分类： 天文学 >> 天文学 提交时间： 2024-08-14 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： Long period variable (LPV) stars are very promising distance indicators in the infrared bands. We selected asymptotic giant branch (AGB) stars in the Large and Small Magellanic Cloud (LMC and SMC) from the Gaia Data Release 3 LPV catalog, and classified them into oxygen-rich (O-rich) and carbon-rich (C-rich) AGB stars. Using the Wide-field Infrared Survey Explorer database, we determined the W1- and W2-band period–luminosity relations (PLRs) for each pulsation-mode sequence of AGB stars. The dispersion of the PLRs of O-rich AGB stars in sequences C′ and C is relatively small, around 0.14 mag. The PLRs of LMC and SMC are consistent in each sequence. In the W2 band, the PLR of large-amplitude C-rich AGB stars is steeper than that of small-amplitude C-rich AGB stars, due to their more circumstellar dust. By two methods, we find that some PLR sequences of O-rich AGB stars in the LMC are dependent on metallicity. The coefficients of the metallicity effect are β = –0.533 ± 0.213 mag dex1 and β = –0.767 ± 0.158 mag dex1 for sequence C in W1 and W2 bands, respectively. The significance of the metallicity effect in W1 band for the four sequences is 2.2−3.5σ. Both of these imply that distance measurements using O-rich Mira may need to take the metallicity effect into account.
分类： 天文学 >> 天文学 提交时间： 2025-06-13 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： This paper statistically analyzes the seeing data at the Lenghu site Platform C from 2018 to 2024, during which extensive construction modified the original landscape. The study focuses on the impacts of meteorological factors and building obstructions. The results reveal a progressive degradation in seeing as the monitoring setup passively changed: the median values were 0.″76 (the original location), 0.″83 during the Terrace, and 0.″99 at the new Dome (temporarily considered the permanent monitoring location). Once the instruments are fully deployed, wind speed and wind direction critically affect seeing quality, with optimal conditions occurring when the wind speed is 2–6 m s−1 and the wind direction is between 180° and 270°. However, in 2023 and 2024, the wind speeds decreased, and the prevailing wind direction shifted from southwest to northwest, correlating with poorer seeing. Computational Fluid Dynamics simulations reveal that the construction of the Wide Field Survey Telescope altered the local wind field, increasing turbulence around the Dome,especially when the winds blow from 225° to 255°. In contrast,Platform A,located in a higher and more open area,consistently maintained better seeing,particularly after midnight,likely due to fewer obstructions and lower nocturnal heat release.
分类： 天文学 >> 天文学 提交时间： 2024-12-06 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： Timing newly discovered pulsars requires gradually building up a timing model that connects observations taken days to months apart. This sometimes can be challenging when our initial knowledge of the pulsar's position is arcminutes off from its true position. Such a position error leads to significant arrival time shifts as a result of the Earth's orbital motion. Traditional down-hill fitting timing algorithms become ineffective when our model predicts the wrong pulse rotations for our next observation. For some pulsars whose model prediction is not too far off, the correct rotation number could be found by trial-and-error methods. For the remaining challenging pulsars, a more generalized method is called for. This paper proposes a GPU-based algorithm that could exhaustively search a large area of trail positions for probable timing solutions. This could help find phase-connected timing solutions for new pulsars using brute force.
分类： 天文学 >> 天文仪器与技术 提交时间： 2024-07-31 合作期刊: 《天文技术与仪器（英文）》
Suonanben
Fengquan Wu
Kai He
Shijie Sun
Wei Zhou
Minquan Zhou
Cong Zhang
Jiaqin Xu
Qisen Yan
Shenzhe Xu
Jiacong Zhu
Zhao Wang
Ke Zhang
Haitao Miao
Jixia Li
Yougang Wang
Tianlu Chen
Xuelei Chen
摘要：Detecting primordial fluctuations from the cosmic dark ages requires extremely large low-frequency radio telescope arrays deployed on the far side of the Moon. The antenna of such an array must be lightweight, easily storable and transportable, deployable on a large scale, durable, and capable of good electrical performance. A membrane antenna is an excellent candidate to meet these criteria. We study the design of a low-frequency membrane antenna for a lunar-based low-frequency (<30 MHz) radio telescope constructed from polyimide film widely used in aerospace applications, owing to its excellent dielectric properties and high stability as a substrate material. We first design and optimize an antenna in free space through dipole deformation and coupling principles, then simulate an antenna on the lunar surface with a simple lunar soil model, yielding an efficiency greater than 90% in the range of 12–19 MHz and greater than 10% in the range of 5–35 MHz. The antenna inherits the omni-directional radiation pattern of a simple dipole antenna in the 5–30 MHz frequency band, giving a large field of view and allowing detection of the 21 cm global signal when used alone. A demonstration prototype is constructed, and its measured electrical property is found to be consistent with simulated results using |S11| measurements. This membrane antenna can potentially fulfill the requirements of a lunar low-frequency array, establishing a solid technical foundation for future large-scale arrays for exploring the cosmic dark ages.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Xiangli Qian
Huiying Sun
Tianlu Chen
Danzengluobu
Youliang Feng
Qi Gao
Quanbu Gou
Yiqing Guo
Hongbo Hu
Mingming Kang
Haijin Li
Cheng Liu
Maoyuan Liu
Wei Liu
Bingqiang Qiao
Xu Wang
Zhen Wang
Guangguang Xin
Yuhua Yao
Qiang Yuan
摘要： The High Altitude Detection of Astronomical Radiation (HADAR) experiment is a refracting terrestrial telescope array based on the atmospheric Cherenkov imaging technique. It focuses the Cherenkov light emitted by extensive air showers through a large aperture water-lens system for observing very-high-energy-rays and cosmic rays. With the advantages of a large field-of-view (FOV) and low energy threshold, the HADAR experiment operates in a large-scale sky scanning mode to observe galactic sources. This study presents the prospects of using the HADAR experiment for the sky survey of TeV {\gamma}-ray sources from TeVCat and provids a one-year survey of statistical significance. Results from the simulation show that a total of 23 galactic point sources, including five supernova remnant sources and superbubbles, four pulsar wind nebula sources, and 14 unidentified sources, were detected in the HADAR FOV with a significance greater than 5 standard deviations ({\sigma}). The statistical significance for the Crab Nebula during one year of operation reached 346.0 {\sigma} and the one-year integral sensitivity of HADAR above 1TeV was ~1.3%-2.4% of the flux from the Crab Nebula.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Xiangli Qian
Huiying Sun
Tianlu Chen
Danzengluobu
Youliang Feng
Qi Gao
Quanbu Gou
Yiqing Guo
Hongbo Hu
Mingming Kang
Haijin Li
Cheng Liu
Maoyuan Liu
Wei Liu
Bingqiang Qiao
Xu Wang
Zhen Wang
Guangguang Xin
Yuhua Yao
Qiang Yuan
摘要： The High Altitude Detection of Astronomical Radiation (HADAR) experiment is a refracting terrestrial telescope array based on the atmospheric Cherenkov imaging technique. It focuses the Cherenkov light emitted by extensive air showers through a large aperture water-lens system for observing very-high-energy-rays and cosmic rays. With the advantages of a large field-of-view (FOV) and low energy threshold, the HADAR experiment operates in a large-scale sky scanning mode to observe galactic sources. This study presents the prospects of using the HADAR experiment for the sky survey of TeV {\gamma}-ray sources from TeVCat and provids a one-year survey of statistical significance. Results from the simulation show that a total of 23 galactic point sources, including five supernova remnant sources and superbubbles, four pulsar wind nebula sources, and 14 unidentified sources, were detected in the HADAR FOV with a significance greater than 5 standard deviations ({\sigma}). The statistical significance for the Crab Nebula during one year of operation reached 346.0 {\sigma} and the one-year integral sensitivity of HADAR above 1TeV was ~1.3%-2.4% of the flux from the Crab Nebula.
点击量
通过
点击量
下载量
评论
待评议
