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Keywords = 2.5-m-wide field survey telescope

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22 pages, 12185 KiB  
Article
Airborne Strapdown Gravity Survey of Sos Enattos Area (NE Sardinia, Italy): Insights into Geological and Geophysical Characterization of the Italian Candidate Site for the Einstein Telescope
by Filippo Muccini, Filippo Greco, Luca Cocchi, Maria Marsella, Antonio Zanutta, Alessandra Borghi, Matteo Cagnizi, Daniele Carbone, Mauro Coltelli, Danilo Contrafatto, Peppe Junior Valentino D’Aranno, Luca Frasca, Alfio Alex Messina, Luca Timoteo Mirabella, Monia Negusini and Eleonora Rivalta
Remote Sens. 2025, 17(13), 2309; https://doi.org/10.3390/rs17132309 - 5 Jul 2025
Viewed by 425
Abstract
Strapdown gravity systems are increasingly employed in airborne geophysical exploration and geodetic studies due to advantages such as ease of installation, wide dynamic range, and adaptability to various platforms, including airplanes, helicopters, and large drones. This study presents results from an airborne gravity [...] Read more.
Strapdown gravity systems are increasingly employed in airborne geophysical exploration and geodetic studies due to advantages such as ease of installation, wide dynamic range, and adaptability to various platforms, including airplanes, helicopters, and large drones. This study presents results from an airborne gravity survey conducted over the northeastern sector of Sardinia (Italy), using a high-resolution strapdown gravity ensuring an accuracy of approximately 1 mGal. Data were collected at an average altitude of 1800 m with a spatial resolution of 3.0 km. The survey focused on the Sos Enattos area near Lula (Nuoro province), a candidate site for the Einstein Telescope (ET), a third-generation gravitational wave observatory. The ideal site is required to be geologically and seismically stable with a well-characterized subsurface. To support this, we performed a new gravity survey to complement existing geological and seismic data aimed at characterizing the mid-to-shallow crustal structure of Sos Enattos. Results show that the strapdown system effectively detects gravity anomalies linked to crustal sources down to ~3.5 km, with particular emphasis within the 1–2 km depth range. Airborne gravity data reveal higher frequency anomalies than those resolved by the EGM2008 global gravity model and show good agreement with local terrestrial gravity data. Forward modeling of the gravity field suggests a crust dominated by alternating high-density metamorphic rocks and granitoid intrusions of the Variscan basement. These findings enhance the geophysical understanding of Sos Enattos and support its candidacy for the ET site. Full article
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19 pages, 12053 KiB  
Article
A Comprehensive Study on the Mid-Infrared Variability of Blazars
by Xuemei Zhang, Zhipeng Hu, Weitian Huang and Lisheng Mao
Universe 2024, 10(9), 360; https://doi.org/10.3390/universe10090360 - 7 Sep 2024
Viewed by 1330
Abstract
We present a comprehensive investigation of mid-infrared (MIR) flux variability at 3.4 μm (W1 band) for a large sample of 3816 blazars, using Wide-field Infrared Survey Explorer (WISE) data through December 2022. The sample consists of 1740 flat-spectrum radio quasars (FSRQs), 1281 BL [...] Read more.
We present a comprehensive investigation of mid-infrared (MIR) flux variability at 3.4 μm (W1 band) for a large sample of 3816 blazars, using Wide-field Infrared Survey Explorer (WISE) data through December 2022. The sample consists of 1740 flat-spectrum radio quasars (FSRQs), 1281 BL Lac objects (BL Lacs), and 795 blazars of uncertain type (BCUs). Considering Fermi Large Area Telescope detection, we classify 2331 as Fermi blazars and 1485 as non-Fermi blazars. Additionally, based on synchrotron peak frequency, the sample includes 2264 low-synchrotron peaked (LSP), 512 intermediate-synchrotron peaked (ISP), and 655 high-synchrotron peaked (HSP) sources. We conduct a comparative analysis of short- and long-term intrinsic variability amplitude (σm), duty cycle (DC), and ensemble structure function (ESF) across blazar subclasses. The median short-term σm values were 0.1810.106+0.153, 0.1040.054+0.101, 0.1350.076+0.154, 0.1730.097+0.158, 0.1770.100+0.156, 0.0960.050+0.109, and 0.1060.058+0.100 mag for FSRQs, BL Lacs, Fermi blazars, non-Fermi blazars, LSPs, ISPs, and HSPs, respectively. The median DC values were 71.0322.48+14.17, 64.0222.86+16.97, 68.9625.52+15.66, 69.4022.17+14.42, 71.2421.36+14.25, 63.0333.19+16.93, and 64.6324.26+15.88 percent for the same subclasses. The median long-term σm values were 0.1370.105+0.408, 0.1710.132+0.206, 0.2820.184+0.332, 0.0710.062+0.143, 0.2180.174+0.386, 0.1730.132+0.208, and 0.1010.077+0.161 mag for the same subclasses, respectively. Our results reveal significant differences in 3.4 μm flux variability among these subclasses. FSRQs (LSPs) exhibit larger σm and DC values compared to BL Lacs (ISPs and HSPs). Fermi blazars display higher long-term σm but lower short-term σm relative to non-Fermi blazars, while DC distributions between the two groups are similar. ESF analysis further confirms the greater variability of FSRQs, LSPs, and Fermi blazars across a wide range of time scales compared to BL Lacs, ISPs/HSPs, and non-Fermi blazars. These findings highlight a close correlation between MIR variability and blazar properties, providing valuable insights into the underlying physical mechanisms responsible for their emission. Full article
(This article belongs to the Section Galaxies and Clusters)
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24 pages, 18810 KiB  
Review
Hot Stars, Young Stellar Populations and Dust with Swift/UVOT
by Michael H. Siegel and Caryl Gronwall
Universe 2024, 10(8), 330; https://doi.org/10.3390/universe10080330 - 16 Aug 2024
Cited by 1 | Viewed by 887
Abstract
In this review, we highlight the contributions made by the Swift/UVOT instrument to the understanding of the ultraviolet (UV) attenuation and extinction properties of interstellar dust and provide insight into hot stars and young stellar populations. The study of these two fields is [...] Read more.
In this review, we highlight the contributions made by the Swift/UVOT instrument to the understanding of the ultraviolet (UV) attenuation and extinction properties of interstellar dust and provide insight into hot stars and young stellar populations. The study of these two fields is interconnected: UV-bright objects can only be understood if the effects of foreground dust are accounted for, but foreground dust can only be accounted for by studying the properties of UV-bright objects. Decades worth of work have established that the effects of dust on background starlight vary in the ultraviolet, with proposed extinction laws having a wide variety of slopes and a strong “bump” spectroscopic feature at 2175 Å. We show that UVOT is uniquely suited to probe variations in the UV extinction law, specifically because of the uvm2 filter that is centered on the bump and the telescope’s ability to resolve nearby stellar populations. When used in combination with optical and infrared imaging, UVOT can provide strong constraints on variations in the extinction law, both from galaxy to galaxy and within individual galaxies, as well as the properties of young stellar populations. Surveys of UVOT have included the Milky Way, the galaxies of the Local Group, the Local Volume Legacy Survey (LVLS) and two deep fields. All of these are being utilized to provide the most detailed information yet about the UV dust attenuation law and the connection of its variation to underlying physical processes as well as the UV properties of hot stars and young stellar populations. Full article
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18 pages, 828 KiB  
Article
Kilonova-Targeting Lightcurve Classification for Wide Field Survey Telescope
by Runduo Liang, Zhengyan Liu, Lei Lei and Wen Zhao
Universe 2024, 10(1), 10; https://doi.org/10.3390/universe10010010 - 25 Dec 2023
Cited by 3 | Viewed by 2025
Abstract
With the enhancement of the sensitivity of gravitational wave (GW) detectors and capabilities of large survey facilities, such as the Vera Rubin Observatory Legacy Survey of Space and Time (LSST) and the 2.5 m Wide Field Survey Telescope (WFST), we now have the [...] Read more.
With the enhancement of the sensitivity of gravitational wave (GW) detectors and capabilities of large survey facilities, such as the Vera Rubin Observatory Legacy Survey of Space and Time (LSST) and the 2.5 m Wide Field Survey Telescope (WFST), we now have the potential to detect an increasing number of distant kilonova (KN). However, distinguishing KN from the plethora of detected transients in ongoing and future follow-up surveys presents a significant challenge. In this study, our objective is to establish an efficient classification mechanism tailored for the follow-up survey conducted by WFST, with a specific focus on identifying KN associated with GW. We employ a novel temporal convolutional neural network architecture, trained using simulated multi-band photometry lasting for 3 days by WFST, accompanied by contextual information, i.e., luminosity distance information by GW. By comparison of the choices of contextual information, we can reach 95% precision and 94% recall for our best model. It also performs good validation of photometry data on AT2017gfo and AT2019npv. Furthermore, we investigate the ability of the model to distinguish KN in a GW follow-up survey. We conclude that there is over 80% probability that we can capture true KN in 20 selected candidates among ∼250 detected astrophysical transients that have passed the real–bogus filter and cross-matching. Full article
(This article belongs to the Special Issue Newest Results in Gravitational Waves and Machine Learning)
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22 pages, 1636 KiB  
Article
Precise and Efficient Pointing Control of a 2.5-m-Wide Field Survey Telescope Using ADRC and Nonlinear Disturbance Observer
by Yang Liu, Yongting Deng, Hongwen Li, Jianli Wang and Dejun Wang
Sensors 2023, 23(13), 6068; https://doi.org/10.3390/s23136068 - 30 Jun 2023
Cited by 5 | Viewed by 1748
Abstract
Linear active disturbance rejection control (LADRC) has been widely used to improve the tracking accuracy and anti-disturbance performance of telescope servo control under disturbances. However, the linear extended state observer (LESO) is sensitive to noise, and its bandwidth is limited by the resonant [...] Read more.
Linear active disturbance rejection control (LADRC) has been widely used to improve the tracking accuracy and anti-disturbance performance of telescope servo control under disturbances. However, the linear extended state observer (LESO) is sensitive to noise, and its bandwidth is limited by the resonant frequency of the telescope. To enhance the LARDC’s ability to attenuate disturbances, a novel cascade anti-disturbance structure (NCADS) with LADRC on the outer speed loop and a nonlinear disturbance observer (NDOB) on the inner current loop is proposed. The NDOB compensates for the dominant disturbance through feedforwarding the q-axis current reference, and the LESO compensates for the residual disturbance on the outer speed loop. First, the NCADS is introduced in a three-closed-loop control framework of PMSM. Then, the design method of the controller for each loop and the NDOB are presented, the parameter-tuning method based on bandwidth is demonstrated, and the convergence of the NDOB is proved. Furthermore, to improve the searching and tracking efficiency of wide-field survey telescopes, the nonlinear tracking differentiator (NTD) was modified to plan the transition process of the position loop, which only needs to set the maximum speed and acceleration of the telescope. Finally, simulations and experiments were performed on a 2.5-m-wide field survey telescope. The experimental results verify that the proposed NCADS method has a better anti-disturbance performance and higher tracking precision than the conventional method, and the improved NTD method does not need to tune parameters and achieved a fast and smooth transition process of the position loop. Full article
(This article belongs to the Special Issue Advances in Mechatronics Systems and Robotics: Sensing and Control)
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15 pages, 414 KiB  
Article
Prospects of Searching for Type Ia Supernovae with 2.5-m Wide Field Survey Telescope
by Maokai Hu, Lei Hu, Ji-an Jiang, Lin Xiao, Lulu Fan, Junjie Wei and Xuefeng Wu
Universe 2023, 9(1), 7; https://doi.org/10.3390/universe9010007 - 22 Dec 2022
Cited by 13 | Viewed by 2356
Abstract
Type Ia supernovae (SNe Ia) are thermonuclear explosions of carbon-oxygen white dwarfs (WDs) and are well-known as a distance indicator. However, it is still unclear how WDs increase their mass near the Chandrasekhar limit and how the thermonuclear runaway happens. The observational clues [...] Read more.
Type Ia supernovae (SNe Ia) are thermonuclear explosions of carbon-oxygen white dwarfs (WDs) and are well-known as a distance indicator. However, it is still unclear how WDs increase their mass near the Chandrasekhar limit and how the thermonuclear runaway happens. The observational clues associated with these open questions, such as the photometric data within hours to days since the explosion, are scarce. Thus, an essential way is to discover SNe Ia at specific epochs with optimal surveys. The 2.5 m Wide Field Survey Telescope (WFST) is an upcoming survey facility deployed in western China. In this paper, we assess the detectability of SNe Ia with mock observations of the WFST. Followed by the volumetric rate, we generate a spectral series of SNe Ia based on a data-based model and introduce the line-of-sight extinction to calculate the brightness from the observer. By comparing with the detection limit of the WFST, which is affected by the observing conditions, we can count the number of SNe Ia discovered by mock WFST observations. We expect that the WFST can find more than 3.0×104 pre-maximum SNe Ia within one year of running. In particular, the WFST could discover about 45 bright SNe Ia, 99 early phase SNe Ia, or 1.1×104 well-observed SNe Ia with the hypothesized Wide, Deep, or Medium modes, respectively, suggesting that the WFST will be an influential facility in time-domain astronomy. Full article
(This article belongs to the Special Issue Supernovae Observations and Researches)
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16 pages, 3893 KiB  
Article
EXPLANATION: Exoplanet and Transient Event Investigation Project—Optical Facilities and Solutions
by Gennady Valyavin, Grigory Beskin, Azamat Valeev, Gazinur Galazutdinov, Sergei Fabrika, Iosif Romanyuk, Vitaly Aitov, Oleg Yakovlev, Anastasia Ivanova, Roman Baluev, Valery Vlasyuk, Inwoo Han, Sergei Karpov, Vyacheslav Sasyuk, Alexei Perkov, Sergei Bondar, Faig Musaev, Eduard Emelianov, Timur Fatkhullin, Sergei Drabek, Vladimir Shergin, Byeong-Cheol Lee, Guram Mitiani, Tatiana Burlakova, Maksim Yushkin, Eugene Sendzikas, Damir Gadelshin, Lisa Chmyreva, Anatoly Beskakotov, Vladimir Dyachenko, Denis Rastegaev, Arina Mitrofanova, Ilia Yakunin, Kirill Antonyuk, Vladimir Plokhotnichenko, Alexei Gutaev, Nadezhda Lyapsina, Vladimir Chernenkov, Anton Biryukov, Evgenij Ivanov, Elena Katkova, Alexander Belinski, Eugene Sokov, Alexander Tavrov, Oleg Korablev, Myeong-Gu Park, Vladislav Stolyarov, Victor Bychkov, Stanislav Gorda, A. A. Popov and A. M. Sobolevadd Show full author list remove Hide full author list
Photonics 2022, 9(12), 950; https://doi.org/10.3390/photonics9120950 - 8 Dec 2022
Cited by 9 | Viewed by 3024
Abstract
Over the past decades, the achievements in astronomical instrumentation have given rise to a number of novel advanced studies related to the analysis of large arrays of observational data. One of the most famous of these studies is a study of transient events [...] Read more.
Over the past decades, the achievements in astronomical instrumentation have given rise to a number of novel advanced studies related to the analysis of large arrays of observational data. One of the most famous of these studies is a study of transient events in the near and far space and a search for exoplanets. The main requirements for such kinds of projects are a simultaneous coverage of the largest possible field of view with the highest possible detection limits and temporal resolution. In this study, we present a similar project aimed at creating an extensive, continuously updated survey of transient events and exoplanets. To date, the core of the project incorporates several 0.07–2.5 m optical telescopes and the 6-m BTA telescope of the Special Astrophysical Observatory of RAS (Russia), a number of other Russian observatories and the Bonhyunsan observatory of the Korea Astronomy and Space Science Institute (South Korea). Our attention is mainly focused on the description of two groups of small, wide-angle optical telescopes for primary detection. All the telescopes are originally designed for the goals of the project and may be of interest to the scientific community. A description is also given for a new, high-precision optical spectrograph for the Doppler studies of transient and exoplanet events detected within the project. We present here the philosophy, expectations and first results obtained during the first year of running the project. Full article
(This article belongs to the Special Issue Optical Systems for Astronomy)
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11 pages, 997 KiB  
Article
Morphologies of Wolf–Rayet Planetary Nebulae Based on IFU Observations
by Ashkbiz Danehkar
Galaxies 2022, 10(2), 45; https://doi.org/10.3390/galaxies10020045 - 8 Mar 2022
Viewed by 2970
Abstract
Integral field unit (IFU) spectroscopy of planetary nebulae (PNe) provides a plethora of information about their morphologies and ionization structures. An IFU survey of a sample of PNe around hydrogen-deficient stars has been conducted with the Wide Field Spectrograph (WiFeS) on the ANU [...] Read more.
Integral field unit (IFU) spectroscopy of planetary nebulae (PNe) provides a plethora of information about their morphologies and ionization structures. An IFU survey of a sample of PNe around hydrogen-deficient stars has been conducted with the Wide Field Spectrograph (WiFeS) on the ANU 2.3-m telescope. In this paper, we present the Hα kinematic observations of the PN M 2-42 with a weak emission-line star (wels), and the compact PNe Hen 3-1333 and Hen 2-113 around Wolf–Rayet ([WR]) stars from this WiFeS survey. We see that the ring and point-symmetric knots previously identified in the velocity [N ii] channels of M 2-42 are also surrounded by a thin exterior ionized Hα halo, whose polar expansion is apparently faster than the low-ionization knots. The velocity-resolved Hα channel maps of Hen 3-1333 and Hen 2-113 also suggest that the faint multipolar lobes may get to a projected outflow velocity of ∼100 ± 20 km s1 far from the central stars. Our recent kinematic studies of the WiFeS/IFU survey of other PNe around [WR] and wels mostly hint at elliptical morphologies, while collimated outflows are present in many of them. As the WiFeS does not have adequate resolution for compact (≤6 arcsec) PNe, future high-resolution spatially-resolved observations are necessary to unveil full details of their morpho-kinematic structures. Full article
(This article belongs to the Special Issue Asymmetric Planetary Nebulae 8e)
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