分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Non-Maxwellian $\kappa$ electron energy distributions (EEDs) have been proposed in recent years to resolve the so-called ``electron temperature and abundance discrepancy problem'' in the study of planetary nebulae (PNe). Thus the need to develop diagnostic tools to determine from observations the EED of PNe is raised. Arising from high energy levels, the ultraviolet (UV) emission lines from PNe present intensities that depend sensitively on the high-energy tail of the EED. In this work, we investigate the feasibility of using the \ion{C}{2}]$\lambda$2326/\ion{C}{2}$\lambda$1335 intensity ratios as a diagnostic of the deviation of the EED from the Maxwellian distribution (as represented by the $\kappa$ index). We use a Maxwellian decomposition approach to derive the theoretical $\kappa$-EED-based collisionally excited coefficients of \ion{C}{2}, and then compute the \ion{C}{2} UV intensity ratio as a function of the $\kappa$ index. We analyze the archival spectra acquired by the {\it International Ultraviolet Explorer} and measure the intensities of \ion{C}{2} UV lines from 12 PNe. By comparing the observed line ratios and the theoretical predictions, we can infer their $\kappa$ values. With the Maxwellian-EED hypothesis, the observed \ion{C}{2}]$\lambda$2326/\ion{C}{2}$\lambda$1335 ratios are found to be generally lower than those predicted from the observed optical spectra. This discrepancy can be explained in terms of the $\kappa$ EED. Our results show that the $\kappa$ values inferred range from 15 to infinity, suggesting a mild or modest deviation from the Maxwellian distribution. However, the $\kappa$-distributed electrons are unlikely to exist throughout the whole nebulae. A toy model shows that if just about 1--5 percent of the free electrons in a PN had a $\kappa$-EED as small as $\kappa=3$, it would be sufficient to account for the observations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Non-Maxwellian $\kappa$ electron energy distributions (EEDs) have been proposed in recent years to resolve the so-called ``electron temperature and abundance discrepancy problem'' in the study of planetary nebulae (PNe). Thus the need to develop diagnostic tools to determine from observations the EED of PNe is raised. Arising from high energy levels, the ultraviolet (UV) emission lines from PNe present intensities that depend sensitively on the high-energy tail of the EED. In this work, we investigate the feasibility of using the \ion{C}{2}]$\lambda$2326/\ion{C}{2}$\lambda$1335 intensity ratios as a diagnostic of the deviation of the EED from the Maxwellian distribution (as represented by the $\kappa$ index). We use a Maxwellian decomposition approach to derive the theoretical $\kappa$-EED-based collisionally excited coefficients of \ion{C}{2}, and then compute the \ion{C}{2} UV intensity ratio as a function of the $\kappa$ index. We analyze the archival spectra acquired by the {\it International Ultraviolet Explorer} and measure the intensities of \ion{C}{2} UV lines from 12 PNe. By comparing the observed line ratios and the theoretical predictions, we can infer their $\kappa$ values. With the Maxwellian-EED hypothesis, the observed \ion{C}{2}]$\lambda$2326/\ion{C}{2}$\lambda$1335 ratios are found to be generally lower than those predicted from the observed optical spectra. This discrepancy can be explained in terms of the $\kappa$ EED. Our results show that the $\kappa$ values inferred range from 15 to infinity, suggesting a mild or modest deviation from the Maxwellian distribution. However, the $\kappa$-distributed electrons are unlikely to exist throughout the whole nebulae. A toy model shows that if just about 1--5 percent of the free electrons in a PN had a $\kappa$-EED as small as $\kappa=3$, it would be sufficient to account for the observations.
分类： 工程与技术科学 >> 工程与技术科学其他学科 提交时间： 2023-01-10 合作期刊: 《Art & Design Research》
摘要： Traditional dwellings with high regional artistic expression, is an important carrier of China's national culture, regional characteristics, ethnic customs. The wooden architecture of the Dong Nationality 's residential houses originated from the southern stilt-style architecture. Its unique construction technology is a treasure of national culture. Studying the aesthetic implication of Dong residential buildings will help people understand Dong culture more deeply. From the perspective of artistic aesthetics, this paper makes a detailed study of the dwellings of Dong people from five aspects: the environmental beauty of man-nature harmony, the beauty of building materials, the beauty of structure, the beauty of architectural skills and the beauty of culture. Hope to help readers understand the spiritual core of Dong culture, to better protect the Dong residential buildings wooden.
分类： 其他 >> 综合 提交时间： 2023-01-02 合作期刊: 《Art & Design Research》
摘要： Traditional dwellings with high regional artistic expression, is an important carrier of China 's national culture, regional characteristics, ethnic customs. The wooden architecture of the Dong Nationality 's residential houses originated from the southern stilt-style architecture. Its unique construction technology is a treasure of national culture. Studying the aesthetic implication of Dong residential buildings will help people understand Dong culture more deeply. From the perspective of artistic aesthetics, this paper makes a detailed study of the dwellings of Dong people from five aspects: the environmental beauty of man-nature harmony, the beauty of building materials, the beauty of structure, the beauty of architectural skills and the beauty of culture. Hope to help readers understand the spiritual core of Dong culture, to better protect the Dong residential buildings wooden.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Over the last few years, broken symmetry within crystals has attracted extensive attention since it can improve the control of light propagation. In particular, low-symmetry Bravais crystal can support shear polaritons which has great potential in thermal photonics. In this work, we report a twist-induced near-field thermal control system based on the low-symmetry Bravais crystal medium (\b{eta}-Ga2O3). The near-field thermal radiation (NFTR) between such crystal slabs is nearly four orders of magnitude larger than the blackbody limit, exceeding the NFTR from other traditional dielectric materials. Moreover, we show that this crystal can serve as an excellent platform for twist-induced near-field thermal control. Due to the intrinsic shear effect, the twist-induced modulation supported by low-symmetry Bravais crystal exceeds that by high-symmetry crystal. We further clarify how the shear effect affects the twist-induced thermal-radiation modulation supported by hyperbolic and elliptical polaritons and show that the shear effect significantly enhances the twist-induced thermal control induced by the elliptical polariton mode. These results open new directions for thermal-radiation control in low-symmetry materials, including geological minerals, common oxides, and organic crystals.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： We consider the near-field radiative energy transfer between two separated parallel plates: graphene supported by a substrate and a magneto-optic medium. We first study the scenario in which the two plates have the same temperature. An electric current through the graphene gives rise to nonequilibrium fluctuations and induces energy transfer. Both the magnitude and direction of the energy flux can be controlled by the electric current and an in-plane magnetic field in the magneto-optic medium. This is due to the interplay between the nonreciprocal photon occupation number in the graphene and nonreciprocal surface modes in the magneto-optic plate. Furthermore, we report that a tunable thermoelectric current can be generated in the graphene in the presence of a temperature difference between the two plates.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present observations of the carbon-rich protoplanetary nebula (PPN) CRL 2688 made with the Institut de Radioastronomie Millimetrique (IRAM) 30 m telescope in the 3mm and 2mm bands. In total, 196 transition lines belonging to 38 molecular species and isotopologues are detected, among which, to our best knowledge, 153 transition lines and 13 species are the first report for this object. Additionally, in order to contribute to future research, we have collected observational data on the molecular lines of CRL 2688 from the literature and compiled them into a single unified catalog. We find that the molecular abundance of CRL 2688 cannot be explained by the standard model of a circumstellar envelope. The implications of metal-bearing molecules on circumstellar chemistry are discussed.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We investigate how the existence of hydrogen molecules on grain surfaces may affect H$_2$ formation efficiency in diffuse and translucent clouds. Hydrogen molecules are able to reduce the desorption energy of H atoms on grain surfaces in models. The detailed microscopic Monte Carlo method is used to perform model simulations. We found that the impact of the existence of H$_2$ on H$_2$ formation efficiency strongly depends on the diffusion barriers of H$_2$ on grain surfaces. Diffuse cloud models that do not consider surface H$_2$ predict that H atom recombination efficiency is above 0.5 over a grain temperature (T) range 10 K and 14 K. The adopted H$_2$ diffusion barriers in diffuse cloud models that consider surface H$_2$ are 80$\%$ H$_2$ desorption energies so that H$_2$ can be trapped in stronger binding sites. Depending on model parameters, these diffuse cloud models predict that the recombination efficiency is between nearly 0 and 0.5 at 10 K $\leq$ T $\leq$ 14 K. Translucent cloud model results show that H$_2$ formation efficiency is not affected by the existence of surface H$_2$ if the adopted average H$_2$ diffusion barrier on grain surfaces is low (194 K) so that H$_2$ can diffuse rapidly on grain surfaces. However, the recombination efficiency can drop to below 0.002 at T $\geq$ 10 K if higher average H$_2$ diffusion barrier is used (255 K) in translucent cloud models.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The spotted detached eclipsing binary (DEB) offers insights into starspots on the binary. Three spotted DEBs, KIC 8097825, KIC 6859813, and KIC 5527172, which were observed by the Kepler photometry and LAMOST spectroscopy, are studied in this work. The physical parameters of binaries are determined by binary modeling. The sizes, lifetimes, 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 inferred from timescale estimation. The difference may be the result of the surface differential rotation. The 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 of literature, we compare the starspots on binaries with those on the single stars. The spot sizes of starspots on 65% 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 days. SDRs for half of the binaries are consistent with those of single star systems, while another 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 the single star systems. Binaries with luminosity ratios close to the unit tend to have more double dips.
分类： 生物学 >> 植物学 >> 植物生物化学、植物生物物理学 提交时间： 2016-05-04
摘要： The importance of the nitrate (NO3−) transporter for yield and nitrogen-use efficiency (NUE) in rice was previously demonstrated using map-based cloning. In this study, we enhanced the expression of the OsNRT2.1 gene, which encodes a high-affinity NO3− transporter, using a ubiquitin (Ubi) promoter and the NO3−-inducible promoter of the OsNAR2.1 gene to drive OsNRT2.1 expression in transgenic rice plants. Transgenic lines expressing pUbi:OsNRT2.1 or pOsNAR2.1:OsNRT2.1 constructs exhibited the increased total biomass including yields of approximately 21% and 38% compared with wild-type (WT) plants. The agricultural NUE (ANUE) of the pUbi:OsNRT2.1 lines decreased to 83% of that of the WT plants, while the ANUE of the pOsNAR2.1:OsNRT2.1 lines increased to 128% of that of the WT plants. The dry matter transfer into grain decreased by 68% in the pUbi:OsNRT2.1 lines and increased by 46% in the pOsNAR2.1:OsNRT2.1 lines relative to the WT. The expression of OsNRT2.1 in shoot and grain showed that Ubi enhanced OsNRT2.1 expression by 7.5-fold averagely and OsNAR2.1 promoters increased by about 80% higher than the WT. Interestingly, we found that the OsNAR2.1 was expressed higher in all the organs of pUbi:OsNRT2.1 lines; however, for pOsNAR2.1:OsNRT2.1 lines, OsNAR2.1 expression was only increased in root, leaf sheaths and internodes. We show that increased expression of OsNRT2.1, especially driven by OsNAR2.1 promoter, can improve the yield and NUE in rice.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： A new thermonuclear $^{17}$O($n$,$\gamma$)$^{18}$O rate is derived based on a complete calculation of the direct-capture (DC) and resonant-capture contributions, for a temperature region up to 2 GK of astrophysical interest. We have firstly calculated the DC and subthreshold contributions in the energy region up to 1 MeV, and estimated the associated uncertainties by a Monte-Carlo approach. It shows that the present rate is remarkably larger than that adopted in the JINA REACLIB in the temperature region of 0.01 $\sim$ 2 GK, by up to a factor of $\sim$80. The astrophysical impacts of our rate have been examined in both $s$-process and $r$-process models. In our main $s$-process model which simulates flash-driven convective mixing in metal deficient asymptotic giant branch stars, both $^{18}$O and $^{19}$F abundances in interpulse phases are enhanced dramatically by factors of $\sim 20$--$40$ due to the new larger $^{17}$O($n$,$\gamma$)$^{18}$O rate. It shows, however, that this reaction hardly affects the weak $s$-process in massive stars since the $^{17}$O abundance never becomes significantly large in the massive stars. For the $r$-process nucleosynthesis, we have studied impacts of our rate in both the collapsar and neutron burst models, and found that the effect can be neglected, although an interesting "loophole" effect is found owing to the enhanced new rate, which significantly changes the final nuclear abundances if fission recycling is not involved in the model, however, these significant differences are almost completely washed out if the fission recycling is considered.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Excitation of hybrid modes constituted by different material-supported polaritons is a common way to enhance the near-field radiative energy transport, which has fascinating promise in applications of thermal photonics. Here, we investigate near-field thermal radiation mechanisms in heterostructure composed of hBN film and black phosphorus single layer. The results show that this heterostructured system can give rise to a remarkable enhancement for photon tunneling, outperforming the near-field thermal radiation properties of its building blocks, as well as some other representative heterostructures. Moreover, we find that the anisotropic hybrid effect can induce a remarkable topological reconstitution of polaritons for hBN film and black phosphorus, forming a novel anisotropic hybrid polaritons. Notably, such hybrid modes show significant topological differences compared to hBN film and black phosphorus in the type-I Reststrahlen band due to the anisotropic anticrossing hybridization effect. Lastly, we systematically analyze the evolution of such hybrid polariton modes as a function of hBN film thickness and the corresponding influence on radiative properties of the heterostructure. This work may benefit the applications of near-field energy harvesting and radiative cooling based on hybrid polaritons in anisotropic two-dimensional material and hyperbolic film.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in Guizhou, China, we detect the 21cm neutral atomic hydrogen absorption in the young planetary nebula IC 4997. The absorption arises from a shell also associated with Na I D lines. The H I shell has a mass of $1.46\times10^{-2}$ M$_\odot$ and a dynamic age of 990yr. The column density of H I is estimated to be $7.1\times10^{20}$ cm$^{-2}$, which can be well explained in terms of a photodissociation region around the ionized nebula, limited by self shielding of H$_2$. We find that the atomic-to-ionized hydrogen ratio is 0.6, suggesting that H I substantially contributes to overall nebular mass.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Hanzi Huang
Yetian Huang
Yu He
Haoshuo Chen
Yong Zhang
Qianwu Zhang
Nicolas K. Fontaine
Roland Ryf
Yingxiong Song
Yikai Su
摘要： We experimentally demonstrate a record net capacity per wavelength of 1.23~Tb/s over a single silicon-on-insulator (SOI) multimode waveguide for optical interconnects employing on-chip mode-division multiplexing and 11$\times$11 multiple-in-multiple-out (MIMO) digital signal processing.
分类： 核科学技术 >> 核探测技术与核电子学 分类： 核科学技术 >> 核仪器、仪表 提交时间： 2024-02-07
摘要： A new measurement method for the spatial distribution of neutron beam flux in boron neutron capture therapy (BNCT) is being developed based on the two-dimensional Micromegas detector. To address the issue of long processing time in traditional offline position reconstruction methods, this paper proposes an FPGA-based online position reconstruction method, grounded in the micro time projection chamber principle. This method encapsulates key technical aspects: self-adaptive serial link technique built upon the dynamical adjustment of delay chain length, fast sorting and coordinate matching technique based on the mapping between signal timestamps and random access memory (RAM) addresses, and precise start point merging technique utilizing a circular combined RAM. The performance test of the self-adaptive serial link shows the bit error rate of the link is better than 10^-12 at a confidence level of 99%, ensuring reliable data transmission. The combined experiment of the readout electronics and the Micromegas detector shows a spatial resolution of approximately 1.4 mm, surpassing the current method's resolution level of 5 mm. The beam experiment confirms that the readout electronics system can obtain the flux spatial distribution of neutron beam online, thus validating the feasibility of the position reconstruction method. The online position reconstruction method avoids traditional methods such as bubble sorting and traversal searching, simplifying the design of logic firmware and reducing the time complexity from O(n^2) to O(n). This study contributes to the advancement in measuring neutron beam flux for BNCT.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jian-Jie Qiu
Yong Zhang
Jun-ichi Nakashima
Jiang-Shui Zhang
Nico Koning
Xin-Di Tang
Yao-Ting Yan
Huan-Xue Feng
摘要： Context. IRAS 19312+1950 is an isolated infrared source that exhibits a characteristic quasi-point-symmetric morphology in the near- and mid-infrared images and is also very bright in molecular radio lines. Because of its unique observational characteristics, various observational studies have been conducted and several hypotheses have been proposed regarding its origin, which is still unclear. So far, it has been suggested that it could be a peculiar evolved star, a young stellar object, or even a red nova remnant. Regardless of which type of object it is ultimately classified as, IRAS 19312+1950 is exceptionally bright in the infrared and molecular radio lines and therefore will undoubtedly be crucial as a prototype of this kind of object having a peculiar nature or unusual evolutionary phase. Aims. This study aims to reveal the molecular composition of the central part of IRAS 19312+1950 by performing an unbiased molecular radio line survey and discussing the origin of the object from a molecular chemical point of view. Methods. We carried out a spectral line survey with the IRAM 30 m telescope towards the center of IRAS 19312+1950 in the 3 and 1.3 mm windows. Results. In total, 28 transition lines of 22 molecular species and those isotopologues are detected towards IRAS 19312+1950, some of which exhibit a broad and a narrow components. Seventeen thermal lines and 1 maser line are newly detected. The molecular species of C$^{17}$O, $^{30}$SiO, HN$^{13}$C, HC$^{18}$O$^{+}$, H$_{2}$CO, and $c$-C$_{3}$H$_{2}$ are detected for the first time in this object. Conclusions. Our results, in combination with previous studies, favor the hypothesis that IRAS 19312+1950 might be a red nova remnant, in which the progenitors that merged to become a red nova may have contained at least two evolved stars with oxygen-rich and carbon-rich chemistry, respectively.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jian-Jie Qiu
Yong Zhang
Jun-ichi Nakashima
Jiang-Shui Zhang
Nico Koning
Xin-Di Tang
Yao-Ting Yan
Huan-Xue Feng
摘要： Context. IRAS 19312+1950 is an isolated infrared source that exhibits a characteristic quasi-point-symmetric morphology in the near- and mid-infrared images and is also very bright in molecular radio lines. Because of its unique observational characteristics, various observational studies have been conducted and several hypotheses have been proposed regarding its origin, which is still unclear. So far, it has been suggested that it could be a peculiar evolved star, a young stellar object, or even a red nova remnant. Regardless of which type of object it is ultimately classified as, IRAS 19312+1950 is exceptionally bright in the infrared and molecular radio lines and therefore will undoubtedly be crucial as a prototype of this kind of object having a peculiar nature or unusual evolutionary phase. Aims. This study aims to reveal the molecular composition of the central part of IRAS 19312+1950 by performing an unbiased molecular radio line survey and discussing the origin of the object from a molecular chemical point of view. Methods. We carried out a spectral line survey with the IRAM 30 m telescope towards the center of IRAS 19312+1950 in the 3 and 1.3 mm windows. Results. In total, 28 transition lines of 22 molecular species and those isotopologues are detected towards IRAS 19312+1950, some of which exhibit a broad and a narrow components. Seventeen thermal lines and 1 maser line are newly detected. The molecular species of C$^{17}$O, $^{30}$SiO, HN$^{13}$C, HC$^{18}$O$^{+}$, H$_{2}$CO, and $c$-C$_{3}$H$_{2}$ are detected for the first time in this object. Conclusions. Our results, in combination with previous studies, favor the hypothesis that IRAS 19312+1950 might be a red nova remnant, in which the progenitors that merged to become a red nova may have contained at least two evolved stars with oxygen-rich and carbon-rich chemistry, respectively.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Qi Gao
Jian-Rong Shi
Hong-Liang Yan
Chun-Qian Li
Tian-Yi Chen
Jing- Hua Zhang
Shuai Liu
Tai-Sheng Yan
Xiao-Jin Xie
Ming-Yi Ding
Yong Zhang
Yong-Hui Hou
摘要： Standard stellar evolution model predicts a severe depletion of lithium (Li) abundance during the first dredge-up process (FDU). Yet a small fraction of giant stars are still found to preserve a considerable amount of Li in their atmospheres after FDU. Those giants are usually identified as Li-rich by a widely used criterion, A(Li) $ > 1.5$\,{\it dex}. A large number of works dedicated to search for and investigate this minority of the giant family, and the amount of Li-rich giants has been largely expanded, especially in the era of big data. In this paper, we present a catalog of Li-rich giants found from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey with Li abundances derived from a template matching method developed for LAMOST low-resolution spectra. The catalog contains $10,535$ Li-rich giants with Li abundances from $\sim 1.5$\,{\it dex} to $\sim 4.9$\,{\it dex}. We also confirm that the ratio of Li-rich phenomenon among giant stars is about one percent, or for a more expression, $1.29\%$ from our statistically important sample. This is the largest Li-rich giant sample ever reported to date, which significantly exceeds amount of all the reported Li-rich giants combined. The catalog will help the community to better understand the Li-rich phenomenon in giant stars.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Zhong-Rui Bai
Hao-Tong Zhang
Hai-Long Yuan
Dong-Wei Fan
Bo-Liang He
Ya-Juan Lei
Yi-Qiao Dong
Si-Cheng Yu
Yong-Heng Zhao
Yong Zhang
Yong-Hui Hou
Yao-Quan Chu
摘要： LAMOST Data Release 5, covering $\sim$17,000 $deg^2$ from $-10^{\circ}$ to $80^{\circ}$ in declination, contains 9 millions co-added low resolution spectra of celestial objects, each spectrum combined from repeat exposure of two to tens of times during Oct 2011 to Jun 2017. In this paper, We present the spectra of individual exposures for all the objects in LAMOST Data Release 5. For each spectrum, equivalent width of 60 lines from 11 different elements are calculated with a new method combining the actual line core and fitted line wings. For stars earlier than F type, the Balmer lines are fitted with both emission and absorption profiles once two components are detected. Radial velocity of each individual exposure is measured by minimizing ${\chi}^2$ between the spectrum and its best template. Database for equivalent widths of spectral lines and radial velocities of individual spectra are available online. Radial velocity uncertainties with different stellar type and signal-to-noise ratio are quantified by comparing different exposure of the same objects. We notice that the radial velocity uncertainty depends on the time lag between observations. For stars observed in the same day and with signal-to-noise ratio higher than 20, the radial velocity uncertainty is below 5km/s, and increase to 10km/s for stars observed in different nights.
分类： 天文学 >> 天文仪器与技术 提交时间： 2024-02-07 合作期刊: 《天文技术与仪器（英文）》
JUST Team
Chengze Liu
Ying Zu
Fabo Feng
Zhaoyu Li
Yu Yu
Hua Bai
Xiangqun Cui
Bozhong Gu
Yizhou Gu
Jiaxin Han
Yonghui Hou
Zhongwen Hu
Hangxin Ji
Yipeng Jing
Wei Li
Zhaoxiang Qi
Xianyu Tan
Cairang Tian
Dehua Yang
摘要：The Jiao Tong University Spectroscopic Telescope (JUST) is a 4.4-meter f/6.0 segmented-mirror telescope dedicated to spectroscopic observations. The JUST primary mirror is composed of 18 hexagonal segments, each with a diameter of 1.1 m. JUST provides two Nasmyth platforms for placing science instruments. One Nasmyth focus fits a field of view of 10 ′ and the other has an extended field of view of 1.2° with correction optics. A tertiary mirror is used to switch between the two Nasmyth foci. JUST will be installed at a site at Lenghu in Qinghai Province, China, and will conduct spectroscopic observations with three types of instruments to explore the dark universe, trace the dynamic universe, and search for exoplanets: (1) a multi-fiber (2000 fibers) medium-resolution spectrometer (R=4 000−5 000) to spectroscopically map galaxies and large-scale structure; (2) an integral field unit (IFU) array of 500 optical fibers and/or a long-slit spectrograph dedicated to fast follow-ups of transient sources for multi-messenger astronomy; (3) a high-resolution spectrometer (R~100 000) designed to identify Jupiter analogs and Earth-like planets, with the capability to characterize the atmospheres of hot exoplanets.
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