An Exposure Meter of Lijiang Fiber-fed High-Resolution Spectrograph

In 2016,an exposure meter was installed on the Lijiang Fiber-fed High-Resolution Spectrograph to monitor the coupling of starlight to the science fiber during observations.Based on it,we investigated a method to estimate the exposure flux of the CCD in real time by using the counts of the photomultiplier tubes(PMT)of the exposure meter,and developed a piece of software to optimize the control of the exposure time.First,by using flat-field lamp observations,we determined that there is a linear and proportional relationship between the total counts of the PMT and the exposure flux of the CCD.Second,using historical observations of different spectral types,the corresponding relational conversion factors were determined and obtained separately.Third,the method was validated using actual observation data,which showed that all values of the coefficient of determination were greater than 0.92.Finally,software was developed to display the counts of the PMT and the estimated exposure flux of the CCD in real-time during the observation,providing a visual reference for optimizing the exposure time control.

Lijiang 2.4-meter Telescope and its instruments

The Lijiang 2.4-meter Telescope(LJT), the largest common-purpose optical telescope in China,has been available to the worldwide astronomical community since 2008. It is located at the Gaomeigu site,Lijiang Observatory(LJO), in the southwest of China. The site has very good observational conditions.During its 10-year operation, several instruments have been equipped on the LJT. Astronomers can perform both photometric and spectral observations. The main scientific goals of LJT include recording photometric and spectral evolution of supernovae, reverberation mapping of active galactic nuclei, investigating the physical properties of binary stars and near-earth objects(comets and asteroids), and identification of exoplanets and all kinds of transients. Until now, the masses of 41 high accretion rate black holes have been measured, and more than 168 supernovae have been identified by the LJT. More than 190 papers related to the LJT have been published. In this paper, the general observation conditions of the Gaomeigu site is introduced at first. Then, the structure of the LJT is described in detail, including the optical, mechanical, motion and control system. The specification of all the instruments and some detailed parameters of the YFOSC is also presented. Finally, some important scientific results and future expectations are summarized.

Astronomical Site Monitoring System at Lijiang Observatory

We installed two sets of Astronomical Site Monitoring Systems(ASMSs)at Lijiang Observatory(GMG),for the running of the 2.4-meter Lijiang optical telescope(LJT)and the 1.6-meter Multi-channel Photometric Survey Telescope(Mephisto).The Mephisto is under construction.The ASMS has been running on robotic mode since 2017.The core instruments:Cloud Sensor,All-Sky Camera and AutonomousDIMM that are developed by our group,together with the commercial Meteorological Station and Sky Quality Meter,are combined into the astronomical optical site monitoring system.The new Cloud Sensor's Cloud-Clear Relationship is presented for the first time,which is used to calculate the All-Sky cloud cover.We designed the Autonomous-DIMM located on a tower,with the same height as LJT.The seeing data have been observed for a full year.ASMS's data for the year 2019 are also analysed in detail,which are valuable to observers.

A novel hybrid algorithm for lucky imaging

Lucky imaging is a high-resolution astronomical image recovery technique with two classic implementation algorithms,i.e.image selecting,shifting and adding in image space,and data selecting and image synthesizing in Fourier space.This paper proposes a novel lucky imaging algorithm where with space-domain and frequency-domain selection rates as a link,the two classic algorithms are combined successfully,making each algorithm a proper subset of the novel hybrid algorithm.Experimental results show that with the same experiment dataset and platform,the high-resolution image obtained by the proposed algorithm is superior to that obtained by the two classic algorithms.This paper also proposes a new lucky image selection and storage scheme,which can greatly save computer memory and enable lucky imaging algorithm to be implemented in a common desktop or laptop with small memory and to process astronomical images with more frames and larger size.In addition,through simulation analysis,this paper discusses the binary star detection limits of the novel lucky imaging algorithm and traditional ones under different atmospheric conditions.

Mutual eclipses of J2 Europa by J1 Io observed at Yunnan Observatory in 2009

Mutual events between natural satellites include mutual occultation and mutual eclipse. Mutual eclipse is another kind of mutual occultation as viewed from the center of the Sun instead of the Earth. Two mutual eclipses of J2 Europa by J1 Io （2009 Aug. 28 and Sept. 12） were observed at Yunnan Observatory during the PHEMU09 international campaign. We will calculate the astrometric data of these Galilean satellites by analyzing and fitting the light curves we obtained. The limb-darkening was considered during modeling the light intensity of eclipsed satellites in the penumbra zone, by taking the Lommel-Seeliger scattering law into account. Several dynamical quantifies, such as the relative coordinates of the eclipsing satellite from the eclipsed one △α cos δ and △δ, impact parameter and mid-time corresponding to the impact parameter and the deviations O - C of observed △α cos d and △δ relative to ephemerides, were obtained for each event respectively.

CCD Photometry of Asteroid (147) Protogeneia

We measured the light-curve of the asteroid （147） Protogeneia in November 2004, with a CCD detector attached to the 1-meter telescope at the Yunnan Observatory, China. The synodic period and maximum amplitude of （147） at this apparition are 7.852 hours and 0.25 mag, respectively. The value of a/b for （147）, from a preliminary estimation, is not less than 1.26：1.

Discovery of extended structures around two evolved planetary nebulae M2–55 and Abell 2

We report a multi-wavelength study of two evolved planetary nebulae(PNs)M 2–55 and Abell 2.Deep optical narrow-band images([O III],Hα,and[N II])of M 2–55 reveal two pairs of bipolar lobes and a new faint arc-like structure.This arc-shaped filament around M 2–55 appears as a well-defined boundary from southwest to southeast,strongly suggesting that this nebula is in interaction with its surrounding interstellar medium.From the imaging data of Wide-field Infrared Survey Explorer(WISE)all-sky survey,we discovered extensive mid-infrared halos around these PNs,which are approximately twice the size of their main nebulae seen in the visible.We also present a mid-resolution optical spectrum of M 2–55,which shows that it is a high-excitation evolved PN with a low electron density of 250 cm^-3.Furthermore,we investigate the properties of these nebulae from their spectral energy distributions(SEDs)by means of archival data.

Chromospheric activity on the late-type star V1355 Ori using Lijiang 1.8-m and 2.4-m telescopes

We obtained new high-resolution spectra using the Lijiang 1.8-m and 2.4-m telescopes to inves- tigate the chromospheric activities of V1355 Ori as indicated in the behaviors of Ca n H＆K, Hγ HT, H/3, Na1 D1, D2, Ha and Ca II infrared triplet （IRT） lines. The observed spectra show obvious emissions above the continuum in Ca II H＆K lines, absorptions in the Hδ, Hγ, H/3 and NaI D1, D2 lines, variable behavior （filled-in absorption, partial emission with a core absorption component or emission above the continuum） in the Ha line, and weak self-reversal emissions in the strong filled-in absorptions of the Ca II IRT lines. We used a spectral subtraction technique to analyze our data. The results show no excess emission in the H6 and H7 lines, very weak excess emissions in the Na I D1, D2 lines, excess emission in the H/3 line, clear excess emission in the Ha line, and excess emissions in the Ca II IRT lines. The value of the ratio of EWs542/EWsa9s is in the range 0.9 to 1.7, which implies that chromospheric activity might have been caused by plage events. The value of the ratio EHδ/EHβ is above 3, indicating that the Balmer lines would arise from prominence-like material. We also found time variations in light curves associated with equiva- lent widths of chromospheric activity lines in the Na I D1, phenomena can be explained by plage events, which are activity indicators. D2, Ca II IRT and Ha lines in particular. These consistent with the behavior of chromospheric

Astrometry of three near Earth asteroids with the Lijiang 2.4 m telescope

Under the framework of observational campaigns organized by the GAIA Follow Up Network for Solar System Objects, three near Earth asteroids, 367943 Duende, 99942 Apophis and 2013 TV135, were observed with the Lijiang 2.4m telescope administered by Yunnan Observatories. The software package PRISM was used to calibrate the CCD fields and measure the positions of 99942 Apophis and 2013 TV135, and our own software was used for 367943 Duende. A comparison of the results show that the ephemerides of INPOP10a and JPL are consistent for 99942 Apophis and 2013 TV135, however, they are quite inconsistent for 367943 Duende. Moreover, we have found that differences between the mean values in the ephemerides of INPOP10a and JPL are about 72＂ and -199＂ in right ascension and declination respectively for 367943 Duende. Moreover, the ephemeris published by JPL is reliable in terms of the mean observed-minus-calculated （O - C） residuals in right ascension and declination of about 2.72＂ and 1.49＂ respectively.

Exploring U.S.-China climate cooperation through linked carbon markets

Emissions trading systems(ETSs)are a widely used policy tool for driving emissions reductions and serve as an avenue for international climate cooperation.Following the recent global agreement on carbon market standards at COP26,this study explores linked ETSs as an avenue for the U.S.and China to cooperate on climate action.The emissions,energy,and economic effects of linked ETSs are analyzed through the China-in-Global Energy Model(C-GEM),a multi-regional,computable general equilibrium model.Assuming the development of national economy-wide ETSs,two scenarios are developed linking China and the U.S.:1)a bilateral U.S.-China ETS linkage 2)a multilateral ETS linkage that includes China,the U.S.,and nations in Southeast Asia.Results indicate that emissions and energy consumption outcomes would be similar in the bilateral and multilateral scenarios.However,economic outcomes are more favorable in the multilateral linkage scenario.When China and the U.S.engage in bilateral ETS linkage,China predominantly benefits from additional support for domestic decarbonization while the U.S.benefits from increased GDP compared to without ETS linkage.Adding Southeast Asia to establish multilateral linkage improves GDP outcomes for all participants,reducing adverse effects on China's GDP while boosting GDP for the U.S.and Southeast Asia.For policymakers considering the design and implementation of international ETSs,this study presents updated modeling on the effects of ETS linkage on each country as well as the economic benefits of expanding participation to additional regions.

A representative CO_(2) emissions pathway for China toward carbon neutrality under the Paris Agreement's 2℃target

In 2021,China updated its nationally determined contributions(NDCs)under the Paris Agreement,which prompts a more accurate mea-surement of its emissions inventory and a reasonable pathway toward carbon neutrality by 2060.This study reviews the estimates using the bottom-up emissions factor method or the top-down atmospheric CO_(2) concentration inversion method to derive China's CO_(2) emissions inventory and finds that CO_(2) emissions from energy combustion and industrial processes in Chinese mainland range from 11.3-12.0 GtCO_(2) in 2021.Based on a comprehensive review of pathways proposed by domestic and international studies and an analysis of the origins of their differences,we proposed the Tsinghua-CMA pathway that coordinates the 2℃global temperature rise control target with China's current CO_(2) emissions status and mitigation policies.The pathway requires China's CO_(2) emissions to peak around 2028-2029 at about 12.8 GtCO_(2),then decline steadily to about 11.2 GtCO_(2) in 2035,3.6 GtCO_(2) in 2050,and 0.9 GtCO_(2) in 2060.Compared to a reference scenario without updated NDCs,this pathway would result in an economic cost of about 0.9%cumulative GDP between 2020 and 2060,only 1/4-1/3 of the cost associated with pathways that align with the 1.5℃target.We recommended that China improves emissions accounting by cross-validating bottom-up and top-down approaches and regularly updating the pathway toward carbon neutrality while maintaining consistency with its evolving CO_(2) emissions inventory,policy trends,and global CO_(2) emission budget updates.

An inversion model based on GEOS-Chem for estimating global and China's terrestrial carbon fluxes in 2019

The 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories added the method of assimilating atmospheric CO_(2) concentrations to invert carbon sources and sinks;however,many global carbon inversion models are not publicly available.In addition,our regional assimilation inversion system,CCMVS-R(China Carbon Monitoring,Verification and Supporting for Regional),needs a global carbon inversion model with higher assimilation efficiency to provide boundary conditions.Here,an inversion model based on the global atmospheric chemistry model GEOS-Chem and a more accurate and easier-to-implement ensemble square root Kalman filter(EnSRF)algorithm is constructed and used to infer global and China's carbon fluxes in 2019.Atmospheric CO_(2) concentrations from ObsPack sites and five additional CO_(2) observational sites from China's Greenhouse Gas Observation Network(CGHGNET)were used for data assimilation to improve the estimate.The inverted annual global terrestrial and oceanic carbon uptake is 2.12 and 2.53 Pg C per year,respectively,accounting for 21.1%and 25.1%of global fossil fuel CO_(2) emissions.The remaining 5.41 Pg C per year in the atmosphere is consistent with the global atmospheric CO_(2) growth rates of 5.44 Pg C per year reported by the National Oceanic and Atmospheric Administration(NOAA),showing that the inversion model can provide a reasonable estimate of global-scale natural carbon sinks.The inverted terrestrial carbon sink of China is 0.37 Pg C per year,accounting for approximately 13%of China's fossil CO_(2) emissions.

Effect of annealing time and phosphorus addition on bake hardening behavior of ultra-low carbon bake hardening steel

The relationship of the P and C grain boundary segregation and its effect on bake hardening behavior were investigated in ultra-low carbon bake hardening (ULC-BH)steel with and without P addition annealed at 810 ℃ for various time using electron probe micro-analyzer,electroh backscattered diffraction,and three-dimensional atomic probe techniques.Results revealed that P addition and annealing duration considerably affected the bake hardening behavior of experimental steel. The BH value of ULC-BH steel without P addition is lower than that with P addition within a short annealing time,and the difference in the BH value gradually decreases as the annealing duration is prolonged.P segregation is dominant in terms of a high P bulk content in steels with P addition at the expense of C segregation during annealing.By contrast,opposite effects are observed in low carbon bake hardening steel.The high residual solute C content in steel with P addition is due to P segregation at the grain boundary.Site competition is mainly responsible for the lower BH value in ULC-BH steel without P addition than that with P addition.As the annealing time is further extended,C segregation begins at grain boundary despite the delayed P segregation,leading to a gradual decrease in the solute concentration in the matrix of steels with P addition.C and P segregations reach the equilibrium as the annealing time increases to 60 min at 810 ℃ in the two steel samples.Theoretical calculations reveal that the residual solute C concentration in the matrix decreases to zero,and this finding is consistent with the change trend of the bake hardening value.Hence,the C segregation at grain boundary. adversely influences the bake hardening property of ULC-BH steel.