in the predominantly neutral photodissociation regions separating the H II region from the molecular cloud. We have developed theoretical models for the C II radio recombination lines from photodissociation regions. The results show that the I(C91 alpha)/I(C158) intensity ratio is a sensitive function of the temperature and density of the emitting gas. We have also extended theoretical models for photodissociation regions to include the C II recombination lines. Comparison with these models show that, in the central portion of the Orion region, the C91 alpha line originates in dense (10(exp 6) per cu cm), warm (500-1000 K) gas. Even at large projected distances (approximately 1 pc), the inferred density is still high (10(exp 5) per cu cm) and implies extremely high thermal pressures. As in the case of the (C II) 158 microns line, the large extent of the C91 alpha line shows that (FUV) photons can penetrate to large distances from the illuminating source. The decline of the intensity of the incident radiation field with distance from Theta(sup 1) C seems to be dominated by geometrical dilution, rather than dust extinction. Finally, we have used our models to calculate the intensity of the 9850 A recombination line of C II. The physical conditions inferred from this line are in good agreement with those determined from the radio recombination and the far-infrared fine-structure lines. We show that the ratio of the 9850 A to the C91 alpha lines is a very good probe of very high density clumps.

Natta, A.↗

NASA NTRS2016

Robust Thermal Control of Propulsion Lines for Space Missions

In spacecraft that have propulsion lines that are located externally with open bus architecture, the lines are typically insulated by Multi Layer Insulation (MLI) blankets to protect them thermally from the cold space environment. In addition to heat loss through the insulation, mechanical supports used to attach the lines to the spacecraft structure also create heat leaks from the lines. These lines typically have very low thermal conduction in the axial direction, so the heat balance in the lines tends to be very local without much heat spreading. The typical allowable temperature range for hydrazine-based lines is +15/+50°C. This tight temperature range has to be maintained for every location on these lines. For typical spacecraft, these lines can be several meters long. Temperature control is typically achieved by closed loop monitoring of temperatures along the lines and the corresponding powering of the heaters in a bang-bang approach to maintain the temperatures within the dead band of the control loop. The temperatures of propulsion lines are a function of several parameters with heat loss characteristics of the MLI being the key one. Unfortunately, this same key characteristic (MLI effective emittance) has a large variation along its length due to its dependence on workmanship, which in turn leads to large uncertainties in the propulsion lines’ local temperatures. Because of the poor conduction along the axial direction, heat balance along the length varies dramatically from one location to the next, even few inches apart, depending on the combination of the controlling parameters. This paper describes various robust design and implementation approaches that have been investigated to greatly reduce the randomness associated with predicting the temperature of these propulsion lines.

Bhandari, Pradeep↗

NASA NTRS2023

AI-3000K Infrared Line List for Hot CO 2

AI-3000K is a semi-empirical IR line list constructed for hot CO 2 spectra analysis and simulation up to 3000 – 4000 K. Compared to previously published Ames-1000K and UCL-4000, it represents a major upgrade, utilizing a new algorithm for optimization and including the latest improvements in potential energy surface (PES), dipole moment surface (DMS), and room temperature IR line list (Ames-2021 296K). To maximize the success of introducing experimental based accurate line positions, a new PES (X01d) was refined with respect to >800 selected CDSD2019 [Tashkun et al. JQSRT (2019) 228, 124] energy levels in the range of 0 – 24,000 cm -1 , with σ rms = 0.5 – 0.7 cm -1 . Most differences between the X01d PES based levels and CDSD2019 energies are within ± 2 cm -1 . A new DMS is fitted from extrapolated CCSD(T)/aug-cc-pV(T,Q,5)Z dipole calculations, with σ rms = 5.1 × 10 -6 au for 11,155 geometries up to 40,000 cm -1 , denoted Ames-2021–40K. Compared to the best available Ames-2021 DMS and room temperature IR line list [Huang et al J. Phys. Chem. A (2022) 126, 5940], the relative intensity differences are expected to be ∼ 1 ‰. The line position accuracy of ''X01d + Ames-2021–40K'' IR line list is significantly improved by adopting CDSD2019 energy levels up to 24,000 cm -1 (J ≤ 150). The Einstein A21 coefficients for E' < 15,000 cm -1 transitions are replaced by more accurate values from the Ames-2021 296K IR line list. In short, the AI-3000K is the X01d PES and Ames-2021–40K DMS based line list enhanced with the A 21 of Ames-2021 296K line list and CDSD energy levels. It provides continuous coverage from 0 to 20,000 cm -1 for the four most abundant isotopologues: 12 C 16 O 2 (626), 13 C 16 O 2 (636), 16 O 12 C 18 O (628), and 16 O 12 C 17 O (627). The impacts of isotopologue and E'/E'' cutoffs have been examined. Intensity convergence (not accuracy) of AI-3000K line list is quantitatively estimated in 1 cm -1 bins. It is better than 99% in the whole range of 0 – 20,000 (or 10,000) cm -1 at 1000 K (or 2000 K), or better than 90% in the whole range of 0 – 15,000 (or 9000) cm -1 at 2000 K (or 3000 K), respectively. Convergence beyond 3000 K will require a new PES and DMS for E' > 40,000 cm -1 . The AI-3000K and HITEMP based IR simulations are compared to high resolution shock tube experiments for CO 2 -Ar mixture up to 2000 K. With line position accuracy comparable to that of HITEMP, AI-3000K IR line list yields better agreements at more frequencies. Potential sources of discrepancies with experiment are discussed.

AI-3000K↗

DOE OSTI2014

Evidence for active galactic nucleus feedback in the broad absorption lines and reddening of MRK 231 {sup ,}

We present the first J-band spectrum of Mrk 231, which reveals a large He I* λ10830 broad absorption line with a profile similar to that of the well-known Na I broad absorption line. Combining this spectrum with optical and UV spectra from the literature, we show that the unusual reddening noted by Veilleux et al. is explained by a reddening curve like those previously used to explain low values of total-to-selective extinction in Type Ia supernovae. The nuclear starburst may be the origin and location of the dust. Spatially resolved emission in the broad absorption line trough suggests nearly full coverage of the continuum emission region. The broad absorption lines reveal higher velocities in the He I* lines (produced in the quasar-photoionized H II region) compared with the Na I and Ca II lines (produced in the corresponding partially ionized zone). Cloudy simulations show that a density increase is required between the H II and partially ionized zones to produce ionic column densities consistent with the optical and IR absorption line measurements and limits, and that the absorber lies ∼100 pc from the central engine. These results suggest that the He I* lines are produced in an ordinary quasar BAL wind that impacts upon, compresses, and accelerates the nuclear starburst's dusty effluent (feedback in action), and the Ca II and Na I lines are produced in this dusty accelerated gas. This unusual circumstance explains the rarity of Na I absorption lines; without the compression along our line of sight, Mrk 231 would appear as an ordinary iron low-ionization, broad absorption line quasar.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

THE FORMATION OF IRIS DIAGNOSTICS. VII. THE FORMATION OF THE O i 135.56 NM LINE IN THE SOLAR ATMOSPHERE

The O i 135.56 nm line is covered by NASA's Interface Region Imaging Spectrograph (IRIS) small explorer mission which studies how the solar atmosphere is energized. We study here the formation and diagnostic potential of this line by means of non-local thermodynamic equilibrium modeling employing both 1D semi-empirical and 3D radiation magnetohydrodynamic models. We study the basic formation mechanisms and derive a quintessential model atom that incorporates essential atomic physics for the formation of the O i 135.56 nm line. This atomic model has 16 levels and describes recombination cascades through highly excited levels by effective recombination rates. The ionization balance O i/O ii is set by the hydrogen ionization balance through charge exchange reactions. The emission in the O i 135.56 nm line is dominated by a recombination cascade and the line is optically thin. The Doppler shift of the maximum emission correlates strongly with the vertical velocity in its line forming region, which is typically located at 1.0–1.5 Mm height. The total intensity of the line emission is correlated with the square of the electron density. Since the O i 135.56 nm line is optically thin, the width of the emission line is a very good diagnostic of non-thermal velocities. We conclude that the O i 135.56 nm line is an excellent probe of the middle chromosphere, and compliments other powerful chromospheric diagnostics of IRIS such as the Mg ii h and k lines and the C ii lines around 133.5 nm.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2015

An Analysis of Representative Heating Load Lines for Residential HSPF Ratings

This report describes an analysis to investigate representative heating loads for single-family detached homes using current EnergyPlus simulations (DOE 2014a). Hourly delivered load results are used to determine binned load lines using US Department of Energy (DOE) residential prototype building models (DOE 2014b) developed by Pacific Northwest National Laboratory (PNNL). The selected residential single-family prototype buildings are based on the 2006 International Energy Conservation Code (IECC 2006) in the DOE climate regions. The resulting load lines are compared with the American National Standards Institute (ANSI)/Air-Conditioning, Heating, and Refrigeration Institute (AHRI) Standard 210/240 (AHRI 2008) minimum and maximum design heating requirement (DHR) load lines of the heating seasonal performance factor (HSPF) ratings procedure for each region. The results indicate that a heating load line closer to the maximum DHR load line, and with a lower zero load ambient temperature, is more representative of heating loads predicted for EnergyPlus prototype residential buildings than the minimum DHR load line presently used to determine HSPF ratings. An alternative heating load line equation was developed and compared to binned load lines obtained from the EnergyPlus simulation results. The effect on HSPF of the alternative heating load line was evaluated for single-speed and two-capacity heat pumps, and an average HSPF reduction of 16% was found. The alternative heating load line relationship is tied to the rated cooling capacity of the heat pump based on EnergyPlus autosizing, which is more representative of the house load characteristics than the rated heating capacity. The alternative heating load line equation was found to be independent of climate for the six DOE climate regions investigated, provided an adjustable zero load ambient temperature is used. For Region IV, the default DOE climate region used for HSPF ratings, the higher load line results in an ~28% increase in delivered heating load and an ~52% increase in the estimated heating operating cost over that given in the AHRI directory (AHRI 2014).

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

NASA NTRS1977

The structure of W49 A as deduced from molecular and recombination line observations

The molecular cloud complex W49 A has been observed in the 2.6-mm CO line, the 2-cm H2CO line, and the H76-alpha recombination line. These observations are most consistent with a picture of the complex in which a large H II region lies between two massive molecular clouds. Using a simple hydrodynamic model coupled with calculations of radiative transfer in the recombination lines, it is found that many of the spectral-line and continuum observations obtained on this region can be naturally explained, including: (1) the multiple structure observed in the molecular lines and the single structure in the recombination lines; (2) the local standard of rest (LSR) velocities of both the molecular and recombination lines; (3) the velocity gradients observed in the lines; (4) the continuum emission from the H II region; and (5) the line widths and line-to-continuum ratios of the recombination lines.

Mufson, S. L.↗

NASA NTRS2003

The XMM-Newton Iron Line Profile of NGC 3783

We report on observations of the iron K line in the nearby Seyfert 1 galaxy, NGC 3783, obtained in a long, 2 orbit (approx. 240 ks) XMM-Newton observation. The line profile obtained exhibits two strong narrow peaks at 6.4 keV and at 7.0 keV, with measured line equivalent widths of 120 and 35 eV respectively. The 6.4 keV emission is the K(alpha) line from near neutral Fe, whilst the 7.0 keV feature probably originates from a blend of the neutral Fe K(beta) line and the Hydrogen-like line of Fe at 6.97 keV. The relatively narrow velocity width of the K(alpha) line (approx. less than 5000 km/s), its lack of response to the continuum emission on short timescales and the detection of a neutral Compton reflection component are all consistent with a distant origin in Compton-thick matter such as the putative molecular torus. A strong absorption line from highly ionized iron (at 6.67 keV) is detected in the time-averaged iron line profile, whilst the depth of the feature appears to vary with time, being strongest when the continuum flux is higher. The iron absorption line probably arises from the highest ionization component of the known warm absorber in NGC 3783, with an ionization of log xi approx 3 and column density of N(sub H) approx. 5 x 10(exp 22)/sq cm and may originate from within 0.1 pc of the nucleus. A weak red-wing to the iron K line profile is also detected below 6.4 keV. However when the effect of the highly ionized warm absorber on the underlying continuum is taken into account, the requirement for a relativistic iron line component from the inner disk is reduced.

Reeves, J. N.↗

NASA NTRS2010

Pulsed Airborne Lidar Measurements of Atmospheric CO2 Column Absorption and Line Shapes from 3-13 km Altitudes

We have developed a pulsed lidar technique for measuring the tropospheric CO2 concentrations as a candidate for NASA's planned ASCENDS space mission. Our technique uses two pulsed laser transmitters allowing simultaneous measurement of a CO2 absorption line in the 1570 nm band, O2 extinction in the Oxygen A-band and surface height and backscatter. The lidar measures the energy and time of flight of the laser echoes reflected from the atmosphere and surface. The lasers are rapidly and precisely stepped in wavelength across the CO2 line and an O2 line region during the measurement. The direct detection receiver uses a telescope and photon counting detectors, and measures the background light and energies of the laser echoes from the surface along with scattering from any aerosols in the path. The gas extinction and column densities for the CO2 and O2 gases are estimated from the ratio of the on- and off- line signals via the DIAL technique. Time gating is used to isolate the laser echo signals from the surface, and to reject laser photons scattered in the atmosphere. The time of flight of the laser pulses are also used to estimate the height of the scattering surface and to identify cases of mixed cloud and ground scattering. We have developed an airborne lidar to demonstrate the CO2 measurement from the NASA Glenn Lear-25 aircraft. The airborne lidar steps the pulsed laser's wavelength across the selected CO2 line with 20 steps per scan. The line scan rate is 450 Hz, the laser pulse widths are 1 usec, and laser pulse energy is 24 uJ. The time resolved laser backscatter is collected by a 20 cm telescope, detected by a photomultiplier and is recorded by a photon counting system. We made initial airborne measurements on flights during fall 2008. Laser backscatter and absorption measurements were made over a variety of land and water surfaces and through thin clouds. The atmospheric CO2 column measurements using the 1572.33 nm CO2 lines. Two flights were made above the US Department of Energy's (DOE) SGP ARM site at altitudes from 3-8 km. These flights were coordinated with DOE investigators who flew an in-situ CO2 sensor on a Cessna aircraft under the path. The increasing CO2 line absorptions with altitudes were evident and comparison with in-situ measurements showed agreements to 6 ppm. In spring 2009 we improved the aircraft's nadir window and during July and August we made 9 additional 2 hour long flights and measured the atmospheric CO2 absorption and line shapes using the 1572.33 nm CO2 line. Measurements were made at stepped altitudes from 3-13 km over a variety of surface types in Nebraska, Illinois, the SGP ARM site, and near and over the Chesapeake Bay in North Carolina and eastern Virginia. Strong laser signals and clear CO2 line shapes were observed at all altitudes, and some measurements were made through thin clouds. The flights over the ARM site were underflown with in-situ measurements made from the DOE Cessna. Analysis shows that the average signal levels follow predicted values, the altimetry measurements had an uncertainty of about 4 m, and that the average optical line depths follow the number density calculated from in-situ sensor readings. The Oklahoma and east coast flights were coordinated with a LaRC/ITT CO2 lidar on the LaRC UC-12 aircraft, a LaRC in-situ CO2 sensor, and the Oklahoma flights also included a JPL CO2 lidar on a Twin Otter aircraft. More details of the flights, measurements, analysis and scaling to space will be described in the presentation.

Abshire, James↗

NASA NTRS2011

Structural Analysis of Pressurized Small Diameter Lines in a Random Vibration Environment

The pressurization and propellant feed lines for the Ares 1 Upper Stage Reaction and Roll Control Systems (ReCS and RoCS) were required to be in a high g-load random vibration flight environment. The lines connected the system components and were filled with both liquid hydrazine and gaseous helium. They are considered small and varied between one fourth to one inch in diameter. The random vibration of the lines was considered to be base excitation through the mating components and mounting hardware. It was found that reducing the amount of support structure for the lines added flexibility to the system and improved the line stresses from random vibration, but caused higher stresses from the static g-loads. The locations and number of brackets were optimized by analyzing the mode shapes of the lines causing high stresses. The use of brackets that only constrain motion in the direction of concern further reduced the stresses in the lines. Finite element analysis was used to perform the analysis. The lines were pre-stressed by temperature and internal pressure with fluid and insulation included as non-structural mass. Base excitation was added to the model using Power Spectral Density (PSD) data for the expected flight loads. The random vibration and static g-load cases were combined to obtain the total stress in the lines. This approach advances the state of the art in line analysis by using FEA to predict the stresses in the lines and to optimize the entire system based on the expected flight environment. Adding flexibility to lines has been used in piping system for temperature loads, but in flight environments flexibility has been limited for the static stresses. Adding flexibility to the system in a flight environment by reducing brackets has the benefit of reducing stresses and weight

Davis, Mark↗

NASA NTRS2012

Electron Stark Broadening Database for Atomic N, O, and C Lines

A database for efficiently computing the electron Stark broadening line widths for atomic N, O, and C lines is constructed. The line width is expressed in terms of the electron number density and electronatom scattering cross sections based on the Baranger impact theory. The state-to-state cross sections are computed using the semiclassical approximation, in which the atom is treated quantum mechanically whereas the motion of the free electron follows a classical trajectory. These state-to-state cross sections are calculated based on newly compiled line lists. Each atomic line list consists of a careful merger of NIST, Vanderbilt, and TOPbase line datasets from wavelength 50 nm to 50 micrometers covering the VUV to IR spectral regions. There are over 10,000 lines in each atomic line list. The widths for each line are computed at 13 electron temperatures between 1,000 K 50,000 K. A linear least squares method using a four-term fractional power series is then employed to obtain an analytical fit for each line-width variation as a function of the electron temperature. The maximum L2 error of the analytic fits for all lines in our line lists is about 5%.

Liu, Yen↗

NASA NTRS2018

Quantitative validation of Ames IR intensity and new line lists for (32/33/34)S(16)O2, (32)S(18)O2 and (16)O(32)S(18)O

The quality of Ames-296K SO2 Infrared (IR) line list intensities is first validated by quantitative exploration of several dipole moment surfaces (DMSs) and partition sum convergence. The DMSs are computed with several of Dunning’s correlation-consistent basis sets and their vibrational dependence are compared to the empirical model derived from Stark effect experiments reported by D. Patel, D. Margolese, and T.R. Dykea [J.Chem.Phys. 70, 2740 (1979)]. The effective dipole deviations from the DMS adopted in the Ames IR lists is 0.2-0.4% for vibrational states up to 3v3. The vibrational dependence of the dipole moment is also in good agreement, except for nv1. Partition sum convergence at 296K is confirmed by new calculations with rotational quantum number J up to 150 and upper state E’ up to 8000 cm-1. The isotopologue consistency of the Ames IR line lists is superior relative to the regular Effective Hamiltonian (EH) models and Effective Dipole Moment (EDM) models. The v1+v2 and v2+v3 intensity consistency check reveals the recently reported experimental intensities need significant improvement or re-analysis. After the accuracy, convergence, and isotopologue consistency have been confirmed, the theoretical Ames-296K intensities are combined with the experimental line positions or EH models that experimental spectroscopists published after 2009. Three high-resolution IR line sets are reported for the (32/33/34)S(16)O2, (32)S(18)O2 and (16)O(32)S(18)O isotopologues: (1) the “New Lines Sets” include experimentally measured line positions; (2) the “Expanded Line Sets” include possible transitions among new rovibrational levels assigned in experiments and ground state (GS) levels predicted by reliable EH models; (3) the “Ames + MARVEL Sets” include possible transitions among all those levels reported in a recent MARVEL analysis. [Tóbiás et al, JQSRT 208, 152 (2018)]. Compared to the limited data in High-resolution TRANsmission molecular absorption database (HITRAN), these line sets have significantly improved the data coverage up to 4000 cm-1. Some missing bands can be traced to the unpublished experimental data. The isotopologue consistency of these line sets will help identify the uncertainties and defects in the experimental EH and EDM models. These line sets are good candidates for the next HITRAN update, if line shape parameters are available. The line sets can be downloaded from supplementary files or from the Ames Molecular Spectroscopic Database at http://huang.seti.org.

Xinchuan Huang↗

DOE OSTI2025

Determining Drying Conditions to Mitigate Hanford Transfer Line Corrosion

Radioactive waste is stored in underground, carbon-steel double-shell tanks at the Department of Energy Hanford site.1,2,3 The underground transfer lines are used to transfer the waste between the tanks and other assets at the Hanford tank farm facilities. The transfer lines constructed before 1990 are pipe-in-pipe design with most of the lines having carbon steel carrier pipe and carbon steel encasements. The lines constructed after 1990 have a stainless-steel carrier with a carbon steel encasement. The carrier lines, which are in contact with the waste, provide a critical confinement function, while the encasements provide secondary containment to reduce the risk of a release and contamination to the environment. In 2022, a visual inspection of the annulus between the encasement and the carrier for one of the pre-1990 transfer lines revealed standing liquid in contact with the carrier pipe. Additionally, a significant build-up of corrosion products on the exterior of the carrier pipe and the interior of the encasement pipe was observed. To assess the extent of condition, borescope inspections were performed in the encasement space of additional transfer lines in the facility to provide a baseline. The inspection revealed that of the lines inspected, 29 had either moisture present or evidence that moisture had been present in the past (e.g., waterline corrosion where the pipe had been exposed to standing water). Additional inspections indicated several instances of pitting corrosion on the interior of the encasement and exterior the carrier transfer lines. An image of the carrier pipe with several pits is presented in Figure 1(a) and the profiled image of the transfer line section along with the pit depths are presented Figure 1(b). As seen in the figure, the deepest pit was 73 mils on the pipe section. These lines were designated as “do-not-use” until further compensatory actions are implemented to return the lines to service.

Shukla, Pavan K. [Savannah River National Laborato↗

DOE OSTI2014

The impact of gas bulk rotation on the Lyα line

We present results of radiative transfer calculations to measure the impact of gas bulk rotation on the morphology of the Lyα emission line in distant galaxies. We model a galaxy as a sphere with an homogeneous mixture of dust and hydrogen at a constant temperature. These spheres undergo solid-body rotation with maximum velocities in the range 0-300 km s{sup –1} and neutral hydrogen optical depths in the range τ{sub H} = 10{sup 5}-10{sup 7}. We consider two types of source distributions in the sphere: central and homogeneous. Our main result is that rotation introduces a dependence of the line morphology with viewing angle and rotational velocity. Observations with a line of sight parallel to the rotation axis yield line morphologies similar to the static case. For lines of sight perpendicular to the rotation axis, both the intensity at the line center and the line width increase with rotational velocity. Along the same line of sight, the line becomes single peaked at rotational velocities close to half the line width in the static case. Notably, we find that rotation does not induce any spatial anisotropy in the integrated line flux, the escape fraction or the average number of scatterings. This is because Lyman scattering through a rotating solid-body proceeds identically to the static case. The only difference is the Doppler shift from the different regions in the sphere that move with respect to the observer. This allows us to derive an analytic approximation for the viewing-angle dependence of the emerging spectrum, as a function of rotational velocity.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2018

Using Computational Fluid Dynamics to Assess Dynamic Line Rating in Southern Idaho

The overall goal of the study is to combine computational fluid dynamics (CFD) simulations with weather data that is collected over a 1-year long period across southern Idaho to calculate the dynamic line ratings (DLR) of several transmission lines. These ratings can be compared to the static rating assumptions to show the potential for additional current carrying capacity along transmission lines through account for additional effects of convective cooling from the wind. The region of interest is quite large, sized at 144 km by 98 km; in order to cover this large region, the CFD simulations are split into four separate regions of over 80 million computational cells each. The weather data that was collected suggest initial assumptions used to make the static ratings were vastly over predicted with regards to summer temperatures and solar irradiance. The weather data is ran through the General Line Ampacity State Solver (GLASS) tool that was developed by Idaho National Laboratory (INL) to parse large quantities of weather data across thousands of transmission midpoint spans in the region. For shorter lines, the dynamic line ratings often show large improvement over static ratings. The case study here shows over 95% of the time DLR values are above static values on the short transmission lines. However, for long lines, a conundrum occurs, where due to the large number of weather stations associated with the line, there is often a single weather station which may read local wind speeds of zero. This often defaults the line rating to be limited by natural convective cooling and does not show as much improvement over static as might be expected from the weather data if DLR calculations are used with a minimum ampacity across all midpoints. Other methods with transient state calculations should be utilized for long lines.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2025

Dynamic Line Rating Models and Their Potential for a Cost‐Effective Transition to Carbon‐Neutral Power Systems

Most transmission system operators (TSOs) currently use seasonally steady-state models considering limiting weather conditions that serve as reference to compute the transmission capacity of overhead power lines. The use of dynamic line rating (DLR) models can avoid the construction of new lines, market splitting, false congestions, and the degradation of lines in a cost-effective way. DLR can also be used in the long run in grid extension and new power capacity planning. In the short run, it should be used to help operate power systems with congested lines. The operation of the power systems is planned to have the market trading into account; thus, it computes transactions hours ahead of real-time operation, using power flow forecasts affected by large errors. In the near future, within a “smart grid” environment, in real-time operation conditions, TSOs should be able to rapidly compute the capacity rating of overhead lines using DLR models and the most reliable weather information, forecasts, and line measurements, avoiding the current steady-state approach that, in many circumstances, assumes ampacities above the thermal limits of the lines. Here, this work presents a review of the line rating methodologies in several European countries and the United States. Furthermore, it presents the results of pilot projects and studies considering the application of DLR in overhead power lines, obtaining significant reductions in the congestion of internal networks and cross-border transmission lines.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗

DOE OSTI2014

Constraining sub-parsec binary supermassive black holes in quasars with multi-epoch spectroscopy. II. The population with kinematically offset broad Balmer emission lines

A small fraction of quasars have long been known to show bulk velocity offsets (of a few hundred to thousands of km s{sup –1}) in the broad Balmer lines with respect to the systemic redshift of the host galaxy. Models to explain these offsets usually invoke broad-line region gas kinematics/asymmetry around single black holes (BHs), orbital motion of massive (∼sub-parsec (sub-pc)) binary black holes (BBHs), or recoil BHs, but single-epoch spectra are unable to distinguish between these scenarios. The line-of-sight (LOS) radial velocity (RV) shifts from long-term spectroscopic monitoring can be used to test the BBH hypothesis. We have selected a sample of 399 quasars with kinematically offset broad Hβ lines from the Sloan Digital Sky Survey (SDSS) Seventh Data Release quasar catalog, and have conducted second-epoch optical spectroscopy for 50 of them. Combined with the existing SDSS spectra, the new observations enable us to constrain the LOS RV shifts of broad Hβ lines with a rest-frame baseline of a few years to nearly a decade. While previous work focused on objects with extreme velocity offset (>10{sup 3} km s{sup –1}), we explore the parameter space with smaller (a few hundred km s{sup –1}) yet significant offsets (99.7% confidence). Using cross-correlation analysis, we detect significant (99% confidence) radial accelerations in the broad Hβ lines in 24 of the 50 objects, of ∼10-200 km s{sup –1} yr{sup –1} with a median measurement uncertainty of ∼10 km s{sup –1} yr{sup –1}, implying a high fraction of variability of the broad-line velocity on multi-year timescales. We suggest that 9 of the 24 detections are sub-pc BBH candidates, which show consistent velocity shifts independently measured from a second broad line (either Hα or Mg II) without significant changes in the broad-line profiles. Combining the results on the general quasar population studied in Paper I, we find a tentative anti-correlation between the velocity offset in the first-epoch spectrum and the average acceleration between two epochs, which could be explained by orbital phase modulation when the time separation between two epochs is a non-negligible fraction of the orbital period of the motion causing the line displacement. We discuss the implications of our results for the identification of sub-pc BBH candidates in offset-line quasars and for the constraints on their frequency and orbital parameters.

79 ASTRONOMY AND ASTROPHYSICS↗