Multiple Velocity Components Research Articles

ATOMS: ALMA three-millimetre observations of massive star-forming regions – XVI. Neutral versus ion line widths

ABSTRACT It has been suggested that the line width of ions in molecular clouds is narrower than that of the co-existing neutral particles, which has been interpreted as an indication of the decoupling of neutral turbulence from magnetic fields within a partially ionized environment. We calculate the principal component analysis (PCA) correlation coefficients of CCH versus H$^{13}$CO$^{+}$ and H$^{13}$CN versus H$^{13}$CO$^{+}$. We find aside from H$^{13}$CN, CCH could also be strongly spatial correlated with H$^{13}$CO$^{+}$ in high-mass star-forming regions. CCH and H$^{13}$CO$^{+}$ line emissions are strongly spatial correlated with each other in 48 per cent sources with a PCA correlation coefficient over 0.7. So, we investigate the ambipolar diffusion (AD) effect using CCH and H$^{13}$CO$^{+}$ lines as a neutral/ion pair in a sample of 129 high-mass star-forming clumps. We conduct a careful analysis of line widths of the CCH–H$^{13}$CO$^{+}$ pair pixel-by-pixel in 12 sources, which show a strong correlation in CCH–H$^{13}$CO$^+$ emission and no obvious outflows or multiple velocity components. The mean velocity dispersion of CCH is about the same as H$^{13}$CO$^{+}$ in 12 sources. In low-density regions of most sources, CCH shows a broader velocity dispersion than H$^{13}$CO$^{+}$. However, the AD effect is not significant from a statistical point of view.

Filamentary mass accretion towards the high-mass protobinary system G11.92–0.61 MM2

ABSTRACT We present deep, sub-arcsecond ($\sim$2000 au) resolution ALMA 0.82-mm observations of the former high-mass prestellar core candidate G11.92–0.61 MM2, recently shown to be an $\sim$500 au-separation protobinary. Our observations show that G11.92–0.61 MM2, located in the G11.92–0.61 protocluster, lies on a filamentary structure traced by 0.82-mm continuum and N$_2$H$^+$(4-3) emission. The N$_2$H$^+$(4-3) spectra are multipeaked, indicative of multiple velocity components along the line of sight. To analyse the gas kinematics, we performed pixel-by-pixel Gaussian decomposition of the N$_2$H$^+$ spectra using scousepy and hierarchical clustering of the extracted velocity components using acorns. Seventy velocity- and position-coherent clusters (called ‘trees’) are identified in the N$_2$H$^+$-emitting gas, with the eight largest trees accounting for $\gt $60 per cent of the fitted velocity components. The primary tree, with $\sim$20 per cent of the fitted velocity components, displays a roughly north–south velocity gradient along the filamentary structure traced by the 0.82-mm continuum. Analysing an $\sim$0.17 pc-long substructure, we interpret its velocity gradient of $\sim$10.5 km s$^{-1}$ pc$^{-1}$ as tracing filamentary accretion towards MM2 and estimate a mass inflow rate of $\sim 1.8\times 10^{-4}$ to 1.2$\times 10^{-3}$ M$_\odot$ yr$^{-1}$. Based on the recent detection of a bipolar molecular outflow associated with MM2, accretion on to the protobinary is ongoing, likely fed by the larger scale filamentary accretion flows. If 50 per cent of the filamentary inflow reaches the protostars, each member of the protobinary would attain a mass of 8 M$_\odot$ within $\sim 1.6\times 10^5$ yr, comparable to the combined time-scale of the 70-μm- and mid-infrared-weak phases derived for ATLASGAL-TOP100 massive clumps using chemical clocks.

Probing the physics of star formation (ProPStar)

Context. The detections of narrow channels of accretion toward protostellar disks, known as streamers, have increased in number in the last few years. However, it is unclear whether streamers are a common feature around protostars that were previously missed, or if they are a rare phenomenon. Aims. Our goals are to obtain the incidence of streamers toward a region of clustered star formation and to trace the origins of their gas to determine whether they originate within the filamentary structure of molecular clouds or from beyond. Methods. We used combined observations of the nearby NGC 1333 star-forming region, carried out with the NOEMA interferometer and the IRAM 30m single dish. Our observations cover the area between the systems IRAS 4 and SVS 13. We traced the chemically fresh gas within NGC 1333 with HC3N molecular gas emission and the structure of the fibers in this region with N2H+ emission. We fit multiple velocity components in both maps and used clustering algorithms to recover velocity-coherent structures. Results. We find streamer candidates toward 7 out of 16 young stellar objects within our field of view. This represents an incidence of approximately 40% of young stellar objects with streamer candidates in a clustered star-forming region. The incidence increases to about 60% when we only considered embedded protostars. All streamers are found in HC3N emission. Conclusions. Given the different velocities between HC3N and N2H+ emission, and because by construction, N2H+ traces the fiber structure, we suggest that the gas that forms the streamers comes from outside the fibers. This implies that streamers can connect cloud material that falls onto the filaments with protostellar disk scales.

Full L- and M-band high resolution spectroscopy of the S CrA binary disks with VLT-CRIRES+

Context. The Cryogenic IR echelle Spectrometer (CRIRES) instrument at the Very Large Telescope (VLT) was in operation from 2006 to 2014. Great strides in characterizing the inner regions of protoplanetary disks were made using CRIRES observations in the L- and M-band at this time. The upgraded instrument, CRIRES+, became available in 2021 and covers a larger wavelength range simultaneously. Aims. Here, we present new CRIRES+ Science Verification data of the binary system S Coronae Australis (S CrA). We aim to characterize the upgraded CRIRES+ instrument for disk studies and provide new insight into the gas in the inner disk of the S CrA N and S systems. Methods. We analyze the CRIRES+ data taken in all available L- and M-band settings, providing spectral coverage from 2.9 to 5.5 μm. Results. We detect emission from 12CO (v = 1−0, v = 2−1, and v = 3−2), 13CO (v = 1−0), hydrogen recombination lines, OH, and H2O in the S CrA N disk. In the fainter S CrA S system, only the12 CO v = 1−0 and the hydrogen recombination lines are detected. The 12CO v = 1−0 emission in S CrA N and S shows two velocity components, a broad component coming from ~0.1 au in S CrA N and ~0.03 au in S CrA S and a narrow component coming from ~3 au in S CrA N and ~5 au in S CrA S. We fit local thermodynamic equilibrium slab models to the rotation diagrams of the two S CrA N velocity components and find that they have similar column densities (~8×1016−4×1017 cm−2), but that the broad component is coming from a hotter and narrower region. Conclusions. Two filter settings, M4211 and M4368, provide sufficient wavelength coverage for characterizing CO and H2O at ~5 μm, in particular covering low- and high-J lines. CRIRES+ provides spectral coverage and resolution that are crucial complements to low-resolution observations, such as those with JWST, where multiple velocity components cannot be distinguished.

Fast fitting of spectral lines with Gaussian and hyperfine structure models

The fitting of spectral lines is a common step in the analysis of line observations and simulations. However, the observational noise, the presence of multiple velocity components, and potentially large data sets make it a non-trivial task. We present a new computer program Spectrum Iterative Fitter (SPIF) for the fitting of spectra with Gaussians or with hyperfine line profiles. The aim is to show the computational efficiency of the program and to use it to examine the general accuracy of approximating spectra with simple models. We describe the implementation of the program. To characterise its performance, we examined spectra with isolated Gaussian components or a hyperfine structure, also using synthetic observations from numerical simulations of interstellar clouds. We examined the search for the globally optimal fit and the accuracy to which single-velocity-component and multi-component fits recover true values for parameters such as line areas, velocity dispersion, and optical depth. The program is shown to be fast, with fits of single Gaussian components reaching on graphics processing units speeds approaching one million spectra per second. This also makes it feasible to use Monte Carlo simulations or Markov chain Monte Carlo calculations for the error estimation. However, in the case of hyperfine structure lines, degeneracies affect the parameter estimation and can complicate the derivation of the error estimates. The use of many random initial values makes the fits more robust, both for locating the global $ minimum and for the selection of the optimal number of velocity components.

Infall of material onto the filaments in Barnard 5

Aims. We aim to study the structure and kinematics of the two filaments inside the subsonic core Barnard 5 in Perseus using high-resolution (≈2400 au) NH3 data and a multi-component fit analysis. Methods. We used observations of NH3(1,1) and (2,2) inversion transitions using the Very Large Array (VLA) and the Green Bank Telescope (GBT). We smoothed the data to a beam of 8" to reliably fit multiple velocity components towards the two filamentary structures identified in B5. Results. Along with the core and cloud components, which dominate the flux in the line of sight, we detected two components towards the two filaments showing signs of infall. We also detected two additional components that can possibly trace new material falling into the subsonic core of B5. Conclusions. Following a comparison with previous simulations of filament formation scenarios in planar geometry, we conclude that either the formation of the B5 filaments is likely to be rather cylindrically symmetrical or the filaments are magnetically supported. We also estimate infall rates of 1.6 × 10−4 M⊙ yr−1 and 1.8 × 10−4 M⊙ yr−1 (upper limits) for the material being accreted onto the two filaments. At these rates, the filament masses can change significantly during the core lifetime. We also estimate an upper limit of 3.5 × 10−5 M⊙ yr−1 for the rate of possible infall onto the core itself. Accretion of new material onto cores indicates the need for a significant update to current core evolution models, where cores are assumed to evolve in isolation.

The Extended [C ii] under Construction? Observation of the Brightest High-z Lensed Star-forming Galaxy at z = 6.2

We present results of [C ii] 158 μm emission line observations, and report the spectroscopic redshift confirmation of a strongly lensed (μ ∼ 20) star-forming galaxy, MACS0308-zD1 at z = 6.2078 ± 0.0002. The [C ii] emission line is detected with a signal-to-noise ratio >6 within the rest-frame UV-bright clump of the lensed galaxy (zD1.1) and exhibits multiple velocity components; the narrow [C ii] has a velocity full width half maximum (FWHM) of 110 ± 20 km s−1, while broader [C ii] is seen with an FWHM of 230 ± 50 km s−1. The broader [C ii] component is blueshifted (−80 ± 20 km s−1) with respect to the narrow [C ii] component, and has a morphology that extends beyond the UV-bright clump. We find that, while the narrow [C ii] emission is most likely associated with zD1.1, the broader component is possibly associated with a physically distinct gas component from zD1.1 (e.g., outflowing or inflowing gas). Based on the nondetection of λ 158μm dust continuum, we find that MACS0308-zD1's star formation activity occurs in a dust-free environment indicated by a strong upper limit of infrared luminosity ≲9 × 108 L ⊙. Targeting this strongly lensed faint galaxy for follow-up Atacama Large Millimeter/submillimeter Array and JWST observations will be crucial to characterize the details of typical galaxy growth in the early Universe.

TRAO Survey of Nearby Filamentary Molecular Clouds, the Universal Nursery of Stars (TRAO-FUNS). III. Filaments and Dense Cores in the NGC 2068 and NGC 2071 Regions of Orion B

We present the results of molecular line observations performed toward the NGC 2068 and NGC 2071 regions of the Orion B cloud as the TRAO-FUNS project to study the roles of the filamentary structure in the formation of dense cores and stars in the clouds. Gaussian decomposition for the C18O spectra with multiple velocity components and the application of a friends-of-friends algorithm for the decomposed components allowed us to identify a few tens of velocity-coherent filaments. We also identified 48 dense cores from the observations of N2H+ using a core finding tool, FellWalker. We performed a virial analysis for these filaments and dense cores, finding that the filaments with N2H+ dense core are thermally supercritical, and the filaments with a larger ratio between the line mass and the thermal critical line mass tend to have more dense cores. We investigated the contribution of the nonthermal motions in dense cores and filaments, showing the dense cores are mostly in transonic/subsonic motions while their natal filaments are mostly in supersonic motions. This may indicate that gas turbulent motions in the filaments have been dissipated at the core scale to form the dense cores there. The filaments with (dynamically evolved) dense cores in infalling motions or with NH2D bright (or chemically evolved) dense cores are all found to be gravitationally critical. Therefore, the criticality of the filament is thought to provide a key condition for its fragmentation, the formation of dense cores, and their kinematical and chemical evolution.

FAUST

Context. Deuterium in H-bearing species is enhanced during the early stages of star formation. However, only a small number of high-spatial-resolution deuteration studies exist towards protostellar objects, leaving the small-scale structures of these objects unrevealed and understudied. Aims. We aim to constrain the deuterium fractionation ratios in a Class 0/I protostellar object in formaldehyde (H2CO), which has abundant deuterated isotopologues in this environment. Methods. We used the Atacama Large Millimeter Array (ALMA) within the context of the Large Program Fifty AU STudy of the chemistry in the disk/envelope system of Solar-like protostars (FAUST) to observe the Class 0/I protobinary system [BHB2007] 11, whose emission components are embedded in circumstellar disks that have radii of 2 to 3 au. The system is surrounded by a complex filamentary structure (the so-called streamers) connected to the larger circumbinary disk. In this work, we present the first study of formaldehyde D-fractionation towards this source with detections of H2CO 3(0,3)–2(0,2), combined with HDCO 4(2,2)–3(2,1), HDCO 4(1,4)–3(1,3) and D2CO 4(0,4)–3(0,3). These observations probe the structures of the protobinary system, enabling us to resolve multiple velocity components associated with the methanol hot spots also uncovered by FAUST data, as well as the colder external envelope. In addition, based on the kinematics seen in our observations of the H2CO emission, we propose the presence of a second large-scale outflow. Results. The results derived from our ALMA observations agree with the current literature in that we only find the deuterated species HDCO and D2CO in the central regions of the core, while undeuterated H2CO is found more ubiquitously. From our radiative transfer modelling, we the column density of H2CO to be in the range of (3-8) × 1014 cm−2 and that of HDCO to be within (0.8−2.9) × 1013 cm−2. The column density for the single detected velocity component of D2CO is within (2.6–1.3) × 1012 cm−2. This yields an average D/H ratio for formaldehyde in [BHB2007] 11 of $0.02_{ - 0.01}^{ + 0.02}$ from HDCO. The results of our kinematic model suggest that the dynamic feature is inconsistent with a streamer-like nature given the flat and outflowing velocity relation; we therefore tentatively conclude that the feature is an asymmetric molecular outflow launched by a wide-angle disk wind.

A Nitrogen-rich Supernova Remnant in M31: Interaction with the Circumstellar Medium at Late Times

We present the discovery of a supernova remnant in M31 which is unlike any other remnant known in that galaxy. An optical ground-based spectrum of WB92-26 taken at the MMT and sampling most of this marginally resolved object reveals strong lines of [O ii], [Ne iii], H i, [O iii], [O i], [N ii] and [S ii], though the H i lines are very weak and the [N ii] lines are very strong. Multiple velocity components are visible in those lines, with broad wings extending to −2000 and +1500 or 2000 km s−1 (the heliocentric velocity of M31 is −300 km s−1). The lines show strong peaks or shoulders near −750, −50, and +800 km s−1 in the M31 frame. The density implied by the [S ii] ratio combined with the X-ray luminosity, FUV flux, and optical size lead us to conclude that the optical emission lines are generated by shock waves, not photoionization. Consideration of the velocity structure indicates that the emission is from a shock in the circumstellar medium (CSM). This CSM must be depleted in hydrogen and enriched in helium and nitrogen through CNO processing, and it must have had a high velocity before the explosion of the parent star, to explain the broad wings in the emission lines. We estimate the CSM shell to have a mass of 2 M ⊙, implying a core-collapse SN. It is likely that Eta Car will produce a remnant resembling WB92-26 a few thousand years after it explodes.

Evidence for Multiple Shocks from the γ-Ray Emission of RS Ophiuchi

In 2021 August, the Fermi Large Area Telescope, H.E.S.S., and MAGIC detected GeV and TeV γ-ray emission from an outburst of recurrent nova RS Ophiuchi. This detection represents the first very high-energy γ-rays observed from a nova, and it opens a new window to study particle acceleration. Both H.E.S.S. and MAGIC described the observed γ-rays as arising from a single, external shock. In this paper, we perform detailed, multi-zone modeling of RS Ophiuchi’s 2021 outburst, including a self-consistent prescription for particle acceleration and magnetic field amplification. We demonstrate that, contrary to previous work, a single shock cannot simultaneously explain RS Ophiuchi’s GeV and TeV emission, in particular the spectral shape and distinct light-curve peaks. Instead, we put forward a model involving multiple shocks that reproduces the observed γ-ray spectrum and temporal evolution. The simultaneous appearance of multiple distinct velocity components in the nova optical spectrum over the first several days of the outburst supports the presence of distinct shocks, which may arise either from the strong latitudinal dependence of the density of the external circumbinary medium (e.g., in the binary equatorial plane versus the poles) or due to internal collisions within the white dwarf ejecta (which power the γ-ray emission in classical novae).

Structure and Kinematics of Sh2-138—A Distant Hub-filament System in the Outer Galactic Plane

We present a molecular line study of the Sh2-138 (IRAS 22308+5812) hub-filament system with the aim of investigating its structure and kinematics. Archival CO molecular line data from the Canadian Galactic Plane Survey (CO(J = 1–0)) for the wider region (∼50′ × 50′) and the James Clerk Maxwell Telescope (CO(3–2), 13CO(3–2), and C18O(3–2)) for the central portion (∼5′ × 5′) have been utilized. Analysis of the CO(1–0) spectra for the extended region in conjunction with the identification of the hub and filament using a column density map and the getsf tool, respectively, reveals a complex structure with the spectral extraction for the central position displaying multiple velocity components. Based on the Herschel 70 μm warm dust emission, one of the filaments in the extended region was inferred to be associated with active star formation, and is host to a Bolocam 1.1 mm clump of ∼1606 M ☉. An integrated intensity map of 13CO(3–2) emission, constructed from clumps detected at above 5σ in position–position–velocity space, reveals three filamentary structures (labeled the western filament (W-f), southwestern filament (SW-f), and southeast filament (SE-f)) in the central portion. Velocity gradients observed in 13CO(3–2) position–velocity slices point to longitudinal gas flow along the filaments into the central region. Filaments W-f, SW-f, and SE-f were calculated to have observed line masses of ∼32, 33.5, and 50 M ☉ pc−1, respectively. The cloud was found to be dominated by supersonic and nonthermal motions, with high Mach numbers (≳3) and a low thermal-to-nonthermal pressure ratio (∼0.01–0.1).

Velocity-coherent substructure in TMC-1: inflow and fragmentation

ABSTRACT Filamentary structures have been found nearly ubiquitously in molecular clouds and yet their formation and evolution is still poorly understood. We examine a segment of Taurus Molecular Cloud 1 (TMC-1) that appears as a single, narrow filament in continuum emission from dust. We use the Regularized Optimization for Hyper-Spectral Analysis (ROHSA), a Gaussian decomposition algorithm that enforces spatial coherence when fitting multiple velocity components simultaneously over a data cube. We analyse HC5N (9–8) line emission as part of the Green Bank Ammonia Survey and identify three velocity-coherent components with ROHSA. The two brightest components extend the length of the filament, while the third component is fainter and clumpier. The brightest component has a prominent transverse velocity gradient of 2.7 ± 0.1 km s−1 pc−1 that we show to be indicative of gravitationally induced inflow. In the second component, we identify regularly spaced emission peaks along its length. We show that the local minima between pairs of adjacent HC5N peaks line up closely with submillimetre continuum emission peaks, which we argue is evidence for fragmentation along the spine of TMC-1. While coherent velocity components have been described as separate physical structures in other star-forming filaments, we argue that the two bright components identified in HC5N emission in TMC-1 are tracing two layers in one filament: a lower density outer layer whose material is flowing under gravity towards the higher density inner layer of the filament.

Formation of hub–filament structure triggered by a cloud–cloud collision in the W33 complex

ABSTRACT Hub–filament systems are suggested to be the birth cradles of high-mass stars and clusters, but the formation of hub–filament structure is still unclear. Using FUGIN 13CO (1–0), C18O (1–0) and SEDIGISM 13CO (2–1) survey data, we investigate the formation of hub–filament structure in the W33 complex. The W33 complex consists of two colliding clouds, called W33-blue and W33-red. We decompose the velocity structures in W33-blue by fitting multiple velocity components and find a continuous and monotonic velocity field. Virial parameters of Dendrogram structures suggest the dominance of gravity in W33-blue. The strong positive correlation between velocity dispersion and column density indicates that the non-thermal motions in W33-blue may originate from gravitationally driven collapse. These signatures suggest that the filamentary structures in W33-blue result from the gravitational collapse of a compressed layer. However, the large-scale velocity gradient in W33-blue may originate mainly from cloud–cloud collision and feedback of active star formation, instead of filament-rooted longitudinal inflow. From the results observed above, we argue that cloud–cloud collision triggers the formation of hub–filament structures in the W33 complex. Meanwhile, the appearance of multiple-scale hub–filament structures in W33-blue is likely an imprint of the transition from a compressed layer to a hub–filament system.

Evidence for an Interaction between the Galactic Center Clouds M0.10–0.08 and M0.11–0.11

We present high-resolution (∼2–3″; ∼0.1 pc) radio observations of the Galactic center cloud M0.10−0.08 using the Very Large Array at K and Ka band (∼25 and 36 GHz). The M0.10−0.08 cloud is located in a complex environment near the Galactic center Radio Arc and the adjacent M0.11−0.11 molecular cloud. From our data, M0.10−0.08 appears to be a compact molecular cloud (∼3 pc) that contains multiple compact molecular cores (5+; <0.4 pc). In this study, we detect a total of 15 molecular transitions in M0.10−0.08 from the following molecules: NH3, HC3N, CH3OH, HC5N, CH3CN, and OCS. We have identified more than sixty 36 GHz CH3OH masers in M0.10−0.08 with brightness temperatures above 400 K and 31 maser candidates with temperatures between 100 and 400 K. We conduct a kinematic analysis of the gas using NH3 and detect multiple velocity components toward this region of the Galactic center. The bulk of the gas in this region has a velocity of 51.5 km s−1 (M0.10−0.08) with a lower-velocity wing at 37.6 km s−1. We also detect a relatively faint velocity component at 10.6 km s−1 that we attribute to being an extension of the M0.11−0.11 cloud. Analysis of the gas kinematics, combined with past X-ray fluorescence observations, suggests M0.10−0.08 and M0.11−0.11 are located in the same vicinity of the Galactic center and could be physically interacting.

The velocity structure of the intracluster medium during a major merger: Simulated microcalorimeter observations

Major mergers between galaxy clusters can produce large turbulent and bulk flow velocities in the intracluster medium (ICM) and thus imprint useful diagnostic features in X-ray spectral emission lines from heavy ions. As successfully achieved by Hitomi in observations of the Perseus cluster, measurements of gas velocities in clusters from high-resolution X-ray spectra will be achievable with upcoming X-ray calorimeters such as those on board XRISM, Athena, or a Lynx like mission. An interesting application to clusters involves detecting multiple velocity components or velocity gradients from diagnostic observations of specific interesting locations across the cluster. To explore this possibility in the case of a major head-on cluster merger, we performed velocity analyzes of a cluster-cluster merger from a hydrodynamical simulation by means of X-ray synthetic spectra with a spectral resolution on the order of a few eV. We observed the system along two extreme line-of-sight directions: (1) perpendicular to the plane of the merger and (2) along the merger axis. In these geometrical configurations, we found that clear non-Gaussian shapes of the iron He-like Kα line at 6.7 keV are expected. While the velocity dispersion predicted from the simulations can be retrieved for the brightest 100 ks pointings with XRISM Resolve, some discrepancy with respect to the expected value is noted and can be attributed to the complex non-Gaussian line shapes. Measurements in low surface brightness regions, especially when multiple velocity components are present along the line of sight, require high signal-to-noise ratio and the larger collecting area of the Athena X-IFU calorimeter is therefore required. With the latter, we also investigated the ICM temperature and velocity gradient across the merger bow shock edge, from 20″-wide annuli extracted from a single 1 Ms X-IFU observation. For both temperature and velocity dispersion, we found best-fit values that are consistent with predictions from the simulations within 1-σ. The uncertainties on the inferred velocity dispersion are, however, too large to place any stringent constraints on the shallow gradient downstream of the shock. Additionally, we present simulated images of the thermal and kinetic Sunyaev–Zeldovich effects from this merging system, using the above viewing configurations and compare the results at angular resolutions appropriate for future observatories such as CMB-S4 and the Atacama Large Aperture Submillimeter Telescope (AtLAST).

Efficient Loads Surrogates for Waked Turbines in an Array

Accurately and efficiently predicting wind turbine structural loading is a crucial step in wind farm design. Without considering structural loading, wind farm optimization could negatively impact turbine fatigue and ultimate loads, especially for waked and partially waked turbines, which could result in higher maintenance costs and reduced turbine lifetime. However, predicting turbine loads throughout an array is a costly step, as these quantities require time-accurate results across long time histories, which is often intractable for large array optimization. Therefore, surrogate models that link array spacing to load outputs are often used, but the surrogates are then unique to the inflow conditions and array configurations in the training library. This work develops surrogate models for many wind turbine load outputs based solely on rotor plane velocity measurements, with no required input about array configuration or freestream inflow parameters. Surrogate models were constructed for many turbine quantities of interest (QoI), considering mean, standard deviation, ultimate, and fatigue loads. In general, most QoI statistics were accurately captured, as measured by predicted vs. actual correlation coefficient, confirming the suitability of the approach. Temporal mean values of the QoI required only temporal mean measurements of the rotor plane inflow velocity. However, accurate prediction of temporal standard deviation, ultimate, and fatigue values of QoI also required temporal standard deviations of the rotor plane velocity field. Poor surrogate performance was observed when too many correlated inputs were used, such as multiple velocity components. If the fewest inflow parameters are used to construct the surrogates, the average correlation coefficient value for all output QoI statistics is 0.89. Surrogates for standard deviations and damage equivalent loads (DELs) of turbine QoIs generally had lower accuracy and tower-base and shaft load channels posed the most difficult to capture accurately. The results suggest that these surrogates could be easily paired with analytic wake models, which are frequently used for pre-construction wind farm array optimization, to account for turbine loading in addition to power production. By including the optimal inflow conditions, the surrogate accuracy can improve to an average correlation coefficient value for all output QoI statistics of 0.92. This work has established the ability to build accurate surrogates for mean, standard deviation, ultimate load, and DEL turbine QoI values based on the rotor plane inflow velocity, and identified which inflow conditions lead to greater surrogate accuracy.

UV Counterpart of an X-Ray Ultrafast Outflow in IRAS 17020+4544

We report on the discovery of a UV absorption counterpart of a low-ionization X-ray ultrafast outflow (UFO) in the narrow-line Seyfert 1 galaxy IRAS 17020+4544. This UV signature of the UFO is seen as a narrow and blueshifted Lyα absorption feature in the far-UV spectrum, taken with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST). The Lyα feature is found to be outflowing with a velocity of −23,430 km s−1 (0.078 c). We carry out high-resolution UV spectroscopy and photoionization modeling to study the UFO that is seen in the HTS/COS spectrum. The results of our modeling show that the UV UFO corresponds to a low-ionization, low-velocity component of the X-ray UFO found previously with XMM-Newton’s Reflection Grating Spectrometer. The other higher-velocity and higher-ionization components of the X-ray UFOs are not significantly detected in the HST/COS spectrum, consistent with predictions of our photoionization calculations. The multiple ionization and velocity components of the UFOs in IRAS 17020+4544 suggest a scenario where a powerful primary UFO entrains and shocks the ambient medium, resulting in formation of weaker secondary UFO components, such as the one found in the UV band.

HCN and HCO+ in Planetary Nebulae: The Next Level

Abstract Observations of HCN and HCO+ have been carried out toward 13 planetary nebulae (PNe) using the facilities of the Arizona Radio Observatory (ARO). These nebulae represent a wide range of morphologies and ages (∼2000–28,000 yr). For both molecules, the J = 1 → 0 transitions at 88–89 GHz and the J = 3 → 2 lines at 265–267 GHz were measured, together with CO lines (J = 1 → 0, 2 → 1, and 3 → 2, depending on the source), using the ARO 12 m and Submillimeter Telescopes. HCN and HCO+ were detected with at least one transition in 10 nebulae: He 2-459, Hu 1-1, K3-52, K3-65, M1-8, M1-40, M1-59, M2-53, M4-17, and NGC 6445. HCO+ was additionally identified via two transitions in Na 2. Some observed line profiles were complex, with multiple velocity components tracing varied outflows. From radiative transfer modeling, column densities were established for HCN and HCO+: N tot(HCN) = 0.005–1.1 × 1014 and N tot(HCO+) = 0.008–9.5 × 1013 cm−2. Gas densities of n(H2) ∼ 105–107 cm−3 were also determined for all PNe. Fractional abundances with respect to H2, calculated using CO as a proxy, are f(HCN) ∼ 0.2–1.5 × 10−7 and f(HCO+) ∼ 0.3–5.1 × 10−8. The abundances of HCN and HCO+ did not significantly vary with nebular age to 28,000 yr. Combined with previous observations, at least 30 PNe contain HCN and/or HCO+, indicating that polyatomic molecules are common constituents of these objects. The data strongly support a scenario where dense ejecta from PNe seed the interstellar medium with molecular material.

Optical time-of-flight and spectroscopic investigation of laser produced barium plasma in presence of magnetic field and ambient gas

Optical-time-of-flight and time-resolved spectroscopy of barium ions and neutral have been performed to study the multiple velocity components and spectral behaviour of laser-produced barium plasma in the presence of ambient gas and magnetic field. Initial structured temporal profiles of ionic and neutral species in vacuum due to different velocity components get more pronounced in the presence of ambient gas, magnetic field and combination of both. Multi-Shifted Maxwell-Boltzmann distribution functions are used to analyse different velocity components. Each component behaves differently with ambient gas and magnetic field which is reflected in their shape and intensity variation. The observed results are explained on the basis of characteristic expansion of the plasma plume under different ambient conditions and possible role of excitation and ionization processes.