Sky Area Research Articles

Low voltage optical fiber positioner robot based on minimum inductance hollow cup motors

With the further transformation of The Large Sky Area Multi-Object Fiber Spectroscopic Telescope, the new generation of fiber positioner robot chooses a 4 mm hollow cup motor with minimum phase inductance. Because the load of the fiber positioner robot is constant and the inertia of the motor is very small, an open loop positioning control method based on Space Vector Pulse Width Modulation is proposed, and the specific open loop parameters are directly tuned by relevant experimental strategies. The critical factors of the open loop driving mode are discussed in detail from four aspects: subdivision, fundamental frequency, wave generation mode and peak current. Based on the actual fiber positioner robot, the hardware driver and assessment platform are built. The positioning tests show that the method proposed is practical and effective, and meets the precision positioning demand of the new generation optical fiber positioner robot.

A pixelated approach to galaxy catalogue incompleteness: improving the dark siren measurement of the Hubble constant

ABSTRACT The use of gravitational wave standard sirens for cosmological analyses is becoming well known, with particular interest in measuring the Hubble constant, H0, and in shedding light on the current tension between early- and late-time measurements. The current tension is over 4σ and standard sirens will be able to provide a completely independent measurement. Dark sirens (binary black hole or neutron star mergers with no electromagnetic counterparts) can be informative if the missing redshift information is provided through the use of galaxy catalogues to identify potential host galaxies of the merger. However, galaxy catalogue incompleteness affects this analysis, and accurate modelling of it is essential for obtaining an unbiased measurement of H0. Previously most methods have assumed uniform completeness within the sky area of a gravitational wave event. This paper presents an updated methodology in which the completeness of the galaxy catalogue is estimated in a directionally dependent matter, by pixelating the sky and computing the completeness of the galaxy catalogue along each line of sight. The H0 inference for a single event is carried out on a pixel-by-pixel basis, and the pixels are combined for the final result. A reanalysis of the events in the first gravitational wave transient catalogue leads to an improvement on the measured value of H0 of approximately 5 per cent compared to the 68.3 per cent highest density interval of the equivalent LIGO and Virgo result, with H0 = $68.8^{+15.9}_{-7.8}$ km s−1 Mpc−1.

Properties and evolutions of starspots on three detached eclipsing binaries in the LAMOST–Kepler survey

ABSTRACT Spotted detached eclipsing binaries (DEBs) offer insights into starspots on binaries. In this work, we study three spotted DEBs, KIC 8097825, KIC 6859813 and KIC 5527172, which have been observed using Kepler photometry and Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) spectroscopy. The physical parameters of binaries are determined by binary modelling. The size, lifetime and single/-double-dip ratio (SDR) of starspots are derived by starspot analysis. KIC 8097825 has large starspots. KIC 6859813 has a spot rotation period shorter than its orbital period but the system should be synchronized by inference from time-scale estimation. The difference may be the result of the surface differential rotation. KIC 5527172 has a long spot lifetime and an M-dwarf component with an inflation radius. The primaries of these binaries and the secondary of KIC 8097825 have spots. Adding spotted DEBs from the literature, we compare the starspots on binaries with those on the single stars. The spot sizes of starspots on 65 per cent of binaries are smaller than the median of those on single stars. The lifetimes of starspots on binaries are consistent with those on single stars when the rotation periods are larger than 3 d. SDRs for half of the binaries are consistent with those of single-star systems, while the other half are smaller. The relative lifetime positively correlates with the rms and SDR but negatively correlates with the rotation period. These relations are similar to those of spots on single-star systems. Binaries with luminosity ratios close to the unit tend to have more double dips.

Cross-correlation of Planck cosmic microwave background lensing with DESI galaxy groups

ABSTRACT We measure the cross-correlation between galaxy groups constructed from DESI Legacy Imaging Survey DR8 and Planck cosmic microwave background (CMB) lensing, over overlapping sky area of 16 876 $\rm deg^2$. The detections are significant and consistent with the expected signal of the large-scale structure of Universe, over group samples of various redshift, mass, and richness Ng, and over various scale cuts. The overall signal-to-noise ratio is 40 for a conservative sample with Ng ≥ 5, and increases to 50 for the sample with Ng ≥ 2. Adopting the Planck 2018 cosmology, we constrain the density bias of groups with Ng ≥ 5 as bg = 1.31 ± 0.10, 2.22 ± 0.10, and 3.52 ± 0.20 at 0.1 < z ≤ 0.33, 0.33 < z ≤ 0.67, and 0.67 < z ≤ 1, respectively. The group catalogue provides the estimation of group halo mass and therefore allows us to detect the dependence of bias on group mass with high significance. It also allows us to compare the measured bias with the theoretically predicted one using the estimated group mass. We find excellent agreement for the two high-redshift bins. However, it is lower than the theory by ∼3σ for the lowest redshift bin. Another interesting finding is the significant impact of the thermal Sunyaev Zel’dovich. It contaminates the galaxy group-CMB lensing cross-correlation at $\sim \! 30{{\ \rm per\ cent}}$ level, and must be deprojected first in CMB lensing reconstruction.

Number and Distribution of Fiducial Fibers in a Spectroscopic Survey Telescope

To date, the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) has been in operation for 12 yr. To improve the telescope's astronomical observation accuracy, the original open-loop fiber positioning system of LAMOST is in urgent need of upgrading. The upgrade plan is to install several fiber view cameras (FVCs) around primary mirror B to build a closed-loop feedback control system. The FVCs are 20 m from the focal surface. To reduce a series of errors when the cameras detect the positions of the optical fibers, we designed fiducial fibers on the focal surface to be fiducial points for the cameras. Increasing the number of fiducial fibers can improve the detection accuracy of the FVC system, but it will also certainly reduce the number of fiber positioners that can be used for observation. Therefore, the focus of this paper is how to achieve the quantity and distribution that meet the requirements of system detection. In this paper, we introduce the necessity of using fiducial fibers, propose a method for selecting their number and present several methods for assessing the uniformity of their distribution. Finally, we implement particle swarm optimization to find the best distribution of fiducial fibers.

Calibrating Photometric Redshift Measurements with the Multi-channel Imager (MCI) of the China Space Station Telescope (CSST)

The China Space Station Telescope (CSST) photometric survey aims to perform a high spatial resolution (∼0.″15) photometric imaging for the targets that cover a large sky area (∼17,500 deg2) and wide wavelength range (from NUV to NIR). It expects to explore the properties of dark matter, dark energy, and other important cosmological and astronomical areas. In this work, we evaluate whether the filter design of the Multi-channel Imager (MCI), one of the five instruments of the CSST, can provide accurate photometric redshift (photoz) measurements with its nine medium-band filters to meet the relevant scientific objectives. We generate the mock data based on the COSMOS photometric redshift catalog with astrophysical and instrumental effects. The application of upper limit information of low signal-to-noise ratio data is adopted in the estimation of photoz. We investigate the dependency of photoz accuracy on the filter parameters, such as band position and width. We find that the current MCI filter design can achieve good photoz measurements with accuracy σ z ≃ 0.017 and outlier fraction f c ≃ 2.2%. It can effectively improve the photoz measurements of the main CSST survey using the Survey Camera to an accuracy σ z ≃ 0.015 and outlier fraction f c ≃ 1.5%. This indicates that the original MCI filters are proper for the photoz calibration.

Search for the Metal-weak Thick Disk from the LAMOST DR5

Based on the data release of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope survey (LAMOST DR5) and the Gaia Early Data Release 3 (Gaia EDR3), we construct a sample containing 46,109 giant (log g ≤ 3.5 dex) stars with heliocentric distance d ≤ 4 kpc, and the sample is further divided into two groups of the inner (R GC < 8.34 kpc) and outer region (R GC > 8.34 kpc). The L Z distributions of our program stars in the panels with different [Fe/H] and [α/Fe] suggest that the thick-disk consists of two distinct components with different chemical compositions and kinematic properties. For the inner region, the metal-weak thick disk (MWTD) significantly contributes when [α/Fe] > +0.2 dex and [Fe/H] < −0.8 dex, while the canonical thick-disk (TD) dominates when [Fe/H] > −0.8 dex. However, MWTD clearly appears only when [α/Fe] > +0.2 dex and [Fe/H] < −1.2 dex for the outer region, and its proportion is lower than that of the inner region within the same metallicity. Similar results can be obtained from the V ϕ distribution. The higher fraction of MWTD in the inner region than that in the outer region implies that MWTD may form in the inner disk, and is observational evidence about the inside-out disk formation scenario.

A Fusion-Based Defogging Algorithm

To solve the problem that traditional dark channel is not suitable for a large sky area and can easyily distort defogged images, we propose a novel fusion-based defogging algorithm. Firstly, an improved remote sensing image segmentation algorithm is introduced to mix the dark channel. Secondly, we establish a dark-light channel fusion model to calculate the atmospheric light map. Furthermore, in order to refine the transmittance image without reducing restoration quality, the grayscale image corresponding to the original image is selected as a guide image. Meanwhile, we optimize the set value of the defogging intensity parameter ω in the transmission estimation formula as the value of atmospheric light. Finally, a brightness/color compensation model based on visual perception is generated for image correction. Experimental results demonstrate that the proposed algorithm achieves superior performance on UAV foggy images in both subjective and objective evaluation, which verifies the effectiveness of the proposed algorithm.

Real-time defogging hardware accelerator based on improved dark channel prior and adaptive guided filtering

Image defogging has important application value in preprocessing technology and computer vision system. Dark channel prior (DCP) is simple and effective in many defogging algorithms, but the time-consuming sorting comparison and a large number of calculation refinement processes limit its real-time processing capabilities. For real-time applications, we proposed a hardware architecture for single-image defogging, which gives full play to hardware parallel processing capability and algorithmic parallelism. First, an average statistical approach is used to estimate atmospheric light. Then, the refined dark channel map is used for transmittance estimation to reduce the blocking effect. The transmittance is linearly corrected to prevent color distortion in outdoor scenes containing sky areas. Finally, a guided filter algorithm is introduced in the transmittance refinement, and its fast mean filter uses an adaptive window to process the image boundary. The hardware implementation of the proposed method uses field programmable gate array device is Zynq-7000. Experimental results show that our design obtains good performance with low-complex hardware implementation and shorter execution time. It only takes 7.43 ms to process a 1280 × 720 image, and the frame rate can reach 135 fps at a clock rate of 125 MHz, which can be used as a real-time hardware accelerator for image processing.

The GLEAMing of the first supermassive black holes: II. A new sample of high-redshift radio galaxy candidates

AbstractWhile unobscured and radio-quiet active galactic nuclei are regularly being found at redshifts$z &gt; 6$, their obscured and radio-loud counterparts remain elusive. We build upon our successful pilot study, presenting a new sample of low-frequency-selected candidate high-redshift radio galaxies (HzRGs) over a sky area 20 times larger. We have refined our selection technique, in which we select sources with curved radio spectra between 72–231 MHz from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. In combination with the requirements that our GLEAM-selected HzRG candidates have compact radio morphologies and be undetected in near-infrared$K_{\rm s}$-band imaging from the Visible and Infrared Survey Telescope for Astronomy Kilo-degree Infrared Galaxy (VIKING) survey, we find 51 new candidate HzRGs over a sky area of approximately$1200\ \mathrm{deg}^2$. Our sample also includes two sources from the pilot study: the second-most distant radio galaxy currently known, at$z=5.55$, with another source potentially at$z \sim 8$. We present our refined selection technique and analyse the properties of the sample. We model the broadband radio spectra between 74 MHz and 9 GHz by supplementing the GLEAM data with both publicly available data and new observations from the Australia Telescope Compact Array at 5.5 and 9 GHz. In addition, deep$K_{\rm s}$-band imaging from the High-Acuity WidefieldK-band Imager (HAWK-I) on the Very Large Telescope and from the SouthernHerschelAstrophysical Terahertz Large Area Survey Regions$K_{\rm s}$-band Survey (SHARKS) is presented for five sources. We discuss the prospects of finding very distant radio galaxies in our sample, potentially within the epoch of reionisation at$z \gtrsim 6.5$.

Application of Multi-Scale Convolution Neural Network Optimization Image Defogging Algorithm in Image Processing

To improve the ability to detect and identify smog images in complex road traffic scenes, smog images need to be defogged, and an optimized image defogging algorithm on the basis of multi-scale convolutional neural network (MCNN) is proposed. The physical model of road traffic scene smog scattering is constructed, and the image is divided sky area, road surface area and road sky boundary area. The road sky boundary line is the boundary line between road surface and sky area. The dark channel of traffic scene smog image is established by Canny edge detection and MCNN optimization, and the smog image is subjected to detail compensation and gray enhancement processing through prior knowledge. After substituting the atmospheric light value and transmittance map into the atmospheric scattering model (ACM), the MCNN learning model is combined to realize the filtering processing and defogging optimization of smog images in complex road traffic scenes. The color saturation, defogging degree, peak signal-to-noise ratio (PSNR), texture effect as well as other aspects of the image are taken as test indexes for the simulation experiment. The simulation results show that the color saturation, defogging degree and image definition of the defogged haze images in complex road traffic scenes are higher by using this method, which improves the output PSNR of the defogged haze images in complex road traffic scenes, and has a good application value in image defogging.

Give Me a Few Hours: Exploring Short Timescales in Rubin Observatory Cadence Simulations

Abstract The limiting temporal resolution of a time-domain survey in detecting transient behavior is set by the time between observations of the same sky area. We analyze the distribution of visit separations for a range of Vera C. Rubin Observatory cadence simulations. Simulations from families v1.5–v1.7.1 are strongly peaked at the 22 minute visit pair separation and provide effectively no constraint on temporal evolution within the night. This choice will necessarily prevent Rubin from discovering a wide range of astrophysical phenomena in time to trigger rapid follow-up. We present a science-agnostic metric to supplement detailed simulations of fast-evolving transients and variables and suggest potential approaches for improving the range of timescales explored.

Contribution of Gaia Sausage to the Galactic Stellar Halo Revealed by K Giants and Blue Horizontal Branch Stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, Sloan Digital Sky Survey, and Gaia

Abstract We explore the contribution of the Gaia Sausage to the stellar halo of the Milky Way by making use of a Gaussian mixture model (GMM) and applying it to halo star samples of Large Sky Area Multi-Object Fiber Spectroscopic Telescope K giants, Sloan Extension for Galactic Understanding and Exploration K giants, and Sloan Digital Sky Survey blue horizontal branch stars. The GMM divides the stellar halo into two parts, of which one represents a more metal-rich and highly radially biased component associated with an ancient, head-on collision referred to as the Gaia Sausage, and the other one is a more metal-poor and isotropic halo. A symmetric bimodal Gaussian is used to describe the distribution of spherical velocity of the Gaia Sausage, and we find that the mean absolute radial velocity of the two lobes decreases with the Galactocentric radius. We find that the Gaia Sausage contributes about 41%–74% of the inner (Galactocentric radius r gc &lt; 30 kpc) stellar halo. The fraction of stars of the Gaia Sausage starts to decline beyond r gc ∼ 25–30 kpc, and the outer halo is found to be significantly less influenced by the Gaia Sausage than the inner halo. After the removal of halo substructures found by integrals of motion, the contribution of the Gaia Sausage falls slightly within r gc ∼ 25 kpc but is still as high as 30%–63%. Finally, we select several possible Sausage-related substructures consisting of stars on highly eccentric orbits. The GMM/Sausage component agrees well with the selected substructure stars in their chemodynamical properties, which increases our confidence in the reliability of the GMM fits.

Optimization of Embodied energy and operational energy of school design by comparing conventional and sustainable Material configurations

In recent times, the use of sustainable building materials is gaining momentum as the general public has started understanding the energy exploitation and also ill effects of using pollutant emitting materials. Also, usage of high energy-intensive materials is on the decline as all international agencies have started making a strong call on climate change (carbon release). Therefore, usage of materials with less embodied energy is the need of the hour. Hence this study aims at exploring the possibilities to optimize the embodied energy and operational energy by selecting sustainable building materials, ventilation and lighting aspects in the design of school buildings. Two designs of school buildings have been done, namely conventional and Regenerative. The conventional design has typically used construction materials like RCC, fired clay brick etc., whereas in regenerative design materials of less embodied energy like CSEB blocks, no VOC paints, etc., have been used. Also in regenerative design, effective ventilation strategies and more openness to sky areas have been done in order to make buildings more passive. Embodied energy for all building components like floor, roof, foundations, wall has been calculated separately and cumulated for the entire floor area. Operational energy was also calculated for both conventional and regenerative design using modeling software plugin. As findings, both embodied energy and operational energy was found to be low for regenerative design when compared with conventional design. As a result, a design with low embodied energy and operational energy has been proposed with all supporting data. Future studies can be done on different material configurations for wall, roofs, floors, foundations and Embodied energy as output for each variable of input. For different ventilation and lighting configurations, operational energy can be found.

First photometric investigation of two short-period eclipsing binaries ASAS J105115-6032.1 and GDS J1056047-604149

ASAS J105115-6032.1 (hereafter ASAS J1051) and GDS J1056047-604149 (hereafter GDS J1056) are two short-period contact binaries close to each other in the Antarctica sky area. By analyzing the light curves from AST3-1, the first photometric solutions are presented using the Wilson–Devinney (W–D) method. It is detected that both systems are W-type contact binaries with mass ratios of q = 3.2621(0.0083) and q = 4.843(0.014), respectively. Both of them have a moderate degree of contact factor of f = 46.9(1.2)% and f = 43.9(1.2)%. The asymmetries in the light curve of the intermediate-contact system GDS J1056 (strong O’Connell effect) are interpreted by a dark spot on the more massive component. For the first time, we carried out the O−C diagram analysis based on many photometric data. The results indicate an orbital period increase at a rate of dP/dt=+5.28×10−7d⋅yr−1 for ASAS J10511. As for GDS J1056, a period decrease of dP/dt=−5.41×10−7d⋅yr−1, superimposed with a cyclic period change with a semi-amplitude of 0.00744 d and a period of 11.97 yr, is discovered. The cyclic period change may be caused by the light travel-time effect via the presence of a tertiary companion with a lowest mass of M3 = 0.35(0.03)M⊙. The period increase in ASAS J1051 can be explained by the mass transfer from the less massive component to its companion. In contrast, the period decrease in GDS J1056 reveals an opposite direction of mass transfer. The facts suggest that these two intermediate-contact binaries will evolve into shallow- and deep-contact binary systems.

Remote sensing of light pollution in the Western Balkan countries

The article deals with the problem of light pollution in the area of the Western Balkan countries (Bosnia and Herzegovina, Serbia, Montenegro, Macedonia, Kosovo, Albania). The survey presented in this article examines the radiance data obtained by remote sensing using the SUOMI satellite. The article shows the situation concerning light pollution between 2013 and 2021. It also makes an analysis of the changes in terms of light pollution by individual countries. The article also highlights the changes in the dark sky areas, which, with a specific set of measures to limit light pollution, could represent the future areas of the "Dark Sky" protected parks.

PERIOD CHANGES OF MIRA VARIABLES IN THE M16-M17 REGION

We analyzed the light curves of 165 AGB variables, mostly Miras, in the sky area centered between M16 and M17 (l = 16, b = 0), using the OGLE GVS database in the IC band. Comparison with the published light curves, derived about 50 years earlier by P. Maffei using Kodak I-N photographic plates, allowed us to find no significant period changes in any star. Remarkably, a few stars of the sample appear to have substantially changed their average luminosity, the most striking case being KZ Ser. We provide a better identification for three stars: IX Ser, NSV 10522, and NSV 10326, all of them being Miras. We classify the light curves of 6 stars, discovered but not classified by Maffei, (GL Ser, NSV 10271, NSV 10326, NSV 10522, NSV 10677, and NSV 10772) five of them being new Miras, and confirm the R CrB nature of V391 Sct. The magnitude scale used by Maffei is compared to the modern IC one.

Compact object candidates with K/M-dwarf companions from LAMOST low-resolution survey

Searching for compact objects (black holes, neutron stars, or white dwarfs) in the Milky Way is essential for understanding the stellar evolution history, the physics of compact objects, and the structure of our Galaxy. Compact objects in binaries with a luminous stellar companion are perfect targets for optical observations. Candidate compact objects can be achieved by monitoring the radial velocities of the companion star. However, most of the spectroscopic telescopes usually obtain stellar spectra at a relatively low efficiency, which makes a sky survey for millions of stars practically impossible. The efficiency of a large-scale spectroscopic survey, the Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST), presents a specific opportunity to search for compact object candidates, i.e., simply from the spectroscopic observations. Late-type K/M stars are the most abundant populations in our Galaxy. Owing to the relatively large Keplerian velocities in the close binaries with a K/M-dwarf companion, a hidden compact object could be discovered and followed-up more easily. In this study, compact object candidates with K/M-dwarf companions are investigated with the LAMOST low-resolution stellar spectra. Based on the LAMOST Data Release 5, we obtained a sample of $56$ binaries, each containing a K/M-dwarf with a large radial velocity variation $\Delta V_{\rm R} > 150~{\rm km~s}^{-1}$. Complemented with the photometric information from the Transiting Exoplanet Survey Satellite, we derived a sample of $35$ compact object candidates, among which, the orbital periods of $16$ sources were revealed by the light curves. Considering two sources as examples, we confirmed that a compact object existed in the two systems by fitting the radial velocity curve. This study demonstrates the principle and the power of searching for compact objects through LAMOST.

Stellar Populations of Galaxies in the LAMOST Spectral Survey

Abstract We first derive the stellar population properties: age and metallicity for ∼43,000 low redshift galaxies in the DR7 of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey, which have no spectroscopic observations in the Sloan Digital Sky Survey (SDSS). We employ a fitting procedure based on the small-scale features of galaxy spectra so as to avoid possible biases from the uncertain flux calibration of the LAMOST spectroscopy. We show that our algorithm can successfully recover the average age and metallicity of the stellar populations of galaxies down to signal-to-noise ratio ≥5 through testing on both mock galaxies and real galaxies comprising LAMOST and their SDSS counterparts. We provide a catalog of the age and metallicity for ∼43,000 LAMOST galaxies online. As a demonstration of the scientific application of this catalog, we present the Holmberg effect on both age and metallicity of a sample of galaxies in galaxy pairs.

Finding Rare Quasars: VLA Snapshot Continuum Survey of FRI Quasar Candidates Selected from the LOFAR Two-Metre Sky Survey (LoTSS)

The radiative and jet power in active galactic nuclei is generated by accretion of material on to supermassive galactic-centre black holes. For quasars, where the radiative power is by definition very high, objects with high radio luminosities form 10 per cent of the population, although it is not clear whether this is a stable phase. Traditionally, quasars with high radio luminosities have been thought to present jets with edge-brightened morphology (Fanaroff-Riley II—FR II) due to the limitations of previous radio surveys (i.e., FRIs were not observed as part of the quasar population). The LOw Frequency ARray (LOFAR) Two-metre Sky Survey (LoTSS) with its unprecedented sensitivity and resolution covering wide sky areas has enabled the first systematic selection and investigation of quasars with core-brightened morphology (Fanaroff-Riley I—FR). We carried out a Very Large Array (VLA) snapshot survey to reveal inner structures of jets in selected quasar candidates; 15 (25 per cent) out of 60 sources show clear inner jet structures that are diagnostic of FRI jets and 13 quasars (∼22 per cent) show extended structures similar to those of FRI jets. Black hole masses and Eddington ratios do not show a clear difference between FRI and FRII quasars. FRII quasars tend to have higher jet powers than FRI quasars. Our results show that the occurrence of FRI jets in powerful radiatively efficient systems is not common, probably mainly due to two factors: galaxy environment and jet power.