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A variable cross-section combustion chamber with different inner cone length L is designed, composing of an annular part with divergent width and a cylinder part without inner cone. Ethylene-air and hydrogen-air continuous rotating detonation (CRD) experimental tests are conducted. The results show that the ethylene-air CRD wave can be achieved in the variable cross-section combustor with the short inner cone. The propagation velocity of ethylene-air CRD wave can be 1661.37 m/s with the equivalence ratio of 0.91 and L of 10 mm. With L increasing from 0 mm to 30 mm, the combustion mode varies in the single wave mode, the sawtooth wave mode, and the hybrid mode. The combustor width is not the main factor leading to the failure of detonation in this study. The acceleration of propellent mixture caused by the expansion of the annulus channel, and the downstream movement and reduction of recirculation zone around the inner cone both increase the difficulty in CRD realization. While the hydrogen-air CRD can self-sustain with the intensive reaction zone in the annular part in the critical configuration of ethylene-air CRD. This study will contribute to the understandings of self-sustaining mechanism of CRD in the divergent combustor and the combustor design of the hollow chamber. • A combustor composing of a divergent annular part and a cylinder part is designed. • Coupling of reaction zone and shock wave in hybrid mode is verified quantitatively. • Combustor width is not the main factor leading to failure in divergent combustor. • Propellent acceleration and recirculation zone reduction destory CRD realization. • H 2 -air CRD self-sustain in annular part in the critical combustor of C 2 H 4 -air CRD. [ABSTRACT FROM AUTHOR]

A method for resident space object detection in video stream processing using a set of matched filters has been proposed. Matched filters are constructed based on the connection between the Fourier spectrum shape of the difference frame and the magnitude of the linear velocity projection onto the observation plane. Experimental data were obtained using the mobile optical surveillance system for low-orbit space objects. The detection problem in testing mode was solved for raw video data with intensity signals from three satellites: KORONAS-FOTON, CUSAT 2/FALCON 9, and GENESIS-1. Difference frames of video data with the AQUA satellite pass were used to construct matched filters. The satellites were automatically detected at points where the difference in the value of their linear velocity projection and the reference satellite was close in value. An initial approximation of the satellites slant range vector and position vector has been obtained based on the values of linear velocity projection onto the frame plane. It has been established that the difference in the inclination angle between the detected satellite intensity signal Fourier image and the reference satellite mask corresponds to the difference in the inclinations of these objects. The proposed method allows for detecting and estimating the initial approximation of the slant range and position vector of artificial and natural space objects, such as satellites, debris, and asteroids.

Abstract The phenomenon known as strong thermal emission velocity enhancement (STEVE) is a purple/mauve arc-shaped atmospheric glow observed at lower latitudes of the auroral oval on the duskside. Simultaneous observations using a ground-based camera and a low-altitude satellite have shown that STEVE is accompanied by rapid westward ion flows. Such fast ion flows are termed the subauroral ion drift (SAID) or subauroral polarization stream (SAPS). Similarly, an eastward fast ion flow known as the dawnside auroral polarization stream (DAPS) is observed within the Region 1 current on the dawnside. If the optical phenomenon triggered by SAID/SAPS corresponds to STEVE, a comparable optical phenomenon should be driven by DAPS. Thus far, however, such a phenomenon has not been reported. This study discovers, for the first time, a purple-colored optical phenomenon characterized by the fast eastward ion flows, a possible signature of DAPS, occurring poleward of the bright green arc in the post-midnight sector. We present color all-sky images obtained by a ground-based commercial digital camera, along with wide-coverage optical measurements and in-situ data from low-altitude satellites. The results imply that this glow requires not only a high-speed ion flow but also its sharp latitudinal gradient at the boundary between the Region 1 and 2. Graphical Abstract

The phenomenon known as strong thermal emission velocity enhancement (STEVE) is a purple/mauve arc-shaped atmospheric glow observed at lower latitudes of the auroral oval on the duskside. Simultaneous observations using a ground-based camera and a low-altitude satellite have shown that STEVE is accompanied by rapid westward ion flows. Such fast ion flows are termed the subauroral ion drift (SAID) or subauroral polarization stream (SAPS). Similarly, an eastward fast ion flow known as the dawnside auroral polarization stream (DAPS) is observed within the Region 1 current on the dawnside. If the optical phenomenon triggered by SAID/SAPS corresponds to STEVE, a comparable optical phenomenon should be driven by DAPS. Thus far, however, such a phenomenon has not been reported. This study discovers, for the first time, a purple-colored optical phenomenon characterized by the fast eastward ion flows, a possible signature of DAPS, occurring poleward of the bright green arc in the post-midnight sector. We present color all-sky images obtained by a ground-based commercial digital camera, along with wide-coverage optical measurements and in-situ data from low-altitude satellites. The results imply that this glow requires not only a high-speed ion flow but also its sharp latitudinal gradient at the boundary between the Region 1 and 2. [ABSTRACT FROM AUTHOR]

Particle dampers (PD) can be embedded in structures fabricated via selective laser melting (SLM) because the raw powder (particle diameter : several tens of micrometers) remains in closed spaces during SLM. However, most PD studies have focused on coarse particle sizes larger than 1 mm and low frequencies below 100 Hz; there is insufficient evaluation of PD attenuation characteristics and particle behavior for particle sizes from tens of micrometers to sub-millimeters and in the 100 to 1000 Hz band. In this study, the equivalent viscous damping coefficients of spherical zirconia balls with nominal sizes of 0.05, 0.10, 0.20, and 0.40 mm are measured under different vibration accelerations (from 9 to 148 m/s2(rms)) and frequencies (from 100 to 800 Hz) to experimentally investigate the effect of fine particle diameters on the damping properties. It is deduced that in the frequency range above 200 Hz, the equivalent viscous damping coefficients of the coarse particle diameter are greater than those of fine particles at accelerations below the range of 15.7–22.4 m/s2(rms). In contrast, the equivalent viscous damping coefficients of the fine particles are greater than those of the coarse particles at accelerations above the 15.7–22.4 m/s2(rms) range. In addition, to determine the reason for these tendencies, the behavior of particles with a nominal size of 0.05 mm, which is close to the raw powder, is observed through a window using a high-speed microscope camera. The results reveal that in the low acceleration range, the inertial force does not overcome the static friction force owing to poor flowability caused by adhesion force, and the particles are always stationary with respect to the sealed container.

Characterizing the temporal evolution of the three‐dimensional structure of the Io plasma torus is essential to understand the dynamics of the Jovian magnetosphere. Optical imaging is a powerful tool to uncover the global torus structure. Currently, two ground‐based optical telescopes with diameters of 0.8 and 1.8 m, respectively, are under construction at the Lenghu Observatory for Planetary Science on the Tibetan Plateau of China, to systematically observe the Io plasma torus at wavelengths between 392 and 1,100 nm. These telescopes will begin to operate in the end of 2023. In order to support the inversion and scientific interpretation of the Io plasma torus images, we perform systematic simulations of the Io plasma torus in this work. First, a three‐dimensional model of electron and ion densities and electron temperature is constructed first. Then, the emissions of O+ 372.7 nm, O+ 372.9 nm, S+ 406.9 nm, S+ 671.8 nm, S+ 673.1 nm, and S++ 953.2 nm are simulated from the perspective of observing from the Earth. The simulated emission intensities and distributions are consistent with previous observations. This work provides a state‐of‐the‐art convenient tool for ground‐based telescope observation of the Io plasma torus at a specific site and time and also benefits future inversion of images to obtain physical parameters of Io plasma torus. Plain Language Summary: The Io plasma torus is composed of ionized material encircling Jupiter near Io's orbital radius. Volcanic eruptions on Io, the most geologically active object in the solar system, are the main source of plasmas in the Io plasma torus. The dynamics and evolutions of the Io plasma torus is crucial to understand the mass and energy transportation in Jovian magnetosphere. The bight lines of ionized sulfur make optical imaging a useful tool for studying the global structure of the torus. Two new telescopes are being constructed at Lenghu, Qinghai, China, for this purpose. To instruct future observations and help interpret the images captured by these telescopes, we compiled a three‐dimensional model of the torus with state‐of‐the‐art plasma models from the literature and simulated the emissions at certain wavelengths of light. The simulation results match well with previous observations and will be useful for analyzing data obtained by the new telescopes. This work will provide a valuable tool for studying the Io plasma torus and obtaining physical parameters of this structure. Key Points: Io plasma torus is an important structure in the Jovian magnetosphere to understand its evolutionA three‐dimensional empirical model of the torus is compiled and used to simulate the images from ground stationsThe simulated images torus consistent well with ground observations and would be valuable for future observations at Lenghu station [ABSTRACT FROM AUTHOR]

Abstract Characterizing the temporal evolution of the three‐dimensional structure of the Io plasma torus is essential to understand the dynamics of the Jovian magnetosphere. Optical imaging is a powerful tool to uncover the global torus structure. Currently, two ground‐based optical telescopes with diameters of 0.8 and 1.8 m, respectively, are under construction at the Lenghu Observatory for Planetary Science on the Tibetan Plateau of China, to systematically observe the Io plasma torus at wavelengths between 392 and 1,100 nm. These telescopes will begin to operate in the end of 2023. In order to support the inversion and scientific interpretation of the Io plasma torus images, we perform systematic simulations of the Io plasma torus in this work. First, a three‐dimensional model of electron and ion densities and electron temperature is constructed first. Then, the emissions of O+ 372.7 nm, O+ 372.9 nm, S+ 406.9 nm, S+ 671.8 nm, S+ 673.1 nm, and S++ 953.2 nm are simulated from the perspective of observing from the Earth. The simulated emission intensities and distributions are consistent with previous observations. This work provides a state‐of‐the‐art convenient tool for ground‐based telescope observation of the Io plasma torus at a specific site and time and also benefits future inversion of images to obtain physical parameters of Io plasma torus.

A specialized ground‐based system has been developed for simultaneous observations of pulsating aurora (PsA) and related magnetospheric phenomena with the Arase satellite. The instrument suite is composed of (a) six 100 Hz sampling high‐speed all‐sky imagers (ASIs), (b) two 10 Hz sampling monochromatic ASIs observing 427.8 and 844.6 nm auroral emissions, (c) a 20 Hz sampling fluxgate magnetometer. The 100 Hz ASIs were deployed in four stations in Scandinavia and two stations in Alaska, which have been used for capturing the main pulsations and quasi 3 Hz internal modulations of PsA at the same time. The 10 Hz sampling monochromatic ASIs have been operative in Tromsø, Norway with the 20 Hz sampling magnetometer. Combination of these multiple instruments with the European Incoherent SCATter (EISCAT) radar enables us to detect the low‐altitude ionization due to energetic electron precipitation during PsA and further to reveal the ionospheric electrodynamics behind PsA. Since the launch of the Arase satellite, the data from these instruments have been examined in comparison with the wave and particle data from the satellite in the magnetosphere. In the future, the system can be utilized not only for studies of PsA but also for other classes of aurora in close collaboration with the planned EISCAT_3D project. Key Points: An integrated package of instruments for high‐time resolution measurements of pulsating aurora was deployed in Scandinavia and AlaskaThe system has enabled us to capture the fine‐scale spatio‐temporal variations of pulsating aurora in a wide areaData from those instruments have also been used for simultaneous observations of pulsating aurora with the Arase satellite [ABSTRACT FROM AUTHOR]

We present a study of the [O iii ] λ 5007 line profile in a subsample of eight active galactic nuclei (AGNs) and six non-AGNs in the optically selected green valley at z < 0.5 using long-slit spectroscopic observations obtained with the 11 m Southern African Large Telescope. Gaussian decomposition of the line profile was performed to study its different components. We observe that the AGN profiles are more complex than the non-AGN ones. In particular, in most AGNs (5/8) we detect a blue wing of the line. We derive the FWHM velocities of the wing and systemic component, and find that the AGNs show higher FWHM velocities than the non-AGNs in their core component. We also find that the AGNs show blue wings with a median velocity width of approximately 600 km s−1, and a velocity offset from the core component in the range −90 to −350 km s−1, in contrast to the non-AGN galaxies, where we do not detect blue wings in any of their [O iii ] λ 5007 line profiles. Using the spatial information in our spectra, we show that at least three of the outflow candidate galaxies have centrally driven gas outflows extending across the whole galaxy. Moreover, these are also the galaxies which are located on the main sequence of star formation, raising the possibility that the AGNs in our sample are influencing the star formation of their host galaxies (such as positive feedback). This is in agreement with our previous work where we studied the star formation, morphology, and stellar population properties of a sample of green valley AGNs and non-AGN galaxies. [ABSTRACT FROM AUTHOR]

For the initial orbit determination of uncharted space objects, the operation method for obtaining three or more streak images was proposed and a design parameter analysis of a narrow field of view optical observation system was performed for this purpose. The proposed operational concept consists of repetitive forms of point tracking, streak center point prediction, mount gimbal maneuver, and streak image acquisition for unknown space objects. The central point prediction was performed using Kalman Filter based on a constant acceleration model and analysis was performed in terms of telescope mount gimbal maneuver and stabilization performance by fixing the exposure time for streak shooting. As a result of the simulation for the entire optical observation system, the ratio of the error value defined from the telescope center point to the streak center point is within 2% with respect to FOV. Consecutive streak images can be reliably obtained using the proposed system. [ABSTRACT FROM AUTHOR]

The stellar initial mass function (IMF) is expressed by ϕ (m) ∝ m − α with the slope α, and known as a poorly constrained but very important function in studies of star and galaxy formation. There are no sensible observational constraints on the IMF slopes beyond the Milky Way and nearby galaxies. Here we combine two sets of observational results, (1) cosmic densities of core-collapse supernova (CCSN) explosion rates and (2) cosmic far-UV radiation (and infrared reradiation) densities, which are sensitive to massive (≃8–50 M ⊙) and moderately massive (≃2.5–7 M ⊙) stars, respectively, and constrain the IMF slope at m > 1 M ⊙ with a freedom of redshift evolution. Although no redshift evolution is identified beyond the uncertainties, we find that the cosmic-average IMF slope at z = 0 is α = 1.8–3.2 at the 95% confidence level that is comparable with the Salpeter IMF, α = 2.35, which marks the first constraint on the cosmic-average IMF. We show a forecast for the Nancy Grace Roman Space Telescope supernova survey that will provide significantly strong constraints on the IMF slope with δ α ≃ 0.5 over z = 0–2. Moreover, as for an independent IMF probe instead of (1), we suggest to use diffuse supernovae neutrino background (DSNB), relic neutrinos from CCSNe. We expect that the Hyper-Kamiokande neutrino observations over 20 yr will improve the constraints on the IMF slope and the redshift evolution significantly better than those obtained today, if the systematic uncertainties of DSNB production physics are reduced in the future numerical simulations. [ABSTRACT FROM AUTHOR]

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The Wide-Field Imager for Solar Probe (WISPR) on the Parker Solar Probe (PSP) mission maps the brightness produced by the zodiacal dust cloud (ZDC) from an historically unprecedented viewpoint. The brightness results from the scattering of photospheric light by dust particles in the ZDC, and is called zodiacal light (ZL). We exploit the PSP nominal science encounters in orbits 10 through 16 for an in-depth study of the location and brightness evolution of the symmetry axis of the ZL in images taken with the WISPR outer telescope (WISPR-O). During these 11 day encounters, PSP covered heliocentric distances between 0.25 and 0.0617 au (∼53.78−13.28 R _☉ ) and ∼255° in helioecliptic longitude from within the orbital plane of Venus. The unique WISPR-O viewpoint, which comprises line-of-sight elongations of 80° ± 27°, has led to further insights about the ZDC. Namely, we find that the gravitational pull of the planets warps the ZDC symmetry plane and shifts the ZDC towards the solar system barycenter, creating an east–west asymmetry in the ZL brightness. Additionally, our analysis provides the first consistent observational evidence of a circumsolar dust enhancement resulting from the sublimation of dust grains at ∼25 R _☉ . Overall, the WISPR observations from the PSP platform are opening a new window in the remote sensing of the ZDC.

We report radar, photometric, and visible-wavelength spectrophotometry observations of NEA 2018 EB obtained in 2018. The radar campaign started at Goldstone (8560 MHz, 3.5 cm) on April 7, and it was followed by more extensive observations from October 5 to 9 by both Arecibo (2380 MHz, 12.6 cm) and Goldstone. 2018 EB was observed optically on April 5, 8, and 9 and again on October 18. Spectrophotometry was obtained on October 19 with the SOAR telescope, and the data suggest that 2018 EB is an Xk-class object. The echo power spectra and delay-Doppler radar images revealed that 2018 EB is a binary system. Radar images constrained the satellite's diameter to ${0.15}_{-0.05}^{+0.02}$ km, but the data were not sufficient for shape modeling. Shape modeling of lightcurves and radar data yielded an oblate primary with an effective diameter D = 0.30 ± 0.04 km and a sidereal rotation period of ${4.3}_{-0.5}^{+0.6}$ hr. Measurements of delay-Doppler separations between the centers of mass of the primary and the satellite, along with the timing of a radar eclipse observed on October 9, resulted in an orbit fit for the satellite with a semimajor axis of ${0.50}_{-0.01}^{+0.04}$ km, an eccentricity of 0.15 ± 0.04, a period of ${16.85}_{-0.26}^{+0.33}$ hr, and an orbit pole constrained to the ecliptic longitudes and latitudes of $\lambda ={93}_{-{43}^{^\circ }}^{+{27}^{^\circ }}$ and $\beta ={48}_{-{18}^{^\circ }}^{+{7}^{^\circ }}$ . The system mass was estimated to be ${2.03}_{-0.08}^{+0.52}\times {10}^{10}$ kg, which yielded a bulk density of ${1.4}_{-0.5}^{+0.6}$ g cm ^−3 . Our analysis suggests that 2018 EB has a low optical albedo of p _V = 0.028 ± 0.016 and a relatively high radar albedo of η _OC = 0.29 ± 0.11 at Arecibo and η = 0.22 ± 0.10 at Goldstone.

Ground-based optical observation of GEO space debris plays an essential role in tracking, identifying, cataloging, and classifying space debris. The factors that affect the brightness of space debris include size, surface material, illumination geometry, attitude, shape, position, and so on. In order to better understand the influence of the above factors on the brightness of space debris, the synthetic light curves are analyzed. The Ashikhmin–Shirley model is chosen to simulate the light curves of space debris. The effects of orbit, attitude, model parameters, and the location of the observation station on the synthetic light curves are analyzed by the control variable method. Based on the Markov Chain Monte Carlo method (MCMC), the optimal model parameters that characterize the surface material of space debris can be obtained by comparing the synthetic light curves with the observed light curves under certain shape, orbit, and attitude characteristics. The results are roughly in good agreement with those measured in the laboratory. [ABSTRACT FROM AUTHOR]

The threat of icing caused by supercooled water droplets on aircraft components such as wings and compressors is a serious concern for aviation safety, and the surface roughness of these components can experience alterations due to environmental corrosion or damage. However, the potential impact of surface roughness variation on their susceptibility to icing remains unclear. In this study, the freezing experiments of sessile water droplets on the surfaces of a typical aero-engine titanium alloy (ZTC4) with varying roughness were conducted using a laser confocal micro-Raman spectrometer with a heating/freezing stage. Three freezing stages were captured via an optical microscope, and the temperature changes of water droplet during the cooling process were explored through heat transfer simulation. In addition, the relationship between Raman peaks and temperatures of frozen droplets was quantified. The results of 200 repeated experiments demonstrated that the freezing temperatures of sessile water droplets exhibited a two-parameter Weibull distribution, and there was a nonlinear positive correlation between the mean freezing temperature and surface roughness, which implied that environmental corrosion or damage leading to an increase in surface roughness may significantly elevate the probability of component icing and safety issues. • The freezing and heat transfer process of droplets were explored through optical observation and numerical simulation. • The relationship between Raman peaks and temperatures of frozen droplets was quantified. • The freezing temperature of water droplets exhibited Weibull distribution. • The positive correlation between freezing temperature and surface roughness was revealed. [ABSTRACT FROM AUTHOR]

In this paper, the growth of finger-like droplets inside various polymer membrane embryos induced by non-solvent phase separation (NIPS) is studied in details by using a standardized optical microscopic observation method. The boundary conditions of the phase separation are well-defined by microfluidics technology. The growth of finger-like droplets and Marangoni convection inside them are tracked and recorded by high-speed camera of sharp resolutions. Effects of the geometry of the membrane embryos (thickness/shape/size), humidity of the atmosphere and the viscosity of the embryos on the growth of finger-like droplets are systematically studied. Except the qualitative observations that are consistent to previous relative reports, more quantitative data are provided in this paper. The diffusing speed of the interface of the developing large droplets is measured by template matching algorithm. Strikingly, the time-dependent diffusing speed of the developing large droplets shows a wave-like declining pattern, which indicates that fluctuating boundary conditions are surrounding the membrane embryos. The Reynolds number of the flow inside the developing large droplets is estimated at the order of 10−5, the magnitude of which is 2 order smaller than that of a swimming sperm. [Display omitted] • The traditional optical direct observation method is improved to study the growth of finger-like droplets. • Both quantitatively and qualitative data are provided to illustrate the growth dynamics of finger-like droplets. • Macro-flows (Marangoni convection) inside the developing large droplets are clearly observed and analyzed. [ABSTRACT FROM AUTHOR]

This paper defines an effectiveness index for optical continuous observation of unknown space objects and presents a range of design variables combinations that can satisfy the effectiveness index from a telescope/mount control system perspective using integrated simulation. The overall system-level simulation was implemented and the tracking performance was analyzed by considering design variables such as target position prediction and frame rate, image processing time and measurement error, target trajectory characteristics, and maneuver performance of mount gimbal. As a result of the analysis, it was confirmed that the continuous tracking performance of the optical observation system is dependent on the combination of frame rate and mount maneuver performance. In a situation where an optical observation system is designed or a similar system is implemented using COTS, an appropriate combination of parameters between design variables can be found through effectiveness analysis simulation as in this study. [ABSTRACT FROM AUTHOR]

• A discharge test for scaled wind turbine is performed to examine the lightning discharge characteristics of rotating wind turbines. • The physical process of long gap discharge of stationary and rotating wind turbine with different electrode forms was observed. • The mechanism on lightning striking to rotating wind turbines is studied. • The upward leader develops slightly faster in the rotating condition. In this study, a discharge test for scaled wind turbine is performed to examine the lightning discharge characteristics of rotating wind turbines, and an observation platform is designed. Moreover, the wind turbines are subjected to discharge simulation with rod and arc electrodes, and high-speed and single-lens reflex cameras are used to observe the physical discharge process. Under the rod electrode, the downward leader is initiated first, and its length occupies a larger proportion of the discharge gap. The discharge contains multiple stepped leaders. When the gap distance is less than 4 m, the probability of occurrence of negative stepped leaders may be smaller. As the gap distance increases, the number of stepped leaders increases significantly. Under the arc electrode, the upward leader is initiated first, and its length accounts for a larger proportion of the discharge gap. With the rotation of the wind turbine, the upward leader is initiated earlier and the length is longer. Furthermore, the speed of its development does not differ significantly. The discharge simulation process under the arc electrode is similar to natural lightning strikes on wind turbines. [ABSTRACT FROM AUTHOR]

To settle the realization difficulty of continuous rotating detonation (CRD) fueled by hydrocarbon, a cavity-based annular combustor scheme was proposed in our previous study, and its feasibility was well demonstrated. This paper mainly focuses on effects of the cavity location on CRD. The results show that the CRD operating range reduces, as the cavity moves downstream. When cavity is arranged in the detonation zone, the cavity-stabilized flame is coordinated with the reaction zone of detonation. The cavity can intensify the CRD initiation, and CRD waves propagate as co-rotating two-wave mode with higher outlet pressure, higher frequency, and higher stability. When cavity is downstream arranged out the detonation zone, it has little impact on improving the CRD initiation. CRD waves propagate as counter-rotating two-wave mode with lower outlet pressure, lower frequency, and poor stability. In these cases, the majority of reaction zone of detonation concentrates on the upstream annular part, and the cavity-stabilized flame is separated from the reaction zone of detonation, acting as afterburning. A new quantitative approach, the axial distribution of chemiluminescence intensity, has been proposed in this paper, and the separation and move processes of cavity-stabilized flame are verified quantitatively based on it. [ABSTRACT FROM AUTHOR]

We present results from an optical search for Local Group dwarf galaxy candidates associated with the Ultra-Compact High Velocity Clouds (UCHVCs) discovered by the ALFALFA neutral hydrogen survey. The ALFALFA UCHVCs are isolated, compact H i clouds with projected sizes, velocities, and estimated H i masses that suggest they may be nearby dwarf galaxies, but that have no clear counterpart in existing optical survey data. We observed 26 UCHVCs with the WIYN 3.5 m telescope and One Degree Imager (ODI) in two broadband filters and searched the images for resolved stars with properties that match those of stars in typical dwarf galaxies at distances

Galactic science encompasses a wide range of subjects in the study of the Milky Way and Magellanic Clouds, from young stellar objects to X-ray binaries. Mapping these populations, and exploring transient phenomena within them, are among the primary science goals of the Vera C. Rubin Observatory’s Legacy Survey of Space and Time. While early versions of the survey strategy dedicated relatively few visits to the Galactic Plane region, more recent strategies under consideration envision a higher cadence within selected regions of high scientific interest. The range of galactic science presents a challenge in evaluating which strategies deliver the highest scientific returns. Here we present metrics designed to evaluate Rubin survey strategy simulations, based on the cadence of observations they deliver within regions of interest to different topics in galactic science, using variability categories defined by timescale. We also compare the fractions of exposures obtained in each filter with those recommended for the different science goals. We find that the baseline _ v2.x simulations deliver observations of the high-priority regions at sufficiently high cadence to reliably detect variability on timescales >10 days or more. Follow-up observations may be necessary to properly characterize variability, especially transients, on shorter timescales. Combining the regions of interest for all the science cases considered, we identify those areas of the Galactic Plane and Magellanic Clouds of highest priority. We recommend that these refined survey footprints be used in future simulations to explore rolling cadence scenarios, and to optimize the sequence of observations in different bandpasses.

We present a study of the [O iii ] λ 5007 line profile in a subsample of eight active galactic nuclei (AGNs) and six non-AGNs in the optically selected green valley at z < 0.5 using long-slit spectroscopic observations obtained with the 11 m Southern African Large Telescope. Gaussian decomposition of the line profile was performed to study its different components. We observe that the AGN profiles are more complex than the non-AGN ones. In particular, in most AGNs (5/8) we detect a blue wing of the line. We derive the FWHM velocities of the wing and systemic component, and find that the AGNs show higher FWHM velocities than the non-AGNs in their core component. We also find that the AGNs show blue wings with a median velocity width of approximately 600 km s ^−1 , and a velocity offset from the core component in the range −90 to −350 km s ^−1 , in contrast to the non-AGN galaxies, where we do not detect blue wings in any of their [O iii ] λ 5007 line profiles. Using the spatial information in our spectra, we show that at least three of the outflow candidate galaxies have centrally driven gas outflows extending across the whole galaxy. Moreover, these are also the galaxies which are located on the main sequence of star formation, raising the possibility that the AGNs in our sample are influencing the star formation of their host galaxies (such as positive feedback). This is in agreement with our previous work where we studied the star formation, morphology, and stellar population properties of a sample of green valley AGNs and non-AGN galaxies.

We have measured the complex refractive indices, from 0.4 to 1.6 μ m, of five laboratory-generated organic refractory materials (tholins) produced at low temperature (150 K) using plasma chemistry in the stream of a supersonic expansion in NASA Ames’ COsmic SImulation Chamber (COSmIC) facility. Three samples were produced from N _2 :CH _4 gas precursors (with different voltages inducing different degrees of ionization in the plasma), one sample was produced from N _2 :CH _4 :C _2 H _2 , and one sample was produced from Ar:CH _4 in order to produce a purely carbonaceous sample. The optical constants, n and k , of the samples were determined using spectral reflectance measurements. We observe that both n and k appear to be correlated with the nitrogen content in the solid sample, with samples containing more nitrogen having higher n and k . Comparisons to previous laboratory studies and Titan aerosol optical constants derived from observations show that the COSmIC tholins with a higher nitrogen content (higher n and k ) are closer analogs of Titan aerosols. We also present a new analysis of Cassini Visible Infrared Mapping Spectrometer observations of Titan’s atmosphere in the visible to near infrared using the COSmIC tholin optical constants in a radiative transfer model. The COSmIC tholin sample produced from N _2 :CH _4 with the lowest energy level has a spectral behavior that appears well suited to reproduce the observed Titan aerosol properties. This study has therefore demonstrated that this COSmIC tholin sample has valuable and promising optical properties for the analysis of Cassini’s Titan atmospheric observations.

Optical starlight can be partially polarized while propagating through the dusty, magnetized interstellar medium (ISM). The polarization efficiency describes the polarization intensity fraction per reddening unit, P _V / E ( B − V ), related to the interstellar dust grains and magnetic field properties. The maximum value observed, [ P _V / E ( B − V )] _max , is thus achieved under optimal polarizing conditions of the ISM. Therefore, the analysis of polarization efficiency observations across the Galaxy contributes to the study of magnetic field topology, small-scale magnetic fluctuations, grain-alignment efficiency, and composition. Infrared observations from Planck satellite have set [ P _V / E ( B − V )] _max to 13% mag ^−1 . However, recent optical polarization observations in Planck's highly polarized regions showed polarization efficiency values between 13.6% mag ^−1 and 18.2% mag ^−1 (depending on the extinction map used), indicating that [ P _V / E ( B − V )] _max is not well constrained yet. We used V -band polarimetry of the Interstellar Polarization Survey (consisting of ∼10,500 high-quality observations distributed in 34 fields of 0.°3 × 0.°3) to accurately estimate the polarization efficiency in the ISM. We estimated the upper limit of P _V / E ( B − V ) with the weighted 99th percentile of the field. In five regions, the polarization efficiency upper limit is above 13% mag ^−1 . Furthermore, we found [ P _V / E ( B − V )] ${}_{\max }={15.8}_{-0.9}^{+1.3}$ % mag ^−1 using diffuse intermediate-latitude (∣ b ∣ > 7.°5) regions with apparently strong regular Galactic magnetic field in the plane-of-sky. We studied the variations of P _V / E ( B − V ) across the sky and tested toy models of polarization efficiency with Galactic longitude that showed some correspondence with a uniform spiral magnetic field.

Time-domain astronomy is an active research area now, which requires frequent observations of the whole sky to capture celestial objects with temporal variations. In the optical band, several telescopes in different locations could form a distributed telescope array to capture images of celestial objects continuously. However, there are millions of celestial objects to observe each night, and only limited telescopes could be used for observation. Besides, the observation capacity of these telescopes would be affected by different effects, such as the sky background or the seeing condition. It would be necessary to develop an algorithm to optimize the observation strategy of telescope arrays according to scientific requirements. In this paper, we propose a novel framework that includes a digital simulation environment and a deep reinforcement learning algorithm to optimize observation strategy of telescope arrays. Our framework could obtain effective observation strategies given predefined observation requirements and observation environment information. To test the performance of our algorithm, we simulate a scenario that uses distributed telescope arrays to observe space debris. Results show that our algorithm could obtain better results in both discovery and tracking of space debris. The framework proposed in this paper could be used as an effective strategy optimization framework for distributed telescope arrays, such as the Sitian project or the TIDO project.

We conduct hard X-ray to radio multiwavelength spectral energy distribution (SED) decomposition for 57 local luminous and ultraluminous infrared galaxies observed with the Nuclear Spectroscopic Telescope Array and/or Swift/Burst Alert Telescope in the GOALS sample. We modify the latest SED-fitting code X-CIGALE by implementing the infrared (IR) CLUMPY model, allowing us to conduct the multiwavelength study with the X-ray torus model XCLUMPY self-consistently. Adopting the torus parameters obtained by the X-ray fitting, we estimate the properties of the host galaxies, active galactic nucleus (AGN) tori, and polar dust. The star formation rates (SFRs) become larger with merger stage and most of them are above the main sequence. The SFRs are correlated with radio luminosity, indicating starburst emission is dominant in the radio band. Although polar-dust extinction is much smaller than torus extinction, the UV-to-IR (mainly IR) polar dust luminosities are ∼2 times larger than the torus ones. The polar-dust temperature decreases while the physical size, estimated by the temperature and dust sublimation radius, increases with AGN luminosity from a few tens of parsec (early mergers) to kiloparsec scales (late mergers), where the polar dust likely comes from expanding (i.e., evolving) dusty outflows. A comparison between the SFRs and intrinsic AGN luminosities suggests that starbursts occur first and AGNs arise later, and overall their growth rates follow the simultaneous coevolution local galaxy–SMBH mass relation. We confirm the coexistence of intense starbursts, AGNs, and large-scale outflows in late mergers, supporting a standard AGN feedback scenario.

The stellar initial mass function (IMF) is expressed by ϕ ( m ) ∝ m ^− ^α with the slope α , and known as a poorly constrained but very important function in studies of star and galaxy formation. There are no sensible observational constraints on the IMF slopes beyond the Milky Way and nearby galaxies. Here we combine two sets of observational results, (1) cosmic densities of core-collapse supernova (CCSN) explosion rates and (2) cosmic far-UV radiation (and infrared reradiation) densities, which are sensitive to massive (≃8–50 M _⊙ ) and moderately massive (≃2.5–7 M _⊙ ) stars, respectively, and constrain the IMF slope at m > 1 M _⊙ with a freedom of redshift evolution. Although no redshift evolution is identified beyond the uncertainties, we find that the cosmic-average IMF slope at z = 0 is α = 1.8–3.2 at the 95% confidence level that is comparable with the Salpeter IMF, α = 2.35, which marks the first constraint on the cosmic-average IMF. We show a forecast for the Nancy Grace Roman Space Telescope supernova survey that will provide significantly strong constraints on the IMF slope with δ α ≃ 0.5 over z = 0–2. Moreover, as for an independent IMF probe instead of (1), we suggest to use diffuse supernovae neutrino background (DSNB), relic neutrinos from CCSNe. We expect that the Hyper-Kamiokande neutrino observations over 20 yr will improve the constraints on the IMF slope and the redshift evolution significantly better than those obtained today, if the systematic uncertainties of DSNB production physics are reduced in the future numerical simulations.

Ground-based optical observation of GEO space debris plays an essential role in tracking, identifying, cataloging, and classifying space debris. The factors that affect the brightness of space debris include size, surface material, illumination geometry, attitude, shape, position, and so on. In order to better understand the influence of the above factors on the brightness of space debris, the synthetic light curves are analyzed. The Ashikhmin–Shirley model is chosen to simulate the light curves of space debris. The effects of orbit, attitude, model parameters, and the location of the observation station on the synthetic light curves are analyzed by the control variable method. Based on the Markov Chain Monte Carlo method (MCMC), the optimal model parameters that characterize the surface material of space debris can be obtained by comparing the synthetic light curves with the observed light curves under certain shape, orbit, and attitude characteristics. The results are roughly in good agreement with those measured in the laboratory.

An apparatus to record the growing process of laser-induced periodic surface structure (LIPSS) pulse-by-pulse has been constructed. Application of oblique incidence resulted in the formation of LIPSS whose period is longer than the laser wavelength and optical observation of fringes was enabled. Here we show the result of our observations using the apparatus and demonstrate the capability of this method. [ABSTRACT FROM AUTHOR]

The characteristics of the air gap discharge are of interest among researchers on high voltage and lightning study. This letter uses a self-developed high-speed observation system to measure the propagation velocity of the current impulse after the air gap breakdown in the rod-to-plane discharge with dc voltage. In addition, the discharge channel is captured by a still camera. From the time difference of arrival of light signals in different receiving channels of high-speed observation system, it shows that the propagation velocity of the current impulse is in the range from 4.3 ± 0.36 × 106 to 1.1 ± 0.09 × 107 m/s. [ABSTRACT FROM AUTHOR]

Methane-air Continuous Rotating Detonation (CRD) has been firstly achieved in this paper in the hollow chamber with a Laval nozzle, and the diameter of the chamber is just 100 mm. The contraction ratio of the Laval nozzle is a key factor for the CRD realization. CRD can only be obtained when the contraction ratio is no less than 4, but its ER operating range decreases in the increase of contraction ratio from 4 to 10. For all the success cases, the average propagation frequency and velocity are in the ranges of 5.32–5.65 kHz and 1670.48–1774.10 m/s, respectively, and the velocity deficits are less than 10%. Based on the high-speed photography images, the approach of chemiluminescence intensity integral is proposed in this paper, and the propagation characteristics of the flame are analyzed quantitatively. The propagation velocities of the flame and shock wave are agreed well with each other, indicating that the typical feature of detonation wave, i.e., the coupling of the flame and the shock wave, is verified quantitatively. • Methane-air CRD is firstly achieved without additional oxygen and hydrogen. • Realization is in the small hollow chamber with the diameter of 100 mm. • The average velocity of success cases is in the range of 1670.48–1774.10 m/s. • Chemiluminescence intensity integral is proposed as a new image processing method. • The velocity coupling of flame and shock wave is verified quantitatively. [ABSTRACT FROM AUTHOR]

The realization and stable operating of Continuous Rotating Detonation (CRD) Engine fueled by hydrocarbon and air is still a problem deserving to be settled. In order to optimize the detonation combustion organization in the annular combustor, an especial cavity structure in the inner cylinder is firstly proposed in this paper. Series of experiments have been conducted for investigating the effect of cavity structure. The results show that ethylene-air CRD has been realized in the annular combustor with cavity. CRD waves propagate steadily with higher pressure and propagation velocity in the larger operating range. The cavity contributes to the propagation mode transformation from two-waves in hetero-rotating mode to two-waves in homo-rotating mode. In the cavity combustor, the propagation velocity is 1228.68 m/s on stoichiometric equivalence ratio (ER) accounting for 67.4% of the corresponding CJ velocity. The permanent flame stabilized in re-circulation zone works as the pilot flame, which has been verified by high-speed photograph images. • In annular combustor, the cavity structure in inner cylinder is firstly proposed. • The pilot flame stabilized in re-circulation zone in the cavity is verified. • The cavity structure can change the ethylene-air CRD propagation mode. • Ethylene-air CRD waves propagate steadily with higher pressure and velocity. • The highest velocity is 1228.68 m/s, occupying 67.4% of corresponding CJ velocity. [ABSTRACT FROM AUTHOR]

Atmospheric clouds and fogs can weaken the intensity of the visible light by absorption, refraction, scattering and reflection, which greatly affect the detection effect of ground-based optical observation instruments. To solve this problem, near-earth space-based optical observation platform is a good choice which is more flexible and cheaper than satellite-based optical observation platform in space. This paper describes the whole design of the near-earth space optical observation payload cabin including electronics design and mechanical design. The payload capacity is 100Kg and supports 4x RS422, 4x CameraLink, 4x analog video and 4x LAN, it can provide energy supply, mode control, temperature control, data storage and data transmission services for the experiment loads. The payload cabin developed in this paper has participated in the actual experiment and reached to an altitude of 20 Km, and then safely landed after staying for 2 h in the stratosphere. The scientific load obtained real and reliable experimental data and the optical loads also obtained precious data and images during the experiment. The payload cabin developed in this experiment will take ultraviolet spectrograph, low-light level night vision device, planetary telescope and multi-band airglow imager to an altitude above 20Km for experiment in the near future. [ABSTRACT FROM AUTHOR]

The optically accessible racetrack-like combustor designed for observation using high-speed photography is proposed. Series of Continuous Rotating Detonation (CRD) experiments with different combustor width, injection scheme, propellant and equivalence ratio are conducted. The operating domain results show that combustor width is a key factor for CRD realization. Ethylene CRD can be achieved on larger width combustor. Two propagation modes, namely, two waves in hetero-rotating mode and single wave mode, are achieved in the experiment. Based on the high-frequency pressures and high-speed photography images, the propagation characteristics and flowfield structures are discussed in detail. Some special flowfield structures are also observed and analyzed, including streak structure and downstream shock wave-ahead structure. The study will enhance the understanding of flowfield structure and flame dynamics of CRD Wave. [ABSTRACT FROM AUTHOR]

Abstract The luminosity of lightning channel is closely related to the lightning current. In the present paper, a lightning channel luminosity detection system (LCLDS), comprising of an avalanche photodiode module, a neutral density filter, an extension tube and an adjustable horizontal slit, is assembled. By using the impulse current generator, lightning impulse currents with different amplitudes and also different waveforms were produced in a 15-mm open-air gap between two graphite-rod electrodes. The luminosity and the current of discharge channel were measured synchronously. The experiments looking into the influencing factors of luminosity measurement, including the alignment of the silt and the slit width, were carried out. Obtained results show that the slit opening center of LCLDS should be aligned to the center of the discharge gap. Otherwise, in the case of improper alignment, the measured luminosity waveforms associated with the same injected current might be quite different in the amplitudes as well as in the waveforms. Moreover, the peak luminosity increases linearly with increasing slit width, whereas the luminosity waveforms are practically unaffected, implying that, in the practical application, the slit width can be adjusted to alter the luminosity signal output according to the actual need. Obtained results here can establish the foundation to develop the correlation between the current and the corresponding luminosity in the future. Highlights • The slit opening center of lightning channel luminosity detection system should be aligned to the center of the discharge gap. • The humps of luminosity waveforms found in the lightning flashes is due to improper alignment. • Peak luminosity increases linearly with increasing slit width. [ABSTRACT FROM AUTHOR]

In an optical observing system, three pairs of observations at equal time intervals are required for the orbit determination method to obtain orbital information of an unknown space objects. In this paper, we propose a method of estimating a streak for acquiring three pairs of observations using one streak image information. Satellite trajectory simulation data were generated for nine cases using the STK program in order to verify the characteristics of the orbit of space object and estimation performance. Simulation was performed by applying three approaches that can estimate the next streak position after a few seconds from one streak image information, and the estimation performance was evaluated. Linear vector method and Kalman Filter method based on the linear assumption tend to increase the estimation error in the region where the nonlinearity is large. However estimation method using the polynomial curve fitting based on the least square method showed smaller and uniform error result than the previous methods. [ABSTRACT FROM AUTHOR]

By using the Optical Wide-field Patrol (OWL) network developed by the Korea Astronomy and Space Science Institute (KASI) we generated the right ascension and declination angle data from optical observation of Low Earth Orbit (LEO) satellites. We performed an analysis to verify the optimum number of observations needed per arc for successful estimation of orbit. The currently functioning OWL observatories are located in Daejeon (South Korea), Songino (Mongolia), and Oukaïmeden (Morocco). The Daejeon Observatory is functioning as a test bed. In this study, the observed targets were Gravity Probe B, COSMOS 1455, COSMOS 1726, COSMOS 2428, SEASAT 1, ATV-5, and CryoSat-2 (all in LEO). These satellites were observed from the test bed and the Songino Observatory of the OWL network during 21 nights in 2014 and 2015. After we estimated the orbit from systematically selected sets of observation points (20, 50, 100, and 150) for each pass, we compared the difference between the orbit estimates for each case, and the Two Line Element set (TLE) from the Joint Space Operation Center (JSpOC). Then, we determined the average of the difference and selected the optimal observation points by comparing the average values.

The study on breakdown characteristics at microscale is very vital to the plasma physics community and micro/nanoelectronic industries. However, the dynamic development processes including the electron avalanche and discharge channel during the breakdown event are still unclear experimentally so far due to the restriction of the in-situ diagnostic technique. In this paper, an optical diagnostic technique is put forward to achieve an in-situ observation of the dynamic breakdown process across microgaps at atmospheric pressure. By using the nanosecond temporally and micron spatially resolved optical measurement method, the light emission appearances of microgap breakdown under nanosecond pulse have been captured and imaged directly. The initial and propagation mechanisms for electrical breakdown across the very small air gap are discussed based on the light emission properties. Results show that the light emission initiates from the cathode as the initial electron avalanche, then the avalanche transits to the streamer due to the space charge effect and photoionization, and propagates towards the anode with a velocity of 4.40×103 m/s, demonstrating a cathodedirected streamer in the pulsed breakdown. The space charge induced field enhancement and photoionization are proved to play a significant role in the pulsed breakdown across microgaps. In addition, the time to breakdown is estimated to be about 20ns while the formative time lag is about 9ns through the temporal sequence of the optical images. The in-situ optical measurement technique presented in this paper would be of a great help for better understanding the physical mechanism of microgap breakdown. [ABSTRACT FROM AUTHOR]

The OWL-Net (Optical Wide-field patroL Network) is composed of 0.5-m wide-field optical telescopes spread over the globe (Mongolia, Morocco, Israel, South Korea, and USA). All the observing stations are identical, operated in a fully robotic manner, and controlled by the headquarters located in Daejeon, Korea. The main objective of the OWL-Net is to obtain the orbital information of Korean LEO and GEO satellites using purely optical means and to maintain their orbital elements. The aperture size of the mirror is 0.5 m in the Ritchey-Chretien configuration, and its field of view is 1.1 deg on the CCD sensor. The telescope is equipped with an electrically cooled 4 K CCD camera with a 9-µm pixel size, and its pixel scale is 1 arcsec/pixel. A chopper wheel with variable speed is adopted to obtain multiple points in a single shot. Each observatory is equipped with a heavy-duty environment monitoring system for robust robotic observation. The headquarters has components for status monitoring, scheduling, network operation, orbit calculation, and database management. The test-phase operation of the whole system began in early 2017, although test runs for individual sites began in 2015. Although the OWL-Net has 7 observation modes for artificial satellites and astronomical objects, we are concentrating on a few modes for LEO satellites and calibration during the early phase. Some early results and analysis for system performance will be presented, and their implications will be discussed. [ABSTRACT FROM AUTHOR]